4486709

DEPTH AND REFOCUSING PULSES FOR USE WITH

INHOMOGENEOUS RADIOFREQUENCY COILS IN

NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY

additional to the first excitation pulse, where these additional pulses are twice as long as the first pulse.

New Patents

GRADIENT FIELD COIL SYSTEM

Max R Bendall, Burbank, Queensland, 4123. Australia

In a pulsed nuclear magnetic resonance method of analysis, in which a single radiofrequency pulse is applied using an irradiation coil which provides an inhomogeneous radiofrequency field across the sample volume, the in- homogeneity of this field ensures that some sam- ple regions experience a radiofrequency pulse which is closer to a pi/2 pulse angle than for other regions, resulting in a larger signal intensity from the former regions as compared to the latter. If a second pulse is applied after the first, prior to ac- quisition of the signal, and if the phase of this pulse is alternated through the four phases: 0 degrees, 90 degrees, 180 degrees and 270 degrees, during a series of transients, then, provided the receiver phase is changed by 180 degrees when the second pulse phase is changed by 90 degrees, the signal intensity will accumulate from regions where the second pulse angle is pi radians and there will be discrimination against regions where the second pulse angle differs markedly from pi radians. This discrimination towards certain sample regions can be improved by adding further pulses after the second pulse pro- vided the phase of each additional pulse is alter- nated through all four 90 degrees phase shifts, during a series of transients, independently of the phase alternation of the other pulses, and pro- vided that for each individual 90 degrees phase shift, the receiver phase is changed by 180 degrees. In its simplest form, such a series of pulses may be represented by theta;(2 theta( + /- x, +/-y))n indicating n phase alternated pulses

4486711

FOR NUCLEAR SPIN TOMOGRAPHY

Georg Frese, Horst Siebold, Erlangen, Federal Republic Of Germany assigned to Siemens Ak- tiengesellschaft

A gradient coil system for an image-generating, nuclear magnetic resonance tomographic ap- paratus, particularly a zeugmatographic ap- paratus. The gradient coil system is arranged on a hollow cylindrical support body having an axis which extends along the z-direction of an x, y, z coordinate system which has an origin in the cen- ter of an imaging region. The gradient coil sys- tem contains, in addition to ring-shaped individual coils for generating field gradients which are substantially constant in the imaging region, a plurality of saddle-shaped coils which are symmetrically arranged through the imaging center for generating field gradients in the x and y directions. The saddle-shaped coils have straight conductor sections extending in the z- direction and arc-shaped conductor sections which extend perpendicularly with respect to the z-axis and along the circumferential direction of the support body. In accordance with the inven- tion, a further arc-shaped conductor section is connected in parallel with the arc-shaped con- ductor sections, the further arc-shaped con- ductor section facing a plane of symmetry. All of the arc-shaped conductor sections are displaced in the z-direction from the plane of symmetry by predetermined distances, and each arc-shaped conductor section has an electric linkage factor which is responsive to the distance between the particular arc-shaped conductor section and the plane of symmetry.