Myocardial perfusion imaging-derived left ventricular strain: Regional abnormalities associated with transthyretin cardiac amyloidosis

Background

Transthyretin (ATTR) cardiac amyloidosis is associated with an apical-sparing strain pattern on TTE. We hypothesize that strain indices derived from myocardial perfusion imaging (MPI) can identify this abnormality.

Methods

A group with ATTR amyloidosis was compared to age-matched controls with LVH but without amyloidosis who underwent PET or SPECT MPI. Strain values were used to calculate the apical strain index (ASI), apex-to-base ratio (ABR), and ejection fraction to global strain ratio in multiple planes.

Results

A direct comparison using Welch's t-tests reveals 6 statistically significant metrics. After regression analysis, the circumferential ASI and ABR at rest remain significantly greater in the ATTR group compared to controls.

Conclusion

MPI-derived strain from the circumferential plane at rest may distinguish cardiac amyloidosis from other forms of LVH. If these findings are confirmed with validation studies, routine MPI-derived strain analysis could identify patients with subclinical amyloidosis who may benefit from further testing.

4D display of CT LV endocardial and epicardial models morphed from PET Rb-82 perfusion studies accurately quantifies segmental myocardial thickening

BACKGROUND

MPI-derived LV wall thickening assessments for diagnostic purposes has been part of clinical guidelines for two decades. It relies on visual evaluation of tomographic slices or regional quantification displayed in 2D polar maps. 4D displays have not entered clinical usage nor have they been validated on their potential to provide equivalent information. The purpose of this work was to validate a 4D realistic display recently designed to quantitatively represent the thickening information from gated MPI into CT-morphed endocardial and epicardial moving surfaces.

METHODS

Forty patients who underwent 82Rb PET were selected based on LV perfusion quantification. CTA templates of heart anatomy were selected to represent the LV anatomy. Generic CT-derived LV endocardial and epicardial surfaces were modified to represent the end diastolic (ED) phase according to PET-derived ED LV dimensions and wall thickness. These CT myocardial surfaces were then morphed by means of thin plate spline (TPS) techniques, according to the gated PET slices count changes (WThPET) and LV wall motion (WMoPET). A geometric thickening (GeoTh) equivalent to LV WThPET was defined on epicardial and endocardial CT surfaces over the cardiac cycle and the two measures compared. WThPET and GeoTh correlations were performed on a case-by-case basis, by segment and by pooling all 17 segments. Pearson's correlation coefficients (PCC) were calculated to assess the equivalence of the two measures.

RESULTS

Two cohorts of patients (normal and abnormal) were identified based on SSS. R coefficients were as follows: for all pooled segments PCCstress and PCCrest were respectively 0.91 and 0.89 (normal), and 0.9 and 0.91 (abnormal); when individual 17 segments were considered mean PCCstress = 0.92 [0.81-0.98] and mean PCCrest = 0.93 [0.83-0.98] for the abnormal perfusion group; mean PCCstress = 0.89 [0.78-0.97] and mean PCCrest = 0.89 [0.77-0.97] for the normal. When individual studies were considered, R was always > .70 with the exception of five abnormal studies. Inter-user analysis was also conducted.

CONCLUSIONS

Our novel technique for the visualization of LV wall thickening by means of 4D CT endocardial and epicardial surface models accurately replicated 82Rb slice thickening results showing promise for its usage for diagnostic purposes.

Quantitation of diffuse myocardial ischemia with mental stress and its association with cardiovascular events in individuals with recent myocardial infarction

Microcirculatory dysfunction during psychological stress may lead to diffuse myocardial ischemia. We developed a novel quantification method for diffuse ischemia during mental stress (dMSI) and examined its relationship with outcomes after a myocardial infarction (MI). We studied 300 patients ≤ 61 years of age (50% women) with a recent MI. Patients underwent myocardial perfusion imaging with mental stress and were followed for 5 years. dMSI was quantified from cumulative count distributions of rest and stress perfusion. Focal ischemia was defined in a conventional fashion. The main outcome was a composite outcome of recurrent MI, heart failure hospitalizations, and cardiovascular death. A dMSI increment of 1 standard deviation was associated with a 40% higher risk for adverse events (HR 1.4, 95% CI 1.2-1.5). Results were similar after adjustment for viability, demographic and clinical factors and focal ischemia. In sex-specific analysis, higher levels of dMSI (per standard deviation increment) were associated with 53% higher risk of adverse events in women (HR 1.5, 95% CI 1.2-2.0) but not in men (HR 0.9, 95% CI 0.5-1.4), P 0.001. A novel index of diffuse ischemia with mental stress was associated with recurrent events in women but not in men after MI.

Left Ventricular Strain from Myocardial Perfusion PET Imaging: Method Development and Comparison to 2-Dimensional Echocardiography

This study aimed to develop a measure of longitudinal, radial, and circumferential myocardial strain at rest and regadenoson during pharmacologic stress using 82Rb PET electrocardiography-gated myocardial perfusion imaging (MPI). Methods: We retrospectively identified 80 patients who underwent rest and regadenoson-stress CT attenuation-corrected 82Rb PET and had a standard resting transthoracic echocardiogram (TTE) with global longitudinal strain (GLS) analysis within 3 mo. A method was developed to compute longitudinal, radial, and circumferential strain from PET MPI at stress and rest. PET MPI-derived strain and left ventricular function were compared with resting TTE measures as the clinical reference standard. Interobserver agreement of PET MPI strain and left ventricular ejection fraction processing was reported. Results: Longitudinal strain assessed with resting TTE GLS showed good correlation with PET MPI at stress (r = 0.68, P < 0.001) and rest (r = 0.58, P < 0.001). Resting TTE GLS also correlated with PET MPI radial strain at stress (r = -0.70, P < 0.001) and rest (r = -0.59, P < 0.001) and circumferential strain at stress (r = 0.67, P < 0.001) and rest (r = 0.69, P < 0.001). The left ventricular ejection fraction showed good correlation between resting TTE and PET MPI at stress (r = 0.83, P < 0.001) and rest (r = 0.80, P < 0.001). Bland-Altman analysis indicated positive bias of TTE GLS compared with PET MPI longitudinal strain at stress (mean difference = 5.1%, 95% CI = [-2.5, 12.7]) and rest (mean difference = 4.2%, 95% CI = [-4.3, 12.8]). Reproducibility of PET MPI longitudinal strain showed good agreement at stress (concordance correlation coefficient = 0.73, P < 0.001) and rest (concordance correlation coefficient = 0.74, P < 0.001), with Bland-Altman analysis showing a small bias in the longitudinal direction at stress (mean difference = -0.2%) and rest (mean difference = -1.0%). Conclusion: Strain measured with PET MPI using an automated technique correlated well with resting GLS strain obtained by TTE, and the measure is reproducible. Strain from PET MPI should be investigated further to establish reference ranges and assess its value in routine clinical practice.

A Pilot Study of Neurobiological Mechanisms of Stress and Cardiovascular Risk

Objective

Coronary heart disease is a leading cause of death and disability. Although psychological stress has been identified as an important potential contributor, mechanisms by which stress increases risk of heart disease and mortality are not fully understood. The purpose of this study was to assess mechanisms by which stress acts through the brain and heart to confer increased CHD risk.

Methods

Coronary Heart Disease patients (N=10) underwent cardiac imaging with [Tc-99m] sestamibi single photon emission tomography at rest and during a public speaking mental stress task. Patients returned for a second day and underwent positron emission tomography imaging of the brain, heart, bone marrow, aorta (indicating inflammation) and subcutaneous adipose tissue, after injection of [18F]2-fluoro-2-deoxyglucose for assessment of glucose uptake followed mental stress. Patients with (N=4) and without (N=6) mental stress-induced myocardial ischemia were compared for glucose uptake in brain, heart, adipose tissue and aorta with mental stress.

