3-Hydroxy-3-methylglutaryl-CoA lyase deficiency studied using 2-dimensional proton nuclear magnetic resonance spectroscopy.

1H-NMR spectroscopy has been applied to identify components in the urine of subjects with a deficiency of the enzyme 3-hydroxy-3-methylglutaryl-CoA lyase. One-dimensional spectra of samples from a pair of non-identical twins with this disorder were very similar and are probably diagnostic. The most intense signals were from singlets. Complete assignment of these major components was made possible by the use of 2-dimensional chemical shift correlated spectroscopy since several long-range couplings were detected. 2-dimensional spectroscopic techniques may therefore be of value in the identification of singlets in multicomponent systems.

An automatic method for determining the centre of rotation of a mechanically scanned reflection UCT system.

A method will be described for determining the centre of rotation of a mechanically scanned reflection ultrasound computed tomography system. It is based on the principle of obtaining opposing images of a test object containing many point targets. The method is automatic in the sense that the centre of rotation is calculated by a computer without the need for an operator to make direct measurements on the mechanical system. For the particular reflection UCT system described here, the centre of rotation is obtained in 3-5 min with a repeatability (+/-2 SD) of +/-0.3 mm. Ways in which even higher accuracy can be obtained are discussed. The basic principle of the method is applicable to any concentric imaging system for which a good approximation to an ideal point target can be produced.

Experimental studies in transmission ultrasound computed tomography.

The reconstruction of the speed-of-sound distribution within a target can be achieved by CT techniques from measurements on transmitted ultrasonic pulses. The mathematical relationship between speed-of-sound imaging and the conventional CT situation is explained. An experimental system, which has been developed to investigate speed-of-imaging and other forms of in-vivo ultrasound CT, is described, along with the techniques used for data acquisition and image reconstruction. These include measurement of pulse time-of-flight by the threshold or cross-correlation methods. Techniques for reducing artifacts in speed-of-sound images are also described, such as median filtering and modified Shepp-Logan filtering. These techniques have been used to obtain high quality speed-of-sound images of various phantoms. Images of tissue in-vitro have been less satisfactory, because of refraction and attenuation effects. Ways of overcoming these difficulties in an improved system are proposed.

Towards a protocol for measurement of maximum spatial peak temporal average acoustic intensity from diagnostic B mode ultrasound scanners in the field.

The Northern Regional Medical Physics Department has been involved in measurement of the acoustic output of diagnostic ultrasound equipment for several years. As the complexity of diagnostic ultrasound equipment has increased, so have the problems of measuring the acoustic outputs of this equipment in the field. Measurements made in the field are often made on unfamiliar pieces of equipment and under tight constraints of time. In these circumstances the magnitude and the conditions under which the true maximum Ispta value occurs may not always be found. The aim of a measurement protocol is therefore to facilitate the measurement of Ispta in the field, so that the measured maximum Ispta value is as close as possible to the 'true maximum' Ispta value. To be of practical benefit the protocol must be succinct and easy to use, as well as applicable to most if not all types of scanner. Our experience has led us to believe that this is possible and that the benefits of a well designed measurement protocol will far outweigh any disadvantages. The development of two measurement protocols is discussed in this paper. The time required to carry out each measurement depends on the number of assumptions made about the operation of the scanner in the protocol used. The first protocol makes very few assumptions about the operation of a scanner; the results from measurements made using this protocol can be used to assess the validity of the much larger number of assumptions made in the second protocol. The results from measurements on three types of scanner using the two protocols are presented. The results demonstrate the validity of most of the assumptions made by the protocols and the potential benefits of using a protocol for measurement of maximum Ispta in the field in terms of reduced measurement time and greater consistency.

The influence of ultrasound scanner beam width on femur length measurements.

Systematic differences have been found in measurements of femur lengths made with (1) a Hitachi EUB 25, representative of older machines in use when most of the femur length-gestation curves were produced; and (2) a modern high resolution machine (Acuson 128). It is proposed that these differences may be accounted for by the different beam widths of the two systems. Six operators measured the femur lengths of several normal fetuses using both machines. Analysis of the results revealed a highly significant (p < 0.005) difference between machines, that did not correlate with femur length (r = -0.022). The mean difference was 1.02 +/- 0.33 mm (Hitachi larger). The mean femur length was 46.44 mm (n = 57). Pulse-echo beam plots showed that, for the probes used, the Hitachi 6 dB beam width is greater than the Acuson beam width by typically 2 mm, depending on the range and Acuson focus setting. This beam width difference can account for the difference in femur length measurements, if allowance is made for the variable angle between femurs and ultrasound beams. The results suggest that femur length-gestation curves for use with modern machines should be based on measurements made with modern machines.

