Attenuation-corrected thallium-201 single-photon emission tomography using a gadolinium-153 moving line source: clinical value and the impact of attenuation correction on the extent and severity of perfusion abnormalities

Data Management and Network Architecture Effect on Performance Variability in Direct Attenuation Correction via Deep Learning for Cardiac SPECT: A Feasibility Study

Attenuation correction (AC) is important for accurate interpretation of SPECT myocardial perfusion imaging (MPI). However, it is challenging to perform AC in dedicated cardiac systems not equipped with a transmission imaging capability. Previously, we demonstrated the feasibility of generating attenuation-corrected SPECT images using a deep learning technique (SPECTDL) directly from non-corrected images (SPECTNC). However, we observed performance variability across patients which is an important factor for clinical translation of the technique. In this study, we investigate the feasibility of overcoming the performance variability across patients for the direct AC in SPECT MPI by proposing to develop an advanced network and a data management strategy. To investigate, we compared the accuracy of the SPECTDL for the conventional U-Net and Wasserstein cycle GAN (WCycleGAN) networks. To manage the training data, clustering was applied to a representation of data in the lower-dimensional space, and the training data were chosen based on the similarity of data in this space. Quantitative analysis demonstrated that DL model with an advanced network improves the global performance for the AC task with the limited data. However, the regional results were not improved. The proposed data management strategy demonstrated that the clustered training has potential benefit for effective training.

Direct Image-Based Attenuation Correction using Conditional Generative Adversarial Network for SPECT Myocardial Perfusion Imaging

Attenuation correction (AC) is important for an accurate interpretation and quantitative analysis of SPECT myocardial perfusion imaging. Dedicated cardiac SPECT systems have invaluable efficacy in the evaluation and risk stratification of patients with known or suspected cardiovascular disease. However, most dedicated cardiac SPECT systems are standalone, not combined with a transmission imaging capability such as computed tomography (CT) for generating attenuation maps for AC. To address this problem, we propose to apply a conditional generative adversarial network (cGAN) for generating attenuation-corrected SPECT images (SPECT_GAN ) directly from non-corrected SPECT images (SPECT_NC ) in image domain as a one-step process without requiring additional intermediate step. The proposed network was trained and tested for 100 cardiac SPECT/CT data from a GE Discovery NM 570c SPECT/CT, collected retrospectively at Yale New Haven Hospital.The generated images were evaluated quantitatively through the normalized root mean square error (NRMSE), peak signal to noise ratio (PSNR), and structural similarity index (SSIM) and statistically through joint histogram and error maps. In comparison to the reference CT-based correction (SPECT_CTAC ), NRMSEs were 0.2258±0.0777 and 0.1410±0.0768 (37.5% reduction of errors); PSNRs 31.7712±2.9965 and 36.3823±3.7424 (14.5% improvement in signal to noise ratio); SSIMs 0.9877±0.0075 and 0.9949±0.0043 (0.7% improvement in structural similarity) for SPECT_NC and SPECT_GAN , respectively. This work demonstrates that the conditional adversarial training can achieve accurate CT-less attenuation correction for SPECT MPI, that is quantitatively comparable to CTAC. Standalone dedicated cardiac SPECT scanners can benefit from the proposed GAN to reduce attenuation artifacts efficiently.

Improved diagnostic accuracy of thallium-201 myocardial perfusion single-photon emission computed tomography with CT attenuation correction

BACKGROUND

The benefits of attenuation correction (AC) in technetium-99m myocardial perfusion imaging (MPI) have been well established. However, the value of thallium (Tl-201) AC and routine computed tomography AC (CTAC) were less well established. The aims of this study were to evaluate the diagnostic performance of thallium (Tl-201) MPI with additional CTAC and to determine which participants would benefit most.

METHODS AND RESULTS

A total of 108 consecutive patients who underwent Tl-201 MPI and received coronary angiography within 3 months were enrolled. Diagnostic performance was determined by sensitivity, specificity, and receiver operating characteristic curve analysis. Subgroup analyses were performed using gender and obesity. CTAC improved the area under the curve (0.84 vs. 0.77, P = 0.037 at patient level), primarily due to a significant improvement in specificity (0.78 vs. 0.57, P = 0.013) and no significant difference in sensitivity (0.79 vs. 0.82, P = 0.75). In subgroup analysis, CTAC was most helpful in obese subjects, men, and especially right coronary artery lesions.

CONCLUSIONS

CTAC significantly improved diagnostic performance primarily by increasing the specificity, and the improvements were significantly greater in obese patients and male patients. These findings suggest that CTAC should be applied to Tl-201 MPI as routine clinical practice.

Attenuation correction in myocardial perfusion imaging affects the assessment of infarct size in women with previous inferior infarct

BACKGROUND

Myocardial perfusion imaging is a well-established diagnostic tool in patients with known or suspected coronary artery disease. Numerous clinical trials have shown that attenuation correction (AC) in single photon emission computed tomography (SPECT) improves the diagnostic accuracy of myocardial perfusion imaging over non-AC SPECT, differentiating between scar and attenuation artifacts. We have previously shown that attenuation artifacts produce an overestimation of the size of inferior infarcts in the male population. It is assumed that women are less affected by inferior attenuation artifacts than men.

PURPOSE

The aim of this study is to evaluate the role of AC in the assessment of infarct size in female patients with a history of myocardial inferior infarct.

PATIENTS AND METHODS

We studied a population of 66 consecutive women, with a history of previous inferior myocardial infarct, by SPECT/computed tomography (CT) with 370+370 MBq of technetium-99m labeled compounds by a 2-day stress-rest protocol. Both AC and uncorrected gated-SPECT/CT studies were reconstructed after scatter and motion correction by ordered-subset expectation maximization iterative reconstruction and resolution recovery. The coregistration of the transmission and emission scans was verified for all patients; any misalignment was realigned manually. Uncorrected and corrected SPECT images were analyzed by software QPS/QGS package using a 17-segment model. For each segment, perfusion and wall motion were quantified using a five-point score according to the American Society of Nuclear Cardiology guidelines. Summed stress, summed rest score (SRS), and summed difference score of the inferior left ventricle wall (inferior, inferoseptal, inferolateral, and apical inferior segments) were calculated. A linear correlation was used to assess the relationship between perfusion and the regional wall motion score as determined by uncorrected gated-SPECT.

RESULTS

The results of quantitative analysis of non-AC and CT-AC SPECT images, respectively, were as follows: summed stress score: 9.47±5.01 and 6.58±4.77% (P<0.001); SRS was 6.05±5.02 and 4.14±4.12% (P<0.001); the summed difference score was 2.92±2.74 and 2.52±2.63% (P=NS), respectively. The correlation between corrected and uncorrected SRS and the regional summed wall motion score of the same segment was R=0.31 versus R=0.34.

CONCLUSION

In the female population, like in men, attenuation artifacts affect the calculation of the infarct size of the inferior wall, with overestimation of the infarct size in uncorrected images. The AC regional perfusion score (SRS) better correlates with the regional wall motion score of the inferior wall in women with previous inferior infarct.

