Veterinary Medicine - April 2009 - (Page 179)

PEER-RE VI E WED Exploring your Options Making the leap to digital radiography? You have two basic types of equipment to choose from. Now, which one is better for you? Sarah M. Puchalski, DVM, DACVR DIGITAL RADIOGRAPHY EQUIPMENT O ne of the rst steps in switching to digital radiography is deciding what type of system to purchase. Two broad classes of digital radiography equipment are available for veterinarians: cassette-based, or computed, radiography (CR) and direct (capture) radiography (DR).1,2 This article focuses on primary capture devices instead of secondary capture devices such as image digitizers (scanners) and digital cameras. In general, secondary capture devices have important limitations from both a medicolegal and an image quality standpoint. CR CR was the rst digital radiography system used in medical imaging. These systems have many features analogous to traditional lm-screen systems (Figure 1) because a cassette is used to house a photo-stimulable phosphor sheet.2 The latent image is stored in the phosphor sheet similar to how undeveloped lm stores the latent image in lm-screen technology (Figure 2). CR radiographs are obtained in a traditional manner: all the views of the study are taken, and then the cassettes are moved en masse Sarah M. Puchalski, DVM, DACVR Department of Surgical and Radiological Sciences School of Veterinary Medicine University of California Davis, CA 95616 to a digital processor. Each cassette is then individually fed into the processor where the storage phosphor sheet is removed and scanned by a laser. The laser imparts energy onto the storage phosphor sheet, liberating light from the latent image stored therein. The light emitted from the phosphor sheet is digitized to produce the digital radiograph. The processor requires 60 to 90 seconds to produce an image from each cassette, and the cassettes are re-used numerous times. During this processing time, the next cassette cannot be fed in, though many processors accept multiple cassettes (two to four) at one time. CR may slow work ow if the number of radiographic projections exceeds the number of cassette receptacles on the processor.3 This problem may arise in multiple-view studies such as orthopedic or pre-purchase examinations. Thus, the CR work ow is similar to that of traditional radiographic lm.4,5 Because of the delay in image processing, it will take several minutes to identify errors in radiographic technique, speci cally positioning. In small-animal practice, it may simply entail repositioning of the animal, while mobile equine practitioners will not recognize the need for retakes until the cassettes are returned to the processor, which is most commonly housed in a stationary location such as the clinic. More recently, portable CR processors have become commercially available to help obviate this inconvenience. CR requires purchasing the cassettes, a processor, and equipment for viewing and storing the images. The cassettes have the same physical dimensions as lm-based cassettes and do not require any modi cation to the X-ray generator, tables, or grids. In general, CR is a slightly less expensive digital radiographic modality that will provide many of the advantages of digital imaging to a veterinary practice. DR DR, or direct X-ray (DX), generally refers to one of three system types. The unifying characteristics of these systems are that an image is produced nearly instantaneously and that the same X-ray detector is used for every exposure.1,2,6-8 Two systems fall into the at panel detector category. These systems are a commonly used DR system in veterinary medicine. The other type of DR system is a charge-coupled device (CCD) camera. Flat panel detectors The DR at 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 VETERINARY MEDICINE April 2009 179

Table of Contents Feed for the Digital Edition of Veterinary Medicine - April 2009

Veterinary Medicine - April 2009 Contents Idea Exchange Practical Matters An Update on Gallbladder Mucoceles in Dogs Digital Radiography Equipment Benefits and Considerations How to Perform a Two-portal Laparoscopic Ovariectomy Author Guidelines CE Form/Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - April 2009

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.