GWpy is a Python software package that provides an intuitive, object-oriented interface through which to access, process, and visualise data from gravitational-wave detectors. GWpy provides a number ...of new utilities for studying data, as well as an improved user interface for a number of existing tools. The ease-of-use, along with extensive online documentation and examples, has resulted in widespread adoption of GWpy as a basis for Python software development in the international gravitational-wave community.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study validates a new quantitative perfusion SPECT algorithm for the assessment of myocardial perfusion. The algorithm is not based on slices and provides fully 3-dimensional sampling and ...analysis independent of assumptions about the geometric shape of the left ventricle.
Radiopharmaceutical- and sex-specific normal limits and thresholds for perfusion abnormality in 20 segments of the left ventricle were developed for separate, dual-isotope rest 201Tl-exercise 99mTc-sestamibi SPECT in 36 patients with <5% before-scanning likelihood of coronary artery disease (CAD) (group 1) and 159 patients with perfusion abnormalities (group 2). These thresholds were validated in 131 patients (group 3) by comparison with expert visual interpretation. Thresholds for automatic segmental scores were developed and validated for groups 2 and 3, respectively. The accuracy of CAD detection was assessed in 94 patients, who underwent coronary angiography (group 4).
Overall sensitivity for detection of stress and rest segmental perfusion abnormality was 91% and 96%, respectively, for men and 89% and 79%, respectively, for women. Overall specificity for stress and rest was 87% and 90%, respectively, for men and 88% and 90%, respectively, for women. Agreement between automatic and visual scores was good (weighted K of 0.71 and 0.60 for stress and rest images, respectively). Sensitivity and specificity were 88% for the detection of > or =70% stenosis. For the detection of left anterior descending, left circumflex, and right coronary artery stenosis, sensitivity was 84%, 86%, and 88%, respectively, and specificity was 84%, 88%, and 81%, respectively.
The new quantitative perfusion SPECT approach is highly sensitive and specific for the detection and localization of CAD, provides accurate automatic scores for the assessment of regional perfusion, and overcomes the low-specificity limitations of previous quantitative algorithms.
Objectives. The purpose of this study was to determine the prognostic value of automatic quantitative analysis in exercise dual-isotope myocardial perfusion single-photon emission computed tomography ...(SPECT) and to compare the prognostic value of quantitative analysis to semiquantitative visual SPECT analysis.
Background. Extent, severity and reversibility of exercise myocardial perfusion defects have been shown to correlate with prognosis. However, most studies examining the prognostic value of SPECT in chronic coronary artery disease (CAD) have been based on visual analysis by experts.
Methods. We studied 1,043 consecutive patients with known or suspected CAD who underwent rest Tl-201/exercise Tc-99m sestamibi dual-isotope myocardial perfusion SPECT and were followed up for at least 1 year (mean 20.0 ± 3.7 months). After censoring 59 patients with early coronary artery bypass grafting or percutaneous transluminal coronary angioplasty, <60 days after nuclear testing, the final population consisted of 984 patients (36% women, mean age 63 ± 12 years).
Results. During the follow-up period, 28 hard events (14 cardiac deaths, 14 nonfatal myocardial infarctions) occurred. Patients with higher defect extent (>10%), severity (>150) and reversibility (>5%) by quantitative SPECT defect analysis, as well as those with an abnormal scan (>2 abnormal segments, summed stress score >4 and summed difference score >2) by semiquantitative visual SPECT analysis, had a significantly higher hard event rate compared to patients with a normal scan (p < 0.001). With both visual and quantitative analyses, hard event rates of approximately 1% with normal scans and 5% with abnormal scans (p > 0.05) were observed over the 20-month follow-up period. A Cox proportional hazards regression model showed that chi-square increased similarly with the addition of quantitative defect extent and visual summed stress score variables after considering both clinical and exercise variables (improvement chi-square = 11 for both, p < 0.0007). There were no significant differences in the areas under receiver operating characteristic curves between quantitative and visual analysis (p > 0.70). Linear regression analysis also indicated that quantitative assessments correlated well with visual semiquantitative assessments.
