Aju P. Pazhenkottil

Nuclear Myocardial Perfusion Imaging with a Cadmium-Zinc-Telluride Detector Technique: Optimized Protocol for Scan Time Reduction

We aimed at establishing the optimal scan time for nuclear myocardial perfusion imaging (MPI) on an ultrafast cardiac γ-camera using a novel cadmium-zinc-telluride (CZT) solid-state detector technology. Methods: Twenty patients (17 male; BMI range, 21.7–35.5 kg/m2) underwent 1-d 99mTc-tetrofosmin adenosine stress and rest MPI protocols, each with a 15-min acquisition on a standard dual-detector SPECT camera. All scans were immediately repeated on an ultrafast CZT camera over a 6-min acquisition time and reconstructed from list-mode raw data to obtain scan durations of 1 min, 2 min, etc., up to a maximum of 6 min. For each of the scan durations, the segmental tracer uptake value (percentage of maximum myocardial uptake) from the CZT camera was compared by intraclass correlation with standard SPECT camera data using a 20-segment model, and clinical agreement was assessed per coronary territory. Scan durations above which no further relevant improvement in uptake correlation was found were defined as minimal required scan times, for which Bland–Altman limits of agreement were calculated. Results: Minimal required scan times were 3 min for low dose (r = 0.81; P < 0.001; Bland–Altman, −11.4% to 12.2%) and 2 min for high dose (r = 0.80; P < 0.001; Bland–Altman, −7.6% to 12.9%), yielding a clinical agreement of 95% and 97%, respectively. Conclusion: We have established the minimal scan time for a CZT solid-state detector system, which allows 1-d stress/rest MPI with a substantially reduced acquisition time resulting in excellent agreement with regard to uptake and clinical findings, compared with MPI from a standard dual-head SPECT γ-camera.

Incremental prognostic value of multi-slice computed tomography coronary angiography over coronary artery calcium scoring in patients with suspected coronary artery disease

AIMS The purpose of this study was to assess the relationship between calcium scoring (CS) and multi-slice computed tomography coronary angiography (MSCTA) and to determine if MSCTA has an incremental prognostic value to CS. METHODS AND RESULTS In 432 patients (59% male, age 58 +/- 11 years) referred for cardiac evaluation owing to suspected coronary artery disease (CAD), CS and 64-slice MSCTA were performed. The following events were combined in a composite endpoint: all-cause mortality, non-fatal infarction, and unstable angina requiring revascularization. CS was 0 in 147 (34%) patients, CS 1-99 was present in 122 (28%), CS 100-399 in 75 (17%), CS 400-999 in 56 (13%), and CS > or = 1000 in 32 (7%). MSCTA was normal in 133 (31%) patients, MSCTA 30-50% stenosis was observed in 190 (44%), and MSCTA > or =50% stenosis in 109 (25%). During follow-up [median 670 days (25th-75th percentile: 418-895)], an event occurred in 21 patients (4.9%). After multivariate correction for CS, MSCTA > or = 50% stenosis, the number of diseased segments, obstructive segments, and non-calcified plaques were independent predictors with an incremental prognostic value to CS. CONCLUSION MSCTA provides additional information to CS regarding stenosis severity and plaque composition. This additional information was shown to translate into incremental prognostic value over CS.

Diagnostic Value of 13N-Ammonia Myocardial Perfusion PET: Added Value of Myocardial Flow Reserve

The ability to obtain quantitative values of flow and myocardial flow reserve (MFR) has been perceived as an important advantage of PET over conventional nuclear myocardial perfusion imaging (MPI). We evaluated the added diagnostic value of MFR over MPI alone as assessed with 13N-ammonia and PET/CT to predict angiographic coronary artery disease (CAD). Methods: Seventy-three patients underwent 1-d adenosine stress–rest 13N-ammonia PET/CT MPI, and MFR was calculated. The added value of MFR as an adjunct to MPI for predicting CAD (luminal narrowing ≥ 50%) was evaluated using invasive coronary angiography as a standard of reference. Results: Per patient, the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of MPI for detecting significant CAD were 79%, 80%, 91%, 59%, and 79%, respectively. Adding a cutoff of less than 2.0 for global MFR to MPI findings improved the values to 96% (P < 0.005), 80%, 93%, 89% (P < 0.005), and 92% (P < 0.005), respectively. Conclusion: The quantification of MFR in 13N-ammonia PET/CT MPI provides a substantial added diagnostic value for detection of CAD. Particularly in patients with normal MPI results, quantification of MFR helps to unmask clinically significant CAD.

