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Expert Advice July 2016 Issue

Dear Doctor - Choosing the proper imaging on dogs

Q My dog keeps falling over and also keeps turning her head to the left. Her veterinarian says she needs MRI, but the cost is $1,400 plus a few hundred dollars for anesthesia to keep her still during the procedure. Couldn’t he check inside her head with an x-ray, or even a CT scan, which would be much less expensive?
Bonnie Lynde
Jupiter, Florida

Dear Ms. Lynde,
A Because your dog keeps falling and turning her head involuntarily, your vet no doubt suspects a neurological problem, and it frequently takes MRI, or magnetic resonance imaging, to pick up abnormalities in the brain or spine that would be causing the issue.

Consider that most diseases and tumors and inflammation in the brain have increased water content and thus, a high concentration of what are called mobile hydrogen atoms. Well, MRI works by using a magnetic field to temporarily align the mobile hydrogen atoms and thereby get contrast in its images that would pick up mild differences between normal and abnormal tissue. And it uses radio waves to get cross-sectional images, that is, three-dimensional pictures rather than just flat ones. That would help a veterinary radiologist detect, say, a tumor pressing on a sensitive part of the brain.

On an an x-ray, by contrast, the brain and spinal cord cannot be seen at all — they are essentially invisible. An x-ray instead sees major abnormalities and dramatic changes in the size, shape, or content of organs. It’s not going to pick up an abnormality that is more nuanced because it can only distinguish, say, bone from soft tissue and fluid. It can’t tell if soft tissue is normal or abnormal — it will all come out the same shade of gray. In fact, the liver and spleen look identical on an x-ray. The vet only knows which organ it is by its location — and can then tell if, for instance, it’s twice its normal size. And an x-ray gives only a two-dimensional view.

A CT scan will give a three-dimensional view but is otherwise similar to an x-ray — it won’t show subtleties in tissue density that give clues to disease.

Other kinds of imaging include ultrasound and nuclear medicine. Ultrasound can differentiate between different things going on in one organ. It can see the flow of blood through the chambers of the heart in real time, for instance. It can see whether the valves open and close properly, and so on. It can even see differences in fluid types, distinguishing normal urine with urine that has blood or crystals in it. But it cannot see the brain or spinal cord. The surrounding bone of the skull and spinal column block ultrasound waves.

Nuclear medicine provides information on how an organ, or a system in the dog’s body, is functioning rather than what it looks like per se. It works by tagging cells or specific drugs with radioactivity so it can be seen how they move through or are processed by organs. A veterinarian can use different molecules for tagging, depending on what is being investigated — perhaps the path of red blood cells if internal bleeding is suspected.

Nuclear medicine and ultrasound cost a few hundred dollars, while an x-ray might only cost $100. A CT scan will cost anywhere from $500 to $1,200, depending on the complexity of the study plus a few hundred more for the anesthesia. MRI requires going deepest into pockets, with the price tag coming to roughly $1,500 to $2,000 once you add in the cost of the anesthesia to keep the dog still. It’s when your vet says your dog needs a procedure like MRI that pet health insurance comes in very handy.

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