Figure 6a. Parametric imaging of the wash-in rate allows detection and localization of prostate cancer in a 65-year-old man. (a) Histologic step section (original magnification, x1; hematoxylineosin stain) at the middle level of the prostate gland shows cancerous tissue (black lines and dots) in the lateral and medial peripheral zone in the left lobe and in the transitional zone in the right lobe. (b) Unenhanced T1-weighted MR image shows the placement of four regions of interest, according to the histologic findings, in cancerous tissue (1), normal tissue in the peripheral zone (2), normal tissue in the inner two-thirds of the transitional zone (3), and normal tissue in the outer one-third of the transitional zone (4). (c) Time–signal intensity curves for the four regions of interest in b (x-axis, time in seconds; y-axis, signal intensity in arbitrary units [au]) show wash-in rates of 9.7 au/sec for cancerous tissue (1), 2.1 au/sec for normal tissue in the peripheral zone (2), 4.3 au/sec for normal tissue in the inner two-thirds of the transitional zone (3), and 1.3 au/sec for normal tissue in the outer one-third of the transitional zone (4). (d) Parametric MR image at a level corresponding to that in a shows a wash-in rate of more than 5.7 au/sec, which was used as the threshold for differentiating cancerous tissue from normal tissue on the basis of an analysis of receiver operating characteristic curves. The parametric map of wash-in rates concords with the histologic findings. (Reprinted, with permission, from reference 17.)