Hybrid PET/MR in Cardiac Imaging.

In the last few years, technological advances in MR imaging, PET detectors, and attenuation correction algorithms have allowed the creation of truly integrated PET/MR imaging systems, for both clinical and research applications. These machines allow a comprehensive investigation of cardiovascular diseases, by offering a wide variety of detailed anatomical and functional data in combination. Despite significant pathophysiologic mechanisms being clarified by this new data, its clinical relevance and prognostic significance have not been demonstrated yet.

Polygenic Risk Scores for Prediction of Subclinical Coronary Artery Disease in Persons With Human Immunodeficiency Virus (HIV): The Swiss HIV Cohort Study.

BACKGROUND: In people with human immunodeficiency virus (HIV) (PWH), individual polygenic risk scores (PRSs) are associated with coronary artery disease (CAD) events. Whether PRSs are associated with subclinical CAD is unknown. METHODS: In Swiss HIV Cohort Study participants of European descent, we defined subclinical CAD as presence of soft, mixed, or high-risk plaque (SMHRP) on coronary computed tomography (CT) angiography, or as participants in the top tertile of the study population's coronary artery calcium (CAC) score, using noncontrast CT. We obtained univariable and multivariable odds ratios (ORs) for subclinical CAD endpoints based on nongenetic risk factors, and validated genome-wide PRSs built from single nucleotide polymorphisms associated with CAD, carotid intima-media thickness (IMT), or longevity in the general population. RESULTS: We included 345 genotyped participants (median age, 53 years; 89% male; 96% suppressed HIV RNA); 172 and 127 participants had SMHRP and CAC, respectively. CAD-associated PRS and IMT-associated PRS were associated with SMHRP and CAC (all P < .01), but longevity PRS was not. Participants with unfavorable CAD-PRS (top quintile) had an adjusted SMHRP OR = 2.58 (95% confidence interval [CI], 1.18-5.67), and a CAC OR = 3.95 (95% CI, 1.45-10.77) vs. bottom quintile. Unfavorable nongenetic risk (top vs. bottom quintile) was associated with adjusted SMHRP OR = 24.01 (95% CI, 9.75-59.11), and a CAC-OR = 65.07 (95% CI, 18.48-229.15). Area under the receiver operating characteristic curve increased when we added CAD-PRS to nongenetic risk factors (SMHRP: 0.75 and 0.78, respectively; CAC: 0.80 and 0.83, respectively). CONCLUSIONS: In Swiss PWH, subclinical CAD is independently associated with an individual CAD-associated PRS. Combining nongenetic and genetic cardiovascular risk factors provided the most powerful subclinical CAD prediction.

Management of transthyretin amyloidosis.

Transthyretin amyloidosis (ATTR amyloidosis) is a disease caused by deposition of transthyretin fibrils in organs and tissues, which causes their dysfunction. The clinical heterogeneity of ATTR amyloidosis and the variable presentation of symptoms at early disease stages, historically meant treatment delays. Diagnostic tools and therapy options of ATTR amyloidosis have markedly improved in recent years. The first Swiss Amyloidosis Network (SAN) meeting (Zurich, Switzerland, January 2020) aimed to define a consensus statement regarding the diagnostic work-up and treatment for systemic amyloidosis, tailored to the Swiss healthcare system. A consortium of 45 clinicians and researchers from all Swiss regions and universities was selected by the SAN committee to represent all sub-specialty groups involved in care of patients with amyloidosis. A steering committee conducted the literature search and analysis, wrote the critical synthesis and elaborated a list of statements that were evaluated by all the participants. These recommendations will improve outcomes and quality of life for patients with ATTR amyloidosis. A global review of these guidelines is planned every 3 years with a formal meeting of all the involved experts.

Combined Cardiac PET-CT and Transcatheter Closure for Left Internal Mammary Artery Side Branch Steal Syndrome.

