Sudan University of Science & Technology College of Medical Radiological Science Department of Radiological Technology
SD0000012
IMAGING ARTIFACTS Comparative Sludy in X- Ray Ct & Medical Ultrasound
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July 1998-Khartoum I 2. CONTENTS.
1.1 RESEARCH PROPOSAL.
1.2 INTRODUCTION. Contents
Part one (1) Section one [1] 1. Acknowledgement. 2. Contents. 1.1 Research Proposal. 1.2Introduction. Part two (2) 2.1 Artifacts in X-RayCT. 2.1.1 Equipment 2.1.2 .Technique 2.1.3 Patient 2.2 Reducing of Artifacts in CT. 2.2.1 Equipment 2.2.2 Technique 2.2.3 Patient Part three (3) 3.1 Artifact in Medical Ultrasound. 3.1.1 Equipment 3.1.2 Technique 3.1.3 Patient 3.2 Reduction of Artifacts in Ultrasound 3.2.1 Equipment 3.2.2 Technique 3.2.3 Patient Part Four (4) 4.1 Comparative Studies Tables. 4.2 Data Collection. 4.3 Discussion of Results. Part Five (5) 5.1 Q.C 5.2 Conclusion & Recommendation Reference Appendix r
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My B9S Khartoum Chapter One Research Proposal: Imaging Artifacts: A Comparative Study In X-Ray CT & Medical Ultrasound Introduction: This study draws attention forwards the quality of imaging process. Concerning the factors that may observe the diagnosis out come which represents the aim of the whole process of imaging technology. Imaging artifacts is one of the major limitation factor that after and decrease the value of diagnosis and out come in conventional radiography we can estimate the factors that cause artifacts which could be easily evaluated because most of the parameters in imaging process are fixed to some extend and the accessing of the imaging approximately in direct mode. But the errors which leads to artifacts skill arise in digital imaging "Concerning CTV U/S", the accessing process taken over several steps involve conversion from analogue format to digital and vice versa; and application of computer technology program needs careful awareness. Tiny errors many arise artifact, issue, errors leads to artifact, on digital imaging can't predicted unless listed and discussed on a cord of practices according to the operational protocol. Statement of problem: The digital imaging nowadays cover most of investigations done in radiography department ever the conventional process started earlier and cover along of time and the technologist gain experience skill errors lead to artifacts seem to be more while digital imaging replace the conventional imaging in a fast steps it carry also the same errors with the new errors, that may warser the new practice as a whole. Reasons for Choice This Project: There were a lot of errors in different department that deals with digital imaging can be observed by any general observer this issue reflected on the fetal report at the level of diagnosis and this will affect the quality of patient cane and may be the morbidity rate as well as mortality rate. Objectives of the Project: The main objective of this study is to high light the artifacts and the source of errors that lead to artifact formation and we can summarize the main objectives on the following points: (1) Consider and identify the artifacts on each modality. (2) Show the cause of artifact. (3) Resolve and eliminate the reasons that lead to artifacts formation in imaging. (4) Establish proper quality control techniques issue set tha base line limits of artifact causation. Hypothesis: 1- The presence of artifact creates problems in diagnosis. 2-The cause errors leading to imaging artifact that affect the diagnosis more in digital U/S than CT. 3- Lack of quality assurance programs maximizes the presence of faults leading to imaging artifact. 4- Imaging artifacts affects the quality of patient care and delay medical diagnosis and treatment, and hence increase patient waiting time. Previous Studies: From what we read in the previous research studies (1,2,3) we did notice that there was just listing of faults without indicating any reason (s) or causes except in medical ultrasound. However, we planned to research it from our locate experts in CT and medical ultrasound in the teaching hospitals and medical centres according to the values of the code of practice. Research Methodology: In this study of have taken the scientific method in the field of X-ray CT and medical ultrasound imaging. Data Collection: 1-Questionnaire. 2- Interviews. Using both in the following variable: a. Equipment factors. b. Patient factors. c. Technique. Place & Period of Study: Sudan- Khartoum March/July 1998 (Teaching Hospitals and Medical Imaging Centers). Introduction
Diagnostic imaging is an important element in the practice of the modern medicine without it medical treatment would have been impossible. Radiation medicine had seen many changes since 1895, where only early tuals. A radiation therapy and radoidiagnosis. Today imaging has many source of electromagnetic radiation "EMRs" and each source has its advantages over the other. However, medical radiation education had also seen more advances in the medical sciences and medical education, which lead to the discoveries of new methods, and techniques in these fields. There were also new approaches to refine and perfect the practice of radiologic techniques and to reduce radiation exposure, patient waiting time and cost. We have seen lots of new imaging modalities, quality assurance and quantity control procedures in all modalities to produce images of high quality and more diagnostic information. Here, we have taken the lead to research and study carefully how we could participate in the area of reducing image retakes and study the reasons of image artifacts in diagnostic imaging. In this regaid we are researching on artifacts in X-ray computed tomography and medical ultrasound and considering how these artifacts may be eliminated. PART 10W
ARTIFACTS IN X-RAY CT. 2.1.1 TECHNIQUE 2.1.2 EQUIPMENT 2.1.3 PATIENT
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8 Artifacts
This section deals with experience gained with the original model
EMI 160 xl60 matrix scanner. Modification, because of the experience with EMI CT 1010 scanner and other scanning systems, is expected. This section should be of considerable value in the understanding of the basic causes of artifact production and sources of error despite such modifications.
Artifacts:
Motion and high-differential attenuation value of adjacent tissues are principal cause of artifacts. Technical errors are also responsible.
Motion Artifacts:
Motion of a point places that point different computed positions during the scanning cycle. This false representation usually produces a linear artifact called a "streak". Point A scanned at 0 degree is again scanned at 180 degrees with an interval time delay. A change in point A position will produce computer error in the form of a streak. Computer error due to movement will, therefore, be more marked along the vertical (Odegree/180degrees) line, because of motion during the time that elapses between the two readings. The head can rotate in all directions, producing a variety of streaking outside or inside the skull vault. Assuming that the scanning time is constant, head support, patient cooperation and sedation are factors to consider in order to diminish motion artifact. The faster scanning cycle of the newer CT systems reduces the degree of motion artifact. The EMI CT 1010 scanner has a 240-degree scanning angle option designed to decrease streaking that result from patient motion.
High-Attenuation Differential Artifacts:
Streaking also occurs at interfaces of high-attenuation differentials, such as air-bone, air-brain, bone-brain and metal-brain. The computer "overloads" due the high differential values and produces the streak.
The high-Vat dense petrous pyramids possibly combined with air in the ears may cause transpontine streaking that obscures the cerebellopotine angle. Surgical clips, metallic plates, Holder valves and shunt reservoirs produce streaking. Using a scanning angle of 240 degree or starting the scanning cycle at 90 degree can be helpful in decreasing artifacts due to metal or other high-differential attenuation situation.
Postpneumeoncephalography air can produce streaking or simply "overshoot" at the air-fluid level. Overshoot appears as thin band of contrasting Vat adjacent to the zone of the high-differential values. Nevertheless, CT scanning in the presence of air or other contrast in the subarachnoid space can be diagnostically useful. Overshoot also produces a thin band of low Vat subjacent to the skull (the false subarachnoid space). A zone of artifactiually increased Vat simulates "gray matter" on the original EMI scanner. This overshoot phenomenon is seen subjacent to the false subarachnoid space. Other mechanisms than overshoot may also be responsible for the false gray matter. More modern machines are apparently able to demonstrate true gray matter. Elimination of metal from shunt mechanisms eliminates metallic-streak artifacts.
10 Source of Error:
Technical source of error includes improper selection of window level and window width, improper Polaroid printing and improper patient positioning. Several other situation are also potential sources of error, including "partial-volume" phenomenon and incorrect measurement of surface area. The partial volume phenomenon is the effect of matrix averaging of heterogeneous tissues. Partial volume phenomenon leads to misinterpretation, such as spurious "hydrocephalus" Postpneumeonce- phalography. It also leads to Vat and volumetric measurement error, particularly of small highly contrasting regions. Use of the higher detail matrix systems, combined with thin-section technique, diminishes this averaging problem. Magnification factors for measurement must be accurately calculated in order to avoid misrepresentation of size. This calculation should based on data obtained by scanning a phantom of known dimension, or by measurement of structure of known size that appears on the CT scan.
The level of section may also be misinterpreted. Systems to locate accurately the plane of section have been developed. Sagittal CT sectioning devices are still in the experimental stage. Coronal section technique is discussed in chapter 13.
Human sources of error in interpretation also occur. The jugular tubercle may be prominent and is found at high level in basilar invagination. In such cases, the jugular tubercle may mimic a high-Vat lesion such as a meningioma or acoustic neurinoma. PART TOW
2.12
ARTIFACTS IN X-RAY CT.
