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S L Bacharach

Publications and source records attributed to S L Bacharach.

At least 37 records · Page 2Linked to original sources
PubMed1996

Effect of smoothing during transmission processing on quantitative cardiac PET scans.

UNLABELLED: The effects of attenuation in cardiac PET are large and are produced by varied and inhomogeneous attenuating media. Although a measured attenuation correction can potentially provide an exact correction for attenuation, it introduces noise into the attenuation-corrected emission scan. Transmission smoothing reduces this noise but can introduce error of its own. This study investigates these errors in absolute and relative quantitation and estimates their magnitude in a clinical setting. METHODS: Fluorodeoxyglucose cardiac PET scans of 24 subjects were processed using measured attenuation correction with different levels of transmission smoothing. Mean activity concentrations were determined in septal, anterior and lateral regions of the left ventricle at each level of transmission smoothing. A theoretical derivation of the effects of transmission smoothing is presented, so that the observed effects could be compared with theory-based predictions. RESULTS: In addition to the reduction of noise, transmission smoothing produced two further effects: (a) a previously unreported reduction in noise-induced bias, which is beneficial and (b) introduction of errors due to bad estimates of attenuation correction factors resulting from smoothing over regions where attenuation changes. The first effect was observed over all regions of the left ventricle, whereas the second reduced counts primarily in the lateral wall. Twenty-millimeter smoothing reduced noise-induced bias by an average of 4% (compared with 6-mm smoothing). This same smoothing caused an additional 9% decrease in the lateral wall as a result of the adjacent lung-lateral wall boundary. CONCLUSION: Transmission smoothing reduces both noise and noise-induced bias, but near transitions between differently attenuating media (e.g., lung-myocardial borders) may produce errors in absolute and relative quantitation. The data presented here document the magnitudes of these effects, permitting one to ensure that artifactually introduced inhomogeneities are kept small.

Artifacts↗
PubMed1996

Quantitative imaging of iodine-124 with PET.

UNLABELLED: PET is potentially very useful for the accurate in vivo quantitation of time-varying biological distributions of radiolabeled antibodies over several days. The short half-lives of most commonly used positron-emitting nuclides make them unsuitable for this purpose. Iodine-124 is a positron emitter with a half-life of 4.2 days and appropriate chemical properties. It has not been widely used because of a complex decay scheme including several high energy gamma rays. However, measurements made under realistic conditions on several different PET scanners have shown that satisfactory imaging and quantitation can be achieved. METHODS: Whole-body and head-optimized scanners with different detectors (discrete BGO, block BGO and BaF2 time-of-flight), different septa and different correction schemes were used. Measurements of resolution, quantitative linearity and the ability to quantitatively image spheres of different sizes and activities in different background activities were made using phantoms. RESULTS: Compared with conventional PET nuclides, resolution and quantitation were only slightly degraded. Sphere detectability was also only slightly worse if imaging time was increased to compensate for the lower positron abundance. CONCLUSION: Quantitative imaging with 124I appears to be possible under realistic conditions with various PET scanners.

Half-Life↗
PubMed1996

Left ventricular ejection fraction: comparison of results from planar and SPECT gated blood-pool studies.

UNLABELLED: Global ejection fraction (EF) from planar gated blood-pool (GBP) imaging is a widely accepted measure of cardiac function. It has been suggested that planar GBP could be replaced by SPECT. In this article, we compare counts-based global EF measured from SPECT and planar images and investigate reasons for discrepancies between the two. METHODS: Twenty-three subjects were imaged with both planar and SPECT GBP. SPECT short-axis slices were projected to create reprojected images. Reprojected SPECT (rSPECT) images were created in both the true long-axis view and also in a view typical of planar studies (found to be 60 degrees from the true long-axis). Thus, angle of view effects on global EF could be investigated. In addition, we studied the effects of background and attenuation. RESULTS: Long-axis rSPECT EF correlated well with planar EF (r = 0.89) but EF values were significantly higher for rSPECT than for planar (slope = 1.4, intercept = -8 EF units; p < 0.001). We found that background correction may not be necessary with rSPECT, but neither background nor attenuation explained the observed discrepancy between rSPECT and planar EFs. This discrepancy was found to be caused by atrial overlap in the planar image and disappeared when the SPECT slices were reprojected at the same angle of view as the planar images. CONCLUSION: Global EF can be easily measured from rSPECT GBP images. Long-axis rSPECT EFs are, however, greater than planar EFs by a factor of 1.4 because atrial overlap causes a significant drop in planar EF in planar images. These results suggest that (long-axis) rSPECT EFs may be more accurate than planar EFs.