A survey of the acoustic outputs of diagnostic ultrasound equipment in current clinical use.

Surveys published up to 1991 have highlighted a steady increase in the acoustic outputs from diagnostic ultrasound equipment. Since 1991 we have made measurements of the maximum peak negative pressure (p-) and spatial peak temporal average intensity (ISPTA) produced by 223 probes from 82 scanning systems in current clinical use in the Northern Region in the UK. Measurements have also been made of the maximum total acoustic power generated by 45 probes from 17 scanners. The results from these measurements are presented in this article and compared to the results of a similar survey of equipment from both the Northern and Wessex Regions in the UK and published in 1991. The comparison shows that measured ISPTA values have increased approximately sixfold in B mode and approximately threefold in colour Doppler mode. Also, measured total acoustic power values have doubled in pulsed Doppler mode. The present survey also draws attention to some particularly high ISPTA values obtained from a number of probes and scanning systems. This survey has shown that measurements of acoustic outputs from diagnostic ultrasound scanners in current clinical use are substantially higher than reported in earlier surveys and, for certain scanners, the acoustic outputs from scanned beam modes of operation can reach levels hitherto only found in pulsed Doppler mode.

A comparison of AIUM/NEMA thermal indices with calculated temperature rises for a simple third-trimester pregnancy tissue model. American Institute of Ultrasound in Medicine/National Electrical Manufacturers Association.

Temperature rises due to diagnostic ultrasound exposures have been calculated for a simple third-trimester pregnancy tissue model. This consisted of a layer of soft tissue representing the abdominal/uterine wall, a layer of liquid and a layer of fetal bone. The ultrasound field parameter used in the calculations was the temporal average of the square of the acoustic pressure (p2TA), measured in water but corrected for attenuation in the tissue model. The three-dimensional (3-D) distribution of p2TA was measured for five probes operating in B-mode, and four probes operating in pulsed Doppler and color flow imaging modes. The calculated temperature rises were compared to the AIUM/NEMA-defined thermal indices appropriate to third-trimester scanning. In B-mode, the ratio of calculated temperature rise to thermal index varied between 0.62 and 1.25, with calculated temperature rises as high as 1.4 degrees C. In color-flow imaging mode, this ratio varied between 1.26 and 2.45 and, in pulsed Doppler mode, between 1.46 and 2.92, with calculated temperature rises as high as 1.8 degrees C and 5.8 degrees C, respectively. These results indicate that, for scanning situations where bone is insonated through an overlying low attenuation liquid layer, the thermal index may substantially underestimate the maximum temperature rise that could occur.

Evaluation of subjective assessment of liver function from radionuclide images.

The appearance of non-hepatic uptake in 99Tcm-colloid images is an important indicator of poor liver function. We undertook this study to evaluate the ability of experienced observers to assess liver function from radionuclide images. A simple model was used to simulate the changing distribution of 99Tcm-colloid in the liver, spleen and bone marrow as the liver function and mass were varied. Suitable images of these three organs were isolated from real studies and used as "templates" to create realistic simulated 99Tcm-colloid images, with the count densities of liver, spleen and bone marrow determined by the model. These images were presented in random order to several observers, who were asked to assess liver function. Comparison of the estimated with the true function shows that visual assessment is systematically inaccurate, with underestimation of poor function and overestimation of good function. It is also imprecise, especially for livers with only midly impaired function. Observers were also affected by changing liver mass and were more likely to judge small livers to be abnormal. We suggest that objective assessment using a quantitative technique should be used as an adjunct to visual inspection for the evaluation of liver function.

Repeatability of peripheral pulse measurements on ears, fingers and toes using photoelectric plethysmography.

Peripheral pulses have been recorded and analysed to determine the accuracy with which pulse transit times (PTTs) can be measured. Measurements of PTT between the ECG Q-wave and various peripheral sites were made in 10 normal subjects on 10 separate days. Mean values were determined for the ears (174 ms), fingers (245 ms), and toes (361 ms). The technique was sufficiently accurate to detect small changes in PTT due to changes in posture; sitting to lying, 5.2 ms. When comparing simultaneous measurements on bilateral sites only small differences in PTT were discovered, and these were not significant in the study group as a whole. However, these differences were significant in some individuals. When the subjects raised a single arm or leg, significant differences (38 ms and 49 ms respectively) were recorded between sides. The day-to-day repeatability sigma (expressed as the square root of the within-subject mean square variance) of individual PTT measurements on a subject (supine) was for ears, fingers and toes respectively 9.4, 9.2 and 12 ms. For right-left differences the repeatability was 7.2, 5.9 and 14 ms. Hence changes in PTTs, or differences between right and left sides, can be detected from single measurements with 95% confidence if they exceed approximately 20 ms in ears or fingers and 30 ms in toes.