THE IMPACT OF FIELD-STRENGTH ON IMAGE QUALITY IN MRI

As clinical MRI has evolved, there have been numerous arguments for th e use of different held strengths, Those favoring high magnetic held ( 1.5 T and above) include higher signal-to-noise ratio, capability for MR spectroscopy, and other forms of functional MRI, high speed imaging , and high resolution imaging. However, cost remains a significant lim itation to the wider dissemination of high held MRI, There are definit e cost advantages (capital, operating, siting) to the use of lower hel d MRI. Much debate has occurred over the past decade regarding the rel ative diagnostic benefits of high held MRT versus lower held MRI, but few randomized, controlled clinical trials have compared diagnostic ac curacy of MRI at various held strengths, In this article, we review th e physical principles of the held strength dependence of MRI in relati on to image quality. The assessment of the importance of held strength in MR is incomplete without some analysis of diagnostic accuracy vers us field strength, Such analysis is difficult to accomplish in an unbi ased manner. The use of receiver-operator-characteristic (ROC) analysi s is probably the best available method to measure diagnostic accuracy of various imaging methods without bias. An ROC study of diagnostic a ccuracy of 0.5 T versus 1.5 T MRI, examining several common clinical c ategories, has recently been conducted at our institution, Results fro m this study demonstrate diagnostic equivalence between these two held strengths in at least two common clinical disease categories (MS and internal derangement of the knee), These results are discussed and rel ated to results from previous held strength studies.