2022 Volume 8 Issue 1 Pages 120-122
The usefulness of stress myocardial perfusion single-photon emission computed tomography (SPECT) in the diagnosis of coronary artery disease (CAD) is well established (1, 2). Recently developed cadmium-zinc-telluride (CZT)-SPECT has high sensitivity, high spatial resolution, and high energy-spectrum resolution. CZT-SPECT has high diagnostic accuracy, and also improves acquisition time and reduces radiation exposure, compared to conventional SPECT (3). The first report of CZT -SPECT was documented about diagnostic accuracy and low radiation exposure in obese patients in 2012 (4, 5). Increasing of the CZT-SPECT use for low radiation exposure is reasonable. A simultaneous acquisition stress 201Tl/rest 99mTc dual-isotope myocardial perfusion SPECT (MPS) protocol (SDI protocol) reported by Makita et al. has high diagnostic performance to detect significant CAD (6). However, this protocol may have a pitfall of potentially missing the presence of ischemic myocardium because of the different radioisotope use to diagnose CAD.
201Tl is known to have a high sensitivity in detecting ischemic myocardium because of good myocardial blood flow tracking (high myocardial extraction fraction), compared to 99mTc tracers (sestamibi or tetrofosmin) (7). After the first simultaneous acquisition of stress 201Tl/rest 99mTc in the SDI protocol, we routinely recommend to have a second acquisition of stress 201Tl/rest 99mTc after a meal break for 1–2h (Figure 1). Even when the diagnosis of ischemic or non-ischemic myocardium based on the first acquisition alone shows a fixed defect, it may be possible to diagnose ischemic myocardium by comparing the 201Tl redistribution images.
An 80-year-old male, who has a history of chronic kidney disease and diabetes mellitus, during hospitalization for urinary tract infection, developed heart failure and underwent stress MPS for eliminating CAD. When comparing stress 201Tl and rest 99mTc imaging, fixed defects were observed in the apical anterior wall and apex (summed stress score [SSS] 6, summed rest score [SRS] 6, and summed difference score [SDS] 0) (Figure 2A, white arrows). However, when comparing stress 201Tl images between the first and second acquisitions, ischemic myocardium was observed (SSS 6, SRS 4, SDS 2) (Figure 2B, yellow arrows). Coronary artery angiography (CAG) showed 90% stenosis in proximal left anterior descending artery (LAD) (Figure 3). Although MPS showed a small amount of ischemia, but a proximal lesion in the LAD, then percutaneous coronary intervention was performed.
In discussion, there are two possibilities that in this situation. Different extraction fraction between two tracers (stress 201Tl and rest 99mTc) may miss a slight difference of myocardial perfusion even after the normalization. Another possibility is that 99mTc tracer may not be enough to track a resting ischemia in critical stenosis. This case reveals 90% of stenosis in the LAD, which causes a minimum blood flow and myocardial counts with 99mTc at rest. However, delayed 201Tl image may help to reveal a resting ischemia with its redistributional characteristic. In conclusion, even a small amount of ischemic myocardium can be diagnosed with redistribution image in SDI protocol, which is expected to improve diagnostic accuracy. In addition, one of the reasons to develop SDI protocol was time saving of total examination which is less than 30 min. Adding redistribution image of 201Tl within 60 min after stress test may show recognizable ischemia. This waiting time between 1st and 2nd 201Tl images is shorter than that with regular stress / redistribution protocol with 201Tl. Finally, American Society of Nuclear Cardiology has proposed that the exposure dose for more than 50% of all examinations be 9 mSv per test or less. CZT-SPECT achieved to reduce radiation exposure of 201Tl by its high sensitivity. Minimum usage is 50 MBq of 201Tl and 125 MBq of 99mTc in SDI protocol achieved totally 8.0 mSv/ test, which was less than 9 mSv.
Acknowledgments
We deeply appreciate clinical radiological technologists (Mr. Yoshitaka Hori and Takahito Terada) for their assistance to prepare this manuscript.
Sources of funding
None.
Conflicts of interest
None.
References
1. Hachamovitch R, Hayes SW, Friedman JD, Cohen I, Berman DS. Comparison of the short-term survival benefit associated with revascularization compared with medical therapy in patients with no prior coronary artery disease undergoing stress myocardial perfusion single photon emission computed tomography. Circulation 2003; 107: 2900–7.
2. Nanasato M, Nakajima K, Fujita H, Zen K, Kohsaka S, Hashimoto A, et al. Rationale and design of J-ACCESS 4: prognostic impact of reducing myocardial ischemia identified using ECG-gated myocardial perfusion SPECT in Japanese patients with coronary artery disease. J Cardiol 2014; 63: 159–64.
3. Cantoni V, Green R, Acampa W, Zampella E, Assante R, Nappi C, et al. Diagnostic performance of myocardial perfusion imaging with conventional and CZT single-photon emission computed tomography in detecting coronary artery disease: A meta-analysis. J Nucl Cardiol 2021; 28: 698–715.
4. Gimelli A, Bottai M, Genovesi D, Giorgetti A, Di Martino F, Marzullo P. High diagnostic accuracy of low-dose gated-SPECT with solid-state ultrafast detectors: preliminary clinical results. Eur J Nucl Med Mol Imaging 2012; 39: 83–90.
5. Gimelli A, Bottai M, Giorgetti A, Genovesi D, Filidei E, Marzullo P. Evaluation of ischaemia in obese patients: feasibility and accuracy of a low-dose protocol with a cadmium-zinc telluride camera. Eur J Nucl Med Mol Imaging 2012; 39: 1254–61.
6. Makita A, Matsumoto N, Suzuki Y, Hori Y, Kuromura K, Yoda S, et al. Clinical feasibility of simultaneous acquisition rest 99mTc/Stress 201Tl dual-isotope myocardial perfusion single-photon emission computed tomography with semiconductor camera. Circ J 2016; 80: 689–95.
7. Klein R, Beanlands RSB, deKemp RA. Quantification of myocardial blood flow and flow reserve: Technical aspects. J Nucl Cardiol 2010; 17: 555–70.
