Dual-[11C]tracer single-acquisition positron emission tomography studies.

The ability to study multiple physiologic processes of the brain simultaneously within the same subject would provide a new means to explore the interactions between neurotransmitter systems in vivo. Currently, examination of two distinct neuropharmacologic measures with positron emission tomography (PET) necessitates performing two separate scans spaced in time to allow for radionuclide decay. The authors present results from a dual-tracer PET study protocol using a single dynamic-scan acquisition where the injections of two tracers are offset by several minutes. Kinetic analysis is used to estimate neuropharmacologic parameters for both tracers simultaneously using a combined compartmental model configuration. This approach results in a large reduction in total study time of nearly 2 hours for carbon-11-labeled tracers. As multiple neuropharmacologic measures are obtained at nearly the same time, interventional protocols involving a pair of dual-tracer scans become feasible in a single PET session. Both computer simulations and actual human PET studies were performed using combinations of three different tracers: [11C]flumazenil, N-[11C]methylpiperidinyl propionate, and [ 11 C]dihydrotetrabenazine. Computer simulations of tracer-injection separations of 10 to 30 minutes showed the feasibility of the approach for separations down to 15 to 20 minutes or less. Dual-tracer PET studies were performed in 32 healthy volunteers using injection separations of 10, 15, or 20 minutes. Model parameter estimates for each tracer were similar to those obtained from previously performed single-injection studies. Voxel-by-voxel parametric images were of good quality for injections spaced by 20 minutes and were nearly as good for 15-minute separations, but were degraded noticeably for some model parameters when injections were spaced by only 10 minutes. The authors conclude that dual-tracer single-scan PET is feasible, yields accurate estimates of multiple neuropharmacologic measures, and can be implemented with a number of different radiotracer pairs.

Statistical brain mapping of 18F-FDG PET in Alzheimer's disease: validation of anatomic standardization for atrophied brains.

UNLABELLED: Despite the increased use of statistical mapping to detect brain functional changes in Alzheimer's disease (AD), potential artifacts introduced by stereotactic anatomic standardization of atrophied brains have not been examined carefully. We investigated the effects of anatomic standardization by Statistical Parametric Mapping (SPM) and NEUROSTAT. METHODS: First, 10 AD patients and 10 age-matched healthy volunteers underwent 18F-FDG brain PET imaging. Each image set was standardized to a stereotactic brain template using SPM or NEUROSTAT, followed by pixel normalization to the global or cerebellar activity. Within-group comparisons of standardized image sets by each method and a between-group comparison of healthy volunteers and AD patients were performed using the statistical analysis routines of SPM. Second, simulated PET image sets were generated from segmented MR image sets of 5 healthy volunteers and 5 AD patients. Using the anatomic standardization parameters estimated on the simulated image sets, original gray matter MR image sets were transformed to the stereotactic coordinate system. Between-group subtraction analyses of the transformed gray matter image sets between healthy volunteers and AD groups were performed to examine the accuracy of cortical gray matter matching. RESULTS: Between-group comparison by SPM or NEUROSTAT showed generally similar areas of hypometabolism in bilateral temporoparietal, posterior cingulate, and left frontal cortices. Both methods showed possible deformation artifacts in the anterior part of the corpus callosum. The localization of the peak hypometabolism varied considerably between the two methods when global normalization was applied. The use of a common brain template for standardization resulted in asymmetric differences in cortical margins, indicating systematic differences in the deformation algorithms. The realistic simulation study revealed gray matter mismatches to be 20% greater with SPM than with NEUROSTAT. CONCLUSION: Although different statistical mapping methods may yield grossly similar patterns of hypometabolism in AD, the extent, severity, and peak location of metabolic changes can be inconsistent. Deformation accuracy appears to be more prone to atrophy. These limitations need to be considered carefully in the application and interpretation of brain mapping analysis in atrophied brains.

Attenuation corrected cardiac perfusion SPECT.

