Worldwide Diagnostic Reference Levels for Single-Photon Emission Computed Tomography Myocardial Perfusion Imaging: Findings From INCAPS

ObjectivesThis study sought to establish worldwide and regional diagnostic reference levels (DRLs) and achievable administered activities (AAAs) for single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI).BackgroundReference levels serve as radiation dose benchmarks to compare individual laboratories against aggregated data, helping to identify sites in greatest need of dose reduction interventions. DRLs for SPECT MPI have previously been derived from national or regional registries. To date there have been no multiregional reports of DRLs for SPECT MPI from a single standardized dataset.MethodsData were submitted voluntarily to the INCAPS (International Atomic Energy Agency Nuclear Cardiology Protocols Study), a cross-sectional, multinational registry of MPI protocols. A total of 7,103 studies were included. DRLs and AAAs were calculated by protocol for each world region and for aggregated worldwide data.ResultsThe aggregated worldwide DRLs for rest-stress or stress-rest studies employing technetium Tc 99m–labeled radiopharmaceuticals were 11.2 mCi (first dose) and 32.0 mCi (second dose) for 1-day protocols, and 23.0 mCi (first dose) and 24.0 mCi (second dose) for multiday protocols. Corresponding AAAs were 10.1 mCi (first dose) and 28.0 mCi (second dose) for 1-day protocols, and 17.8 mCi (first dose) and 18.7 mCi (second dose) for multiday protocols. For stress-only technetium Tc 99m studies, the worldwide DRL and AAA were 18.0 mCi and 12.5 mCi, respectively. Stress-first imaging was used in 26% to 92% of regional studies except in North America where it was used in just 7% of cases. Significant differences in DRLs and AAAs were observed between regions.ConclusionsThis study reports reference levels for SPECT MPI for each major world region from one of the largest international registries of clinical MPI studies. Regional DRLs may be useful in establishing or revising guidelines or simply comparing individual laboratory protocols to regional trends. Organizations should continue to focus on establishing standardized reporting methods to improve the validity and comparability of regional DRLs.     

Underestimation of Extent and Severity of Coronary Artery Disease by Dipyridamole Stress Thallium-201 Single-Photon Emission Computed Tomographic Myocardial Perfusion Imaging in Patients Taking Antianginal Drugs

Objectives. This study evaluated the diagnostic value of dipyridamole plus low level treadmill exercise (dipyridamole stress) thallium-201 single-photon emission computed tomography (SPECT) in patients taking antianginal drugs.

Background. Dipyridamole stress is the major substitute for maximal exercise in patients referred for myocardial perfusion imaging. Although antianginal drugs are commonly suspended before exercise, dipyridamole stress is usually performed without discontinuing these drugs.

Methods. Twenty-six patients underwent two dipyridamole perfusion studies: the first without (SPECT-1) and the second with (SPECT-2) antianginal treatment. Twenty-one patients (81%) received calcium antagonists, 19 (73%) received nitrates, and 8 (31%) received beta-blockers. Eighteen of the patients underwent coronary angiography. Data are presented as the mean value ± SD.

Results. Visual scoring yielded significantly larger and more severe reversible perfusion defects for SPECT-1 than for SPECT-2. Quantitative analysis showed larger perfusion defects on stress images of SPECT-1 in the left anterior descending coronary artery (LAD) (25 ± 21% vs. 17 ± 15%, p = 0.003), left circumflex coronary artery (LCx) (56 ± 35% vs. 48 ± 36%, p = 0.03) and right coronary artery (RCA) (36 ± 27% vs. 25 ± 24%, p = 0.008) territories. Individual vessel sensitivities in the LAD, LCx and RCA territories were 93%, 79% and 100% for SPECT-1 and 64%, 50% and 70% for SPECT-2, respectively. These differences were highly significant for the LAD (p = 0.004) and LCx (p = 0.00004) territories. The overall individual vessel sensitivity of SPECT-1 was significantly higher than that of SPECT-2 (92% vs. 62%, p = 0.000003). Specificity was not significantly different in SPECT-1 compared with SPECT-2 (80% and 93%, p = 0.33).

Conclusions. Continued use of antianginal drugs before dipyridamole plus low level treadmill exercise thallium-201 SPECT may reduce the extent and severity of myocardial perfusion defects, resulting in underestimation of coronary artery disease.     

Assessment of Graft Patency Rate After Coronary Artery Bypass Surgery by Exercise TL-201 Single Photon Emission Computed Tomography

