A. Field of Invention
This invention relates to a direction-finding system for locating reflecting interfaces, in particular of concretions in the biologic tissue of the human body. Such concretions may include, for example, gall, bladder, and kidney stones. The direction-finding system has an ultrasound pulse source, which pulses are readily transmitted through some substances, such as liquids (e.g. water) and biological tissues, and reflected by the interfaces between the liquids and other substances, and are recorded by ultrasound receivers. Additional devices transform the received ultrasonic echoes into stereophonic audible signals.
B. Description of the Prior Art
Image-forming ultrasonic display units are frequently used in the field of medicine. Other devices are known which evaluate the movement of a reflecting interface in the body (e.g. heart muscle movement of the embryo) by the Doppler effect have monophonic audio signals, as an output possibly including a threshold circuit which suppresses echo signals that are too weak, and hence not usable.
These ultrasound echo devices known in medical technology, however, permit only a non-dimensional, monophonic acoustic identification (e.g. a beep) or they indicate the output signal of a Doppler effect detector.
Problems in locating acoustically reflecting objects in the human body arise in particular in extracorporal acoustic lithotripsy wherein image-forming x-ray and ultrasonic methods are used.
As the conditions of propagation of x-rays and of sound waves in the human body are different, a congruent localization of the concretion using both systems does not result. The radiological observation of a stone furnishes shadow images usable for locating said stone, but the correlation of the stone position to the focus point of the shock wave generator is rendered difficult when the focusing dimension is small. A useful depth and lateral localization can therefore not be carried out with satisfactory certainty.
If image-forming ultrasonic methods are used for locating stones, the representations produced according to the present state of the art are interpretable only by highly specialized personnel, and reflections not produced by the stone may easily be misinterpreted. This problem is particularly prominent in distinguishing between a stone, a bone, or, a gas-containing area.
A stereophonic signal presentation in connection with position-finding problems of the blind has been proposed already in ultrasonic blind-guiding devices (DAGA '80--Fortschritte der Akustik, VDE-Verlag, Berlin 1980, pages 767 ff.). The problems of ultrasound transmissivity of biologic tissue and of water were of no importance in that field. Hence that description of a stereophonic ultrasonic direction-finding system does not teach the design of an apparatus applicable in medical technology.
Ultrasonic direction-finding systems are also known in other fields. Thus, for example for the localization of ships ultrasound pulses of short duration are emitted, the reflected echos are detected by a receiver ("transducer") and the transit time of the echo pulses is measured.
The graphic representation of sonar signals is described in U.S. Pat. Nos. 2,528,725 to 2,528,730.