Results

Patients with mental stress-induced ischemia showed a pattern of increased uptake in the heart, medial prefrontal cortex, and adipose tissue with stress. In the heart disease group as a whole, activity increase with stress in the medial prefrontal brain and amygdala correlated with stress-induced increases in spleen (r=0.69, p=0.038; and r=0.69, p=0.04 respectfully). Stress-induced frontal lobe increased uptake correlated with stress-induced aorta uptake (r=0.71, p=0.016). Activity in insula and medial prefrontal cortex was correlated with post-stress activity in bone marrow and adipose tissue. Activity in other brain areas not implicated in stress did not show similar correlations. Increases in medial prefrontal activity with stress correlated with increased cardiac glucose uptake with stress, suggestive of myocardial ischemia (r=0.85, p=0.004).

Conclusions

These findings suggest a link between brain response to stress in key areas mediating emotion and peripheral organs involved in inflammation and hematopoietic activity, as well as myocardial ischemia, in Coronary Heart Disease patients.

Indicators of abnormal PET coronary flow capacity in detecting cardiac ischemia

Coronary flow capacity (CFC) categorizes severity of left ventricular (LV) ischemia by PET myocardial blood flow (MBF). Our objective was to correlate abnormal CFC with other indicators of regional ischemia. Data were examined retrospectively for 231 patients evaluated for known/suspected CAD who underwent rest and regadenoson-stress ⁸²Rb PET/CT. MBF and myocardial flow reserve (MFR) were quantified, from which CFC was categorized as Normal CFC (1), Minimally reduced (2), Mildly reduced (3), Moderately reduced (4), and Severely reduced (5) for the three main arterial territories as well as globally. Relative perfusion summed stress score (SSS) and systolic phase contraction bandwidth (BW) were assessed. Accuracy to detect arteries with CFC ≥ 4 was highest for a Regional Index combining SSS and BW (88 ± 3%). A Global Index formed from stress ejection fraction, SSS and BW was the most accurate means of identifying patients with global CFC ≥ 4 (84 ± 3%). Arteries with abnormal CFC derived from absolute myocardial blood flow measurements are accurately identified by composite parameters combining regionally aberrant relative perfusion patterns and asynchrony.

18F-flurpiridaz positron emission tomography segmental and territory myocardial blood flow metrics: incremental value beyond perfusion for coronary artery disease categorization

AIMS

We determined the feasibility and diagnostic performance of segmental 18F-flurpiridaz myocardial blood flow (MBF) measurement by positron emission tomography (PET) compared with the standard territory method, and assessed whether flow metrics provide incremental diagnostic value beyond relative perfusion quantitation (PQ).

METHODS AND RESULTS

All evaluable pharmacological stress patients from the Phase III trial of 18F-flurpiridaz were included (n = 245) and blinded flow metrics obtained. For each coronary territory, the segmental flow metric was defined as the lowest 17-segment stress MBF (SMBF), myocardial flow reserve (MFR), or relative flow reserve (RFR) value. Diagnostic performances of segmental and territory MBF metrics were compared by receiver operating characteristic (ROC) areas under the curve (AUC). A multiple logistic model was used to evaluate whether flow metrics provided incremental diagnostic value beyond PQ alone. The diagnostic performances of segmental flow metrics were higher than their territory counterparts; SMBF AUC = 0.761 vs. 0.737; MFR AUC = 0.699 vs. 0.676; and RFR AUC = 0.716 vs. 0.635, respectively (P < 0.001 for all). Similar results were obtained for per-vessel coronary artery disease (CAD) ≥70% stenosis categorization and per-patient analyses. Combinatorial analyses revealed that only SMBF significantly improved the diagnostic performance of PQ in CAD ≥50% stenoses, with PQ AUC = 0.730, PQ + segmental SMBF AUC = 0.782 (P < 0.01), and PQ + territory SMBF AUC = 0.771 (P < 0.05). No flow metric improved diagnostic performance when combined with PQ in CAD ≥70% stenoses.

CONCLUSION

Assessment of segmental MBF metrics with 18F-flurpiridaz is feasible and improves flow-based epicardial CAD detection. When combined with PQ, only SMBF provides additive diagnostic performance in moderate CAD.

Clinical implications of compromised 82Rb PET data acquisition

BACKGROUND

We wished to document the prevalence and quantitative effects of compromised 82Rb PET data acquisitions on myocardial flow reserve (MFR).

METHODS AND RESULTS

Data were analyzed retrospectively for 246 rest and regadenoson-stress studies of 123 patients evaluated for known or suspected CAD. An automated injector delivered pre-determined activities of 82Rb. Automated quality assurance algorithms identified technical problems for 7% (9/123) of patients. Stress data exhibited 2 instances of scanner saturation, 1 blood peak detection, 1 blood peak width, 1 gradual patient motion, and 2 abrupt patient motion problems. Rest data showed 1 instance of blood peak width and 2 abrupt patient motion problems. MFR was lower for patients with technical problems flagged by the quality assurance algorithms than those without technical problems (1.5 ± 0.5 versus 2.1 ± 0.7, P = 0.01), even though rest and stress ejection fraction, asynchrony and relative myocardial perfusion measures were similar for these two groups (P > 0.05), suggesting that MFR accuracy was adversely affected by technical errors.

CONCLUSION

It is important to verify integrity of 82Rb data to ensure MFR computation quality.

Determination of [N-13]-ammonia extraction fraction in patients with coronary artery disease by calibration to invasive coronary and fractional flow reserve

BACKGROUND

This study presents a new extraction fraction (EF) model based on physiological measures of invasive coronary flow reserve (CFR) and fractional flow reserve (FFR) in patients with suspected coronary artery disease (CAD) and normal index microcirculatory resistance (IMR). To ascertain the clinical relevance of the new EFs, flow measurements using the newly patient-determined EFs were compared to flow measurements using traditional animal-determined EFs.

METHODS

39 patients were retrospectively selected that included a total of 91 vascular territories with invasive coronary angiography physiological measures. [N-13]-ammonia dynamic rest/adenosine-stress PET imaging was conducted in all patients and absolute myocardial flow was estimated using four published compartmental models. The extraction fraction during hyperemic flow was iteratively estimated by maximizing the agreement between invasive CFR and FFR with the non-invasive analogs myocardial flow reserve (MFR) and relative flow reserve (RFR) at similar physiological states, respectively.

RESULTS

Using the new patient-determined EFs, agreement between CFR vs MFR for Model 1 and 2 was moderate and poor for Model 3 and 4. All models showed moderate agreement for FFR vs RFR. When using published models of animal-determined EFs, agreement between CFR vs MFR remained moderate for Model 1 and 2, and poor for Model 3 and 4. Similarly, all models showed moderate agreement for FFR vs RFR using animal-determined EF values. None of the observed differences were statistically significant.

CONCLUSIONS

Flow measurements using extraction fraction correction for [N-13]-ammonia based on calibration to invasive intracoronary angiography physiological measures in patients with CAD were not discordant from those reported in the literature. Either patient-determined or traditional animal-determined EF correction, when used with the appropriate flow model, yields moderate agreement with invasive measurements of coronary flow reserve and fractional flow reserve.

Development, diagnostic performance, and interobserver agreement of a 18F-flurpiridaz PET automated perfusion quantitation system

BACKGROUND

Computerized methodologies standardize the myocardial perfusion imaging (MPI) interpretation process.

METHODS

To develop an automated relative perfusion quantitation approach for 18F-flurpiridaz, PET MPI studies from all phase III trial participants of 18F-flurpiridaz were divided into 3 groups. Count distributions were obtained in N = 40 normal patients undergoing pharmacological or exercise stress. Then, N = 90 additional studies were selected in a derivation group. Following receiver operating characteristic curve analysis, various standard deviations below the mean normal were used as cutoffs for significant CAD, and interobserver variability determined. Finally, diagnostic performance was compared between blinded visual readers and blinded derivations of automated relative quantitation in the remaining N = 548 validation patients.

RESULTS

Both approaches yielded comparable accuracies for the detection of global CAD, reaching 71% and 72% by visual reads, and 72% and 68% by automated relative quantitation, when using CAD ≥ 70% or ≥ 50% stenosis for significance, respectively. Similar results were observed when analyzing individual coronary territories. In both pharmacological and exercise stress, automated relative quantitation demonstrated significantly more interobserver agreement than visual reads.

