Planar pulmonary scintigraphy is still regularly performed for the evaluation of pulmonary embolism (PE). However, only about 50-80% of cases can be resolved by this approach. This study evaluates the ability of tomographic acquisition (single photon emission computed tomography, SPECT) of the perfusion scan to improve the radionuclide diagnosis of PE. One hundred and fourteen consecutive patients with a suspicion of PE underwent planar and SPECT lung perfusion scans as well as planar ventilation scans. The final diagnosis was obtained by using an algorithm, including D-dimer measurement, leg ultrasonography, a V/Q scan and chest spiral computed tomography, as well as the patient outcome. A planar perfusion scan was considered positive for PE in the presence of one or more wedge shaped defect, while SPECT was considered positive with one or more wedge shaped defect with sharp borders, three-plane visualization, whatever the photopenia. A definite diagnosis was achieved in 70 patients. After exclusion of four 'non-diagnostic' SPECT images, the prevalence of PE was 23% (n =15). Intraobserver and interobserver reproducibilities were 91%/94% and 79%/88% for planar/SPECT images, respectively. The sensitivities for PE diagnosis were similar for planar and SPECT perfusion scans (80%), whereas SPECT had a higher specificity (96% vs 78%; P =0.01). SPECT correctly classified 8/9 intermediate and 31/32 low probability V/Q scans as negative. It is concluded that lung perfusion SPECT is readily performed and reproducible. A negative study eliminates the need for a combined V/Q study and most of the 'non-diagnostic' V/Q probabilities can be solved with a perfusion image obtained by using tomography.

Alternative strategies using conditional probability analysis for the diagnosis of coronary artery disease (CAD) were examined in 93 infarct-free women presenting with chest pain. Another group of 42 consecutive female patients was prospectively analyzed. For this latter group, the physician had access to the pretest and posttest probability of CAD before coronary angiography. These 135 women all underwent stress electrocardiographic, thallium scintigraphic, and coronary angiographic examination. The pretest and posttest probabilities of coronary disease were derived from a computerized Bayesian algorithm. Probability estimates were calculated by the four following hypothetical strategies: SO, in which history, including risk factors, was considered; S 1, in which history and stress electrocardiographic results were considered; S2, in which history and stress electrocardiographic and stress thallium scintigraphic results were considered; and S3, in which history and stress electrocardiographic results were used, but in which stress scintigraphic results were considered only if the poststress probability of CAD was between 10% and 90%, i.e., if a sufficient level of diagnostic certainty could not be obtained with the electrocardiographic results alone. The strategies were compared with respect to accuracy with the coronary angiogram as the standard. For both groups of women, S2 and S3 were found to be the most accurate in predicting the presence or absence of coronary disease (p < .05). However, it was found with use of S3 that more than one-third of the thallium scintigrams could have been avoided without loss of accuracy. It was also found that diagnostic catheterization performed to exclude CAD as a diagnosis could have been avoided in half of the patients without loss of accuracy. Studies in the prospective group of 42 women confirmed that S2 and S3 had the best diagnostic accuracy. We also observed a higher prevalence of angiographically documented coronary disease in this group (48% vs 26% in the first group of 93 women). In this prospectively studied group, there was a smaller proportion of patients with a low probability estimate of CAD (29% of the patients with a probability of .10% in the prospective group vs 58% of the patients in the first group). Our results suggest that the treating physician's prior knowledge of probability estimates reduced the number of unnecessary diagnostic coronary angiographic procedures performed. Circulation 71, No. 3, 535-542, 1985. THE APPLICATION of probability methods to the diagnosis of coronary artery disease (CAD) is an important conceptual advance. IA The validity of probability analysis for diagnosing CAD has already been demonstrated by comparison of the calculated probability of disease with coronary angiographic results.5-10 Another potential application of probability analysis is to

SPECT performed within 36 hours of onset predicts clinical outcome, but different clinical and SPECT indices with threshold values should be chosen according to the relevant outcome end point.

The diagnostic value of exercise electrocardiography and thallium myocardial scintigraphy for the detection of restenosis was assessed in 111 patients undergoing control angiography 6 months after successful coronary angioplasty. All patients were free of symptoms at the time of the study. A diameter reduction of 70% or more at the site of angioplasty was considered restenosis. The sensitivity of exercise electrocardiography is low (64%). Exercise ECG and scintigraphy are highly specific (respectively 90% and 93%). The predictive value of a positive ECG or thallium scintigraphy is poor (respectively 53% and 63%). The value of a negative scintigraphic result is slightly better than the predictive value of a negative ECG (98% vs 95%; NS). A negative exercise scintigraphy almost excludes severe restenosis. These non-invasive tests seem suitable for the detection of asymptomatic restenosis.

Despite its better sensitivity compared with CT, SPECT performed without the acetazolamide test provides no additional clinically useful information on the vascular risk factors and etiology in TIA patients.