Biomedical subjects
Publications and source records attributed to J C Somer.
A survey of present opinions on the safety of diagnostic ultrasound applications is presented together with some data on output levels. Physical mechanisms involved in potential adverse effects are described. Labelling requirements of the equipment are defined and specified. These requirements are contained in a recent proposal of the Netherlands' Committee on the Safety of Ultrasound.
This paper evaluates deconvolution (inverse filtering) as applied to ultrasonic imaging systems, and discusses the obstacles which are encountered employing the technique in practice. A minicomputer is used to generate artificial echo signals, simulating rf signals resulting from a set of point reflectors in a homogeneous medium, as recorded by an electronically focused group-steered linear array scanner. Two-dimensional deconvolution in combination with a Wiener noise reduction filter (i.e., a Wiener-Inverse filter) is applied to these simulated rf signals, which were contaminated with white noise. The efficacy of the Wiener-Inverse filter is defined in terms of its ability to resolve two point reflectors with a lateral spacing equal to the local -6 dB width of the ultrasonic beam. In favorable circumstances, the targets are resolved at signal-to-noise ratios (SNR) better than 20 dB, where SNR is defined as the maximum signal power divided by the average noise power level. Nonlinear effects due to quantization or signal clipping are investigated. In order to improve the resolution of an rf signal with a dynamic range of 40 dB, the input signal should be digitized at a minimum of 12 bits. The problem of signal clipping can be circumvented by oversampling. The two-dimensional Wiener-Inverse filter is defined in terms of both temporal and spatial properties of the insonification. Effects of wave diffraction give rise to a depth-dependent ultrasonic beam. As a result of a misfit of the Wiener-Inverse filter and the local properties of the ultrasonic beam, erroneous noisy texture arises in the image. Adaptation of the Wiener-Inverse filter with respect to the beam properties gives acceptable results, at the expense of a rather large computational effort.
In ultrasound phased-array imaging systems the receiver directivity pattern is steered by controlling the delay of echoes from the array elements. A new processing technique is introduced that provides the required delay first by properly phasing the echo carrier, and successively by delaying the echo envelope. This latter operation is based on a new analogue sampled-data delay-line. Independent control of phase delay offers a simple means of compensating for random phase errors due to non-uniformity of the array elements response.
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A new form of ultrasound diagnostic possibility is presented (the electroscan). The basic principles of this two dimensional method are described. Special attention is given to the probe consisting of an array of 21 elements of piezo-electric material. The results of this method in four patients are discussed (meningioma, arteriovenous aneurysm, subdural haematoma, and a baby with hydrocephalus). The baby with hydrocephalus showed diagnostic problems which could be understood from the pneumoencephalographic findings. The electroscan method seems to offer good possibilities for the diagnosis of brain lesions, if these have a consistency different from that of normal brain tissue.
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