We report on a patient with left internal mammary artery (LIMA) side branch steal syndrome and refractory angina who underwent successful transcatheter LIMA side branch closure after cardiac positron emission tomography-computed tomography assessment. The procedure resulted in improved myocardial ischemia, hyperemic blood flow, coronary flow reserve, and anginal symptoms. (Level of Difficulty: Advanced.).

Deep learning-assisted ultra-fast/low-dose whole-body PET/CT imaging.

PURPOSE: Tendency is to moderate the injected activity and/or reduce acquisition time in PET examinations to minimize potential radiation hazards and increase patient comfort. This work aims to assess the performance of regular full-dose (FD) synthesis from fast/low-dose (LD) whole-body (WB) PET images using deep learning techniques. METHODS: Instead of using synthetic LD scans, two separate clinical WB 18F-Fluorodeoxyglucose (18F-FDG) PET/CT studies of 100 patients were acquired: one regular FD (~ 27 min) and one fast or LD (~ 3 min) consisting of 1/8th of the standard acquisition time. A modified cycle-consistent generative adversarial network (CycleGAN) and residual neural network (ResNET) models, denoted as CGAN and RNET, respectively, were implemented to predict FD PET images. The quality of the predicted PET images was assessed by two nuclear medicine physicians. Moreover, the diagnostic quality of the predicted PET images was evaluated using a pass/fail scheme for lesion detectability task. Quantitative analysis using established metrics including standardized uptake value (SUV) bias was performed for the liver, left/right lung, brain, and 400 malignant lesions from the test and evaluation datasets. RESULTS: CGAN scored 4.92 and 3.88 (out of 5) (adequate to good) for brain and neck + trunk, respectively. The average SUV bias calculated over normal tissues was 3.39 ± 0.71% and - 3.83 ± 1.25% for CGAN and RNET, respectively. Bland-Altman analysis reported the lowest SUV bias (0.01%) and 95% confidence interval of - 0.36, + 0.47 for CGAN compared with the reference FD images for malignant lesions. CONCLUSION: CycleGAN is able to synthesize clinical FD WB PET images from LD images with 1/8th of standard injected activity or acquisition time. The predicted FD images present almost similar performance in terms of lesion detectability, qualitative scores, and quantification bias and variance.

Expert recommendation from the Swiss Amyloidosis Network (SAN) for systemic AL-amyloidosis.

Systemic amyloidosis is a heterogeneous group of diseases associated with protein misfolding into insoluble beta-sheet rich structures that deposit extracellularly in different organs, eventually compromising their function. There are more than 30 different proteins, known to be amyloidogenic with “light chain” (AL)-amyloidosis being the most common type, followed by transthyretin (ATTR)-, and amyloid protein A (AA)-amyloidosis. Systemic amyloidosis is a rare disease with an incidence of around 10 patients in 1 million inhabitants. Recently several new therapeutic options have been developed for subgroups of amyloidosis patients, and the introduction of novel therapies for plasma cell myeloma has led to an increase in the therapeutic armamentarium for plasma cell disorders, including AL amyloidosis. Among them, proteasome inhibitors, immunomodulatory agents (-imids), and monoclonal antibodies have been successfully introduced into clinical practice. Still, high-quality data from randomised controlled trials regarding the benefit of these cost-intensive drugs in AL amyloidosis are widely lacking, and due to the rarity of the disease many physicians will not gain routine experience in the management of these frail patients. The diagnosis of AL amyloidosis relies on a close collaboration between clinicians, pathologists, imaging experts, and sometimes geneticists. Diagnosis and treatment options in this complex disorder should be discussed in dedicated multidisciplinary boards. In January 2020, the first meeting of the Swiss Amyloidosis Network took place in Zurich, Switzerland. One aim of this meeting was to establish a consensus guideline regarding the diagnostic work-up and the treatment recommendations for systemic amyloidosis tailored to the Swiss health care system. Forty-five participants from different fields in medicine discussed many aspects of amyloidosis. These are the Swiss Amyloidosis Network recommendations which focus on diagnostic work-up and treatment of AL-amyloidosis.