Conclusions. The findings of this study indicate that automatic quantitative analysis of exercise stress myocardial perfusion SPECT is similar to semiquantitative expert visual analysis for prognostic stratification. These findings may be of particular clinical importance in laboratories with less experienced visual interpreters.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Background. Little is known about changes of myocardial perfusion in patients undergoing coronary revascularization or medical therapy. The purpose of this observational study was to assess the ...long-term effects of revascularization or conservative therapy on serial quantitative myocardial perfusion single photon emission computed tomography (SPECT). Methods and Results. The study population consisted of 421 patients who underwent serial rest thallium-201/stress technetium-99m sestamibi dual-isotope myocardial perfusion SPECT with at least a 1-year interval between the 2 studies and who had abnormal quantitative scan results on the first stress SPECT. The mean interval between scans was 32.7 ± 15.9 months. Patients were divided into 3 groups according to stress defect extent: group 1 had small stress defects (4%-10%, n = 145), group 2 had intermediate stress defects (>10%-20%, n = 144), and group 3 had extensive stress defects (>20%, n = 132) at baseline. Forty patients in group 1, 44 in group 2, and 54 in group 3 underwent coronary revascularization between 2 SPECT studies; the others had conservative therapy. In group 3 patients with revascularization, stress defect extent and reversible defect extent were remarkably reduced (14.5% ± 13.6% and 13.1% ± 12.5%, respectively; both P < .0001), with greater improvement in those patients reporting increased use of cardiac medications; resting defect extent was slightly reduced (1.9% ± 6.4%, P < .05). In group 3 patients with conservative therapy, a small reduction in stress defect extent was noted (2.3% ± 8.3%, P < .05). In group 2, there were modest, similar reductions in reversible defect extent in both the patients with revascularization (2.7% ± 7.7%, P < .05) and those with conservative therapy (1.8% ± 7.3%, P < .05), as well as a small but significant reduction in stress defect extent in those with conservative therapy (2.1% ± 8.2%, P < .05). In group 1 patients, no significant changes in stress, rest, or reversible defect extent were found with either therapy. Conclusions. The findings of this study show that improvement in quantitative myocardial perfusion abnormalities over time occurs in some patients with either revascularization or conservative therapy and suggest that, in patients with extensive defects, greater improvement may be seen in those who undergo revascularization. (J Nucl Cardiol 2001;8:428-37.)
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We have developed a new, completely automatic 3-dimensional software approach to quantitative perfusion SPECT. The main features of the software are myocardial sampling based on an ellipsoid model; ...use of the entire count profile between the endocardial and epicardial surfaces; independence of the algorithm from myocardial shape, size, and orientation and establishment of a standard 3-dimensional point-to-point correspondence among all sampled myocardial regions; automatic generation of quantitative measurements and 5-point semiquantitative scores for each of 20 myocardial segments and automatic derivation of summed perfusion scores; and automatic generation of normal limits for any given patient population on the basis of data fractionally normalized to minimize hot spot artifacts.
The new algorithm was tested on the tomographic images of 420 patients studied with a rest 201TI (111-167 MBq, 35 s/projection)-stress 99mTc-sestamibi (925-1480 MBq, 25 s/projection) separate dual-isotope protocol on a single-detector camera, a dual-detector 90 degrees camera, and a triple-detector camera.
The algorithm was successful in 397 of 420 patients (94.5%) and 816 of 840 image datasets (97.1%), with a statistically significant difference between the success rates of the 201TI images (399/ 420, or 95.0%) and the 99mTc images (417/420, or 99.3%; P < 0.001). Algorithm failure was caused by extracardiac uptake (10/24, or 41.7%) or inaccurate identification of the valve plane because of low count statistics (14/24, or 58.3%) and was obviated by simply limiting the image volume in which the software operates. Reproducibility of measurements of summed perfusion scores (r = 0.999 and 1 for stress and rest, respectively), global defect extent (r = 0.999 and 1 for stress and rest, respectively), and segmental perfusion scores (exact agreement = 99.9%, kappa = 0.998 for stress and 0.997 for rest) was extremely high.
Automatic 3-dimensional quantitation of perfusion from 201Tl and 99mTc-sestamibi images is feasible and reproducible. The described software, because it is based on the same sampling scheme used for gated SPECT analysis, ensures intrinsically perfect registration of quantitative perfusion with quantitative regional wall motion and thickening information, if gated SPECT is used.
Quantitation of regional myocardial function is valuable in patients with coronary artery disease. This study assessed normal heterogeneity and developed and validated normal limits for quantitative ...regional motion and thickening by gated myocardial perfusion SPECT.
Patients underwent rest (201)Tl/exercise (99m)Tc-sestamibi gated SPECT. Reference values of motion and thickening for 20 myocardial segments were obtained in 105 patients with <5% likelihood of coronary disease (low-likelihood group). Criteria for abnormality of motion and thickening were defined for each segment, using receiver operator characteristic analysis, in 101 patients with coronary disease (training group). Semiquantitative visual interpretation was used as the gold standard. These criteria were prospectively validated in 100 patients (validation group). Criteria for grading motion and thickening abnormalities by severity levels were also defined and validated.
