CHAPTER 9 Digital and Advanced Imaging Equipment
KEY TERMS active matrix array direct-to-digital radiographic systems photostimulated luminescence amorphous dual-energy x-ray absorptiometry picture archiving and communication analog-to-digital converter F-center system aspect ratio fill factor preprocessing cinefluorography frame rate postprocessing computed radiography image contrast refresh rate detective quantum efficiency image enhancement special procedures laboratory Digital Imaging and Communications image management and specular reflection in Medicine group communication system teleradiology digital fluoroscopy image restoration thin-film transistor digital radiography interpolation window level digital subtraction angiography liquid crystal display window width digital x-ray radiogrammetry Nyquist frequency
OBJECTIVES At the completion of this chapter the reader should be able to do the following: • Describe the basic methods of obtaining digital cathode-ray tube cameras, videotape and videodisc radiographs recorders, and cinefluorographic equipment and discuss • State the advantages and disadvantages of digital the quality control procedures for each radiography versus conventional film/screen • Describe the various types of electronic display devices radiography and discuss the applicable quality control procedures • Discuss the quality control procedures for evaluating • Explain the basic image archiving and management digital radiographic systems networks and discuss the applicable quality control • Describe the basic methods of obtaining digital procedures fluoroscopic images • Describe the basic quality control process for special • Explain how digital subtraction angiography is performed procedures equipment • Discuss the quality control procedures for evaluating • Explain the various methods for obtaining bone mineral digital fluoroscopy density measurements • Describe the basic principle of image production from multiformat cameras, laser cameras, dry laser printers,
OUTLINE Digital Radiographic Imaging Computed Radiography Disadvantages of Computed Systems 132 (CR) 134 Radiography versus Secondary Capture 133 Advantages of Computed Conventional Laser Scanning Digitizer 133 Radiography versus Radiography 138 Charge-Coupled Device Conventional Scanner 134 Radiography 137
131 132 CHAPTER 9 Digital and Advanced Imaging Equipment
Digital Radiography 139 Digital Subtraction Videotape, Videodisc, and Digital Indirect-conversion or Angiography 146 Recorders 160 Scintillator Digital Temporal Mask Components 160 Radiography System 140 Subtraction 147 Quality Control of Analog and Direct-conversion or Time-Interval Difference Digital Recorders 160 Photoconductor Digital Subtraction 147 Cinefluorography and Radiography System 140 Dual-Energy Subtraction 148 Photofluorography 161 Comparison of Computed Quality Control of Digital Image Archiving and Management Radiography with Digital Fluoroscopy Units 148 Networks 162 Radiography 141 Electronic Display Devices 149 Miscellaneous Special Procedures Quality Control of Digital Cathode-Ray Tube Displays 149 Equipment 163 Radiographic Imaging Liquid Crystal Displays 150 Film Changers 164 Systems 141 Plasma Displays 151 Pressure Injectors 164 Digital Fluoroscopy 145 Quality Control of Electronic Bone Densitometry Systems 164 Last Frame–Hold 145 Display Devices 151 Single-Photon Road Mapping 145 Multiformat Cameras 153 Absorptiometry 164 Digital Temporal Components 153 Single-Energy X-Ray Filtering 145 Brightness 154 Absorptiometry 165 Image Enhancement 145 Contrast 154 Dual-Photon Image Restoration 145 Exposure Time 155 Absorptiometry 165 Image Intensifier Tube Digital Quality Control of Multiformat Dual-Energy X-Ray Fluoroscopy Systems 145 Cameras 155 Absorptiometry 165 Flat-panel Digital Fluoroscopy Laser Cameras 156 Quantitative Computed Systems 146 Components 156 Tomography 165 Continuous Fluoroscopy Quality Control of Laser Quantitative Ultrasound 165 Mode 146 Cameras 158 Digital X-Ray Pulsed Interlaced Scan Dry Laser Printers 158 Radiogrammetry 166 Mode 146 Cathode-Ray Tube Cameras 159 Quality Control of Bone Pulsed Progressive Scan Components 159 Densitometry Equipment 166 Mode 146 Quality Control of Cathode-Ray Summary 166 Slow Scan Mode 146 Tube Cameras 160
