radiation dose and not compromise image quality. This is an important consideration in observing and working within the as low as reasonably achievable (ALARA) philosophy established by the ICRP.
DIGITAL RADIOGRAPHY MODALITIES: MAJOR SYSTEM COMPONENTS
Digital radiographic imaging systems generally referred to as DR has replaced the workhorse of diagnostic radiography, FSR. DR is defined by the American Association of Physicists in Medicine (AAPM) [4] as “radiographic imaging technology producing digital projection images such as those using photostimulable storage phosphor (computed radiography or CR), amorphous selenium, amorphous silicon, charge‐coupled device (CCD), and metal oxide semiconductor‐field effect transistor (MOSFET) technology.” DR includes computed radiography (CR) and flat‐panel digital radiography (FPDR); digital fluoroscopy (DF); digital mammography (DM); digital radiographic tomosynthesis (DRT) and digital breast tomosynthesis (DBT); and CT. These modalities are described in detail by Seeram [5].
The overall major system components of any DR modality are illustrated in Figure 2.4, and includes an x‐ray generator, an x‐ray tube, a digital detector, a computer, an image display monitor, and finally a digital communications system.
1 The x‐ray generator provides the electrical power to the x‐ray tube to provide the appropriate radiation exposure for the examination under investigation.
2 The patient is exposed and a latent image is created on the digital detector.
3 The latent image is processed by the computer and subsequently displayed on a monitor for viewing and interpretation.
4 The image can be stored and communicated to remote sites for viewing.
Each of the DR modalities listed above will be reviewed below with respect to major imaging system components only. The details of each of these modalities work will be described in later chapters.
Figure 2.4 The overall major system components of any DR modality includes an x‐ray generator, an x‐ray tube, a digital detector, a computer, an image display monitor, and finally a digital communications system.
Computed radiography
The major components of a CR system are shown in Figure 2.5. These components include the imaging plate (IP), the IP processor, IP erasure, and image display monitor. After the IP is exposed as shown, a latent image is created on the IP. Subsequently, the IP is placed in the processor where it is scanned by a laser beam to render the latent image visible which is then displayed for viewing and interpretation. The IP is exposed to a bright light to erase any residual image, so that it can be used again.
Flat‐panel digital radiography
The major system components of a FPDR system are shown in Figure 2.6 and include an x‐ray generator, an x‐ray tube, a flat‐panel digital detector, a computer, an image display monitor, and finally a digital communications system.
The flat‐panel digital detectors for FPDR fall into two categories, namely, the indirect conversion digital detector and the direct conversion digital detector. A significant difference between CR and FPDR systems is that the latter does not include a separate physical image reader but rather a digital processor is included in the design of the flat‐panel detector, so that the latent image formed on the detector is subsequently rendered visible by the built‐in digital processor. The image is then displayed on a monitor for viewing and interpretation.
Digital fluoroscopy
Fluoroscopy produces dynamic images acquired in real‐time to allow for the study of motion of organ systems and hollow internal structures such as the gastrointestinal tract, as well as blood circulatory system. The major system components of a DF system (Figure 2.7) consist of a flat‐panel digital detector to allow for the creation of real‐time dynamic images processed by a computer and subsequently displayed as a square image on the viewing monitor, compared to a circular image typical of the older image intensifier‐based DF systems. This display method eliminates what is known as pin cushion distortion effects characteristic of the older digital fluoroscopic systems.
Figure 2.5 The major components of a CR system include the imaging plate (IP), the IP processor, IP erasure, and image display monitor.
Figure 2.6 The major system components of a FPDR system include an x‐ray generator, an x‐ray tube, a flat‐panel digital detector, a computer, an image display monitor, and finally a digital communications system.
Figure 2.7 The major system components of a DF system consist of a flat‐panel digital detector to allow for the creation of real‐time dynamic images processed by a computer and subsequently display the image as a square image on the viewing monitor, compared to a circular image typical of the older image intensifier‐based digital fluoroscopy systems. This display method eliminates what is known as pin cushion distortion effects characteristic of the older digital fluoroscopic systems.
Digital mammography
Major components of a DM system currently utilize CR detectors and flat‐panel digital detectors including direct and indirect conversion detectors to image the breast. Image acquisition and processing is similar to that described above for FPDR. Additionally, associated applications of DM include DBT and DRT. While DBT is designed to examine only the breast, DRT images other body regions, such as the chest abdomen, extremities, for example.
