Radiology Continuing Education Series
Course 6 of 6
Pros and Cons of Digital Radiography-CR vs. DR

Course 1 – Physics of Radiology
Course 2 – Choosing the Appropriate Exposure Factors
Course 3 – Recording the Image
Course 4 – Poor Quality Films-Causes and Corrections
Course 5 – Radiation Safety-Importance and Procedures
Course 6 – Pros and Cons of Digital Radiography-CR vs. DR

Everyone wants to know about digital radiography these days. This is good. Assuming you understand what the real benefits of digital radiology are and you have decided to purchase a system. Currently you have two choices computed radiography (CR) or direct digital radiography (DR).

The first wave of digital radiography…Computed Radiography:
Computed radiography systems replace the film, intensifying screen, with an imaging plate and cassette used in traditional radiography systems. Additionally, the wet film processor used in conventional radiography is replaced with a digital imaging Scanner/reader.

The steps of obtaining a digital radiography with a CR system are as follows:
1.) The imaging plate is placed in the bucky tray, an exposure is made
2.) The imaging plate is 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.)
3.) The imaging plate is “erased” manually or some systems will automatically erase the plate inside the imaging reader and is ready to use for another exposure.

Simple enough, however, there are a few things to keep in mind:
With some systems you must tell the image reader what is on the imaging plate before you put it in the imaging reader. Huh? That’s right the image reader uses a different processing algorithm for each different type of image. For example, a lateral tarsus will be processed differently than a DMPLO metacarpal projection. Most of the time this is not a big deal. However, this is an extra step that was not necessary in conventional radiography.

Depending on the imaging reader and size of the radiograph, it takes about 25-90 seconds to read each imaging plate and plus 45 seconds to erase. This sounds similar to a conventional radiographic processor; however, there is one difference. The digital imaging reader takes 25-90 seconds BUT you can only put one plate in at a time.

The conventional wet processor takes 90 seconds but you can have additional films going through every 10 seconds, which reduces the average film processing time to 10 seconds after the first radiograph. This decrease in efficiency is not substantial unless you take a lot of films. Most companies, therefore, have imaging readers that can accept many imaging plates at one time. Many companies also have imaging plate readers that will read plates at faster than 25-90 seconds. However, these high speeds, multi-plate image readers cost more and are generally not included in the “base” packages that are advertised to veterinarians.

Imaging plates are expensive. For all practical purposes these plates shouldn’t 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.

When CR was developed it was developed to allow a digital system to “retrofit” on to existing radiography machines. This is a big selling point of computed radiography systems. 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.

CR systems also allow for an easy method of mobile radiography. In human hospitals this was necessary for bedside examinations and in veterinary medicine this lead to the introduction of CR for equine radiography. In the past, the CR manufacturers claimed that this was a significant advantage over the DR systems.

In summary:
CR Advantages
A digital image is generated
Ability to retrofit to existing radiography equipment
Mobile radiography is easily accomplished
Excellent image quality
Less expensive than DR
More than one Vet can use Scanner at a time
CR Disadvantages
Still have to use an imaging plate
Little real time saving benefit over traditional radiography

CR Vs DR Part 2: 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. This imaging sensor is either permanently affixed to an x-ray table or attached to the DR computer by a wire cable. Currently there are no viable wireless systems that I am aware of.** One vendor said that the reason there are currently no wireless systems is that DICOM images are very large images and current wireless technology cannot hand this volume of information effectively.

The steps involved in obtaining a DR image are follows:
The imaging sensor is exposed by x-rays
An image appears on the computer screen
In veterinary medicine, this advantage is enormous. Imagine if you could expose a radiograph and without letting the animal move, look over your shoulder to see if you needed to repeat a radiograph. If you did you would just adjust your position and retake it without ever letting the animal off of the table.

In human medicine, the time savings involved with DR are substantial. In one report the fastest throughput time of patients for different radiography systems was CR: 7.50 min, conventional radiography: 7.5 min, DR: 3 min. Since we must position our veterinary patients and as a result we are “position limited” I believe the increased efficiency that DR systems provide will be a huge benefit to veterinarians. Currently, however, DR systems are not a digital radiography panacea. There are disadvantages. One disadvantage of DR at this time is the cost. These systems are more expensive than CR system. Another disadvantage is that DR systems (at least all of the ones I have seen) do not retrofit to existing radiography equipment as easily as CR. Therefore, you may have to purchase a new x-ray machine or have your present units modified to work with your DR imaging sensor. The imaging sensor appears to be calibrated to a specific type x-ray machine. This is one of the reasons that these systems are more expensive than CR systems.

Finally, mobile radiography and cross table radiography are not (currently) as easily accomplished with DR. With mobile DR systems the imaging sensor is attached to the x-ray machine by a wire cable. Overall the system functioned good, however, the wires were something of a nuisance. In stationary DR systems the imaging sensor is attached to the x-ray table and cannot be removed for cross table imaging or for use with any other x-ray unit.

