Introduction to Sectional Anatomy
Dr. Ahmed Alsharef Farah
Dr. Ahmed Alsharef Farah 1 • The ability to see inside the body for medical purposes has been around since 1895, when Wilhelm Conrad Roentgen discovered x-rays. • Since that time, medical imaging has evolved from the static 2-dimensional (2D) image of the first x-ray to the 2D cross-section image of computed tomography (CT), and finally to the 3-dimensional (3D) imaging techniques used today. • Sectional anatomy emphasizes the physical relationship between internal structures.
Dr. Ahmed Alsharef Farah 2 Orientation of body slices - a transverse CT image through the abdomen.. Dr. Ahmed Alsharef Farah 3 Comparison of Traditional Anatomy and Sectional Anatomy:
• The traditional approach to anatomy is to study an entire organ. • In sectional anatomy, the anatomy is viewed on what is commonly called a slice of the body.
Dr. Ahmed Alsharef Farah 4 • Visualization of an entire organ may require several sequential slices. • Sophisticated imaging equipment can take the information from the slices and create a three-dimensional (3D) image. • Correct orientation is critical to proper identification of structures.
Dr. Ahmed Alsharef Farah 5 Now, a couple of cautionary notes for learning sectional anatomy:
1. A given organ varies in appearance at different levels in the same individual.
Dr. Ahmed Alsharef Farah 6 A, T10 level. B, T11 level. C, T12 level.
• Images of the liver at three different levels. • Notice the changes in appearance at the different levels.
Dr. Ahmed Alsharef Farah 7 2. Attempting to memorize images likely will lead to mistakes, because no two images are the same. Every individual is different, and even images of the same individual taken at the same level differ because of breathing and involuntary movements. The key is understanding, not memorization.
Dr. Ahmed Alsharef Farah 8 The importance of cross-sectional anatomy:
• The knowledge of the appearances and relationships of anatomical structures in transverse and vertical section help in precise diagnosis, as well as the detailed planning of therapy.
Dr. Ahmed Alsharef Farah 9 Anatomic positions and planes:
• In anatomic position, the body is standing erect, face and toes pointing forward, and arms at the side with the palms facing forward. • Sectional images are acquired and displayed according to one of the four fundamental anatomic planes that pass through the body.
Dr. Ahmed Alsharef Farah 10 The four anatomic planes are defined as follows:
1. Sagittal plane: a vertical plane that passes through the body, dividing it into right and left portions. 2. Coronal plane: a vertical plane that passes through the body, dividing it into anterior (ventral) and posterior (dorsal) portions.
Dr. Ahmed Alsharef Farah 11 3. Axial (transverse) plane: a horizontal plane that passes through the body, dividing it into superior and inferior portions 4. Oblique plane: a plane that passes diagonally between the axes of two other planes
Dr. Ahmed Alsharef Farah 12 Anatomic positionDr. Ahmed and Alsharef planes Farah of the body. 13 Body cavities:
• The body consists of two main cavities: 1. The dorsal cavity: is located posteriorly and includes the cranial and spinal cavities. 2. The ventral cavity: the largest body cavity, is subdivided into the thoracic and abdominopelvic cavities.
Dr. Ahmed Alsharef Farah 14 • The thoracic cavity is further subdivided into two lateral pleural cavities and a single, centrally located cavity called the mediastinum. • The abdominal cavity can be subdivided into the abdominal and pelvic cavities.
Dr. Ahmed Alsharef Farah 15 A, Sagittal view of body cavities. B, Anterior view of body cavities.
Dr. Ahmed Alsharef Farah 16 Abdominal and pelvic divisions:
• The abdomen is bordered superiorly by the diaphragm and inferiorly by the superior pelvic aperture (pelvic inlet). • The abdomen can be divided into quadrants or regions. • These divisions are useful in identifying the general location of internal organs and provide descriptive terms for the location of pain or injury in a patient’s history.
Dr. Ahmed Alsharef Farah 17 Regions:
• The abdomen can be further divided by four planes into nine regions. • The two horizontal planes are the transpyloric and transtubercular planes. • The transpyloric plane is found midway between the xiphisternal joint and the umbilicus, passing through the inferior border of the L1 vertebra.
Dr. Ahmed Alsharef Farah 18 • The transtubercular plane passes through the tubercles on the iliac crests, at the level of the L5 vertebral body. • The two sagittal planes are the midclavicular lines. • Each line runs inferiorly from the midpoint of the clavicle to the midinguinal point.
Dr. Ahmed Alsharef Farah 19 The nine regions can be organized into three groups: 1. Superior: Right hypochondrium. Epigastrium. Left hypochondrium. 2. Middle: Right lateral. Umbilical. Left lateral. 3. Inferior: Right inguinal. Hypogastrium. Left inguinal.
