MAGNETIC-RESONANCE-IMAGING OF DIFFUSION IN THE PRESENCE OF BACKGROUND GRADIENTS AND IMAGING OF BACKGROUND GRADIENTS

The measurement of the self-diffusion coefficient D by an NMR technique that uses an applied gradient GA can be corrupted by systems that have a background magnetic field gradient G0 and also by imaging gradients G1, when used in an imaging mode. In a nonimaging mode, the corrupting cross term GA · G0can be eliminated in the diffusion measurement by use of an alternating-pulse-field-gradient (APFG) sequence that allows an accurate and uncorrupted measurement of D. A Carr-Purcell echo train enables the measurement of the expectation value, 〈DG20〉; assuming D and G0 to be uncorrelated will allow 〈G20〉 to be determined. An image of D or of 〈DG20〉 may be obtained without the corrupting GA · G0 and GA · GI terms by appending a standard imaging sequence to an APFG sequence or a Carr-Purcell sequence, respectively; assuming D and G0 to be uncorrelated will allow (〈G20〉 to be determined within each pixel. Measurements of D and 〈G20〉 and their images are made in apple flesh in which minute air bubbles are shown to produce the large 〈G20〉. Their values in an 81 g Golden Delicious apple at a measuring frequency of 100 MHz were D = 1.42 × 105 cm2/s and [formula]. © 1994 by Academic Press, Inc.