TECHNIQUE Technical Artifacts:
Indexing inaccuracies produce a characteristic linear artifact called "herringbone" artifact. High signal/noise ratio is necessary for a high- quality scan. As the signal/noise ratio diminishes, a mottled compromised image results as with improper tubecrystal alignment or inherent fault in tube or crystal. Technical error can also produce artifacts. Changing crystal photomultiplier technique during the scanning cycle will produce a characteristic linear artifact. Figure (I)
Technical Error Artifact Troticollosed Patient, Pantopaque Droplets
Section IB (conventional scan). The higher right petrous pyramids (PP) and orbital rooF (OR) appears in this plane of section due to patient troticollis. Pantopaque droplets (arrows) surround brain stem. Displacement of the fourth ventricle (4) toward the right side is suspected, but difficult to confirm
Figure (2) llasilnr Impression, Prominent Dens, and Jugular Tubercles
Section IA (conventional scan). Prominent jugular tubercles (JT) posterior to petrous pyramids (PP). Dens behind lower aspect of clivus(CL) Globe (G).
Figure(3)
Technical Error Artifact
Characteristic linear artifact caused by changing crystal photomultipiier technique during the scanning cycle
IP- PART TOW
1.2
ARTIFACTS IN X-RAY CT. EQUIPMENT
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Indexing Error Artifact
Herringbone pattern caused by indexing error
Figure (12)
X-ray Tube - Crystal Alignment Artifact
Molt led artifact produced by improper tube- crystal alignment
Figure (13)
High-Differential Metal-Brain Artifact- Streak
Surgical metallic clips causing computer overload with resultant streaking.
16 Figure (14)
High-Differentia! Hone-Brain Vat Artifact- Overshoot
Section 2A (conventional scan). Thin black band of false subarachniod space (!) Thicker band of false gray matter (2)
Figure (15) a and b
Artifacts
In order to eliminate metal-bone and metal- brain artifact due to ventricular shunting, reservoirs and valves made of plastic can be used
(a) Section 2B (conventional scan)
(b) Section 3A (conventional scan)
Fimbriated tip of high-Vat shunts (arrow) in right frontal horn Left frontal horn (FH) Choroid plexus (CP). Subdural hematoma (arrowheads) No streaking from base of shunt tube (SH) due to lack of metal Left ventricle (I.V). Figure (16) n and b
Overshoot Artifact anil Partial Volume Phenomenon Computer Tomographic Pneunwencephahgram
Brovv-up (a) and brow-down (b) scans at frontal horn level. Brow-down (b) section closer to infraorbitomeatal plane than brovv-up (a) High-and low-Vat streaks at air margins, particularly in the vertical direction, are noted. Atrium (AT), third ventricle (3), interhemispheric (IMF) and Sylvian fissures (SF). quadrigeminal plate (QPC) and superior cerebella cisterns (SCC), frontal horn (FH).
The seemingly larger frontal horns brow-up is mostly an illusion due to averaging of air and brain tissue at the ventricular margin. This average is therefore heavily weighted toward the appearance of larger frontal horn on the Polaroid print. Careful examination of the brow-down section reveals almost the same size frontal horn There probably is a degree of ventricular expansion with air filling, however, Figure (18)
High-Differential Metal-lirain Artifact- Streak
Severe streaking caused by frontal bone metallic
Figure (19)
High-Differential Air-Brain Artifact- Overshoot
Section 2B (postventriculogram). Air also present in subarachnoid space. Frontal horn air (FH A) Overshoot horizontal interface (arrows) between air and CSF (AVat= 1000) of frontal horns Subarachnoid air outlines subarachnoid cyst (CY) anderiorly (arrowheads). Lateral ventricle atrium (AT)
i9 PART TOW
2.1.3
ARTIFACTS IN X-RAY CT. PATIENT Figure(4)
High-Differential Bone-Brain Artifact-Streak
Multiple spurious high-Vat zones (arrows) subjacent to bone obscuring posterior fossa anatomy. Motion contributes to streaking in this case Combined causes of artifacts are very common
Figure(5)
High-differential Bone-Brain Artifact-Streak
A transpontine low-Vat streak (arrow) is often produced in association with dense petrous pyramids Inion bone-brain streak (crossed arrow)
Figure(6)
Motion Artifact-streak
Multiple vertical streaks (white lines) at scan periphery caused by patient motion Figure (7)
Motion Artifact-streak
Multiple streaks inside and outside of brain image produced by patient motion.
Figure(8)
High-Differential Air-Skull Artifact-streak
The large quantity of air surrounding the small head results in "lighten image-like" streaking. Replacement ofthe water bag and adjusting the photomultiplier technique in the EMI CT 1010 VVx scanner alleviates this type of difficulty.
Figure(9)
High-Differential Air-Drain Artifact-Streak, Partial Volume Phenomenon
Reciprocal high- and low-Vat artifactual zones (arrows) surrounding air-filled frontal horns. These streaks are the result of computer overload The impression of frontal horn dilation is largely due to computer averaging (partial volume phenomenon). Normal-sized third ventricle (3), atria (AT), and left occipital horn (Oil) PART THREE
3.1
ARTIFACTS IN MEDIGAL ULTRA SOUND 3.1.1 EQUIPMENT Sonogram Abbreviations: BI: Bladder
D: Diaphragm
E: Echoes
GBI: Gallbladder
K: Kidney
L: Liver
RK: Right Kidney
T: Tornado effect
Ut: Uterus
Artifacts in ultrasonic images can be classified into three categories:
1. Artifacts related to instrument problems, which occur when the equipment is not functioning satisfactory. 2. Technique-dependent artifacts, in which the appearance is produced by unsatisfactory operator technique.
3. Artifacts due to the way tissues affect sound. These artifacts cannot be avoided. Each of these spurious sonographic appearances must be recognized so that the deceptive finding can be disregarded, eliminated, or used as a diagnostic aid.
This chapter will initially cover artifacts relating to real-time and static scanning, and then artifacts seen with static scanning only. Artifactiual Noise: Artifactual noise is caused by electrical interference from nearby equipment e.g. in an intensive care unit; Figure (20).
RECOGNITION Such noise has a repetitive pattern unlike the overall increase in echogenicity seen with too much gain. This type of noise produces a "pattern" over the normal ultrasound image.
FIGURE X ° Interference from nearby equipment causes artifacts on the CRT (arrow).
Figure (20): Interference from nearby equipment causes artifacts on the CRT (arrow).
Calibration Problems-Incorrect Distance Markers
Calibration problems may not be apparent on the image, but subsequent measurements using another ultrasonic system or phantom may show erroneous caliper measurements.
DIAGNOSTIC CONFUSION Measurements such as the biparietal diameter may be wrong with tragic clinical consequences.
RECOGNITION Only by comparison with other systems or by calibratior] check can such subtle measurement changes be detected. Main Bang Artifact:
There can be many echoes from the skin-transducer interface in the immediate subcutaneous tissues. There is such a strong interface between the skin and the transducer that it is almost impossible to avoid the main bang artifact completely with older transducers. Witli new technology, this artifact is seldom seen because of electronic focusing. Poor technique, however, can still create this artifact (Figure 22).
DIAGNOSTIC CONFUSION: Subuctaneous and skin lesions will be hidden within the main bang artifact.
riOUBE 400 Main bang artifact With older units this is caused by a strong interface between skin and the transducer. Too much near gain (arrow) can also be a reason
Figure (22): Main bang artifact. With older units this is caused by a strong interface between the skin and the transducer. Too much near gain (arrow) can also be a reason Veiling: Bands of increased echogenicity can be seen at certain depth if all focal zones are used simultaneously, producing the veiling artifact (figure 23). DIAGNOSTIC CONFUSION The impression of a mass may be created within the area of veiling. Masses may be overlooked at the interface of the different focal zones.
RECOGNITION A band of increased echoes unrelated to the strong interfaces within the images is seen at a certain depth.
FIGURE J^TVeiling. Focusing zones are well delineated transverse echo areas (arrows). Utilize only the focusing zone in the area of interest to eliminate the focal banding.
Figure (23): Veiling Focusing zones are well-delineated trs isverse echo areas (arrows) Utilize only the focusing zone in the area of interest to eliminate the focal banding
J27 A bsence of Focusing:
Electronic focusing and the use of acoustic lenses have increased the number of focal zones available with a single transducer and greatly increased the resolution of the image. If the focal zone option is not used with newer electronic systems much blurring of echo interfaces is seen (Figure 24).
DIAGNOSTIC CONFUSION Discrete lines appear thick, and subtle masses may be overlooked.
RECOGNITION. The echoes in the unfocused area are large. Echoes normally seen as dots in the image are seen as a short line.
Figure (24): Absence focusing. There is blurring of the echoes when focusing is not utilized (arrow)
28 Focusing and Persistence versus Festal Heart Motion: "Focusing" and "persistence" improve the quality of the image at the expense of frame rate; a wavy motion across the image is commonplace if these controls are used.
