Rapid cardiac hybrid imaging with minimized radiation dose for accurate non-invasive assessment of ischemic coronary artery disease

BACKGROUND

Ischemic coronary artery disease (CAD) is a major cause for morbidity and mortality resulting in a continuously increasing number of diagnostic interventions. We have validated a new hybrid imaging method using minimized radiation dose for rapid non-invasive prediction of invasive coronary angiography (CA) findings with regard to coronary lesion detection and revascularization.

METHODS

Forty patients referred for elective invasive coronary angiography (CA) due to suspected CAD were prospectively enrolled to undergo a low-dose CTCA with prospective ECG-triggering and a stress-only SPECT-MPI scan administering half of the standard low-dose stress (99m)Tc-tetrofosmin activity. The latter was acquired immediately after adenosine stress (omitting the standard 30-60 min waiting time). After fusing CTCA and SPECT-MPI decisions towards conservative management versus revascularization strategy based on hybrid images were compared to the decisions taken by the interventional operator in the catheterization laboratory based on CA. The latter served as standard of reference.

RESULTS

Hybrid images yielded sensitivity, specificity, positive and negative predictive values and accuracy of 100%, 96.0%, 100%, 93.8% and 97.5% for predicting coronary revascularization. The estimated mean effective radiation doses were significantly lower for hybrid imaging (4.7 ± 1.0 mSv) than for invasive CA (8.7 ± 4.2 mSv; P<0.001 vs. hybrid). Total non-invasive protocol time was below 60 min, comparing favourably to standard SPECT protocols.

CONCLUSIONS

Rapid cardiac hybrid imaging allows accurate prediction of invasive CA findings and of treatment decision despite minimized radiation dose and protocol time.

Validation of a new contrast material protocol adapted to body surface area for optimized low-dose CT coronary angiography with prospective ECG-triggering

In patients with large total blood volume contrast material (CM) dilution decreases coronary attenuation in CT coronary angiography (CTCA). As increased blood volume is well paralleled by body surface area (BSA) we assessed a BSA-adapted CM protocol to compensate for dilution effects. Low-dose CTCA with prospective ECG-triggering was performed in 80 patients with a BSA-adapted CM bolus ranging 40-105 ml and injection rate ranging 3.5-5.0 ml/s for a BSA of <1.70 to >or=2.5 m(2). Eighty control patients matched for BSA who had previously undergone routine CTCA with a fixed CM protocol of 80 ml at 5 ml/s served as reference group. The average vessel attenuation from the proximal right (RCA) and the left main coronary artery (LMA) was assessed. Correlation of BSA with vessel attenuation was assessed in both groups. BSA-matching of all patients was successful (BSA-adapted group 1.98 +/- 0.15 m(2), range 1.66-2.39 m(2) versus reference group 1.98 +/- 0.17 m(2), range 1.59-2.38 m(2); P = 0.74). Mean CM bolus was significantly smaller in the BSA-adapted versus the reference group (70.9 +/- 14.1 vs. 80.0 +/- 0 ml, P < 0.001). There was no correlation in the BSA-adapted group (r = -0.07, P = 0.53, SEE = 0.15), while coronary attenuation was inversely related to BSA in the reference group (r = -0.59, P < 0.001, SEE = 0.14). We have successfully validated a BSA-adapted contrast material protocol which results in a comparable coronary contrast enhancement independent of individual BSA. This was achieved despite a significant reduction in the overall contrast material amount.

Usefulness of additional coronary calcium scoring in low-dose CT coronary angiography with prospective ECG-triggering impact on total effective radiation dose and diagnostic accuracy

RATIONALE AND OBJECTIVES

To determine the impact of additional coronary calcium scoring on total effective radiation dose and diagnostic accuracy of low-dose computed tomography coronary angiography (CTCA) with prospective electrocardiogram (ECG) triggering.

MATERIALS AND METHODS

Sixty-one consecutive patients underwent 64-slice CTCA using prospective ECG triggering, calcium scoring, and invasive quantitative coronary angiography, the latter served as standard of reference. Diagnostic accuracy was calculated for CTCA, calcium scoring, and for the combination of both. Receiver operator characteristic analyses were performed to determine cutoffs for prediction of significant coronary artery stenoses.