CONCLUSIONS

Our automated method of 18F-flurpiridaz relative perfusion analysis provides a quantitative, objective, and highly reproducible assessment of PET MPI in normal and CAD subjects undergoing either pharmacological or exercise stress.

Clinically viable myocardial CCTA segmentation for measuring vessel-specific myocardial blood flow from dynamic PET/CCTA hybrid fusion

Background

Positron emission tomography (PET)-derived LV MBF quantification is usually measured in standard anatomical vascular territories potentially averaging flow from normally perfused tissue with those from areas with abnormal flow supply. Previously we reported on an image-based tool to noninvasively measure absolute myocardial blood flow at locations just below individual epicardial vessel to help guide revascularization. The aim of this work is to determine the robustness of vessel-specific flow measurements (MBF^vs) extracted from the fusion of dynamic PET (dPET) with coronary computed tomography angiography (CCTA) myocardial segmentations, using flow measured from the fusion with CCTA manual segmentation as the reference standard.

Methods

Forty-three patients’ ¹³NH₃ dPET, CCTA image datasets were used to measure the agreement of the MBF^vs profiles after the fusion of dPET data with three CCTA anatomical models: (1) a manual model, (2) a fully automated segmented model and (3) a corrected model, where major inaccuracies in the automated segmentation were briefly edited. Pairwise accuracy of the normality/abnormality agreement of flow values along differently extracted vessels was determined by comparing, on a point-by-point basis, each vessel’s flow to corresponding vessels’ normal limits using Dice coefficients (DC) as the metric.

Results

Of the 43 patients CCTA fully automated mask models, 27 patients’ borders required manual correction before dPET/CCTA image fusion, but this editing process was brief (2–3 min) allowing a 100% success rate of extracting MBF^vs in clinically acceptable times. In total, 124 vessels were analyzed after dPET fusion with the manual and corrected CCTA mask models yielding 2225 stress and 2122 rest flow values. Forty-seven vessels were analyzed after fusion with the fully automatic masks producing 840 stress and 825 rest flow samples. All DC coefficients computed globally or by territory were ≥ 0.93. No statistical differences were found in the normal/abnormal flow classifications between manual and corrected or manual and fully automated CCTA masks.

Conclusion

Fully automated and manually corrected myocardial CCTA segmentation provides anatomical masks in clinically acceptable times for vessel-specific myocardial blood flow measurements using dynamic PET/CCTA image fusion which are not significantly different in flow accuracy and within clinically acceptable processing times compared to fully manually segmented CCTA myocardial masks.

Early onset of left ventricular regional asynchrony in arteries with sub-clinical stenosis

BACKGROUND

Asynchrony has been reported to be a marker of ischemic-induced left ventricular dysfunction, the magnitude of which correlates with extent of epicardial coronary disease. We wished to determine whether normal-appearing arterial territories with mild degrees of asynchrony have lower 82Rb PET absolute myocardial blood flow (MBF) and/or lower myocardial flow reserve (MFR).

METHODS AND RESULTS

Data were examined retrospectively for 105 patients evaluated for known/suspected CAD who underwent rest/regadenoson-stress 82Rb PET/CT and quantitative coronary angiography. Rest and stress absolute MBF and MFR were quantified from first-pass 82Rb PET curves. Regional relative myocardial perfusion summed stress score (SSS), summed rest score (SRS), regional phase bandwidth (BW), and regional semi-quantitative asynchrony visual scores of (Asynch) were assessed. We found that in apparently normal arteries (SSS < 4, SRS < 4 and stenosis < 70%), those with abnormally low MFR < 2.0 compared to those with MFR ≥ 2.0 had larger phase BW (186 ± 79° vs 158 ± 67°, P = .02), and more visually apparent Asynch (5.7 ± 4.2 vs 3.9 ± 3.6, P = .02), which was associated with increasing stenosis values (ρ = 0.44, P < .0001).

CONCLUSION

A subgroup of coronary territories with normal relative perfusion and normal or non-obstructive coronary disease may have reduced MFR, which is signaled physiologically by a mild degree of left ventricular asynchrony.

Vessel-specific quantification of absolute myocardial blood flow, myocardial flow reserve and relative flow reserve by means of fused dynamic 13NH3 PET and CCTA: Ranges in a low-risk population and abnormality criteria

OBJECTIVES

The goal of the present work is to present a novel methodology for the extraction of MBF, MFR and RFR along coronary arteries by means of multimodality image fusion of dynamic PET and CCTA images.

BACKGROUND

FFR is the reference standard to identify flow-limiting lesions, but its invasiveness limits broad application. New noninvasive methodologies are warranted to stratify patients and guide treatment.

METHODS

A group of 16 low-risk CAD subjects who underwent both 13NH3 PET and CCTA were analyzed. Image fusion techniques were employed to align the studies and CCTA-derived anatomy used to identify coronaries trajectories. MBF was calculated by means of a 1-tissue compartmental model for the standard vascular territories and along patient-specific vessel paths from the base to the apex of the heart.

RESULTS

Low-risk ranges for MBF. MFR and RFR for LAD, LCX and rPDA were computed for the entire cohort and separated by gender. Computed low-risk ranges were used to assess a prospective patient with suspected CAD.

CONCLUSIONS

Our vessel-specific functional indexes and 3D displays offer promise to more closely replicate what is commonly performed during a catheterization session and have the potential of providing effective noninvasive tools for the identification of flow-limiting lesions and image-guided therapy.

Diagnostic performance of an artificial intelligence-driven cardiac-structured reporting system for myocardial perfusion SPECT imaging

OBJECTIVES

To describe and validate an artificial intelligence (AI)-driven structured reporting system by direct comparison of automatically generated reports to results from actual clinical reports generated by nuclear cardiology experts.

BACKGROUND

Quantitative parameters extracted from myocardial perfusion imaging (MPI) studies are used by our AI reporting system to generate automatically a guideline-compliant structured report (sR).

METHOD

A new nonparametric approach generates distribution functions of rest and stress, perfusion, and thickening, for each of 17 left ventricle segments that are then transformed to certainty factors (CFs) that a segment is hypoperfused, ischemic. These CFs are then input to our set of heuristic rules used to reach diagnostic findings and impressions propagated into a sR referred as an AI-driven structured report (AIsR). The diagnostic accuracy of the AIsR for detecting coronary artery disease (CAD) and ischemia was tested in 1,000 patients who had undergone rest/stress SPECT MPI.

RESULTS

At the high-specificity (SP) level, in a subset of 100 patients, there were no statistical differences in the agreements between the AIsr, and nine experts' impressions of CAD (P = .33) or ischemia (P = .37). This high-SP level also yielded the highest accuracy across global and regional results in the 1,000 patients. These accuracies were statistically significantly better than the other two levels [sensitivity (SN)/SP tradeoff, high SN] across all comparisons.

CONCLUSIONS

This AI reporting system automatically generates a structured natural language report with a diagnostic performance comparable to those of experts.

Relationship of 82Rb PET territorial myocardial asynchrony to arterial stenosis

OBJECTIVE

82Rb PET/CT rest/regadenoson-stress data enable quantification of left ventricular rest and stress function, perfusion, and asynchrony. Our study was conducted to determine which parameters best identify patients with multi-vessel disease (MVD) and individual stenosed arteries.

METHODS

PET/CT data were reviewed retrospectively for 105 patients referred for evaluation of CAD, who also underwent angiography. % arterial stenosis was determined quantitatively at a core laboratory. Severe stenosis was defined as ≥ 70%, and MVD as 2 or more stenosed arteries. Segmental MBF was calculated from first-pass data for arterial territories. Regional rest and stress systolic and diastolic asynchrony (Asynch) scores were determined from visual examination of phase polar maps.

RESULTS

65 vessels had stenoses ≥ 70%. 15 patients had MVD. ROC area under curve (ROC AUC) for identifying patients with MVD was 83% for Asynch and 73% for MFR. ROC AUC for identifying individual arterial territories with stenoses ≥ 70% was 81% and 72% for Asynch and MFR.

CONCLUSION

82Rb PET/CT accurately identified patients with MVD and individual stenosed territories, with regional asynchrony measurements contributing significantly to identify patients with CAD.