DIAGNOSTIC CONFUSION Structures that move rapidly such as the fetal heart may not be seen, and one can erroneously infer that a fetus is dead. RECOGNITION: A wavy image motion is visible when the image is closely examined. Rapid motion of the transducer exaggerates this finding. Grating lobes:
A grating lobe artifact is caused by the periodic spacing of the phased array or, more commonly, linear array elements. Grating lobes travel at an angle to the main beam, and depending on whether the lobe hits the object before or after the main beam, a curvilinear echo may be seen either at a shallower or deeper depth than the structure causing the artifact (figure 26)
DIAGNOSTIC CONFUSION An apparent septum may be present within an amniotic sac or other cystic process.
RECOGNITION: The septum, which is slightly curved, is usually related to a strong curvilinear interface in the mid-portion of the linear array field.
Figure (26): A grating artifact (arrow) may sometimes occur above or below a strong linear interface (eg the diaphragm) when using an array system, particularly a linear array Photographic Artifacts:
Photographic artifacts are a major problem. If the contrast is set incorrectly, subtle metastatic lesions may be lost in the overall grayness of the image. Undue brightness may also obscure subtle texttiral alterations.
Dust on the Camera: If dust is allowed to settle onto a camera lens or cathode ray tube, small echo-genic areas will be seen on the camera image. Similar artifacts can occur with Polaroid images (figure 27).
DIAGNOSTIC CONFUSION If the echogenic mass lies within the liver, confusion with a metastatic lesion may occur.
RECOGNITION: A similar echogenic area occurs in the same location on every film.
Figure (27): A
31 PART THREE
%Mm la MM
ARTIFACTS CAUSED RY TECHNIQUE:
3-2 Noise:
Noise is created by excess gain (figure 28). Gain may be turned up to a point where low-level echoes occur in unstructured fluid-filled areas such as the bladder.
DAIGNOSTIC CONFUSION: Excess gain may give the impression that the crystic lesion contains internal material or is solid.
Figure (28): Low-level echoes (noise) are seen in the fluid-filled bladder.
Side Lobes:
Side lobes are secondary echoes outside the main beam, that exist with all transducers.
DIAGNOSTIC CONFUSION Noise is created within the image. RECOGNITION: Recognition is difficult unless quality control tests are performed. Operator scanning speed:
If the sonographer scans rapidly, artifacts known as dropout lines are created (figure 29). Most digital units receive information rapidly enough to avoid this artifact. Some units appear to have gaps between the lines of the image because they have not been "smoothed". Computer processing can eliminate these little gaps between beam lines in cosmetic but uninformative fashion (i.e. the gaps are filled in with false echoes).
Figure (29): Dropout lines (arrows) are created when the scanning speed is too rapid Operator Pressure: Applying too much or uneven pressure while scanning can distort the image.
DIAGNOSTIC CONFUSION Scanning the fetal trunk using too much pressure with a linear array may make it appear to have a flattened ovoid shape rather than the preferred round shape (figure 30).
Figure (30): Pressure artifacts. A. Too much pressures over the fetal trunk produces a flattened ovoid shape. B. A. Lighter scanning pressure creates a round mink and correct measurement PART THREE
3.1.3
Artifacts Caused by Sound-tissue
Patient Artifacts from Strongly Reflective Structures (Shadowing):
Gas, bone, and, to a much lesser extent, muscle do not conduct sound well. When sound strikes a strong interface such as gas or bone, one of two responses may be produced. Either there is no sound conduction through the area (shadowing), or numerous secondary reverberations are produced, causing a series of echogenic lines extending into the tissues (ring down).
DIAGNOSTIC CONEUSION Large-shadowing artifacts may obscure a deep pathologic process (e.g. nodes).
RECOGNITION. The reverberation pattern seen with bones is series of alternating lines (figure 31 A), whereas that seen with gas is usually a more diffuse, vaguely outlined pattern with considerable noise - the "tornado" effect. A linear series of parallel bands may also be seen with gas - the "ring down" effect (figure 31 B).
CORRECTION TECHNIQUE The sonographer should attempt to scan around gas or bone, obtaining scans of the areas below these structures from an oblique angle.
Figure (31): Reverberation artifacts. A. A longitudinal scan of the thing. Notice the reverberations (alternating lines) extending below the bone interface (arrows). B. Gas may cause the creation of a line of reverberation echoes (arrow), the "ring down" effect, or a vague sonolucent area of acoustic shadowing, the "tornado" effect. Benefit: Shadowing occurs when the sound beam hits a highly reflective surface such as gallstones, renal stoner, or surgical clips, allowing a diagnosis of an acoustically dense structure. The shadowing can be made more obvious by increasing the frequency of the transducer (figure 32).
Figure (32): Large acoustic interfaces due to gallstone are associated with shadowing (arrow). Shadowing is accentuated with higher frequency. Reverberation Artifacts: Whenever sound passes out of a structure with an acoustic impedance that is markedly different from its neighbor, a large amount of sound is returned to the transducer. The amount of sound returning may be so great that it is sent from the transducer back into tissues, causing s duplication of the original structure. The second wave has traveled twice as far as the first one, the third echo three times as far, and so fourth. The distance between each successive echo will equal the distance between the original two interfaces. The second echo and each successive echo parallel the original interface.
DIAGNOSTIC CONFUSION: Such reverberation artifacts are most commonly seen adjacent to the bladder anterior wall (figure 33), but also occur elsewhere in the body in soft tissue as well as fluid; they may mimic a mass. Reverberations from the anterior surface wall can make a simple cyst appear complex (figure 33).
Figure (34): Echoes due to reverberations are parallel to the anterior body wall (arrow) of the bladder Figure (35): Reverberations (r) from the body wall may be seen to extend down into a renal cyst. B. when the scan angle is changed, the reverberations are no longer seen within the cyst. (c).
RECOGNITION: Reverberation artifacts of this type may occur at some distance from the original interface (e.g. behind the posterior wall of the bladder). A second apparent bladder resembling fluid-filled bowel appears to lie where measurement shows the sacrum should lie (figure 36). Mirror Artifacts: If a sonographic structure has a curved appearance, it may focus and reflect the sound like a mirror. RECOGNITION. Mirror artifacts occur most commonly when scanning the diaphragm. Theoretically, there should be no echoes from the lungs because they are full of gas, but in fact there is a duplication of the structures within the liver above the diaphragm in all normal individual (figure 37). On the left this mirror image can create a false impression of a pleural effusion because the diaphragm is also duplicated. This artifact occurs when the patient is scanned in an oblique axis in the coronal position. Lesions within the liver or spleen adjacent to the diaphragm can be "duplicated" in the lung.
Benefit. If this mirror image is absent in the lung, it can be deduced that a pleural effusion is present (see figure 37).
Figure (36): Mirror anifact behind the posterior wall of the bladder with creation of an apparent cystic lesion posterior to the bladder (arrow)
4-f Transducer
Diaphragm
Figure (37): Mirror artifacts. A. In the normal patient there is a mirror image of the liver tissue above the diaphragm at the site of the lung (arrow). B Diagram of how the artifact is created. C. When there is a pleural effusion, an echo-free area is seen above the diaphragm.
4-2 Enhancement Effect: As the sound beam passes through fluid-filled structures or structure containing many cysts, it is not attenuated and there is an increase in the amplitude (brightness) of the echoes distal to the fluid (figure 38).
DIAGNOSTIC CONFUSION. A true pathologic condition may be obliterated by the increased gain distal to fluid-filled structure (e.g. fibroid uterus behind the bladder).
BENEFIT. Acoustic enhancement is almost always beneficial and may be useful in differentiating between solid and cystic lesions, in addition to aiding the sonographer in seeing deep structures.
Figure (38): Enhancement effect. A. Increased echoes obscure the structures behind the bladder owing to enhancement of the sound passing through the bladder (arrow). E Decreasing the gain allows.the uterus to be seen clearly. Frezonal Zone Artifacts: The near field of the transducer contains artifactiual echoes.
DIAGNOSTIC CONFUSION: Lesions can be missed if they lie close to the skin because much of the information in this area is noise (see figure 39).
RECOGNITION: There is little textural information in the first centimeter or two of the images. Split-Image Artifact: A duplicate image occurs when the transducer is placed in the midline in the pelvis. The curved rectus muscles cause a bending (refraction) of the sound beam. The beam is bent toward the midline from both sides of the muscle layer. The system is unaware that refraction has occurred. The echoes that are returned to the transducer are placed at the "assumed" distance and direction. The original structure is duplicated (figure 40). This artifact can occur with a phased array or a linear array probe, but is more frequent with linear array systems. DIAGNOSTIC CONFUSION A double image is created. A single sac can be mistaken for a twin pregnancy, or there may appear to be two IUDs.
