Diagnostic utility of tomographic myocardial perfusion imaging with technetium 99m furifosmin (Q12) compared with thallium 201: Results of a phase III multicenter trial

Background  

Based on physical properties, ^99mTc-labeled perfusion agents offer several advantages over ²⁰¹Tl for myocardial perfusion imaging. The results of in vivo and experimental studies, along with preliminary experience in human subjects, have shown ^99mTc-labeled furifosmin to be a promising new perfusion tracer. The purpose of this study was to evaluate the safety of a new myocardial perfusion agent, ^99mTc-labeled furifosmin (Q12), and determine the concordance of furifosmin perfusion scintigraphy to ²⁰¹Tl imaging. In addition, we sought to determine the normalcy rate of myocardial scintigraphy with furifosmin.     

Myocardial uptake of thallium 201 and technetium 99m-labeled sestamibi after ischemia and reperfusion: Comparison by quantitative dual-tracer autoradiography in rabbits

Background  

Myocardial scintigraphy with^99mTc-labeled sestamibi (^99mTc-sestamibi) or²⁰¹Tl is used to assess regional perfusion in acute coronary syndromes associated with metabolic or functional abnormalities, such as acute coronary thrombosis with reperfusion and ischemia at rest. However, the initial uptake of these agents may be affected by a recent ischemic insult because the myocardial retention of these tracers depends on cellular metabolism.     

Reduced variability of interpretation and improved image quality with a technetium 99m myocardial perfusion agent: Comparison of thallium 201 and technetium 99m-labeled tetrofosmin

Background  

The purpose of this study was to determine the relative image quality and interobserver variability among four readers for²⁰¹Tl and^99mTc-labeled tetrofosmin myocardial perfusion images.^99mTc-labeled perfusion agents, with near-optimal physical characteristics for gamma camera imaging, may allow for superior image quality and improved consistency of interpretation. However, most studies to date have demonstrated only similarity in the diagnostic accuracy between technetium agents and thallium. Tetrofosmin is a recently developed^99mTc-labeled agent that has shown promising results in early clinical trials.     

Small field-of-view dedicated cardiac SPECT systems: impact of projection truncation

Purpose  

Small field-of-view (FOV) dedicated cardiac SPECT systems suffer from truncated projection data. This results in (1) neglect of liver activity that otherwise could be used to estimate (and subsequently correct) the amount of scatter in the myocardium by model-based scatter correction, and (2) distorted attenuation maps. In this study, we investigated to what extent truncation impacts attenuation correction and model-based scatter correction in the cases of ^99mTc, ²⁰¹Tl, and simultaneous ^99mTc/²⁰¹Tl studies. In addition, we evaluated a simple correction method to mitigate the effects of truncation.     

Comparison of technetium 99m Q12 and thallium 201 for detection of angiographically documented coronary artery disease in humans

Background

^99mTc-labeled Q12 (^99mTc-Q12) is a new imaging agent that produces myocardial visualization in humans. This study examined the hypothesis that a 100-minute rest-exercise tomographic imaging protocol after injection of^99mTc-Q12 can be used to detect the presence or absence of coronary artery stenoses.

Methods and Results

Imaging with²⁰¹Tl and^99mTc-Q12 was performed in 20 patients with angiographically documented coronary artery disease and 10 “normal” subjects including two patients with chest pain and normal coronary arteriograms and eight subjects with a very low likelihood of occlusive coronary disease.^99mTc-Q12 was imaged beginning 15 minutes after injection at rest and with exercise. In the 20 patients, a corresponding myocardial defect was detected in blinded fashion in 18 with²⁰¹Tl and 17 with^99mTc-Q12 (difference not significant). Of 10 patients without evidence of coronary disease, nine had a normal²⁰¹Tl scan and eight had a normal^99mTc-Q12 scan (difference not significant). Agreement of^99mTc-Q12 and²⁰¹Tl imaging for detection of regional myocardial perfusion defects was excellent (κ=0.88). Identification of the presence or absence of angiographically documented coronary disease in individual coronary artery distributions was 80% and 82% for²⁰¹Tl imaging and 73% and 87% for^99mTc-Q12 (difference not significant).

Conclusion

^99mTc-Q12, used in a rest-exercise sequence that can be completed in 100 minutes, provided identification of regional myocardial perfusion defects similar to that of²⁰¹Tl.     

