Diagnostic Imaging

Among the most useful tools for doctors to evaluate patients is diagnostic imaging. This includes radiographs (x-rays), fluoroscopy, ultrasonography (ultrasound), scintigraphy, computed tomography (CAT scans/CT scans), and magnetic resonance imaging (MRI scans). Each of these provides different kinds of images, and in some instances more than one may be suggested by your doctor to evaluate a particular problem in your pet. All share the goal of providing pictures of internal structures.

The most familiar imaging tool and most frequently used is radiography with x-rays. Anatomy can be discerned because of differences in contrast between fat, water, bone and metal. Most of the body’s soft tissues are either water-dense or fat-dense. The most commonly taken x-rays are those of the chest cavity, abdominal cavity, limbs, spinal column, and skull.

Because dogs and cats are generally not amenable to holding still, especially in an awkward position, some form of restraint is usually required to take x-rays. In some instances this may involve humans (technicians, doctors or even clients) holding the animal in position while the x-rays are taken. This is more commonly done in primary care veterinary offices. At VSES we minimize the use of manual restraint by humans. There are several good reasons for this. First, animals that are hand-restrained may still squirm and may be uncomfortable. Second, we often have to take more than a single film and this adds to the distress of the patient and radiation exposure for the involved humans. While the amount of radiation received by the pet is minimal, even with multiple x-rays, our concern is cumulative dosing in people and therefore minimizing human exposure. At a busy referral/emergency center such as VSES, where many more radiographs are made than at most typical primary care veterinary offices, human exposure to radiation is a real concern. For these and other reasons we use alternative methods of restraint. Where appropriate we will immobilize the fully conscious pet with sandbags and strings. However, there are many instances where this also will be inadequate to prevent motion and pain. Therefore we employ judicious use of chemical restraint, using various sedatives or anesthetics. Nowadays we have many choices for such drugs, and this translates to greater safety and for many pets only a brief sedation from which they are fully recovered within just a few minutes. Your doctor will discuss with you the need for x-rays and what type of restraint is needed. Please accept his or her judgment, and understand that under no circumstances can we permit clients to be present or help hold their pet during radiography, even if this is how things were done at another veterinary hospital.

In addition to plain x-rays we sometimes use radiographs to do contrast studies. In these instances a dye material is administered that on radiographs has a metallic density. The contrast agent (“dye”) most of us are familiar with is barium, and this is most commonly used to evaluate the digestive tract. However, contrast studies are also used (with different dye agents) to evaluate the urinary system (excretory urograms or intravenous pyelograms – IVP’s), blood vessels (angiograms), and spinal cord (myelograms), among others.

The next most commonly utilized imaging tool at VSES is ultrasonography. High frequency sound waves are used to provide more narrowly focused pictures of internal structures. Details that might be difficult to discern on radiographs can often be seen with ultrasound. Ultrasound can also provide “real-time” images of structures to detect such things as movement. We are all most familiar with this in the use of ultrasonography to examine developing fetuses in pregnant women. Real time imaging also permits ultrasound-guided aspiration (placing a small hypodermic needle into a structure to collect some fluid or cells, such as is done for amniocentesis) or biopsy of internal structures. More so than radiographs, the success of ultrasonic imaging is directly linked to the skill and training of the ultrasonographer. Individuals highly trained in ultrasound imaging (such as the internists and cardiologists at VSES) may be able to make diagnoses, obtain samples, and provide treatment guidance far better than a less skilled or experienced examiner even when using identical machines. This is important to bear in mind if another veterinarian recommends an ultrasound exam. You should not be afraid to ask anyone proposing to do an ultrasound exam on your pet what their experience level and training is.

Fluorsocopy is used on occasion to evaluate such things as swallowing function, angiography (motion studies of blood flow or interventional radiology and interventional cardiology using special catheters), and can be used in orthopedic surgery to evaluate placement of drills, screws, and so forth. It is real-time x-ray imaging. Fluoroscopy is used to place cardiac pacemakers and vessel stents or coils. VSES currently utilizes fluoroscopic equipment at a cooperating human medical facility.

Scintigraphy is a form of what is generally called “nuclear medicine”. Don’t be alarmed! Scintigraphy involves the administration of minute quantities of a radioactively-labeled substance into the body, and then monitoring and measuring where the radio-labeled substance goes after administration. Bone scans are one form of scintigraphy. Thyroid scans are another. The pictures provided with scintigraphy are crude compared with other imaging modalities, but have the advantage of providing functional images, indicating normal or abnormal function of target organs. At present VSES refers patients to other facilities for scintigraphic evaluations.

