Detection of arterial dilatation in the distal aorta--lower limb arteries using continuous wave Doppler ultrasound.

Continuous wave Doppler ultrasound techniques were used to obtain signals from the common femoral, popliteal, posterior tibial and dorsalis pedis arterial sites and the ankle systolic pressure indices in 54 patients with arteriographic, ultrasound "B"-Scan or surgical confirmation of arterial dilatation. The Doppler-shifted signals were spectrum-analysed and processed using a maximum frequency detector. The maximum frequency envelopes were examined retrospectively to determine whether there were any characteristics of the signals which could be used as diagnostic indicators of arterial dilatation. Ankle systolic pressure indices (ASPI), pulsatility index (PI), and delta, derived from the Laplacian transform method, were used in an attempt to quantify any changes produced by dilatation. The results indicate that characteristic and distinctive maximum frequency envelope signatures can be identified with arterial dilatation but that parameters such as ASPI and PI cannot distinguish these changes from the normal state and the Laplacian transform parameter "delta" places the dilatation cases in the minor stenosis category. However, generalised dilatation can be detected with a sensitivity of 85% if pattern recognition techniques are used.

The role of continuous wave Doppler imaging in a vascular unit.

A continuous wave (CW) Doppler imaging system has been used in the assessment of patients with suspected carotid artery disease. In 137 comparisons with conventional angiography the sensitivity of CW Doppler Imaging was 91% and specificity 93% respectively in the detection of greater than 50% diameter internal carotid stenosis. The main diagnostic criterion for greater than 50% internal carotid stenosis was the presence of a peak internal carotid systolic Doppler shift frequency greater than 4 KHz. An examination protocol is recommended which combines CW Doppler imaging with common carotid waveform changes and the temporal artery compression test.

Application of statistical techniques to data obtained from Doppler ultrasound examination of the extracranial arteries.

Techniques of increasing sophistication are being used to analyse the data obtained from continuous wave Doppler Ultrasound examination of patients with suspected arterial disease in the extracranial circulation. This study was carried out in order to compare the results of using relatively simple parameters such as the A/B ratio and the Index of Circulatory Resistance, ICR, and more recent techniques such as Principal Component Analysis on the changes apparent in the common carotid arterial waveform, particularly in the presence of disease in the internal carotid artery. This information was obtained from patients undergoing angiography so that the Doppler ultrasound results could be compared directly with an invasive assessment of the arteries under study. The signals obtained were processed off line using a Kay Sonograph Spectrum Analyser. The resulting maximum frequency envelope was further processed using a statistics package on a 2970 ICL computer. The A/B and ICR values were calculated manually. The preliminary results, calculated from 105 comparisons between Doppler ultrasound and angiography, suggest that techniques, such as Principal Components Analysis, are best able to cope with the waveform changes obtained in this study.

Accuracy of an electromagnetic three-dimensional ultrasound system for carotid artery imaging.

Freehand, three-dimensional (3-D) ultrasound (US) systems, which incorporate an electromagnetic tracking device to register the 3-D spatial location of images acquired using a standard linear array scan-probe, are a flexible and cost-effective solution for many clinical applications. The reconstruction accuracy of one such system was investigated by using a precision-made phantom. The error in 3-D distance measurements, under conditions appropriate to US investigations of the carotid arteries, was found to be -0.45 +/- 1.30 mm, equivalent to -0.53 +/- 3.39% (mean +/- SD). The results are relevant to data acquired using a single sweep scan and for distances in the range 25.00 to 79.06 mm. Both the overall accuracy and precision in point-target location were found to be relatively unaffected by scan depth, and the precision of point-target location was found to be poorest in the elevational direction. In conclusion, the system tested in our laboratory performed with high accuracy, adopting a setup and scan-sweep identical to that used for imaging of the carotid arteries in 3-D.

Optimisation and evaluation of an electromagnetic tracking device for high-accuracy three-dimensional ultrasound imaging of the carotid arteries.

Electromagnetic tracking devices provide a flexible, low cost solution for three-dimensional ultrasound (3-D US) imaging. They are, however, susceptible to interference. A commercial device (Ascension pcBIRD) was evaluated to assess the accuracy in locating the scan probe as part of a digital, freehand 3-D US imaging system aimed at vascular applications. The device was optimised by selecting a measurement rate and filter setting that minimised the mean deviation in repeated position and orientation measurements. Experimental evaluation of accuracy indicated that, overall, absolute errors were small: the RMS absolute error was 0.2 mm (range: -0.7 to 0.5 mm) for positional measurements over translations up to 90 mm, and 0.2 degrees (range: -0.8 to 0.9 degrees ) for rotational measurements up to 30 degrees. In the case of position measurements, the absolute errors were influenced by the location of the scanner relative to the scan volume. We conclude that the device tested provides an accuracy sufficient for use within a freehand 3-D US system for carotid artery imaging.

