Development of educational image databases and e-books for medical physics training.

Medical physics education and training requires the use of extensive imaging material and specific explanations. These requirements provide an excellent background for application of e-Learning. The EU projects Consortia EMERALD and EMIT developed five volumes of such materials, now used in 65 countries. EMERALD developed e-Learning materials in three areas of medical physics (X-ray diagnostic radiology, nuclear medicine and radiotherapy). EMIT developed e-Learning materials in two further areas: ultrasound and magnetic resonance imaging. This paper describes the development of these e-Learning materials (consisting of e-books and educational image databases). The e-books include tasks helping studying of various equipment and methods. The text of these PDF e-books is hyperlinked with respective images. The e-books are used through the readers' own Internet browser. Each Image Database (IDB) includes a browser, which displays hundreds of images of equipment, block diagrams and graphs, image quality examples, artefacts, etc. Both the e-books and IDB are engraved on five separate CD-ROMs. Demo of these materials can be taken from www.emerald2.net.

Consequences of using different soil texture determination methodologies for soil physical quality and unsaturated zone time lag estimates.

Elucidation of when the loss of pollutants, below the rooting zone in agricultural landscapes, affects water quality is important when assessing the efficacy of mitigation measures. Investigation of this inherent time lag (t(T)) is divided into unsaturated (t(u)) and saturated (t(s)) components. The duration of these components relative to each other differs depending on soil characteristics and the landscape position. The present field study focuses on tu estimation in a scenario where the saturated zone is likely to constitute a higher proportion of t(T). In such instances, or where only initial breakthrough (IBT) or centre of mass (COM) is of interest, utilisation of site and depth specific "simple" textural class or actual sand-silt-clay percentages to generate soil water characteristic curves with associated soil hydraulic parameters is acceptable. With the same data it is also possible to estimate a soil physical quality (S) parameter for each soil layer which can be used to infer many other physical, chemical and biological quality indicators. In this study, hand texturing in the field was used to determine textural classes of a soil profile. Laboratory methods, including hydrometer, pipette and laser diffraction methods were used to determine actual sand-silt-clay percentages of sections of the same soil profile. Results showed that in terms of S, hand texturing resulted in a lower index value (inferring a degraded soil) than that of pipette, hydrometer and laser equivalents. There was no difference between S index values determined using the pipette, hydrometer and laser diffraction methods. The difference between the three laboratory methods on both the IBT and COM stages of t(u) were negligible, and in this instance were unlikely to affect either groundwater monitoring decisions, or to be of consequence from a policy perspective. When t(u) estimates are made over the full depth of the vadose zone, which may extend to several metres, errors resulting from the use of hydraulic parameters generated from hand texture data will be resultantly greater, and may lead to flawed predictions regarding the achievability of water policy targets. For this reason laboratory analysis, regardless of method, should be preferred to simple field assessments.

Time-averaged mean velocity for volumetric blood flow measurements: an in vitro model validation study using physiological femoral artery flow waveforms.

This study assesses the accuracy of the volume flow measurement of the ATL HDI 3000 duplex ultrasound scanner using a model of the femoral arterial circulation. The beam profile of the transducer was measured, and used to identify regions of the beam where there may be poor insonation characteristics. The flow measurement accuracy was not found to be influenced by the vessel depth between 1.0 cm and 8.0 cm in a 0.7 cm diameter vessel. Overall accuracy was 3%+/-9%. Vessels in excess of 0.9 cm produced larger errors. In the model system, pulse rates between 60 bpm and 120 bpm had no significant effect on the measurement accuracy (p > 0.01). The results of this study suggest that accurate measurements of femoral arterial blood flow are possible. Further work will be required to assess the accuracy of the technique in vivo.

An objective feature extraction technique applied to the Doppler waveforms from the groin: a prospective study.

A group of 80 patients presenting with lower limb ischaemia were classified according to their arteriographic findings. The maximum frequency envelope from the Doppler waveforms obtained from the common femoral artery were retrospectively analysed using a mathematical feature extraction technique, principal component analysis (PCA). Two of the three coefficients uniquely describing each waveform were plotted and classified according to their arteriographic groupings. The best separating planes were then defined. Twenty-eight new patients were subsequently prospectively assessed using the principal components and separating planes defined in the previous study. The results were compared with the arteriographic findings and showed that PCA represents a significant improvement in diagnostic accuracy when compared with other techniques.

Latex vessels with customized compliance for use in arterial flow models.