CT-based SPECT attenuation correction and assessment of infarct size: results from a cardiac phantom study

RATIONALE

Myocardial perfusion SPECT is a commonly performed, well established, clinically useful procedure for the management of patients with coronary artery disease. However, the attenuation of photons from myocardium impacts the quantification of infarct sizes. CT-Attenuation Correction (AC) potentially resolves this problem. This contention was investigated by analyzing various parameters for infarct size delineation in a cardiac phantom model.

METHODS

A thorax phantom with a left ventricle (LV), fillable defects, lungs, spine and liver was used. The defects were combined to simulate 6 infarct sizes (5-20% LV). The LV walls were filled with 100120 kBq/ml ^99mTc and the liver with 10-12 kBq/ml ^99mTc. The defects were filled with water of 50% LV activity to simulate transmural and non-transmural infarction, respectively. Imaging of the phantom was repeated for each configuration in a SPECT/CT system. The defects were positioned in the anterior as well as in the inferior wall. Data were acquired in two modes: 32 views, 30 s/view, 180° and 64 views, 15 s/view, 360° orbit. Images were reconstructed iteratively with scatter correction and resolution recovery. Polar maps were generated and defect sizes were calculated with variable thresholds (40-60%, in 5% steps). The threshold yielding the best correlation and the lowest mean deviation from the true extents was considered optimal.

RESULTS

AC data showed accurate estimation of transmural defect extents with an optimal threshold of 50% [non attenuation correction (NAC): 40%]. For the simulation of non-transmural defects, a threshold of 55% for AC was found to yield the best results (NAC: 45%). The variability in defect size due to the location (anterior versus inferior) of the defect was reduced by 50% when using AC data indicating the benefit from using AC. No difference in the optimal threshold was observed between the different orbits.

CONCLUSION

Cardiac SPECT/CT shows an improved capability for quantitative defect size assessment in phantom studies due to the positive effects of attenuation correction.

Prognostic value of extracardiac incidental findings on attenuation correction cardiac computed tomography

BACKGROUND

Attenuation corrected computed tomography (CTAC) is often performed to improve the specificity of single-photon emission tomography imaging. Extracardiac incidental findings are frequently observed. It is unclear whether these findings have any prognostic value.

METHODS

Consecutive patients (n = 1139) at a tertiary care center were retrospectively evaluated for incidental findings on CTAC. Clinically significant incidental findings were defined as findings warranting physician follow-up. Information regarding subsequent resource utilization was obtained by chart review. Cox proportional hazard model adjusted for demographic and clinical variables was used to evaluate association of these incidental findings with all-cause and cancer-specific mortality.

RESULTS

A total of 135 (12%) patients with incidental findings were identified, 83 of whom (68%) were newly diagnosed. Lung nodules were the most common finding, present in 92 (68%) patients. Over a median follow-up of 468 days, incidental findings were not significantly associated with increased risk of all-cause mortality (HR 1.34; 95% CI 0.77-2.33, P = 0.29) but was significantly associated with cancer-specific mortality (HR 3.21; 95% CI 1.26-8.14, P = 0.01). This association remained statistically significant when the analysis was limited to newly diagnosed incidental findings. Among patients with incidental findings, follow-up radiographic studies were conducted in 87%, and invasive procedures performed in 32%. Physician office-based follow-up of these findings occurred in 42% of patients and incidental finding-related hospitalization occurred in 14%.

CONCLUSIONS

This study shows that incidental findings are common and were associated with all-cause and cancer-specific mortality but only the later remained statistically significant after multivariable adjustment.

Is computed tomography attenuation correction more efficient than gated single photon emission computed tomography analysis in improving the diagnostic performance of myocardial perfusion imaging in patients with low prevalence of ischemic heart disease?

OBJECTIVE

The purpose of this study was to compare computed tomography (CT)-based attenuation correction (AC) using a hybrid single photon emission computed tomography (SPECT)-CT system and quantitative analysis of wall thickening using gated SPECT with regard to the diagnostic accuracy of myocardial perfusion imaging.

MATERIALS AND METHODS

We prospectively included 70 patients with low prevalence of acute coronary artery disease who underwent a myocardial stress-rest SPECT study. Interpretation was based on supine nongated SPECT data with (AC) or without (NC) CT-based attenuation correction, and on gated SPECT data without attenuation correction (GNC). The scintigraphic diagnosis was obtained using standard automated quantitative analysis software and compared with a 23±14 months' clinical follow-up for 57 patients or with the results of a coronary angiography for 13 patients.

RESULTS

The sensitivity, specificity, and overall accuracy were, respectively, 77, 60, and 63% for NC SPECT, 67, 81, and 79% for AC SPECT, and 69, 98, and 93% for GNC SPECT. The initial diagnosis was modified in about one-third of the cases for both AC and GNC, this rate being independent of any clinical parameter (including BMI) except sex (two to four times more artifact correction in men).

CONCLUSION

Its widespread availability, cost effectiveness, safety in terms of radiation exposure, and ability to significantly improve myocardial perfusion imaging specificity and accuracy make gated SPECT a self-sufficient modality for coronary artery disease screening and follow-up, whereas CT-AC should be discussed on a case-by-case basis.

CT-based attenuation correction in Tl-201 myocardial perfusion scintigraphy is less effective than non-corrected SPECT for risk stratification

BACKGROUND

Previous studies advocate the use of attenuation correction in myocardial perfusion scintigraphy (MPS) for patient risk stratification.

METHODS

Six-hundred and thirty-seven unselected patients underwent Tl-201 MPS by a hybrid SPECT/CT system. Attenuation-corrected (AC) and non-corrected (NAC) images were interpreted blindly and summed stress scores (SSS) were calculated. Study endpoints were all-cause mortality and the composites of death/non-fatal acute myocardial infarction (AMI) and death/AMI/late revascularization.

RESULTS

During a follow-up of 42.3 ± 12.8 months 24 deaths, 13 AMIs and 28 revascularizations were recorded. SSS groups formed according to event rate distribution across SSS values were: 0-4, 5-13, >13 for NAC and 0-2, 3-9, >9 for AC. Kaplan-Meier functions were statistically significant between NAC SSS groups for all study endpoints. AC discriminated only between SSS 0-2 and >9 for death/AMI and between 0-2 and 3-9 for death/AMI/revascularization. In the univariate Cox regression abnormal NAC (SSS > 4) was accompanied with much higher hazards ratios than abnormal AC (SSS > 2). In the multivariate model abnormal AC yielded no significance for either endpoint whereas abnormal NAC proved independent from other covariates for the composite endpoints.

CONCLUSION

Our results challenge the effectiveness of CT-based AC for risk stratification of patients referred for MPS.

Risk stratification using line source attenuation correction with rest/stress Tc-99m sestamibi SPECT myocardial perfusion imaging

BACKGROUND

Although line source attenuation correction (AC) in SPECT MPI studies improves diagnostic accuracy, its prognostic value is less understood.

METHODS

Consecutive patients (n = 6,513) who underwent rest/stress AC ECG-gated SPECT MPI were followed for cardiac death or non-fatal myocardial infarction (MI). A 17-segment model and AC summed stress score (SSS) were used to classify images.