Adult↗
PubMed1996

Noise reduction in PET attenuation correction by maximum likelihood histogram sharpening of attenuation images.

UNLABELLED: A new method for PET transmission data processing was developed and found to reduce transmission noise in 18F-FDG cardiac emission images. This method is based on a model that describes the measured attenuation image histogram as some unknown true underlying histogram, blurred by noise. METHODS: Emission data from an elliptical phantom (cardiac insert) and three humans were reconstructed using transmission data of varying duration with varying levels of smoothing. Biases and noise levels (cardiac sector analysis) were evaluated for the phantom (simulated replicates) and human emission images. RESULTS: The estimated attenuation histograms typically displayed three distinct peaks corresponding to air, lung and soft tissue without a priori assumptions of the underlying mu values. This method effectively sharpened the histogram peaks and performed well for the phantom and human data. For intermediate transmission noise levels, biases in the phantom sector values were <4%. The human sector results were more variable but consistent with the phantom results. Noise reduction (approximately 30%) was demonstrated across all smooth levels for the phantom data. CONCLUSION: This histogram sharpening method introduces only small bias in the cardiac sector values while achieving an increase in effective transmission scan time of 50-100%. Alternatively, histogram sharpening permits less transmission data smoothing without increased noise.

Algorithms↗
PubMed1995

Artifactual inhomogeneities in myocardial PET and SPECT scans in normal subjects.

UNLABELLED: It has been well established that PET and SPECT scans of human myocardium are subject to partial volume related effects, which can cause artifactual regional variations in activity around the myocardium. This study investigated the sources and magnitude of such artifactual inhomogeneity in subjects with normal cardiac function. METHOD: Using multi-slice, gated MRI scans from 9 normal subjects, we examined separately the influences on measured activity of wall motion, axial resolution and the relationship between wall thickness and in-plane resolution. RESULTS: Two patterns of artifactual inhomogeneity were found: a depression in activity at the antero-apex and an elevation in activity in the free wall compared with the septum. Thus, in ungated PET images the true apical/septal ratio was artifactually reduced by a factor of 0.89 (0.92 for SPECT), while the true free wall/septal ratio was enhanced by a factor of 1.12 (1.19 for SPECT). Gating improved uniformity in end-systolic (ES) images but degraded uniformity in end-diastolic (ED) images. With gating, the true PET apical/septal ratio was artifactually reduced by only 0.97 at ES, and 0.82 at ED. Similar behavior was found for SPECT. Improvements in axial resolution were found to have little effect on artifactual variations. CONCLUSION: We find that the relationship between in-plane resolution and wall thickness, but not axial resolution, is of prime importance in determining the degree of artifactual inhomogeneity in ungated scans of normal human myocardium. Gating improved ES but degraded ED homogeneity.

Adult↗
PubMed1994

Clinical significance of reduced regional myocardial glucose uptake in regions with normal blood flow in patients with chronic coronary artery disease.

