Evaluation of ischaemia in obese patients: feasibility and accuracy of a low-dose protocol with a cadmium-zinc telluride camera

Improving multi-pinhole CZT myocardial perfusion imaging specificity without changing sensibility by using adapted filter parameters

BACKGROUND

Meta-analysis show the diagnostic performance of cardiac dedicated multi-pinhole cadmium-zinc-telluride myocardial perfusion imaging (MPI) with a sensibility around 0.9 and a specificity around 0.7. The aim of the present study is to explore a simple method to generate less artefact on MPI using single photon emission computed tomography (SPECT) and to enhance specificity without changing sensibility.

RESULTS

From October 2018 to March 2019, 200 patients who underwent SPECT with [99mTc]Tc-tetrofosmin were prospectively recruited: 100 patients with ischemia or necrosis diagnosis (first arm), and 100 patients with myocardial reversible SPECT artefact (second arm). Each SPECT was explored using two image process based on a Butterworth prefilter and post-filter: the original image processing (reconstruction A) with a cut-off frequency equals to 37% of the Nyquist frequency and order equals to 7, and a second image processing (reconstruction B) with a cut-off frequency equals to 25% of the Nyquist frequency and order equals to 5. For each patient, sum stress or rest score with and without septum (SSRS and SSRSws) were calculated with the two reconstructions. No significant statistical difference between SSRSa and SSRSb was identified for the first arm (P = 0.54) and the relative difference ∆r was - 0.5 ± 11.1% (95% CI - 2.7 to 1.7). We found a significant statistical difference between SSRSa and SSRSb for the second arm (p < 0.0001) and the relative difference ∆r was 69.7 ± 16.2% (95% CI 66.6-72.9).

CONCLUSION

In conclusion, using a Butterworth prefilter and post-filter cut-off frequency equal to 25% of the Nyquist frequency before iterative reconstruction generates less artefact and improves myocardial SPECT specificity without affecting sensibility compared with the original reconstruction.

Diagnostic performance of IQ·SPECT with high-speed scanning: A preliminary quality control study in obese patients

BACKGROUND

IQ·SPECT is a recently introduced collimator design for myocardial perfusion imaging (MPI). Little data exist on use of this collimator type in obese patients, particularly Class 2 or 3 [body mass index (BMI) > 35 kg/m2].

METHODS

Two consecutive rest-stress MPI scans were prospectively acquired using a conventional collimator and IQ·SPECT (acquisition times of 20 and 7 minutes, respectively) in 20 patients with a BMI of >30 kg/m2. Assigned by two blinded, independent readers, image quality (on a 5-point scale) and metrics of myocardial perfusion [summed stress score (SSS), summed rest score (SRS) and summed difference score (SDS)] were compared. Software-based left ventricular ejection fraction (EF) was also correlated.

RESULTS

Mean BMI was 39.6 ± 7.6 kg/m2. Class 2 or 3 obesity was present in 12 patients (BMI, 44.1 ± 6.8 kg/m2). Gated/non-gated images from IQ·SPECT revealed fair to good quality scores (median ≥ 3.25), which were inferior to the conventional collimator (median ≥ 4.0; P ≤ 0.01). Significant correlative indices were achieved when comparing IQ·SPECT and conventional collimators for EF values (r = 0.86, P < 0.01), SSS (r = 0.75, P < 0.0001) and SRS (r = 0.60, P < 0.005), but not for SDS (r = 0.15).

CONCLUSION

IQ·SPECT was comparable to conventional SPECT in obese patients. The reduced acquisition time of IQ·SPECT may allow for improved throughput with no loss in diagnostic accuracy.

Comparison between N13NH3-PET and 99mTc-Tetrofosmin-CZT SPECT in the evaluation of absolute myocardial blood flow and flow reserve

BACKGROUND

PET/CT is the standard for quantitative assessments of myocardial blood flow (MBF), but it requires short-lived-tracers, costly, and not widely available. SPECT with Cadmium Zinc Telluride (CZT) detectors allows dynamic acquisition and quantitation of MBF. The study aims were to compare MBF measurements by 99mTc-tetrofosmin-CZT to N13NH3 PET/CT after regadenoson-induced coronary hyperemia and to evaluate the effect of attenuation correction (AC).