Evaluation of simultaneous 201Tl/99mTc dual-isotope cardiac SPECT imaging with model-based crosstalk compensation using canine studies

Background

Simultaneous ²⁰¹Tl/^99mTc-sestamibi dual-isotope myocardial perfusion SPECT imaging can reduce imaging time and produce perfectly registered rest/stress images. However, crosstalk from ^99mTc into ²⁰¹Tl images can significantly reduce ²⁰¹Tl image quality. We have developed a model-based compensation (MBC) method to compensate for this crosstalk. The method has previously been validated with phantom and simulation studies. In this study, we evaluated the MBC method using a canine model.

Methods

Left anterior descending or left circumflex coronary artery stenoses were created in 50 adult mongrel dogs weighing 20-30 kg. The dogs were injected with 111 MBq (3 mCi) of ²⁰¹Tl at rest, and a SPECT study acquired. Stress was induced by administering adenosine to the dog, followed by injection of 740 MBq (20 mCi) of ^99mTc-sestamibi at peak stress. A second SPECT study was performed with data acquired in both ²⁰¹Tl and ^99mTc energy windows to provide simultaneous dual-isotope projection data. The images were reconstructed using the ordered-subsets expectation-maximization reconstruction algorithm with compensation for attenuation, scatter, and detector response. For simultaneously acquired ²⁰¹Tl data, we also applied the MBC method to compensate for crosstalk contamination from ^99mTc.

Results

Without compensation, ^99mTc crosstalk increased the estimated ²⁰¹Tl activity concentration in the rest images and reduced defect contrast. After MBC, the ²⁰¹Tl images were in good agreement with the registered single-isotope images and ex vivo count data. The ischemic (IS) to non-ischemic (NIS) region ²⁰¹Tl activity concentration ratios were computed for single-isotope and dual-isotope studies. The correlation with ex vivo IS-NIS ratios was 0.815 after MBC, compared to the 0.495 from data without compensation. In addition, the regression line for the IS-NIS ratios with MBC was almost parallel to the line of identity with a slope of 0.93, compared to a slope of 0.45 without compensation.

Conclusions

These results demonstrate that model-based crosstalk compensation can provide substantial reduction of crosstalk effects in simultaneously acquired myocardial perfusion SPECT images in living biological systems.     

Combined thallium 201/technetium 99m-labeled pyrophosphate tomography for identification of the “culprit” vessel in acute myocardial infarction

Background

Many previous investigations have used the presence of transient ischemic ²⁰¹Tl perfusion defect to localize coronary artery stenosis. This study reports the results of ²⁰¹Tl tomography alone and combined ²⁰¹Tl/^99mTc-labeled pyrophosphate (^99mTc PYP) tomography employed to identify the infarct-related vessel in patients with acute myocardial infarction (AMI).

Methods and Results

All short-axis images were evaluated by dividing each left ventricular slice into eight equal sectors. In addition, for combined ²⁰¹Tl/^99mTc PYP tomography, two sectors were added to evaluate involvement of the right ventricle. In a preevaluation phase of the study, the sectors were assigned to the supplying coronary arteries in 75 patients with single chronic myocardial infarction related to the left anterior descending coronary artery (LAD), left circumflex artery (LCX), or right coronary artery (RCA). In this pilot phase, ²⁰¹Tl tomograms were reviewed in conjunction with the angiographic data. This assignment was then tested prospectively in 117 patients with AMI. As confirmed by angiography, the AMI was related to the LAC, LCX, and RCA in 54, 17, and 46 patients, respectively. Sensitivity and specificity for ^99mTc PYP accumulation on combined ²⁰¹Tl/^99mTc PYP tomography were 98% a nd 100% for the LAD, 88% and 99% for the LCX, and 98% and 96% for the RCA, respectively. For ²⁰¹Tl tomography, sensitivity and specificity for identification of the culprit vessel were 94% and 89% for the LAD, 82% and 91% for the LCX, and 72% and 96% for the RCA, respectively.

Conclusion

This prospective study demonstrates that combined ²⁰¹Tl/^99mTc PYP tomography is highly accurate for identification of the infarct-related artery in AMI, even in patients with multivessel disease. Positive contrast visualization of myocardial necrosis in both the left and right ventricle allows for reliable differentiation between AMI related to the LCX or RCA territory. In comparison, for ²⁰¹Tl tomography the sensitivity to detect the culprit vessel, particularly the LCX and RCA, appears to be lower than for ²⁰¹Tl/^99mTc PYP imaging, particularly in patients with prior infarction or right dominant coronary artery.     