RESULTS

Of the 6,513 patients, cardiac death or non-fatal MI occurred in 267 (4.1%), over 2.0 ± 1.4 years. The AC-SSS in patients with a cardiac event (5.6 ± 7.8) was significantly higher than in those without (1.9 ± 4.6, P < .001). The annualized cardiac event rate in patients with an AC-SSS 1-3 (3.6%) was significantly higher than in those with an AC-SSS = 0 (1.1%, P < .001) but similar to that in those with an AC-SSS 4-8 (2.9%, P = .4). Accordingly, patients were classified to AC-SSS = 0, 1-8, and >8 with annualized cardiac event rates of 1.1%, 3.2%, and 8.5%, respectively (P < .0001). In multivariate analysis, an AC-SSS 1-8 and >8 emerged as independent predictors of cardiac events (P < .02 and P < .0001, respectively).

CONCLUSION

Rest/stress ECG-gated SPECT MPI with line source AC provides highly effective and incremental risk stratification for future cardiac events.

Relationship between silent myocardial ischemia and coronary artery disease risk factors

BACKGROUND

The association between silent myocardial ischemia (SMI) and coronary artery disease (CAD) risk factors in asymptomatic patients with no prior history of CAD referred for stress myocardial perfusion imaging (MPI) is unknown.

METHODS

We retrospectively evaluated patients who underwent MPI over a 3.4-year period to identify those who did not have chest pain, dyspnea, or known CAD. The presence of risk factors was categorized as none, 1-2, 3-4, and ≥5. MPI was performed using a rest thallium-201/stress Tc-99m sestamibi protocol, and read using a standard five-point perfusion score (0 = normal to 4 = absent) and a 17-segment left ventricular model. Summed stress score and summed rest score were derived as the sum of individual segmental scores at stress and rest, respectively. SMI was diagnosed if the summed differences score (SDS) was ≥2. Prognostically significant ischemia was defined by a SDS ≥ 8.

RESULTS

Among 1,354 asymptomatic patients, SMI was present in 97 (7.2%) and prognostically significant in 60 (4.4%). The prevalence, but not severity, of SMI increased with increasing CAD risk factors--0 for none, 4.1% for 1-2, 8.8% for 3-4, and 12% for those with ≥5 CAD risk factors (P value for trend = .001), in patients <74 years of age. Of the 59 (4.4%) patients who underwent coronary angiography, only 31 (2%) had significant anatomical CAD.

CONCLUSIONS

The prevalence of SMI and prognostically significant ischemia is low in asymptomatic patients without known CAD, and is related to the number of CAD risk factors in patients younger than 74 years of age.

Adding attenuation corrected images in myocardial perfusion imaging reduces the need for a rest study

BACKGROUND

The American Society of Nuclear Cardiology and the Society of Nuclear Medicine conclude that incorporation of attenuation corrected (AC) images in myocardial perfusion scintigraphy (MPS) will improve diagnostic accuracy. The aim was to investigate the value of adding AC stress-only images for the decision whether a rest study is necessary or not.

METHODS

1,261 patients admitted to (99m)Tc MPS were studied. The stress studies were interpreted by two physicians who judged each study as "no rest study necessary" or "rest study necessary", by evaluating NC stress-only and NC + AC stress-only images. When there was disagreement between the two physicians, a third physician evaluated the studies. Thus, agreement between 2 out of 3 physicians was evaluated.

RESULTS

The physicians assessed 214 more NC + AC images than NC images as "no rest study necessary" (17% of the study population). The number of no-rest-study-required was significantly higher for NC + AC studies compared to NC studies (859 vs 645 cases (p < 0.0001). In the final report according to clinical routine, ischemia or infarction was reported in 23 patients, assessed as "no rest study necessary" (22 NC + AC cases; 8 NC cases), (no statistically significant difference). In 11 of these, the final report stated "suspected/possible ischemia or infarction in a small area".

CONCLUSIONS

Adding AC stress-only images to NC stress-only images reduce the number of unnecessary rest studies substantially.

Normal stress databases in myocardial perfusion scintigraphy--how many subjects do you need?

BACKGROUND

Commercial normal stress databases in myocardial perfusion scintigraphy (MPS) commonly consist of 30-40 individuals. The aim of the study was to determine how many subjects are needed.

METHODS

Four normal stress databases were developed using patients who underwent 99mTc MPS: non-corrected images (NC) for male, NC for female, attenuation-corrected images (AC) for male and AC for female subjects. 126 male and 205 female subjects were included. The normal database was created by alternatingly computing the mean of all normal subjects and normalizing the subjects with respect to this mean, until convergence. Coefficients of variation (CV) were created for increasing number of included patients in the four different normal stress databases.

RESULTS

Normal stress databases with < 35 subjects had a high CV. Mean CV -2 standard deviations (SD) decreased with 28% between two and five included subjects, 71% between two and 35 subjects and 83% between two and 100 included subjects for NC man.

CONCLUSIONS

We conclude that the commonly used 30-40 individuals for making a normal stress database might not be enough due to the high CV. We propose that normal stress databases should consist of more than 30-40 individuals, preferably more than 50 individuals, both for NC and AC studies.

Small average differences in attenuation corrected images between men and women in myocardial perfusion scintigraphy: a novel normal stress database

Background

The American Society of Nuclear Cardiology and the Society of Nuclear Medicine state that incorporation of attenuation-corrected (AC) images in myocardial perfusion scintigraphy (MPS) will improve image quality, interpretive certainty, and diagnostic accuracy. However, commonly used software packages for MPS usually include normal stress databases for non-attenuation corrected (NC) images but not for attenuation-corrected (AC) images. The aim of the study was to develop and compare different normal stress databases for MPS in relation to NC vs. AC images, male vs. female gender, and presence vs. absence of obesity. The principal hypothesis was that differences in mean count values between men and women would be smaller with AC than NC images, thereby allowing for construction and use of gender-independent AC stress database.

Methods

Normal stress perfusion databases were developed with data from 126 male and 205 female patients with normal MPS. The following comparisons were performed for all patients and separately for normal weight vs. obese patients: men vs. women for AC; men vs. women for NC; AC vs. NC for men; and AC vs. NC for women.

Results

When comparing AC for men vs. women, only minor differences in mean count values were observed, and there were no differences for normal weight vs. obese patients. For all other analyses major differences were found, particularly for the inferior wall.

Conclusions

The results support the hypothesis that it is possible to use not only gender independent but also weight independent AC stress databases.

Predictors of an ischemic electrocardiographic response in patients with exercise-induced myocardial ischemia

BACKGROUND

The determinants of an ischemic electrocardiographic (ECG) response in patients with exercise-induced ischemia on single-photon emission computed tomography (SPECT) remain poorly defined. Specifically, it is unknown whether the occurrence of an ischemic ECG response is related to the extent and/or severity of SPECT ischemia.

