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Biomedical subjects

S L Bacharach

Publications and source records attributed to S L Bacharach.

117 records · Page 7Linked to original sources
PubMed1977

A real-time system for multi-image gated cardiac studies.

A minicomputer-based system is described that allows real-time construction and simultaneous display, in flicker-free movie format, of a cardiac-cycle-spanning sequence of ECG-gated scintigraphic images. In as little as 2 min, the endless-loop flicker-free movier clearly displays cardiac anatomy, time-dependent volume variations of cardiac chambers, and abnormalities of cardiac wall motion that would be difficult or impossible to detect from static gated images. Simultaneously, a time-activity curve with high temporal resolution can be generated from a previously defined region of interest, thereby quantifying additional parameters of cardiac function. Because the movie and time-activity curve are displayed in real time and require only a short data-collection interval to achieve statistical reliability, the physician can use the system interactively, modifying the form, intensity, or duration of diagnostic and therapeutic interventions based on the observed response. This system is well suited for intervention studies, for continuous cardiac monitoring, and for the rapid screening of patients with suspected cardiac disease.

Computers↗
PubMed1977

ECG-gated scintillation probe measurement of left ventricular function.

A nonimaging, ECG-gated scintillation-probe system is described that permits real-time quantification, at high temporal resolution, of the time variation of left ventricular (LV) volume over a complete, average cardiac cycle. Linearity between counting rate and volume, probe positioning, and background correction were investigated for both cylindrically collimated (CC) and parallel-hole-collimated (PC) detectors. In 53 patient studies, results obtained with these probes were compared with results obtained from an ECG-gated gamma camera system (CS) with high temporal resolution. Time-activity curves obtained by all three devices were essentially identical in shape (for CC against CS, r=0.93; for PC against CS, r=0.98) and in intracycle timing. Left-ventricular ejection fractions obtained with the probes showed workable agreement with the camera; for CC against CS, r=0.85 (N=31; for PC against CS, r=0.90 (N=21). When LV background is removed as a source of error, the correlation between (PC) probe and camera is improved (r=0.95, N=21). This suggests that the portable probe system be used in circumstances where exact knowledge of LV background is minimally important--e.g., continuous bedside monitoring of changes in LV function.

Adult↗
PubMedDate not supplied

Attenuation correction in cardiac positron emission tomography and single-photon emission computed tomography.

Quantitation in cardiac positron emission tomography (PET) and single-photon emission computed tomography (SPECT) depends on being able to correct for several physical factors that tend to distort the data. One of the most important of these corrections is the correction for attenuation. For PET, cardiac attenuation correction is a reality, although certain problems remain to be solved. For SPECT, recent developments in gamma camera hardware and reconstruction methods have finally made it possible to attempt attenuation correction in a clinical setting. This article reviews the methods available to perform attenuation correction in both PET and SPECT, with emphasis on the commonality between the problems encountered and solutions proposed for each modality.

Heart↗
PubMedDate not supplied

Segmentation of gated Tl-SPECT images and computation of ejection fraction: a different approach.

BACKGROUND: We 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). METHODS: The 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 Tl-201-SPECT images where the true underlying borders were known, and actual Tl-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. RESULTS: The 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. CONCLUSIONS: Alternate approaches for segmentation and computation of function have been presented and validated. They might also be advantageously incorporated into other existing techniques.

Algorithms↗
PubMedDate not supplied

Measurement of myocardial wall thickening from PET/SPECT images: comparison of two methods.

PURPOSE: We compared two methods for measuring myocardial wall thickening from nuclear medicine perfusion scans. The first method uses the percent change in peak activity, and the second method models a profile measured across the myocardium. METHOD: Mathematical simulations of the myocardium were used. In addition, images with PET or SPECT resolution were created from real MR images. Known amounts of noise were then added. RESULTS: The percent peak thickening (% PT) is nonlinear with true percent thickening, especially for PET resolutions [7 mm full width at half-maximum (FWHM)]. For the peak method, low levels of noise (10%) introduced an error of 8%PT for PET and of 16%PT for SPECT. Additional smoothing reduced these errors. For the fitted model, at 10% noise, the error in thickening was large: 2.3 mm for PET and 7.8 mm for SPECT. CONCLUSION: The fitted model works well only with good resolution and low noise (e.g., 7 mm FWHM and 10%). The peak method is also sensitive to noise, especially for poorer resolutions. Additional smoothing gives more reliable results for the peak method but not the fitted method. The peak method is therefore the more generally reliable, but even this method may only allow classification of myocardial thickening into broad categories.

Adult↗
PubMedDate not supplied

Realignment of emission contaminated attenuation maps with uncontaminated attenuation maps for attenuation correction in PET.

PURPOSE: We investigated aligning a transmission (T) scan with a subsequent emission contaminated transmission (T+E) scan. This would permit correction for patient motion and thereby use of a single T scan to correct E scans taken hours or days apart. METHOD: Scans from 15 patients were used to produce 200 T scans contaminated with two levels of either [18F]fluorodeoxyglucose or [13N]ammonia E data. Known misalignments were introduced between each T+E scan and the corresponding T scan, and each pair was subsequently realigned. Realignment errors were compared with those obtained for uncontaminated T scans. RESULTS: The realignment errors increase with the contamination level and depend slightly on the contaminant. However, even at the highest level of contamination studied, the mean absolute translation errors remained less than the voxel size and the mean absolute rotation errors were < 2.5 degrees. CONCLUSION: AT+E scan can be accurately realigned with a T scan. This suggests that attenuation correction could be performed by using a high quality T scan taken days or hours earlier and aligning this T scan with a short T scan taken immediately after E imaging.

Heart↗
PubMedDate not supplied

Stochastic analysis of 133xe clearance for determining regional cerebral blood flow in a primate model.

A technique for stochastic analysis of 133Xe washout using a computer-assisted Anger camera is described. The technique produces functional maps of both regional cerebral blood flow (rCBF) and error in rCBF. The calculational limitations of the technique are discussed and an experimental estimate made of the physical limitations associated with the low energy photon emitted by 133Xe. The method is demonstrated in a rhesus monkey model before and after surgical occlusion of the middle cerebral artery.

Animals↗