Left ventricular dysfunction in coronary artery disease: Comparison between rest-redistribution thallium 201 and resting technetium 99m methoxyisobutyl isonitrile cardiac imaging

Background

We compared rest-redistribution thallium 201 and resting technetium 99m methoxyisobutyl isonitrile (MIBI) cardiac imaging in 29 men with angiographically proven coronary artery disease and regional ventricular dysfunction. Left ventricular ejection fraction at radionuclide angiography was 35%±9%.

Methods and Results

Regional left ventricular wall motion was assessed on gated^99mTc MIBI images according to a 3-point scale (0=normal, 1=hypokinetic, 2=akinetic or dyskinetic).²⁰¹Tl and^99mTc MIBI uptake values were analyzed quantitatively. A total of 435 myocardial segments were classified on the basis of wall motion analysis into three groups: group 1 (normal wall motion;n=201), group 2 (hypokinetic;n=132), and group 3 (akinetic or dyskinetic;n=102).²⁰¹Tl and^99mTc MIBI uptake values were significantly higher in groups 1 and 2 compared with group 3 (p<0.05) and in group 1 compared with group 2 (p<0.05). When²⁰¹Tl and^99mTc MIBI uptake values were directly compared, no significant differences in groups 1 and 2 were observed. In group 3,^99mTc MIBI uptake (67%±14%) was significantly lower (p<0.001) than initial (72%±11%) and delayed²⁰¹Tl uptake (73%±12%).

Conclusion

Thus rest-redistribution²⁰¹Tl and resting^99mTc MIBI cardiac imaging reflect the severity of left ventricular dysfunction in coronary artery disease. However, in segments with severely impaired regional ventricular function,²⁰¹Tl uptake is significantly higher than^99mTc MIBI uptake.     

Improved diagnostic accuracy of planar imaging with technetium 99m-labeled tetrofosmin compared with thallium-201 for the detection of coronary artery disease

Background

Receiver operating characteristic (ROC) curve analysis provides detailed information about the performance of a diagnostic test.

Methods and Results

As part of a multicenter phase III trial, 160 patients with known or suspected coronary artery disease underwent planar stress-rest^99mTc-labeled tetrofosmin and stress-redistribution²⁰¹Tl imaging within 14 days of each other, to compare the diagnostic accuracy of these imaging modalities by ROC curve analysis. Coronary arteriography was used as the reference standard and greater than 70% stenosis was considered significant. ROC curve analysis showed improved detection of coronary artery disease with^99mTc-labeled tetrofosmin compared with²⁰¹Tl, with ROC curve areas of 0.765 versus 0.644, respectively (p=0.02).^99mTc-labeled tetrofosmin also better identified single-vessel disease in those without previous myocardial infarction (ROC curve areas of 0.684 vs 0.510 for^99mTc-labeled tetrofosmin and²⁰¹Tl, respectively;p=0.04) and enhanced the detection of multivessel disease in those with previous myocardial infarction (ROC curve areas of 0.764 vs 0.638, respectively;p=0.02).

Conclusions

Detailed assessment of diagnostic performance by ROC curve analysis shows that, for planar imaging,^99mTc-labeled tetrofosmin enhances the detection of coronary artery disease compared with²⁰¹Tl.     

Simultaneous dual-isotope imaging based on an artificial neural network for evaluating myocardial perfusion and fatty acid metabolism

Background

We contrived a scatter correction method based on an artificial neural network (ANN) and applied it to the simultaneous evaluation of myocardial perfusion and fatty acid metabolism in single-photon emission computed tomography (SPECT).

Methods

The count data of three energy windows were used as inputs of the ANN. The count ratios of the estimated primary-to-total photons for ^99mTc and ¹²³I, which were used to reconstruct ^99mTc and ¹²³I images, were calculated using the ANN. In a phantom study, single- and dual-isotope imaging with ^99mTc/¹²³I and ²⁰¹Tl/¹²³I was performed by means of a cardiac phantom simulating patients with and without obesity. In a human study, five normal volunteers and ten patients with myocardial infarction underwent myocardial perfusion and fatty acid metabolism imaging with single and dual SPECT with combinations of ^99mTc-methoxyisobutylisonitrile/¹²³I-beta-methyl(p-iodophenyl)pentadecanoic acid (BMIPP) and ²⁰¹Tl/¹²³I-BMIPP as tracers.