Figure (40): Split-image artifact. A. Scanning transversely in the midline of the pelvis can create a duplication of the structure, which is situated in the midline due to refraction. A double image of a Copper 7 IUD is seen in the uterus (arrows). Note the dimple in the contour of the uterine wall (larger arrow) at the intersection of the two images. B When scanning away from the midline in the transverse plane, a better image is displayed. The true configuration of the Cu 7 IUD is seen (arrow). The dimple has disappeared. Slice-Thickness Artifact:
When the interface between a fluid-filled "cyst" and soft tissue is acutely angled, the beam, which is relatively wide (2-3 mm), may strike both tissue and fluid simultaneous. Low-level artifactiual echoes will be displayed within the fluid (figure 41).
DAIGNISTIC CONFUSION: Low-level echoes in the posterior aspect of a cyst may be thought to be evidence of abnormal cyst contents.
RECOGNITION. Echoes are seen at the posterior aspect of the cyst and develop as the transducer moves from the center of the cyst.
Slice thickness
Artifact echoes
Figure (41): Slice-thickness artifact. A. Echoes in the posterior part of the gallbladder relate to the slice thickness artifact. The diagram shows the beam intersecting an oblique segment of the cyst wall B. Sonogram demonstrates low level echoes apparently in the posterior part of the gallbladder where the gallbladder angle is steep.
4-6 Comet Effect: A very strong acoustical interface, such as an air bubble, or a metallic structure, such as a suture, creates a dense echogenic line extending through the image known as the comet effect (figure 42).
DIAGNOSTIC CONFUSION. The echogenic line may be mistaken for a real structure.
BENEFIT. The presence of the line indicates a very strong interface and may allow recognition of metallic structures such as clips.
Figure (42): The comet effect is demonstrated on this longitudinal view of the liver. At the diaphragm echogenic lines can be seen extending towards the lung (arrow). Static Scanning Artifacts:
Lateral Plane Distortion (X-Y axis Miscaiibration, Misregistration, and Misalignment) There is marked distortion of the shape of an organ, causing around structure to look oval when the lateral plane is distorted.
DIAGNOSTIC CONFUSION: organs assume the wrong shape and look oval rather than round.
RECOGNITION. It is impossible to scan from either side of the abdomen with a static scanner because the two images will not intersect. Quite severe X-Y axis distortion may be present before it is obvious on the scan (figure 43).
Figure (43): Misregistration. A. Transverse view of the right kidney scanning in one direction. Note gas-filled bowel to the right of the kidney (arrow) and echoes from the main bang artifact at the skin. B. Scanning the right kidney but angling from the other direction. Note the distortion of the kidney borders due to misregistration (arrows). C. There is no distortion of the right kidney. Registration is now in alignment. Note irregular shadowing due to gas in bowel adjacent to the kidney. Beam Depth Problem:
Artifacts are present beyond the focal zone of the transducer in the far part of the field when there are beam depth problems (figure 44). The echoes in this region are much coarser, and major lesions may be missed if a long-focus transducer is not used. Because considerable lateral beam spread occurs, small pinpoint structures appear as transverse 1ine,s. DIAGNOSTIC CONFUSION: Subtle small lesions may be missed because of the coarse echogenic structure at depth (e.g. small metastases in the liver).
Figure (44): The near segment of this liver contains artifactiual information owing to beam distortion in the frezonal zone (small arrow). Lateral beam spread beyond the focal zone (large arrow) causes wide echoes with little information. Compounding: Often the best way to complete a B-scan is to form numerous small sector scans to create one overall image. At the junction of the small sector scans artifact is created because the transducer can be accurately aligned only rarely (figure 45). DIAGNOSTIC CONFUSION: The intersection of two sector scans can be thought to represent a pathologic process.
Figure (45): compound scanning causes this artifact; the image is not aligned (left arrow). " ^"; > ^v; A : >;>-*. ^\-r
! ! - i . Real-Time and Static Scanning Artifacts Artifacts Caused By Equipment
Artifactiual Noise Reduction: Equipment can be modified to prevent such interface if it occurs in the ultrasound laboratory. You may be able to disconnect the interfering equipment during the scan. Gel warmers are often responsible. Calibration Problems-Incorrect Distance Markers Reduction: Calibration checks should be performed frequently (once a month). See chapter 49. Measurements should be performed in the center of the image where calibration is most correct and not at the edge of the video monitor. Main Bang Artifact Reduction: A higher frequency transducer diminishes the problem. Decrease the near field gain. Use of a stand-off pad will avoid a main bang artifact to some extent. Veiling Reduction: When the veiling cannot be corrected by adjusting the time gain compensation controls, use only one focal zone. Absence of Focal Zone Reduction:
Use the focal zone option, and the echoes will appear discrete. Use of a single focal zone gives better information at a defined depth than when multiple focal zones are used. Focusing and Persistence versus Fetal Reduction: Use only a single focal zone and a little persistence. Pixel Mismatch Reduction Use a different transducer. Get the transducer repaired. Grating Lobes Reduction: Imaging with a different transducer or changing the patient's position shows that the supposed echo is artifactiual. Photographic Artifact Reduction: Use the focusing system that comes with the transducer at the depth at which the noise is greatest. Dust On the Camera Reduction:
Make sure that the camera is dusted frequently. REDUCTION IN ARTIFACT CAUSED BY
3.1.2 Redaction Of Noise (Technique): Decrease gain without losing structural information. Redaction Of transducer Selection problems:
Observe the principles of TGC usage discussed in chapter 4. Redaction Of Banding:
Use a transducer with a different frequency and focus and alter the TGC setting. Redaction Of Contact problems: Attempt to reposition the transducer or use a transducer with a smaller face (footprint). Redaction Of Movement (breathing) : Ask the patient to hold his or her breath, or utilize the cine loop control to review the last frames of the scan and freeze when the most desirable image appears. Redaction Of Operator scanning Speed: Use only sufficient pressure to keep the transducer in contact with the skin. REDUCTION IN ARTIFACT CAUSED BY
PATIENT
'Wit*' Redaction Of Interactions The sonographer should attempt to scan around gas or bone, obtaining scans of the areas below these structures from an oblique angle. Redaction Of Reverberation Artifacts: Distinguish such artifacts from real structures by (1) using transducers of a different frequency, (2) bouncing the transducer on the abdominal wall and noticing that the second linear structure moves in exactly the same fashion as the strong echo nearest the transducer, and (3) scanning the same area from a different angle. Redaction Of Mirror Artifacts:
Try to scan the same area from another position. Redaction Of Enhancement Effect:
The sonographer should diminish the overall gain and adjust the TGC if the condition is pathologic document the increased acoustic enhancement behind the structure. Redaction Of Fresnet Zone:
The use of a high frequency transducer the size of the fresnel zones when scanning superficial structures. Placing the transducer at a distance from the skin surface by the use ofa stand-off pad moves the area of interest into the focal zone; the fresnel zone of distortion then lies within the area of the image occupied by the stand - off pad. Redaction Of Split - Image Artifact: To avoid the refraction of the sound beam through the rectus muscle, scan from a site other than the midline Redaction Of Slice Thickness Artifact:
Scanning from a different angle shows that there are no echoes within the area where the slice thickness artifact was seen. Redaction Of Comet Effect: Scan from a different angle and the line will either disappear or be projected onto a different site. Redaction Of static Scanning Artifacts: Weekly calibration shows this problem early. Aservice person will be needed to correct it. Redaction Of Beam Depth Probe: These artifacts are unavoidable even with the correct TGC setting if transducer with a more appropriate focal zone is not used. Redaction Of Compounding:
Repeat the scan using a smoother technique, preferable using a single pass. Recognition of the artifact is possible if one observes where the transducer skin lines join.
When the area of interest is behind a fluid-filled structure many echoes occur within this area of acoustic enhancement. Several small sector scans are desirable in such a case. With a single pass only the structures posterior to the bladder are enhanced. Using several smalls passes; areas not affected by enhancement can be scanned with gain increased, creating an overall cosmetic improvement in the image. *¥ m m
^ ;,; y . 74/ %, & ?>****•& ** **' ** ** ********** f • **** *-* * **s*** ** **fr£*** ***y***** CT U/S 1. X-Raytube 1- Noise
2. Detectors 2- Calibration problem
3. Operator errors 3- Main bang artifact
4. High-differential metal-brain 4- Veiling artifact
artifacts-streaks 5- Absence of focusing
5. High differential metal -brain 6- Focusing persistence
artifacts streak. 7- Pixel mismatch.
6. High differential air - brain 8- Grating lobes artifact.
artifact overshoot 9- The patient position.
7. Overshoot artifact and partial 10- Dust of the camera in
volume phenomenon cephalagam. photographic.
8. High differential brain-vat 11- Polaroid image artifact.
artifact overshoot.
9. Indexing error artifact.
10. X-ray tube crystal. Alignment
artifact.
1- Technical errors. 1- Noise Artifact
2- Technical errors artifact 2- Transducer selection problem
troticollosed patient 3- Transducer artifact
pantopaque droplets. 4- Contract problem
3- Basil or Impression 5- Movement artifact
6o 4- Prominent dens and jugular 6- Operator scanning speed.
tubercles 7- Operator pressure
1- Patient motion streak. 1- Shadow.