Diagnostic performance of the quantification of myocardium at risk from MPI SPECT/CTA 2G fusion for detecting obstructive coronary disease: A multicenter trial

BACKGROUND

The effective non-invasive identification of coronary artery disease (CAD) and its proper referral for invasive treatment are still unresolved issues. We evaluated our quantification of myocardium at risk (MAR) from our second generation 3D MPI/CTA fusion framework for the detection and localization of obstructive coronary disease.

METHODS

Studies from 48 patients who had rest/stress MPI, CTA, and ICA were analyzed from 3 different institutions. From the CTA, a 3D biventricular surface of the myocardium with superimposed coronaries was extracted and fused to the perfusion distribution. Significant lesions were identified from CTA readings and positioned on the fused display. Three estimates of MAR were computed on the 3D LV surface on the basis of the MPI alone (MARp), the CTA alone (MARa), and the fused information (MARf). The extents of areas at risk were used to generate ROC curves using ICA anatomical findings as reference standard.

RESULTS

Areas under the ROC curve (AUC) for CAD detection using MARf was 0.88 (CI = 0.75-0.95) and for MARp and MARa were, respectively 0.82 (CI = 0.69-0.92) and 0.75 (CI = 0.60-0.86) using the ≥70% stenosis criterion. AUCs for CAD localization (all vessels) using MARf showed significantly higher performance than either MARa or MARp or both.

CONCLUSIONS

Using ICA as the reference standard, MAR as the quantitative parameter, and AUC to measure diagnostic performance, MPI-CTA fusion imaging provided incremental diagnostic information compared to MPI or CTA alone for the diagnosis and localization of CAD.

Rb-82 PET/CT left ventricular mass-to-volume ratios

Left ventricular (LV) mass:volume ratios indexed to body size (Mi/Vi) provide risk stratification for cardiac events. We sought to determine whether Rb-82 PET mass and volume indices are similar to MRI normal values for low likelihood subjects, and whether abnormal indices are related to abnormal myocardial blood flow (MBF). Data were analyzed retrospectively for 194 patients referred for rest/stress Rb-82 PET. LV EF, volume and mass values were calculated and mass:volume ratios were indexed to patients' height and weight. MBF was computed from the first pass dynamic component of PET data. 53 patients at low likelihood of CAD had PET Mi/Vi = 1.35 ± 0.27, consistent with the MRI literature range of 1.0-1.5. Compared to patients with normal indexed volume (Vi), patients with abnormally high Vi had lower rest MBF (0.56 ± 0.24 vs 0.93 ± 0.57 ml/g/min, p = 0.0001), and lower stress MBF (0.97 ± 0.52 vs. 1.83 ± 0.96 ml/g/min, p < 0.0001). Stress EF < 50% predicted abnormal Vi with 90% accuracy. Patients with Mi/Vi < 1.0 had abnormally low rest EF (45 ± 16% vs. 60 ± 15%, p < 0.0001) and low rest MBF (0.58 ± 0.25 vs. 0.96 ± 0.59 ml/g/min, p < 0.0001). In our study population, abnormal LV volume and mass correlated with lower rest and stress MBF and EF, suggesting that the pathophysiologic explanation of these patients' increased risk is more extensive obstructive CAD.

Relationships between left ventricular asynchrony and myocardial blood flow

OBJECTIVE

82Rb PET protocols enable determination of left ventricular asynchrony (LVAS) at rest and stress, along with myocardial blood flow (MBF). We hypothesized that in patients with resting LVAS, MBF differs between those with stress-induced LVAS improvement and those with stress-induced LVAS deterioration.

METHODS

We retrospectively analyzed 82Rb rest/regadenoson stress PET studies of 195 patients evaluated for known or suspected coronary artery disease. MBF was computed from first-pass data; function and relative perfusion were computed from myocardial equilibrium data. LVAS was defined as phase contraction bandwidth (BW) above 82Rb gender-specific normal limits, with changes defined as BW moving into or out of normal ranges.

RESULTS

Among the 195 patients, 64 had LVAS at rest, of whom 13 reverted to normal and 51 continued to have LVAS with stress. Patients who did not improve had lower stress MBF (1.04 ± 0.69 vs 1.58 ± 0.67, p = .02) and coronary flow reserve (1.94 ± 1.16 vs 3.04 ± 1.22, p = .01) than those who did improve. ROC analysis indicated that the parameter most strongly associated with improvement in asynchrony for patients with resting LVAS was reduction in MBF heterogeneity (ROC area (accuracy) = 84%, sensitivity = 92%, and specificity = 67%).

CONCLUSION

LVAS is highly correlated with MBF and CVR, with stress-induced improvement in synchronicity most strongly associated with improved MBF homogeneity.

Left ventricular mechanical synchrony from stress and rest 82Rb PET myocardial perfusion ECG-gated studies: differentiating normal from LBBB patients

BACKGROUND

We have previously reported normal values for LV mechanical synchrony from post-stress exercise (99m)Tc SPECT studies; the goal of this study was to develop normal values for mechanical synchrony from pharmacologic stress and rest (82)Rb PET studies and compare these values to a population of LBBB patients.

METHODS AND RESULTS

The normal population consisted of 40 patients with a low likelihood of coronary artery disease. The LBBB population consisted of 23 patients with ECG evidence of LBBB. All patients were imaged with pharmacologic stress and processed using SyncTool™ (Emory Cardiac Toolbox™). Means and standard deviations were calculated for the stress and rest phase parameters. Normal male and female phase standard deviation were 15.0 ± 7.0 and 13.2 ± 7.7, respectively, for stress (P = NS), and 22.7 ± 13.2 and 16.6 ± 14.3 for rest (P = NS). Normal male and female histogram bandwidth were 38.1 ± 13.3 and 32.0 ± 13.5, respectively, for stress (P = NS) and 50.8 ± 18.7 and 44.4 ± 44.9 for rest (P = NS). ROC analysis yielded a sensitivity/specificity as high as 80%/90% for males, and 92%/75% for females (P = NS).

CONCLUSIONS

Normal values for LV mechanical synchrony have been developed for (82)Rb pharmacologic stress and rest PET studies; furthermore, the stress pharmacologic values do not differ significantly from our previously reported exercise post-stress SPECT normal values. Finally, ROC analysis confirmed that these normal values were able to differentiate normal and LBBB populations.

Temporal resolution of multiharmonic phase analysis of ECG-gated myocardial perfusion SPECT studies

BACKGROUND

Multiharmonic phase analysis (MHPA) was developed to assess left-ventricular dyssynchrony from gated myocardial perfusion single-photon emission computed tomography (GSPECT) studies. This study was intended to determine the temporal resolution of MHPA.

METHODS

A reference normal GSPECT study with 128 frames/cycle was simulated using NCAT, a nonuniform rational B-splines-based cardiac torso phantom. It was shifted in the time domain to insert phase delays. Realistic GSPECT studies (8 or 16 frames/cycle) were then obtained by down-sampling the reference and shifted studies. All GSPECT projections were generated with attenuation, scatter, collimator blurring, and Poisson noise. Seventeen regional phases were calculated from the GSPECT reconstructions (filtered back-projection without compensation for physical factors), using linear interpolation for the reference study, and MHPA for the realistic studies. Comparing the regional phases between the realistic studies without and with shifts determined whether MHPA could identify certain phase delays.

RESULTS

When there were enough counts/pixel (>10 counts/pixel), MHPA with either 1, 2, or 3 harmonics could resolve a phase difference of 5.6 degrees , corresponding to 1/64 of the cardiac cycle.

CONCLUSIONS

With clinically equivalent counts, the temporal resolution of MHPA is 1/64 of a cardiac cycle. Achieving this high temporal resolution from data with low temporal resolution demonstrates the benefit of replacing discrete points with continuous harmonic functions.

