MR imaging at high magnetic fields

Recently, more investigators have been applying higher magnetic field strengths (3-4 Tesla) in research and clinical settings. Higher magnetic field strength is expected to afford higher spatial resolution and/or a decrease in the length of total scan time due to its higher signal intensity. Besides MR signal intensity, however, there are several factors which are magnetic field dependent, thus the same set of imaging parameters at lower magnetic field strengths would provide differences in signal or contrast to noise ratios at 3 T or higher. Therefore, an outcome of the combined effect of all these factors should be considered to estimate the change in usefulness at different magnetic fields. The objective of this article is to illustrate the practical scientific applications, focusing on MR imaging, of higher magnetic field strength. First, we will discuss previous literature and our experiments to demonstrate several changes that lead to a number of practical applications in MR imaging, e.g. in relaxation times, effects of contrast agent, design of RF coils, maintaining a safety profile and in switching magnetic field strength. Second, we discuss what will be required to gain the maximum benefit of high magnetic field when the current magnetic field (< or = 1.5 T) is switched to 3 or 4 T. In addition, we discuss MR microscopy, which is one of the anticipated applications of high magnetic field strength to understand the quantitative estimation of the gain benefit and other considerations to help establish a practically available imaging protocol.