RESULTS

Mean effective radiation dose was 2.1 + or - 0.7 mSv (range, 1.0-3.3 mSv) for CTCA and 1.1 + or - 0.1 mSv (range, 0.9-1.4 mSv) for calcium scoring. Per-patient sensitivity, specificity, positive predictive value, and negative predictive value were 100%, 85.7%, 89.2%, and 100% for CTCA, and 72.7%, 82.1%, 82.8%, and 71.9% for calcium scoring. Adding calcium-scoring with a cutoff at 133 in patients aged >50.7 years with nondiagnostic CTCA improved the respective values of diagnostic accuracy of the entire study population to 100%, 96.4%, 97.1%, and 100%; the added value of calcium scoring was confined to only three patients (5%), who were reclassified from false positive to true negative.

CONCLUSION

Specificity and PPV of low-dose CTCA may be further improved by combining it with coronary calcium scoring. However, only a fraction of patient may benefit, whereas exposing the entire population to more than 50% increase in effective radiation dose.

Ultrafast nuclear myocardial perfusion imaging on a new gamma camera with semiconductor detector technique: first clinical validation

PURPOSE

To assess the diagnostic performance of a novel ultrafast cardiac gamma camera with cadmium-zinc-telluride (CZT) solid-state semiconductor detectors for nuclear myocardial perfusion imaging (MPI).

METHODS

The study group comprised 75 consecutive patients (55 men, BMI range 19-45 kg/m(2)) who underwent a 1-day (99m)Tc-tetrofosmin adenosine-stress/rest imaging protocol. Scanning was performed first on a conventional dual-detector SPECT gamma camera (Ventri, GE Healthcare) with a 15-min acquisition time each for stress and rest. All scans were immediately repeated on an ultrafast CZT camera (Discovery 530 NMc, GE Healthcare) with a 3-min scan time for stress and a 2-min scan time for rest. Clinical agreement (normal, ischaemia, scar) between CZT and SPECT was assessed for each patient and for each coronary territory using SPECT MPI as the reference standard. Segmental myocardial tracer uptake values (percent of maximum) using a 20-segment model and left ventricular ejection fraction (EF) values obtained using CZT were compared with those obtained using conventional SPECT by intraclass correlation and by calculating Bland-Altman limits of agreement.

RESULTS

There was excellent clinical agreement between CZT and conventional SPECT on a per-patient basis (96.0%) and on a per-vessel territory basis (96.4%) as shown by a highly significant correlation between segmental tracer uptake values (r=0.901, p<0.001). Similarly, EF values for both scanners were highly correlated (r=0.976, p<0.001) with narrow Bland-Altman limits of agreement (-5.5-10.6%).

CONCLUSION

The novel CZT camera allows a more than fivefold reduction in scan time and provides clinical information equivalent to conventional standard SPECT MPI.

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 gamma-camera using a novel cadmium-zinc-telluride (CZT) solid-state detector technology.

METHODS

Twenty patients (17 male; BMI range, 21.7-35.5 kg/m(2)) underwent 1-d (99m)Tc-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 gamma-camera.

Coronary CT angiography and myocardial perfusion imaging to detect flow-limiting stenoses: a potential gatekeeper for coronary revascularization?

AIMS

To evaluate the diagnostic accuracy of a combined non-invasive assessment of coronary artery disease with coronary CT angiography (CTA) and myocardial perfusion imaging (MPI) for the detection of flow-limiting coronary stenoses and its potential as a gatekeeper for invasive examination and treatment.

METHODS AND RESULTS

In 78 patients (mean age 65 +/- 9 years) referred for coronary angiography (CA), additional CTA and MPI (using single-photon emission-computed tomography) were performed and the findings not communicated. Detection of flow-limiting stenoses (justifying revascularization) by the combination of CTA and MPI (CTA/MPI) was compared with the combination of quantitative coronary angiography (QCA) plus MPI (QCA/MPI), which served as standard of reference. The findings of both combinations were related to the treatment strategy (revascularization vs. medical treatment) chosen in the catheterization laboratory based on the CA findings. Sensitivity, specificity, positive and negative predictive value, and accuracy of CTA/MPI for the detection of flow-limiting coronary stenoses were 100% each. More than half of revascularization procedures (21/40, 53%) was performed in patients without flow-limiting stenoses and 76% (47/62) of revascularized vessels were not associated with ischaemia on MPI.