The physical characteristics of the arterial wall exert a major influence over blood flow patterns and the pulse wave velocity is strongly affected by the elasticity of the vessel. We have developed a technique for manufacturing latex tubing which has physical characteristics similar to those of human arteries. Tubes were produced by painting a plastic rod of diameter 7 x 10(-3) m (the internal diameter of the superficial femoral artery) with liquid latex. The number of coats applied controlled the thickness, and hence the elasticity of the resulting tube. Values of compliance and pulse wave velocity were similar to those observed in vivo. The tubing was tested in a model of the femoral arterial circulation and the typical triphasic arterial now was seen. The mean flow in the vessels was also analysed, and found to be higher for the more elastic vessels, supporting existing mathematical theories and qualitative physiological data. These vessels provide a reliable method of producing physiologically accurate test segments for use in a range of arterial flow models.

Real-time analysis of Doppler waveforms.

The usefulness of objective analysis of Doppler waveforms is now well established but to date such measures have generally not been available in real-time. This Paper describes a real-time data analysis and collection system in use with a duplex scanner which is capable of producing objective measures of waveform shape during the investigation. It is shown as an example that this information can be used to identify, with high accuracy, babies likely to be classified at birth as distressed as early as the 34th week of pregnancy.

The clinical effectiveness of hand held Doppler examination for diagnosis of reflux in patients with varicose veins.

OBJECTIVE: To assess the accuracy of hand held Doppler (HHD) as a rapid screening test for selecting varicose vein patients for duplex imaging. DESIGN: Prospective single blind study of consecutive patients in a randomised trial. MATERIALS: Use of hand held Doppler and duplex ultrasound scanners. METHODS: One thousand two hundred and eighteen legs (943 patients) were examined by HHD and then duplex. HHD examiners recorded whether they would normally have requested duplex. RESULTS: HHD results of one Clinical Assistant (166 limbs) were significantly poorer than all others and his results were excluded from analysis. Duplex would not have been requested in 645 of 1052 (62%) limbs. Among these HHD missed significant reflux in the long saphenous vein in 18 (3%) and the short saphenous in 25 (4%). Reasons for requesting duplex were popliteal fossa reflux (202); recurrent (94) or atypical (86) varicose veins; and possible previous thrombosis (67). Differences were observed between staff and units in requests for duplex; and in thoroughness and style of duplex reporting. CONCLUSIONS: Selective use of HHD can avoid duplex imaging for many patients, with a low failure rate for detecting correctable venous reflux. Observed variations between individuals and units in results of HHD and duplex imaging have implications for the increasing use of duplex by clinicians.

The blood supply of colorectal liver metastases.

Post-mortem studies suggest that liver metastases obtain the majority of their nutrition from the hepatic artery; however, cytotoxic arterial perfusion with or without hepatic-artery ligation has not proved entirely successful as a therapeutic regime. In this study we have measured blood flow into colorectal liver metastases using xenon-133 (133Xe) clearance in patients undergoing surgery for colorectal cancer. Pre-operative measurements after direct parenchymal injection gave a mean flow of 41.5 +/- 22.5 ml/min/100 g which after hepatic arterial occlusion perfusion, was reduced to a mean of 5% of the pre-occlusion value. Dynamic blood-flow studies using the gamma camera were performed in the post-operative period by administration of 133Xe into both hepatic arterial and portal venous catheters. The initial distribution images indicated a predominant arterial perfusion to the metastases, but after hepatic-artery ligation, portal-vein perfusion to the metastases was statistically significantly increased. Hence, a compensatory haemodynamic mechanism exists which may account for the poor results of hepatic-artery ligation and perfusion alone.

Carotid artery blood flow: single factor classification of Doppler waveforms.

The usefulness of principal components factor analysis as a way of classifying Doppler waveforms from the carotid artery has been established. The waveform is first reduced to a small set of coefficients which capture, via their associated principal components, the essential shape of the waveform. The vector of these coefficients can be used to classify the waveform by finding the position of this vector in a classification space relative to one or more classifying surfaces. This short communication will show how these two steps may be combined to produce a single factor for classification.

A simple quantitative screening test for the detection of extracranial carotid artery disease.

