[en] The nuclear medicine physician uses visual interpretation of a movie-like display of the beating human heart to detect wall motion abnormalities which might be related to impaired cardiac function. The present work is directed toward extracting more information from the heart motion study, and presenting it in a useful manner. A spatially adaptive smoothing routine using a quadtree image representation gives an improvement in mean squared error compared to the S9 smoother commonly used for nuclear medicine studies. Functional images show the two-dimensional distribution of parameters of the heart motion. The most popular, the first harmonic phase functional image, formed from the first Fourier harmonic fit to each pixel time-activity curve, is subject to significant artifacts which make a simple interpretation of it difficult. A multi-harmonic approximation is more accurate and offers a wealth of unique parameters with which to construct more directly meaningful functional images

[en] Improvement in MR imaging signal-to-noise ratio (S/N) with the use of reduced read-out gradients is well known, as is the use of increased read-out gradients to diminish chemical shift effects. However, the optimization of read-out gradient strengths for specific clinical applications is not well documented. The authors compared image quality (in terms of S/N, tissue contrast and boundary definition) in 20 patients with brain lesions and 20 patients with head and neck lesions. All patients were scanned on a 1-T system using gradient strengths of 11.56 mT/cm and 0.78 mT/cm. The authors found improved S/N and increased contrast in the low bandwidth images of the CNS. Chemical shift effects were negligible in these images but were increased and significantly degraded in the head and neck examination. Therefore, the authors recommend a choice of two bandwidths for ''neuroradiologic'' examinations: low for CNS studies and high for head and neck studies

[en] A velocity spectrum may allow the flow within small vessels to be characterized even when the vessels are only a few pixels in cross-sectional area. An anisotropic three-dimensional Fourier-transformed MR imaging sequence with a bipolar velocity-encoding gradient in the third dimension produced velocity spectra of a phantom containing a jet and a stenosis. The low spatial resolution spectra downstream of the jet and at the inlet, neck, and outlet of the stenosis exhibited differences from normal laminar flow, the differences were consistent with the expected distribution of velocities

[en] A 90⁰-r-90⁰ -image pulse sequence spatially maps magnetic field distortions arising from susceptibility differences. Three phantoms having three concentric cylinders of fluid were imaged. The outer and inner cylinders of each contain a 5-mM NiCl/sub 2/ solution. The middle cylinders contain either NiCl/sub 2/, sunflower oil, or 9-mMDyCl/sub 3/. Sunflower oil exhibits only a chemical shift, while dysprosium has both chemical shift and a significant susceptibility difference compared with nickel-doped water. Images of the NiCl/sub 2/ and sunflower oil phantoms are similar, while those of dysprosium show marked field distortions. Varying tau to phase-encode the resonant frequency allows quantitative measurement of field distortion