Image artifacts, especially those caused by photon attenuation, commonly affect the specificity of cardiac SPECT perfusion imaging. Although often suspected by characteristic patterns identified in female and male patients respectively, the widely variable body habitus of individual patients are associated with unpredictable variations in tissue attenuation. The accuracy of PET perfusion imaging has long benefited from correction methods for soft tissue attenuation. This paper reviews recent developments in attenuation correction methods for cardiac SPECT perfusion imaging. Several commercial methods are now available. Initial reports indicate these methods have varied greatly in their clinical success. Some methods have demonstrated significant improvements. However, others have created more artifacts than they have cured. Recent developments suggest very significant clinical advantages can be achieved with robust, well-validated methods for attenuation corrected SPECT in the diagnostic evaluation of coronary heart disease, high risk coronary disease, and women.

Maximum-likelihood transmission image reconstruction for overlapping transmission beams.

In many transmission imaging geometries, the transmitted "beams" of photons overlap on the detector, such that a detector element may record photons that originated in different sources or source locations and thus traversed different paths through the object. Examples include systems based on scanning line sources or on multiple parallel rod sources. The overlap of these beams has been disregarded by both conventional analytical reconstruction methods as well as by previous statistical reconstruction methods. We propose a new algorithm for statistical image reconstruction of attenuation maps that explicitly accounts for overlapping beams in transmission scans. The algorithm is guaranteed to monotonically increase the objective function at each iteration. The availability of this algorithm enables the possibility of deliberately increasing the beam overlap so as to increase count rates. Simulated single photon emission tomography transmission scans based on a multiple line source array demonstrate that the proposed method yields improved resolution/noise tradeoffs relative to "conventional" reconstruction algorithms, both statistical and nonstatistical.

Improved detection of left main coronary artery disease with attenuation-corrected SPECT.

BACKGROUND: Myocardial perfusion imaging has demonstrated a limited sensitivity as a means of accurately identifying left main (LM) coronary disease. Because regional quantitative perfusion biases are eliminated with attenuation corrected (AC) single photon emission computed tomography (SPECT), as compared with uncorrected (NC) SPECT, we hypothesized that AC SPECT would demonstrate increased diagnostic accuracy for the detection of significant LM coronary stenosis. METHODS AND RESULTS: We studied 28 patients (23 men, 5 women; mean age, 66+/-9 years) with significant LM stenoses (> or =50%) and 34 control patients (27 men, 7 women; mean age, 65+/-11 years) with 2-vessel coronary disease. Rest thallium-201 and stress technetium 99m sestamibi SPECT imaging with and without AC were performed, as described earlier. Both AC and NC images were analyzed visually and quantitatively in comparison with corresponding normal databases. A greater sensitivity for detection of an LM defect pattern (64% vs. 7%, P = .0009) with equivalent specificity (94% vs. 100%, P = not significant) was demonstrated by means of visual analysis of AC SPECT images. More disease was demonstrated in a greater number of territories with AC SPECT images than with NC images (2.14+/-0.97 for AC images vs. 1.43+/-0.84 for NC images, P = .0001). Similar improvement in the detection of LM disease was shown by means of automated quantitative analysis (57% for AC SPECT vs 14% for NC SPECT, P = .0005), again with no loss in specificity. CONCLUSIONS: AC SPECT with the University of Michigan method in consecutive patients with LM stenoses and a select control population with severity matched multivessel coronary disease significantly improved the diagnostic accuracy of myocardial perfusion imaging for the identification of LM coronary disease, compared with uncorrected SPECT.

Clinical review of attenuation-corrected cardiac SPECT.

Rather than the introduction of a heralded technologic advancement in cardiac SPECT imaging challenging the accuracy of PET perfusion imaging, the commercial introduction of attenuation correction has been met with at least as many negative as positive reports. Some studies have reported significant improvements in specificity or specificity and sensitivity, especially for high-risk patterns of coronary artery disease; others have reported no improvement or a decrease in accuracy resulting from the introduction of troublesome artifacts. Although this review has attempted to emphasize the positive aspects of attenuation-corrected cardiac SPECT perfusion imaging and the potential for improved patient care it may provide, several negative reports continue to appear. Still there has been sufficient positive data reported to suggest that with fully developed, accurate, and robust correction methods, significant gains in SPECT assessments of the presence and extent of CHD, patient risk, and myocardial viability can be anticipated. Ultimately attenuation correction for cardiac SPECT should have a positive impact on the management of patients with coronary artery disease with important savings in lives and health care dollars.