Results

Technetium-99m yielded more homogeneous images than ²⁰¹Tl because of the lower degree of photon attenuation, especially in the condition of obese patients, resulting in clearer visualization of the perfusion-metabolism mismatch. Dual ^99mTc/¹²³I SPECT offered comparable images with single SPECT in assessing myocardial damage.

Conclusions

The method effectively separated ^99mTc and ¹²³I primary photons and proved applicable to ^99mTc/¹²³I dual-isotope myocardial SPECT.     

Comparison of reinjection thallium 201 and resting technetium 99m sestamibi tomographic images for the quantification of infarct size after acute myocardial infarction

Background

Both thallium 201 and technetium 99m sestamibi have been used to quantitate infarct size at rest. Exercise²⁰¹Tl scintigraphy has been shown to have powerful prognostic information after myocardial infarction. A single study using these agents that could provide data on infarct size and prognosis would be of value. The purpose of this study was to compare estimates of infarct size by use of²⁰¹Tl and^99mTc sestamibi and to correlate these measurements with left ventricular ejection fraction in patients after acute myocardial infarction.

Methods and Results

The study group consisted of 20 patients who underwent low-level²⁰¹Tl stress studies with reinjection and^99mTc sestamibi resting studies within 4 days. Acute reperfusion was attempted in 18 of 20 patients. For^99mTc sestamibi tomographic imaging, infarct size was quantitated with 60% of maximal counts per slice for five short-axis slices as described in multiple previous studies. The postreinjection delayed²⁰¹Tl images acquired 4 hours after stress were quantitated according to the same threshold method.²⁰¹Tl patient images were also quantitated with a commercially available polar map program and compared with sex-matched control subjects. Ejection fraction was determined for each patient by radionuclide ventriculography 6 weeks later. Ejection fraction was well preserved for the group: mean 0.53±0.10. Infarct size with^99mTc sestamibi was 12%±13% of the left ventricle, which was significantly smaller than either method with²⁰¹Tl: threshold method, 29%±18% of left ventricle; polar map method, 25%±17% of left ventricle (both²⁰¹Tl estimates,p<0.0001 vs^99mTc sestamibi;²⁰¹Tl, 70% threshold vs²⁰¹Tl polar map,p=0.04). There was a significant correlation between infarct size with^99mTc sestamibi and that with²⁰¹Tl (r=0.72 to 0.73;p<0.001). Infarct size with^99mTc sestamibi, however, provided the closest correlation with ejection fraction (r=0.81;p<0.001), with the two²⁰¹Tl quantitative methods providing very similar correlations (r=0.69;p<0.001).

Conclusions

Infarct size with reinjection²⁰¹Tl imaging correlates significantly with resting infarct size with^99mTc sestamibi, although it provides significantly larger estimates. Although both approaches can be combined with a same-day exercise protocol, the closer correlation of infarct size with ejection fraction at 6 weeks suggests that resting infarct size with^99mTc sestamibi may be slightly more accurate.     

Factors affecting the myocardial activity acquired during exercise SPECT with a high-sensitivity cardiac CZT camera as compared with conventional Anger camera

Purpose

Injected doses are difficult to optimize for exercise SPECT since they depend on the myocardial fraction of injected activity (MFI) that is detected by the camera. The aim of this study was to analyse the factors affecting MFI determined using a cardiac CZT camera as compared with those determined using conventional Anger cameras.

Methods

Factors affecting MFI were determined and compared in patients who had consecutive exercise SPECT acquisitions with ²⁰¹Tl (84 patients) or ^99mTc-sestamibi (87 patients) with an Anger or a CZT camera. A predictive model was validated in a group of patients routinely referred for ²⁰¹Tl (78 patients) or ^99mTc-sestamibi (80 patients) exercise CZT SPECT.

Results

The predictive model involved: (1) camera type, adjusted mean MFI being ninefold higher for CZT than for Anger SPECT, (2) tracer type, adjusted mean MFI being twofold higher for ²⁰¹Tl than for ^99mTc-sestamibi, and (3) logarithm of body weight. The CZT SPECT model led to a +1?±?26 % error in the prediction of the actual MFI from the validation group. The mean MFI values estimated for CZT SPECT were more than twofold higher in patients with a body weight of 60 kg than in patients with a body weight of 120 kg (15.9 and 6.8 ppm for ^99mTc-sestamibi and 30.5 and 13.1ppm for ²⁰¹Tl, respectively), and for a 14-min acquisition of up to one million myocardial counts, the corresponding injected activities were only 80 and 186 MBq for ^99mTc-sestamibi and 39 and 91 MBq for ²⁰¹Tl, respectively.

