Ultrasound scanning apparatus

Apparatus for deriving signals indicating a condition of tissue within a volume of a body comprising means (2) for launching spaced supersonic pulses into a body under examination and means (6) for detecting the power of supersonic waves scattered from locations along a plurality of known paths. Signals proportional to the squares of the amplitudes of the reflected waves are generated, and the squares are integrated to give the desired indication. Gain control means (42,44,48,50) are provided from compensating for changes in amplitude ofh scattered supersonic waves resulting from their passage through blood or tissue, the increased attenuation with frequency of the spectrum of the launched pulses (60) and the focussing of the launched pulses (62). Compensation (54) for ring-down and the attenuation of the chest wall is also provided.