The increasing role of quantification in clinical nuclear cardiology: the Emory approach

Single photon emission computed tomography (SPECT) myocardial perfusion imaging has attained widespread clinical acceptance as a standard of care for patients with known or suspected coronary artery disease. A significant contribution to this success has been the use of computer techniques to provide objective quantitative assessment in interpreting these studies. We have implemented the Emory Cardiac Toolbox (ECTb) as a pipeline to distribute the software tools that we and others have researched, developed, and validated to be clinically useful so that diagnosticians everywhere can benefit from our work. Our experience has demonstrated that integration of all software tools in a common platform is the optimal approach to promote both accuracy and efficiency. Important attributes of the ECTb approach are (1) our extensive number of normal perfusion databases for SPECT and positron emission tomography (PET) studies, each created with at least 150 patients; (2) our use of Fourier analysis of regional thickening to ensure proper temporal resolution and to allow accurate measurement of left ventricular function and dyssynchrony; (3) our development of PET tools to quantify myocardial hibernation and viability; (4) our development of 3-dimensional displays and the use of these displays as a platform for image fusion of perfusion and computed tomography angiography; and (5) the use of expert systems for decision support. ECTb is an important tool for extracting quantitative parameters from all types of cardiac radionuclide distributions. ECTb should continue to play an important role in establishing cardiac SPECT and PET for flow, function, metabolism, and innervation clinical applications.

RENEX: an expert system for the interpretation of 99mTc-MAG3 scans to detect renal obstruction

A renal expert system (RENEX) has been developed to assist physicians detect renal obstruction in patients undergoing pre- and postfurosemide 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) scans. RENEX uses quantitative parameters extracted from the dynamic renal scan data and heuristic rules in the form of a knowledge base (KB) obtained from expert interpreters to conclude whether a kidney is obstructed.

METHODS

Normal limits were established for 47 quantitative parameters extracted from the 99mTc-MAG3 scans of 100 potential renal donors. From these data the domain expert estimated 5 boundary conditions for each parameter: (i) definitely abnormal, (ii) probably abnormal, (iii) equivocal, (iv) probably normal, and (v) definitely normal. A sigmoid-type curve was then generated from these 5 boundary conditions, creating a parameter knowledge library used for converting the value of a prospective patient's individual quantitative parameters to a certainty factor (CF). Sixty heuristic rules were extracted from the domain expert to generate the KB for detecting obstruction. A forward-chaining inference engine was developed using the MYCIN combinatories (an approximation of Bayes theorem) to determine obstruction. A justification engine was implemented, which recorded the sequence of each rule that was fired and the current CF value of all input and output parameters at the time of instantiation to track and justify the logic of the conclusions. The entire system was fine tuned and tested using a pilot group of 32 patients (11 males, 21 females; mean age, 56.8 +/- 17.2 y; 63 kidneys) deemed by an expert panel to have 41 unobstructed kidneys, 13 obstructed kidneys,and 9 equivocal findings.

RESULTS

RENEX agreed with the expert panel in 92% (12/13) of the obstructed kidneys, 93% (38/41) of the unobstructed kidneys, and 78% (7/9) of the kidneys interpreted as equivocal for obstructions. Processing time per patient was practically instantaneous using a 3.0-GHz personal computer programmed using interactive data language.

CONCLUSION

We have developed a renal expert system for detecting renal obstruction using pre- and postfurosemide 99mTc-MAG3 renal scans, at a standardized expert level. These encouraging preliminary results warrant a prospective study in a large population of patients with and without renal obstruction to establish the diagnostic performance of this system.

Onset of left ventricular mechanical contraction as determined by phase analysis of ECG-gated myocardial perfusion SPECT imaging: development of a diagnostic tool for assessment of cardiac mechanical dyssynchrony

BACKGROUND

A count-based method using technetium-99m sestamibi electrocardiography-gated myocardial perfusion single photon emission computed tomography imaging has been developed to extract the left ventricular (LV) regional phase of contraction (onset of mechanical contraction [OMC]) throughout the cardiac cycle. This study was performed to develop OMC normal databases and dynamic OMC displays for assessment of cardiac mechanic dyssynchrony.

METHODS AND RESULTS

LV regional phases were extracted from 90 enrolled normal subjects (45 men and 45 women) by use of the Emory Cardiac Toolbox and then submitted to statistical analysis to generate the normal databases. The LV OMC wave was dynamically propagated over the perfusion polar map by blackening either sequential phase bins or all past phases. The developed OMC normal databases consisted of peak phase (134.5 degrees +/- 14.3 degrees for men and 140.2 degrees +/- 14.9 degrees for women), phase SD (14.2 degrees +/- 5.1 degrees for men and 11.8 degrees +/- 5.2 degrees for women), and phase histogram bandwidth (38.7 degrees +/- 11.8 degrees for men and 30.6 degrees +/- 9.6 degrees for women), skewness (4.19 +/- 0.68 for men and 4.60 +/- 0.72 for women), and kurtosis (19.72 +/- 7.68 for men and 23.21 +/- 8.16 for women). Both statistical analysis and dynamic OMC displays were incorporated into a user interface as a diagnostic tool.

CONCLUSION

The OMC normal databases and dynamic OMC displays should help clinicians evaluate cardiac mechanic dyssynchrony. Prospective clinical trials are needed to validate whether this tool can be used to select patients with severe heart failure symptoms who might benefit from cardiac resynchronization therapy.

Assessment of cardiac wall motion and ejection fraction with gated PET using N-13 ammonia

BACKGROUND

Cardiac gating is not routinely used in cardiac positron emission tomography (PET). The aim of this study was to determine the feasibility of assessing regional wall motion, ejection fraction (EF), cardiac volumes, and mass with nitrogen-13 ammonia (N-13 ammonia) at the time of PET myocardial perfusion imaging.

METHODS

We studied 12 healthy volunteers (mean age, 28 +/- 8 years) and 53 patients with documented coronary artery disease (CAD) (mean age, 59 +/- 11 years). All subjects received a single administration of approximately 600 MBq (16 mCi) of N-13 ammonia intravenously. A 6-minute dynamic scan was performed for quantitative assessment of myocardial perfusion at rest, followed by a separate, 13-minute static scan acquired in the gated mode (8 equal bins). Gated data was imported into the Emory Toolbox. Wall motion was evaluated by dividing the myocardium into 9 anatomic regions graded semiquantitatively.

RESULTS

Healthy volunteers had a normal EF (61 +/- 6), end systolic volume (ESV) (37 +/- 15 mL), end diastolic volume (EDV) (89 +/- 25 mL), and cardiac mass (116 +/- 18 g). In contrast, patients with CAD showed reduced EF (32 +/- 13%) and increased ESV (129 +/- 56 mL), EDV (188 +/- 68 mL), and cardiac mass (173 +/- 45 g) (P < 0.001 for each). In patients with CAD, EF measured by gated PET correlated significantly to independent measurements of EF (P < 0.001).

CONCLUSIONS

Gating of cardiac perfusion images obtained after administration of N-13 ammonia is feasible and appears to be an accurate means of evaluating regional and global cardiac function. Gating can provide important additional diagnostic and prognostic information.

Gated stress-only 99mTc myocardial perfusion SPECT imaging accurately assesses coronary artery disease