Normal thickening decreased substantially along the longitudinal axis of the left ventricle, from 69% +/- 13% at the apex to 25% +/- 11% at the basal segments, whereas normal motion varied within the same ventricular plane. Validation of the criteria for abnormality yielded high accuracy in the detection of motion abnormalities (sensitivity, 88%; specificity, 92%) and thickening abnormalities (sensitivity, 87%; specificity, 89%). Quantitative motion and thickening segmental scores showed good agreement with visual scores.
Normal regional myocardial contraction by gated myocardial perfusion SPECT is characterized by a substantial apex-to-base decline in thickening and by circumferential heterogeneity in endocardial motion. The assignment of segment-specific threshold values for defining motion and thickening abnormalities provided reasonably accurate identification and grading of regional myocardial dysfunction.
We developed a completely automatic technique to reorient transaxial images into short-axis (oblique) myocardial perfusion SPECT images.
The algorithm starts by isolating (segmenting) the left ...ventricle (LV) myocardium using a combination of iterative clusterification and rule-based location/size/shape criteria. The three-dimensional, mid-myocardial LV surface is initially estimated as the locus of the trilinearly interpolated maxima for the count profiles originating from the center of mass of the segmented LV. The final mid-myocardial surface is obtained by iteratively applying this process, incorporating additional constraints of shape and texture and using the nonsegmented, nonthresholded transaxial image to obtain information on hypoperfused areas of the myocardium. It is then fitted to an ellipsoid, of which the major axis is assumed to represent the long axis of the LV, and the three-dimensional image volume is resliced perpendicularly to it.
The algorithm was retrospectively applied to 400 dual-isotope studies (200 rest 201TI, 200 stress 99mTc-sestamibi) from 200 consecutive patients. Segmentation was successful in 394/400 (98.5%) of the patients. The reproducibility of computer-based reorientation was perfect and significantly better than either intraobserver or interobserver reproducibility.
Automatic reorientation offers the potential for consistently faster and more accurate image processing and analysis and is an important step towards totally operator-less management of myocardial perfusion SPECT data.
Gender-matched stress normal limits and criteria for abnormality for rest-stress 99mTc-sestamibi same-day myocardial perfusion imaging were developed and validated in 160 patients who were imaged ...using previously developed optimized acquisition, processing and quantitative protocols. The gender-matched mean and standard deviation of the normal response were calculated using 35 male and 25 female patients with a < 5% likelihood of coronary artery disease. Receiver-operating curve analysis using expert visual interpretation as the "gold standard" was used to determine the optimal criteria for abnormality detection, in terms of standard deviations from the mean and minimum defect size for each of the four major zones of the polar map, in a pilot population consisting of an additional 35 male and 25 female patients with a variety of perfusion defects. The optimum standard deviations resulted in the following true-positive/true-negative rates when quantitative results were compared to visual analysis for the anterior, septal, lateral, and inferior segments in the combined male and female pilot populations: 84%/86%, 70%/75%, 86%/76% and 69%/76%, respectively. The final criteria were then applied to a prospective population consisting of 33 male and 7 female patients. This analysis resulted in the following true-positive/true-negative rates for overall perfusion abnormalities and abnormalities of the LAD, LCX and RCA vascular territories: 97%/67%, 94%/73%, 73%/90% and 72%/91%, respectively. The optimized 99mTc-sestamibi stress normal limits and criteria for abnormality correlate well with expert visual interpretation of stress myocardial perfusion defects.
We have observed that filtered backprojection may cause artifactual decreased myocardial wall uptake in the reconstructed images if the hepatic-to-cardiac activity ratio (HCR) in 99mTc clinical ...myocardial SPECT studies is sufficiently high (> 1).
To quantitatively relate hepatic uptake to this phenomenon, a commercial chest and heart phantom was modified with the addition of a customized liver insert, which was filled with various concentrations of 99mTc to simulate HCRs of 0:1, 1:1 and 2:1. The phantom was imaged with a high-sensitivity, three-detector camera, low-energy, high-resolution (LEHR) collimation and 180 degrees noncircular orbits.
Quantitative circumferential profile analysis of the reoriented SPECT images demonstrated artifactual inferior/inferoseptal maximal activity decreases of 17.8% and 46.2% for the 1:1 and 2:1 HCRs, compared to the 0:1 HCR. Hepatic scatter probably partly mitigates the decrease. Smoothing the projection data before reconstruction worsened the artifacts' severity. Using Butterworth filters of order 5 and cutoff frequencies of 0.1, 0.2 and 0.215 Nyquist (clinical standard) resulted in artifactual inferior wall activity decreases of 5%, 8% and 16%, compared to using the same filter with a cutoff of 0.3 for an HCR of 2:1.
These data indicate that if count statistics are good and liver uptake is high, higher frequency cutoffs in pre-reconstruction filters may improve specificity in 99mTc-labeled myocardial perfusion SPECT studies.
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