Gopal Srinivasan

Stress-induced reversible and mild-to-moderate irreversible thallium defects : Are they equally accurate for predicting recovery of regional left ventricular function after revascularization?

BACKGROUND In patients with coronary artery disease, stress-redistribution-reinjection thallium scintigraphy provides important information regarding myocardial ischemia and viability. Although both reversible and mild-to-moderate irreversible thallium defects retain metabolically active, viable myocardium, we hypothesized that stress-induced reversible thallium defects may better differentiate reversible from irreversible regional left ventricular dysfunction after revascularization. METHODS AND RESULTS Twenty-four patients with chronic coronary artery disease underwent prerevascularization and postrevascularization exercise-redistribution-reinjection thallium single photon emission CT, gated MRI, and radionuclide angiography. After revascularization, mean left ventricular ejection fraction increased from 30+/-9% to 37+/-13% at rest (P<0.001). Before revascularization, abnormal contraction at rest was observed in 56 of 110 reversible and 20 of 37 mild-to-moderate irreversible thallium defects (51% and 54%, respectively). After revascularization, regional contraction improved in 44 of 56 reversible compared with 6 of 20 mild-to-moderate irreversible thallium defects (79% and 30%, respectively; P<0.001). The final thallium content (maximum tracer uptake on redistribution-reinjection images) was significantly higher in regions with reversible defects that improved than in those that did not improve after revascularization (86+/-16% versus 66+/-9%, P<0.001). In contrast, final thallium content was similar in regions with mild-to-moderate irreversible defects that improved and in those that did not improve after revascularization (69+/-9% versus 65+/-10%, P=NS). Furthermore, when asynergic regions were grouped according to the final thallium content, at 60% threshold value, functional recovery was observed in 83% of regions with reversible defects compared with 33% of regions with mild-to-moderate irreversible defects (P<0.001). CONCLUSIONS These findings suggest that although both reversible and mild-to-moderate irreversible thallium defects after stress retain viable myocardium, the identification of reversible thallium defect on stress in an asynergic region more accurately predicts recovery of function after revascularization. Even at a similar mass of viable myocardial tissue (as reflected by the final thallium content), the presence of inducible ischemia is associated with an increased likelihood of functional recovery.

[18F]Fluorodeoxyglucose Single Photon Emission Computed Tomography Can It Replace PET and Thallium SPECT for the Assessment of Myocardial Viability?

Background —New high-energy collimators for single photon emission computed tomography (SPECT) cameras have made imaging of positron-emitting tracers, such as [ 18 F]fluorodeoxyglucose ( 18 FDG), possible. We examined differences between SPECT and PET technologies and between 18 FDG and thallium tracers to determine whether 18 FDG SPECT could be adopted for assessment of myocardial viability. Methods and Results —Twenty-eight patients with chronic coronary artery disease (mean left ventricular ejection fraction [LVEF]=33±15% at rest) underwent 18 FDG SPECT, 18 FDG PET, and thallium SPECT studies. Receiver operating characteristic curves showed overall good concordance between SPECT and PET technologies and thallium and 18 FDG tracers for assessing viability regardless of the level of 18 FDG PET cutoff used (40% to 60%). However, in the subgroup of patients with LVEF≤25%, at 60% 18 FDG PET threshold value, thallium tended to underestimate myocardial viability. In a subgroup of regions with severe asynergy, there were considerably more thallium/ 18 FDG discordances in the inferior wall than elsewhere (73% versus 27%, P 18 FDG by SPECT and PET was compared in 137 segments exhibiting severely irreversible thallium defects (scarred by thallium), 59 (43%) were viable by 18 FDG PET, of which 52 (88%) were also viable by 18 FDG SPECT. However, of the 78 segments confirmed to be nonviable by 18 FDG PET, 57 (73%) were nonviable by 18 FDG SPECT ( P Conclusions —Although 18 FDG SPECT significantly increases the sensitivity for detection of viable myocardium in tissue declared nonviable by thallium (to 88% of the sensitivity achievable by PET), it will occasionally (27% of the time) result in falsely identifying as viable tissue that has been identified as nonviable by both PET and thallium.BACKGROUND New high-energy collimators for single photon emission computed tomography (SPECT) cameras have made imaging of positron-emitting tracers, such as [18F]fluorodeoxyglucose (18FDG), possible. We examined differences between SPECT and PET technologies and between 18FDG and thallium tracers to determine whether 18FDG SPECT could be adopted for assessment of myocardial viability. METHODS AND RESULTS Twenty-eight patients with chronic coronary artery disease (mean left ventricular ejection fraction [LVEF]=33+/-15% at rest) underwent 18FDG SPECT, 18FDG PET, and thallium SPECT studies. Receiver operating characteristic curves showed overall good concordance between SPECT and PET technologies and thallium and 18FDG tracers for assessing viability regardless of the level of 18FDG PET cutoff used (40% to 60%). However, in the subgroup of patients with LVEF< or =25%, at 60% 18FDG PET threshold value, thallium tended to underestimate myocardial viability. In a subgroup of regions with severe asynergy, there were considerably more thallium/18FDG discordances in the inferior wall than elsewhere (73% versus 27%, P<.001), supporting attenuation of thallium as a potential explanation for the discordant observations. When uptake of 18FDG by SPECT and PET was compared in 137 segments exhibiting severely irreversible thallium defects (scarred by thallium), 59 (43%) were viable by 18FDG PET, of which 52 (88%) were also viable by 18FDG SPECT. However, of the 78 segments confirmed to be nonviable by 18FDG PET, 57 (73%) were nonviable by 18FDG SPECT (P<.001). CONCLUSIONS Although 18FDG SPECT significantly increases the sensitivity for detection of viable myocardium in tissue declared nonviable by thallium (to 88% of the sensitivity achievable by PET), it will occasionally (27% of the time) result in falsely identifying as viable tissue that has been identified as nonviable by both PET and thallium.

