A review of experimental transverse Doppler studies

The possibility of detecting useful Doppler information when the ultrasound beam is transversely oriented to the flow, has so far been studied by several authors. A new theory, in particular, has demonstrated that the focusing properties of piezoelectric transducers involve a Doppler signal bandwidth proportional to the transverse velocity component. The key element to perform reliable "transverse" Doppler experimental studies is thus an efficient spectrum analyzer, capable of performing accurate and repeatable bandwidth measurements. The authors review here experimental tests of the new theory, independently done in several laboratories by means of a specially developed computerized spectrum analyzer. The results of these tests include the demonstration that the "transverse" Doppler bandwidth is invariant with the range of cell depth and dimensions. It is also discussed how the basic transverse Doppler technique can be conveniently extended to allow the two- and three-dimensional estimation of the flow vector. Experimental evidence about the possibility of using the new theory to give a correct interpretation of in vivo transverse spectrograms is also presented.>