CR vs. DR in a nutshell

Once you have decided that digital radiography makes sense for your veterinary practice, you have two classes of options that are available to you. These are computed radiography (CR) and direct digital radiography (DR).

An introduction to CR

Computed radiography systems were first introduced in the 1980’s.  With CR systems, the film, intensifying screen, and cassette used in traditional radiography systems are replaced with an imaging plate. The imaging plate has a similar look and feel to a traditional film cassette.

The wet film processor used in conventional radiography is replaced with a digital imaging reader. These imaging readers can have various shapes and sizes depending on the manufacturer.

With CR the overall feel and workflow of acquiring an image is very similar to traditional film. As is the case with film, the CR cassette is placed in the bucky and an exposure is made.

The imaging plate is then removed from the bucky tray and placed in an imaging reader. Inside the imaging reader, the imaging plate is exposed to a series of laser lights that read the information on the plate and a radiograph appears on a computer monitor. (If you were wondering this conversion to light represents and analog process so computed radiography is not, technically, completely digital.) The imaging plate is then "erased" inside the imaging reader and is ready to use for another exposure.

This entire processing step takes about 60-90 seconds per image. It should be noted, however, that although the overall processing time is similar to traditional film you must remember that for all of the common systems on the veterinary market, you can only put one plate in at a time. The conventional wet processor takes 90 seconds but you can have many films going through at any given moment, which reduces the average film processing time to less than 90 seconds. This decrease in efficiency is substantial if you take many exposures but is generally offset by the fact that you will have fewer repeats with CR because of the increased latitude (forgiveness) of the imaging system. Many veterinarians find that despite this processing time, their efficiency is increased with CR because of the decreased number of repeats needed to obtain a diagnostic image.

One concern veterinarians have about CR is replacement costs for CR plates. At the imaging volumes at most veterinary practices, for all practical purposes CR imaging plates should not wear out.  However, they can be dropped or kicked and must be replaced if they break. Additionally, usually only a few plates are included in the "base package" that is offered to veterinarians. If you have a busy practice you will invariably need more plates. Therefore, you should consider the cost of additional plates when you evaluate these systems.

A main selling point of CR is that it can easily and effortlessly "retrofit" on to existing radiography machines. What this means is that in order to use a CR system in your practice you can just use the digital imaging plate instead of your cassettes. You don't need to purchase a new x-ray machine and installation costs are minimal.

CR systems also allow for an easy method of mobile or cross table radiography. This is important to some veterinary practices who do postoperative radiographs in the OR and to veterinarians working with exotics, as cross table radiography is common with exotics.

In summary:

1. CR Advantages
   1. A digital image is generated
   2. Ability to retrofit to existing radiography equipment
   3. Mobile or cross table radiography is easily accomplished
   4. Excellent image quality
   5. Initially less expensive than DR
2. CR disadvantages
   1. Still must process an imaging plate
   2. Similar workflow to film. Time savings may be possible through decreased repeats but the workflow is essentially similar to film radiography

Introduction to Direct Digital Radiography (DR)

Direct digital radiography (DR) is a method of digital radiography where the conventional radiographic cassette and film are replaced with a digital imaging sensor. The workflow of DR is similar to that of a photographic digital camera. Basically, you take an image and it appears on a computer screen. The processing step of film radiography and CR is eliminated with DR.

In veterinary medicine, eliminating the processing step is advantageous because your technical staff is now able to expose radiograph and without letting the animal move, evaluate the image to see if the image need to get repeated for positioning issues. This improved efficiency and improved workflow is the main benefit of DR over CR or traditional film radiography.

There are two types of DR detectors that are available on the veterinary market. These are flat panel detectors in which an imaging plate is affixed to the x-ray table.

The other main kind of DR system is called a CCD (charge couple device) detector. With a CCD camera, the “guts” of the x-ray machine are replaced by the camera, which is quite large.

Flat panel DR detectors are the technology that is primarily used on the human side and as a class of detector flat panel detectors perform well. CCD detectors have received less traction in human medicine. Although there are a number of CCD detectors with very good to excellent image quality, as a class, the quality varies considerably with the particular CCD camera and the company making the camera.

The main disadvantage of DR at this time is the initial cost as these systems are more expensive than CR to purchase and, in many cases, maintain, than CR.

Another disadvantage is that nearly all DR systems are fixed to the x-ray table. This prevents mobile radiography or cross table radiography.

In summary:

1. DR Advantages
   1. No processing time and immediate image acquisition
   2. No imaging plates or cassettes to hassle with
   3. Excellent image quality
2. DR Disadvantages
   1. More expensive than CR
   2. Cannot perform cross table or mobile radiography
   3. The imaging sensor is more expensive to replace than an imaging plate or cassette

Which modality is right for your clinic?

That answer is not so easy. Spend 5 minutes on the show floor at any major veterinary show and you will see CR vendors bashing DR vendors and vice versa. To give you an idea of what that is like, in the new book from Animal insides Press we present you a point counter point. In the CR corner is Dr. Matt Wright DACVR. In the opposite corner, making the case for DR is Dr. William Hornof DVM DACVR. As you will see there is no right or wrong to the question “CR or DR?” You need to evaluate your situation and decide what is right for your practice.