In summary:
DR Advantages
Short processing time and image acquisition
No imaging plates or cassettes to hassle with

DR Disadvantages
More expensive than CR
Mobile radiography necessitates a wire cable between computer and imaging sensor
Cannot perform cross table radiography when the imaging sensor is attached to the table
The imaging sensor is more expensive to replace than an imaging plate or cassette
Existing x-ray equipment needs to be modified.

CR vs. DR Part 3: Conclusion
In conclusion, CR and DR are the two leading technologies available to acquire digital radiographs. Each has their advantages and disadvantages. Which should you buy?
As far as I am concerned, the images produced by CR and DR (assuming your machine is functioning properly) are for all practical purposes equal and equal to film images. The decision to purchase a CR or DR machine is not about the image. Rather, the CR vs DR decision really comes down to your situation (i.e. finances, need for mobile radiography, etc.)

However, with all technology purchases you must keep in mind that technology changes. CR was the first digital radiography technology. Many hospitals prefer the use of a CR based digital system and are happy with the results. CR continues to be a viable alternative to DR because it is less expensive, can be used by several vets on more than one patient at a time and for the ease in which mobile radiography is accomplished with CR. Some human hospitals use a combination of DR and CR. These hospitals have a DR machine as their stationary machine and a CR unit for portable radiography. My guess is that CR will continue to be the system of choice for most Vets.

Recently, I have been getting a lot of questions from veterinarians regarding digital radiography. Private practitioners are mainly interested in learning about the different types of digital radiography (CR VS. DR.) and how they can implement these systems into their practice. Digital radiographs give (almost) the exact same information as a properly exposed film based radiograph. If this is so then why bother? Hopefully, the following discussion will answer the question.

“What are the real benefits of digital radiography?”
Benefit number 1- Decreased Costs: Cost savings come from a number of places. For example:
No film costs
No processor to maintain
No film jackets to purchase
No real estate costs for a room to store old films
No time spent searching for old films
No time spent filing film

With some digital radiography systems there is an increase throughput, increased efficiency of the radiology department and no retakes.

These cost savings all depend on you going to a completely filmless environment. Remember, there is no cost savings unless you go completely filmless. By filmless, I mean just that… hard copy image at all. If you intend to print your images on an inkjet printer or a dry laser printer your costs go up (and Decrease efficiency) compared to conventional radiography!
Unfortunately, the transition to a filmless environment may not be that easy.

If you are considering going go filmless you must consider the following:
1. What are you going to do with the images?
2. Are you going to install computers in each exam room so clients can
see their radiographs (which will require an in house computer network) or are you going to
bring clients into the darkroom to see them?
3. How will you archive the images so you can easily retrieve them?
What if your computer system crashes or catches a virus? In the case of a crash, do you have redundancy in your image archive?

These problems are not insurmountable but remember that all solutions to these problems cost money and take time to implement. Human hospitals have an IT staff to deal with these issues.

Benefit number 2 – Decreased Retakes: In human medicine digital radiography has decreased the number of retakes dramatically which increases efficiency and decreases costs. Digital radiography allows you to decrease retakes because there is increased latitude of the imaging system (i.e. digital radiography is more forgiving with exposure problems).

Benefit number 3- Decreased Radiation Dose to the Patient and Personnel: That is the digital imaging systems needs less radiation to function properly. This is not an indisputable fact. System speeds for most digital systems are between 100-400. However, in practice some people I have talked to actually increase the technique (i.e. more radiation) with these systems.

Benefit number 4- Increased Efficiency: There is no question that digital radiography has increased the efficiency of human radiology departments dramatically. They have become so efficient that some hospitals have eliminated radiology suites (as well as the technicians jobs) because they no longer needed them. However, in some veterinary practices I doubt that we will see a substantial benefit with regard to efficiency. Remember, in veterinary medicine we must spend a good deal of time getting ready (fixing to shoot as they said during my residency) to take a radiograph (i.e. positioning animals).
Some vendors also don’t tell you that processing (window leveling selection) of the digital image is both necessary and time consuming. This decreases efficiency dramatically.

Benefit number 5- Perk to the Radiologist: If I were a radiologist, I would hope that every veterinarian installs a digital system. This way I can work from home like many of the human radiologists. Needless to say, this benefit will probably help many veterinarians in private practice and save postage for referrals.

Benefit number 6- Increased Interactivity with Referring Clinicians: Many human hospitals have systems where referring clinicians can log into the radiology server and look at their patients radiographs. Many of these systems have methods where the radiologists can mark on the films and leave a message for the referring clinician. This keeps the referring clinician in the loop and increases referrals. This can benefit most veterinarians in private practice.

Benefit number 7- No Lost Films: This is a tangible benefit provides that you have good method of archiving and retrieving your films. An archiving database may not be included with your system. Ask your vendor. If not, these database systems (properly called PACS systems) can be expensive.