2- High differential air-skull 2- Reverberation.
artifact streak. 3- Enhancement effect
3- High, differential air-brain 4- Frezonal zone.
artifact streak. Partial 5- Split-image.
volume phenomenon. 6- Comet effect.
4- High differential bore-brain 7- Static scanning
artifact streak. 8- Beam depth problems.
5- High differential bore-brain 9- Compounding.
artifact streak.
6- Patient motion
(A) Pt movement
(B) Cardiac motion
(C) Breathing/ swallowing
1- High density artifact.
2- Poor patient position. PARTFOUR
4.1
DATA COLLECTION AND DISCUSSION OF RESULTS
62 Questionnaire onem & ,-
Artifacts in CT Imaging
if ^_JU (V)
Types of CT Artifacts (H.D = High Differential)
A. CT Equipment Artifacts
1-X-Raytube
2- Detectors
3- Operator errors
4- High-differential metal-brain artifacts-streaks
5- High differential metal - brain artifacts streak.
6- High differential air - brain artifact overshoot
7- Overshoot artifact and partial volume phenomenon cephalagam
8- High differential brain-vat artifact overshoot.
9- Indexing error artifact.
10- X-ray tube crystal. Alignment artifact. B. CT Technique artifact
1-Technical errors.
2-Technical errors artifact troticollosed patient pantopaque
droplets.
3- Basil or Impression prominent dens and jugular tubercles
C. CT patient Artifact
1- Patient motion streak.
2- High differential air-skull artifact streak.
3-High differential air-brain artifact streak. Partial volume
phenomenon.
4- High differential bore-brain artifact streak.
5- High differential bore-brain artifact streak.
6- Patient motion
(A) Pt movement
(B) Cardiac motion
(C) Breathing/ swallowing
1- High density artifact.
2- Poor patient position. Questionnaire Twon^
Artifacts in Medical Ultrasound
£-Uai
Types of ultrasound Artifacts
A. U/S Equipment Artifacts
1- Noise
2- Calibration problem
3- Main bang artifact
4- Veiling artifact
5- Absence of focusing
6- Focusing persistence
7- Pixel mismatch.
8- Grating lobes artifact.
9- The patient position. 10- Dust of the camera in photographic.
11 - Polaroid image artifact.
B. U/S Technique artifact
1-Noise Artifact
2- Transducer selection problem
3- Transducer artifact
4- Contract problem
5- Movement artifact
6- Operator scanning speed.
7- Operator pressure
C U/S patient Artifact
1- Shadow.
2- Reverberation.
3 - Enhancement effect
4- Frezonal zone.
5- Split-image.
6- Comet effect.
7- Static scanning
8- Beam depth problems.
9- Compounding.
66 Interview No. one CT scan artifacts
1- From your experience in CT investigation what is the common artifacts?
2- Is there any effects at the level of diagnosis caused by artifacts ?
3- What do you think, about problems arise from artifacts ?
4- What is the problems in your opinion that lead to artifacts in your section ?
5- What is your suggestion and direction to avoid this artifacts ?
6- What is artifacts that caused by patient which represented ? Interview No. two Medical Ultrasound Artifact l-From your experience in U/S investigation what is the common artifacts?
2- Is there any effects at the level of diagnosis caused by artifacts ?
3- What do you think, about problems arise from artifacts ?
4- What is the problems in your opinion that lead to artifacts in your section ?
5- What is your suggestion and direction to avoid this artifacts ?
6- What is artifacts that caused by patient which represented ? Analysis of Data collection
Summary of information collected by questioner which shown on tables with conclusion summary
Table (1)
Participant Number % sonographer 3 30% Sonologist 4 40% Engineers 3 30%
100%
50% 40% 30% 30%
A B C
A sonologists B sonolgraphers C engineers
from the table "1" above we find that the staff that answered the questioner consist of sonologists, represent 40% and sonolgraphers represent 30% and medical engineers represent 30%.
Table (2) type of equipment Number % Japanese 8 80% American 2 20% Others 2 20% 100% 80%
50%
20%
A B
A Japanese B American C Others
from the table "2" above we find that most of the participant use Japanese machines which represent 80% and the type of the machines which are American types and others which represents 20%, this means the result is mostly dependence on Japanese machines.
Table (3) type of U.S Equipment artifact.
Type of calibration dust of poloroid noise veiling absence of focusin-g grating pixel artifact the artifact focusing presistence lopes mismach camera number 6 4 1 6 2 1 1 % 60% 40% 10% 60% 30% 20% 10% 10% 10% Fig (A)
100%
60%
50% 40% 30% 2Q% 10%
A B C D
A calibration + noise artifact B dust of the camera C veiling artifact D absence of focusing E poloroid + focusing the presetence + grating lobes and pixel mismach
From Table (3) above we find that there are tow peaks can concerning calibration problem and noise artifact caused by equipment represent 60% and the lowest cause contributed derived from focusing presistence, grating lobes and pixel mismach, and ploroid artifact which represent 10%. For all general view look Fig (A).
Table (4) Type of U/S Technique artifact
noise transducer tranducer contact movement operator operator focusing artifact selection artifact problem artifact scanning pressure presistence problem speed number 4 8 3 2 1 4 % 40% 80% 30% 30% 20% 10% 40% 100% 80%
50% 40% 30% 20% 10%
A B D
A transducer selection problem B noise artifact + operator pressure C transducer artifact + contact problem D movement artifact E operator scanning spped
From Table (4) we find that there is one peak offered by causes of U/S technique artifact due to transducer selection problem which represent 80%, and the lowest artifact caused by technique is concerning operator scanning speed which represent 10%.
Table (5) Type of U/S Patient artifact.
Type of shadow reverbrat- enhancem- frezonal split comet static beam compounding artifact ion ent effect zone image effect effect depth problem number 6 7 3 2 1 5 1 % 60% 70% 30% 30% 20% 10% 30% 50% 10%
n Fig (A)
100%
70% 60% 50% 50°A
30% 20%
A B C D F
A reverberation B shadow C beam depth problem D enhancement effect + frezonal zone + static effect E there is no patient artifact F compound + comet effect ^^^
From Table (4) we find that there is one peak concerning patient artifact (reverberation) which represent 70% and the lowest caused by the patient is comet effect and compounding which represent 10%. Summary of information collected by the personal contact (interview) which shown on tables with conclusion summary.
Table (1)
types of artifact number % noise 2 40% no preparation (gases) 2 40% probes problem 1 20%
100%
60%
50% 40% 40%
2H%
A B C D
A noise B no preparation C probes problem
From the table above we recognize that the most predominant artifacts is due to noise and gases artifact which represent 40% and the lowers cause is due to probes problem which represent 20%.
Table (2) Effect of artifact in the imaging result types of artifact number % yes 4 80% no 1 20% u 100% 80%
50%
211%
A B
A Yes B No
From Table (2) above we find that 80% of the participant agreed that artifact affect the final imaging result, 20% of them agreed that artifact do not have any effect on the imaging.
Table (3) Expectation of U/S artifact artifact may lead to number % wrong diagnosis 4 80% not affect in the diagnosis 1 20%
100% 80%
50%
20%
A B
75 A wrong diagnosis B No affect in the diagnosis
From Table (3) above we have concluded that 80% of the participant agreed that artifact lead to wrong diagnosis in U/S imaging while 20% said that artifact does not affect the final result.
