IMAGING LOW-CONCENTRATION METABOLITES IN THE PRESENCE OF A LARGE BACKGROUND SIGNAL

A pulse sequence (CD-CHESS) is described that addresses the challenge of imaging low-concentration metabolites whose chemical shifts are clo se to that of water. This sequence avoids the problems of the basic ch emical-shift-selective (CHESS) imaging sequences, which produce an ima ge contaminated by residual signal from the undesired component. Sever al signal suppression schemes are combined with the basic 2D CHESS ima ging sequences and examined using a specially constructed chemical-shi ft phantom. The degree of suppression for the new enhanced CHESS seque nces is compared with that of the basic CHESS sequences and the SUBMER GE-CHESS sequence. The most effective sequence incorporates cw irradia tion and soft-pulse saturation with the basic CHESS sequence. The CDCH ESS imaging sequence produces a suppression ratio of better than 1000 to 1 when the desired and undesired peaks are 1 ppm apart. The effecti veness of the CD-CHESS sequence is demonstrated by imaging the sugar p rotons in a phantom composed of 10% (w/v) sucrose in water. The CD-CHE SS sequence is used for the selective imaging of sugars in peas, demon strating that it can be extended to the broad lines normally encounter ed in biological specimens. (C) 1995 Academic Press, Inc.