Conclusion

Myocardial activities acquired during exercise CZT SPECT are strongly influenced by body weight and tracer type, and are dramatically higher than those obtained using an Anger camera, allowing very low-dose protocols to be planned, especially for ^99mTc-sestamibi and in non-obese subjects.     

Novel method for quantitative evaluation of cardiac amyloidosis using 201TlCl and 99mTc-PYP SPECT

Objective

The degree of myocardial technetium-^99m-pyrophosphate (^99mTc-PYP) accumulation in cardiac amyloidosis is conventionally evaluated by the PYP score. This method involves qualitative visual evaluation on two-dimensional images. Here, we performed three-dimensional quantitative analysis using software developed in our laboratory.

Methods

We performed dual myocardial imaging using thallium-²⁰¹-chloride (²⁰¹Tl-Cl) and ^99mTc-PYP in cases of suspected cardiac amyloidosis and calculated the PYP accumulation rates of all myocardial pixels showing ^99mTc-PYP accumulation. We defined this procedure as quantitative evaluation of the degree of ^99mTc-PYP accumulation in the myocardium. Patients were divided into two groups with and without a diagnosis of cardiac amyloidosis, and we examined the PYP accumulation rates in both groups. In addition, we examined the PYP scores of the two groups by conventional qualitative evaluation.

Results

The PYP scores of the cardiac amyloidosis group were significantly higher than those of the other group. The PYP accumulation rates of the cardiac amyloidosis group were significantly higher than those of the other group. There were significant differences in the PYP accumulation rate and PYP score between the two groups. There was considered to be a threshold between the two groups in the case of the PYP accumulation rate.

Conclusions

When the threshold of the PYP score was defined as 3+ and that of the PYP accumulation rate as 41.5?%, the sensitivity of the PYP score and PYP accumulation rate was 84.6?%. However, the specificity of the PYP accumulation rate was higher than that of the PYP score. Quantitative evaluation by the PYP accumulation rate of the degree of ^99mTc-PYP accumulation in the myocardium may be useful in the diagnosis of cardiac amyloidosis.     

Current status of stress myocardial perfusion imaging pharmaceuticals and radiation exposure in Japan: Results from a nationwide survey

Background

Ionizing radiation generated during medical imaging procedures is a matter of concern. However, the current status of radiopharmaceutical use in stress myocardial perfusion imaging (MPI) and the radiation exposure from these radiopharmaceuticals is unknown in Japan.

Methods and Results

A nationwide survey was conducted from June through July 2016. The questionnaires on the radiopharmaceuticals used and their administered doses during stress MPI were sent to 641 nuclear medicine facilities. The responses were collected from 431 facilities and the effective dose (ED) for an adult with standard body weight was calculated. Forty-three percent of the facilities used only ²⁰¹TlCl, 35% used only ^99mTc radiopharmaceuticals, and the remaining 22% used both. The two main reasons for using ²⁰¹TlCl instead of ^99mTc radiopharmaceuticals were “more familiarity with the usage of ²⁰¹TlCl than ^99mTc radiopharmaceuticals” and “apprehension about increasing the burden of physicians performing tracer injection twice.” The mean ED was 14.0 ± 5.5 mSv (range, 3.9 to 25.2 mSv), which was higher than that reported in other countries.

Conclusions

The ED of stress MPI radiopharmaceuticals in Japan is probably higher than the world standard because more than 50% of the facilities still use ²⁰¹TlCl. We recommend revising the routine stress MPI protocol to reduce the effects of ionizing radiation.

     

Radiation dosimetry and biodistribution of <Superscript>99m</Superscript>Tc-ethylene dicysteine-deoxyglucose in patients with non-small-cell lung cancer

Purpose  

To assess the radiation dosimetry and biodistribution of ^99mTc-labeled ethylene dicysteine deoxyglucose (^99mTc-EC-DG) in patients with non-small-cell lung cancer (NSCLC).     

Thallium 201 for detection of viable myocardium: Comparison of different reinjection protocols

Background  

The finding of false fixed²⁰¹Tl defects by the conventional stress-redistribution protocol is a well-known phenomenon. The aim of this study was to compare two different²⁰¹Tl reinjection protocols to identify viable myocardium in the same group of patients.     

Regional concordance and discordance between rest thallium 201 and sestamibi imaging for assessing tissue viability: Comparison with postrevascularization functional recovery

Background  

Whether the combined analysis of rest ²⁰¹Tl and sestamibi uptake provides additional information regarding myocardial viability in patients with coronary artery disease is still to be investigated.     