METHODS AND RESULTS

Among 3,294 patients who underwent exercise SPECT using a rest thallium-201/exercise Tc-99m sestamibi protocol, 699 (21%) patients had myocardial ischemia defined as summed difference score (SDS) ≥2. The extent of SPECT ischemia was further defined as the total number of segments with difference score ≥1, and severity of ischemia as the largest difference score among all segments. Patients with ischemic ECG changes (n = 315) were significantly older and had a significantly greater prevalence of hyperlipidemia. SDS (7.4 ± 2.2 vs 4.7 ± 1.9, P < .0001), extent (4.2 ± 2.6 vs 2.9 ± 1.7, P < .0001), and severity (2.8 ± 0.9 vs 2.3 ± 0.8, P < .0001) of SPECT ischemia were greater among patients with ischemic ECG changes. In multivariate analysis, age and SDS (which is a composite of the extent and severity of ischemia) were associated with ischemic ECG. When analyzed in a separate model which did not include SDS, both severity of SPECT ischemia (OR 1.42, CI 1.13-1.79) and extent of SPECT ischemia (OR 1.21, CI 1.10-1.33) were independently associated with ischemic ECG.

CONCLUSIONS

Among patients with exercise-induced myocardial ischemia by SPECT, age and SDS were associated with ischemic ECG changes. When analyzed separately, the severity and extent of SPECT ischemia were both independent predictors of ischemic ECG changes.

Combined quantitative analysis of attenuation corrected and non-corrected myocardial perfusion SPECT: Method development and clinical validation

BACKGROUND

Attenuation corrected myocardial perfusion SPECT (AC-MPS) has been demonstrated to improve the specificity of detecting coronary artery disease (CAD) by visual analysis which utilizes both non-corrected (NC) and AC data. However, the combined automated quantification of NC and AC-MPS has not been previously described. We aimed to develop a combined quantitative analysis from AC and NC data to improve the accuracy of automated detection of CAD from AC-MPS.

METHODS

Stress total perfusion deficit (TPD) values were generated by standard analysis for NC (NC-TPD), AC (AC-TPD) and by combined NC-AC analysis (NA-TPD), in which the hypoperfusion severity in each polar map location was defined as the average of AC and NC severity computed by comparison with separate AC and NC normal limits. Ischemic TPD was also calculated as the difference between stress TPD and rest TPD for each measure. Stress/rest Tc-99m sestamibi MPS studies in 650 patients with correlating coronary angiography and in 345 patients with a low-likelihood (LLk) of CAD were used to assess diagnostic performance of combined NC-AC analysis.

RESULTS

NA-TPD had a higher receiver-operator-characteristic area under the curve (ROC-AUC) (0.87) than NC-TPD (0.85; P < .01) or AC-TPD (0.85; P < .01) for detection of stenosis >or=70% in angiographic group. It also had higher specificity (75%) vs NC-TPD (65%; P < .0001), or AC-TPD (70%; P = .016). In LLk group, the normalcy rate of NA-TPD (95%) was higher than for NC-TPD (90%; P < .01) and similar to AC-TPD (94%; P = NS). NA-TPD had higher ROC-AUC than that for 17-segment expert visual scoring of stress scans in angiographic group (0.84; P = .01), comparable accuracy (81%) and similar normalcy rates (95% vs 97%; P = NS). Ischemic TPD by combined NC-AC analysis had higher ROC-AUC than that for any ischemic measure. Similar to stress NA-TPD, it also obtained the similar performance results as compared with ischemic TPD based on NC or AC and higher sensitivity (89% vs 85%; P = .0295) as compared with ischemic visual score in angiographic group.

CONCLUSION

Combined NC-AC MPS quantification using either stress or ischemic TPD shows significant improvements for ROC-AUC and specificity of MPS in the detection of CAD compared with standard NC-MPS or AC-MPS and comparable performance to expert visual scoring. This technique may lead to an enhancement in a fully automated quantification for the perfusion analysis by AC-MPS.

Impact of image reconstruction on phase analysis of ECG-gated myocardial perfusion SPECT studies

OBJECTIVES

Phase analysis (SyncTool) has been developed to assess left-ventricular (LV) dyssynchrony from gated myocardial perfusion single-photon emission computed tomography (GSPECT) studies. Conventionally, GSPECT data are reconstructed using filtered backprojection (FBP). This study is intended to determine the impact of various iterative reconstruction methods on SyncTool.

METHODS

Thirty consecutive patients, acquired using a Philips CardioMD system, were enrolled in this study. The GSPECT data were reconstructed using FBP, maximum likelihood expectation maximization (MLEM), MLEM with three-dimensional resolution recovery (Astonish), MLEM with Vantage attenuation correction (AC), and MLEM with Vantage AC and three-dimensional Monte Carlo-based scatter correction (ACSC), respectively. The reconstructed data were then submitted to SyncTool to measure LV dyssynchrony (phase standard deviation and histogram bandwidth). The paired t-test was used to compare the LV dyssynchrony indices given by MLEM, Astonish, AC, and ACSC, respectively, with those given by the FBP.

RESULTS

No statistical significance was observed for any comparison between iterative reconstruction methods and the FBP.

CONCLUSION

Reconstruction methods have insignificant impact on the LV dyssynchrony indices, indicating that the standard FBP reconstruction is sufficient for accurate phase analysis, supporting the widespread clinical use of SyncTool in measuring LV dyssynchrony.

Risk stratification with attenuation corrected stress Tc-99m sestamibi SPECT myocardial perfusion imaging in the absence of ECG-gating due to arrhythmias

BACKGROUND

Despite growing recognition of attenuation correction (AC) utilizing an external radiation source, prognostic studies using AC are lacking.

METHODS

Consecutive patients (n = 419) who underwent stress Tc-99m sestamibi SPECT imaging with AC but without ECG-gating, due to arrhythmia, were followed for cardiac death or non-fatal myocardial infarction (MI). A 17-segment model and the summed stress score (SSS) were used to classify both the non-AC and AC images.

RESULTS

The 419 patients had a mean age of 71.5 +/- 11.7 years and most (70.6%) underwent pharmacologic stress. In follow-up, 35 (8.4%) patients suffered an adverse cardiac event. Patients with AC-SSS 1-3 and AC-SSS 4-8 had similar cardiac event rates (11.4% vs 10.5%, P = NS). Accordingly, AC-SSS cutoffs of 0, 1-8, and >8 were selected to classify perfusion as normal, mildly abnormal, and moderately to severely abnormal with annualized event rates of 2.1%, 10.8%, and 18.7%, respectively (P < .001). In multivariable analysis, AC-SSS >8 was the most powerful predictor of cardiac events followed by AC-SSS 1-8, history of CAD, age >75 and pharmacologic stress.

CONCLUSIONS

AC provides powerful risk stratification when added to clinical variables in patients undergoing stress Tc-99m sestamibi SPECT imaging without ECG-gating. Moreover, smaller/less severe defects on AC data are more significant than if the same defects were seen on non-AC data.