Table (4) Types of U/S due to cause (by %)
Reason of U/S artifact number % unknown 1 20% noise 2 40% calibration 1 20% skills 1 20%
100% 80%
50% 40%
20% 20% 20%
A B C D
A noise B unknown C calibration D skills
From Table (4) above we can conclude that the most causes of U/S artifact in the department is due to noise from the power supply and bad earthing which represent 40% and the other causes by miscalibration of U/S unit and skills of the operator, which represent 20% of the total. Table (5) Suggestion for the reduction of the artifact in the LJ/S imaging
Directions to avoid number occurrence of artifact prepration of pt 40% equipment earthing 20% equipment calibartion 20% operator skills 20%
100% 80%
50% 40%
20% 20% 20%
A B C D
A no preparation of patient B good earthing C check calibration D operator skill
From Table (5) we can conclude that direction to avoid artifact,40% of them suggested to consider good patient preparation, and 20% suggested routine calibration of equipment and 20% suggested that better operator skills. Table (6) Artifact due to patient artifact due to patient number % preparation of patient 4 40% un co-operative pt. 2 20% Movement of the pt. 1 10% Obese pt. 1 10% Uncontact probe 1 10%
100% 80%
50% 40% 20% 10% 10% 10%
A B C D E
A preparation of pt. B un co-operative pt. C movement of the pt. D obese pt. E uncontact probe
From Table (6) we conclude that 40% agreed that artifact are due to pt. Preparation. 20% suggested that those artifact are due to co-operative pt. 10% suggested that artifact were due to movement of the patient, 10% have also suggested the cause due to patient obesity and finally 10% have suggested the cause to be due to uncontact probe. For details of data collection of questioner look table A,B, and C. Table (A) U/S Equipment artifact
No. Department Participant job Type of equipment Type of artifact 1. government sonographer Japanese 1- calibration problem 2- dust of camera 2. government engineer Japanese 1- calibration problem 2- poloroid artifact 3. private sonologist Japanese 1- noise 4. government sonologist Japanese 1- calibration problem 2- veiling artifact 5. government sonologist American 1-noise 2-calibration problem 3- main bang artifact 4- dust of camera 5- absence of focusing 6. private engineer Japanese 1-noise 2- absence of focusing 3- dust of camera 7. government engineer Japanese American others 1- noise 2- calibration 3- veiling artifact 4- absence of focusing 5- focusing presistance 6- grating lobes artifact 7- pixel mismach 8- dust of camera 9- noise 8. private sonographer Japanese 1 - noise 9. government sonographer others 1- calibration 10. government sonologist Japanese 2- veiling artifact
8o Table (C) U/S Patient Artifact
No. Department Participant job Type of equipment Type of artifact 1. government sonographer Japanese 1 - not found engineer Japanese 1 - no found 2. government sonologist Japanese 1- reverberation 2- frezonal zone 3. private sonologist Japanese 1- shadow 4. government 2- reverberation 3- beam depth problem sonologist American 1- enhancement effect 5. government 2- split image 3- static scanning engineer Japanese 1- shadow 2- reverberation 6. private 3- enhancement effect 4- frezonal zone 5- static scanning 7. government 6- beam depth problem 7- compounding engineer Japanese American others 1- shadow 2- reverberation 3- enhancement effect 4- frezonal zone 5- split image 6- comet effect 7- static scanning 8- depth problem 8. private sonographer Japanese 1- shadow 2- reverberation 9. government sonographer others 3- beam depth problem 10. government sonologist Japanese 1- shadow 2- reverberation 1- shadow 2- reverberation 3- beam depth problem
82 Table U/S Technique Artifact
No. Department Participant job Type of equipment Type of artifact 1. government sonographer Japanese 1- not found 2. government engineer Japanese 1- transducer selection problem 3. private sonologist Japanese 1- noise artifact 4. government sonologist Japanese 1- transducer selection problem 2- movement artifact 3- operator pressure 5. government sonologist American 1 - noise artifact 2- transducer selection problem 3- transducer artifact 4- contact problem 6. private engineer Japanese 1- transducer selection problem 2- transducer artifact 3- operator pressure 7. government engineer Japanese, American, others 1-noise artifact 2- transducer selection problem 3- transducer artifact 4- contact problem 5- movement artifact 6- operator scanning speed 7- operator pressure 8. private sonographer Japanese 1-noise artifact 2- transducer selection problem 9. government sonographer others 1- transducer selection problem 10. government sonologist Japanese 1- transducer selection problem 2- contact problem 3- operator pressure Table (1) CT Equipment Artifact
Types of CT artifact Number % 1-X-Raytype 5 50% 2- Detectors 6 60% 3- Operators errors 4 40% 4- High differential metal brain artifact streak 8 80% 5- High differential air brain artifact over shoot 6 60% 6- Overshoot artifact and partial volume phenomena cephalogram 4 40% 7- high differential brain-vat artifact overshoot 1 10% 8- Indexing error artifact 1 10% 9- X-Ray crystal. Alignment artifact 2 20%
90% 80% 70% 60% 1—1 50% 40% 30% 20% 10% n n 6 7 8
Key: 1- X-Ray tube detectors operator errors high differential metal-brain artifacts streak. High differential air brain artifact over shoot Overshoot artifact and partial volume phenomena cephalogram high differential brain-vat artifact overshoot Indexing error artifact X-Ray crystal. Alignment artifact
From the table above we have recognized that the most predominant artifact is due to " high differential metal brain artifact streak "represents
8 $• 80% the second peak is detectors artifact and it represents 60% the lowest contribution came from " high differential brain vat artifact overshoot " and indexing error artifact represent 10% for both of them.
Table (2) Technique Artifact type of equipment Number % Technical errors 3 30% 1 - Technical errors 3 30% 2- Technical errors artifact troticollosed pt. pantopaque 2 20% droplets 3- Bast or impression prominent deus and jugular tubercles 1 10%
30%
20%
10%
1 Key: 1- Patient motion streak. High differential air-skull artifact streak. High differential air-brain artifact streak. Partial volume phenomena. High differential bore-brain artifact streak . 5- patient motion.
From the table above we can recognize that the most predominant artifact is technical errors and it represent 70%, the second peak is technical errors artifact troticollosed pt. pantopaque droplets and represent 20%, the lowest contribution come from Basil or impression prominent deus and jugular tubercles represent 10%. Table (3) CT Patient Artifact
Type of artifact number % 1- Pt. Motion streak 5 50% 2- High differential air-skull streak. 6 60% 3- High differential bone-brain artifact streak. Partial volume 4 40% phenomena. 4- High differential bone-brain artifact streak. 4 40% 5- Pt. Motion 8 80%
80% 70% 60% 50% 40% 30% 20% 10%
Key: 1- Patient Motion streak. 2- High differential air-skull artifact streak. 3- High differential air-brain artifact streak. Partial volume phenomena. 4- High differential bore-brain artifact streak . 5- patient motion.
From the table above we can recognized that the most predominant artifact pt. Motion and represent 80% the second peak is high differential air-skull artifact streak represent 60% the lowest contribution come from high differential bone-brain artifact streak. Partial volume phenomena and high differential bone-brain artifact streak represent 40% for both of them.
89- Summary of information collected by personal contact which is shown on tables with conclusion summary Most probable artifacts in CT image cause by table one
Types No. % 1- Blurring of the image " streaks " 3 70% 2- Calibration problem 1 20% 3- High atomic number material in teeth 1 10%
100%
70% 70%
40% II 40% III 10% 10% lit HI
A B C
Key: A Blurring of the image B calibration C High atomic number material in teeth
From Table we can conclude that the most predominant artifacts are streaks which represent 70%, the second peaks formed by patient motion which represent 20%, the lowest artifact source were due to high atomic number material which represent 10%. Table (2) Change in image information
Types No. % 1- Yes 4 80% 2- Yes 3- Yes 4- Yes 5- No. 1 20%
100% 80% 80%
20% 20%
A B
From the table above we can conclude that most artifacts due to the level of diagnosis which represent 80% and the lowest cause which is about 20% considered not having any change in diagnosis.
Table (3) Expectation of Artifact in image result
Types No. % 1- Unknown 1 20% 2- Wrong diagnosis 3 60% 3- 4- Ci 5- Not effect to the diagnosis 1 20% 60% 60%
20% 20% 20%
A B C Key: A Unknown B Wrong diagnosis C Not affect to the diagnosis
From the table above we can conclude that 60% of the faults lead to wrong diagnosis, 20% were due to unknown causes and only 20% which did not have any affect on image information or diagnosis.
Table (4) Reasons of faults in CT image Types No. % 1- Due calibration of CT 1 20% 2- Use of CT control 2 40% 3- Due motion of pt. 2 50% 4- Due 3 rd generation 1 10%
60%
50% 50%
20% 20% 20% 20% 10%
A B C D Key: of table (4) A Due contribution of the CT unit B Use of CT control Due motion of pt. D Due 3rd generation of CT
From the table above we can conclude that the most predominant artifacts due to motion due to pt. Which represent 50%, the second peaks is due to use of apparatus which represent 20%, the third peaks is due to wrong calibration which represent 20% and finally the lowest contribution were caused by third generation which represent 10%.
Table (5) Suggestion for reduction of artifacts in CT image
Types No. % 1- Instruction to pt. To put away all F,B 2 40% 2- Equipment maintenance. 2 40% 3- Sedation. 2 20%
40% 40% 40%
20%
A B C
Key: A Instruction to the pt. To put away all F.B B Equipment maintenance C Sedation
From the table above we have concluded that the most predominant artifacts are due to equipment calibration (40%), 40% is also found due to lack of communication with patient and 20% due sedation.
9/ Table (6) Artifacts due to patient
Types No. % 1- Streak 5 100% 2- « 3- 4- 5-
100% 100%
From the above table (6) we have concluded that streaks took 100% of the image artifacts. 5.1
OF CT. AND ULTRA SOUND Quality Assurance of C.T:
Quality assurance may be defined as the testing of the system to ensure consistency and acceptability of performance.
There are many tests available to assess the performance of the scanner, some of which are carried out by the manufactures, although departmental staff should be able to regularly monitor the equipment without any loss of patient throughput.
The amount of quality assurance required depends on the type of work undertaken by the scanner. A detailed quality assurance programme be necessary if radiotherapy planning and research work is undertaken, but a less intensive programme will be required if only general work is undertaken.
