Quantitative Measurement of T1, T2, ￼, and Proton Density
While the majority of clinical MRI today is qualitative, 1H NMR in tissue began with quantitative evaluations of relaxation times. Even before the development of MRI, Belton et al. [1-3], Hazelwood et al. [4,5], Damadian et al. [6-9], and a number of other investigators [10-15] characterized 1H relaxation times in a variety of normal and diseased tissues. In fact, the observation of T1 and T2 di›erences between normal and cancerous tissue by Damadian et al.  was, arguably, the primary motivating factor for the development of practical signal localization with gradients, leading to the development of contemporary MRI. With this development, however, methods for robust measurement of tissue water proton relaxation became more complicated and, consequently, somewhat overlooked by the majority of the MRI community. šis is particularly true of those involved in the application of MRI to clinical diagnostics. In fact, the vast majority of clinical cancer MRI performed today, including scans for tumor diagnostics, aims to simply maximize tissue contrast in order to visualize tumors and perhaps measure their size. Nonetheless, an ever-growing body of literature is developing to warrant the application of MRI protocols that quantitatively measure tissue water proton relaxation characteristics. In the context of cancer imaging, the most relevant clinical example is the use of dynamic measurements of T1 following contrast
agent injection to characterize tumor vasculature via dynamic contrast enhanced (DCE) MRI (see Chapter 10).