Prognostic value of cardiac hybrid imaging integrating single-photon emission computed tomography with coronary computed tomography angiography

Aims Although cardiac hybrid imaging, fusing single-photon emission computed tomography (SPECT) myocardial perfusion imaging with coronary computed tomography angiography (CCTA), provides important complementary diagnostic information for coronary artery disease (CAD) assessment, no prognostic data exist on the predictive value of cardiac hybrid imaging. Hence, the aim of this study was to assess the prognostic value of hybrid SPECT/CCTA images. Methods and results Of 335 consecutive patients undergoing a 1-day stress/rest (99m)Tc-tetrofosmin SPECT and a CCTA, acquired on stand-alone scanners and fused to obtain cardiac hybrid images, follow-up was obtained in 324 patients (97%). Survival free of all-cause death or non-fatal myocardial infarction (MI) and free of major adverse cardiac events (MACE: death, MI, unstable angina requiring hospitalization, coronary revascularizations) was determined using the Kaplan-Meier method for the following groups: (i) stenosis by CCTA and matching reversible SPECT defect; (ii) unmatched CCTA and SPECT finding; and (iii) normal finding by CCTA and SPECT. Coxs proportional hazard regression was used to identify independent predictors for cardiac events. At a median follow-up of 2.8 years (25th-75th percentile: 1.9-3.6), 69 MACE occurred in 47 patients, including 20 death/MI. A corresponding matched hybrid image finding was associated with a significantly higher death/MI incidence (P < 0.005) and proved to be an independent predictor for MACE. The annual death/MI rate was 6.0, 2.8, and 1.3% for patients with matched, unmatched, and normal findings. Conclusion Cardiac hybrid imaging allows risk stratification in patients with known or suspected CAD. A matched defect on hybrid image is a strong predictor of MACE.

Low-dose computed tomography coronary angiography with prospective electrocardiogram triggering: feasibility in a large population.

OBJECTIVES We sought to assess the feasibility of prospective electrocardiogram triggering for achieving low-dose computed tomography coronary angiography (CTCA) in a large population. BACKGROUND Prospective electrocardiogram triggering dramatically reduces radiation exposure for CTCA but requires heart rate (HR) control to obtain diagnostic image quality. Its feasibility in daily clinical routine has therefore remained to be elucidated. METHODS We evaluated 612 patients consecutively referred for CTCA by 64-slice computed tomography. Intravenous metoprolol (2 to 30 mg) was administered if necessary to achieve a target HR below 65 beats/min. Image quality was assessed on a semiquantitative 4-point scale for each coronary segment. RESULTS Forty-six (7.5%) patients were deemed ineligible due to irregular heart rhythm (n = 19), insufficient response to metoprolol (n = 21), renal insufficiency (n = 3), or inability to follow breath-hold commands (n = 3). Mean effective radiation dose was 1.8 ± 0.6 mSv with a diagnostic image quality in 96.2% of segments. Finally, low-dose CTCA allowed a firm diagnosis with regard to the presence or absence of coronary artery disease in 527 (86.1%) patients. Intravenous metoprolol to achieve an HR below 65 beats/min was used in 64.4% of patients. Incidence of nondiagnostic segments was inversely related to HR (r = -0.809, p < 0.001). Below an HR cutoff of 62 beats/min, only 1.2% of coronary segments were nondiagnostic. CONCLUSIONS Low-dose CTCA by electrocardiogram triggering is feasible in the vast majority of an every-day population. However, HR control is crucial, as an HR below 62 beats/min favors diagnostic image quality.