The amount of quality assurance also depends on the type of system. Systems, which are, stable and require minimum servicing will not require a detailed quality assurance programme, but a newly installed scanner should be repeatedly tested for a given period of time. If the results of these checks are satisfactory a reduction can take place in the quality assurance, which can then be undertaken by the service engineer.
However, it should not be taken for granted that a newly installed scanner, purchased for its reputation of stability and reliability will be stable in every aspect of its performance. If two identical scanners are situated in adjacent hospitals or even within the same department each scanner will develop its own "character" and idiosyncrasies. Thus it is good policy to keep the same service engineer who can then learn the idiosyncrasies of the one system. Quality assurance is carried out by using a selection of phantoms from the variety available. These phantoms come in many different forms, i.e. circular or body shaped, and are used to test various parameters.
a. Single structure phantoms are made from polystyrene, which is filled, with water. This type of phantom is used to test a specific parameter.
b. Composite phantoms are made from several materials with known accurate CT numbers. These phantoms may allow an interchange of "plugs" of varying materials to be either inserted or removed.
c. Calibration phantoms are used to check the accuracy of CT numbers. If the CT numbers are not within the manufacture's specification calibration scans are undertaken using these phantoms. The information obtained is used to reconstruct a; subsequent tests or patient scans.
There are varieties of tests that can be carried out using the above phantoms, which include:
(1) CT number of water.
(2) kVp response.
(3) Spatial resolution.
(4) Low contrast resolution.
(5) Radiation dose. (1) CT number of water:
This test should be carried out daily using the same phantom and a consistent technique. For example, 120 kVp, 200mA3 seconds with 10mm collimation on a standard algorithm using a 256x256 matrix.
If this is routinely performed every morning it will monitor the system for linearity of CT number. If the CT number changes, it may indicate a problem with the tube, kVp or mA. This test also ensures that the processing image display and archiving facilities are correctly functioning. All test scans should be kept for comparative studies.
(2) kVp response:
A test using a composite phantom may be carried out weekly to check the system's kVp response to materials other than water.
(3) Spatial resolution:
Spatial resolution is the ability of the system to detect the separation of adjacent closely spaced objects. A spatial phantom is used, and by applying a constant radiographic technique, for example, 120 kVp, 200mA, 3 seconds, 10mm collimation and standard algorithm, the resolving power of the scanner can be monitored.
(4) Low contrast resolution:
An interchange of "plugs" of varying CT number are used with the composite phantom to check the sensitivity of the scanner. (5) Radiation dose:
The radiation dose from the scanner should be checked fortnightly or when a kVp calibration has been undertaken, or whenever there is a tube change. A polystyrene phantom with holes for the insertion of thermoluminescent dosimeters is used. A series of scans should be made using the body and brain technique factor.
There are several other tests, which should be routinely conducted on the system, including: (1) Table indexing. (2) Patient alignment lights. (3) Hardcopy camera.
(1) Table Indexing:
For reasons already mentioned, it is essential to be able to position the table accurately. The table drive mechanism is subject to wear and tea therefore, tables accuracy should be checked using phantom with a pin inserted at a specific point. A scan is taken, the table then table indexed out of the aperture as finally returned to the first scan position. The table should re-align accurately, a second scan is then taken, which be identical to the first one. Many gantr have numerical readout showing the distance (mm) that the table has traveled.
(2) Patient alignment lights:
The patient alignment lights should be checked weekly at the time as (1).
(3) Hardcopy camera:
Shutter exposures and gray scale should be routine checked. Many of the above tests will be carried out by the service engineer as part of the servicing arrangement. However, that operator should carry out independent tests ensuring that machine is regularly monitored.
As well as the general mechanical service it is essential that the scanner is kept scrupulously clean. Any spillages during scanning session should be cleaned up immediately.
Quality Assurance of U/S:
To benefit from ultrasound as diagnostic aid, one must be fully aware of its drawbacks and limitations, as the interpretation of the picture can other wise give misleading results. Therefore only through knowledge of how to avoid some of the most obvious pitfalls will enable the user to obtain maximum benefit from the equipment.
In the following, a few of the most common reasons for impairment of picture quality are dealt with using the knowledge gained in the theory chapter.
Electronic Circuit:
Vast number picture artifacts may originate from the electronic circuits involved in the generation and processing of the ultrasound. Many of these artifacts can be readily recognized, andonly some of the most significant artifacts originating from the restriction in the design and operation of well-engineered ultrasound equipment are discussed here.
Noise Artifacts:
A common source of spurious echoes in any ultrasound equipment for medical diagnostics is the inherent noise generated in the electronic circuitry. It is generally the noise level of the input amplifier alone. Which limits equipment performance with respect to low-level signals. With doppler equipment, however, distortion and spurious modulation will also have a considerable limiting effect with respect to low-level performance.
The so-called signal-to-noise ratio is given by the ratio of useful signal to noise at any echo amplitude:
Signal-to-noise ratio = useful signal amplitude Noise amplitude Noise is no problem in the near field of the transducer in non-doppler systems. As receiver amplification here is moderate. Further away from the transducer, where the compensation circuit amplification is high, the input noise may become excessive. To obtain a picture of diagnostic significance the signal-to-noise ratio should not be less than 3dB (1.4 times) at any displayed signal amplitude.
Quantisation, i.e. the division of an analogue signal into a finite number of amplitude group, is a source of noise peculiar to digital storage systems.
Detection Thresholds:
It is quite possible that the minimum signal, which the system can process, is several dB above the noise level. If this is the case, the useful dynamic range will be less than the stated signal-to-noise level. If the minimum signal which could be processed is 8 dB above the noise level, and the signal-to-noise ratio is 10 dB with a particular echo signal, this signal can only decrease a further 2 dB before it is no longer registered. A common reason for this might be deliberate rejection effect at an echo envelope detector. Storage:
Conversion circuits for gray-scale displays should not added all the amplitudes registered for any given point on the display, because this will not allow several scans of the same structure in one single store operation without blurring the picture excessively with analogue and causing overflow with digital storage. Thus last-value-write or speak-hold types of circuits should be used avoid artifacts.
Digital storage systems have the problem of quantisation noise already mentioned. Furthermore, the quantisation will also give rise to an additional threshold effect at the lowest signal levels, which is not experienced with analogue systems. With a number of gray-scale values exceeding some 12-14 respect to both brightness position and threshold effects can generally be neglected.
Compensation Setting:
The compensation should be set to minimize the number of artifacts, but at the same time giving the maximum detail in the representation of the examined tissue. A reasonable initial setting will normally be given in the instruction manual for the particular equipment. With digital systems automatic resetting to this position will often occur at switch-on. This setting can then be modified at will.
Care should be taken not to get artifacts from transducer ringing (too high an initial gain) and amplifier noise or spurious echoes (excessive final gain). Too low gain settings should also be avoided, as this will aggravate possible threshold and noise problems by not utilizing the maximum useful-signal handling capacity of the equipment.
\QQ Gray-Scale Adjustment:
Incorrect setting of the gray-scale conversion circuit can lead to severe picture artifacts due to the factors mentioned above.
If the system has a storage system with accessible controls, efforts to improve a given scan should not be attempted by adjusting the amplification and background level of the circuit. Once the optimal setting for this part of the system has been found, the contrast range of the converter, which is quite small compared to that of the human eye, will fit the dynamic range of the electronic processing circuit optimally.
Further adjustments will cause the gray-scale range to fall outside the dynamic range of the processing circuit output, making the picture either too bright or too dark. In either case, the usable gray-scale part of the display is reduced as a result of either too small a signal or overload of the conversion circuit, and the gray-scale information obtainable is reduced.
Scanning Rate:
When scanning moving objects in the body with a static display, the picture will not be very sharp, and may be almost useless as far as the moving objects are concerned except for such moderately moving structures as the aorta. This is due to the very long scanning time, i.e. effectively an extremely low scanning rate compared with the rate of the movement of the objects. When using a dynamic scanner, the problem no longer exists if the scanning rate is sufficiently high. A scanning rate of more than 16-20 picture updates per second will, dependent on scanning and display system generally be sufficient to avoid artifacts.
lot Dependent on the particular structure studied, the effect of too low a scanning rate with a dynamic scanner may be far worse than the blurring caused by moving objects with the static display systems. Besides the unavoidable reduction of sharpness, the shape of the moving structure and its rate of movement can be heavily distorted due to a stroboscopic phenomenon known as aliasing. What actually happens is that the system is unable to differentiate between successive movement cycle, and is displaying the information more or less at random so that both the shapes and the movement of the moving hinge is heavily distorted. It should be emphasized, that this is an extreme case unlikely to occur with normal scanners, except when scanning rapidly moving heart valves.
Selecting the Transducer:
Resolution:
The effective diameter of the beam is dependent on the diameter of the piezoelectric crystal. The gain level of receiver will also affect the apparent effectively beamwidth since with a low gain level, only the highest-amplitude portions of the beam will give detectable echoes.
