Figure 1
Click on the image to enlarge

With the advent of compact, actively shielded MRI magnets, it is now practical to site a 3.0T scanner in a clinical MR suite. The Mayo Clinic installed a whole-body 3.0 Tesla MRI unit at the Charlton North building in 1999. Figure 1 shows architectural plans. Note that the 50 square-meter scan room (Figure 1-right) is not much larger than the neighboring 1.5 T room (Figure 1-left). Also, the stray magnetic fields, (indicated in units of Gauss = 0.0001 Tesla) are well contained within the scan room. The 3.0T system is a General Electric VH/i scanner based on the Magnex 3T-94 actively shielded magnet. It is equipped with 40mT/m whole-body gradients. This system has received FDA 510(k) clearance.

Figure 2a Figure 2b Click on either image to enlarge

The main advantage of very high field MRI is that the signal to noise ratio (S/N) scales approximately linearly with field strength B₀ in the range of 1.5 to 3.0 Tesla. This S/N improvement is illustrated by Figure 2, which shows a MR angiogram comparison on a normal volunteer between the standard field strength of 1.5T, and 3.0T. All acquisition parameters are identical, and neither scan used intravenous contrast agents. Note the improved appearance of the smaller vessels at 3.0T.

The 3.0T scanner at Mayo is used for both routine clinical and research purposes. For example, from October 1999 through August 2000, over 1400 patients exams have been performed on the 3.0T. This high-volume clinical usage differs from other institutions, which in the past have limited the use of their 3.0T scanners primarily to clinical and pure research. In order to enable our routine clinical use, Mayo developed several novel clinical applications tailored for 3.0T [1-4]. As an indication of the wide interest in 3.0T clinical MRI, Mayo has hosted seven site visits from academic institutions, some from as far as Spain and Australia.

Areas of active research on the 3.0T scanner include high spatial resolution MR angiography, anatomical imaging, and functional neuro MRI. Another area of interest is coil development. Currently our 3.0T scanner is equipped with a transmit-receive head coil only. To fully utilize the advantages of 3.0T scanning, additional radiofrequency coils are being developed at Mayo, and in partnership with several commercial vendors. There are opportunities available for interested graduate students to pursue doctoral research in these areas.