Improved Outcome Prediction by SPECT Myocardial Perfusion Imaging After CT Attenuation Correction

The aim of this study was to determine the impact of attenuation correction with CT (CT-AC) on the prognostic value of SPECT myocardial perfusion imaging (SPECT MPI). Methods: The summed stress score (SSS; 20-segment model) was obtained from filtered backprojection (FBP) and iterative reconstruction with CT-AC in 876 consecutive patients undergoing a 1-d stress–rest 99mTc-tetrofosmin SPECT MPI study for the evaluation of known or suspected coronary artery disease. Survival free of major adverse cardiac events (MACEs; cardiac death or nonfatal myocardial infarction) and survival free of any adverse cardiac events (including cardiac hospitalization, unstable angina, and late coronary revascularization) were analyzed by Kaplan–Meier analysis. Results: At a mean follow-up of 2.3 ± 0.6 y, a total of 184 adverse events occurred in 145 patients, including 35 MACEs (16 cardiac deaths [rate, 1.8%] and 19 nonfatal myocardial infarctions [rate, 2.2%]). With FBP, an SSS of 0–3 best distinguished patients with a low MACE rate (0.6%), followed by an SSS of 4–8 (4.3%), with increased MACE rate, and an SSS of 9–13 (3.8%), which was comparable. By contrast, with CT-AC the discrimination of low from intermediate MACE rate was best observed between an SSS of 0 (0%) and an SSS of 1–3 (3.7%), with a plateau at an SSS of 4–8 (3.2%). Conclusion: CT-AC for SPECT MPI allows improved risk stratification. The prognostically relevant SSS cutoff is shifted toward lower values.

Impact of cardiac hybrid single-photon emission computed tomography/computed tomography imaging on choice of treatment strategy in coronary artery disease

Aims Cardiac hybrid imaging by fusing single-photon emission computed tomography (SPECT) myocardial perfusion imaging with coronary computed tomography angiography (CCTA) provides important complementary diagnostic information for coronary artery disease (CAD) assessment. We aimed at assessing the impact of cardiac hybrid imaging on the choice of treatment strategy selection for CAD. Methods and results Three hundred and eighteen consecutive patients underwent a 1 day stress/rest 99mTc-tetrofosmin SPECT and a CCTA on a separate scanner for evaluation of CAD. Patients were divided into one of the following three groups according to findings in the hybrid images obtained by fusing SPECT and CCTA: (i) matched finding of stenosis by CCTA and corresponding reversible SPECT defect; (ii) unmatched CCTA and SPECT finding; (iii) normal finding by both CCTA and SPECT. Follow-up was confined to the first 60 days after hybrid imaging as this allows best to assess treatment strategy decisions including the revascularization procedure triggered by its findings. Hybrid images revealed matched, unmatched, and normal findings in 51, 74, and 193 patients. The revascularization rate within 60 days was 41, 11, and 0% for matched, unmatched, and normal findings, respectively (P< 0.001 for all inter-group comparisons). Conclusion Cardiac hybrid imaging with SPECT and CCTA provides an added clinical value for decision making with regard to treatment strategy for CAD.

Validation of CT Attenuation Correction for High-Speed Myocardial Perfusion Imaging Using a Novel Cadmium-Zinc-Telluride Detector Technique

The aim of this study was to validate attenuation correction (AC) using low-dose standard CT for myocardial perfusion imaging (MPI) on a novel ultra fast γ-camera with cadmium-zinc-telluride (CZT) detector technology. Methods: Sixty-six patients (body mass index ± SD, 27.2 ± 3.5 kg/m2; range, 19.1–36.0 kg/m2) underwent a 1-d 99mTc-tetrofosmin adenosine stress–rest imaging protocol with 15-min acquisitions on a standard dual-head SPECT camera. All scans were repeated within minutes on the CZT camera, with 3-min acquisitions for stress (low dose) and 2-min acquisitions for rest (high dose) as recently established. We compared maximum myocardial uptake (20-segment model) from CZT versus standard SPECT MPI by intraclass correlation without and with CT AC. In addition, clinical agreement for each coronary territory for all scans from both devices was assessed, and Bland–Altmann (BA) limits of agreement for percentage uptake were calculated. Results: The clinical agreement between CZT and standard SPECT cameras was 96% for noncorrected low- and high-dose images (r = 0.90 and BA = −18 to 15, and r = 0.91 and BA = −15 to 16, respectively), and agreement after AC was 96% for low- and 99% for high-dose images (r = 0.87 and BA = −16 to 14, and r = 0.88 and BA = −16 to 14, respectively). Conclusion: Our results support that AC of MPI on the novel CZT camera, compared with AC MPI on a conventional SPECT camera, is feasible because it provides a high correlation of segmental tracer uptake and an excellent clinical agreement.