In today's cost containment environment it is important to consider changes to standard protocols which would reduce cost, particularly if there is no significant loss of diagnostic accuracy. The aim of the present study was to assess the usefulness of a gated stress-only Tc sestamibi protocol in comparison to conventional gated dual isotope rest-stress myocardial perfusion single photon emission computed tomography (SPECT) in the detection and localization of coronary artery disease (CAD). Sixty-five consecutive patients (65+/-10 years, 22 women) who had undergone conventional gated perfusion SPECT were chosen retrospectively. Fifty-three of these 65 patients had previous coronary arteriography, 45 with at least one stenosis, eight without stenosis, and 12 of these 65 patients had <5% likelihood of CAD. Three readers interpreted the gated stress-only and dual isotope studies in separate sessions blinded to (1). their previous readings, (2). the interpretation by others, and (3). the angiographic results. Readers used a five-point scale to score their visual and quantitative assessment of perfusion, function and compromised vascular territory. Their average score was used for determination of the accuracy by using receiver operating characteristic (ROC) analysis of the techniques. The areas under ROC curves were determined for the detection of CAD and localization of vascular territories. Fifty-four of these patients had 97 significant stress induced perfusion defects as determined by the CEqual quantitative program. The agreement between protocols for the assessment of reversibility in these 97 defects was analysed. There were no statistically significant differences between dual isotope rest/stress and gated stress-only studies for the detection and localization of CAD. The area under the dual isotope rest/stress ROC curve was 0.78+/-0.07 compared to the area under the gated stress-only ROC curve of 0.80+/-0.06, resulting in P=0.30. For the combined vessels comparison of the area under the dual isotope rest/stress ROC curve was 0.73+/-0.04 versus the area under the gated stress-only ROC curve of 0.74+/-0.04, resulting in P=0.27. Similar non-significant differences were obtained when comparing the area under the dual isotope versus gated stress-only ROC curves for the left anterior descending vascular territory (LAD, 0.61+/-0.08 vs 0.660.08, P=0.14), the left circumflex vascular territory (LCX, 0.82+/-0.07 vs 0.81+/-0.06, P =0.47) or the right coronary vascular territory (RCA, 0.80+/-0.06 vs 0.78+/-0.06, P=0.28). The analysis of the reversibility of stress induced perfusion defects yielded a global agreement between protocols of 93% (kappa=0.42). The differences were due to the expert readers, using the gated stress-only protocol, misinterpreting some patients with attenuation artefacts, subendocardial infarction and functional stunning. These results show that the lower cost gated stress-only myocardial Tc myocardial perfusion SPECT studies are comparable to the conventional dual isotope studies when the clinical question is the detection and localization of coronary artery disease. Nevertheless, we also showed that this approach is limited when attempting to interpret the reversibility of stress induced perfusion defects in patients who exhibit attenuation artefacts, subendocardial infarction and functional stunning.

Feasibility of detecting cardiac torsion in myocardial perfusion gated SPECT data

BACKGROUND

The dynamic twisting component of cardiac motion is not accounted for by radionuclide techniques so that maps of perfusion and wall thickening are motion-blurred by torsion. This study examined whether torsion can be estimated from gated single photon emission computed tomography data and whether torsion corrections affect cardiac measurements.

METHODS AND RESULTS

Technetium 99m sestamibi myocardial perfusion gated tomograms were selected retrospectively for 52 patients who had x-ray contrast arteriograms: 12 with normal perfusion (group 1), 12 with abnormal perfusion (group 2), and 28 studied after angioplasty (group 3). The 8 gated perfusion maps were transformed by contrast normalization, the count minimums of which were tracked to quantify torsion. Measured torsion was used to correct maps of perfusion and wall thickening. Torsion was found to be visually detectable equally well in groups 1 and 2. Apical torsion was significantly greater for group 1 than groups 2 and 3 (15 degrees +/- 9 degrees vs 9 degrees +/- 15 degrees and 2 degrees +/- 12 degrees ) and was opposite in sign for patients with apical aneurysms (-4 degrees +/- 13 degrees ) and for patients after coronary artery bypass grafting (CABG) (-4 degrees +/- 15 degrees ). Maximum percent count differences were 10% +/- 16% between torsion-corrected versus uncorrected perfusion maps. The greatest wall thickening differences were seen for patients with left ventricular apical aneurysms and for patients after CABG versus group 1 (10% +/- 6% and 8% +/- 6% vs 3% +/- 1%, respectively).

CONCLUSIONS

It is feasible to detect cardiac torsion in the majority of Tc-99m sestamibi myocardial perfusion scans. Abnormal twisting patterns distinguished patients after CABG and those with left ventricular aneurysms from subjects with normal perfusion in a manner similar to magnetic resonance imaging observations.

Comparison between ECTb and QGS for assessment of left ventricular function from gated myocardial perfusion SPECT

BACKGROUND

The most widely distributed software packages to compute left ventricular (LV) volume and ejection fraction (EF) from gated perfusion tomograms are QGS and the Emory Cardiac Toolbox (ECTb). Because LV modeling and time sampling differ between the algorithms, it is necessary to document relationships between values produced by them and to establish normal limits individually for each software package in order to interpret results obtained for individual patients.

METHODS AND RESULTS

Gated single photon emission computed tomography technetium 99m sestamibi myocardial perfusion studies were collected and analyzed for 246 patients evaluated for coronary artery disease. QGS and ECTb values of ejection fraction (EF), end-diastolic volume (EDV), and end-systolic volume were found to correlate linearly (r = 0.90, 0.91, and 0.94, respectively), but EF and EDV were significantly lower for QGS than with ECTb (53% +/- 13% vs 61% +/- 13 and 102 +/- 45 mL vs 114 +/- 50 mL, respectively). To compare calculations for healthy subjects between the two software packages, data were also selected for 50 other patients at low likelihood for coronary artery disease, for whom EF and EDV were significantly lower for QGS compared with ECTb (62% +/- 9% vs 67% +/- 8% and 84 +/- 26 mL vs 105 +/- 33 mL, respectively). The ECTb lower limit was 51% for EF and the upper limits were 171 mL for EDV and 59 mL/m(2) for mass-indexed EDV, compared with limits of 44%, 137 mL, and 47 mL/m(2) for QGS.

CONCLUSIONS

Although correlations were strong between the two methods of computing LV functional values, statistical scatter was substantial and significant biases and trends observed. Therefore, when both software packages are used at the same site, it will be important to take these differences into consideration and to apply normal limits specific to each set of algorithms.

Evaluation of left ventricular endocardial volumes and ejection fractions computed from gated perfusion SPECT with magnetic resonance imaging: comparison of two methods

BACKGROUND

Two methods of computing left ventricular volumes and ejection fraction (EF) from 8-frame gated perfusion single photon emission computed tomography (SPECT) were compared with each other and with magnetic resonance (MR) imaging.

METHODS AND RESULTS

Thirty-five subjects underwent 8-frame gated dual-isotope SPECT imaging and 12- to 16-frame gated MR imaging. Endocardial boundaries on short-axis MR images were hand traced by experts blinded to any SPECT results. Volumes and EF were computed with the use of Simpson's rule. SPECT images were analyzed for the same functional variables with the use of 2 automatic programs, Quantitative Gated SPECT (QGS) and the Emory Cardiac Toolbox (ECTb). The mean difference between MR and SPECT EF was 0.008 for ECTb and 0.08 for QGS. QGS showed a slight trend toward higher correlation for EF (r = 0.72, SE of the estimate = 0.08) than ECTb (r = 0.70, SE of the estimate = 0.09). For both SPECT methods, left ventricular volumes were similarly correlated with MR, although SPECT volumes were higher than MR values by approximately 30%.

CONCLUSIONS

QGS and ECTb values of cardiac function computed from 8-frame gated perfusion SPECT correlate very well with each other and correlate well with MR. Averaged over all subjects, ECTb measurements of EF are not significantly different from MR values but QGS significantly underestimates the MR values.

Diagnostic performance of an expert system for the interpretation of myocardial perfusion SPECT studies

An expert system (PERFEX) developed for the computer-assisted interpretation of myocardial perfusion SPECT studies is now becoming widely available. To date, a systematic validation of the diagnostic performance of this expert system for the interpretation of myocardial perfusion SPECT studies has not been reported.

METHODS

To validate PERFEX's ability to detect and locate coronary artery disease (CAD), we analyzed 655 stress/rest myocardial perfusion prospective SPECT studies in patients who also underwent coronary angiography. The patient population comprised CAD patients (n = 480) and healthy volunteers (n = 175) (449 men, 206 women). Data from 461 other patient studies were used to implement and refine 253 heuristic rules that best correlated the presence and location of left ventricular myocardial perfusion defects on SPECT studies with angiographically detected CAD and with human expert visual interpretations. Myocardial perfusion defects were automatically identified as segments with counts below sex-matched normal limits. PERFEX uses the certainty of the location, size, shape, and reversibility of the perfusion defects to infer the certainty of the presence and location of CAD. The visual interpretations of tomograms and polar maps, vessel stenosis from coronary angiography, and PERFEX interpretations were all accessed automatically from databases and were used to automatically generate comparisons between diagnostic approaches.

