PubMed Health⌕ Search

Biomedical subjects

E V Garcia

Publications and source records attributed to E V Garcia.

At least 19 recordsLinked to original sources
PubMed2003

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.

Aged↗
PubMed2001

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

UNLABELLED: 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.

Adult↗
PubMed2000

Echocardiographic validation of gated SPECT ventricular function measurements.

UNLABELLED: Left ventricular (LV) volumes are valuable prognostic indicators in the management of coronary artery disease and traditionally have been obtained by x-ray contrast angiography or echocardiography. There now are several scintigraphic methods to compute volumes that are based on different LV modeling assumptions. Both the reasons that calculations from different nuclear techniques can disagree with one another and the relationship of these values to the more conventional echocardiographic measurements must be investigated thoroughly for calculations to be interpretable for individual patients. METHODS: Echocardiographic volumes were determined in 33 retrospective subjects with coronary artery disease (mean age, 61 +/- 12 y; 42% men; 70% with abnormal perfusion and 58% with abnormal segmental wall motion) using the modified Simpson's rule technique applied to digitized apical 4-chamber and apical 2-chamber views of 4 averaged heartbeats. These volumes were compared with those from 3 gated SPECT methods based on Simpson's rule LV modeling similar to standard echocardiographic algorithms (SPECT EF from St. Luke's-Roosevelt Hospital) (method 1), Gaussian myocardial count profile curve fitting (QGS from Cedars-Sinai Medical Center) (method 2), and an endocardial model based on perfusion sampling and count-based thickening (Cardiac Toolbox from Emory University) (method 3). RESULTS: By ANOVA, there were no significant differences among ejection fractions (EFs), but there were for volumes. Paired t test analysis showed volumes from methods 2 and 3 to be significantly larger than echocardiographic volumes and larger than those of method 1. Linear regression analysis comparing gated SPECT and echocardiographic volumes showed a nearly identical strong correlation (r = 0.92; P < 0.000001) for all 3 methods. Excellent correlation also was found among gated SPECT volumes from the 3 methods (r = 0.94). Bland-Altman analysis and t tests showed that method 1 volumes (70 +/- 61 mL) were the same as for echocardiography (77 +/- 55 mL), but volumes were overestimated by method 2 (105 +/- 74 mL) and method 3 (127 +/- 92 mL), particularly for larger volumes. Pearson coefficients for EFs compared with echocardiography were r = 0.82, 0.75, and 0.72 for methods 1-3, respectively. EFs correlated strongly among the 3 gated SPECT methods (r = 0.86-0.92). The Fisher z test showed no differences among these methods for any of the volume or EF linear correlation analyses. CONCLUSION: All gated SPECT parameters correlated well with echocardiographic values. However, the gated SPECT method for which underlying assumptions most closely resembled those commonly used in echocardiography produced mean volume values closest in agreement with echocardiographic measurements.

Analysis of Variance↗
PubMed2000

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

UNLABELLED: 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.

Area Under Curve↗
PubMed1999

Attenuation and scatter compensation in myocardial perfusion SPECT.

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

Cardiovascular Diseases↗
PubMed1999

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

UNLABELLED: 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.

Computer Simulation↗
PubMed1998

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.

Adult↗
PubMed1997

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.

Aged↗
PubMed1995

Measuring technetium-99m-MAG3 clearance with an improved camera-based method.

UNLABELLED: Because commercially available camera-based methods are not optimized, they fail to account for dose infiltration, table attenuation and correspondence between time of injection and starting the camera. We have developed a more optimized technique to calculate camera-based clearances and applied this technique in the design of a camera-based clearance method for 99mTc-MAG3. METHODS: Technetium-99m-MAG3 scintigraphy was performed in 20 patients who had varying degrees of renal function. Data were acquired posteriorly in supine patients at 2 sec/frame for 24 frames, 15 sec/frame for 16 frames and 30 sec/frame for 40 frames. Background correction was performed using an automated elliptical region of interest. Renal depth was estimated using improved regression equations and an empirically determined attenuation coefficient derived from phantom studies. Corrections were made for table attenuation and time discrepancies between dose injection and starting the camera. The percent injected dose in the kidney at 1-2, 1-2.5 and 2-3 min postinjection and the percent injected dose at those time periods corrected for body surface area were correlated with MAG3 clearance based on a single injection, two-compartment model. RESULTS: There was high correlation between the percent injected dose in the kidney at all three time periods and the multisample clearance. Correcting for body surface areas significantly improved the correlation coefficients. Consequently, regression equations were developed to predict multisample clearance based on percent dose and body surface area. CONCLUSION: The optimization features described in this method should improve precision when sequential studies are conducted in the same patient.

