3T-MRI (3 Tesla magnetic resonance imaging) is MRI done with a stronger magnet. Magnet “strength” is like “pixels” in digital cameras. The stronger the magnet—or greater the number of pixels—the better the images. “Tesla” is a unit of “magnetic field.” By using a magnet that has 3 Teslas (“3T”), we get better and sharper pictures, and can get them in less time weaker magnets. A 3T-MRI produces better images than 1.5, OPEN MRI or any MRI with a weaker magnetic field.
Musculoskeletal MRI is better at 3T for several reasons. 3T has higher “signal to noise” than other MRI scanners and this makes MR imaging of the joints faster, sharper (higher resolution) and more detailed (for trabecular detail). Increased trabecular detail—known to be better at higher field strengths—shows stress fractures much more clearly and important as treatment for a bone bruise can be different from the treatment you would receive for a fracture.
3T MRI is also twice as sensitive to contrast enhancement. This makes indirect arthrography an option at 3T. With a 3T MRI, we can give you an arthrogram without having to inject contrast into the joint. This reduces the costs and saves you, the patient, the pain and possible infection related to an injection. Complications are also reduced; sometimes injections do not actually get into the joint. Studies on our 3T MRI cost the same as MRIs on lesser scanners and are more detailed in contrast and enhancement.
Fat saturation of the joints is also improved at 3T. So when you combine fat saturation (fat sat) with “contrast” better, more sensitive, studies of areas of inflammation, tumors and healing result. Increased blood flow and enhancement is easier to detect when you use fat sat and is easier to detect at 3T. The images our machine produces are so incredible that some orthopedic surgeons say they have NEVER seen such detail on an MRI. Hamstring injuries look much better and more extensive at 3T, as do “groin hernias.” At 3T, using this combination of fat saturation and contrast, areas of subtle inflammation—previously undetectable—are now visible. Also, we are able to scan with a very small field of view, which is essentially like being able to enlarge (or do a close-up of) the area we are studying. This is a great advantage when scanning hands and feet. Details of the bones, joints and wrists that were previously only seen in pathological or autopsy specimens are visible on these more powerful, 3t MRI scanners. We are able to see details of the response to treatment of rheumatoid arthritis medication in a non-invasive manner. .
The extra power of 3T MRI lets us scan most areas in contiguous (and thinner) sections. This means we are able to scan up to 30% more of the body. Due to time considerations, other MRI scanners scan with a “skip”—scanning one or more slice and then skipping a section before scanning the next slice. A very small tumor or lesion might hide in the area that is “skipped.” Because 3T imaging is faster as well as stronger, we are able to scan everything in the area of question without making the patient stay in the scanner for hours. Contiguous imaging means there is simply nowhere for an abnormality to hide. Our scans are often 512x512 matrix and 2mm thin—about 8 times the resolution of any other scanner. At 3T, we can do this in 3 minutes. This translates into several important advantages. Scanning more quickly means the patient doesn’t have to remain still for as long a period, which means the chances of getting a motion-free scan are greatly increased. The 3-minute scan mentioned above is actually done in two parts (two runs) so you only have to stay still for 1.5 minutes at a time to get motion-free images. This means that even the most fidgety or claustrophobic person can usually get a diagnostic scan. Higher signal to noise (which is doubled at 3T) theoretically means the scan can be done four times faster than at 1.5T (we do not recommend getting an MRI at less than 1.5T). In practice, however, we prefer to say we scan “twice as fast.” People have a harder and harder time remaining absolutely still for long periods of time. Being able to produce a better scan in half the time is a great step forward.
Bringing more sensitivity to trabecular detail makes our bony imaging much more detailed and greatly increases sensitivity to bone marrow tumors and subtle stress fractures.
The ability to scan with thinner sections and higher resolution also directly impacts our ability to see abnormalities. Images of lower resolution and detail are less likely to show abnormalities. Being able to scan with more pixels has given us the ability to see very subtle things, like small areas of arteriovenous shunting, or subtle areas of inflammation or microtrauma. Individual fibers of the anterior cruciate ligament of the knee or the subtle fibers of the calcaneofibular ligament in the ankle are visible at 3T. We see more and, as a direct result, can diagnose more abnormalities.
Ionizing radiation is a very big problem in our current society. Most patients are never told that the risk of getting cancer is 1/500 for children per CT scan and 1/1000 in adults. And a CTA (computer tomography angiographic) study is even worse at 3 times the amount of radiation. CT colonoscopy can be up to 4 times the radiation dose.
This is a 3-T MR editorial submitted by Dr Philip W Chao MD. His website www.3t-mri.net .
Dr Philip W Chao has worked in Delaware to produce the best MRIs possible since 1990. He has monitored hundreds of thousands of MRIs over his career at the University of Pennsylvania and working for the people of Delaware. He is a board certified neuroradiologist and recently passed his maintenance of certification examination in 2006. He is also trained in body MRI and was the body MRI fellow at the University of Pensylvania from 1988 through 1990.
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