Volume localization with a single surface coil
Year: 1989
Type: article
Abstract: Recently surface coils have been used to obtain high S/N spectra from a variety of tissues and organs. Volume localization has been achieved by using DEPTH pulses ( I ) or rotating-frame techniques (2). These surface-coil localization techniques take advantage of inhomogeneity in the RF field to select a volume from the sample. For example, applying the depth-pulse sequence in Fig. la produces transverse magnetization (as a function of pulse angle e) defined by (cos* e/ 3 ) (cos 6/ 5 ) (sin 3 fl) . This eliminates signal from the 450”, 270”, and 180” high-flux contour regions with a drop of 29% in signal intensity from the 90” contour region, or the volume of interest. Effective use of the DEPTH pulse method requires knowledge of the 7r/2 pulse duration. The volume selected by DEPTH pulses and rotating-frame techniques includes unwanted signals arising from superficial regions close to the coil due to the B1 contours which curve back to the surface of the sample. Bendall et al. (3) have used concentric surface coils with DEPTH pulses to eliminate this surface signal. The additional hardware that has been developed to implement this technique (3,4) does not allow double tuning of either coil, and thus time-correlated ‘H and 31P spectra from localized volumes are not possible. Consequently it is important to develop single-surface-coil methods for obtaining well-localized spectra. We report here single-surface-coil methods that, respectively, (i) correlate the 7r/2 pulse duration with depth into the sample; (ii) allow the volume of interest (VOI) to be shimmed, rather than the entire sample; and (iii) eliminate superficial signals in the 90” contour region. Using these methods we have been able to obtain well-localized ‘H and 31P spectra using a single doubly tuned surface coil. These three methods will be discussed sequentially. Correct choice of the 7r/2 duration is critical in DEPTH-pulse localization techniques. Since the correct pulse duration will vary from sample to sample depending on transmitter power, loading of the coil, placement of sample, and the depth of the volume of interest, it is important to determine the ?r/ 2 duration for each experimen-
Authors: J.W Pan, H.P Hetherington, J.R Hamm, D.L Rothman, R.G Shulman
Institution: Yale University
Language: English
Subfield: Radiology, Nuclear Medicine and Imaging
Field: Medicine
Domain: Health Sciences
Open Access status: hybrid
Funder: National Institutes of Health
OpenAlex ID: W1980834904