Adult↗
PubMed1995

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

UNLABELLED: 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.

Coronary Circulation↗
PubMed1994

Left ventricular dilatation and multivessel coronary artery disease on thallium-201 SPECT are important prognostic indicators in patients with large defects in the left anterior descending distribution.

This study examines the importance of left ventricular (LV) dilatation, and evidence of multivessel coronary artery disease identified on thallium-201 (TI-201) single-photon emission computed tomographic (SPECT) scintigrams, for predicting long-term outcome in patients with an extensive left anterior descending (LAD) perfusion deficit. Impaired contractility of the left ventricle determined by low ejection fraction, elevated LV end-systolic volume, and dilatation of the left ventricle are known as major predictors of mortality after myocardial infarction. TI-201 single-photon emission computed tomography primarily reveals status of perfusion/redistribution, but also contains indirect information on LV function. To date, there are no TI-201 SPECT data on impaired function of the left ventricle (LV dilatation) and extent of perfusion deficits, discussed together as correlates of survival. Patient data were prospectively collected in the computer data base at Emory University. A large perfusion defect involving more than one third of the LAD territory was identified in 291 of 2,652 consecutive patients examined with TI-201 SPECT initial and 3-hour redistribution studies. Follow-up data were obtained for 284 patients (98%) at 38 +/- 14 months. Of the 291 patients, 58 died. The most powerful multivariate correlates of death were LV dilatation, multivessel disease, and the ratio of the LAD severity stress score to total severity of SDs stress score. Cox model analysis was used to determine correlates of survival. Three-year survival for patients with LV dilatation was 73% versus 89% without LV dilatation (p < 0.001). Three-year survival in patients with 1-vessel disease ("LAD only") was 94% versus 78% for multivessel disease (p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary Disease↗
PubMed1994

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

UNLABELLED: 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.

Animals↗
PubMed1994

Myocardial perfusion imaging using single-photon emission computed tomography.

Myocardial perfusion single-photon emission computed tomography (SPECT) provides three-dimensional physiological information to assess myocardial blood flow at stress and rest and myocardial viability. The availability of perfusion agents with different uptake mechanisms, thallium 201, technetium 99m-sestamibi, and 99mTc-teboroxime, has created considerable flexibility in how these agents are imaged and interpreted. The higher photon flux and fixed distribution of 99mTc sestamibi allows for multiple-gated acquisition, which yields the potential for the assessment of myocardial thickening. Pharmacological agents, such as dipyridamole, adenosine, and dobutamine, may be used with myocardial perfusion SPECT as an alternate stress procedure in patients who cannot exercise adequately. SPECT reconstruction is limited by the current lack of clinically implemented algorithms to compensate for photon scatter and attenuation or for finite spatial resolution. Data-based quantification procedures that compare a patient's results to a database of normal patients assist the diagnosticians in circumventing these limitations.

Algorithms↗
PubMed1994

Reproducibility of thallium-201 exercise SPECT studies.

UNLABELLED: A detailed analysis of intrapatient reproducibility of exercise SPECT thallium studies is presented. METHODS: Twenty patients in stable condition were re-examined with exercise-redistribution SPECT201 Tl within 3-9 days without intervening procedures. At peak stress, 3.5 mCi 201Tl were given intravenously 1 min prior to exercise termination. SPECT imaging started at 5 and 180 min. Acquisition and processing protocols were the same for all studies. Coronary angiography was performed on 19 patients and showed coronary artery disease (CAD) in 18, and no CAD in one; one patient did not have coronary arteriography. RESULTS: For 16 of 20 patients, exercise levels and ECG were comparable for both studies. Ten patients reproduced ST-segment depression; two reproduced angina; one had left bundle branch block (LBBB) on both studies after 1 min of exercise. The remaining seven patients had no ECG changes or symptoms during exercise. Four of 20 (20%) thallium scans differed: three in degree of redistribution and one (5%) in presence of a second stress defect. In three of four patients whose thallium studies showed some nonreproducibility, there were differences in exercise. Thallium results were identical in 15 of 16 patients whose ECG/exercise tests were reproducible (94%). Interobserver agreement was 95%. CONCLUSION: There was excellent reproducibility of 201Tl SPECT scintigraphy in patients who reproduced exercise test performance and symptoms.

Coronary Angiography↗