Dr. Ahmed Alsharef Farah 20 Dr. Ahmed Alsharef Farah 21 Quadrants: • The midsagittal plane and transverse plane intersect at the umbilicus to divide the abdomen into four quadrants: 1. Right upper quadrant (RUQ). 2. Right lower quadrant (RLQ). 3. Left upper quadrant (LUQ). 4. Left lower quadrant (LLQ).
Dr. Ahmed Alsharef Farah 22 Dr. Ahmed Alsharef Farah 23 Orientation of sections and images:
• For orientation of a transverse (axial) slice, imagine that the patient is supine and you are standing at the person’s feet looking up into the patient’s body. • All axial cross-sectional images in clinical practice are viewed that is, from ‘below’ and ‘looking up’.
Dr. Ahmed Alsharef Farah 24 View from below looking up
Dr. Ahmed Alsharef Farah 25 • Thus, all axial sections should be considered, learned and even displayed with an orientation logo shown in Figure Below. • This is the same orientation as that used for other images (e.g. chest X-ray). Here, again, the right of the patient is on the viewer’s left.
Dr. Ahmed Alsharef Farah 26 • The orientation logo in Figure Below is suitable for the head, neck, thorax, abdomen and pelvis.
Dr. Ahmed Alsharef Farah 27 • In the limbs, however, when only one limb is displayed, further clarification is required. • All depends on whether a right or left limb is being examined. • To assist this quandary, a medial and a lateral marker is provided in Figure Below.
Dr. Ahmed Alsharef Farah 28 • The orientation of coronal images has also been standardized so that they are viewed with the patient’s right on the left, exactly as for a chest X-ray or when talking to the patient face to face. • There is no firm standardization of sagittal images.
Dr. Ahmed Alsharef Farah 29 A = anterior P = posterior R = right L = left S = superior I = inferior
A, Axial CT of liver. B, 3D CT of hips (anterior view).
Dr. Ahmed Alsharef Farah 30 Image display:
• Each digital image can be divided into individual regions called pixels or voxels that are then assigned a numerical value corresponding to a specific tissue property of the structure being imaged. • The numerical value of each voxel is assigned a shade of gray for image display.
Dr. Ahmed Alsharef Farah 31 Representation of a pixel and voxel.
Dr. Ahmed Alsharef Farah 32 • In CT, the numerical value (CT number) is referenced to a Hounsfield unit (HU), which represents the attenuating properties or density of each tissue. • Water is used as the reference tissue and is given a value of zero.
Dr. Ahmed Alsharef Farah 33 • A CT number greater than zero will represent tissue that is denser than water and will appear in progressively lighter shades of gray to white. • Tissues with a negative CT number will appear in progressively darker shades of gray to black.
Dr. Ahmed Alsharef Farah 34 CT numbers and windowingDr. Ahmed Alsharef onFarah axial CT of chest. 35 • In magnetic resonance (MR), the gray scale represents the specific tissue relaxation properties of T1, T2, and proton density.
Dr. Ahmed Alsharef Farah 36 MRI Image contrast.
T1-weighted T2-weighted PD-weighted
Dr. Ahmed Alsharef Farah 37 Multi-planar Reformation (Reformat) (MPR):
• Images reconstructed from data obtained along any projection through the cube result in a sagittal, coronal, axial, or oblique image.
Dr. Ahmed Alsharef Farah 38 Multi-planarDr. Ahmedreformation Alsharef Farah and 3D. 39 Multi-planar reformations of brain. Dr. Ahmed Alsharef Farah 40 3D Imaging
Shaded Surface Display (SSD):
• Includes only information from the surface of an object. • The voxels located on the edge of a structure are used to show the outline or outside shell of the structure
Dr. Ahmed Alsharef Farah 41 Shaded surface display (SSD).
Dr. Ahmed Alsharef Farah 42 Maximum Intensity Projection (MIP):
• The MIP selects only the voxel with the highest value for inclusion in the displayed image.
Dr. Ahmed Alsharef Farah 43 Maximum intensity projection (MIP).
Dr. Ahmed Alsharef Farah 44 Volume Rendering (VR):
• All voxels contribute to the image. • This allows VR images to display multiple tissues and show their relationships to one another. • The pixels in the final VR image can be assigned a color, brightness, and degree of opacity.
Dr. Ahmed Alsharef Farah 45 Volume rendering (VR). Dr. Ahmed Alsharef Farah 46 End of this lecture…
Dr. Ahmed Alsharef Farah 47