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Imaging- CT, MRI, X-ray

X-Rays And Advanced Imaging

What to Expect with medical imaging

(X-ray, ultrasound, myelogram, CT and MRI and how they work)

permission to reprint by Sharon Seltzer, Dog Wheelchair LIFE

Dogs today are lucky compared to those in the past when it comes to diagnosing and treating health problems. Science has opened a whole new world of diagnostic imaging tests for our canine and feline fur kids that can see far into their bodies. So why then do so many pet parents dread hearing the news that your dog needs an MRI?

MRI (Magnetic Resonance Imaging)

An MRI is used to confirm a diagnosis that cannot be confirmed another way. For a surgery, an MRI confirms the herniated disc location. Usually an MRI is just prior to a disc surgery as planning for the procedure.

When my veterinarian said Sophie needed an MRI to determine which part of her spine was causing her paralysis; I wanted to grab her and run out of the office. Hearing the words MRI for the first time was frightening and confusing. I didn’t know what to expect. I think my reaction was pretty typical. Pet parents know the names of tests like ultrasounds, CAT scans and MRIs, but we don’t know how they work or which test is best for our dog’s condition.

MRI confirms the herniated disc location. MRI’s are usually taken right before a disc surgery as planning for the procedure.
An MRI is used to confirm a diagnosis that cannot be confirmed another way.

I was afraid the MRI was too stressful for Sophie and would make her condition worse. I worried about the cost of the test and wanted assurance it was going to give us a confirmed diagnosis.

If your veterinarian is suggesting an MRI for your paraplegic dog, here is information about how the procedure works, what problems it best diagnoses and how to prepare your dog. But before reading ahead, I was told an excellent piece of advice from a veterinary neurologist that you should keep in mind, “An MRI is used to confirm a diagnosis that cannot be confirmed another way. It should not be scheduled as a way to make an initial diagnosis.”

MRI’s are the newest diagnostic imaging test and the most expensive. They can cost $2,000 – $4,000. This is in part because the equipment runs as much as $1 million to buy and needs to be stored in a specially housed area to protect the rest of a veterinary hospital from its strong magnetic field. The magnet in an MRI is up to 40,000 times as strong as the earth’s magnetic field. Therefore it can ruin nearby computers and medical equipment.

With that in mind, MRI’s are less harmful to a dog’s body than an x-ray because the scan doesn’t use radiation.

An MRI works by using a magnetic field and radio waves to create images that are clearer and more detailed than other type of diagnostic scan. The procedure can show abnormalities, injuries and diseases of the spine that may not be seen with any other method.

An MRI scan magnetizes the cells of an organ while precise images are taken and sent to a computer that interprets the information. Patients lie flat on a table that slides into a domed-shaped machine that looks like a small tunnel. Your dog’s collar will be removed for the procedure to be sure there is no metal near the equipment. Because of the special nature of the test your dog’s MRI will probably take place at a specialty center or neurological veterinary office and not at your dog’s regular veterinary clinic.

Patients cannot move during an MRI or the pictures will be blurred so dogs must be anesthetized. That means you will not be able to give your dog food or water 12 hours before the scan and your dog will need time in the recovery unit to wake up. Dogs may continue to be groggy and not quite themselves for several hours after an MRI and should be taken directly home to relax.

MRI’s are performed to determine:

Abnormalities with the spinal anatomy and alignment
Congenital anomalies of the spine
Bone, disk, ligament or spinal cord injury after spine trauma
IVDD – Intervertebral disk disease, degenerated, bulging or herniated disks.
Spine joint disease
Compression fractures
Compression of the spinal cord and nerves
Inflammation of the spinal cord or nerves
Infection in the spine
Tumors in the vertebrae, spinal cord, nerves or the surrounding soft tissues

Common “imaging tests” used by veterinarians.

Old school Radiograph/X-rays are still a good test

X-rays were the primary “go to” diagnostic tool in the past and they still reveal a lot of useful information to veterinarians. An x-ray is a black and white two-dimensional image of the inside of the body. X-rays work by passing radiation through a particular area and an image is captured on film, like a photograph. X-rays work best on dense tissue such bones so they are good at determining if a limb is broken or if a hard mass is present, but they are less accurate in seeing problems such as the fluid from a ruptured disc in the spine.

Ultrasound (Sonogram)

An ultrasound uses sound waves to see inside a dog’s body and like the x-ray, the procedure is painless. A device is pressed along the outside of a suspected diseased organ or injured area and as the sound waves are absorbed, a live moving image is formed that can be seen on the screen of monitor.

Ultrasounds are relatively quick and do not require anesthesia or even sedation in most cases. Depending on the location of the organ being examined, a dog might have to lie in a specially designed u-shaped bed so a veterinarian can get a better look. Your dog will need to have the hair shaved from the area to be evaluated, as hair interferes with the images.

An ultrasound is typically done after other tests like blood work, x-rays and a physical examine indicate a possible problem. The test can see into organs and soft tissue which is not possible on an x-ray. The imaging test can pick up problems such as fluid in the spine and brain or disease in an organ like the liver or heart.