Comparison between stress myocardial perfusion SPECT recorded with cadmium-zinc-telluride and Anger cameras in various study protocols

Purpose

The results of stress myocardial perfusion SPECT could be enhanced by new cadmium-zinc-telluride (CZT) cameras, although differences compared to the results with conventional Anger cameras remain poorly known for most study protocols. This study was aimed at comparing the results of CZT and Anger SPECT according to various study protocols while taking into account the influence of obesity.

Methods

The study population, which was from three different institutions equipped with identical CZT cameras, comprised 276 patients referred for study using protocols involving ²⁰¹Tl (n?=?120) or ^99mTc-sestamibi injected at low dose at stress (^99mTc-Low; stress/rest 1-day protocol; n?=?110) or at high dose at stress (^99mTc-High; rest/stress 1-day or 2-day protocol; n?=?46). Each Anger SPECT scan was followed by a high-speed CZT SPECT scan (2 to 4 min).

Results

Agreement rates between CZT and Anger SPECT were good irrespective of the study protocol (for abnormal SPECT, ²⁰¹Tl 92 %, ^99mTc-Low 86 %, ^99mTc-High 98 %), although quality scores were much higher for CZT SPECT with all study protocols. Overall correlations were high for the extent of myocardial infarction (r?=?0.80) and a little lower for ischaemic areas (r?=?0.72), the latter being larger on Anger SPECT (p?<?0.001). This larger extent was mainly observed in 50 obese patients who were in the ²⁰¹Tl or ^99mTc-Low group and in whom stress myocardial counts were particularly low with Anger SPECT (228?±?101 kcounts) and dramatically enhanced with CZT SPECT (+279?±?251 %).

Conclusion

Concordance between the results of CZT and Anger SPECT is good regardless of study protocol and especially when excluding obese patients who have low-count Anger SPECT and for whom myocardial counts are dramatically enhanced on CZT SPECT.

     

The relationship between reverse redistribution of 99mTc-tetrofosmin in sub-acute phase and left ventricular functional recovery in chronic phase in patients with acute myocardial infarction

Objective  

The purpose of this study was to clarify the relationship between reverse redistribution (RRD) of ^99mTc-tetrofosmin (^99mTc-TF) and left ventricular functional recovery in patients with acute myocardial infarction (AMI).     

Low-dose single acquisition rest 99mTc/stress 201Tl myocardial perfusion SPECT protocol: phantom studies and clinical validation

Purpose

We developed and tested a single acquisition rest ^99mTc-sestamibi/stress ²⁰¹Tl dual isotope protocol (SDI) with the intention of improving the clinical workflow and patient comfort of myocardial perfusion single photon emission computed tomography (SPECT).

Methods

The technical feasibility of SDI was evaluated by a series of anthropomorphic phantom studies on a standard SPECT camera. The attenuation map was created by a moving transmission line source. Iterative reconstruction including attenuation correction, resolution recovery and Monte Carlo simulation of scatter was used for simultaneous reconstruction of dual tracer distribution. For clinical evaluation, patient studies were compared to stress ^99mTc and rest ^99mTc reference images acquired in a 2-day protocol. Clinical follow-up examinations like coronary angiography (CAG) and fractional flow reserve (FFR) were included in the assessment if available.

Results

Phantom studies demonstrated the technical feasibility of SDI. Artificial lesions inserted in the phantom mimicking ischaemia could be clearly identified. In 51/53 patients, the image quality was adequate for clinical evaluation. For the remaining two obese patients with body mass index?>?32 the injected ²⁰¹Tl dose of 74 MBq was insufficient for clinical assessment. In answer to this the ²⁰¹Tl dose was adapted for obese patients in the rest of the study. In 31 patients, SDI and ^99mTc reference images resulted in equivalent clinical assessment. Significant differences were found in 20 patients. In 18 of these 20 patients additional examinations were available. In 15 patients the diagnosis based on the SDI images was confirmed by the results of CAG or FFR. In these patients the SDI images were more accurate than the ^99mTc reference study. In three patients minor ischaemic lesions were detected by SDI but were not confirmed by CAG. In one of these cases this was probably caused by pronounced apical thinning. For two patients no relevant clinical follow-up information was available for evaluation.

Conclusion

The proposed SDI protocol has the potential to improve clinical workflow and patient comfort and suggests improved accuracy as demonstrated in the clinical feasibility study.