Acoustical Imaging: Theory Limitations and Relationships to other Imaging Modalities
The basic physics of ultrasound is reviewed. Ultrasonic diagnosis employs frequencies in the low megahertz range which is generated and detected by piezoelectric transducers. Pulse-echo information may be displayed as an A-scan, an M-mode recording, as a two-dimensional B-scan (often obtained in real time), or as a C-scan. The Doppler effect gives rise to audible shift frequencies in ultrasound reflected from moving structures. This can be used for flow studies and for imaging. Ultrasonic methods, which are generally limited to the study of soft tissues, provide information which may be complementary to that obtainable with other diagnostic techniques; but they compete for financial resources, and the technologies are continuously changing.
KeywordsCharacteristic Impedance Ultrasonic Pulse Doppler Shift Frequency Ultrasonic Imaging Ultrasonic Field
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