In recent years, diagnostic imaging has undergone an electronic display device (computer monitor). The explosion in technology with the advent of computer- computer matrix is made up of tiny squares called ized imaging, magnetic resonance imaging (MRI), and pixels (a contraction of the term picture element). digital archiving and retrieval systems. All of these tech- The more pixels in a matrix, the smaller each nologies are now commonplace in diagnostic imaging pixel becomes, thereby increasing spatial resolution departments and can be subject to variations with age (Fig. 9-1). The production of digital radiographic and use; therefore, quality control protocols should be images is rapidly replacing this method of film/screen in place to monitor for these variations so that they radiography. Creating radiographic images in a digital can be kept to a minimum. format has many advantages over the analog format (film/screen images), including:
DIGITAL RADIOGRAPHIC • the reduction of repeat images due to technique error IMAGING SYSTEMS (Most overexposures and slight underexposure can be corrected with software and not have to be Virtually all diagnostic imaging systems can be consid- repeated, but gross underexposure cannot.), ered to have three key components: image acquisition, • simplification in the filing of images (They can be image processing, and image display. Since the late stored electronically rather than in hard copy.), 1890s, radiographic images were acquired by exposing • reduction in the number of lost images (Digital a screen/film combination that required chemical pro- images are stored electronically and can be retrieved cessing and was displayed on a viewbox illuminator. as long as it has been correctly entered and saved in In digital imaging, an image acquisition system the computer system.), obtains image data in the form of an electronic signal, • postprocessing of the image (Detail and contrast can which is processed electronically in a computer mem- be enhanced by the computer software.), ory whereby the image exists as electronic values in • and electronic transmission of images (This allows a computer matrix (rather than as grains of silver on quick access to images by referring physicians and a sheet of polyester plastic), and displayed on an for consultation over large distances.). CHAPTER 9 Digital and Advanced Imaging Equipment 133
64×64 1024×1024 FIGURE 9-1 Images showing the difference in spatial resolution as the size of the matrix increases.
Currently, digital images can be acquired by using Laser Scanning Digitizer. The laser scanning digitizer one of three methods: secondary capture, computed is used to convert an existing radiographic image that radiography (CR), or digital radiography (DR). is recorded on film into a digital format that can be stored and transmitted electronically (Fig. 9-2). It is sim- Secondary Capture ilar in function to a scanner that is used with a personal computer to scan photographic images into the com- This method of creating digital images involves the ini- puter data storage. The existing radiograph is placed in tial creation of an analog image (on film) and then its the digitizer, where it is scanned by a laser and then conversion into a digital format. One method of accom- detected by photosensors on the other side. The signals plishing this conversion would involve taking a photo- sent by the photosensors are then sent through analog- graph of a film radiograph with a digital camera. This to-digital converters (ADCs) and into the computer method has been used for years by diagnostic imaging memory. The higher optical density areas of the film educators (like myself) to obtain digital images. How- image attenuate a higher percentage of the laser light ever, there is considerable loss of resolution even with a large matrix (>3-megapixel) camera. Therefore, it may be acceptable for teaching files or professional meeting presentations but should never be used to make a diagnosis. More acceptable conversion of analog film images to digital format can be accomplished by a laser scanning digitizer or a charge-coupled device (CCD) scanner. Common uses of secondary capture devices include:
• Film radiographs are archived into a picture archiv- ing and communication system (PACS). • Computer-aided diagnosis is a software program whereby the computer can look for abnormalities in mammography and chest radiographs. • Teleradiology is the process of sending digitized images to distant locations for interpretation and consultation. • Duplicate Images allows the original film-based radiograph to remain at the original clinical site while an electronic copy made by the digitizer can FIGURE 9-2 Laser scanning digitizer. (Courtesy Agfa in Bushong be burned onto a CD or DVD and given to the SC: Radiologic Science for Technologists, ed 9, St Louis, 2008, patient. Mosby.)