OBJECTIVES: The objective of this study was to assess the clinical significance of reduced regional fluorine-18 (18F) fluorodeoxyglucose uptake with normal flow in patients with chronic coronary artery disease. BACKGROUND: In patients with ischemic left ventricular dysfunction, 18F-fluorodeoxyglucose uptake may be reduced in some myocardial regions despite normal flow. The significance of this finding is unclear and has not been investigated systematically. METHODS: Twenty-three patients with coronary artery disease and impaired ventricular function (mean ejection fraction [+/- 1 SD] 28 +/- 10%) underwent positron emission tomography with 18F-fluorodeoxyglucose and oxygen-15-labeled water at rest, exercise thallium-201 tomographic imaging with rest reinjection and gated magnetic resonance imaging to measure end-diastolic wall thickness and systolic wall thickening. RESULTS: Of 168 regions with normal flow (> or = 0.7 ml/g per min), 125 (74%) had normal 18F-fluorodeoxyglucose uptake (98 +/- 10%), and the remaining 43 (26%) showed moderately reduced 18F-fluorodeoxyglucose uptake (69 +/- 8%). Systolic wall thickening was absent at rest in 14% of regions with normal 18F-fluorodeoxyglucose uptake compared with 32% of regions with reduced 18F-fluorodeoxyglucose uptake (p < 0.01). Reversible thallium abnormalities were observed in 45 (36%) of 125 regions with normal 18F-fluorodeoxyglucose uptake compared with 27 (63%) of 43 regions with reduced 18F-fluorodeoxyglucose uptake (p < 0.01). This difference was accounted for by a higher proportion of partially reversible defects in regions with reduced 18F-fluorodeoxyglucose uptake compared with regions with normal 18F-fluorodeoxyglucose uptake (42% vs. 18%, respectively, p < 0.01). CONCLUSIONS: Thus, regions with moderately reduced 18F-fluorodeoxyglucose uptake with normal flow occur commonly in patients with ischemic left ventricular dysfunction. The majority of these regions show impaired systolic function at rest and exercise-induced thallium abnormalities that are only partially reversible. These observations suggest that such regions represent an admixture of fibrotic and reversibly ischemic myocardium.

Coronary Circulation↗
PubMed1994

Myocardial viability in patients with chronic coronary artery disease. Comparison of 99mTc-sestamibi with thallium reinjection and [18F]fluorodeoxyglucose.

BACKGROUND: 99mTc-sestamibi and thallium imaging have similar accuracy when used for diagnostic purposes, but whether sestamibi provides accurate information regarding myocardial viability in patients with chronic coronary artery disease has not been established. Since there is minimal redistribution of sestamibi over time, it may overestimate nonviable myocardium in patients with left ventricular dysfunction, in whom blood flow may be reduced at rest. METHODS AND RESULTS: We studied 54 patients with chronic coronary artery disease with a mean ejection fraction of 34 +/- 14%. Patients underwent stress/redistribution/reinjection thallium tomography and, within a mean of 5 days, same-day rest/stress sestamibi imaging using the same exercise protocol and with patients achieving the same exercise duration. Of the 111 reversible thallium defects on either the redistribution or reinjection study, 40 (36%) were determined to be irreversible on the rest/stress sestamibi study, whereas only 3 of 63 irreversible thallium defects despite reinjection (5%) were classified to be reversible by sestamibi imaging. The concordance regarding reversibility of myocardial defects between thallium stress/redistribution/reinjection and same day rest/stress sestamibi studies was 75%. A subgroup of 25 patients also underwent positron emission tomography (PET) studies with 15O-labeled water and [18F]fluorodeoxyglucose (FDG) at rest after an oral glucose load. As in the overall group of 54 patients, there was concordance between thallium and sestamibi imaging regarding defect reversibility in 51 of 73 regions (70%). In the remaining 22 discordant regions (30%), 18 (82%) appeared irreversible by sestamibi imaging but were reversible by thallium imaging. Myocardial viability was confirmed in 17 of 18 regions, as evidenced by normal FDG uptake (10 regions) or FDG/blood flow mismatch (7 regions) on PET. These regions were present in 16 of the 25 patients studied (64%). We then explored methods to improve the sestamibi results. First, when the 18 discordant regions with irreversible sestamibi defects were further analyzed according to the severity of defects, 14 (78%) demonstrated only mild-to-moderate reduction in sestamibi activity (51% to 85% of normal activity), suggestive of predominantly viable myocardium, and the overall concordance between thallium and sestamibi studies increased to 93%. Second, when an additional 4-hour redistribution image was acquired in 18 patients after the injection of sestamibi at rest, 6 of 16 discordant irreversible regions (38%) on the rest/stress sestamibi study became reversible, thereby increasing the concordance between thallium and sestamibi studies to 82%. CONCLUSIONS: These data indicate that same-day rest/stress sestamibi imaging will incorrectly identify 36% of myocardial regions as being irreversibly impaired and nonviable compared with both thallium redistribution/reinjection and PET. However, the identification of reversible and viable myocardium can be greatly enhanced with sestamibi if an additional redistribution image is acquired after the rest sestamibi injection or if the severity of reduction in sestamibi activity within irreversible defects is considered.

