The bedrock of any veterinary digital x-ray installation is a good old x-ray machine. If your x-ray machine is not up to snuff, your digital images will suffer. Whether you are buying a new x-ray machine or you are retrofitting a digital system to your current x-ray machine you need to make sure your x-ray machine is in order before you begin to contemplate a digital purchase.
What kind of x-ray machine should I buy for my veterinary practice or what kind of x-ray machine will work best with my digital x-ray machine?
Many veterinarians buying digital radiography systems do so because their x-ray machine if failing or has failed. . Although x-ray machines all do pretty much the same thing, there are a few important features that you need to consider when buying an x-ray machine.
Generator type: the most important decision you will need to make when buying a digital x-ray machine is the type of generator. The two main types of veterinary x-ray generators are a single phase generator and a high frequency generator. A full discussion of the differences between a single phase and high frequency generators can be found here The short story on the main differences are that relevant to the practicing veterinarian are:
- A high frequency generator will output a greater amount of radiation over time when compared to a single phase generator. This means that your exposure settings will be lower (this is good) with a single phase generator vs. a high frequency generator1
- In theory, high frequency x-ray generators will last longer because the near-constant potential of the waveform will reduce pitting on the x-ray tube. In practice, given the volumes of studies performed at most vet hospitals, I am not sure if this a a significant difference.
- Single phase generators cost less than high frequency generators. That said the cost difference has narrowed in recent years and is less significant than it used to be.
- Digital image quality: EVERY (caps for emphasis) digital radiography company prefers to use a high frequency machine for a digital radiography installation. The improved radiation output will (in theory)2 result in improved image quality.
- High Frequency generators are smaller (size) than single phase generators. If size matters, a high frequency machine will (generally) have a smaller footprint than a single phase machine and the generator is generally placed under the x-ray table.
- Modern high frequency machines are digital technology while single phase machines use analog technology.This makes calibration and service of high frequency machines significantly easier (and potentially less costly). Single phase generator are calibrated by using large and awkward resisters that are very difficult to use to accurately. High frequency machines are calibrated using a microprocessor and the microprocessor keeps them calibrated. Stated another way, high frequency machines can be self calibrated. These high frequency machines also have "on board diagnostics" which facilitate service as these diagnostics help service technicians diagnose and fix problems should they arise with your machine.
The bottom line with all of this is that single phase and high frequency machines will both work. That said, the price difference is no longer that great so high frequency generators are recommended for digital radiography applications if you are buying a new x-ray machine.
Generator Size: X-ray generators generally come in 3 flavors according to the size(output) of the generator. The most common generators are 300, 400, or 500 mA generators. In our opinion, 500mA is overkill. Unless you have a cat practice take the middle road and get the 400mA machine. 300mA will work for most practices but you might be left with grainy digital images wen you need to radiograph that Rottweiler with peritoneal effusion.
Floating table top: A four way float table helps your technician position animals for radiography. With a floating table top, you move the table and not the pet. A floating table top is an upgrade on most x-ray machines that we recommend. Your technicians will love you for it.
Anatomical Programming: The anatomical programming feature is becoming popular. With anatomical programming, rather than using a traditional technique chart, you pick a body part and a thickness and the machine sets the rest. Keep in mind, however, this feature really is really just an automated technique chart. It is not magic and you will need to set the manually set the anatomical programming settings for your digital radiography system.
Brand: X-ray machines last a long time but they do not last forever. You will need parts eventually. Going with a name brand might help save a few headaches in the future. If you cannot find a board or new tube for that machine, you might be looking at replacing the entire unit.
Overall Build: some machines are built rock solid. Some are plastic pieces of cheapness that will make you cringe when you need to radiograph your first thrashing Great Dane after they were hit by a car3
Local support and service: If you have a company fly in and drop off a machine and you do not have someone locally who can fix it, you are asking for problems. You do not necessarily have to buy your x-ray machine from your digital radiography vendor. Maybe you should consider giving your local x-ray person the sale on your x-ray machine and give the digital vendor the sale on the digital piece.
Will my x-ray machine work with a new digital radiography system? Can I retrofit a digital radiography machine to my existing x-ray machine?
In many cases, digital radiography devices can be retrofit to existing x-ray machines. Most x-ray machines will last 20-30 years given the normal volume of use at a veterinary hospital. We see too many installations where veterinarians unnecessarily buy new x-ray machines as part of a digital radiography purchase.
Veterinarians need to realize, however, that x-ray machines do not last forever and if you are going to retrofit a digital system on to an existing x-ray machine installation you need to be absolutely certain that the x-ray machine is in good working order.
X-ray machines will “die deceptively.” When x-ray machines die, they do so like a wounded goat running through the Greek countryside. Rather than exploding into a ball of flames or just shutting down one day, most failing x-ray machines will slowly die by generating variable or intermittent exposures. This slow death is caused by “pitting” of the x-ray tube which results in the tube not being able to generate the amount of radiation that is set on the kV and mA dial.
This slow death can be very subtle and may even go undiagnosed until you retrofit a digital radiography system to your existing x-ray machine. Some digital radiography systems require more x-ray exposure than film and this increased exposure might just put your x-ray machine over the edge. Some digital radiography systems may also be more sensitive to the variable exposures generated by a failing x-ray machine than film.
The best thing to do before retrofitting any digital radiography unit to an existing x-ray machine is to have an x-ray technician come out and run some diagnostics on your x-ray machine. These diagnostics are different than the ones the State does to make sure that your x-ray machine is safe to use. The x-ray technician will measure the output of your x-ray machine with an exposure meter. If there is a significant variability in the output, it is probably best to get a new machine rather than retrofitting a digital system.
Bottom line: If you are buying a new x-ray machine, get a 300 or 400mA, high frequency, x-ray machine with a floating table top from a reputable dealer with local service. If you are retrofitting a digital unit to your x-ray machine, be sure that you have your machine tested by an experienced x-ray technician. If you are retrofitting a system, a single phase or high frequency machine will work provided that you are not buying a CCD machine. With CCD based digital radiography systems you will almost invariably require a high frequency generator.
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1. How much lower you ask? Just take the root mean square of the kVp or multiply the kVp by Root Mean Square (rms) of 70.7%. For example if your kVp on a single phase machine is 95 it will be 67.2 on a high frequency machine. Stated another way, the output of a high frequency machine is about 30% higher than a single phase machine. This is VERY important when comparing vendor claims of exposure and sensitivity of digital radiography systems.
2. Interestingly, these vendors (with the exception of CCD vendors who really do require a high frequency machine) do not seem to have an issue retrofitting to a single phase machine if it will result in a sale. I have made many attempts at determining if there is a significant CLINICAL difference (once the exposures are normalized) in image quality between images obtained on a single phase vs. high frequency machine. Ultimately, I gave up the chase as I could not see a difference and my methods were so far from anything scientific that even this dude (trying to clean up an oil spill with a rake) would question the results. Unfortunately, I do not have the resources to radiograph the same animal with the same system on a different machine and evaluate the images. All I know, is that there are loads of digital retrofits on single phase machines and it would be hard to say that those vets are missing lesions because they do not have a high frequency generator.
3. Now that I think about it, I do not know if I have ever seen an Great Dane that got hit by a car. Maybe their size results in more deaths and they never make it to the x-ray room. Maybe they are better car dodgers. Maybe they are just lazy and don’t run in the road. Who knows?