A simple screening test, using continuous wave Doppler ultrasound, for the detection of all grades of extracranial carotid artery disease has been described. The test is composed of two parts: (1) the determination of the direction of flow at the orbit and (2) on-line principal component factor analysis of the maximum frequency envelope of the Doppler shifted signal obtained from the common carotid artery. A total of 154 vessel segments have been investigated; 69 normal, 41 with a stenosis of 10-49%, 32 with a stenosis of 50-99% and 12 occlusions. Of these, 70 vessel segments were assessed prospectively and they formed the data base from which the principal components and the classification factor were calculated. The remaining 84 vessel segments were analysed prospectively on-line. The combined results gave an overall sensitivity to the detection of disease of 90% and a specificity of 77%. It has been shown that although classification of Doppler waveforms by principal component analysis is a fairly sophisticated technique it is possible, by careful design of the algorithms, to design a near real-time on-line analysis system for derived waveforms such as the maximum frequency envelope.

Clinical study of liver blood flow in man measured by 133Xe clearance after portal vein injection.

During the course of a clinical trial to assess the value of adjuvant liver perfusion of 5-fluorouracil after surgery for colorectal cancer, liver blood flow was measured in 14 patients. Access to the portal circulation was achieved by dilatation and cannulation of the obliterated umbilical vein. The clearance from the liver of a bolus of 133Xe was monitored using a gamma-ray camera so that blood flow from different areas of the liver could be calculated. The clearance curve of 133Xe was a double exponential of which the initial fast component accounted for a consistently high proportion of the total clearance. The perfusion studies have shown wide differences in blood flow to the various areas of the liver in the same patient, in addition to a wide variation in perfusion rate between the 14 patients. This technique of quantitative estimations of liver blood flow to different areas of the liver may have importance in planning operative procedures and understanding the haemodynamic mechanisms involved in liver disease.

Assessment of directional Doppler ultrasound techniques in the diagnosis of carotid artery diseases.

Three diagnostic techniques based on the use of directional doppler ultrasound have been evaluated in comparison with direct percutaneous carotid angiography and arch aortography. The results indicate that the non-invasive techniques provide a safe, atraumatic method of assessing patients with symptoms of extracranial occlusive arterial disease.

A prospective study of the accuracy of Doppler ultrasound in detecting carotid artery disease.

Results are presented from a two year prospective study using a Doppler ultrasound technique for the detection of carotid disease. The patients studied presented with transient cerebral ischaemic attacks or small strokes in the carotid territory. No other form of patient selection was used. Results were compared with those from carotid and arch aortography. 86% of normal vessels and 78% of diseases vessels were correctly classified. It is concluded that this technique offers a safe and accurate screening procedure for the management of patients presenting with transient cerebral ischaemia or small strokes.

Comparison of laser Doppler and Doppler ultrasound in lower limb vascular diagnosis.

This study represents a preliminary investigation into the use of laser Doppler flowmetry in lower limb vascular diagnosis. The method is compared with the accepted method of continuous wave Doppler ultrasound. Fifty-six patients with symptoms of lower limb vascular disease were investigated consecutively and independently using both techniques. In approximately two-thirds of patients the two methods showed broad agreement in their classification of disease severity (correlation coefficient = 0.63, P less than 0.001, n = 41). However, about 30% of those studied had impaired microvascular responses on laser Doppler evaluation with no detectable major vessel disease on continuous wave ultrasound investigation. The results indicate that more information is obtained about a subject's vascular status when results from both methods are combined. Thus laser Doppler flowmetry may be useful adjunct to Doppler ultrasound and segmental pressure measurements in the vascular laboratory.

The effect of dobutamine on middle cerebral artery blood velocity in volunteers: a preliminary study.

Five volunteers given dobutamine up to 4 micrograms/kg/min had significant increases in mean arterial blood pressure, systolic blood pressure, and stroke volume (P less than 0.05). Heart rate did not increase significantly. Pulsatility index, an index of middle cerebral artery maximum blood velocity waveform shape increased significantly in the dobutamine group (P less than 0.05). Time-averaged mean velocity did increase during the dobutamine infusion but the change was not statistically significant. Dobutamine significantly alters the blood velocity profile of the middle cerebral artery in volunteers even in low doses of 4 micrograms/kg/min. Transcranial Doppler may be a useful technique to monitor changes in cerebral artery blood velocity dynamics induced by dobutamine. These measurements can be performed easily and repeatedly at the bedside.

Arteriovenous shunting in quadriplegia.

Arterio-venous shunting has been demonstrated in the limbs of ten subjects with traumatic quadriplegia, as shown by increased venous oxygen concentration and a Doppler sonogram pattern indicative of continuous forward flow. This phenomenon is similar to that seen in the diabetic neuropathic foot, suggesting that autonomic dysfunction is a major factor in the development of foot ulceration in the quadriplegic and in the diabetic.