METHODS

54 patients were evaluated at rest and during vasodilation by 99mTc-tetrofosmin-CZT and N13NH3 PET/CT within 2 weeks. MBF and MBF reserve (MFR) were measured by CZT with or without AC (NAC).

RESULTS

The global rest MBF was 0.76 ± 0.19 mL/min/gr by PET and 0.76 ± 0.24 by AC-CZT (P = NS) and 1.14 ± 0.4 by NAC-CZT (P < 0.001 vs PET and AC-CZT). Stress MBF was higher when measured by PET than AC-CZT (1.87 ± 0.45 vs 1.62 ± 0.68 mL/min/gr, P < 0.0008), but lower than NAC-CZT (2.36 ± 1.1, P < 0.0003). The MBF reserve ratio (MFR) was higher by PET than AC-CZT (2.52 ± 0.56 vs 2.22 ± 1 (P < 0.009) and NAC-CZT (2.18 ± 1.0, P < 0.004). Linear regression was better between PET (MFR and stress MBF) and AC-CZT than between PET and NAC-CZT. ROC curve analysis showed the significant ability of AC-CZT to predict MFR < 2 and stress MBF < 1.7 (AUC = 0.75 and 0.82 respectively) and to differentiate between normal and CAD patients (AUC = 0.747 and 0.892 for MFR and stress MBF, respectively).

CONCLUSIONS

Our data show a reasonable correlation between MBF and MFR measured by N13NH3-PET and 99mTc-Tetrofosmin-CZT SPECT. NAC-CZT overestimates MBF. AC is recommended when using CZT for measuring MBF.

Left ventricular mechanical dyssynchrony assessment in obese patients using the cadmium-zinc telluride SPECT camera

The use of phase analysis techniques to assess left ventricular mechanical dyssynchrony (LVMD) has been well documented. However, artifacts have reduced the accuracy of the assessment due to soft tissue attenuation, so little information is available about the effects of obesity on LVMD. The aim of this study was to evaluate LVMD in patients with simple obesity by SPECT with a new cadmium-zinc telluride (CZT) detector and to explore the effects of obesity on left ventricular wall motion. We retrospectively analyzed 95 patients with myocardial perfusion imaging (MPI) images without perfusion defects, of which 55 were diagnosed with simple obesity (BMI > 30), and 40 non-obese patients (BMI < 25) matched for age and sex were used as controls. The five-point method was used to analyze the MPI images of the two groups, and the complete cardiac function parameters including phase bandwidth (PBW) and phase standard deviation (PSD) were obtained. Although the PBW values of the two groups were within the normal range (cut-off value > 90°), the PBW (35.4 ± 28 vs 24.9 ± 7.5, P < .001; 36.6 ± 18.4 vs 28.7 ± 9.1, P = 0.01) and PSD (8.7 ± 7.6 vs 5.9 ± 2, P = 0.02; 9.2 ± 4.9 vs 7.1 ± 2.7, P = 0.01) of the obese group were larger than the control group under both stressing and resting, and the difference was statistically significant. CZT-SPECT can effectively assess LVMD in obese patients, and they are more likely to develop LVMD, which may be related to their left ventricular volume.

CMR stress testing in a patient with morbid obesity (BMI 58 kg/m2) and suspected coronary artery disease

Background

Severe obesity is asscociated with an increased risk of coronary artery disease (CAD) but non-invasive cardiac imaging modalities have important technical limits.

Case presentation

We report a case of a 58-year old patient with suspected CAD and severely elevated BMI of 58 kg/m².

Conclusions

Stress-CMR was able to non-invasively stratify risk with good imaging quality despite the body dimensions of the patient.

The radiation dose to overweighted patients undergoing myocardial perfusion SPECT can be significantly reduced: validation of a linear weight-adjusted activity administration protocol

BACKGROUND

Large body size can cause a higher proportion of emitted photons being attenuated within the patient. Therefore, clinical myocardial perfusion SPECT (MPS) protocols often include unproportionally higher radioisotope activity to obese patients. The aim was to evaluate if a linear weight-adjusted low-dose protocol can be applied to obese patients and thereby decrease radiation exposure.

