Abstract: An X-ray image intensifier tube (1) includes an entrance section (2) for converting high-energy X-rays of from 100 keV to 120 keV into an electron beam (10). The entrance section (2) had a conversion layer (3) with a filter layer (5) for absorbing a part of comparatively low energy (from 60 keV to 80 keV) of the X-rays and a conversion layer for converting the high-energy X-rays of approximately from 100 keV to 120 keV into radiation whereto the photocathode is sensitive.

Abstract: A zero crossing detection circuit for estimating the ultrasonic attenuation in a region of interest in the body from an A-line signal which is representative of pulses of ultrasound energy reflected from said region. The ultrasound attenuation is estimated from the center frequency f.sub.Z of the returned energy which is calculated from the formula: ##EQU1## as measured at various depths in the body.

Abstract: An ultrasound transducer for medical pulse echo applications is apodized by causing the level of response to vary as a function of position on the transducer aperture. In a preferred embodiment, the response varies as a Gaussian function of distance from the center or centerline of the transducer so that the response at the edge of the transducer is approximately 30% of the response at the center or centerline. The response may be varied by causing the polarization of a piezoelectric ceramic transducer to decrease as a function of distance from the acoustic axis. In a preferred embodiment the transducer comprises a matrix of parallel rods of piezoelectric ceramic in an inert binder. The polarization of the piezoelectric body may be controlled by locally polarizing regions of the transducer with different voltages or for different periods of time. A polarization profile may also be produced by selectively heating localized regions of a previously uniformly polarized transducer to selectively depolarize them.