Longitudinal Progression of Subclinical Coronary Atherosclerosis in Swiss HIV-Positive Compared With HIV-Negative Persons Undergoing Coronary Calcium Score Scan and CT Angiography.

BACKGROUND: People with HIV (HIV+) may have increased cardiovascular event rates compared with HIV-negative (HIV-) persons. Cross-sectional data from the United States and Switzerland, based on coronary artery calcium scan (CAC) and coronary computed tomography angiography (CCTA), suggest, respectively, increased and similar prevalence of subclinical atherosclerosis in HIV+ vs HIV- persons. METHODS: We repeated CAC/CCTA in 340 HIV+ and 90 HIV- study participants >2 years after baseline CAC/CCTA. We assessed the association of HIV infection, Framingham risk score (FRS), and HIV-related factors with the progression of subclinical atherosclerosis. RESULTS: HIV+ were younger than HIV- participants (median age, 52 vs 56 years; P < .01) but had similar median 10-year FRS (8.9% vs 9.0%; P = .82); 94% had suppressed HIV viral load. In univariable and multivariable analyses, FRS was associated with the incidence rate ratio (IRR) of new subclinical atherosclerosis at the follow-up CAC/CCTA, but HIV infection was not: any plaque (adjusted IRR for HIV+ vs HIV- participants, 1.21; 95% CI, 0.62-2.35), calcified plaque (adjusted IRR for HIV+ vs HIV- participants, 1.06; 95% CI, 0.56-2), noncalcified/mixed plaque (adjusted IRR for HIV+ vs HIV- participants, 1.24; 95% CI, 0.69-2.21), and high-risk plaque (adjusted IRR for HIV+ vs HIV- participants, 1.46; 95% CI, 0.66-3.20). Progression of CAC score between baseline and follow-up CAC/CCTA was similar in HIV+ (median annualized change [interquartile range {IQR}], 0.41 [0-10.19]) and HIV- participants (median annualized change [IQR], 2.38 [0-16.29]; P = .11), as was progression of coronary segment severity score (HIV+: median annualized change [IQR], 0 [0-0.47]; HIV-: median annualized change [IQR], 0 [0-0.52]; P = .10) and coronary segment involvement score (HIV+: median annualized change [IQR], 0 [0-0.45]; HIV-: median annualized change [IQR], 0 [0-0.41]; P = .25). CONCLUSIONS: In this longitudinal CAC/CCTA study from Switzerland, Framingham risk score was associated with progression of subclinical atherosclerosis, but HIV infection was not.

Antiretroviral Drugs Associated With Subclinical Coronary Artery Disease in the Swiss Human Immunodeficiency Virus Cohort Study.

BACKGROUND: Coronary artery disease (CAD) events have been associated with certain antiretroviral therapy (ART) agents. In contrast, the influence of ART on subclinical atherosclerosis is not clear. The study objective was to assess the association between individual ART agents and the prevalence and extent of subclinical CAD. METHODS: Coronary artery calcium (CAC) scoring and coronary computed tomography angiography (CCTA) were performed in ≥45-year-old Swiss Human Immunodeficiency Virus Cohort Study participants. The following subclinical CAD endpoints were analyzed separately: CAC score >0, any plaque, calcified plaque, noncalcified/mixed plaque, segment involvement score (SIS), and segment severity score (SSS). Logistic regression models calculated by inverse probability of treatment weights (IPTW) were used to explore associations between subclinical CAD and cumulative exposure to the 10 most frequently used drugs. RESULTS: There were 403 patients who underwent CCTA. A CAC score >0 was recorded in 188 (47%), any plaque in 214 (53%), calcified plaque in 151 (38%), and noncalcified/mixed plaque in 150 (37%) participants. A CAC score >0 was negatively associated with efavirenz (IPTW adjusted odds ratio per 5 years 0.73, 95% confidence interval [CI] 0.56-0.96), tenofovir disoproxil fumarate (0.68, 95% CI 0.49-0.95), and lopinavir (0.64, 95% CI 0.43-0.96). Any plaque was negatively associated with tenofovir disoproxil fumarate (0.71, 95% CI 0.51-0.99). Calcified plaque was negatively associated with efavirenz (0.7, 95% CI 0.57-0.97). Noncalcified/mixed plaque was positively associated with abacavir (1.46, 95% CI 1.08-1.98) and negatively associated with emtricitabine (0.67, 95% CI 0.46-0.99). For SSS and SIS, we found no association with any drug. CONCLUSIONS: An increased risk of noncalcified/mixed plaque was only found in patients exposed to abacavir. Emtricitabine was negatively associated with noncalcified/mixed plaque, while tenofovir disoproxil fumarate and efavirenz were negatively associated with any plaque and calcified plaque, respectively.