Adult↗
PubMed1994

Improvement of the age-related impairment in left ventricular diastolic filling with verapamil in the normal human heart.

BACKGROUND: Left ventricular (LV) diastolic function declines with the normal aging process. Because these changes are related to impaired active LV relaxation as well as to structural alterations, we hypothesized that verapamil might improve LV filling in elderly normal subjects compared with young normal subjects. METHODS AND RESULTS: We studied 27 normal volunteers (between 20 and 71 years old), with normal exercise tests and echocardiograms, by radionuclide angiography before and after 3 to 4 days of oral verapamil therapy. Indexes of global LV function were derived from analysis of background-corrected time-activity curves. Subjects were recruited from three age groups: young (26 +/- 4 years, n = 10), middle-aged (46 +/- 5 years, n = 9), and elderly (66 +/- 3 years, n = 8). Baseline resting heart rate, blood pressure, peak systolic wall stress, and LV ejection fraction did not differ among groups. Baseline peak LV filling rate (expressed in fractional stroke volume per second) was reduced in the middle-aged group (5.8 +/- 1.2, P < .01) and the elderly group (4.3 +/- 1.0, P < .01) compared with the young group (7.8 +/- 1.2). With verapamil, resting heart rate, peak systolic wall stress, LV ejection fraction, and peak ejection rate did not change in any group. Peak filling rate increased in the middle-aged group (to 6.8 +/- 1.5 SV/s, P < .01) and the elderly group (to 5.7 +/- 1.0 SV/s, P < .01) but did not change in the young group (8.0 +/- 1.4 SV/s). Also, time to peak filling rate decreased with verapamil in the elderly group (from 185 +/- 31 to 147 +/- 15 milliseconds, P < .01). The magnitude of change in filling rate was correlated positively with age (r = .55, P < .005). CONCLUSION: Verapamil selectively enhances LV diastolic filling in middle-aged and elderly subjects, compared with young adults, without affecting systolic function. This observation supports the hypothesis that the impairment of LV filling accompanying the normal aging process is, at least in part, a reversible phenomenon.

Adult↗
PubMed1994

Assessment of coronary artery disease by radionuclide cineangiography. History, current applications, and new directions.

In recent years, the utility of radionuclide cineangiography in prognostication has made it a mainstay of management decision making. With evolution of therapeutic modalities and concomitant alteration in management strategies, however, the technique and its application are undergoing parallel evolution to optimize response to current needs. Thus, in addition to standard planar rest and exercise assessment of left ventricular function, newer approaches are involving combined perfusion and function assessment, application of pharmacological stress to permit technically advantageous variations in imaging protocols, and application of SPECT technology in collecting blood pool data for tomographic display and analysis.

Acute Disease↗
PubMed1994

Whither water?

Explore the source record for details and available documents.

Coronary Circulation↗
PubMed1993

Regional systolic function, myocardial blood flow and glucose uptake at rest in hypertrophic cardiomyopathy.

Decreased 18fluorodeoxyglucose (FDG) uptake and blood flow at rest in the ventricular septum, as compared with the lateral wall, have been reported in mildly symptomatic patients with hypertrophic cardiomyopathy (HC). To assess whether regional metabolic heterogeneity in patients with HC is related to heterogeneous regional systolic function, 10 symptomatic patients (mean age 36 +/- 17 years) with HC and no coronary artery disease underwent positron emission tomography with oxygen-15-water and FDG, and nuclear magnetic resonance imaging at rest to assess regional anatomy and systolic function. Regional absolute blood flow was similar between the ventricular septum and lateral wall. In contrast, FDG activity was significantly greater in the lateral wall than in the septum (1,023 +/- 588 vs 767 +/- 388 nCi/ml, respectively; p < 0.01). However, regional systolic wall thickening was also significantly greater in the lateral wall than in the septum (5.3 +/- 4.3 vs 2.4 +/- 4.0 mm, respectively; p < 0.001). Patients were then divided into group A (n = 5) with similar regional wall thickening in the septum and lateral wall, and group B (n = 5) with greater thickening in the lateral wall than in the septum. In both groups, regional blood flow was similar between the septum and lateral wall. However, the regional septal-to-lateral FDG activity ratio was 0.97 +/- 0.31 in group A, and 0.74 +/- 0.25 in group B (p < 0.01); the ratio in group A did not differ from that in 5 normal subjects (1.02 +/- 0.58).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Concordance and discordance between stress-redistribution-reinjection and rest-redistribution thallium imaging for assessing viable myocardium. Comparison with metabolic activity by positron emission tomography.