In vivo mapping of cerebral acetylcholinesterase activity in aging and Alzheimer's disease.

OBJECTIVE: To validate an in vivo method for mapping acetylcholinesterase (AChE) activity in human brain, preparatory to monitoring inhibitor therapy in AD. BACKGROUND: AChE activity is decreased in postmortem AD brain. Lacking a reliable in vivo measure, little is known about central activity in early AD, when the disease is commonly targeted by AChE inhibitor drug therapy. METHODS: Intravenous N-[11C]methylpiperidin-4-yl propionate ([11C]PMP) served as an in vivo AChE substrate. AChE activity was defined using cerebral PET for tracer kinetic estimates of the local rate of [11C]PMP hydrolysis in 26 normal controls and 14 patients with AD. Eleven AD patients also had concomitant in vivo cerebral measures of vesicular acetylcholine transporter (cholinergic terminal) density and glucose metabolism. RESULTS: Cerebral AChE activity measures 1) were independent of changes in tracer delivery to cerebral cortex; 2) agreed with reported postmortem data concerning normal relative cerebral distributions, absence of large age-effect in normal aging, and deficits in AD; 3) correlated in AD cerebral cortex with concomitant in vivo measures of cholinergic terminal deficits, but not with metabolic deficits; and 4) agreed quantitatively with predicted level of cerebral AChE inhibition induced by physostimine. CONCLUSIONS: This in vivo PET method provided valid measures of central AChE activity in normal subjects and AD patients. Applied in early AD, it should facilitate inhibitor treatment by confirming central inhibition, optimizing drug dosage, identifying likely responders, and testing surrogate markers of therapeutic response.

Attenuation-corrected 99mTc-tetrofosmin single-photon emission computed tomography in the detection of viable myocardium: comparison with positron emission tomography using 18F-fluorodeoxyglucose.

OBJECTIVES: The purpose of this study was to assess the efficacy of attenuation-corrected (AC) technetium-99m (99mTc)-tetrofosmin single-photon emission computed tomography (SPECT) in detecting viable myocardium compared to 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET). BACKGROUND: The role of 99mTc-labeled perfusion tracers in the assessment of myocardial viability remains controversial. Attenuation artifacts affect the diagnostic accuracy of SPECT images. METHODS: Twenty-four patients with coronary artery disease (mean left ventricular ejection fraction 30%) underwent resting 99mTc-tetrofosmin SPECT and FDG PET imaging. Both AC and non-attenuation-corrected (NC) SPECT images were generated. RESULTS: Using a 50% threshold for viability by FDG PET, the percentage of concordant segments of viability between 99mTc-tetrofosmin and FDG on the patient basis increased from 79.8%+/-14.0% (mean+/-SD) on the NC images to 90.8%+/-10.6% on the AC images (p=0.002). The percentage of 99mTc-tetrofosmin defect segments within PET-viable segments, an estimate for the degree of underestimation of viability, decreased from 19.8%+/-15.2% on the NC images to 9.7%+/-12.6% on the AC images (p=0.01). Similar results were obtained when a 60% threshold was used to define viability by FDG PET. When the anterior-lateral and inferior-septal regions were separately analyzed, the effect of attenuation correction was significant only in the inferior-septal region. CONCLUSIONS: The results indicate that AC 99mTc-tetrofosmin SPECT improves the detection of viable myocardium mainly by decreasing the underestimation of viability particularly in the inferior-septal region, although some underestimation/overestimation of viability may still occur even with attenuation correction.

Effects of misalignment between transmission and emission scans on attenuation-corrected cardiac SPECT.