Severe Aortic Stenosis and Proximal Left Anterior Descending Artery Stenosis: A Positron Emission Tomography/Computed Tomography Assessment Before and After Transcatheter Aortic Valve Implantation.

We report the case of an 82-year-old patient with symptomatic severe aortic stenosis and calcified proximal left anterior descending (LAD) artery stenosis who underwent a transfemoral transcatheter aortic valve implantation (TAVI) without complex percutaneous coronary intervention. Before TAVI, a positron emission tomography/computed tomography assessment confirmed a reduced global coronary flow reserve (CFR), more pronounced on the LAD territory. One month post-TAVI, a second positron emission tomography/computed tomography scan showed a normalization of the global CFR and more than a doubling in the LAD territory. This case illustrates that mechanisms other than vessel stenosis may play an important role in CFR in the setting of aortic stenosis.

Amyloid PET imaging in cardiac amyloidosis: a pilot study using 18F-flutemetamol positron emission tomography.

OBJECTIVE: Cardiac amyloidosis is a rare disease characterized by amyloid heart deposits and is usually a part of systemic amyloidosis, in relation to systemic light chain (AL) and transthyretin (ATTR wild-type or genetic) amyloidosis. Several recent studies suggest a promising role of amyloid PET imaging to image cardiac amyloidosis, and several PET tracers are now available for in vivo detection of amyloid deposits. The aim of this study was to evaluate 18F-flutemetamol in diagnosing cardiac amyloidosis. METHODS: We performed a pilot study using 18F-flutemetamol (Vizamyl™) in 12 patients, 3 control subjects without cardiac amyloidosis, and 9 subjects with documented cardiac amyloidosis. Mean standardized uptake value (SUV) in the left ventricular myocardium and blood pool was determined and semi-quantitative parameter as target to background ratio (TBR, myocardial/blood pool mean SUV ratio) between 10th and 30th minutes was calculated. RESULTS: Uptake of 18F-flutemetamol in the left ventricular myocardium was noted in all patients with cardiac amyloidosis except one and none in control patient. The TBR was significantly higher in amyloidosis patients than in control subjects: 1.46, interquartile range (IQR) 1.32-2.06 versus 1.06, IQR 0.72-1.1 (p = 0.033). Only one patient in our study had light chain amyloidosis and showed higher TBR than patients with transthyretin amyloid: TBR 3.0 versus TBR median 1.44, IQR 1.33-1.69. CONCLUSION: Amyloid PET tracers such as 18F-flutemetamol could be a promising tool in diagnosing and in therapy response assessment for patients with cardiac amyloidosis.

High efficiency gamma camera enables ultra-low fixed dose stress/rest myocardial perfusion imaging.

