Among the most useful tools we use to evaluate a pet’s condition is diagnostic imaging. This includes radiographs (x-rays), ultrasonography (ultrasound), computed tomography (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 us to evaluate a particular problem in your pet. All of these methods provide ‘pictures’ of internal structures.
The most familiar imaging method and most frequently used at the London Veterinary Clinic is radiography or 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 unwilling to hold still, especially in an awkward position, some form of restraint is usually required to take x-rays. While being held by people is a simple form of restraint, hand-restrained pets may still squirm. We often have to take more than a single film and this adds to the potential distress for the dog or cat and potential radiation exposure for people holding the pet. While the amount of radiation received by the pet is minimal, even with multiple x-rays, our concern is cumulative dosing to people. This is why we use alternative methods of restraint.
Where appropriate we keep a fully conscious pet still with well placed soft-covered surrounding sandbags. There are instances where this is inadequate so we selectively use various sedatives or anesthetics. There are many choices of drugs and often only a brief sedation from which a pet is fully recovered within just a few minutes is used. We will discuss with you the need for x-rays and what type of restraint is needed.
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 most of us are familiar with is barium, and this is sometimes 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).
The next most commonly used imaging method at the London Veterinary Clinic is ultrasonography. High frequency sound waves are used to provide more narrowly focused pictures of internal structures. Details that might be difficult to see on radiographs can often be seen with ultrasound. Ultrasound can also provide “real-time” images of structures to detect such things as movement. Most of us are familiar with ultrasonography to ‘image’ developing fetuses in pregnant women. Real time imaging also permits ultrasound-guided aspiration (placing a small needle into a structure to collect some fluid or cells as is done for amniocentesis in some human pregnancies) 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 may be able to make diagnoses, obtain samples, and provide treatment advice far better than less skilled or experienced vets even when using identical machines. Grant Petrie and Veronica Aksmanovic undertake our ultrasonography.
Computed 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. We refer pets for CT scans to our associates Cambridge Radiology Referrals and Dick White Referrals.
Magnetic resonance imaging (MRI) is a non-x-ray based technology. It uses 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 x-rays or ultrasound. All MR imaging in animals requires anesthesia due to the need for complete immobility during scanning and the relatively longer time needed for MRI than other imaging techniques such as x-rays or CT. There is some overlap between the indications for CT and MRI scanning. The former is generally best for bony details such as elbows, knees and complex fractures. CT is also excellent for pictures of the lungs, and conditions in the ears and nose. MRI is generally superior for brain, spinal cord, and abdominal imaging. If we recommend advanced imaging we will discuss with you the reasons for our preference for either CT or MRI. MRI scans are conducted at our associates, Dick White Referrals.
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. When needed, fluoroscopy is undertaken at Cambridge University.
Scintigraphy involves the administration of minute quantities of a radioactively-labeled substance into the body, 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. We refer patients to Cambridge University for scintigraphic evaluations.