The validation of duplex scanning and continuous wave Doppler imaging: a comparison with conventional angiography.

Colour-coded continuous wave (CW) Doppler imaging and duplex scanning have been assessed prospectively in comparison with biplanar angiography for their accuracy in detecting significant arterial disease in the extracranial circulation. Of 96 comparisons with biplanar angiography, the sensitivity of Doppler imaging was 90% and specificity 98% in the detection of greater than 50% internal carotid stenosis and 86 and 100%, respectively, in the diagnosis of internal carotid occlusion. Of 85 comparisons with biplanar angiography, the sensitivity of duplex scanning was 93% and specificity 98% in the detection of greater than 50% internal carotid stenosis and 92 and 100%, respectively, in the diagnosis of internal carotid occlusion. The value of the peak systolic Doppler shift frequency of the internal carotid artery signal has proved to be the most reliable indicator of greater than 50% stenosis and is utilised in conjunction with a periorbital examination. It is concluded that both Doppler imaging and duplex scanning are effective screening techniques for the presence of significant (greater than 50%) internal carotid artery disease.

The accuracy of duplex scanning in the evaluation of early carotid disease.

The accuracy of duplex scanning in 69 comparisons with biplanar angiography in the detection of early carotid disease has been assessed. The various criteria reported for the categorisation of less than 50% disease have been critically analysed. As part of the study, 50 internal carotid arteries of 25 young, presumed normal medical students of mean age 20 years have been examined. The results suggest that duplex scanning has the ability to grade less than 50% carotid disease into normal, 1-24% and 25-49% stenosis categories. The most sensitive indicator of early disease is obtained from the real-time B-scan. The waveform changes of the maximum frequency envelope were more sensitive than spectral broadening except where full spectral broadening was present. For confident assessment, the real-time B-scan and pulsed Doppler must always be used in conjunction.

Characterisation of carotid artery disease: comparison of duplex scanning with histology.

The ability of duplex scanning to characterise the component tissue of atheromatous lesions of the internal carotid artery and to detect ulceration has been examined in a histological study of 42 carotid endarterectomy specimens. The results suggest that the only component of atheromatous lesions of the internal carotid artery which can be characterised from the B-scan is calcification. The presence of ulceration, intraluminal and intramural thrombus, fibrous intimal thickening and necrosis are not related to the echogenic appearance of internal carotid stenoses and may not be detected reliably. B-mode imaging alone cannot reliably grade greater than 50% internal carotid stenoses, but when this is combined with pulsed Doppler in the technique of duplex scanning, accurate results may be obtained.

The reliability of Doppler ultrasound techniques in the assessment of carotid disease.

The reliability of continuous wave (CW) Doppler imaging and Duplex scanning in the assessment of carotid artery disease has been evaluated prospectively in comparison with biplanar angiography. Of 130 comparisons the sensitivity of Doppler imaging was 89% and specificity 99% in the detection of greater than or equal to 50% internal carotid stenosis, and 87% and 99% respectively in the diagnosis of internal carotid occlusion. Of 118 comparisons the sensitivity of Duplex scanning was 93% and specificity 98% in the detection of greater than or equal to 50% internal carotid stenosis, and 93% and 99% respectively in the diagnosis of internal carotid occlusion. CW Doppler imaging and Duplex scanning are accurate techniques in the diagnosis and categorisation of internal carotid artery disease. CW Doppler imaging is an effective screening technique for the presence of greater than or equal to 50% internal carotid artery stenosis. Duplex scanning also has the potential for improved detection of early internal carotid artery disease and study of the natural history of atherosclerosis.

Extra-tympanic electrocochleography.

A non-invasive technique for recording the cochlear action potential in adults without recourse to sedation or local anaesthesia is presented. This technique has been assessed in two ways: (1) A group of normal subjects was tested to obtain distributions of response amplitude and latency as functions of stimulus intensity. (2) A group of patients with Meniere's disease was tested with trans- and extra-tympanic electrocochleography to compare the intensity amplitude functions and wave-forms obtained from the two methods. On the basis of this study the use of extra-tympanic electrocochleography as a replacement for the trans-tympanic method is discussed.

Comparison of angiography with continuous wave Doppler ultrasound in the assessment of extracranial arterial disease.

Extracranial arterial disease was assessed using non-invasive continuous wave Doppler ultrasound. The results of the Doppler study were compared with those of angiography. There was a positive correlation between the results of angiography and the shape of the Doppler waveform, but the correlation was improved by adding a compression manceuvre to the procedure.

