Spin-warp Imaging Research Articles

4471306 Method of NMR imaging which overcomes T2 ∗ effects in an inhomogeneous static magnetic field

The T2 * effects due to inherent inhomogeneities in the static magnetic field are overcome by the use of a 180° RF pulse to produce a nuclear spin echo suitable for obtaining spatial information and by the adjustment of the pulsed gradients such that the occurrence of the spin echo due to the applied gradients coincides with the occurrence of the nuclear spin echo derived from the rephasing of spins in the presence of the inhomogeneities inherent in the main static magnetic field. The 180° RF pulse is applied with the imaging gradients turned off so that long RF pulse lengths can be used, thus reducing RF power requirements. Exemplary applications of the pulse method to multiple angle projection reconstruction and two-dimensional Fourier transform (spin warp imaging) imaging techniques are also described.

Image restoration from non-uniform magnetic field influence for direct Fourier NMR imaging

A new technique is proposed for NMR image restoration from the influence of main magnetic field non-uniformities. This technique is applicable to direct Fourier NMR imaging. The mathematical basis and details of this technique are fully described. Modification to include image restoration from non-linear field gradient influence is also presented. Computer simulation demonstrates the effectiveness of this technique for both Fourier zeugmatography and spin-warp imaging.

The k-trajectory formulation of the NMR imaging process with applications in analysis and synthesis of imaging methods.

The fundamental operations of nuclear magnetic resonance (NMR) imaging can be formulated, for a large number of methods, as sampling the object distribution in the Fourier spatial-frequency domain, followed by processing the digitized data (often simply by Fourier transformation) to produce a digital image. In these methods, which include reconstruction from projections, Fourier imaging, spin-warp imaging, and echo-planar imaging, controllable gradient fields determine the points in the spatial-frequency domain which are sampled at any given time during the acquisition of data (the free induction decay, or FID). The detailed time dependence of the resulting trajectory of sample points (the k trajectory) determines the relative weight and accuracy with which image information at each spatial frequency is measured, establishing theoretical limitations on image quality achievable with a given imaging method. We demonstrate here that these considerations may be used to compare the theoretical capabilities of NMR imaging methods, and to derive new imaging methods with optimal theoretical imaging properties.

Changes in NMR relaxation time associated with local inflammatory response

T1 and T2 relaxation values and water contents of rat and rabbit tissues have been measured during the course of local inflammatory reaction to turpentine. For rabbits, NMR transverse sectional images were also obtained by spin-warp imaging. Elevations in T1 values around the injection site occurred within 24 h. In rats, T1 values of fibrosed muscle at the centre of the reaction continued to rise as a cyst formed, encapsulating the turpentine. T1 values of the surrounding muscle decreased towards normal as the reaction progressed. Good correlation between relaxation rate and water content was observed. In the rabbits, T1 values measured in vitro around the injection site were compared with the values obtained from NMR images of living and dead rabbits. T1 values obtained immediately after death were consistently lower than values of the same tissues before death. Factors affecting a comparison of T1 values obtained by the different methods are discussed.

Instrumentation for NMR spin-warp imaging

Implementation of a new NMR imaging technique has lead to the introduction of new instrumentation in imaging machines. The authors describe magnetic field gradient drivers and microprocessor control circuits which have increased the versatility of the system. The performance of the imaging method and improved resolution whole body images are discussed.

Instrumentation for NMR spin-warp imaging

Implementation of a new NMR imaging technique has lead to the introduction of new instrumentation in imaging machines. The authors describe magnetic field gradient drivers and microprocessor control circuits which have increased the versatility of the system. The performance of the imaging method and improved resolution whole body images are discussed.