METHODS AND RESULT

Two hundred patients (>110 kg, BMI 18-41, [n = 69], ≤ 110 kg, BMI 31-58, [n = 131]) underwent 99mTc-tetrofosmin stress examination on a Cadmium Zinc Telluride or a conventional gamma camera using new generations of reconstruction algorithm (Resolution Recovery). Patients <110 kg were administered 2.5 MBq/kg, patients between 110 and 120 kg received 430 MBq and patients >120 kg received 570 MBq according to clinical routine. Patients >110 kg had 130% total number of counts in the images compared to patients <110 kg. Recalculating the counts to correspond to an administered activity of 2.5 MBq/kg resulted in similar number of counts across the groups. Image analyses in a subgroup with images corresponding to high activity and 2.5 MBq/kg showed no difference in image quality or ischemia quantification.

CONCLUSION

Linear low-dose weight-adjusted protocol of 2.5 MBq/kg in MPS can be applied over a large weight span without loss of counts or image quality, resulting in a significant reduction in radiation exposure to obese patients.

Performance of cardiac cadmium-zinc-telluride gamma camera imaging in coronary artery disease: a review from the cardiovascular committee of the European Association of Nuclear Medicine (EANM)

The trade-off between resolution and count sensitivity dominates the performance of standard gamma cameras and dictates the need for relatively high doses of radioactivity of the used radiopharmaceuticals in order to limit image acquisition duration. The introduction of cadmium-zinc-telluride (CZT)-based cameras may overcome some of the limitations against conventional gamma cameras. CZT cameras used for the evaluation of myocardial perfusion have been shown to have a higher count sensitivity compared to conventional single photon emission computed tomography (SPECT) techniques. CZT image quality is further improved by the development of a dedicated three-dimensional iterative reconstruction algorithm, based on maximum likelihood expectation maximization (MLEM), which corrects for the loss in spatial resolution due to line response function of the collimator. All these innovations significantly reduce imaging time and result in a lower patient's radiation exposure compared with standard SPECT. To guide current and possible future users of the CZT technique for myocardial perfusion imaging, the Cardiovascular Committee of the European Association of Nuclear Medicine, starting from the experience of its members, has decided to examine the current literature regarding procedures and clinical data on CZT cameras. The committee hereby aims 1) to identify the main acquisitions protocols; 2) to evaluate the diagnostic and prognostic value of CZT derived myocardial perfusion, and finally 3) to determine the impact of CZT on radiation exposure.

Normal Databases for the Relative Quantification of Myocardial Perfusion

PURPOSE OF REVIEW

Myocardial perfusion imaging (MPI) with SPECT is performed clinically worldwide to detect and monitor coronary artery disease (CAD). MPI allows an objective quantification of myocardial perfusion at stress and rest. This established technique relies on normal databases to compare patient scans against reference normal limits. In this review, we aim to introduce the process of MPI quantification with normal databases and describe the associated perfusion quantitative measures that are used.

RECENT FINDINGS

New equipment and new software reconstruction algorithms have been introduced which require the development of new normal limits. The appearance and regional count variations of normal MPI scan may differ between these new scanners and standard Anger cameras. Therefore, these new systems may require the determination of new normal limits to achieve optimal accuracy in relative myocardial perfusion quantification. Accurate diagnostic and prognostic results rivaling those obtained by expert readers can be obtained by this widely used technique.

SUMMARY

Throughout this review, we emphasize the importance of the different normal databases and the need for specific databases relative to distinct imaging procedures. use of appropriate normal limits allows optimal quantification of MPI by taking into account subtle image differences due to the hardware and software used, and the population studied.

Feasibility and diagnostic accuracy of exercise treadmill nitrogen-13 ammonia PET myocardial perfusion imaging of obese patients

BACKGROUND

Treadmill exercise nitrogen-13 ((13)N)-ammonia positron emission tomography (PET) has logistical challenges and limited literature. We aimed to assess its feasibility, image quality, and diagnostic accuracy in obese and nonobese patients.

METHODS AND RESULTS

Between 2009 and 2012, 10,804 patients were referred for myocardial perfusion imaging, including 300 for treadmill PET, of whom 265 were included in this study. Treadmill testing and PET were performed using standard procedures. Image quality, perfusion, and summed stress score (SSS) were assessed. Invasive coronary angiography was performed within 90 days of PET in 43 patients. Mean ± SD body mass index (BMI) was 35.7 ± 7.7 kg/m(2) (range 19.5-63.5 kg/m(2)). Feasibility of treadmill (13)N-ammonia PET was 100%. Exercise duration was less for obese patients than nonobese patients (P < .001). Image quality was rated good for 96.9% of obese and 100% of nonobese patients. For all patients, sensitivity was 86.4% and specificity was 74.4%. Diagnostic accuracy did not change significantly with increasing BMI. SSS remained significant in predicting angiographic coronary artery disease after adjustment for age, sex, and Duke treadmill score.