Computed tomography (CT) and magnetic resonance imaging (MRI) are examples of what many term advanced imaging modalities. They are also called cross-sectional imaging modalities. Another type of scan in this category is positron-emission tomography (PET scan). Though one would think CAT scans would be best for cats and PET scans useful for veterinary imaging, these handy acronyms have little bearing on which scan is most useful for particular patients!

Computed tomography (CAT derives from the older terminology, computed axial tomography) uses x-rays in a 360-degree technique with a special scanning machine. Like plain radiographs the amount of radiation exposure for patients with CT is minimal. Technology has progressed dramatically. Current CT scanners allow complete imaging of even large areas in just a few minutes, and the digital images can then be reformatted to provide 3-dimensional reconstructions. Because patient motion greatly degrades the images, pets are always given short-acting sedation/anesthesia for CT scans. Currently VSES obtains CT scans at a nearby human medical facility.

Magnetic resonance imaging (MRI) is a non-x-ray based technology. It utilizes a powerful magnet and radiofrequency waves to create highly detailed images of virtually any structure in the body. MRI pictures can provide far more detail than either radiographs made with x-rays or ultrasound. Not all MRI’s however are equivalent. Different size magnets and other factors greatly affect resolution or clarity of the images produced, especially in smaller patients (like our pets) or smaller structures. All MR imaging in animals requires anesthesia due to the requirement for complete immobility during scanning and the relatively longer time needed for MRI than other imaging techniques (like CT). The quality of the MRI scanner itself also bears on how much time is needed for a study. So-called low-field magnets in use in some veterinary hospitals (because they are far less expensive to install and maintain) may be very inadequate for certain studies (too long for the scan and images that are too grainy). At VSES we use mid- and high-field, state-of-the-art MRI scanners that permit superior imaging of even the smallest structures in the tiniest patients. VSES has access to nearby MRI scanners used for people, and in 2007 will have in-house state-of-the-art MRI capabilities through Companion MRI of Western New York.

There is some overlap between the indications for CT and MRI scanning. The former is generally best for bony details (such as treatment planning for complex fractures) and also for pictures of the lungs. MRI is generally superior for brain, spinal cord, and abdominal imaging. If your doctor recommends advanced imaging he or she will discuss with you the reasons for their preference for either CT or MRI in the particular situation.

Newer technologies (such as MRI), those that depend on complex equipment, and those that are more time and labor-intensive necessarily cost more, and all imaging is relatively expensive. At VSES we understand this and are sensitive to how we can provide the best single technique or combination of imaging modalities to provide definitive answers for you and your primary care veterinarian at the lowest possible cost. We are available to you and your veterinarian to help guide all diagnostic evaluations and interventions, including those that involve diagnostic imaging.

It is not uncommon for referred patients to already have undergone some imaging before arriving at VSES. We always happily review any provided images from your primary care doctor and strive to avoid unnecessary duplication. However, keep in mind that sometimes more images are required for the specialist or emergency doctor to fully understand your pet’s problem or to determine the proper treatment. We encourage primary care doctors who are contemplating referral to avoid taking initial x-rays or performing preliminary ultrasound exams if such imaging will have no effect on their decision whether to refer. This is the best way to avoid duplication of services or added expense. As a client, you can always inquire of your primary care veterinarian whether any x-rays or ultrasound exams will affect their decision to refer. If so, by all means have them carry on. If not, you can request that they refrain from such imaging so that added expense and duplication of services are avoided.

The same principle holds true for other diagnostic evaluations such as laboratory (blood) tests. If a referral has already been recommended there is often little value to having blood tests performed beforehand, and it is completely inappropriate for referring primary care doctors to draw blood and send the vials to VSES with the client, or to charge for lab work that they themselves are not interpreting or making treatment decisions based on. In those instances where that is done you should be prepared for VSES to charge you for running and interpreting the lab work (or drawing fresher samples if you were sent with tubes of blood). If your primary care doctor charged you as well you should discuss with him or her the propriety of having done so. Lab work charges reflect a combination of drawing the samples, processing them in the laboratory, and finally interpretation by the doctor. The latter is the most important. However, like referral radiographs received with patients, any previously run and interpreted lab work that accompanies the patient to VSES will be cheerfully reviewed at no additional cost.