Aims: We validated a 1-day myocardial perfusion imaging (MPI) protocol using an ultra low-dose(ULD) equal for stress and rest on a cadmium zinc telluride (CZT). Methods and results: Fifty-six patients underwent a 1-day MPI protocol using a standard (SD) 99mTc-tetrofosmin dose at stress (320 MBq) and rest (960 MBq) with 5 min acquisition time each (SD). Within 2 weeks MPI was repeated using ULD 99mTc-tetrofosmin equal for stress and rest (160 MBq) with 15 min acquisition time each (ULD). All scans were performed on a CZT camera (DNM 570c, GE Healthcare). Background subtraction was applied on the rest MPI of the ULD using P-mod software. Presence and extent of perfusion defect were analysed. Pearson's correlation was used to compare ejection fraction (EF), end diastolic volume (EDV), and end systolic volume (ESV) between both protocols. SD revealed ischaemia in 23, scar in 3, and an equivocal finding in 1 patient, while normal findings were documented in 29 patients. ULD resulted in the following findings: ischaemia 23, scar 3, and 30 normal scans. Congruence of SD and ULD was 22/23 for ischaemia, 3/3 for scar, and 29/29 in normal patients; one patient with ischaemia in SD was classified as scar in ULD. Overall agreement of ULD with SD was 98%. The mean extent of defect was comparable between SD and ULD for the stress (10% vs. 11%, respectively, P = NS) and rest studies (5% vs. 7%, respectively, P = NS). An excellent correlation between SD and ULD was found for EF (r = 0.93), EDV (r = 0.95), and ESV (r = 0.97). Conclusion: CZT cameras may enable reliable MPI scanning in patients with known or suspected coronary artery disease using protocols with about a factor 4-decrease in radiation dose exposure compared with traditional protocols.

Gated SPECT myocardial perfusion imaging with cadmium-zinc-telluride detectors allows real-time assessment of dobutamine-stress-induced wall motion abnormalities.

BACKGROUND: Left ventricular (LV) ejection fraction (EF) during high dobutamine stress (HD) by real-time gated-SPECT myocardial perfusion imaging (MPI) on a cadmium-zinc-telluride (CZT) gamma camera was validated versus cardiac magnetic resonance imaging (CMR). METHODS AND RESULTS: After injecting 99mTc-tetrofosmin (320 MBq) in 50 patients (mean age 64 +/- 11 years), EF at rest and post-stress as well as relevant changes in EF at HD (ΔEF ≥ 5%) were assessed. CZT and CMR rest EF values yielded an excellent correlation and agreement (r = 0.96; P < 0.001; Bland-Altman limits of agreement (BA): + 0 to 14.8%). HD EF acquisition was feasible using CZT and correlated better to HD CMR EF than did post-stress CZT EF (r = 0.85 vs 0.76, respectively, all P < 0.001). Agreement in ΔEF detection between HD CMR and immediate post-stress CZT (reflecting standard acquisition using conventional SPECT camera unable to scan during stress) was 45%, while this increased to 85% with real-time HD CZT scan. CONCLUSION: Real-time ultrafast dobutamine gated-SPECT MPI with a CZT device is feasible and provides accurate measurements of HD LV performance.

Prognostic value of revascularising viable myocardium in elderly patients with stable coronary artery disease and left ventricular dysfunction: a PET/CT study.

Sparse information is available on the role of cardiac viability imaging in elderly patients. We aimed at evaluating the prognostic value of FDG-PET/CT in elderly patients with stable coronary artery disease (CAD) and reduced left ventricular ejection fraction (rLVEF) before revascularisation. Elderly patients (> 65 years old, mean 74 ± 7 years old) with CAD and rLVEF were followed after cardiac FDG-PET/CT and stratified according to presence/absence of viable myocardium and subsequent revascularisation. Fatal events of any cause as well as hospitalisations related to acute cardiac conditions were reported as clinical end-points. Predictors of fatal events in patients with viable myocardium (> 1 myocardium segment/20) were analysed. A total of 89 patients were followed (64 viable myocardia; 37 and 27 patients with and without subsequent revascularisation, respectively). The change in LVEF during follow-up (2.1 ± 1.6 years) was 3.8 ± 6.6% (P = 0.013) and - 0.75 ± 2.6% (P = 0.170) in patients with and without revascularisation, respectively. Log-rank (P = 0.037) and multivariate analysis (Wald: 6.305, P = 0.012) showed viable myocardium to be significantly associated with fatal events if not revascularised. Elderly patients with viable myocardium might potentially benefit from revascularisation procedures as improved left ventricular ejection fraction and survival were observed in our retrospective study as compared to patients in whom a revascularisation procedure was denied. Viable myocardium as detected by cardiac FDG PET/CT was associated with better clinical outcomes in elderly patients when revascularised.