BACKGROUND: Stress thallium scintigraphy provides important diagnostic and prognostic information in patients with coronary artery disease by demonstrating regional myocardial ischemia. However, if the clinical question being addressed is whether a region is viable and not whether there is inducible ischemia, then it may be more reasonable to perform rest-redistribution imaging rather than stress-redistribution imaging followed by either reinjection or late redistribution. Therefore, we determined whether stress-redistribution-reinjection and rest-redistribution imaging provide the same information regarding myocardial viability. METHODS AND RESULTS: Both stress-redistribution-reinjection and rest-redistribution thallium single photon emission computed tomographic imaging was performed in 41 patients with chronic stable coronary artery disease, with quantitative analysis of regional thallium activity. Thallium reinjection was performed immediately after the 3- to 4-hour redistribution images were completed. Of the 155 myocardial regions with perfusion defects on the stress images, 91 (59%) were irreversible on conventional 3- to 4-hour redistribution images. When the outcomes of these irreversible regions were assessed after reinjection and compared with rest-redistribution images, there was concordance of data regarding myocardial viability (normal/reversible or irreversible) in 72 of the 91 (79%) irreversible defects. Twenty of the 41 patients also underwent positron emission tomography at rest with [18F]fluorodeoxyglucose and [15O]water. In these patients, stress-redistribution-reinjection and rest-redistribution imaging provided concordant information regarding myocardial viability in 427 (72%) of 594 myocardial regions and discordance in 167 regions. However, when irreversible thallium defects were further analyzed according to the severity of the thallium defect in these discordant regions, 149 of 167 (89%) demonstrated only mild-to-moderate reduction in thallium activity (51% to 85% of normal activity), and positron emission tomography verified 98% of these regions to be metabolically active and viable. Thus, when the severity of thallium activity was considered within irreversible thallium defects, the concordance between stress-redistribution-reinjection and rest-redistribution imaging regarding myocardial viability increased to 94%. CONCLUSIONS: These data indicate that one of two imaging modalities, either stress-redistribution-reinjection or rest-redistribution imaging, may be used for identifying viable myocardium. However, if there are no contraindications to stress testing, stress-redistribution-reinjection imaging provides a more comprehensive assessment of the extent and severity of coronary artery disease by demonstrating regional myocardial ischemia without jeopardizing information on myocardial viability.

Coronary Angiography↗
PubMed1993

Thallium reinjection demonstrates viable myocardium in regions with reverse redistribution.

BACKGROUND: The clinical significance and pathophysiological mechanisms of reverse redistribution on stress-redistribution thallium-201 myocardial scintigraphy in patients with chronic coronary artery disease are unclear. Recent studies have shown that thallium-201 reinjection is a useful technique for the detection of myocardial viability in chronic coronary artery disease. In this investigation we determined whether thallium reinjection distinguishes viable from nonviable myocardium in regions with reverse redistribution. METHODS AND RESULTS: We studied 39 patients with chronic stable coronary artery disease (age, 60 +/- 10 years), all of whom demonstrated reverse redistribution on standard exercise-redistribution thallium single-photon emission computed tomography (SPECT). Reverse redistribution was defined as > or = 10% decrease in relative thallium-201 activity between stress and redistribution images and included either the worsening of a perfusion defect apparent on post-stress images or the appearance of a new defect on the redistribution images. Thallium reinjection was performed immediately after the 3- to 4-hour redistribution study. Of 39 regions with reverse redistribution, 32 (82%) showed enhanced thallium-201 activity (> or = 10% increase) after reinjection. In the other 7 regions (18%), the scintigraphic defect persisted after reinjection. Abnormal Q waves were present in only 8 of 32 (25%) regions with enhanced thallium-201 uptake after reinjection compared with 5 of 7 (71%) regions not responding to reinjection (P < .05). Akinetic or dyskinetic wall motion was present in 3 of 32 (9%) regions showing enhanced uptake after reinjection, in contrast with 5 of 7 (71%) regions not responding to reinjection (P < .01). Critically stenosed or totally occluded coronary arteries supplied 24 of 29 (83%) regions with enhanced thallium-201 uptake after reinjection but only 2 of 7 (28%) regions not showing a positive response to reinjection (P < .05). Collateral circulation was detected in 23 of 29 (79%) regions with a positive thallium reinjection effect but in only 1 of the other 7 regions (P < .01). Sixteen of the 39 patients also underwent positron emission tomography using 18F-fluorodeoxyglucose (FDG) to assess glucose utilization and H2(15)O to assess regional blood flow. The 14 regions with reverse redistribution that responded to reinjection with enhanced thallium uptake all showed either normal patterns of FDG uptake and flow or an ischemic pattern with increased FDG uptake relative to flow. Reduced FDG uptake and reduced flow values were seen in the two regions not responding to thallium reinjection. CONCLUSIONS: These observations indicate that reverse redistribution in chronic coronary artery disease usually reflects viable myocardium, critically dependent upon collateral circulation.