Noninvasive assessment of graft function requires detection of myocardial ischemia. Although T1-201 scintigraphy was primarily used to demonstrate improved perfusion soon after bypass surgery, it may be important in detecting graft stenosis late after surgery, identifying patients with symptoms due to graft occlusion. To investigate this, 38 symptomatic patients aged 58 +/- 10 years who had undergone bypass surgery 3-7 years previously (mean 4.0 +/- 1.2 years) in our center were studied by exercise T1-201 single photon emission computed tomography (SPECT) and coronary angiography. Patients with previous myocardial infarction were not included in the study. Of the 88 coronary bypass grafts examined 42 had significant luminal narrowing (>50%) T1-201 SPECT detected 36 of 42 (86%) stenosed grafts with perfusion defects corresponding to the proper vascular territory. T1-201 SPECT had a higher sensitivity (83% vs 50%, p < 0.01) and predictive accuracy (84% vs 58%, p < 0.02) compared with exercise stress testing in detecting graft stenosis. Sensitivity, specificity, and predictive accuracy of T1-201 SPECT for detection of stenosis were 87%, 93%, and 89% for the left anterior descending coronary artery; 90%, 89%, and 89% for the right coronary artery; and 78%, 76%, and 76% for the circumflex artery, respectively. These results indicate that T1-201 SPECT is a highly sensitive and specific noninvasive technique for detecting and localizing graft stenosis long after coronary bypass surgery.     

肾动脉狭窄支架置入术后冠状动脉旁路移植术的安全性及疗效

目的:探讨冠心病患者肾动脉狭窄支架置入术后行冠状动脉(冠脉)旁路移植术的安全性及疗效.方法:22例行肾动脉狭窄支架置入术后接受冠脉旁路移植术冠心病患者,记录各例临床、冠脉、肾动脉造影情况,随访分析各例肾动脉狭窄支架置入术前后肾功能及冠脉旁路移植术情况,并测定手术前、后及随访期间血清肌酐水平.结果:22例患者均成功置入肾动脉支架(25枚),旁路移植术后72小时血清肌酐较基础测值明显下降[(153±22)μmol/L比(163±31)μmol/L,P<0.05].各例平均移植旁路血管(3.12±0.77)支,术后1例发生脑梗塞.平均随访(15±8)个月,各例血清肌酐水平进一步下降,2例复发胸痛,其中1例接受冠脉支架术,无严重心脏事件生存率95.5%.结论:肾动脉狭窄支架置入术有助于改善患者肾功能,增加冠脉旁路移植术的安全性及改善预后.     

Comparison of Technetium-99m Tetrofosmin and Thallium-201 Single-Photon Emission Computed Tomographic Imaging for Detection of Myocardial Perfusion Defects in Patients With Coronary Artery Disease

Objectives. We compared dipyridamole technetium-99m (Tc-99m) tetrofosmin and thallium-201 (Tl-201) single-photon emission computed tomographic (SPECT) imaging with respect to the detection rate of perfusion abnormalities in 26 patients with angiographic coronary artery disease (CAD).Background. Experimental studies have shown that myocardial extraction of Tc-99m tetrofosmin is lower than that of Tl-201 at high flow rates, resulting in less severe defects with vasodilator stress. It is uncertain whether this results in a lower sensitivity than Tl-201 for detecting coronary stenoses with vasodilator stress in patients.Methods. Twenty-six patients with CAD underwent both dipyridamole Tl-201 and Tc-99m tetrofosmin SPECT. Tomographic images were scored for initial defects and the presence of reversibility. Defect magnitude was computer quantitated.Results. Of the 26 patients, 25 had defects on both Tl-201 and Tc-99m tetrofosmin SPECT images. Of 340 segments analyzed, 102 had defects by Tl-201 and 92 by Tc-99m tetrofosmin (p = NS). Whereas Tl-201 detected 27 fixed defects in 12 patients, Tc-99m tetrofosmin identified 37 fixed defects in 14 patients (p = NS). In contrast, Tl-201 identified more reversible and partially reversible defects than did Tc-99m tetrofosmin (89 vs. 55, p = 0.002). The average defect magnitude (percent normal) was similar for defects concordantly graded as fixed (38 ± 3.0% for Tl-201 vs. 42 ± 4% [mean ± SEM] for Tc-99m tetrofosmin, p = NS). The average defect magnitude for defects concordantly graded as completely reversible was significantly more severe on Tl-201 than on Tc-99m tetrofosmin (49 ± 3% vs. 58 ± 3%) SPECT images. A significantly greater defect magnitude for Tl-201 was also found for defects concordantly classified as partly reversible (30 ± 4% for Tl-201 vs. 45 ± 5% for Tc-99m tetrofosmin).Conclusions. With dipyridamole stress, 1) at least one defect was seen on both Tl-201 and Tc-99m tetrofosmin SPECT images; 2) Tc-99m tetrofosmin SPECT identified fewer reversible defects than did Tl-201, but showed a similar number of fixed defects; 3) the magnitude of reversible defects seen on Tc-99m tetrofosmin images was less, whereas fixed defects were similar for both tracers; 4) reversible defects seen on Tl-201 and not on Tc-99m tetrofosmin SPECT images were predominantly regions perfused by mild coronary stenoses.     

冠状动脉旁路移植术后静脉移植物内膜增生的发病机制

动脉桥管在冠状动脉旁路移植术中广泛使用且明显提高了远期效果,但静脉移植物仍然是使用最多的桥管.研究表明静脉移植物10年通畅率约为60%.静脉移植物再狭窄发病机制包括血流动力学变化导致血管壁受损,血栓形成和血管平滑肌迁移、增生,以及随后发生动脉粥样改变等.本文就静脉移植物再狭窄的发生机制作一综述.