Very high coronary calcium score unmasks obstructive coronary artery disease in patients with normal SPECT MPI.

Objectives To study the clinical impact of a very high coronary artery calcium score (CAC >1000) in patients with no known coronary artery disease (CAD) and normal single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI). The secondary aim was to evaluate whether triple vessel disease would support the notion of balanced ischaemia as an underlying mechanism of false negative SPECT MPI in patients with very high CAC. Background No data exist on the clinical value of high CAC in patients with normal SPECT MPI. Methods 50 patients with suspected CAD and normal stress/rest SPECT MPI and CAC >1000 prospectively underwent invasive coronary angiography as the standard of reference. Coronary lesions with ≥50% luminal diameter narrowing on invasive coronary angiography were considered to represent significant stenosis. Results The median total CAC was 1975 (range 1018–8046). In 37/50 (74%) patients, coronary angiography revealed one-vessel disease (1-VD) (n=15), 2-VD (n=10) or 3-VD (n=12). Twenty-six revascularisations (percutaneous coronary intervention/coronary artery bypass grafting) were performed in seven (6/1), seven (6/1) and 12 (7/5) patients with 1-VD, 2-VD and 3-VD, respectively. Conclusions In patients with normal SPECT MPI, a CAC >1000 confers a high diagnostic added value for detecting CAD. This is not solely based on unmasking balanced ischaemia due to epicardial 3-VD, as it occurred predominantly in patients with 1-VD and 2-VD.

Semiconductor Detectors Allow Low-Dose–Low-Dose 1-Day SPECT Myocardial Perfusion Imaging

Cadmium zinc telluride (CZT) detectors with linear counting rate response enable count subtraction in sequential scanning. We evaluated whether count subtraction eliminated the need for higher activity doses in the second part of the 1-d stress–rest myocardial perfusion imaging (MPI) protocol. Methods: For 50 patients (mean age ± SD, 66 ± 12 y) with visually abnormal (n = 42) or equivocal (n = 8) adenosine-stress MPI (320 MBq of 99mTc-tetrofosmin) on a CZT camera, rest MPI was performed with a low dose (320 MBq) and repeated after injection of an additional 640 MBq of 99mTc-tetrofosmin to achieve a standard 3-fold increased dose at rest (960 MBq), compared with stress (320 MBq). Low-dose rest myocardial perfusion images were reconstructed after subtracting the background activity of the preceding stress scan. Segmental percentage tracer uptake of the 2 rest myocardial perfusion images (320 vs. 960 MBq) was compared using intraclass correlation and Bland–Altman limits of agreement. Patient- and coronary territory–based clinical agreement was assessed. Results: The standard protocol revealed ischemia in 34 (68%) and a fixed defect in 8 (16%) patients, of whom 33 (97%) and 8 (100%) were correctly identified by low-dose MPI (clinical agreement, 98%). Segmental uptake correlated well between low- and standard-dose rest scans (r = 0.94, P < 0.001; Bland–Altman limits of agreement, −11 to +11%). Defect extent was 14.4% (low-dose) versus 13.1% (standard-dose) at rest (P = not statistically significant) and 26.6% at stress (P < 0.001 vs. rest scans). Conclusion: These promising results suggest that accurate assessment of ischemic myocardial disease is feasible with a low-dose–low-dose 1-d SPECT MPI protocol using a CZT device.