Effects of incubator noise on the cochlea of the newborn.

The possible effects of incubator noise on the hearing of premature babies have long been debated. The type of hearing loss found in 12 low-birthweight children was examined; and the variable noise level in regularly used incubators was measured. This noise, applied to guinea pigs continuously during their second week after birth, was shown histologically to destroy a proportion of the sensory cells in the cochlea. Adult guinea pigs, however, were not vulnerable in this way. The conclusion is that there is definite circumstantial evidence of the damaging effect of many incubators on the hearing of premature infants.

Three-dimensional endoanal sonography in assessing anal canal injury.

BACKGROUND: Instrument design limits endosonography of the anal canal to the axial plane, with no capability for longitudinal imaging or measurement. Using three-dimensional reconstructions, the relationship between the radial and linear extent of an anal sphincter tear has been explored, and sex differences in anal canal and sphincter length have been established. METHODS: Three-dimensional reconstructions were performed in 20 controls and 24 patients with faecal incontinence found to have 25 external and five internal sphincter defects. The radial and linear extent of any sphincter tear was measured. In controls the length of the sphincters was compared with the total anal canal length, and the maximum and mean internal sphincter thickness was compared. RESULTS: The radial angle of an internal or external sphincter defect was significantly related to its length (R2 = 96.8 per cent and R2 = 84.4 per cent respectively; both P < 0.001). The anal canal was longer in men than in women (mean(s.d.) 32.6(5.3) versus 25.1(3.4) mm; P < 0.001). The internal anal sphincter was also longer in men (25.6(6.3) versus 19.8(4.0) mm; P < 0.02), but the mean internal sphincter length as a percentage of total anal canal length did not differ (78.3 versus 78.7 per cent; P not significant). The anterior external anal sphincter was longer in men than in women (32.6(5.3) versus 15.3(2.8) mm; P < 0.001), and formed a greater percentage of total anal canal length (100 versus 62.9 per cent; P < 0.001). CONCLUSION: Multiplanar imaging has revealed a direct relationship between the length of a sphincter tear and its radial extent as shown on axial scanning. Marked sex differences in sphincter configuration have been demonstrated. In women the shorter anterior sphincter length highlights the risk of complete sphincter disruption with extensive tears.

Duplex ultrasound monitoring of arterial grafts: prospective evaluation in conjunction with ankle pressure indices after femorodistal bypass.

Duplex scanning and ankle brachial pressure indices have been used to objectively assess 94 femoro-distal bypass grafts 4-8 weeks postoperatively. Twenty grafts were occluded. Of the 74 patent grafts, three distinct groups could be identified on the basis of the non-invasive examination. Group 1. Patent grafts with no evidence of haemodynamically significant disease. Group 2. Patent grafts with localised disease. Group 3. Patent: haemodynamically failed grafts. Ankle brachial pressure indices alone could not differentiate between occluded grafts and grafts that were patent: haemodynamically failed (group 3), or adequately separate between grafts in groups 1 and 2. Duplex scanning when combined with pressure indices identified patent grafts "at risk" due to the presence of haemodynamically significant disease. Life table analysis demonstrated appreciable differences in event free survival between group 1 grafts and "at risk" grafts (groups 2 and 3). Duplex scanning is ideal for regular postoperative surveillance and complements the use of ankle brachial pressure indices in the follow-up of femoro-distal grafts.

Impact of duplex scanning on carotid endarterectomy.

Duplex ultrasound permits safe and accurate assessment of the extracranial vasculature. This paper reports the change in patterns of referral to a specialized vascular unit following its introduction; increased referrals were seen in all specialties except neurology. A widely available and reliable duplex service has revealed more extracranial vascular disease than was previously recognized, and has increased referrals for carotid endarterectomy, thereby increasing surgical workload.

Duplex ultrasound assessment of femorodistal grafts: correlation with angiography.

Fifty-eight grafts have been assessed using duplex scanning and ankle brachial pressure indices. This assessment is compared with the findings by angiography. Eighteen grafts were occluded and 40 patent. Duplex scanning defined graft status with a greater accuracy than pressure indices. Pressure indices alone would not differentiate "satisfactory" grafts from those with localised, haemodynamically significant disease. Only 55% of those grafts with localised stenoses demonstrated a fall of greater than 0.2 in ankle brachial pressure index after exercise. When the information obtained using pressure indices and duplex scanning was combined non-invasive assessment had a sensitivity of 86% and specificity of 94% for detection of localised, haemodynamically significant disease in patent grafts. Haemodynamically significant disease, as defined by angiography, can be detected and localised with duplex scanning complementing the use of pressure indices in graft assessment.