| Artifactual inferior-posterior wall defects as a result of diaphragmatic attenuation of activity are a frequent source of error in myocardial single photon emission computed tomography (SPECT) studies. The purpose of this study is to differentiate the artifacts by quantitative analysis and changing the position of image acquisition.MethodsPatients: 39 normal persons were included in this study, which with the low likelihood of CAD(<5%). There were 26 men and 13 women in the whole subjects with an average of 36. 69 ?. 56yr. Nine persons had a coronary arteriogram and the results were negative according to the traditional diagnostic standard.Imaging: All individuals were imaging supine and prone during one session. 400mg KClO4 were administrated orally to all the subjects prior to image acquisition. Technetium-99m-MIBI was injected intravenously by the-doses of 555-740MBq. The acquisition was performed between 1 to 2 hours after the administration of the agents. The equipment was a dual detector SPECT of Toshiba 7200-A/DI, and the detectors were equipped with low energy high-resolution collimators. The prone acquisition was performedimmediately after supine study, and the imaging conditions were the same with supine study. The projection data were all processed by thejnethod of filter back projection, and the images were reconstructed to short axis, vertical long axis and horizontal tomography. The polar map was made on the basis of continues short axis slices, and it was divided into lateral, anterior, septal and inferior-posterior wall. Moreover, the region of inferior-posterior wall was divided into six regions (R1-R6). The maximal value of the pixel in the polar map was modif icated to 100, and the count in every region was calculated.Image interpretation and the calculation of the parameters:Normalcy rate: The normalcy rate was defined as the number of patients with low likelihood of disease with normal scintigraphic patterns divided by the total number of patients with a low likelihood of disease. The normalcy rate was separately calculated according to the results of supine^ prone and the combination of the both.Kappa: Firstly,' two physicians independently evaluated the SPECT images according to the diagnostic standard in our department, and kappal were calculated. Secondly, the two physicians independently evaluated the images again according to the combinative results of supine and prone study, and kappa2 was calculated.Accumulated scoring of images: All the inferior-posterior region in the SPECT images were scored independently by two experienced physicians using fourpoints scored method, and the accumulated scoring were got separately in supine and prone group.Quantitative polar map analysis: Counts in the different region of polar map (R1-R6 included) were evaluated separately according to the imaging position groups and sexual groups.Study on space position changes in supine and prone anatomic images: Two normal men were selected, one was imaged with CT, and the other with radionuclide cardiac blood pool imaging, both in supine and prone position.Statistical analysis: All continuous measures were summarized as the mean眘d. The mean differences HI the matched region were compared using matched t-test. Comparisons of proportions were made using a chi^square statistics. Probability(p) values of <0. 05 were considered significant. All computations were made using the SPSS statistical software.Results and discussionWhen imaged supine, the normalcy rated was*lower (p<0. 05), but when imaged prone, the normalcy rate was limitedly increased, and new deficits were found in apical-inferior wall. When the presentations on supine and prone images were considered, the normalcy rate was increased in large (p<0. 05). It indicates that the accuracy of judgement was "increased in large by the combinative information got from prone and supine images.Kappal and kappa2 was separately 0. 209 and 0. 5. It shows that the intra-observer difference was greatly dec... |
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