CONCLUSIONS

Treadmill (13)N-ammonia PET is highly feasible, yields good image quality, and has moderately high diagnostic accuracy in a small subset of obese and nonobese patients who are deemed able to perform treadmill exercise.

Feasibility of SPECT myocardial perfusion imaging in the super-obese using a multi-head semiconductor camera with attenuation correction

BACKGROUND

Obesity is not only associated with an increased risk of coronary artery disease, but also decreases the accuracy of many diagnostic modalities pertinent to this disease. Advances in myocardial perfusion imaging (MPI) have mitigated somewhat the effects of obesity, although the feasibility of MPI in the super-obese (defined as a BMI > 50) is currently untested. We undertook this study to assess the practicality of MPI in the super-obese using a multi-headed solid-state gamma camera with attenuation correction.

METHODS

We retrospectively identified consecutive super-obese patients referred for MPI at our institution. The images were interpreted by 3 blinded, experienced readers and graded for quality and diagnosis, and subjectively evaluated the contribution of attenuation correction. Clinical follow-up was obtained from review of medical records.

RESULTS

72 consecutive super-obese patients were included. Their BMI ranged from 50 to 67 (55.7 ± 5.1). Stress image quality was considered good or excellent in 45 (63%), satisfactory in 24 (33%), poor in 3 (4%), and uninterpretable in 0 patients. Rest images were considered good or excellent in 34 (49%), satisfactory in 23 (33%), poor in 13 (19%), and uninterpretable in 0 patients. Attenuation correction changed the interpretation in 34 (47%) of studies.

CONCLUSIONS

MPI is feasible and provides acceptable image quality for super-obese patients, although it may be camera and protocol dependent.

Quantitative high-efficiency cadmium-zinc-telluride SPECT with dedicated parallel-hole collimation system in obese patients: results of a multi-center study

BACKGROUND

Obesity is a common source of artifact on conventional SPECT myocardial perfusion imaging (MPI). We evaluated image quality and diagnostic performance of high-efficiency (HE) cadmium-zinc-telluride parallel-hole SPECT MPI for coronary artery disease (CAD) in obese patients.

METHODS AND RESULTS

118 consecutive obese patients at three centers (BMI 43.6 ± 8.9 kg·m(-2), range 35-79.7 kg·m(-2)) had upright/supine HE-SPECT and invasive coronary angiography > 6 months (n = 67) or low likelihood of CAD (n = 51). Stress quantitative total perfusion deficit (TPD) for upright (U-TPD), supine (S-TPD), and combined acquisitions (C-TPD) was assessed. Image quality (IQ; 5 = excellent; < 3 nondiagnostic) was compared among BMI 35-39.9 (n = 58), 40-44.9 (n = 24) and ≥45 (n = 36) groups. ROC curve area for CAD detection (≥50% stenosis) for U-TPD, S-TPD, and C-TPD were 0.80, 0.80, and 0.87, respectively. Sensitivity/specificity was 82%/57% for U-TPD, 74%/71% for S-TPD, and 80%/82% for C-TPD. C-TPD had highest specificity (P = .02). C-TPD normalcy rate was higher than U-TPD (88% vs 75%, P = .02). Mean IQ was similar among BMI 35-39.9, 40-44.9 and ≥45 groups [4.6 vs 4.4 vs 4.5, respectively (P = .6)]. No patient had a nondiagnostic stress scan.

CONCLUSIONS

In obese patients, HE-SPECT MPI with dedicated parallel-hole collimation demonstrated high image quality, normalcy rate, and diagnostic accuracy for CAD by quantitative analysis of combined upright/supine acquisitions.

