Get the most out of your digital radiography equipment (Proceedings)

Digital radiography is the fastest growing imaging modality in medicine. It is replacing conventional analog imaging in practices across the United States. Eventually all veterinary practices will utilize this modality. Although cost of digital radiography is an issue, vendors continue to offer better equipment and competition in the free market will likely lower start-up costs for practitioners.

Basic concepts of digital radiographic technology

Digital radiography is filmless and uses conventional x-ray equipment (x-ray machine, table, grid, Bucky tray, etc.) to generate an image. There is no dark room, film storage, or processing with chemicals and light boxes are not used to interpret the image. The final image is presented on a computer screen in a digital format. Digital radiography comes in two forms: CR or computed radiography and DDR or direct digital radiography.

• Computed radiography uses a flexible image plate containing phosphors for image capture. When phosphors in the image plate are struck by x-rays incident energy is transferred to electrons of the phosphor to produce a latent image similar to conventional x-ray film. After x-ray exposure the image plate is fed into a "reader" where a laser converts captured energy to light. Light energy is amplified and converted to an electronic signal, which is digitized. Computer software automatically manipulates the digital data and the interpreter is presented with a final image read from a computer monitor.

• With DR the image is acquired on a rigid image plate, which also performs electronic capture and digitization. Unlike CR a reader is not used and digital data is sent directly to the computer via a cable connection. Depending on the system, the direct image plate converts x-ray energy to light and subsequently an electrical signal, or may directly convert x-ray energy to an electrical signal. In either case, time is saved compared to CR because a physical processing step is unnecessary-a distinct advantage in busy small animal practices and in equine imaging.

• Picture Archiving and Communications System (PACS). The PACS is a network that includes the imaging computer, software, image storage and viewing monitors. It facilitates all facets of the imaging process: image review, transmission of images, reporting and, local and remote storage...

• The DICOM file format is used to acquire, review and store digital images. DICOM (Digital Image & Communications in Medicine) file format is the industry and the FDA standard. Once acquired, these files cannot be altered due to several protective layers. However they can be manipulated and saved as another format (.tif, .jpg). DICOM files contain original image data and are used in legal cases. These files are preferred for manipulation by software programs because they are universal and contain all of the image data.

• Advantages of digital imaging

     o Improved contrast

     o Wide range of gray scale

     o Ability to adjust scale of contrast after image is made

     o Potentially faster imaging—throughput

     o Potentially fewer "re-takes"

     o No films and no film storage

     o No processor and no chemicals

     o No lost films

     o Computer friendly

• Disadvantages of digital imaging:

     o Less resolution (detail) compared to conventional radiography

     o High exposure factors

     o More personnel exposure

     o Shorter tube life—x-ray machine

     o Must have multiple digital viewing screens for interpretation

     o Proper interpretation requires a dedicated software program

     o (Microsoft Photo Editor is not enough!)

     o Must have an archiving system

     o Storage on CD ROM disks, is not an acceptable option

     o Expensive

Purchase considerations

The basic rule, "you get what you pay for often applies, so careful of cheap deals and discounts.

Be sure you know if the "package" you are buying is adequate—Ask questions before purchase! An important question is the following-"Do my staff and have the expertise in information technology to handle the switch from analog to digital? " Other considerations follow:

1) Resolution.

     a. What is resolution in lines per mm or inch? Pixel count is not a true measure of the system's resolution. Vendor can supply a test phantom once unit installed-this will give the overall resolution of the system, not just the image plate.

     b. What is resolution of monitor (s)?

2) Monitors.

     a. What type of monitor (monochromatic or color. Will the monitor be calibrated to the software according to current DICOM standards?

     b. Size of monitor-can you view two images simultaneously (VD) and lateral?

3) Bit depth.

     a. Bit depth affects the contrast or gray scale of digital images and is the amount of information that can be stored in a pixel in binary form (1, 0 or 2n).

     b. Therefore, a pixel with a bit depth of 1 (21) can store 2 shades of gray while 8 bits of depth (28) will give 256 gray shades. A bit depth of 10-12 is desirable for veterinary imaging.

4) Archiving. How will images be archived? (hard drive of computer is not acceptable as hard drives will eventually crash)

5) DCOM compliance. Is the system DICOM compliant and has this been tested by sending images to others with different software? What version of DICOM is claimed? Not being compliant will lead to problems when images are sent to distant sites, stored and accessed by another program that is DICOM compliant

6) Image plate (IP)

     a. Does the vendor ensure uniformity and calibration of the image plate?

     b. How often does this need to be done for quality control?

     c. What is the lifetime of the IP?

7) How will images be sent out via the internet—to other DVMs, clients, radiologists, etc? lossless-compressed file formats such as JPG TIF, DICOM, BMP? What kind of connection is needed by those receiving images-? What is download speed? Will you need a, static IP address?

8) How will old conventional radiographs be incorporated in to storage and/or how long will they be kept? Does the vendor supply a scanner to convert old radiographs to digital format and storage?

9) Radiographic exposures

     a. Can the vendor help establish a technique chart. (chart form conventional system will not work).

     b. How much extra exposure needed? (mAs) is needed with the new system (most CR units require increased exposure to produce enough photons to give a quality image). How does this affect tube life and scatter to personnel?

10) Is the x-ray generator presently used acceptable? – and what needs to be done to make it compatible with the CR unit?

11) Most important question! What is the quality and quantity of training for technicians and clinicians? Will the vendor return as needed until everyone is up to speed and images are acceptable?

Summary— Digital radiography is at the forefront of veterinary imaging and will eventually replace conventional film-screen radiography. Advantages of digital radiography include exceptional image contrast and computer friendliness. Disadvantages include suboptimal resolution and expense. These problems will be minimized if potential problems are addressed at purchase.

References

Armburst LJ, Digital Images and Digital Radiographic Image Capture In Thrall DE, editor: Textbook of Veterinary Diagnostic Radiology 5th edition, Philadelphia, 2007, Saunders, pp 22-37.

Moon ML, Daniel GB. Veterinary Clinics of North America: Small Animal Practice, 39(4), 2009