th  - 1987 - 51st ENC Conference

WF60
SENSITIVITY OF SURFACE COILS TO DEEP LYING VOLUMES
William J. Tboma , ~ichael J. Albright ~,
Piotr M. Starewicz" and Truman R. Brown
Fo~Chase Cancer Center, Philadelphia, PA 19111
Siemens Medical Systems, Iselin, NJ 08830
Ne have acquired rith an 8.5 cm-single turn3[urface coil in a 1M bore
magnet operating at 1.5 T a single acquisition P spectrum (26 MHz) of the
human calf that clearly displays ATP J-coupling and has a pbosphocreatine
signal to noise of 25 with a 7 hertz gaussian filter. Obviously, this is
adequate sensitivity for the entire volume. Unfortunately, in many cases, in
order to distinquish amoung various physiological responses, it is required
that the volume selected for observation be restricted. As the volume from
which the signal is derived becomes smaller the sensitivity of the detection
coil becomes critical. It is well known that the most important factors in
coil sensitivity are the distance from the coil to the volume from which the
signal originates, and the Q of the coil. Other factors that are important
include the geometric shape of the coil, number of turns, and shielding of the
coil from dielectric losses.
We have undertaken a study of the sensitivity of surface coils for small
regions as a function of their depth for various surface coil designs,
different turn numbers, various faraday shields, coil radius as a function of
sample volume size, and coil Q. The Q of the coil was measured by determining
the 90 ° pulse at, and the resultant signal from, a 2 cm chamber containing
phenylphosphonate in the center of the coil. Five and 10 cm thick phantoms
of dimensions large compared to the surface coil diameter were filled with
solutions of differing ionic strength and placed between the coils and a 2S ml
spherical sample.
The resultant sensitivity of the various coils rill be reported as a
function of the above parameters.