CONCLUSION

The combined non-invasive approach CTA/MPI has an excellent accuracy to detect flow-limiting coronary stenoses compared with QCA/MPI and its use as a gatekeeper appears to make a substantial part of revascularization procedures redundant.

Long-term prognostic value of 13N-ammonia myocardial perfusion positron emission tomography added value of coronary flow reserve

OBJECTIVES

The goal of this study was to assess the predictive value of myocardial perfusion imaging with (13)N-ammonia positron emission tomography (PET) and coronary flow reserve (CFR) on long-term prognosis in patients with suspected myocardial ischemia.

BACKGROUND

No prognostic data exist on the predictive value of CFR and (13)N-ammonia PET.

METHODS

Perfusion and CFR were assessed in 256 patients using (13)N-ammonia PET, and follow-up was obtained in 245 (96%) patients. Sixteen early revascularized patients were excluded and 229 were assigned to normal versus abnormal perfusion or normal versus abnormal CFR (<2.0). Major adverse cardiac events (MACE) (cardiac death, nonfatal myocardial infarction, late revascularization, or hospitalization for cardiac reasons) were assessed using the Kaplan-Meier method. Cox proportional hazard regression was used to identify independent predictors for cardiac events.

RESULTS

During follow-up (5.4 +/- 2.2 years), 78 patients had at least 1 cardiac event, including 29 cardiac deaths. Abnormal perfusion (n = 126) was associated with a higher incidence of MACE (p < 0.001) and cardiac death (p < 0.05). In patients with normal perfusion, abnormal CFR was independently associated with a higher annual event rate over 3 years compared with normal CFR for MACE (1.4% vs. 6.3%; p < 0.05) and cardiac death (0.5% vs. 3.1%; p < 0.05). In abnormal perfusion, CFR remained predictive throughout the 10-year follow-up (p < 0.001).

CONCLUSIONS

Perfusion findings in (13)N-ammonia PET and CFR are strong outcome predictors. CFR allows further risk stratification, suggesting a "warranty" period of 3 years if normal CFR is associated with normal perfusion. Conversely, in patients with abnormal perfusion, an impaired CFR has added value for predicting adverse outcomes.

First head-to-head comparison of effective radiation dose from low-dose 64-slice CT with prospective ECG-triggering versus invasive coronary angiography

BACKGROUND

Reduction of radiation burden of multidetector computed tomography coronary angiography (CTCA) has remained an important task.

OBJECTIVE

To compare effective radiation dose of low-dose 64-slice CTCA using prospective ECG-triggering versus diagnostic invasive coronary angiography (CA).

METHODS

42 patients referred for elective invasive CA owing to suspected coronary artery disease (CAD) were prospectively enrolled to undergo a low-dose CTCA without calcium scoring within the same day before CA. Dose-area product of diagnostic invasive CA and dose-length product of CTCA were measured, converted into effective radiation dose and compared using Mann-Whitney U tests. In addition, accuracy of CTCA to detect CAD (coronary artery narrowing > or =50%) was assessed using invasive CA as standard of reference. On an intention-to-diagnose basis all non-evaluative vessels were included in the analysis and censored as positive.

RESULTS

The estimated mean effective radiation dose was 8.5 (4.4) mSv (range 1.4-20.5 mSv) for diagnostic invasive CA, and 2.1 (0.7) mSv (range 1.0-3.3 mSv) for CTCA (p<0.001). 19 patients (42.9%) had no CAD by invasive CA. 40 (95.2%) patients have been correctly classified as having CAD (23/23) or no CAD (17/19). Over 97% (551/567) of segments were evaluable. Vessel-based analysis revealed sensitivity, specificity, positive and negative predictive value of 94.2% (CI 0.8% to 1.0%), 94.8% (CI 09% to 1.0%), 89.0% (CI 0.8% to 1.0%), 97.4% (CI 09% to 1.0%) and an accuracy of 94.6%.

CONCLUSIONS

Low dose CTCA allows evaluation of CAD with high accuracy, but delivers a significantly less effective radiation dose to patients compared to diagnostic invasive CA.

