Tuesday, September 14, 2004

Better Living Through Magnetism.....
Does Dr. Rangel have some sort of crystal ball? In his post concerning whole body CT scanning he signed off with this nugget of his rapier wit:
My advice to the wealthy and paranoid; Change over to magnetic resonance whole-body scanning. It may be more harmful to your wallet but it has no proven cancer risk and is just as useless as a screening exam. Have fun!
Well, well from Medscape today comes: Whole-Body Screening MRI: What You and Your Patients Should Know
In recent years, there has been considerable interest in direct patient referral for imaging studies to screen the whole body for disease detection. In general, the majority of the facilities that have been performing whole-body screening have done it with new, fast, multidetector computed tomography (CT) systems. Speed of data acquisition, in the order of a few minutes for the entire body, has made it a compelling method of investigation. There are some limitations and concerns with CT, described briefly below, but the major focus of this Clinical Update is whole-body screening with magnetic resonance imaging (MRI). Within the last few months, this has become a feasible approach, the most important advances being a dramatic increase in data acquisition speed concurrent with maintenance of high image quality.
The article then goes on to describe the recent technological advances which have made the use of MRI as a screening tool feasible. Some hurdles remain, however:
Optimal investigation for many diseases requires using dynamic administration of gadolinium chelate (a type of intravenously administered contrast agent that is in routine use in MRI), and because MRI can image only about 40 cm in vertical length of a person in 1 data acquisition (essentially 1 of 4 major regions: head and neck, chest, abdomen, or pelvis), this would involve too many separate injections of contrast (eg, separate injections for the liver, heart, and breast [in women])......
Presently a confounding variable exists with protocols for whole-body screening. It is widely recognized that several organ systems are currently imaged by MRI with an extremely high level of diagnostic accuracy and reproducible image quality (eg, liver, pancreas, kidneys, brain, spine, musculoskeletal system, gynecologic organs, and major blood vessels) that exceeds the abilities of CT.[4-11] However, despite recent technical advances, described at the beginning of this Clinical Update, the diagnostic accuracy is not high for prostate, coronary vessels, colon, or breast, secondary to such factors as decreased sensitivity, decreased specificity, or inconsistent display of small and/or moving structures.
A nice compare and contrast can be found on this page. In summary:
1.Ionizing radiation is bad if you don't need it. No such problem with MRI
2. Non-contrasted CT is fast and avoids potential reaction problems, but they are lousy as screening studies, not such a problem with MRI.
3. The use of contrast improves sensitivity, but problems abound. Gadolinium is fairly safe.
4. The rate of injection is slower with MRI which causes less side effects

But as of now, CT is far cheaper than MRI. But I'm sure it will be only a matter of time before MRI scanners open up at a strip mall near you.
Cross-posted at Galen's Log
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