Figure 13b: Proton electron double resonance imaging (PEDRI; also known as Overhauser imaging). (a) Time course of PEDRI study of myocardial uptake of free radical probe TEMPONE (4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl) by isolated perfused rat heart. TEMPONE was infused through a side arm proximal to the perfusion cannula at final concentration of about 3 mol/L. Two-dimensional PEDRI sections were then sequentially acquired every 30 seconds, with each scan taking 27 seconds. At low field strength of 0.02 T (201 G), the electron-spin resonance and nuclear MR frequencies are 567 MHz and 856 KHz, respectively, and an Overhauser enhancement of –13 was achieved. (b) Three-dimensional gradient-echo PEDRI images of isolated beating rat heart infused with 3 mol/L TEMPONE. Top left image shows complete three-dimensional surface-rendered image; the other images are cutaways to show internal structure. The image took 4 minutes 30 seconds to acquire at 0.02 T. (Images courtesy of Haihong Li and Jay Zweier, MD, Davis Heart and Lung Research Institute, Ohio State University, Columbus, Ohio.)