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Special MRI Applications
The sophisticated MRI at Snow Canyon Clinic permits numerous highly specialized investigations in addition to the routine imaging we all think about (e.g., brain, joints, spine, etc.); and some of these special applications include compreshensive cardiac imaging, a variety of ways to visualize both arteries and veins anywhere in the body (MRA, or MR angiography), MR spectroscopy (MRS), functional MRI, and a variety of other imaging protocols (see below).
Comprehensive cardiac imaging
Comprehensive cardiac MRI allows a thorough
evaluation of attributes that help determine the health of one's heart, such
as the size of the heart and its chambers, the weight of the heart, abnormalities in
wall motion, abnormalities in valve structure or function, and objective
measurements such
as cardiac output. Cardiac MRI provides the most accurate functional imaging possible for parameters such as chamber size, ejection fraction and volume, etc., and is much superior to echocardiography using ultrasound. It is also the most accurate means of detecting and quantifying scar from a prior heart attack. Such imaging is particularly useful prior to cardiac bypass
operations, as it can help the surgeon place the bypass to an area of the
heart that will benefit.
Through comprehensive cardiac
imaging, we can also image the coronary arteries and determine with high sensitivity and
precision the presence and severity of blockages. Previously, this could be done
only by placing a catheter in an artery, injecting a dye into the heart, and taking x-rays. Coronary artery MRI is completely non-invasive and employs no
dyes or x-rays. It is completely safe and much less expensive than standard coronary
arteriography.
All of Snow Canyon Clinic's cardiac MRI studies are interpreted by
Dr. Scott Flamm at the Cleaveland Clinic .
Vessel imaging
Using special MRI applications, our physicians
can visualize any artery or vein, or region of arteries or veins, in the body. The most common arterial regions we image are the
head, neck, kidney, aorta, and extremities. We can measure any degree of
abnormal vessel narrowing (due to atherosclerosis) or dilation (such as with aneurysms) with high precision. After MRI imaging, we can re-create a model of
the studied vessel system in three dimensions on a computer, allowing our physicians to
evaluate the complete anatomy and even explore the interior of each
vessel.
The exploration of the interior of arteries and veins is referred to as "vascular endoscopy." This is a completely non invasive method that may or may not require an injection of contrast (not iodine, but Gadolinium which does not produce some of the side effects that are seen with iodine). Generally, no contrast is used. However, for the great neck vessels (e.g., the carotid arteries) the use of Gadolinium affords the highest quality studies. Vessel imaging is not a separate study but can be rendered from the same data set as acquired with the particular vascular bed being studied. Many people make the following analogy: "It's just like shrinking yourself to the size of a red blood cell with a video camera and travelling through the circulation, taking pictures of the inner surfaces." The radiologists do not interpret these studies routinely, but your ordering physician at Snow Canyon Clinic finds great value in vascular endoscopy, because we can quantitate the degree of atherosclerotic build up on the inner surface (i.e., the endothelium), and characterize the nature of that build up. That is, the build up may form the shape of a placque, producing a slow narrowing of the vessel, or it may appear to swing pendulously in the vessel interior, suggesting the possibility of the release of that thrombus (clot) which might then embolize (travel) to one of the end organs supplied by that vessel. A young persons vascular endoscopy should have the smooth appearance of a baby's bottom. Higher degrees of disease can easily be assessed. Your ordering physician will sit with you at the computer and explain the study. You will experience a feeling that you are flowing or moving through a vessel, having every opportunity to stop and more carefully measure degrees of narrowing, etc..
Magnetic resonance spectroscopy (MRS)
MRS is a non invasive diagnostic technology that in effect allows for a "virtual biopsy" of the studied tissue. It utilizes MRI technology but provides chemical rather than anatomic information. Gary L. Jones, M.D., Ph.D. has received special training in the utilization of this technology, at the famous Huntington Institute in Pasadena, CA.
MRS has a vide range of clinical applications. Beyond doubt, the most beneficial application of MRS is in the differentiation of a benign from malignant brain tumor. Brain cancer is easily differentiated from other benign lesions such as cysts or more serious conditions such as abscesses (pockets of infection). With cancer, the chemical N-acetylaspartate is diminished while the chemical choline is markedly increased; and depending on the severity of the cancer, lactic acid (a product of anaerobic metabolism) may be increased. Lactic acid generally defines a highly aggressive malignancy.
Furthermore, studies have suggested that MRS is as effective, if not more effective in permitting the physician to "grade" the tumor. That is, "Is this a low grade cancer that can be watched, or a higher grade tumor that requires some degree of treatment?" Such treatment may simply be oral chemotherapy, or may involve surgery followed by chemotherapy and radiation, based largely upon the results of the MRS.