Determinants of vessel contrast in BMI-adapted low dose CT coronary angiography with prospective ECG-triggering

We evaluated the determinants of vessel contrast in prospectively ECG-triggered CT coronary angiography (CTCA). Seventy patients underwent low-dose CTCA using body mass index (BMI)-adapted tube parameters and a fixed contrast material bolus. Contrast to noise ratio (CNR) was calculated from contrast (between coronaries and perivascular tissue) and image noise (standard deviation of aortic attenuation). Cardiac output (CO) was calculated from gated (99m)Tc-tetrofosmin-SPECT. Mean radiation dose was 2.13 +/- 0.69 mSv. Image noise was not affected by BMI (r = 0.1, P = 0.36), while CNR was inversely related to body surface area (BSA) (r = -0.5, P < 0.001) and CO (r = -0.45, P < 0.001). After successfully overcoming the impact of BMI on image noise by adapting tube parameters, CNR mainly depends on coronary vessel contrast. The latter reflects the dilution of the contrast material by blood volume and CO, which are both correlated to BSA. Therefore, BSA adapted contrast administration may help to compensate for this effect.

Low-dose CT coronary angiography using prospective ECG-triggering: impact of mean heart rate and heart rate variability on image quality

RATIONALE AND OBJECTIVES

The aim of this study was to evaluate the effect of mean heart rate (HR) and HR variability on image quality in low-dose computed tomographic coronary angiography (CTCA) using prospective electrocardiographic (ECG) triggering.

MATERIALS AND METHODS

One hundred thirty-six consecutive patients were scheduled for low-dose CTCA using prospective ECG triggering. The image quality of all coronary segments was rated on a 5-point scale by two independent readers (scores of 1-3 were considered diagnostic, and scores of 4 and 5 were considered nondiagnostic). Intravenous beta blockers were administered targeting HR < 65 beats/min before scanning, but not if HR increased during scanning.

RESULTS

After the exclusion of seven patients because of arrhythmia (n = 4) or mean HRs > 65 beats/min despite using beta blockers (n = 3), 129 patients underwent computed tomographic scanning. The estimated mean effective radiation dose was 2.2 +/- 0.7 mSv (range, 1.1-3.5). The mean HR during scanning was 58.4 +/- 6.6 beats/min (range, 44.2-80.1), with a variability of 1.6 +/- 1.0 beats/min (range, 0.2-5.3). Mean HR (r = 0.49, P < .001) but not mean HR variability (r = 0.14) was related to image quality. Nondiagnostic image quality on CTCA was found in 5% of the coronary segments in 21 of 129 patients. However, on receiver-operating characteristic analysis, a cutoff HR of 62 beats/min was determined, below which nondiagnostic segments were significantly less frequent (2% vs 14%, P < .001).

CONCLUSION

Prospective triggering allows low-dose CTCA but requires a low HR. Because a low HR offers a prolonged diastole, widening the optimal phase for scanning, HR variability seems to have a negligible impact on image quality.

Accuracy of low-dose computed tomography coronary angiography using prospective electrocardiogram-triggering: first clinical experience

AIMS

To evaluate the accuracy of low-dose computed tomography coronary angiography (CTCA) using prospective ECG-triggering for the assessment of coronary artery disease (CAD).

METHODS AND RESULTS

A total of 30 patients (19 males, 11 females, mean age 58.8 +/- 9.9 years) underwent low-dose CTCA and invasive coronary angiography (CA) [median 2 days (0, 41)]. Before CT scanning, intravenous beta-blocker was administered in 18 of 30 patients as heart rate (HR) was >65 b.p.m., achieving a mean HR of 55.7 +/- 7.9 b.p.m. CAD was defined as coronary artery narrowing > or =50%, using CA as standard of reference. The estimated mean effective radiation dose was 2.1 +/- 0.7 mSv (range: 1.0-3.3), yielding 96.0% (383/399) of evaluable segments. On an intention-to-diagnose-base, all non-evaluative segments were included in the analysis. Vessels with a non-evaluative segment and no further finding were censored as false positive. Patient-based analysis revealed sensitivity, specificity, positive predictive value, and negative predictive value of 100, 83.3, 90.0, and 100%, respectively. The respective values per vessel were 100, 88.9, 85.7, and 100%, respectively.

CONCLUSION

Prospective ECG-triggering allows low-dose CTCA and provides high diagnostic accuracy in the assessment of CAD in patients with stable sinus rhythm and a low heart rate.