Cardiac Catheterization↗
PubMed1993

Three-dimensional registration of cardiac positron emission tomography attenuation scans.

A method is described and tested which allows three-dimensional registration of two cardiac PET attenuation scans of the same subject acquired at different times. The alignment method is based on maximizing the correlation coefficient between the stacks of slices obtained during each of the two imaging sessions. The method appears accurate to better than 1 mm in x, y and z, and better than 1.5 degrees in the three angles of rotation. The method has been tested by using it to realign deliberately misaligned attenuation scans, and also by using realigned attenuation scans to correct fluorodeoxyglucose (FDG) emission scan data. The FDG emission data reconstructed with the realigned attenuation scans do not differ appreciably from the FDG data obtained using the original attenuation data. The method should be useful in realigning emission data (using the alignment coordinates predicted by realigning the attenuation scans), correcting for subject motion between scans (especially multiple intervention scans) and may allow a subject to leave the scanning table between scans during long imaging sessions.

Deoxyglucose↗
PubMed1992

Effects of regional systolic asynchrony on left ventricular global diastolic function in patients with coronary artery disease.

Patients with coronary artery disease often have impaired left ventricular diastolic filling despite normal global systolic function. The influence of regional systolic asynchrony on diastolic function was assessed by radionuclide angiography in 60 patients with coronary artery disease and normal ejection fraction at rest: group 1 (n = 30) with normal wall motion at rest and group 2 (n = 30) with abnormal wall motion. Data were compared with those obtained from 19 normal volunteers. Age, heart rate, ejection fraction and echocardiographic end-diastolic dimension did not differ among the three groups. Peak filling rate in group 1 and group 2 was similar (2.5 +/- 0.5 and 2.3 +/- 0.6 end-diastolic counts/s, respectively) and significantly lower than that in the normal subjects (2.8 +/- 0.7 end-diastolic counts/s; p less than 0.01 vs. group 2, p less than 0.05 vs group 1). Time to peak filling rate was prolonged in group 2 (184 +/- 27 ms) compared with that in normal subjects (162 +/- 19 ms; p less than 0.01) and group 1 (172 +/- 15 ms; p less than 0.05). Left ventricular end-diastolic pressure was significantly higher in group 2 than in group 1 (14 +/- 7 vs. 10 +/- 5 mm Hg, respectively; p less than 0.05). Asynchrony was assessed by sector analysis of the radionuclide left ventricular region of interest. Diastolic asynchrony was similar in the two patient groups (30 +/- 23 ms in group 2, 26 +/- 16 ms in group 1) and was higher in both groups than in the normal subjects (16 +/- 8 ms; p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1992

Metabolic evidence of viable myocardium in regions with reduced wall thickness and absent wall thickening in patients with chronic ischemic left ventricular dysfunction.