On the flip side, ultrasounds are not good at seeing through air or bone and an x-ray is far better for these purposes. Many times both tests will be scheduled for your pet.

CAT Scan or CT (Computer Axial Tomography) Scan

The CAT or CT scan is the second most expensive imaging test and can cost $1500 – $2000. In this test, your dog lies flat a table that moves through a scanner, which sends x-ray beams through an organ from a variety of angles. Sensors detect the beams and send the signals to a computer that displays an image that looks like a slice of the body. As the table moves slowly through the scanner, a new picture is taken at short intervals, each one a little further back or forward from the previous one. Because the images are taken over a period of time, your dog must be anesthetized in order to keep from moving while going through the scanner.

CT images are white, black, and shades of gray. Depending on how dark or light the gray is, a radiologist can see how well tissue absorbs the x-ray beam and identify abnormal tissue. CAT scans are especially helpful for assessing problems in the spinal cord, the lungs and the brain.

More about X-rays

IVDD dogs have a special risk whenever they are under anesthesia for dentals, x-rays, etc. 5 Things to know about dentals: https://dodgerslist.com/ivdd-precautions-anesthesia/

X-rays used to rule out high suspicion of other diseases

Pressure to the spinal cord does not have to be a disc herniation; it could be a spine fracture or dislocation, a tumor, or a disk infection. X-rays would be used to rule out a high expectation of one of these other diseases. X-rays should be used with caution with a suspected disc episode. The dog’s main defense from further disc damage depends on controlling their trunk muscles. Anesthesia puts those muscles to sleep.

Reading references:

The purpose of x-rays (radiographs) in IVD disease is to help make decisions regarding treatment choices. If IVD disease is the suspected cause, then radiographs are not critical except to a surgeon. If there is reason to suspect something other than a displaced disc (such as a vertebral tumor, infection, or fracture), then x-rays are wholly appropriate. Your veterinarian should discuss with you the purposes and need for any spinal x-rays. Furthermore, obtaining good quality spinal x-rays requires the patient to be completely immobilized, and this usually means employing a general anesthetic. If a dog is going to be treated medically, then knowing the precise location is unimportant. Rochester Veterinary Specialists

Survey radiographs are usually not indicated when intervertebral disk disease is suspected. Although radiographs may show mineralized disks, they are not reliable because they are unable to definitively diagnose which disk is causing the problem and are unable to show the extent of any spinal cord compression. If intervertebral disk disease is the primary consideration, a practitioner should attempt to conserve finances for advanced, confirmatory imaging such as MRI or, in some instances, CT. Glass, ACVM (neurology) et al. “Physistis: a Fracture in an English Bulldog.” Cllnician’s Brief. Oct 2017 p68.

Radiographs are rarely of benefit in dogs with suspected disc disease, unless part of an imaging work-up being conducted for the direct benefit of the surgeon who intends to operate on the dog. …Moreover, obtaining good spinal radiographs that are not burdened with positioning artifacts requires anesthesia and careful technique. So, if unanesthetized radiography is used one may make the animal more uncomfortable by having to hold it in place, and the value of such films, already dubious by definition, is further degraded. And if it makes little sense to take x-rays at the outset, does it make sense to add an anesthetic (and the cost to the client) in order to pursue this form of imaging? Not every disc lesion results in obvious collapse of the disc space, or observation of mineralized material within the vertebral canal or intervertebral foramen. Fingeroth, James, DVM, DACVS.NSAID/steroid Decision-Making, Management, and Referring the “Disc” Case. “Surgery” 2006.

Myelogram: X-ray plus injected contrast agent

Regular X-rays (radiographs) are good for evaluating bony abnormalities (fractures, infection of the bone, tumors of the bone). A healthy intervertebral disk and spinal cord are not visible on a radiograph because they are soft tissue and not bone.

Sometimes an unhealthy disk (degenerative) will become mineralized and this can be seen on the radiograph.

A myelogram is a radiograph, but a contrast agent has been injected around the spinal cord. The contrast agent is a liquid that shows up on the radiograph and highlights around the spinal cord. If something is putting pressure on and compressing the spinal cord the myelogram helps one visualize this.

An MRI uses technology completely different than radiographs and myelograms. It is better at imaging soft tissue than bone. It also allows for a better evaluation of the spine because it provides images in three planes while a myelogram only provides images in two planes.

In general, radiographs are a good screening tool, but not reliable enough to diagnose a herniated intervertebral disk and decide if surgery is warranted.

A myelogram is a good and typically less expensive way of diagnosing a herniated intervertebral disk and deciding if surgery is warranted. It does carry with it some risk (contrast is injected around the spinal cord) and it is not as good as an MRI in evaluating diseases other than herniated intervertebral disks that can cause problems with the spinal cord.

An MRI is the gold standard for imaging the spine. Because of the excellent soft tissue detail and the ability to get images in all three planes. Dr. Andrew Isaacs, DVM Diplomate ACVIM (Neurology) “Myelogram vs. MRI vs. x-rays.” Dodgerslist Neuro Corner. Jan 2012.