Flat panel detectors
Figure 3. A schematic of a scintillation style, flat panel DR detector. X-ray photons pass through the detector and interact
with a scintillation crystal that emits light. Each pixel of the detector houses electrical hardware, which maps the light
as it is emitted. (Illustration by John H. Doval)
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The DR flat panel detectors are further subdivided into panels that scintillate (emit light energy that is digitized and recorded
when X-ray photons interact with the detector elements) (Figure 3) and those that create an electrical current when X-ray photons interact with the detector; the current is then converted
to a radiographic image.9 In either case, this process is nearly instantaneous, and images can generally be viewed within seconds of their acquisition.
Scintillation detectors are the most prevalent type of veterinary DR system.10 Theoretically, in systems that do not scintillate, the lack of the intermediate light-producing step should provide these
systems with superior resolution. The clinical significance of this difference has yet to be determined.1,7-9,11
The various vendors' panels have different physical dimensions, but all have a slightly smaller active detection area than
the overall dimensions of the panel. The size of the radiograph is limited to the detector size, and care should be taken
to choose the correct imaging surface size for the types of patients and studies being produced. Generally, the dimensions
of this type of detector will be different from that of conventional film-screen cassettes, occasionally requiring alterations
in radiographic examination tables or preexisting cassette holders (equine practice). Furthermore, to electronically synchronize
the DR system with the existing generator, a minor system modification, which is usually done by the vendor, is necessary.
As with CR systems, all DR systems require purchasing a means of image storage and review.
CCD cameras
CCD camera radiographic systems generate an X-ray image when X-rays interact with a fluorescent (light-producing) screen that
is attached to the underside of the X-ray table. The light produced from this interaction is then focused by a lens and captured
by the CCD chip. In essence, the CCD camera photographs the light produced from X-rays interacting with a screen.
CCD chips are relatively small (2.5 x 2.5 cm to 8 x 8 cm). The large demagnification factor needed to reduce the size of the
patient's image to the size of the CCD may result in loss of information, which has limited the quality of CCD-based images
in the past.2,10 Advances in CCD technology, however, have overcome this limitation, and CCD-based machines are now accepted in human radiographic
applications.12-15 The veterinary experience with CCD cameras is more limited than with CR and flat panel DR detectors. CCD radiography is
used extensively in human and veterinary dental radiography because of the small field of view.
SUMMARY
This article provides an overview of the technologies used for primary capture of radiographic information. Before the information
is useful it must undergo image processing. Each vendor has a different system for image processing that may involve several
steps that vary in complexity. Image processing contributes in large part to the differences in image appearance when evaluating
the finished product. Although there are marked technical differences among the radiographic systems from the different vendors,
much of the difference in image quality will depend on the vendors' ability to effectively process the image and not necessarily
on the type of equipment used to obtain the image. CR is a relatively inexpensive system of digital radiography that shares
a similar workflow with film-based radiography. DR technologies enable veterinarians to generate radiographic images within
seconds of acquisition.
Sarah M. Puchalski, DVM, DACVR
Department of Surgical and Radiological Sciences
School of Veterinary Medicine
University of California
Davis, CA 95616
Editors' note: This article updates "Exploring your digital radiography options," which appeared in a supplement to Veterinary Medicine's December 2006 issue.
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