13N-ammonia myocardial blood flow and uptake: relation to functional outcome of asynergic regions after revascularization.

OBJECTIVES In this study we determined whether 13N-ammonia uptake measured late after injection provides additional insight into myocardial viability beyond its value as a myocardial blood flow tracer. BACKGROUND Myocardial accumulation of 13N-ammonia is dependent on both regional blood flow and metabolic trapping. METHODS Twenty-six patients with chronic coronary artery disease and left ventricular dysfunction underwent prerevascularization 13N-ammonia and 18F-deoxyglucose (FDG) positron emission tomography, and thallium single-photon emission computed tomography. Pre- and postrevascularization wall-motion abnormalities were assessed using gated cardiac magnetic resonance imaging or gated radionuclide angiography. RESULTS Wall motion improved in 61 of 107 (57%) initially asynergic regions and remained abnormal in 46 after revascularization. Mean absolute myocardial blood flow was significantly higher in regions that improved compared to regions that did not improve after revascularization (0.63+/-0.27 vs. 0.52+/-0.25 ml/min/g, p < 0.04). Similarly, the magnitude of late 13N-ammonia uptake and FDG uptake was significantly higher in regions that improved (90+/-20% and 94+/-25%, respectively) compared to regions that did not improve after revascularization (67+/-24% and 71+/-25%, p < 0.001 for both, respectively). However, late 13N-ammonia uptake was a significantly better predictor of functional improvement after revascularization (area under the receiver operating characteristic [ROC] curve = 0.79) when compared to absolute blood flow (area under the ROC curve = 0.63, p < 0.05). In addition, there was a linear relationship between late 13N-ammonia uptake and FDG uptake (r = 0.68, p < 0.001) as well as thallium uptake (r = 0.76, p < 0.001) in all asynergic regions. CONCLUSIONS These data suggest that beyond its value as a perfusion tracer, late 13N-ammonia uptake provides useful information regarding functional recovery after revascularization. The parallel relationship among 13N-ammonia, FDG, and thallium uptake supports the concept that uptake of 13N-ammonia as measured from the late images may provide important insight regarding cell membrane integrity and myocardial viability.

Segmentation of gated TI-SPECT images and computation of ejection fraction: A different approach