SPECT attenuation correction: an essential tool to realize nuclear cardiology's manifest destiny

Single photon emission computed tomography (SPECT) myocardial perfusion imaging has attained widespread clinical acceptance as a standard of care for cardiac patients. Yet, physical phenomena degrade the accuracy of how our cardiac images are visually interpreted or quantitatively analyzed. This degradation results in cardiac images in which brightness or counts are not necessarily linear with tracer uptake or myocardial perfusion. Attenuation correction (AC) is a methodology that has evolved over the last 30 years to compensate for this degradation. Numerous AC clinical trials over the last 10 years have shown increased diagnostic accuracy over non-AC SPECT for detecting and localizing coronary artery disease, particularly for significantly increasing specificity and normalcy rate. This overwhelming evidence has prompted our professional societies to issue a joint position statement in 2004 recommending the use of AC to maximize SPECT diagnostic accuracy and clinical usefulness. Phantom and animal studies have convincingly shown how SPECT AC recovers the true regional myocardial activity concentration, while non-AC SPECT does not. Thus, AC is also an essential tool for extracting quantitative parameters from all types of cardiac radionuclide distributions, and plays an important role in establishing cardiac SPECT for flow, metabolic, innervation, and molecular imaging, our manifest destiny.

Attenuation-corrected 99mTc-MIBI SPECT in overweight patients with chronic ischaemic dysfunction: a comparison to NH3 PET and implications for the diagnosis of myocardial viability

OBJECTIVE

We determined the value of attenuation correction (AC) of myocardial perfusion estimation with (99m)Tc-MIBI SPECT in overweight patients by comparison of uncorrected (filtered back-projection (FBP) and corrected (an iterative algorithm with a measured attenuation coefficients map (FL-AC)) (99m)Tc-MIBI relative uptake to perfusion data obtained in the same patients with NH3 PET. In addition, the impact of attenuation correction for the assessment of myocardial viability with (99m)Tc-MIBI SPECT was determined using FDG PET as the reference method.

METHODS

Thirty consecutive overweight patients (BMI=28+/-4) with left ventricular dysfunction underwent a resting (99m)Tc-MIBI SPECT and a PET study (NH3 and FDG). (99m)Tc-MIBI SPECT scans were reconstructed without attenuation correction (FBP) and with attenuation correction (FL-AC). The left ventricle was divided into 16 segments, in which the relative uptake was quantified using circumferential profiles. A relative uptake > or = 60% was considered consistent with viable myocardium for FDG and MIBI.

RESULTS

The absolute difference between (99m)Tc-MIBI SPECT and NH3 PET uptakes was less pronounced in the inferior (12+/-10% vs. 17+/-12%, P<0.001), anteroseptal (12+/-11% vs. 16+/-12%, P=0.009) and septal (15+/-12% vs. 18+/-14%, P=0.003) regions (FL-AC vs. FBP, respectively). The sensitivity of MIBI for diagnosing myocardial viability increased from 83 to 100% (P=0.034), without loss in specificity.

CONCLUSION

Attenuation correction improves myocardial perfusion estimation by (99m)Tc-MIBI SPECT in the inferior, anteroseptal and septal regions and increases its sensitivity for the diagnosis of myocardial viability.

Clinical validation of SPECT attenuation correction using x-ray computed tomography-derived attenuation maps: multicenter clinical trial with angiographic correlation

BACKGROUND

Nonuniform attenuation artifacts cause suboptimal specificity of stress single photon emission computed tomography (SPECT) myocardial perfusion images. In phantoms, normal subjects, and patients suspected of having coronary artery disease (CAD), we evaluated a new hybrid attenuation correction (AC) system that combines x-ray computed tomography (CT) with conventional stress SPECT imaging.

METHODS AND RESULTS

The effect of CT-based AC was evaluated in phantoms by assessing homogeneity of normal cardiac inserts. AC improved homogeneity of normal cardiac phantoms from 11% +/- 2% to 5% +/- 1% (P < .001). Attenuation-corrected normal patient files were created from 37 normal subjects with a low likelihood (<3%) of CAD. The diagnostic performance of AC for detection of CAD was evaluated in 118 patients who had stress technetium 99m sestamibi or tetrofosmin stress SPECT imaging and coronary angiography. SPECT images with and without AC were interpreted by 4 blinded readers with different interpretative attitudes. Overall, AC improved the diagnostic performance of all readers, particularly the normalcy rate. The degree of improvement depended on interpretative attitude. Readers prone to high sensitivity or with less experience had the greatest gain in the normalcy rate, whereas a reader prone to higher specificity had improvements in sensitivity and specificity but not the normalcy rate. Importantly, improvement of one diagnostic variable was not associated with worsening of other variables.

CONCLUSION

CT-based AC of SPECT images consistently improved overall diagnostic performance of readers with different interpretive attitudes and experience. CT-based AC is well suited for routine use in clinical practice.

EANM/ESC procedural guidelines for myocardial perfusion imaging in nuclear cardiology

The European procedural guidelines for radionuclide imaging of myocardial perfusion and viability are presented in 13 sections covering patient information, radiopharmaceuticals, injected activities and dosimetry, stress tests, imaging protocols and acquisition, quality control and reconstruction methods, gated studies and attenuation-scatter compensation, data analysis, reports and image display, and positron emission tomography. If the specific recommendations given could not be based on evidence from original, scientific studies, we tried to express this state-of-art. The guidelines are designed to assist in the practice of performing, interpreting and reporting myocardial perfusion SPET. The guidelines do not discuss clinical indications, benefits or drawbacks of radionuclide myocardial imaging compared to non-nuclear techniques, nor do they cover cost benefit or cost effectiveness.

Third Annual Mario S. Verani, MD, Memorial Lecture: The future of clinical nuclear cardiology

It is a great honor and privilege to present the Third Annual Mario S. Verani, MD, Memorial Lecture. Mario Verani (1943-2001) will be remembered foremost for his major contributions to the field of nuclear cardiology (Figure 1). For instance, he was one of the first investigators to recognize that fixed thallium defects were often not just scar but could be reversed by coronary revascularization. This led to an extensive revision of accepted traditional concepts on the meaning of image patterns. Mario's work on risk stratification by myocardial perfusion and function imaging after acute myocardial infarction was equally pioneering. He also laid out the basic principles for the safe use of adenosine for pharmacologic stress testing. Adenosine is now the preferred procedure all over the world in millions of patients. Dr Verani was a founding member and past president (1996-1997) of the American Society of Nuclear Cardiology (ASNC). The day before he died, he received the ASNC Distinguished Service Award. Personally, I will remember Mario as a very dear friend. We spent many hours together at meetings and gatherings all over the world. I still miss his outgoing personality, his warmth, his humor, and his enthusiasm. Above all, I enjoyed his comfortable friendship. That this friendship extended itself naturally to our wives, Regina and Marjan, made it all the more special. One of the best times we had was during a cardiology meeting in Recife, in the country of his birth, Brazil. I was greatly amused and, at the same time, impressed by the admiration and respect bestowed on him by his fellow Brazilians. One evening, we were going some place in the street on foot. We could not walk down the street without Mario being stopped by one or another Brazilian cardiologist who wanted to speak and consult with him. He was clearly greatly admired and appreciated in his country. I jokingly called him "King of Recife," and the king was holding audience. We arrived rather late where we were going... . I will always cherish the memories of our times together. I am grateful that I could visit Mario at his sickbed on the day before he passed away. He was so fragile and, at the same time, so courageous. I felt sad that there was so much that we could have discussed that we did not. Life seems sometimes full of missed opportunities... .

