A UHF probe for NMR micro-imaging experiments.

A long solenoid is capable of producing, at least theoretically, a B1 field that is relatively more homogeneous than other known structures. This paper describes the design of a UHF probe incorporating a one-turn solenoid associated with a pair of parallel-plate transmission line feeders and presents a practical example used in a 360-MHz spectrometer for micro-imaging experiments. Numerical evaluation of the solenoid inductance using King's method for direct calculation of elliptic integrals is also included.

Design data for efficient axial gradient coils: application to NMR imaging.

A new design for an axial magnetic field gradient is described. Implemented in a four-coil configuration, it requires far less power than the conventional Maxwell pair, while maintaining the same field linearity. A practical design tool with a set of curves giving coil dimensions is proposed. Two realizations dedicated to NMR imaging are described and compared with the equivalent Maxwell pair. Substantial power reductions are achieved; in these cases, dc power is reduced by a factor of 5 and switching power by a factor of 15.

The slotted cylinder: an efficient probe for NMR imaging.

The slotted cylinder, an inductive structure with low self-inductance, low electric field, has been studied as a probe for NMR imaging applications. A theoretical calculation allows us to map the magnetic field and to evaluate electrical parameters of the structure. Several implementations, including new designs, have been experimentally tested over a wide range of frequencies (4-40 MHz), and compared to a classical coil probe. This study demonstrates the efficiency of the slotted cylinder for NMR imaging. It is optimized for large conductive samples when imaging at high frequencies (for human head, above 20 MHz).

A computer algorithm for the simulation of any nuclear magnetic resonance (NMR) imaging method.

More than a dozen Nuclear Magnetic Resonance (NMR) imaging methods have been described using different radio-frequency pulse sequences, magnetic field gradient variations, and data processing. In order to have a theoretical understanding in the most general case, we have conceived a computer program for the simulation of NMR imaging techniques. The algorithm uses the solution of the Bloch equations at each point of a simulated object. The direction of every elementary magnetic moment is computed at each instant, and stored in an array giving the global signal to be processed, whatever the pulse and gradient sequence. To test the validity of this program, we have simulated some well-known experimental results. Some applications are presented which contribute to the understanding of image distortions and to techniques such as selective radio-frequency pulse or oscillating gradients. This program can be used to unravel physical and technological causes of image distortions, to have a "microscopic" look at any parameter of an experiment, and to study the contrast given by various NMR imaging techniques as a function of the three NMR parameters, i.e., the hydrogen nuclei density rho and the relaxation times T1 and T2.