RESULTS

Using the physician's reading as a gold standard, PERFEX's sensitivity and specificity levels for detection and localization of disease were, respectively, 83% and 73% for CAD, 76% and 66% for the left anterior descending artery, 90% and 70% for the left circumflex artery, and 74% and 79% for the right coronary artery. These results were extracted from a receiver operating characteristic curve using the average optimal input certainty factor.

CONCLUSION

This study shows that the diagnostic performance of PERFEX for interpreting myocardial perfusion SPECT studies is comparable with that of nuclear medicine experts in detecting and locating CAD.

Clinical impact of arrhythmias on gated SPECT cardiac myocardial perfusion and function assessment

BACKGROUND

We reported previously that mean quantified cardiac functional parameters computed by one gated single photon emission computed tomography (SPECT) technique were not significantly altered by common gating errors. However, it is not known to what extent other gated SPECT approaches that are based on different ventricular modeling assumptions are influenced by arrhythmias, nor are the effects of gating errors on visual analyses and their subsequent clinical implications known.

METHODS

Projection data for 50 patients (aged 64 +/- 12 years; 68% men; 76% with myocardial perfusion defects) undergoing technetium-99m sestamibi gated SPECT who were in sinus rhythm during data acquisition were altered to simulate common arrhythmias. To determine quantitative effects, we performed calculations for original control and altered images by Gaussian myocardial detection (Quantitative Gated SPECT [QGS] program) and by wall thickening derived from gated perfusion polar maps (Emory Cardiac Toolbox program). To evaluate visual assessment in control and simulated-arrhythmia tomograms, 2 experienced blinded observers independently interpreted perfusion from polar maps and wall motion and thickening from tomographic cines, using a 4-point scale.

RESULTS

Although mean functional parameters were scarcely altered, paired t tests showed ejection fraction fluctuations to be significantly different from control values, causing patients to change between abnormal and normal ejection fraction categories (2% of patients by QGS and 14% by Emory Cardiac Toolbox). Visual examination of QGS polar perfusion and function maps showed changes for 72% of cases, although in only 4% were these considered to have potential clinical consequences. The kappa statistic for visual analysis of concordance between control and arrhythmia readings showed that agreement was "excellent" for perfusion, "good" for motion, and "marginal" for thickening.

CONCLUSIONS

As with quantitative measurements, thickening is the parameter most prone to error in the presence of arrhythmias. It is important to test data for gating errors to avoid potentially erroneous measurements and visual readings.

Three-dimensional color-modulated display of myocardial SPECT perfusion distributions accurately assesses coronary artery disease

The objective of this study was to compare visual assessment of 3-dimensional color-modulated (to counts) surface displays with visual assessment of oblique tomographic slices of myocardial SPECT perfusion distributions in the detection and localization of coronary artery disease (CAD).

METHODS

Sixty-two consecutive patients (41 men, 21 women; mean age, 61 +/- 11 y) who had undergone conventional dual-isotope perfusion SPECT were retrospectively chosen; 50 had undergone coronary arteriography previously, and 12 had less than a 5% likelihood of CAD. Four readers interpreted the 3-dimensional displays and slices in separate sessions while unaware of the findings of previous readings, the interpretations of others, and the angiographic results. The readers used a 5-point scoring system. Their average score was used for receiver operating characteristic (ROC) analysis. The area under the ROC curves was determined so that the ability of the 2 methods to detect and localize CAD could be compared.

RESULTS

No significant differences were found between visual interpretation of 3-dimensional displays and visual interpretation of slices.

CONCLUSION

These preliminary results indicate that visual interpretation of 3-dimensional displays of myocardial perfusion SPECT distributions may someday replace visual assessment of conventional slices without loss of diagnostic accuracy.

Determination of Myocardial Viability with ECG-Gated Fluorodeoxyglucose F-18 Positron Emission Tomography

OBJECTIVE: We hypothesize that ECG-gated positron emission tomography (PET) using Fluorodeoxyglucose F-18 (FDG) alone can determine myocardial viability by identifying dysfunctional myocardium with preserved glucose metabolism. We compared the contraction-metabolism pattern of gated FDG PET with the perfusion-metabolism pattern of conventional PET using N-13 ammonia (NH(3)) as a perfusion agent and FDG as a glucose metabolism agent in 21 consecutive patients with chronic coronary artery disease with left ventricular dysfunction (mean ejection fraction 23.6 +/- 7.7%).METHODS: The left ventricle was divided into 17 segments. Uptakes of NH(3) and FDG were scored from absent (0) to normal (4), and wall motion was scored from dyskinesia (-1) to normal (3). Scores were determined by the visual interpretation of the majority of 3 blinded expert readers. Viable myocardium was defined by normal or mildly reduced uptakes of both NH(3) and FDG, perfusion-metabolism mismatch on NH(3)-FDG PET, or normal to mildly reduced uptake of FDG with regional dysfunction on gated FDG PET.RESULTS: Gated FDG PET identified 184 segments as viable, all of which were determined as viable by NH(3)-FDG PET. Among 125 segments identified as nonviable by NH(3)-FDG PET, 76 segments were determined as nonviable by NH(3)-FDG PET. The results provided a positive and negative predictive value of gated FDG PET for the determination of myocardial viability to be 100% and 60.8%, respectively.CONCLUSIONS: Gated FDG PET has a high positive predictive value (100%) for the identification of viable myocardium.

Left ventricular function and perfusion from gated SPECT perfusion images: an integrated method

A new technique for computing left ventricular function, including left ventricular volumes, mass and ejection fraction, has been developed. This method is a logical extension of the results of a standard perfusion quantification technique; thus, it allows integration of perfusion and functional information.

METHODS

Anatomically based models of the endocardial and epicardial surfaces are generated using the myocardial samples for which perfusion values are quantified, for all frames in the cardiac cycle. With these surface points, left ventricular chamber volume and myocardial volume can be computed. A computer simulation was used to determine the sensitivity of the approach to the assumptions of the model. Validation of volume, mass and ejection fraction was performed with correlative MR studies, and ejection fraction and left ventricular volumes were further investigated using correlative first-pass studies.

RESULTS

Automated processing was successful in 96% of the cases analyzed. End diastolic volume, end systolic volume, left ventricular mass and left ventricular ejection fraction correlated with MRI with r = 0.97, 0.99, 0.87, and 0.85, respectively. Ejection fraction from tomography correlated with first-pass values with r = 0.82, and end diastolic and end systolic volumes from tomography correlated with first-pass values with r = 0.85 and r = 0.91, respectively.

CONCLUSION

The new integrated approach is accurate and robust for computing both perfusion and function from perfusion tomograms.

A quantitative evaluation of the three dimensional reconstruction of patients' coronary arteries

BACKGROUND

Through extensive training and experience angiographers learn to mentally reconstruct the three dimensional (3D) relationships of the coronary arterial branches. Graphic computer technology can assist angiographers to more quickly visualize the coronary 3D structure from limited initial views and then help to determine additional helpful views by predicting subsequent angiograms before they are obtained.

METHODS

A new computer method for facilitating 3D reconstruction and visualization of human coronary arteries was evaluated by reconstructing biplane left coronary angiograms from 30 patients. The accuracy of the reconstruction was assessed in two ways: 1) by comparing the vessel's centerlines of the actual angiograms with the centerlines of a 2D projection of the 3D model projected into the exact angle of the actual angiogram; and 2) by comparing two 3D models generated by different simultaneous pairs on angiograms. The inter- and intraobserver variability of reconstruction were evaluated by mathematically comparing the 3D model centerlines of repeated reconstructions.

RESULTS

The average absolute corrected displacement of 14,662 vessel centerline points in 2D from 30 patients was 1.64 +/- 2.26 mm. The average corrected absolute displacement of 3D models generated from different biplane pairs was 7.08 +/- 3.21 mm. The intraobserver variability of absolute 3D corrected displacement was 5.22 +/- 3.39 mm. The interobserver variability was 6.6 +/- 3.1 mm.

CONCLUSIONS

The centerline analyses show that the reconstruction algorithm is mathematically accurate and reproducible. The figures presented in this report put these measurement errors into clinical perspective showing that they yield an accurate representation of the clinically relevant information seen on the actual angiograms. These data show that this technique can be clinically useful by accurately displaying in three dimensions the complex relationships of the branches of the coronary arterial tree.