Contributions of subdiaphragmatic activity, attenuation, and diaphragmatic motion to inferior wall artifact in attenuation-corrected Tc-99m myocardial perfusion SPECT

BACKGROUND

Subdiaphragmatic activity and diaphragmatic motion both contribute to inferior wall artifacts in technetium 99m myocardial perfusion single photon emission computed tomography (SPECT).

METHODS AND RESULTS

We used an anthropomorphic phantom with ventricular wall activity, liver/spleen inserts containing variable Tc-99m activity, and variable vertical (diaphragmatic) motion amplitude. SPECT and transmission scans were obtained on a GE Optima NX camera. Data were processed by use of filtered backprojection or attenuation correction (AC). Resulting myocardial activity maps were analyzed with standardized inferior-anterior and anterior-lateral wall ratios. At a subdiaphragmatic-myocardial activity ratio of 0.5:1, inferior wall attenuation predominates, producing a cold artifact. AC corrects inferior wall activity to the level of the anterior wall irrespective of diaphragmatic motion. At a subdiaphragmatic-myocardial activity ratio of 1:1, inferior wall counts vary widely depending on the proximity of subdiaphragmatic activity to the ventricle. With increasing diaphragmatic amplitude, the overlap of subdiaphragmatic activity and inferior wall worsens, leading to a complex mixture of cold and hot artifacts, not corrected by AC.

CONCLUSIONS

Concentration and proximity of subdiaphragmatic Tc-99m activity relative to myocardium comprise a major factor in the nature and severity of inferior wall artifacts. If the subdiaphragmatic Tc-99m concentration is equivalent to that in the myocardium, complex, potentially uninterpretable hot and cold inferior wall artifacts are produced.

Attenuation correction single-photon emission computed tomography myocardial perfusion imaging

Clinicians now rely heavily on the results of single-photon emission computed tomography (SPECT) myocardial perfusion imaging for diagnosing coronary disease and for planning therapy. However, the technique is imperfect for these purposes, mainly because of technical limitations, the most prominent of which is the effect of soft-tissue attenuation on apparent tracer distribution. Providers have attempted to compensate for this by a number of indirect approaches. Recently, validated hardware and software solutions for directly correcting image data for soft-tissue attenuation have become widely available commercially. Optimal application requires an understanding of the technical details that differ somewhat from system to system, the quality control prerequisites, knowledge of the importance of the transmission map quality, and how dedicated SPECT and SPECT-computed tomography systems present different challenges. In addition, the clinical literature is expanding rapidly, including studies on diagnostic accuracy, image appearances, quantitative analysis, appropriate patients for attenuation correction, clinical utility, incremental value in relation to ECG-gating, and risk stratification.

Value of attenuation correction on ECG-gated SPECT myocardial perfusion imaging related to body mass index

BACKGROUND

Obesity is a growing problem in the United States, and attenuation artifacts are more prevalent in this patient group. This study evaluated the impact of attenuation correction in patients with a high body mass index (BMI).

METHODS AND RESULTS

Three readers interpreted gated attenuation-corrected and non-attenuation-corrected rest/stress technetium 99m sestamibi myocardial perfusion imaging results in 116 patients (BMI <30, n = 60; BMI > or =30, n = 56) who had coronary angiography no more than 60 days after imaging. Readers were blinded to all clinical information and as to whether myocardial perfusion imaging was attenuation-corrected or non-attenuation-corrected. Sensitivity, specificity, and accuracy for detection of coronary artery disease of 70% or greater for attenuation-corrected versus non-attenuation-corrected single photon emission computed tomography (SPECT) were 86% versus 89%, 79% versus 50%, and 84% versus 79%, respectively. Sensitivity, specificity, and accuracy for attenuation-corrected versus non-attenuation-corrected SPECT for patients with BMI less than 30 were 90% versus 90%, 82% versus 64%, and 88% versus 85%, respectively. For BMI of 30 or greater, the results were 82% versus 87%, 76% versus 41%, and 80% versus 73%, respectively. There was a significant difference in specificity overall ( P = .02) and for the category of BMI of 30 or greater ( P = .03).

CONCLUSIONS

This study demonstrates that electrocardiography-gated attenuation-corrected Tc-99m sestamibi SPECT myocardial perfusion imaging improves specificity compared with electrocardiography-gated non-attenuation-corrected SPECT myocardial perfusion imaging, especially in patients with BMI of 30 or greater.

[Diagnostic accuracy of the SPECT of post-stress myocardial perfusion with attenuation and scatter correction]

OBJECTIVE

To evaluate the effect of attenuation and scatter correction (AC-SC) on the diagnostic accuracy of post-stress myocardial perfusion (MP) SPECT.

MATERIAL AND METHODS

The retrospective analysis included 121 patients who had a non-corrected (NC) and AC-SC 99mTc-Tetrofosmin MP SPECT after stress. The left ventricle was divided into 13 segments. Two observers performed a visual assessment of the MP on a scale from 0 (perfusion defect) to 3 (normal uptake). A consensus on concordances and discordances between the NC and AC-SC images was established. Final diagnosis of coronary artery disease (CAD) was established by coronary angiography (CANG) (stenosis > or = 70 %).

RESULTS

The combined analysis of NC and AC-SC images produced 93 concordances and 28 discordances. Of the 93 concordances, both studies were abnormal in 67 patients (abnormal CANG in 57) and normal in 26 patients (normal CANG in 20). Among the 28 discordances, 23 were abnormal NC/normal AC-SC (normal CANG in 18) and 5 normal NC/abnormal AC-SC. In these 5 patients AC-SC generated anterior perfusion defects but the CANG was normal. Overall, the appearance of NC and AC-SC images were in agreement with the CANG findings in the 72 % (87/121) and 78 % (95/121) of the patients, respectively. Sixty-seven of the 90 patients with abnormal NC had also abnormal AC-SC (abnormal CANG in 57) and the other 23 had normal AC-SC (normal CANG in 18). The appearance of AC-SC was in agreement with CANG finding in the 83 % (75/90) of patients with abnormal NC. MP abnormalities in NC normalized by AC-SC were more frequently located in inferior wall

CONCLUSION

AC-SC improves the diagnostic accuracy of post stress NC MP SPECT for the diagnosis of CAD. From these results we consider that AC-SC is of clinical value for the correction of attenuation artifacts, more frequently observed in the inferior wall. The presence of antero-apical perfusion defects in AC-SC with normal NC does not mean CAD. So it is necessary to adjust the normalcy pattern of MP SPECT when AC-SC is performed.

Added value of attenuation-corrected Tc-99m tetrofosmin SPECT for the detection of myocardial viability: comparison with FDG SPECT

BACKGROUND

The aim of this study was to evaluate the value of attenuation correction of technetium 99m tetrofosmin single photon emission computed tomography (SPECT) imaging for the detection of myocardial viability.