UNLABELLED: Misalignment between transmission and emission scans in attenuation-corrected (AC) cardiac SPECT can introduce errors of measured activity. The severity of these errors, however, has not yet been fully elucidated. METHODS: We performed a phantom measurement as well as a study of patients with low likelihood of coronary artery disease. Transmission and emission scans were acquired using a triple-head SPECT system with a collimated 241Am line source and an offset fanbeam collimator. The left ventricular myocardium was divided into five segments, and the mean regional activity was calculated for each segment using a semiquantitative polar map approach. Misalignment between transmission and emission data was created by shifting the emission data along the x, y or z axis. RESULTS: In the heart phantom, a shift between the transmission and emission data produced a decrease or increase in relative regional activity in each segment resulting in heterogeneous activity distribution. A 7-mm (1-pixel) shift produced up to 15% change in relative regional activity, suggesting that even a small misalignment between transmission and emission data can produce serious errors in measured activity. In the clinical data, the effects of misalignment were less significant than those observed in the phantom data but were still measurable and visually identifiable. CONCLUSION: The results indicate that a small misalignment between the transmission and emission data can produce serious errors in measured activity, and, thus, geometrical precision is essential for accurate diagnosis of AC SPECT images.

Attenuation-corrected rest thallium-201/stress technetium 99m sestamibi myocardial SPECT in normals.

BACKGROUND: Rest thallium-201/stress technetium 99m sestamibi protocol is widely used in the clinical setting. Although attenuation correction (AC) represents an important recent development in cardiac single photon emission computed tomography (SPECT) imaging, adjacent extracardiac activity can affect the myocardial count density distribution on AC images, particularly with 201Tl. The aims of this study were to compare normal distribution between AC rest 201Tl and stress 99mTc-sestamibi SPECT images as well as to evaluate the effect of extracardiac activity on AC SPECT images with 99mTc and 201Tl. METHODS AND RESULTS: A phantom measurement and a study of 21 patients with low likelihood of coronary artery disease were performed with a triple-head SPECT system equipped with a americium 241 line source. In the phantom study, the presence of extracardiac activity increased the inferior-to-anterior ratios, particularly with 201Tl (1.01 to 1.32). In the clinical data, reduced count density with 201Tl compared to 99mTc-sestamibi was observed in most of the noninferior segments. On an individual segment basis, 37 (20%) of 189 segments from 11 (52%) of 21 subjects showed reduced count density on the 201Tl image compared to 99mTc-sestamibi by >10% of peak activity. CONCLUSIONS: There is a significant difference in myocardial count density distribution between 99mTc-sestamibi and 201Tl on AC SPECT images, indicating that a careful image interpretation that considers the different normal count density distribution between the tracers and/or a tracer specific normal database is necessary, especially when defect reversibility is of concern. Further work should aim for the incorporation of scatter correction combined with attenuation correction.

Deadtime correction for two multihead Anger cameras in 131I dual-energy-window-acquisition mode.

Two side-by-side energy windows, one at the photopeak and one at lower energy, are sometimes employed in quantitative SPECT studies. We measured the count-rate losses at moderately high activities of 131I for two multihead Anger cameras in such a dual-window-acquisition mode by imaging a decaying source composed of two hot spheres within a warm cylinder successively over a total of 23 days. The window locations were kept fixed and the paralyzable model was assumed. In addition, for the Picker Prism 3000 XP camera, the source was viewed from three different angles separated by 120 degrees and the final results are from an average over these three angles. For the Picker camera, the fits to the data from the individual windows are good (the mean of the squared correlation coefficient equals 0.98) while for the Siemens Multispect camera fits to the data from head 1 and from the lower-energy, monitor window are relatively poor. Therefore, with the Siemens camera the data from the two windows are combined for deadtime computation. Repeated autopeaking might improve the fits. At the maximum count rate, corresponding to a total activity of 740 MBq (20 mCi) in the phantom, the multiplicative deadtime correction factor is considerably larger for the Picker than for the Siemens camera. For the Picker camera, it is 1.11, 1.12, and 1.12 for heads 1-3 with the photopeak window and 1.10 for all heads with the lower-energy monitor window. For the Siemens camera, the combined-window deadtime correction factor is 1.02 for head 1 and 1.03 for head 2. Differences between the deadtime correction factor for focal activity and for the total activity do not support the hypothesis of count misplacement between foci of activity at these count rates. Therefore, the total-image dead time correction is recommended for any and all parts of the image.