The lateral resolution of the transducer is determined by the beamwidth, because an echo from a reflecting surface will be registered all the time it is inside the beam, i.e. points closer together than the beamwidth cannot be resolved. Poor lateral resolution makes it difficult to discriminate between cystic and solid structure, since the picture will be blurred.
If the transducer pattern has many significant side-lobes, as might be the case with transducer of small size compared to the wavelength, ghost- echoes can occur. With pulsed ultrasound, the effect of the side-lobes will 1oZ normally be reduced as compared to a steady-state situation, as many of the interference causing the steady-state side-lobes will not have time to arise.
Internal Echoes:
A badly designed or engineered transducer can give may spurious reflections which have nothing to do with the tissue structures being scanned. Several factors may cause this.
Insufficient backing can give reflections from directions other than that of the tissue, which will be displayed as if they were actually situated in the scanning direction. The backing can be insufficient in respect to both absorption and to transmission from the crystal into the sole material.
Impedance differences between the transducer itself and the transducer coating will result in poor transmission and false echoes. This result may also happen with well-designed transducers if the sole material has been loosened, e.g. after mechanical abuse.
Geometric Distortion and Sound Velocity Variations:
Velocity variations of ultrasound in tissue are generally small. The only major velocity changes occur at boundaries between soft tissue and bone, and at boundaries between tissue and artificial heart valves.
The effect of the increase in sound velocity is that structures behind the high velocity structure will seem to be closer to the transducer than is actually the case, and that angular distortions will arise, so that the assumption of a straight path by the electronic circuits is no longer correct. Fast layers may also give rise to annoying geometric distortion, as they can act as unwanted acoustical lenses in the tissue.
Spurious Reflections:
Spurious reflections can occur from inside of a badly designed or engineered transducer, but are more likely to arise from ultrasound pulses wandering back and forth between a heavily reflecting boundary and the transducer. This phenomenon is popularly known as re-reflection and is quite likely to occur when borders between areas of greatly differing specific acoustic impedance are scanned.
Re-reflections may arise from the strong echoes from the ribs (bone), when not scanning in the intercostal spaces. They will usually be accompanied by some sort of shadow effect, when trying to find a compromise between a high gain to avoid the effect of the attenuation and strong reflections of the ribs, and the low gain preferable to dimmish the re-reflections.
The so-called "rain" that can occur close to the anterior bladder wall when scanning the uterus through the full bladder is also most likely to be re-reflections.
Granulation:
Granulation of an image, or acoustic speckle, can occur with highly directional sources such as those used in diagnostic ultrasound. It means that structures which are known to be continuous, e.g. the myocardium, are displayed on the on the ultrasound image with a granular appearance.
Acoustic speckle is dependent on the relative positions of the transducer and the structure being studied, and the speckle spots diminish in size with increasing resolution. Static B-mode systems and real time systems with multiple simultaneously active transducers operated in compound mode produce less speckle, because many single beams from a variety of positions are used to image the same structure.
Air-Field Structures:
The effect of air in the body structure is that the ultrasound is almost totally reflected. Thus no structures behind a lung or any other internal cavity filled with air can be seen. However, it is to some degree possible to overcome such problems by scanning from different positions.
Shadows and Bones:
Shadows behind a heavily reflecting and/or attenuating structure can easily arise when scanning. This problem is often overcome by scanning obliquely into the hidden area. However, it should be noted that shadows might also yield valuable information, e.g. shadows behind a gall stone.
In theory, bone can give rise to five possible causes of picture artifacts. These are increase in sound velocity; increase in attenuation, considerable reflection, strong reflections and the shadow effect just described.
The strong reflections and the increased attenuation of ultrasound by bone reinforces the limitations caused by the increased velocity and the shadow effect, and makes it almost impossible to penetrates bony structures, as very little energy will be left for detecting tissue structures behind them. Should the bone be penetrated, the large velocity refractions given rise to an angular distortion effect.
Classifications and Dehydration: Classification of tissue structures will be lead to severe attenuation and scattering of the ultrasound beam from the transducer. The main effect of dehydration is also increased scattering in the tissue.
Due to the spurious echoes from the radiated spherical waves, it will be difficult to discriminate between cystic and solid structures. Generally, the picture will look blurred.
Fat:
Fat gives unwanted diffraction and high attenuation of the ultrasound, making it difficult to obtain echoes underneath the far layer, if this is abnormally thick. There is also a tendency to get scattering in fat layers.
Fat has largely the same effect as calcification and dehydration, and makes it difficult to discriminate between cystic and solid structures. Generally, the picture will look blurred.
p 6 PARTins
5.2
CONCLUSION AND RECOMMENDATION CONCLUSION
From this study we have reached the following conclusion :- Imaging artifacts in both X-Ray CT and Ultrasound Image are due to the following:
1. Equipment artifacts. 2. Technique artifacts. 3. Patient artifacts. Each of the above fault contribute by same way or another to the detraction of image quality and hence would lead to retake of image. However, from the analysis of the data collected for this research, which was conducted by questioner and personal interviews we did find that most of the artifact in ultrasound is due equipment calibration problems and noise interference ( from radio and improper earthing 60%). While artifacts from computed tomography is due to high differential metal brain artifacts etc. (80%). From the other hand, the occurrence of technique artifact in the U/S is due transducer selection problem (80%) where as in CT technical errors artifact is about (30%) patient artifacts in ultrasound is only by reverbration which is about 70% while in CT is patient motion which is about 80%, other patient problem artifacts due to patient preparation is 40% while patient movement is 70%. Find to reduce the pressure of artifacts in image the operator should have good command of the control console and he/she should the meaning of all keys in addition to the better patient preparation during the exam as well effective patient communication and use of immobilizing devices. RECOMMENDATION
As regard to imaging artifact or indirectly affecting the final image result, we recommend the following :
1. Quality control must on inseparable programme for both system CT/U/S so as to trouble shoot and prompt diagnosis of imaging familiars before it became serious as to affect the final image quality. 2. There should be routine preventive maintenance by the equipment engineers according to a pre-planned maintenance schedule. 3. When preparing patient for either CT or Ultrasound imaging technologists should make sure that patients are artifact free i.e. free metal buttons, etc. 4 In the teaching curriculum for radiographs there should be inclusion of a complete teaching unit dealing with imaging artifacts in CT and Ultrasound. 5. Continuing inservice education staff orientation and professional development must be an on going process for all staff technologists. 6. In the case of Ultrasound imaging there must be proper connection of the earthing continuity with the imaging unit as well as to isolate the Ultrasound unit from any source of radiofrequency or the meanness of any power source to avoid infrequencies between the two systems as not to effect the real time image on the TV monitor during imaging sessions.
/of References
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Barturm, R., and Crow, H.C. (Eds.). A Manual for Physician and Technical Personnel: Gray-Scale Ultrasound, Real-time in Ultrasound. Philadelphia: Saunders, 1983.
Goldstein, A., and Madrazo, B. L. Slice-thickness artifacts in gray- scale ultrasound. J Clin Ultrasound 9:365-375,1981. Hykes, D., Hedrick, W. R., and Starchman, D. (Eds.). Ultrasound Physics and Instrumentation. New York: Churchill Livingstone, 1985. Laing, F.C. Commonly Encountered Artifacts in Clinical Ultrasound. Seminar in Ultrasound, CT and MRI 4 (1): 27-43, 1983.
Morley, P., Donald, G., and Sanders, R. (Eds.) Ultrasonic Sectional Anatomy. New York: Churchill Livingstone, 1983. Saurbrei, E. E. The spilt image artifact in pelvic ultrasonography: The anatomy and physics. J Ultrasound Med. 4: 29-34, 1985.
Thickman, D. I., et al. clinical manifestations of the comet tail artifact. J ultrasound Med2: 225-230, 1983. Ambrose. J. : Computerized transverse axial scanning (tomography): 2 Clinical application. Br. J. Radiol, 46: 1023-1047, 1973.
Ambrose, J. A. E., Lloyd. G.A.S., WRIGHT, J. E.: A preliminary evaluation of fine matrix computerized axial tomography (Emiscan) in the diagnosis of orbital space-occupying lesions. Br. J. Radiol, 47:747- 751,1974. Baker. H. L., JR.: The impact of computed tomography on neuroradiologic practice. Radiology 116:637-640, 1975.
Brooks, R. A., Drchiro, G.: Theory of image reconstruction in computed tomography, Radiology 117:561 572, 1975. Chernak, E. S., RODRIGUES - ANTUNEZ, A., JELDEN, G. L., DHALIWAL, R. S., LAVIK, P. S.: The use of computed tomography for radiation therapy treatment planning. Radiology 117:613- 614, 1975. Appendix Key to Appriviation of items
U/S: Ultrasound
CT: Computed Tomography
CAT: Computerized Axial Tomography
TGC: Time gain compensatory
EMR: Electromagnetic Radiation
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