PubMed · 6481466
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A S Eadie, T E Hilditch. 1984. Re: Improved intrinsic resolution: does it make a difference?. https://pubmed.ncbi.nlm.nih.gov/6481466/
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Tissue-mimicking phantoms and an automated system have been developed for testing the resolution performance of ultrasound scanners by determining detectability of low to higher contrast spherical lesions over the entire depth of field. Axial, lateral and elevational resolutions are accounted for simultaneously and equally. Tissue-mimicking spherical simulated lesions are either 3 or 4 mm in diameter and have one of four different intrinsic material contrasts. For each diameter and contrast, there is a set of 109 lesions in a regular array with coplanar centers extending from 0.5-15.5 cm in depth. With the scan slice superimposed on the spheres, the image is frame-grabbed for automated analysis. A diameter-dependent lesion signal-to-noise ratio is computed for each pixel position in the image, excluding a 5-mm boundary. Two universal thresholds, resulting from maximization of agreement between the automated system and human observers, give rise to a depth range, or "resolution zone", over which detection exists for each type lesion.
The aims of this study were to assess (1) any angle dependency of color Doppler energy and (2) if computer analysis of the color can distinguish variations in volume flow. Fluid flowing through a silicon tube in a waterbath was insonated and the color in the images analyzed by a computer. The color presentation on the screen decreases rapidly as the angle approaches 90 degrees. At angles that did not produce a saturation of the color in the tube, the computer analysis detected significant differences between different flow volumes. We have concluded that monitoring of volume flow changes by analysis of color Doppler energy is possible, but the angle of insonation must be taken into account.
The magnetization subtraction technique (MS), which is equivalent to the inversion recovery technique in strong magnetic fields, has been implemented in dynamic nuclear polarization-enhanced magnetic resonance imaging (DNPI). The general theoretical basis of the MS method, which can be applied to DNPI or to prepolarized MRI in weak magnetic fields (such as Earth's magnetic field), is introduced. Details are provided about the signal amplitude, dynamic range of the method, and conditions required to observe signal void in samples with specific T1 relaxation times. The experimental results obtained with MS DNPI are presented and discussed. In the experiments, electron spin resonance irradiation frequencies of 199 MHz and 16.2 MHz were employed. Also, T1 contrast manipulation in the polarizing and in the detection magnetic field is discussed and demonstrated for MS DNPI.