Gradient pulses used in most localization techniques induce time-dependent shifts in Bo that strongly distort NMR signals. A postprocessing correction method requiring no additional hardware is proposed. The phase shift produced by the Bo shift is calculated from a reference free induction decay (FI
Distortions of ultrasonic field introduced by the rib cage in echocardiography
β Scribed by Adam D. Savakus; K. Kirk Shung; Norman B. Miller
- Publisher
- John Wiley and Sons
- Year
- 1982
- Tongue
- English
- Weight
- 575 KB
- Volume
- 10
- Category
- Article
- ISSN
- 0091-2751
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β¦ Synopsis
Abstract
In ultrasonic examination of the heart, the anatomy and motion of heart structures can be observed by placing the ultrasonic transducer over an intercostal window adjacent to the sternum. The ultrasonic beam may be reflected, refracted, or scattered from its path by the ribs and soft tissues before reaching the target of interest. This interaction between the tissues and ultrasound beam, which introduces significant changes in ultrasonic beam characteristics, may result in considerable degradation of the lateral resolution of the ultrasonic system, determined largely by the beam width. In this paper, the effect of rib cage on the beam characteristics is examined. It is shown that the rib cage can produce severe distortions of the ultrasonic beam, namely, asymmetry in beam crossβsection, alteration in beam diameter, and deflection of the beam from its central path. It is also demonstrated that this distortion is dependent upon transducer diameter, width of the intercostal window, and transducer angulation relative to the breast plate.
π SIMILAR VOLUMES
We present a numerical modelling of the harmonic sound in two isotropic media, one liquid and the other solid separated by a plane interface. This numerical modelling is carried out by the angular spectrum method. This latter is applied to calculate the displacement potential generated by a rectangu