BackgroundWe describe a set of image processing algorithms and mathematical models that can be advantageously used in schemes for the segmentation of thallium-201-single photon emission computed tomography (SPECT) images and for computation of left ventricular ejection fraction (EF).MethodsThe system consists of two independent blocs for image segmentation and computation of function. The former is based on a multiresolution elliptical coordinate transformation and dynamic contour tracking. Computation of EF is formulated on the basis of both the endocardial and epicardial contours, and we compare this formulation with that using only the endocardial border for images with low signal-to-noise ratios. The accuracy of border detection was validated against manual border tracing on FDG-PET images, simulated TI-201-SPECT images where the true underlying borders were known, and actual TI-201-SPECT images. Finally, we compared EFs computed for FDG-PET, technetium-99m-SPECT and Tl-201—SPECT with those obtained from planar gated blood pool imaging.ResultsThe automatically obtained results always were within the manual uncertainty range. Agreement between myocardial volumes from positron emission tomography and automatically obtained values from the simulated Tl-201-SPECT images was excellent (r=0.95, n=32). Agreement between EFs from planar gated blood pool imaging and the other image modalities was good (FDG-PET: y=5.89+1.21x, r=0.92, see=6.24, n=19, Tc-99m-SPECT: y=−3.86+1.06x, r=0.88, see=7.78, n=9, Tl-201-SPECT: y=17.8+0.81x, r=0.77, see=7.44, n=26). For noisy input data the combined use of information from epicardial and endocardial contours gives more accurate EF values than the traditional formula on the basis of the endocardial contour only.ConclusionsAlternate approaches for segmentation and computation of function have been presented and validated. They might also be advantageously incorporated into other existing techniques.

[18F]Fluorodeoxyglucose Single Photon Emission Computed Tomography

Background —New high-energy collimators for single photon emission computed tomography (SPECT) cameras have made imaging of positron-emitting tracers, such as [ 18 F]fluorodeoxyglucose ( 18 FDG), possible. We examined differences between SPECT and PET technologies and between 18 FDG and thallium tracers to determine whether 18 FDG SPECT could be adopted for assessment of myocardial viability. Methods and Results —Twenty-eight patients with chronic coronary artery disease (mean left ventricular ejection fraction [LVEF]=33±15% at rest) underwent 18 FDG SPECT, 18 FDG PET, and thallium SPECT studies. Receiver operating characteristic curves showed overall good concordance between SPECT and PET technologies and thallium and 18 FDG tracers for assessing viability regardless of the level of 18 FDG PET cutoff used (40% to 60%). However, in the subgroup of patients with LVEF≤25%, at 60% 18 FDG PET threshold value, thallium tended to underestimate myocardial viability. In a subgroup of regions with severe asynergy, there were considerably more thallium/ 18 FDG discordances in the inferior wall than elsewhere (73% versus 27%, P 18 FDG by SPECT and PET was compared in 137 segments exhibiting severely irreversible thallium defects (scarred by thallium), 59 (43%) were viable by 18 FDG PET, of which 52 (88%) were also viable by 18 FDG SPECT. However, of the 78 segments confirmed to be nonviable by 18 FDG PET, 57 (73%) were nonviable by 18 FDG SPECT ( P Conclusions —Although 18 FDG SPECT significantly increases the sensitivity for detection of viable myocardium in tissue declared nonviable by thallium (to 88% of the sensitivity achievable by PET), it will occasionally (27% of the time) result in falsely identifying as viable tissue that has been identified as nonviable by both PET and thallium.BACKGROUND New high-energy collimators for single photon emission computed tomography (SPECT) cameras have made imaging of positron-emitting tracers, such as [18F]fluorodeoxyglucose (18FDG), possible. We examined differences between SPECT and PET technologies and between 18FDG and thallium tracers to determine whether 18FDG SPECT could be adopted for assessment of myocardial viability. METHODS AND RESULTS Twenty-eight patients with chronic coronary artery disease (mean left ventricular ejection fraction [LVEF]=33+/-15% at rest) underwent 18FDG SPECT, 18FDG PET, and thallium SPECT studies. Receiver operating characteristic curves showed overall good concordance between SPECT and PET technologies and thallium and 18FDG tracers for assessing viability regardless of the level of 18FDG PET cutoff used (40% to 60%). However, in the subgroup of patients with LVEF< or =25%, at 60% 18FDG PET threshold value, thallium tended to underestimate myocardial viability. In a subgroup of regions with severe asynergy, there were considerably more thallium/18FDG discordances in the inferior wall than elsewhere (73% versus 27%, P<.001), supporting attenuation of thallium as a potential explanation for the discordant observations. When uptake of 18FDG by SPECT and PET was compared in 137 segments exhibiting severely irreversible thallium defects (scarred by thallium), 59 (43%) were viable by 18FDG PET, of which 52 (88%) were also viable by 18FDG SPECT. However, of the 78 segments confirmed to be nonviable by 18FDG PET, 57 (73%) were nonviable by 18FDG SPECT (P<.001). CONCLUSIONS Although 18FDG SPECT significantly increases the sensitivity for detection of viable myocardium in tissue declared nonviable by thallium (to 88% of the sensitivity achievable by PET), it will occasionally (27% of the time) result in falsely identifying as viable tissue that has been identified as nonviable by both PET and thallium.

