DOPPLER5 (1040793), страница 4

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Blackshear et al. (1979) compared Doppler scanning with Duplex scanning and with Doppler spectral analysis. Their results for Doppler scanners and spectral analysis are presented in the appropriate sections. They investigated 33 patients and compared the results with contrast arteriography. The Duplex scanners correctly identified all eight angiographically normal vessels. Seventy-four per cent ( 1 7 out of 23) of vessels with a 10-49%. stenosis had detectable abnormalities, as did 95%, (21 out of 22) of those with high grade stenosis. The one error in diagnosis was due to an uncooperative patient. Over all carotid lesions the Duplex scanner was successful in 84%. of cases. These results were achieved using the imaging qualities of the scanner together with an audible assessment of the Doppler signals.

Lusby et al. (l980) investigated a series of 46 patients with a history of transient ischaemic attacks, and compared the results of Duplex scanning against carotid angiography. Eighty-five per cent of stenoses of less than 25% stenosis, 90% of stenoses between 26-49% stenosis, 80% between S1-99% stenosis and 100 per cent complete occlusions, were correctly diagnosed. The sensitivity was approximately 91% and specificity 90%. These results agree favourably with those of Blackshear and colleagues.

(v) Direct Comparison of Doppler Imaging and Duplex Scanning Systems

Blackshear et al. (1979) and Lusby et al. (1980) carried out detailed comparisons of Doppler imaging systems with Duplex scanners with contrast arteriography, and the details can be found in the relevant sections, In summary Blackshear et al. showed that for all levels of carotid artery disease the Duplex scanner detected 84%, and the Doppler system 88% Lusby et al. showed that the Duplex system detected 91o. and the Doppler system 88%. They further showed that both detect a significant number of lesions of less than 50% diameter stenosis. 95%, in the case of Duplex and 83% in the case of the Doppler imaging system. The Doppler imaging system appears more reliable in the detection of complete occlusion, although the numbers in the study were small.

A number of examples showing Doppler images, Duplex images and contrast angiograms are illustrated in Figs 5. 19. 5.20, 5.21 and 5.22.

(vi) Conclusions

The results of the various Doppler methods for assessing the cerebral circulation are summarized in Table 5.b. It appears that the method- of spectral broadening allied to either pulsed Doppler or Duplex scanners offers the optimum method presently available for the investigation of small lesions

5.4 NON-INVASIVE MEASUREMENT OF VELOCITY PROFILES AND VOLUME FLOW IN THE CAROTID ARTERIES

Keller et al. (1976) have used a fourteen-channel pulsed Doppler flowmeter to investigate velocity profile and volume flow, non-invasively, in the carotid arteries. The authors quote a resolution of 7 3 MHz of 0 5 mm. The probe is placed at an angle of approximately 45 to the vessel axis and the fourteen channels of information are processed simultaneously using a PDP-12 computer. In a series of measurement on dogs Rutishauser et al. (1974) found a correlation coefficient of 0^.93 between flow rates calculated by this method and electromagnetic flowmetry. Under these laboratory conditions the Doppler results were within ±5% of those from the electromagnetic flowmeter. Flows were measured in the common carotid artery in 22 healthy normal volunteers in 12 patients with occlusion or stenosis of the carotid artery, in one patient with coarctation of the thoracic aorta and stenosis of the brachiocephalic trunk and the left common carotid artery, four patients with intra-cranial occlusions, and five patients with aortic valve insufficiency. The results of these investigations showed that the normal range of common carotid flow was 300-400 ml min^-1. The pathological conditions resulted in flows in the range <180-480 ml min^-1 in the common carotid.

Borodzinski et al. (l976) developed an 8 MHz. pulsed Doppler system for measuring velocity profile and calculating volume flow in the carotid artery. In the normal carotid artery in man the time averaged flow rate was found to be 530 ml min^-1

The MAVIS C^* blood flow computer is a commercially available system which is basically a Doppler imaging system and a volume flow computer. The system has already been described in Chapter 4. An example of the versatility and capability of the equipment is shown in Fig.4.3. Normal common carotid artery flows measured in our own laboratory appear to be in the range 300-450 ml min^-1.

* Advanced Technology Laboratories, Seattle

* GECMedical Equipment Limeted, Wembley, UK

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