A constant depth ultrasonic scanner

Abstract

A method of two-dimensional, pulse-echo ultrasonic scanning is described in which a focused sound beam is used to visualize deep-sited, thin layers of tissue located at a constant depth from an ultrasonic probe and close to its focal plane. Experimental investigation of the system indicates an attainable lateral resolution of the order of 1 mm at 2 MHz, with associated high sensitivity. It is also found that anatomically significant detail is provided by isotropically scattered echoes, without the need to search for specular reflections from major interfaces. Previous approaches to constant depth scanning have employed a cartesian raster scanning pattern, which has been found to have serious limitations in clinical applications, particularly in relation to scanning speed and acoustic contact. A suggested solution to both of these problems is to employ a spiral scanning pattern generated by a transducer which is moved mechanically in such a way that the centre of its active surface is stationary (i.e. at an isocentre) and can thus be held in contact with a single point on a patient's skin.