Grouped-coordinate ascent algorithms for penalized-likelihood transmission image reconstruction.

This paper presents a new class of algorithms for penalized-likelihood reconstruction of attenuation maps from low-count transmission scans. We derive the algorithms by applying to the transmission log-likelihood a version of the convexity technique developed by De Pierro for emission tomography. The new class includes the single-coordinate ascent (SCA) algorithm and Lange's convex algorithm for transmission tomography as special cases. The new grouped-coordinate ascent (GCA) algorithms in the class overcome several limitations associated with previous algorithms. 1) Fewer exponentiations are required than in the transmission maximum likelihood-expectation maximization (ML-EM) algorithm or in the SCA algorithm. 2) The algorithms intrinsically accommodate nonnegativity constraints, unlike many gradient-based methods. 3) The algorithms are easily parallelizable, unlike the SCA algorithm and perhaps line-search algorithms. We show that the GCA algorithms converge faster than the SCA algorithm, even on conventional workstations. An example from a low-count positron emission tomography (PET) transmission scan illustrates the method.

Stereotactic coordinates from ECT sinograms for radionuclide-guided breast biopsy.

UNLABELLED: Raw data from emission scanners contained in ECT sinograms can provide an abundance of information about the position of an object in the camera's field-of-view. Since some cancers can be detected by PET and SPECT which are not seen clearly on mammograms, CT or other scans, sinogram data could potentially be used to guide tumor biopsy. For example, positron-emitting (18F-labeled Fluoro-deoxyglucose) and single-photon emitting (99mTc-labeled-sestamibi) radiopharmaceuticals have been used successfully to detect many types of breast cancer. By utilizing some relatively simple geometric relationships, a sinogram-based method for biopsy of radiopharmaceutical-avid breast masses guided by data from PET and SPECT scanners has been developed and validated in phantom studies. METHODS: A pair of projection views from a series of sinograms is used to calculate the position of photon-emitting objects. Calculated positions of spheres ranging in size from 1.6 to 3.4 cm diameters containing 18F and 99mTc were compared with measured positions. By adding a single radioactive fiducial marker, emission-guided biopsy of simulated breast lesions was performed with a specially designed phantom containing photon-emitting spheres 12.7 mm in diameter. RESULTS: Correlation between calculated and measured object coordinates were excellent (R = 1.0, R = 1.0 and R = 0.998; x, y and z coordinates, respectively). The maximum error in localization was +/- 3 mm. One hundred percent (10 of 10) of the attempted biopsies of simulated tumors were successful. CONCLUSION: A method for rapidly determining the position of photon-emitting objects in an emission scanner has been developed and tested. This technique, which does not require standard emission or anatomic images, could be used with dedicated biopsy machines or incorporated into "add-on" biopsy devices for existing PET or SPECT cameras.

In vivo mapping of cholinergic terminals in normal aging, Alzheimer's disease, and Parkinson's disease.

To map presynaptic cholinergic terminal densities in normal aging (n = 36), Alzheimer's disease (AD) (n = 22), and Parkinson's disease (PD) (n = 15), we performed single-photon emission computed tomography using [123I]iodobenzovesamicol (IBVM), an in vivo marker of the vesicular acetylcholine transporter. We used coregistered positron emission tomography with [18F]fluorodeoxyglucose for metabolic assessment and coregistered magnetic resonance imaging for atrophy assessment. In controls (age, 22-91 years), cortical IBVM binding declined only 3.7% per decade. In AD, cortical binding correlated inversely with dementia severity. In mild dementia, binding differed according to age of onset, but metabolism did not. With an onset age of less than 65 years, binding was reduced severely throughout the entire cerebral cortex and hippocampus (about 30%), but with an onset age of 65 years or more, binding reductions were restricted to temporal cortex and hippocampus. In PD without dementia, binding was reduced only in parietal and occipital cortex, but demented PD subjects had extensive cortical binding decreases similar to early-onset AD. We conclude that cholinergic neuron integrity can be monitored in living AD and PD patients, and that it is not so devastated in vivo as suggested by postmortem choline acetyltransferase activity (50-80%).