Benefit number 8- Digital Radiography is cool: This is not a joke. Digital radiography is very cool and for anyone that likes playing with computers this is a great toy for you to play with. I believe that this sentiment is so strong that it can creates a disconnect between reality and perception in the veterinary practice.

Benefit 9- Increased Soft Tissue Visualization: Notice that nowhere in the benefits list did I even mention the radiograph. As I said before, digital imaging is not about the image. Digital images look beautiful but for the most part you get almost exactly the same information in a digital image that you get in a properly exposed conventional radiograph. I say almost exactly the same information because you do get more information about the soft tissues on musculoskeletal radiographs. One veterinarian said that they thought that there was a lesson that they could see on a digital radiograph that they would have missed on a conventional radiograph. That lesion was a tiny entophyte in the fetlock of a horse that could only be seen with digital magnification.

Identification of this lesson, however, did not change the management of the case. This is, as Martha Stewart would say, “Is a good Thing.” However, once upon a time, there was a thing called zero radiology that promised increased latitude and increased soft tissue visualization (sound familiar): and it did just that. In fact digital radiographs look like zero radiographs. However, zero radiography is, for all practical purposes, a thing of the past. This is because the benefit of the increased latitude and soft tissue visualization did not outweigh the risk of increased exposure or increased cost compared to conventional radiography. Fortunately, digital radiography has a lot more going for it that just increased latitude.

There you have it the benefits of digital radiography. And as you can see digital radiography is not only about the image or increasing your diagnostic capability over traditional radiograph.

Problems with Digital Radiography
Like everything else in this world you have to take the good with the bad. Here are some of the issues that some vendors don’t tell you about.

Problem 1- Cost: Just so we don’t forget…these systems are expensive. Can you justify thousands of dollars to take a radiograph if your current system works fine? Remember, there are no cost savings unless you go filmless and it may be some time before you realize any cost savings.

Problem 2- Unhappy Surgeons: In the past surgeons generally don’t like digital systems for two reasons. First, it used to be difficult on some systems to measure for an implant on a computer screen. For accurate measurement you had to ensure that the image in the screen is exactly the same size of the image that the implant measurement templates are designed for. You could print out a full size digital image of the radiograph but some systems can’t do this.
The second reason surgeons don’t like digital radiography is because it is difficult to asses infection around an implant. As you can see in the images below there is a lucent halo surrounding the implant on the digital image where there is no halo in the conventional image. Some say that this phenomenon is due to using an overzealous sharpening algorithm in post processing. Most new system get around this problem by using new algorithms which prevent this.

Problem 3- Old Technology: This is a general problem plaguing all computer based technology more than anything else. Current technology becomes obsolete so quickly that it is hard to invest in something that will take years to see a return on. For example, one vet school recently purchased their second CAR system because their first on, after 7 years, was “obsolete”. Keep in mind that if in the future your computer system crashes and you get one with a new operating system that doesn’t communicate with your old digital radiography software you may be looking at an expensive problem. Additionally, it may be difficult to find support for, or repair old digital systems in the future.

This problem is a serious consideration for veterinarians. In the past, out of necessity, we have purchased “older” human equipment. In the past this model worked fine. However, this model may not work for digital radiography because purchasing old technology may mean that you will not be able to get support in the (near) future. We have already seen this with ultrasound. Any veterinarian who purchased (or was given) a used ultrasound machine from a human hospital will tell you that if a probe breaks there is a good chance that it either cannot be replaced or the replacement cost is exorbitant.

Problem 4- Not plug and play: It would be great if these systems were as easy to set up as the manufacturers claim. However, for some systems, this is not the case. Rather, expect some degree of frustration learning how to use these systems and getting the algorithms correct for your system.

Generally, this is a problem that can be easily overcome with some dedication.

In conclusion, digital radiography is an exciting new method of obtaining radiographs. Digital radiography can provide a diagnostic advantage over conventional radiographs. The benefits of digital radiography are more economic than anything else. However, in order to realize these economic benefits you must employ a completely filmless radiology environment.
Is digital radiography right for your practice? That all depends.

Personally, I would love a digital system, if I were working in a busy practice. For me, the main benefits are the ability to work from home or on the road, the ability to send radiographs to referring clinician’s to increase their awareness of the case so they can communicate better with their clients, no more lost films, and somewhere down the road, there may be a cost savings since we do a lot of films. Again, in this case digital radiography makes sense.

The case for digital radiography may not be clear cut for many private practitioners though. If you are starting a practice and do not currently have a radiography suite perhaps you should consider digital radiography. If you are having problems generating diagnostic radiographs with your current equipment and a radiologist or radiology technician has identified that the cause is your equipment perhaps you should consider a digital radiography system. However, if you are happy with the radiographs you currently produce maybe you should leave well enough alone and use the money to go on vacation to reward yourself.