Reduced end-diastolic wall thickness with absent systolic wall thickening has been reported to represent nonviable myocardium in patients with chronic coronary artery disease. To assess whether reduced regional end-diastolic wall thickness and absent wall thickening accurately identify nonviable myocardium, 25 patients with ischemic left ventricular dysfunction (ejection fraction at rest 27 +/- 10%) underwent positron emission tomography with oxygen-15-labeled water and 18fluorodeoxyglucose to assess metabolic activity and spin-echo gated nuclear magnetic resonance imaging to measure regional end-diastolic wall thickness and wall thickening. The presence of metabolic activity was defined as 18fluorodeoxyglucose uptake (corrected for partial volume) greater than 50% of that in normal regions. Of 355 myocardial regions evaluated, 266 were hypokinetic or normokinetic at rest and 89 were akinetic (that is, absent wall thickening). 18Fluorodeoxyglucose uptake was observed in 97% of the hypokinetic and normokinetic regions and in 74% of the akinetic regions. End-diastolic wall thickness was greater in akinetic regions with than in those without 18fluorodeoxyglucose uptake (11 +/- 4 vs. 7 +/- 3 mm, p less than 0.01). The highest values for sensitivity and specificity of end-diastolic wall thickness in predicting the absence of metabolic activity in akinetic regions were 74% and 79%, respectively, and corresponded to an end-diastolic threshold of 8 mm. However, the positive predictive accuracy was only 55% and did not improve for other end-diastolic wall thickness values. In all myocardial regions, there was only a weak correlation between 18fluorodeoxyglucose activity and either end-diastolic wall thickness (r = 0.17) or wall thickening (r = 0.32). Thus, metabolic activity is present in many regions with reduced end-diastolic wall thickness and absent wall thickening. These data indicate that assessment of regional anatomy and function may be inaccurate in distinguishing asynergic but viable myocardium from nonviable myocardium.

Adult↗
PubMed1992

Regional thallium uptake in irreversible defects. Magnitude of change in thallium activity after reinjection distinguishes viable from nonviable myocardium.

BACKGROUND: Thallium reinjection immediately after stress-redistribution imaging identifies ischemic but viable myocardium in as many as 50% of the regions characterized by conventional redistribution imaging as irreversibly injured. However, we have previously shown that some regions in which irreversible defects persist despite reinjection are metabolically active, and hence viable, by positron emission tomography. In the current study, we determined whether the severity of reduction in thallium activity within irreversible defects on redistribution images and the magnitude of change in regional thallium activity after reinjection can further discriminate viable from nonviable myocardium in such defects. METHODS AND RESULTS: We studied 150 patients with coronary artery disease by exercise thallium tomography using the rest-reinjection protocol. The three sets of images (stress, redistribution, and reinjection) were then analyzed quantitatively. The increase in regional thallium activity from redistribution to reinjection was computed, normalized to the increase observed in a normal region, and termed "differential uptake." Of the 175 myocardial regions designated to have irreversible thallium defects on conventional 3-4 hour redistribution images, 132 had only mild-to-moderate reduction in thallium activity (51-85% of normal activity), and 43 had severe reduction in thallium activity (less than or equal to 50% of normal activity). Thallium reinjection resulted in enhanced relative activity in 60 of 132 (45%) of the mild-to-moderate irreversible defects and 22 of 43 (51%) of the severe irreversible defects, leaving roughly half of these defects remaining irreversible after reinjection. However, in regions that appeared to remain irreversible despite reinjection, the magnitude of differential uptake differed between mild-to-moderate (74 +/- 14%) and severe (35 +/- 16%) irreversible defects (p less than 0.001). All regions with mild-to-moderate defects demonstrated greater than 50% differential uptake after reinjection. In contrast, all except two of the regions with severe irreversible defects demonstrated differential uptake of less than 50%. Fifteen patients also underwent positron emission tomography at rest with 18F-fluorodeoxyglucose (FDG) and 15O-water. FDG uptake was present in 91% of regions with mild-to-moderate reduction in thallium activity, and the results of differential uptake and FDG data were concordant in 81% of these regions. CONCLUSIONS: These data indicate that the magnitude of thallium uptake after reinjection differs between mild-to-moderate and severe irreversible defects on standard 3-4 hour redistribution images. The substantial differential uptake of thallium (greater than 50%) after reinjection in mild-to-moderate defects, even when relative thallium activity does not increase appreciably (and the defect appears to remain irreversible), coupled with preserved metabolic activity by positron emission tomography, supports the concept that such mild-to-moderate irreversible defects represent viable myocardium.

Adult↗