Model-based correction for scatter and tailing effects in simultaneous 99mTc and 123I imaging for a CdZnTe cardiac SPECT camera

An advantage of semiconductor-based dedicated cardiac single photon emission computed tomography (SPECT) cameras when compared to conventional Anger cameras is superior energy resolution. This provides the potential for improved separation of the photopeaks in dual radionuclide imaging, such as combined use of (99m)Tc and (123)I . There is, however, the added complexity of tailing effects in the detectors that must be accounted for. In this paper we present a model-based correction algorithm which extracts the useful primary counts of (99m)Tc and (123)I from projection data. Equations describing the in-patient scatter and tailing effects in the detectors are iteratively solved for both radionuclides simultaneously using a maximum a posteriori probability algorithm with one-step-late evaluation. Energy window-dependent parameters for the equations describing in-patient scatter are estimated using Monte Carlo simulations. Parameters for the equations describing tailing effects are estimated using virtually scatter-free experimental measurements on a dedicated cardiac SPECT camera with CdZnTe-detectors. When applied to a phantom study with both (99m)Tc and (123)I, results show that the estimated spatial distribution of events from (99m)Tc in the (99m)Tc photopeak energy window is very similar to that measured in a single (99m)Tc phantom study. The extracted images of primary events display increased cold lesion contrasts for both (99m)Tc and (123)I.

Impact of injection dose, post-reconstruction filtering, and collimator choice on image quality of myocardial perfusion SPECT using cadmium-zinc telluride detectors in the rat

Background

The aims of this study were (1) to evaluate the impact of injection dose, post-reconstruction filtering, and collimator choice on image quality of myocardial perfusion single-photon emission computed tomography (SPECT) using cadmium-zinc telluride (CZT) detectors and (2) to determine how these factors affect measured infarct size in the in vivo rat.

Methods

Twenty-four healthy and eight myocardial infarct (MI) rats underwent myocardial perfusion SPECT imaging after injection of various doses (25 to 200 MBq) of ^99mTc-tetrofosmin using a standard (STD) five-pinhole collimator and high-sensitivity (HS) five-pinhole collimator. Image quality score, contrast-to-noise ratio, sharpness index, coefficient of variation (CV), and measured defect size were assessed as measures of image quality.

Results

The image quality score increased and CV decreased as a function of injection dose. The contrast-to-noise ratio increased and sharpness index decreased as a function of Gaussian kernel size. When STD and HS were compared, HS tended to show higher image quality score and lower CV than STD. The use of post-reconstruction filter significantly improved image quality score and lessened CV. The reproducibility of defect size measurements, as assessed by intraclass correlation coefficients (ICC), between the collimators was poor-to-moderate (ICC = −0.31~0.57) with low (25 MBq) injection dose and with no or light (1.5-mm kernel size) filtering, whereas it was good-to-excellent (ICC = 0.75~0.97) with high (200 MBq) dose or low dose with heavy (2.5-mm kernel size) filtering. The filtering-related reproducibility was poor (ICC = −0.18~0.17) for STD with low injection dose, whereas it was good-to-excellent (ICC = 0.79~0.89) for HS. Furthermore, there was a filtering-related underestimation of defect size particularly with the use of heavy smoothing.

Conclusions

Appropriate imaging setting is important to obtain high quality images and thereby reliable measurements using a preclinical myocardial SPECT in the rat. When only a low injection dose (25 MBq) is allowed, we would recommend to use HS with light (1.5-mm kernel size) filtering.

Radiation dose and prognosis of ultra-low-dose stress-first myocardial perfusion SPECT in patients with chest pain using a high-efficiency camera

Although SPECT myocardial perfusion imaging (MPI) provides valuable information about patients with chest pain, there is growing concern regarding its radiation burden and lengthy duration. New high-efficiency (HE) cameras and stress-first protocols both offer the potential to markedly reduce radiation. No previous study has assessed outcomes and radiation doses of patients undergoing MPI on an HE-SPECT camera using an ultra-low-dose stress-first protocol.

METHODS

One hundred patients presenting to the emergency department with chest pain who were candidates for stress-first MPI underwent injection of approximately 185 MBq (5 mCi) of (99m)Tc-tetrofosmin at peak stress, followed by supine and prone imaging on an HE-SPECT camera. Same-day rest imaging was performed on patients with any abnormality on imaging after stress. Radiation effective dose was calculated from administered and residual activities. Patients were contacted 3 mo after discharge, and electronic records were accessed to evaluate the need for reevaluation for chest pain, additional imaging, or cardiac events.