METHODS AND RESULTS

A head-to-head comparison between resting Tc-99m tetrofosmin SPECT and fluorine 18 fluorodeoxyglucose (FDG) SPECT was performed. Both the noncorrected and attenuation-corrected Tc-99m tetrofosmin SPECT images were compared with the FDG images that served as the reference for viability. Consecutive patients (n = 33) with chronic coronary artery disease and left ventricular dysfunction were included. Segmental Tc-99m tetrofosmin and FDG data were displayed in polar maps (17-segment model), and the segments were normalized to peak activity by use of the 4D-MSPECT software program. Segments with normalized FDG activity greater than 50% were considered viable. A similar cutoff value to assess viability was used for the noncorrected and attenuation-corrected Tc-99m tetrofosmin images. Regional contractile function was determined from the gated Tc-99m tetrofosmin images and scored as normokinesia, hypokinesia, or akinesia/dyskinesia. Of all segments, 482 (85%) were viable on FDG SPECT. Of these, 427 (89%) were classified as viable with noncorrected Tc-99m tetrofosmin. Thus 55 (11%) were underestimated with noncorrected Tc-99m tetrofosmin SPECT; these segments were mainly located in the inferior and inferoseptal regions. Attenuation correction changed the classification of 39 (70%) of the underestimated segments to viable. By use of attenuation correction, the agreement between Tc-99m tetrofosmin and FDG imaging improved from 84% to 90%. Similar observations were made when the analysis was restricted to the dysfunctional segments.

CONCLUSION

The addition of attenuation correction to Tc-99m tetrofosmin SPECT significantly improved detection of myocardial viability in patients with chronic coronary artery disease, although minimal underestimation of viability remained as compared with FDG SPECT imaging.

The Assessment of Infarct Size in Postmyocardial Infarction Patients Undergoing Thallium-201 Tomographic Imaging Is Improved Using Attenuation Correction

PURPOSE

Attenuation correction (ATC) has been shown to improve the accuracy of thallium-201 single photon emission computed tomography (SPECT) for the detection and evaluation of patients with coronary artery disease. The purpose of this study was to evaluate the value of ATC for the assessment of infarct size in patients after myocardial infarction (MI).

MATERIALS AND METHODS

Tl-201 SPECT with ATC was performed on 39 patients with 49 previous MIs. This was followed by radionuclide ventriculography for the assessment of global and regional left ventricular function. Uncorrected and corrected 24-hour redistribution SPECT images were analyzed for regional perfusion using a 5-point segmental scoring scale from 0 (normal) to 4 (absent) thallium uptake.

RESULTS

The mean number of segments with scores of >1 and 2 was significantly higher without ATC than with ATC (5.3 +/- 3.6 vs. 3.5 +/- 3.6, P = 0.0001 for scores >1; 3.8 +/- 3.6 vs. 2.5 +/- 3.0, P = 0.0001 for scores of >2, respectively). The mean total number of segments with scores of >1 assessed without ATC was significantly higher compared with that assessed with ATC (16.9 +/- 13.5 vs. 11.2 +/- 12.2, P = 0.0001). Evaluation without ATC demonstrated only a fair correlation between the SPECT parameters (number of segments with scores of >1 and >2, and total score of segments with scores of >1) and left ventricular regional and global function, whereas there was a clear improvement in all the parameters after ATC. With ATC, a decrease in infarct size was demonstrated in 27 of the 49 infarcts (55%).

CONCLUSIONS

The improved correlation with left ventricular function indicates that SPECT imaging with ATC provides a more accurate assessment of infarct size in post-MI patients. The use of nonattenuation-corrected SPECT imaging overestimates infarct size in a majority of patients.

Attenuation correction for single photon emission computed tomography myocardial perfusion imaging

The specificity of cardiac single photon emission computed tomography (SPECT) perfusion imaging is significantly affected by internal photon absorption. Commonly referred to as anterior wall breast and inferior wall diaphragm attenuation artifacts, even when following characteristic patterns in women and men, the reduced activity produced can be difficult to differentiate from real perfusion defects. Unfortunately, wide variations in body habitus result in unpredictable variations in tissue attenuation and the specificity of uncorrected SPECT is unacceptably low in many laboratories. This manuscript reviews recent developments in attenuation correction methods for cardiac SPECT. Several commercial methods are now available, and although the initial success using these methods varied widely, as these methods have been improved successful clinical reports are appearing with increasing frequency. Recent developments have yielded more robust validated methods and significant clinical advantages have been achieved in the diagnostic evaluation of coronary heart disease (sensitivity as well as specificity) and myocardial viability. As these methods continue to mature, further advances should be anticipated.

Prospective clinical comparison of non-corrected and attenuation- and scatter-corrected myocardial perfusion SPECT in patients with suspicion of coronary artery disease

Attenuation artefacts decrease the specificity of myocardial perfusion single-photon emission computed tomography (SPECT). In this paper, the results of a prospective study evaluating the clinical applicability of attenuation and scatter correction in myocardial perfusion SPECT are presented. Of 607 patients in whom post-stress 99mTc-tetrofosmin myocardial perfusion SPECT was performed due to suspicion of coronary artery disease, 99 also underwent coronary angiography (CAG). A simultaneous emission/transmission acquisition was performed. A multiple linear array of 153Gd sources and four independent energy windows were used for attenuation and scatter correction. A blind separate analysis of non-corrected (NC) and attenuation- and scatter-corrected (AC-SC) images was performed with scores of zero (no uptake) to three (normal uptake). The final diagnosis was based on CAG findings, and stenoses of > or =70% were considered to be significant. NC images had a sensitivity of 92% and a specificity of 46%. In AC-SC images, the sensitivity decreased to 76%, but the specificity increased to 71%. The decrease in the sensitivity of AC-SC images was observed in all three coronary regions. Attenuation and scatter correction increased the specificity in the right coronary region, but decreased the specificity in the left anterior descending coronary region. In 13 of the 99 patients, AC-SC images showed false positive findings due to count deficiency in the anterior wall with normal CAG. The size of perfusion defects was decreased in AC-SC images (from 5.01 +/- 2.74 to 3.15 +/- 2.50 segments). The severity of perfusion defects was higher in NC (1.10 +/- 0.60) than in AC-SC (1.28 +/- 0.56) images. The combined evaluation of NC and AC-SC images was in agreement with the CAG findings in 79% of patients. It can be concluded that, when compared with NC images, AC-SC images improved the specificity in the right coronary region and decreased the sensitivity in all three coronary regions. Attenuation and scatter correction may generate anterior wall defects with normal CAG. The analysis of AC-SC images cannot be used alone for the diagnosis of coronary artery disease. In the clinical setting, combined NC and AC-SC images are recommended for the evaluation of post-stress myocardial perfusion SPECT.

Improved coronary disease detection with quantitative attenuation-corrected Tl-201 images

BACKGROUND

The normal distribution of myocardial tracer activity is different in attenuation-corrected images compared with uncorrected images. We therefore postulated that quantitation of attenuation-corrected thallium 201 images with direct comparison to a database of healthy subjects could improve detection of coronary artery stenoses.