[ 18 F]Fluorodeoxyglucose Single Photon Emission Computed Tomography

Background —New high-energy collimators for single photon emission computed tomography (SPECT) cameras have made imaging of positron-emitting tracers, such as [ 18 F]fluorodeoxyglucose ( 18 FDG), possible. We examined differences between SPECT and PET technologies and between 18 FDG and thallium tracers to determine whether 18 FDG SPECT could be adopted for assessment of myocardial viability. Methods and Results —Twenty-eight patients with chronic coronary artery disease (mean left ventricular ejection fraction [LVEF]=33±15% at rest) underwent 18 FDG SPECT, 18 FDG PET, and thallium SPECT studies. Receiver operating characteristic curves showed overall good concordance between SPECT and PET technologies and thallium and 18 FDG tracers for assessing viability regardless of the level of 18 FDG PET cutoff used (40% to 60%). However, in the subgroup of patients with LVEF≤25%, at 60% 18 FDG PET threshold value, thallium tended to underestimate myocardial viability. In a subgroup of regions with severe asynergy, there were considerably more thallium/ 18 FDG discordances in the inferior wall than elsewhere (73% versus 27%, P 18 FDG by SPECT and PET was compared in 137 segments exhibiting severely irreversible thallium defects (scarred by thallium), 59 (43%) were viable by 18 FDG PET, of which 52 (88%) were also viable by 18 FDG SPECT. However, of the 78 segments confirmed to be nonviable by 18 FDG PET, 57 (73%) were nonviable by 18 FDG SPECT ( P Conclusions —Although 18 FDG SPECT significantly increases the sensitivity for detection of viable myocardium in tissue declared nonviable by thallium (to 88% of the sensitivity achievable by PET), it will occasionally (27% of the time) result in falsely identifying as viable tissue that has been identified as nonviable by both PET and thallium.BACKGROUND New high-energy collimators for single photon emission computed tomography (SPECT) cameras have made imaging of positron-emitting tracers, such as [18F]fluorodeoxyglucose (18FDG), possible. We examined differences between SPECT and PET technologies and between 18FDG and thallium tracers to determine whether 18FDG SPECT could be adopted for assessment of myocardial viability. METHODS AND RESULTS Twenty-eight patients with chronic coronary artery disease (mean left ventricular ejection fraction [LVEF]=33+/-15% at rest) underwent 18FDG SPECT, 18FDG PET, and thallium SPECT studies. Receiver operating characteristic curves showed overall good concordance between SPECT and PET technologies and thallium and 18FDG tracers for assessing viability regardless of the level of 18FDG PET cutoff used (40% to 60%). However, in the subgroup of patients with LVEF< or =25%, at 60% 18FDG PET threshold value, thallium tended to underestimate myocardial viability. In a subgroup of regions with severe asynergy, there were considerably more thallium/18FDG discordances in the inferior wall than elsewhere (73% versus 27%, P<.001), supporting attenuation of thallium as a potential explanation for the discordant observations. When uptake of 18FDG by SPECT and PET was compared in 137 segments exhibiting severely irreversible thallium defects (scarred by thallium), 59 (43%) were viable by 18FDG PET, of which 52 (88%) were also viable by 18FDG SPECT. However, of the 78 segments confirmed to be nonviable by 18FDG PET, 57 (73%) were nonviable by 18FDG SPECT (P<.001). CONCLUSIONS Although 18FDG SPECT significantly increases the sensitivity for detection of viable myocardium in tissue declared nonviable by thallium (to 88% of the sensitivity achievable by PET), it will occasionally (27% of the time) result in falsely identifying as viable tissue that has been identified as nonviable by both PET and thallium.

Using Spatial-Temporal Images for Analysis of Gated Cardiac Tomographic Data: The M-Mode Revisited

Recent advances in SPECT and PET technology permit ECG gating of tomographic cardiac images, allowing simultaneous measurement of 3D cardiac ventricular function with perfusion/metabolism. Extracting indices of regional function from these 4D data sets (3D space + time) remains a challenge. All approaches currently used to quantitate gated tomographic sequences deal separately with the spatial and temporal data. As functional information is based on close coupling between spatial and temporal changes, it could be beneficial to produce an image combining spatial and temporal information. In this paper we describe a method for producing such spatialtemporal images and, using gated FDG PET data, test the ability of these images to improve visual and quantitative assessment of cardiac function. Other potential schemes to make use of the space-time nature of this new representation are also discussed.