RESULTS

Stress-only imaging was performed in 69 patients, for whom radiation effective dose averaged 0.99 mSv and study duration, 117 min. Radiation dose averaged 2.22 mSv over all patients. At 3 mo, 96 patients were free of major adverse cardiac events, repeat hospital chest pain evaluation, and repeat imaging or stress testing. One year after MPI and hospital discharge, all patients were living and without acute coronary syndrome.

CONCLUSION

HE-SPECT stress-only imaging can be performed in more than two thirds of chest pain patients without a high pretest probability of a stress perfusion defect, with excellent prognosis, a radiation dose averaging 1 mSv, and a test duration of less than 2 h.

A performance comparison of novel cadmium-zinc-telluride camera and conventional SPECT/CT using anthropomorphic torso phantom and water bags to simulate soft tissue and breast attenuation

PURPOSES

This study was aimed to compare the physical performances of cadmium-zinc-telluride (CZT) camera and conventional Anger camera. An anthropomorphic torso phantom and water bags to simulate breasts were used to evaluate artifacts arising from soft tissue attenuation.

MATERIALS AND METHODS

Linear source studies were performed to evaluate extrinsic resolution of CZT camera (Discovery NM 530c, GE) and conventional single-photon emission computed tomography (SPECT) Anger camera (Symbia T2, Siemens). Three sets of phantom experiments: cardiac phantom only (phantom H), anthropomorphic torso phantom added (phantom T), and torso phantom with water bags attached (phantom B), with Tc-99m were performed on both scanners. Imaging performances were evaluated through count sensitivity, contrast-to-noise ratio, quantitative sharpness profile, wall thickness, perfusion uniformity (measured by standard deviation of perfusion percentage of 20 segments using quantitative perfusion SPECT (QPS) software, Cedars-Sinai), and visual imaging quality (using 20-segment sum defect scores (SDS) of QPS) for CZT camera, conventional SPECT without and with computed tomography transmission attenuation correction (AC).

RESULTS

CZT cameras had higher extrinsic resolution than conventional SPECT. Myocardium count sensitivity of CZT camera is about threefold of conventional SPECT. Contrast-to-noise ratios and sharpness profiles are higher on CZT camera but degraded while extracardiac soft tissue presented. Myocardial walls measured on CZT images were thicker. Images of CZT had lower SDS, while AC reduced the differences of SDS between CZT and CC. Perfusion images from CZT had the better uniformity than SPECT without or with AC. Breast attenuation was less prominent on CZT camera than conventional SPECT, while inferior and inferolateral segments still suffer marked soft tissue attenuation on CZT camera.

CONCLUSIONS

CZT camera has better physical performance and image quality with less artificial perfusion defects than conventional SPECT. CZT camera also has less breast attenuation than conventional SPECT. However, extracardiac soft tissue may degrade the superior performance of CZT camera, and attenuation correction methods are still needed to solve the attenuation issues in inferior and inferolateral myocardium.

Clinical value of supine and upright myocardial perfusion imaging in obese patients using the D-SPECT camera

PURPOSE

We have assessed whether additional upright imaging increases the confidence of interpretation of stress only supine myocardial perfusion imaging (MPI) in obese patients.

METHODS AND RESULTS

Tc-MIBI stress MPI of 101 consecutive patients (M = 49, 62 ± 12 years) with BMI ≥30 scanned on the D-SPECT cardiac camera were assessed. Images were interpreted as diagnostic or equivocal and the need for a rest study was recorded. Stress supine MPI was interpreted first, then gated and finally upright data were added. Defects on supine but not on upright were defined as artefacts and defects seen on both as abnormal. The total perfusion deficit (TPD) was also quantified. There were 27 normal, 22 abnormal, and 52 equivocal supine scans. The median EF was 52%, unaffecting the need for rest imaging. Upright imaging reclassified 32/52 (62%) equivocal studies as normal and 6/52 (11%) as abnormal (P < 0.001). Rest scan was deemed needed in 74/101 patients on supine vs 42/101 on supine/upright (P < 0.001). Supine TPD was normal in 53 and supine/upright TPD was normal in 70 patients (P < 0.001).

CONCLUSION

Supine stress MPI is inadequate in obese patients. The addition of upright imaging significantly increases the ability to interpret scans as diagnostic and may reduce considerably the need for rest imaging.

Diagnostic performance of low-dose rest/stress Tc-99m tetrofosmin myocardial perfusion SPECT using the 530c CZT camera: quantitative vs visual analysis

BACKGROUND

We set out to develop normal databases and prospectively validate abnormality criteria for a low-dose Tc-99m tetrofosmin myocardial perfusion SPECT protocol using the 530c CZT camera.