Clinical validation of three-dimensional color-modulated displays of myocardial perfusion

BACKGROUND

Two-dimensional polar maps have been validated previously with coronary arteriography for determining vascular involvement of defects from a patient's myocardial perfusion distributions with and without quantification. The purpose of this study was to validate previously developed three-dimensional color-modulated surface displays representing myocardial perfusion.

METHODS AND RESULTS

The validation consisted of comparing the agreement between the three-dimensional displays and two-dimensional polar maps in localizing perfusion defects to vascular territories in 30 patients (16 men/14 women) who underwent both a 1-day rest/stress exercise 99mTc-labeled sestamibi study and coronary arteriography. Reading by two experts was used to identify the size and location of quantified defects and corresponding areas of reversibility seen in the polar maps and, on a separate day, in the three-dimensional displays. Agreement between the two-dimensional polar maps and the three-dimensional displays resulted in identical percentages for the localization of both defects and reversibilities: left anterior descending coronary artery, 87% (26/30); left circumflex coronary artery, 97% (29/30); right coronary artery, 97% (29/30); and coronary artery disease, 97% (29/30).

CONCLUSIONS

These results show that the color-modulated three-dimensional displays are at least as good as the CEqual polar maps in localizing a perfusion defect and its reversibility to angiographically defined vascular territories and thus could be used in the routine clinical evaluation of myocardial perfusion.

Prognosis in patients with left ventricular apical aneurysm diagnosed by thallium-201 or Tc-99m sestamibi SPECT images

The prognosis of patients with left ventricular (LV) aneurysm diagnosed by thallium single-photon emission computed tomography (Tl-SPECT) or technetium-99m sestamibi SPECT (MIBI) has not previously been defined. Of 9,505 Tl or MIBI patients, 139 with apical infarct and probable LV aneurysm on tomographic images were identified. Patients were grouped by the presence of divergent versus parallel LV walls. Divergent walls show increasing separation of the walls as they approach the apex on vertical or horizontal long-axis slices. The degree of the deformation at the apex (divergent vs parallel walls), extent of impaired myocardium (total number of pixels in the defect/total number of pixels in the myocardium x 100%), percentage of reversibility, and segmental and total severity of standard deviations of perfusion defects were calculated. Seventy-six patients underwent contrast ventriculography. Patients with divergent walls (n = 57) were older (p = 0.05), had lower ejection fractions (p = 0.012), higher lung uptake (only Tl patients (p = 0.06), and more frequent ST elevation on the resting electrocardiogram (p = 0.009) than patients with nondivergent (parallel) walls. For both groups, the percent impaired myocardium was comparably high (44 +/- 9% vs 46 +/- 10%). Analysis of asynergic segments in 76 patients who underwent contrast ventriculography showed more akinetic, paradoxical, or aneurysmal segments in the apical region of the left ventricle in the group with SPECT divergent walls. Cox model analysis showed divergence as the significant correlate of death. At 5 years, survival for the group with divergent walls was 52% compared with 75% for those with nondivergent walls (p = 0.008). Despite significant apical LV impairment in both groups, mortality was almost twice as high in the group with divergent walls compared with patients with parallel walls. Thus, patients with LV aneurysm diagnosed by radionuclide SPECT perfusion imaging have a higher mortality when displaying a divergent wall pattern than patients with lesser deformity.

Three-dimensional displays of left ventricular epicardial surface from standard cardiac SPECT perfusion quantification techniques

Two methods for generating left ventricular epicardial surface from SPECT perfusion tomograms are described and validated. Both methods use the locations of the maximal reconstructed count values determined from a perfusion quantification procedure as a basis for generating surfaces.

METHODS

The first method fits circular contours, which are perpendicular to the long-axis, to the points obtained from perfusion quantification. The second method applies median and linear filters to the points to remove noise but maintain the basic shape of the surface. Both models are validated against an automatic technique and against the user-traced surfaces of both the perfusion image and an MR image of the same patient.

RESULTS

The median-filtered model was found to be closer to the standard surfaces than the circular model in all cases, and 85% of the points on the median-filtered surfaces were within one SPECT pixel length of the hand-traced MR surfaces.

CONCLUSION

Accurate, three-dimensional left ventricular epicardial surfaces can be generated quickly and easily from already existing perfusion quantification software. The resulting images may be useful for realistic displays of ventricular size, shape and the three-dimensional distribution of perfusion.

Determining the accuracy of calculating systolic wall thickening using a fast Fourier transform approximation: a simulation study based on canine and patient data

The high court yields of 99mTc-sestamibi make possible the acquisition of multiple gated SPECT studies with relatively high count densities. By reorienting these studies into gated short-axis slices, and extracting the three-dimensional myocardial perfusion distribution, we can study wall thickening using an amplitude and phase analysis methodology that examines the change in counts throughout the cardiac cycle. There have been two main concerns raised about this count-based technique: (1) What effect does the sampling rate have on the calculation of systolic wall thickening? and (2) What effect does count density have on the calculation of systolic wall thickening?

METHODS

We designed a simulation study using myocardial wall thickening data obtained from ultrasonic crystals implanted in the myocardium of a normal canine. This data was modified to produce wall thickening curves with various percent systolic wall thickening measurements, sampling rates and count densities.

RESULTS

The results show that using at least eight frames per cardiac cycle, systolic wall thickening can be calculated with enough accuracy to separate normal patients from those with cardiac dysfunction, even in areas of hypoperfused myocardium. Also, the results show the importance of calculating and interpreting phase (onset of contraction) information.

CONCLUSIONS

This count-based technique continues to show promise as a tool for calculating systolic wall-thickening from multiple gated myocardial perfusion SPECT studies, but needs to be validated in a prospective multi-center trial before being applied in a clinical setting.

Multicenter trial validation for quantitative analysis of same-day rest-stress technetium-99m-sestamibi myocardial tomograms

The accuracy of an automated quantitative analysis of same-day rest/stress 99mTc sestamibi SPECT images for detection and localization of coronary artery disease (CAD) was assessed in a multicenter trial consisting of 161 patients from 7 different clinical sites utilizing various camera computer systems.

METHODS

Of the 161 patients, 102 had angiographically documented coronary artery disease, 22 had normal coronary arteriograms, and 37 had a low (< 5%) likelihood of coronary artery disease based on their age, sex, symptoms and the results of their exercise electrocardiograms. The patients were studied using previously optimized image acquisition and processing protocols. An additional population consisting of 45 patients with single-vessel disease were evaluated to determine the optimal criteria for detection of CAD.

RESULTS

The quantitative analysis method was associated with an overall sensitivity of 87%, specificity of 36%, and normalcy rate (true negative rate in the low likelihood patients) of 81%. Sensitivity for overall detection of disease was similar (90%) in patients with and without myocardial infarction (90% versus 89%). The sensitivities and specificities for identification of disease in individual coronary arteries were, respectively, 69% and 76% for LAD, 70% and 80% for LCX, and 77% and 85% for RCA.

CONCLUSION

The results of this study demonstrate that the new objective quantitative method for analysis of same-day rest/stress 99mTc sestamibi SPECT images is accurate for detection and localization of CAD and correlates highly with expert visual interpretation.

Three-dimensional display of cardiac single photon emission computed tomography

Similar to other cardiac imaging modalities, the quest for a three-dimensional display that can be used for visualizing cardiac single photon emission, computed tomography studies has resulted in several techniques: surface shading, surface modeling, and volume rendering. Each of these techniques has its own advantages and disadvantages. Surface shading yields displays that can be used to enhance a patient's or referring clinician's understanding of a diagnosis, but they are rarely used for diagnostic purposes. Surface modeling yields images that can easily be used for diagnostic purposes, but at present have only been applied to cardiac imaging because of the difficulty of modeling other organs. Volume rendering, in some forms, is beginning to be used diagnostically for some hot-spot imaging procedures, but these are basically refined planar procedures and do not yet have application in quantitative tomography. Because of each technique's unique advantages, each will likely appear in some form in clinical cardiovascular nuclear medicine in the future.