Subclinical coronary artery disease in Swiss HIV-positive and HIV-negative persons.

Aims: HIV-positive persons have increased cardiovascular event rates but data on the prevalence of subclinical atherosclerosis compared with HIV-negative persons are not uniform. We assessed subclinical atherosclerosis utilizing coronary artery calcium (CAC) scoring and coronary computed tomography angiography (CCTA) in 428 HIV-positive participants of the Swiss HIV Cohort Study and 276 HIV-negative controls concurrently referred for clinically indicated CCTA. Methods and results: We assessed the association of HIV infection, cardiovascular risk profile, and HIV-related factors with subclinical atherosclerosis in univariable and multivariable analyses. HIV-positive participants (median duration of HIV infection, 15 years) were younger than HIV-negative participants (median age 52 vs. 56 years; P < 0.01) but had similar median 10-year Framingham risk scores (9.0% vs. 9.7%; P = 0.40). The prevalence of CAC score >0 (53% vs. 56.2%; P = 0.42) and median CAC scores (47 vs. 47; P = 0.80) were similar, as was the prevalence of any, non-calcified/mixed, and high-risk plaque. In multivariable adjusted analysis, HIV-positive participants had a lower prevalence of calcified plaque than HIV-negative participants [36.9% vs. 48.6%, P < 0.01; adjusted odds ratio (aOR) 0.57; 95% confidence interval (CI) 0.40-0.82; P < 0.01], lower coronary segment severity score (aOR 0.72; 95% CI 0.53-0.99; P = 0.04), and lower segment involvement score (aOR 0.71, 95% CI 0.52-0.97; P = 0.03). Advanced immunosuppression was associated with non-calcified/mixed plaque (aOR 1.97; 95% CI 1.09-3.56; P = 0.02). Conclusion: HIV-positive persons in Switzerland had a similar degree of non-calcified/mixed plaque and high-risk plaque, and may have less calcified coronary plaque, and lower coronary atherosclerosis involvement and severity scores than HIV-negative persons with similar Framingham risk scores.

Whole-Body SPECT/CT versus Planar Bone Scan with Targeted SPECT/CT for Metastatic Workup.

PURPOSE: The use of SPECT/CT in bone scans has been widespread in recent years, but there are no specific guidelines concerning the optimal acquisition protocol. Two strategies have been proposed: targeted SPECT/CT for equivocal lesions detected on planar images or systematic whole-body SPECT/CT. Our aim was to compare the diagnostic accuracy of the two approaches. METHODS: 212 consecutive patients with a history of cancer were referred for bone scans to detect bone metastases. Two experienced readers randomly evaluated for each patient either planar images with one-field SPECT/CT targeted on equivocal focal uptakes (targeted SPECT/CT) or a whole-body (two-field) SPECT/CT acquisition from the base of the skull to the proximal femurs (whole-body SPECT/CT). The exams were categorized as "nonmetastatic," "equivocal," or "metastatic" on both protocols. The presence or absence of any extra-axial skeletal lesions was also assessed. The sensitivity and specificity of both strategies were measured using the results of subsequent imaging follow-up as the reference standard. RESULTS: Whole-body SPECT/CT had a significantly higher sensitivity than targeted SPECT/CT to detect bone metastases (p = 0.0297) and to detect extra-axial metastases (p = 0.0266). There was no significant difference in specificity among the two approaches. CONCLUSION: Whole-body SPECT/CT is the optimal modality of choice for metastatic workup, including detection of extra-axial lesions, with improved sensitivity and similar specificity compared to targeted SPECT/CT.

Downstream indication to revascularization following hybrid cardiac PET/MRI: preliminary results.