Simultaneous transmission/emission myocardial perfusion tomography. Diagnostic accuracy of attenuation-corrected 99mTc-sestamibi single-photon emission computed tomography.

BACKGROUND: The purpose of the present study was to assess the diagnostic performance of attenuation-corrected (AC) stress 99mTc-sestamibi cardiac single-photon emission computed tomography (SPECT) for the identification of coronary heart disease (CHD). METHODS AND RESULTS: With a triple-detector SPECT system with a 241Am transmission line source, simultaneous transmission/emission tomography (TCT/ECT) was performed on 60 patients with angiographic coronary disease and 59 patients with < or = 5% likelihood of CHD. Iteratively reconstructed AC stress 99mTc-sestamibi perfusion images were compared with uncorrected (NC) filtered-backprojection images. Normal database polar maps were constructed from AC and NC images for quantitative analyses. From the low-likelihood patients, the visual and quantitative normalcy rates increased from 0.88 and 0.76 for NC to 0.98 and 0.95 for AC (P < .05). For the detection of CHD, the receiver operating characteristic curves for the AC images demonstrated improved discrimination capacity (P < .05), and sensitivity/specificity values increased from 0.78/0.46 (NC) to 0.84/0.82 (AC) with visual analysis and from 0.84/0.46 (NC) to 0.88/0.82 (AC) with quantitative analysis. For localization of stenosed vessels, visual and quantitative sensitivity values were 0.51 and 0.63 for NC and 0.64 and 0.78 for AC images (P < .05), respectively. CONCLUSIONS: TCT/ECT myocardial perfusion imaging significantly improves the diagnostic accuracy of cardiac SPECT for the detection and localization of CHD. Clinical use of TCT/ECT imaging deserves serious consideration.

Simultaneous transmission-emission thallium-201 cardiac SPECT: effect of attenuation correction on myocardial tracer distribution.

UNLABELLED: This study evaluates the effect of attenuation correction on regional myocardial tracer distributions defined by 201TI cardiac perfusion SPECT images obtained from healthy volunteers and patients with coronary heart disease. METHODS: A three-detector SPECT system equipped with an 241Am line source and a fanbeam collimator was used for simultaneous transmission/emission (201TI) tomography on 40 patients and 10 normal volunteers. Uncorrected emission images were reconstructed using filtered backprojection (FBP), whereas the attenuation corrected images were iteratively reconstructed with a regularized, least-squares algorithm utilizing the attenuation map computed from the transmission data. Both sets of images were reoriented into short-axis and vertical long-axis slices. Circumferential profile analysis was applied to both datasets of short-axis slices. RESULTS: The normal volunteers demonstrated improved homogeneity in tracer distribution. For a basal short-axis slice, the lateral-to-posterior activity ratio improved from 1.17 +/- 0.12 for FBP to 1.01 +/- 0.07. Basal attenuation appeared properly compensated as the peak basal-to-apical slice activity gradient along the posterior-inferior wall changed from 1.15 +/- 0.12 for FBP to 1.01 +/- 0.09. The apex of the attenuation corrected images showed a significant decrease in activity relative to the base which appeared consistent with anatomic wall thinning. For the inferior and basal septal regions, the defect severity was slightly less in the attenuation corrected images, but the defects were more sharply defined compared to the FBP image defects. CONCLUSION: These results indicate that attenuation correction is clinically feasible and accurately corrects for photon attenuation. Clinical validation, however, is necessary to define the diagnostic benefits.

Triple-head SPECT with 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG): initial evaluation in oncology and comparison with FDG PET.