METHODS AND RESULTS

In 49 patients with angiographic evidence of coronary artery disease and 69 patients with a less than 5% likelihood of coronary artery disease, tomographic Tl-201 myocardial imaging was performed by means of a triple-headed camera with fan-beam collimators and the images were processed with attenuation correction, with attenuation and Compton scatter correction, and without correction. Images were subjectively interpreted in a blinded manner. From the group of 69 patients with a low likelihood of coronary disease, scintigraphic data from the first 20 men and the first 20 women were used to generate normal reference ranges for each of the 3 image-processing methods. Data from the 49 patients with angiographic coronary disease and from the remaining 29 patients with a low likelihood of coronary disease were then analyzed quantitatively in comparison to the gender-matched normal databases. With visual interpretation, attenuation-corrected images yielded an improved detection rate compared with uncorrected images (79% vs 46%, P =.008) for 70% or greater left anterior descending coronary artery stenoses. Attenuation-corrected images also provided an improved normalcy rate for the right coronary artery territory (91% vs 75%, P =.006) and an improved normalcy rate when the images were analyzed overall by patient (88% vs 74%, P =.009). With quantitative analysis, attenuation correction yielded an improved detection rate for patients with a significant coronary artery stenosis compared with uncorrected images (90% vs 71%, P =.016). Defect extent was also increased by attenuation correction. Compared with attenuation correction alone, the addition of scatter correction yielded no incremental improvement in detection rate or normalcy rate. Attenuation-scatter correction did produce a nonsignificant trend toward detection of more of the total number of stenotic arteries compared with uncorrected images (60 vs 48 of 79 arteries).

CONCLUSIONS

With the use of a triple-headed camera with fan-beam collimation, visual analysis of attenuation-corrected Tl-201 images improved detection of left anterior descending coronary artery disease without loss of detection in other coronary territories. Furthermore, quantitative analysis of attenuation-corrected Tl-201 images improved the overall detection rate for coronary artery disease in patients without compromise of the normalcy rate.

The influence of attenuation and scatter compensation on the apparent distribution of Tc-99m sestamibi in cardiac slices

BACKGROUND

Our objective was to study the differences in relative count distributions in the left ventricular walls with attenuation compensation (AC) versus AC and triple-energy-window scatter compensation (SC), compared with standard filtered backprojection (FBP).

METHODS AND RESULTS

Two hundred patients identified as having normal cardiac perfusion with FBP after undergoing either pharmacologically or physiologically induced stress were included in this study. Projection data were reconstructed with FBP, 10 iterations of ordered-subset expectation-maximization (OSEM) with AC, and OSEM with AC+SC. A comparison was made of average percentage of maximum counts within each of 9 regions of CEqual (Marconi Medical Systems, Inc, Cleveland, Ohio) polar maps (ie, the apex, 4 midventricular regions, and 4 basal regions). Compared with OSEM(AC), a slight decrease at the apex exists when SC is included. The elevated inferior-to-anterior count ratio in the midventricular and basal regions noted with OSEM(AC) decreased to close to 1.0 with OSEM(AC+SC). The anterior-to-lateral ratio for both regions was closest to 1.0 for OSEM(AC+SC). In the midventricular region, the lateral-to-septal ratio decreased further below 1.0 with OSEM(AC+SC) than it did with OSEM(AC). This was the only basal ratio not to improve to close to 1.0 with OSEM(AC+SC). In a subset of patients identified at the time of clinical reading as having a possible attenuation-caused decrease in the inferior region, AC elevated the inferior-to-anterior ratio to above 1.0 for the midventricular region. AC+SC resulted in a ratio of near 1.0 for this region. In another subset of patients identified as having anterior attenuation artifacts, compensation methods (either AC or AC+SC) failed to show an improvement compared with FBP.

CONCLUSIONS

AC and SC improve the uniformity of the polar map, especially by bringing the inferior-to-anterior ratio closer to 1.0. Further investigation is necessary to determine the cause of the increased midventricular septal polar map count. In addition, the subset of patients identified as having breast-like attenuation artifacts causing a decreased polar map count in the anterior wall (relative to the inferior wall) also needs further attention.

Combined corrections for attenuation, depth-dependent blur, and motion in cardiac SPECT: a multicenter trial

BACKGROUND

The diagnostic accuracy of cardiac single photon emission computed tomography (SPECT) is limited by image-degrading factors, such as heart or subject motion, depth-dependent blurring caused by the collimator, and photon scatter and attenuation. We developed correction approaches for motion, depth-dependent blur, and attenuation and performed a multicenter validation.

METHODS AND RESULTS

Motion was corrected both transversely and axially with a cross-correlation technique. Depth-dependent blurring was corrected by first back-projecting each projection and then applying a depth-dependent Wiener filter row by row. Attenuation was corrected with an iterative, nonuniform Chang algorithm, based on a transmission scan-generated attenuation map. We validated these approaches in 112 subjects, including 36 women (20 healthy volunteers, 8 angiographically normal patients, and 8 patients with coronary artery disease [CAD] found by means of angiography) and 76 men (23 healthy volunteers, 10 angiographically normal patients, and 43 patients with CAD found by means of angiography). Either technetium 99m or thallium 201 was used for emission; either gadolinium 153 or Tc-99m was used for transmission. Images were reconstructed and blindly interpreted with a 5-point scale for receiver operating characteristic analysis in 2 ways: motion correction plus a Butterworth filter, and combined motion and blur and attenuation corrections. The interpretation by means of consensus was for the overall presence of CAD and vascular territory. The receiver operating characteristic curves for overall presence and each of the 3 main coronary arteries were all shifted upward and to the left and had larger areas under the curve, for combined corrections compared with motion correction and Butterworth. Sensitivity/specificity for motion correction and Butterworth were 84/69, 64/71, 32/94, and 71/81 overall for the left anterior descending, the right coronary artery, and circumflex territories, respectively, compared with 88/92, 77/93, 50/97, and 74/95, respectively, for the combined corrections.

CONCLUSIONS

The proposed combined corrections for motion, depth-dependent blur, and attenuation significantly improve diagnostic accuracy, when compared with motion correction alone.

Attenuation corrected cardiac perfusion SPECT

Image artifacts, especially those caused by photon attenuation, commonly affect the specificity of cardiac SPECT perfusion imaging. Although often suspected by characteristic patterns identified in female and male patients respectively, the widely variable body habitus of individual patients are associated with unpredictable variations in tissue attenuation. The accuracy of PET perfusion imaging has long benefited from correction methods for soft tissue attenuation. This paper reviews recent developments in attenuation correction methods for cardiac SPECT perfusion imaging. Several commercial methods are now available. Initial reports indicate these methods have varied greatly in their clinical success. Some methods have demonstrated significant improvements. However, others have created more artifacts than they have cured. Recent developments suggest very significant clinical advantages can be achieved with robust, well-validated methods for attenuation corrected SPECT in the diagnostic evaluation of coronary heart disease, high risk coronary disease, and women.

Attenuation and scatter compensation in myocardial perfusion SPECT

Nonuniform attenuation, Compton scatter, and limited, spatially varying resolution degrade both the qualitative and quantitative nature of myocardial perfusion SPECT. Physicians must recognize and understand the effects of these factors on myocardial perfusion SPECT for optimal interpretation and use of this important imaging technique. Recent developments in the design and implementation of compensation algorithms and transmission-based imaging promise to provide clinically realistic solutions to these effects and provide the framework for truly quantitative imaging. This achievement should improve the diagnostic accuracy and cost-effectiveness of myocardial perfusion SPECT.