BACKGROUND: Hybrid PET/MRI allows the acquisition of both fluorine-18-fluorodeoxyglucose (F-FDG) PET and cardiac magnetic resonance (CMR) during one session. Whether this will result in different referral to coronary revascularization (CR) is unknown. We compared this new hybrid method with all-nuclear/all-CMR methods in the assessment of viable myocardium and in downstream referral to CR. PATIENTS AND METHODS: Overall, 12 patients with rest perfusion defects on a single photon emission computed tomography (SPECT) were recruited for cardiac viability assessment using a PET/MRI device. Perfusion (SPECT and CMR), metabolism, late gadolinium enhancement (LGE), and contractility were compared using a 20-segments bull's eye for agreement. The patterns of ischemia/viability were compared between all-nuclear, all-CMR, and hybrid methods. Downstream CR was proposed after correlating findings to coronary angiography. RESULTS: The SPECT and CMR perfusion denoted poor agreement [agreement rate (AR): 60%; κ: 0.191, P<0.004]. The added PET metabolism concurred in reclassifying 19.2% of segments with intermediate or unassessable LGE using the hybrid method. Overall, the all-CMR method showed better agreement with the hybrid method than the all-nuclear method for findings of normal (AR: 100%, κ: 1.00 vs. 65.8% %; κ: 0.347, respectively; P<0.001), scar (AR: 85%; κ: 0.675 vs. 80.8%; κ: 0.596, respectively; P<0.001), and ischemic segments (AR: 95.8%; κ: 0.881 vs. 75.8%; κ: 0.168, respectively; P<0.001). Downstream CR was proposed in four, 11, and 12 vessels by the all-nuclear, all-CMR, or hybrid methods, respectively. CONCLUSION: Compared with all-CMR, the hybrid method allowed the reclassification of 19.2% segments. Using CMR perfusion instead of SPECT perfusion had a significant impact on downstream target vessel revascularization.

Absolute Myocardial Blood Flow and Flow Reserve Assessed by Gated SPECT with Cadmium-Zinc-Telluride Detectors Using 99mTc-Tetrofosmin: Head-to-Head Comparison with 13N-Ammonia PET.

Recent advances in SPECT technology including cadmium-zinc-telluride (CZT) semiconductor detector material may pave the way for absolute myocardial blood flow (MBF) measurements by SPECT. The aim of the present study was to compare K1 uptake rate constants as surrogates of absolute MBF and myocardial flow reserve index (MFRi) in humans as assessed with a CZT SPECT camera versus PET. METHODS: Absolute MBF was assessed in 28 consecutive patients undergoing adenosine stress-rest myocardial perfusion imaging (MPI) by 99mTc-tetrofosmin CZT SPECT and 13N-ammonia PET, and MFR was calculated as a ratio of hyperemic over resting MBF. Results from both MPI methods were compared, and correlation coefficients were calculated. The diagnostic accuracy of CZT MFRi to predict an abnormal MFR defined as PET MFR less than 2 was assessed using a receiver-operator-characteristic curve. RESULTS: Median MBF at rest was comparable between CZT and PET (0.89 [interquartile range (IQR), 0.77-1.00] vs. 0.92 [IQR, 0.78-1.06] mL/g/min; P = not significant) whereas it was significantly lower at stress in CZT than PET (1.11 [IQR, 1.00-1.26] vs. 2.06 [IQR, 1.48-2.56] mL/g/min; P < 0.001). This resulted in median MFRi values of 1.32 (IQR, 1.13-1.52) by CZT and 2.36 (IQR, 1.57-2.71) by PET (P < 0.001). The receiver-operator-characteristic curve revealed a cutoff for CZT MFRi at 1.26 to predict an abnormal PET MFR yielding an accuracy of 75%. CONCLUSION: The estimation of absolute MBF index values by CZT SPECT MPI with 99mTc-tetrofosmin is technically feasible, although hyperemic values are significantly lower than from PET with 13N-ammonia, resulting in a substantial underestimation of MFR. Nevertheless, CZT MFRi may confer diagnostic value.