| 摘要 |
Apparatus to detect and/or locate an inhomogeneity (4) in a medium (2) comprises a transducer (1) to transmit frequency-modulated ultrasonic energy through the medium, and a transducer (3) to receive reflected energy. The transducers (1, 3) are connected to a phase-locked loop (12) which maintains a required relationship between the phase of the transmitted modulation and the phase of the received modulation by adjustment of the modulation frequency. The modulation frequency adjustment is kept within predetermined upper and lower frequency limits so that the loop can lock only on to received ultrasonic energy which has travelled a distance within a predetermined region in the medium. The energy may be scanned across the region to produce a profile of the inhomogeneity, such as tissue at a certain depth within a limb. |