Cardiac fusion imaging with low-dose computed tomography using prospective electrocardiogram gating

In a 66-year-old patient with prolonged episodes of chest pain, catheter angiography revealed total occlusions of the right coronary artery and the distal circumflex artery (CX) as well as 2 sequential significant stenoses in the proximal CX and one significant stenosis in the proximal left anterior descending artery (LAD). To identify the culprit lesions with their respective territory, noninvasive assessment of viability was performed by F-18 FDG positron emission tomography (PET) and fused with a low-dose computed tomography coronary angiography using prospective electrocardiogram gating. Fused PET/computed tomography coronary angiography images demonstrated a large scar in the inferior myocardium, corresponding to the total occlusion in the right coronary artery, viable myocardium in the territory of the CX, and infarcted scar tissue with partially preserved viability in the anterior myocardium, corresponding to the presumably recanalized lesion in the LAD. The patient was scheduled for revascularization of the lesions in the LAD and the CX to reverse dysfunctional but viable myocardial segments.

Comparison of diagnostic accuracy of 64-slice computed tomography coronary angiography in patients with low, intermediate, and high cardiovascular risk

RATIONALE AND OBJECTIVES

The aim of this study was to compare the diagnostic accuracy of 64-slice computed tomographic coronary angiography (CTCA) in groups of patients with low, intermediate, and high risk for coronary artery disease (CAD) events.

MATERIALS AND METHODS

The institutional review board approved this study; written informed consent was obtained from all patients. Eighty-eight consecutive patients with suspected CAD (40 women; mean age, 64.3 +/- 9.4 years; range, 39-82) underwent CTCA, calcium scoring, and invasive coronary angiography and were grouped according to their Framingham 10-year risk for hard coronary events into low (<10%), intermediate (10%-20%), and high (>20%) risk categories. Significant stenoses (luminal diameter narrowing > or =50%) were assessed on an intention-to-diagnose-basis; no coronary segment was excluded and nonevaluative segments were rated false positive. To determine differences between groups, Kruskal-Wallis tests were performed for individually determined values of diagnostic performance.

RESULTS

Per-patient sensitivity, specificity, negative predictive, and positive predictive values were 90.0%, 79.2%, 95.0%, and 64.3%, respectively, with low (n = 34), 87.5%, 92.3%, 85.7%, and 93.3%, respectively, with intermediate (n = 29), and 100%, 75.0%, 100%, and 89.5%, respectively, with high risk (n = 25), with a trend toward higher positive predictive value (P = .07). Per-segment negative predictive value was lower with high pretest probability (P < .01). Mean calcium-score units were 90, 220, and 312 (P = .23), and the prevalence of CAD was 29.4%, 55.2%, and 68.0% (P < .01) with low, intermediate, and high risk.

CONCLUSION

Sensitivity and specificity of CTCA are not influenced by the prevalence of CAD, whereas the negative predictive value is lower and the positive predictive value tends to be higher in patients with a high prevalence of CAD.

Coronary 64-slice CT angiography predicts outcome in patients with known or suspected coronary artery disease

The aim of this study was to assess the prognostic value of 64-slice CT angiography (CTA) in patients with known or suspected coronary artery disease (CAD). Sixty-four-slice coronary CTA was performed in 220 patients [mean age 63 +/- 11 years, 77 (35%) female] with known or suspected CAD. CTA images were analyzed with regard to the presence and number of coronary lesions. Patients were followed-up for the occurrence of the following clinical endpoints: death, nonfatal myocardial infarction, unstable angina, and coronary revascularization. During a mean follow-up of 14 +/- 4 months, 59 patients (27%) reached at least one of the predefined clinical endpoints. Patients with abnormal coronary arteries on CTA (i.e., presence of coronary plaques) had a 1st-year event rate of 34%, whereas in patients with normal coronary arteries no events occurred (event rate, 0%, p < 0.001). Similarly, obstructive lesions (> or =50% luminal narrowing) on CTA were associated with a high first-year event rate (59%) compared to patients without stenoses (3%, p < 0.001). The presence of obstructive lesions was a significant independent predictor of an adverse cardiac outcome. Sixty-four-slice CTA predicts cardiac events in patients with known or suspected CAD. Conversely, patients with normal coronary arteries on CTA have an excellent mid-term prognosis.