MRS also allows one to monitor the surgical margins of tumor resection for recurrence, enabling appropriate therapeutic decisions; and it enables one to monitor the response to nonsurgical treatment.
MRS has been studied and some utility found in literally hundreds of other applications, only some of which will be discussed below. MRS is more sensitive in the detection of hypoxic (injury due to lack of oxygen) injury than is MRI, because of the accumulation of lactic acid, a product of anaerobic metabolism.
MRS has been shown to be effective in the diagnosis of Alzheimer's disease and some have advocated it's use for such. A chemical known as N-acetylaspartate is decreased and a chemical known as myosital in increased. However, we find that PET-CT is a much more sensitive and specific for this diagnosis.
Multiple sclerosis may also be diagnosed with the assistance of MRS, but the sensitivity and specificity are not good. It would only be used in combination with other testing. The chemical choline is increased in MS placque, and with an active placque there may be some lactic acid present.
MRS can be especially helpful in the assessment of sequelae of head trauma. It can identify subtle biochemical problems and is useful in predicting the patients clinical outcome. For example, a very low N-acetylaspartate concentration and a very high lactic acid concentration portend a grave prognosis. MRS is particularly helpful in diagnosing the "shaken baby syndrome," and a positive test is almost pathognomic (that is, there can be no other answer).
At Snow Canyon Clinic we use MRS mostly for brain masses, which we believe is where it's greatest value lies; but it's use in the shaken baby syndrome is equally efficacious.
Stroke (Diffusion and Perfusion Imaging)
There are special protocols that can be applied in MRI that allow one to determine the age of a stroke and whether any further brain tissue is threatened. A diffusion scan is a very quick scan that allows our physicians to approximate the age of a stroke. Abnormalities may be seen as early as 10 minutes of the stroke onsed. A diffusion abnormality generally defines brain tissue that has been irreversibly damaged (although exceptions occur). Perfusion scanning is a tanden study that provides information regarding a so called "ischemic penumbra." That is, we can answer the question "Is more brain tissue still at risk for irreversible injury? Most often we might see a diffusion abnormality, say for example, the size of a pea. The diffusion abnormality might be the size of a fig, surroundinng the diffusion abnormality. Such a finding helps us to determine whether to use a clot dissolver (tissue plasminogen activator; TPA). That is, if much more brain is at risk, because we find that the perfusion defect is larger than the diffusion defect, we generally choose to dissolve the clot. On the other hand, if the perfusion and diffusion sizes are comparable it implies that what damage has been done is static, and there is a lesser chance of progressive stroke.
Functional MRI
Functional MRI helps physicians determine which part of the brain is associated with different cognitive, speech, motor or visual skills. These protocols are useful in surgical planning for tumor removal in epilepsy and other conditions (such as mesiotemporal sclerosis) that might cause epilepsy. It will also help to spare eloquent parts of the brain if surgery is contemplated for other reasons. Functional MRI also is often also helpful in helping us to better understand some of the underlying mechanisms of disease.
Other
There are numerous other highly specialized applications for which the Clinic's MRI is helpful. These include breast imaging to rule out cancer. Often, breast tissue is dense or there are fibro fatty changes that make the interpretation of routine mammography less reliable. Breast MRI is more sensitive and specific for breast cancer, especially in the context of the above conditions.
Breast MRI also enables the precise study of breasts with implants - something that mammography cannot do. MRI is the only reliable imaging technique that wil detect silicone leakage.
MR cholecystograms provide information regarding the gall bladder and the various ducts connected to the liver, gall bladder, pancreas and small intestine that is superior to the information provided by invasive technology; and should be the first study of choice in studying gall bladder or ductal disease.
Detailed imaging of the eye and inner ear provide extremely high resolution studies of these structures for tumors (orbital, intraorbital or retro orbital; or acoustic neuroma in the case of the inner ear), extraoccular muscle disease (e.g., that seen in some types of thyroid disease), retinal disease, and many other conditions affecting the eyes, vision, balance, hearing, etc.. Snow Canyon Clinic has even perfected the MRI imaging of the very tiny inner ear structures responsible for balance; the semicircular canals and the cochlea. We also have specialized equipment that allows the study of skin lesions, to differentiate benign from cancerous (this is a work in progress, however).
Virtual colonography is a technology which may eventually replace the invasive colonoscopy for certain diagnostic work. The major limitation is that a biopsy could not be obtained at the time of the study if abnormality was discovered. Thus, traditional colonoscopy remains the standard of care. However, virtual MR colonography is effective in detecting polyps larger than 10 mm. This may be useful, because greater than 10% of colon polyps that contain cancer are larger than 10 mm. Also see our discussion in CT for more information regarding virtual colonography.
Our technologists are all highly trained professionals with special training and expertise in both standard and the more specialized studies.
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