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Imaging ultrasonography was performed during 23 brain and five spinal cord operations with real-time B-mode instruments. Criteria for the utilization of ultrasound at neurosurgical procedures were identified in terms of assistance in the diagnosis or better definition of lesions. The diagnosis criteria were detection and exclusion. Because of the accuracy of preoperative imaging, usually little further help was provided by operative ultrasonography in detecting previously totally unknown abnormalities or excluding lesions found on positive studies. The definition criteria were localization, distinction of tissue features, and assessment of spatial relations. Operative ultrasonography was most useful when applied on the basis of these definition criteria. Operative ultrasonography was considered to be useful in 22 of 28 operations (79 per cent) in which it assisted in exposing, accessing, and extirpating disease.

The role of red cell aggregation as a cause of ultrasonic echogenicity in flowing blood was evaluated by in vitro experiments using fresh human blood. Blood was circulated in tubes of varying diameter (12 mm to 6 mm). In all experiments, echogenicity increased as blood approached static conditions. Echogenicity was greater in tubes with a larger diameter over the same range of blood velocity. However, echogenicity in tubes of various diameters was the same when evaluated in terms of shear rate. Thus, shear rate and not velocity is the flow condition that determines echogenicity. Since shear rate determines the degree of red cell aggregation, while other conditions affecting red cell aggregation (hematocrit, erythrocyte membrane conditions, and plasma macromolecules) are held constant, we conclude that these results provide additional evidence that red cell aggregation is a cause of echogenicity in flowing blood. Furthermore, a red cell aggregation mechanism for blood-flow echogenicity would explain the increased prominence of internal echoes in lower shear rate venous blood flow compared with those of higher shear rate arterial blood flow.

An explanation of the mechanism of ultrasonic echogenicity in flowing blood is proposed based upon an in vitro study that indicates a causal relation between red cell aggregation and these echoes. Echogenicity was measured in vitro at 37 degrees, 24 degrees, and 0 degree C as blood flow shear rates were varied. Echogenicity increased at higher temperatures and lower shear rates. The directions of changes in blood echogenicity exactly paralleled previously known changes in red cell aggregation resulting from changes in temperature. The authors consider this to be further evidence that red cell aggregation is an important cause of low-intensity echoes observed in clinical ultrasonography of the heart and circulation.

The comparative accuracies of operative ultrasonic and radiographic cholangiography to detect biliary calculi 1 mm in diameter inside tubes of different calibers were assessed. One hundred eighty tubes were prepared to provide ten tubes each for the following variables: three sizes of tubes (6, 13, 20 mm), three concentrations of contrast material (15, 30, 60 per cent), and presence or absence of calculi. Real-time B-mode ultrasound scans with a single gain and time gain compensation (TGC) setting were performed and contrast radiographs were also made at a single optimal exposure. Sixty ultrasonic and 180 radiographic examinations were studied. All ultrasonic interpretations were correct regardless of size of tube. Under optimal conditions, radiographic interpretations were also correct. However, whereas a single gain and TGC setting was applicable for all ultrasound examinations, variable contrast concentrations were required for the best radiographic imaging. Optimal radiographic contrast concentrations differed with tube diameters. The authors conclude that both ultrasonic and radiographic contrast imaging are highly accurate for the detection of small biliary calculi. However, contrast radiography requires stricter optimization of variables needed to provide the high accuracy. Thus, operative ultrasonography may be a more practical and reliable diagnostic procedure because of high sensitivity and greater ease of performance and interpretation.

High-resolution real-time ultrasonography was employed during 267 vascular operations in order to diagnose vascular defects such as intimal flaps, strictures, and thrombi. These defects occur at operative areas (e.g., anastomoses, endarterectomized segments, and sites of placement of occlusive clamps) and can lead to serious thrombotic complications in the early post-operative period. Ultrasound detected vascular defects in 83 patients (31.1 per cent). The defects in 59 patients were considered clinically insignificant because of their sizes and locations, and were not re-explored. Early post-operative results of these patients were comparable to those of the patients without demonstrated defects. In 24 patients (9.0 per cent of all patients examined), ultrasonography revealed clinically significant defects which prompted re-exploration. In 20 of these 24 patients, these vascular defects were confirmed and corrected. No defect was found at re-exploration in four patients, but two of them developed early postoperative thrombosis. Ultrasonography and arteriography were compared at 100 operative sites. The two imaging methods were equal in terms of sensitivity, specificity, efficiency, and predictability of a negative test. Predictability of a positive test was 77.8 per cent for ultrasonography and 59.1 per cent for arteriography. This indicates that fewer needless re-explorations would occur following a decision based on ultrasonography. Operative ultrasonography is a simple, safe and accurate technique that should be applied to reconstructive vascular surgery for diagnosis of vascular defects.