PURPOSE: In patients with cancer, performance was assessed of a commercially available triple-head gamma camera fitted with ultra-high energy parallel-hole collimators performing single photon emission computed tomography (SPECT) with 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG). Results were compared with those of positron emission tomography (PET) with FDG. MATERIALS AND METHODS: Performance characteristics were first determined in phantom studies for FDG PET and triple-head gamma camera SPECT systems. In 13 patients with malignancies, FDG PET was followed by SPECT of the same region, and imaging results were independently assessed. RESULTS: Sensitivity of the PET and SPECT systems was 58.3 counts/MBq/min and 4.5 counts/MBq/min, respectively. Reconstructed spatial resolution was approximately 7 mm for PET and 20 mm for SPECT. All known cancer foci were detected at PET. SPECT depicted 11 of the 22 lesions detected at PET, but only five of the 14 lesions less than 3 cm in diameter. CONCLUSION: FDG SPECT performed with a specially collimated triple-head gamma camera depicted some cancers but had an unacceptably low sensitivity compared with PET for lesions less than 3 cm in diameter. PET is preferable for detecting small cancers.

Compartmental analysis of technetium-99m-teboroxime kinetics employing fast dynamic SPECT at rest and stress.

UNLABELLED: We have examined the feasibility of compartmental analysis of 99mTc-teboroxime kinetics in measuring physiological changes in response to adenosine-induced coronary vasodilation. To evaluate the effect of tracer recirculation on 99mTc-teboroxime kinetics in the myocardium, we also compared compartmental analysis with washout analysis (monoexponential fitting), which does not account for this effect. METHODS: Eight healthy male volunteers were imaged using fast dynamic SPECT protocols (5 sec per tomographic image) at rest and during adenosine infusion. A two-compartment model was used and compartmental parameters K1 and k2 (characterizing the diffusion of 99mTc-teboroxime from the blood to the myocardium and from the myocardium to the blood, respectively) were fitted from myocardial time-activity curves and left ventricular input functions. RESULTS: Both K1 and washout estimates for the whole left ventricular myocardium changed significantly in response to coronary vasodilation. Mean stress-to-rest (S/R) ratios were almost two times higher for K1 (S/R = 2.7 +/- 1.1) than for washout estimates (S/R = 1.5 +/- 0.3). Estimation of K1 for all local regions, except the septal wall, is feasible because variations in K1 estimates for all local regions, except the septum during stress, are comparable with those for the global region. CONCLUSIONS: We conclude that quantitative compartmental analysis of 99mTc-teboroxime kinetics provides a sensitive indicator for changes in response to adenosine-induced coronary vasodilation.

Comparison of americium-241 and technetium-99m as transmission sources for attenuation correction of thallium-201 SPECT imaging of the heart.

UNLABELLED: This study compares the ability of 241Am and 99mTc to estimate 201Tl attenuation maps while minimizing the loss in the precision of the emission data. METHODS: A triple-head SPECT system with either an 241Am or 99mTc line source opposite a fan-beam collimator was used to estimate attenuation maps of the thorax of an anthropomorphic phantom. Linear attenuation values at 75 keV for 201Tl were obtained by linear extrapolation of the measured values from 241Am and 99mTc. RESULTS: Lung and soft-tissue estimates from both isotopes showed excellent agreement to within 3% of the measured values for 201Tl. Linear extrapolation did not yield satisfactory estimates for bone from either 241Am (+11.7%) or 99mTc (-15.3%). Patient data were used to estimate the dependence of crosstalk on patient size. Contamination from 201Tl in the transmission window was 5-6 times greater for 241Am compared to 99mTc, while the contamination in the 201Tl data in the transmission-emission detector head (head 1) was 4-5 times greater for 99mTc compared to 241Am. No contamination was detected in the 201Tl emission data of heads 2 and 3 from 241Am, whereas the 99mTc produced a small crosstalk component giving a signal-to-crosstalk ratio near 20:1. Measurements with a fillable chest phantom estimated the mean error introduced into the data from the removal of the crosstalk. CONCLUSION: Based on the measured data, 241Am is a suitable transmission source for simultaneous transmission-emission tomography for 201Tl cardiac studies.