METHODS

All patients received 6 mCi rest/20 mCi stress doses of Tc-99m tetrofosmin. Rest and stress images were obtained over 7-9 and 5-7 minutes according to the chest size. Low-dose CT of the chest was obtained on a standalone CT scanner. Forty patients with very low likelihood (LLK) of coronary artery disease (CAD) were used to define the normal count distributions. The abnormality criteria were prospectively validated in 55 patients who had coronary angiography and in 40 patients with LLK of CAD.

RESULTS

The results for quantitative non-attenuation-corrected (AC) and AC analysis and visual analysis were as follows: sensitivity of 79%, 85%, and 92% (P = NS) and specificity of 44%, 75%, and 56% (P = NS), respectively. The normalcy rates for quantitative non-AC and AC analyses and visual analysis were 95%, 98%, and 98% (P = NS).

CONCLUSIONS

We have developed non-AC and AC normal databases for low-dose rest/stress Tc-99m tetrofosmin myocardial perfusion SPECT protocol using the 530c CZT camera. The per-patient diagnostic performance of quantitative analyses is not significantly different from visual analysis by an experienced reader.

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 (201)Tl (84 patients) or (99m)Tc-sestamibi (87 patients) with an Anger or a CZT camera. A predictive model was validated in a group of patients routinely referred for (201)Tl (78 patients) or (99m)Tc-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 (201)Tl than for (99m)Tc-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 (99m)Tc-sestamibi and 30.5 and 13.1ppm for (201)Tl, 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 (99m)Tc-sestamibi and 39 and 91 MBq for (201)Tl, 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 (99m)Tc-sestamibi and in non-obese subjects.

Gender differences in the evaluation of coronary artery disease with a cadmium-zinc telluride camera

PURPOSE

Coronary artery disease remains one of the most significant causes of morbidity and mortality among women. The published literature shows the importance of standard single photon emission computed tomography in the evaluation of women with known or suspected ischaemic heart disease, in terms of target intervention and clinical treatment. The purpose of the present study was to ascertain the diagnostic accuracy of cadmium-zinc-telluride (CZT) myocardial perfusion imaging according to gender, within a prospective database of patients with known or suspected coronary artery disease, using coronary angiography as the reference standard.

METHODS

Included in the study were 309 consecutive patients, of whom 248 were men (80 %), with known or suspected coronary artery disease and who had been referred to our laboratory for stress-rest myocardial perfusion imaging. All patients underwent coronary angiography within 30 days. All patients underwent a single-day stress-rest low-dose ultrafast protocol. Fifteen minutes after the end of the stress (dose range 185 to 222 MBq of (99m)Tc-tetrofosmin), all patients underwent the first scan with an acquisition time of 7 min. The rest scan (dose range 370 to 444 MBq of (99m)Tc-tetrofosmin) was acquired from 30 min to 45 min after injection, with an acquisition time of 6 min. Images were visually inspected, and summed stress scores (SSS) and summed rest scores (SRS) were obtained.

RESULTS

Image quality was graded "good" or better in more than 90 % of patients. On coronary angiography, left main trunk stenosis, left anterior descending artery stenosis, left circumflex artery stenosis and right coronary artery stenosis were seen in 3, 155 , 142 and 131 patients, respectively. In women, the mean SSS and SRS were 8 ± 5 and 3 ± 1, respectively. Semiquantitative regional and global SSS were good discriminants of coronary artery disease, and the overall area under the receiver operator characteristic (ROC) curve was 0.822 (95 % CI 0.685 - 0.959). The value was comparable to that obtained in men (overall ROC area 0.884, 95 % CI 0.836 - 0.933).

CONCLUSION

A low-dose protocol with a CZT camera can be routinely used in women with known or suspected coronary artery disease without loss of accuracy and with lower radiation exposure of the patients.

The Year in Cardiology 2012: imaging, computed tomography, and cardiovascular magnetic resonance

The year of 2012 has seen many significant publications in cardiac imaging, particularly in the modalities of cardiovascular magnetic resonance and cardiac computed tomography. This article will review in brief some of the most important studies with a particular emphasis on the new evidence base for perfusion imaging both by cardiovascular magnetic resonance and computed tomography.