Simultaneous reconstruction of attenuation and activity in cardiac PET can remove CT misalignment artifacts.

BACKGROUND: Misalignment between positron emission tomography (PET) and computed tomography (CT) data is known to generate artifactual defects in cardiac PET images due to imprecise attenuation correction (AC). In this work, the use of a maximum likelihood attenuation and activity (MLAA) algorithm is proposed to avoid such artifacts in time-of-flight (TOF) PET. METHODS: MLAA was implemented and tested using a thorax/heart phantom and retrospectively on fourteen (13)N-ammonia PET/CT perfusion studies. Global and local misalignments between PET and CT data were generated by shifting matched CT images or using CT data representative of the end-inspiration phase. PET images were reconstructed with MLAA and a 3D-ordered-subsets-expectation-maximization (OSEM)-TOF algorithm. Images obtained with 3D-OSEM-TOF and matched CT were used as references. These images were compared (qualitatively and semi-quantitatively) with those reconstructed with 3D-OSEM-TOF and MLAA for which a misaligned CT was used, respectively, for AC and initialization. RESULTS: Phantom experiment proved the capability of MLAA to converge toward the correct emission and attenuation distributions using, as input, only PET emission data, but convergence was very slow. Initializing MLAA with phantom CT images markedly improved convergence speed. In patient studies, when shifted or end-inspiration CT images were used for AC, 3D-OSEM-TOF reconstructions showed artifacts of increasing severity, size, and frequency with increasing mismatch. Such artifacts were absent in the corresponding MLAA images. CONCLUSION: The proposed implementation of the MLAA algorithm is a feasible and robust technique to avoid AC mismatch artifacts in cardiac PET studies provided that a CT of the source is available, even if poorly aligned.

Evaluation of image reconstruction algorithms encompassing Time-Of-Flight and Point Spread Function modelling for quantitative cardiac PET: phantom studies.

BACKGROUND: To perform kinetic modelling quantification, PET dynamic data must be acquired in short frames, where different critical conditions are met. The accuracy of reconstructed images influences quantification. The added value of Time-Of-Flight (TOF) and Point Spread Function (PSF) in cardiac image reconstruction was assessed. METHODS: A static phantom was used to simulate two extreme conditions: (i) the bolus passage and (ii) the steady uptake. Various count statistics and independent noise realisations were considered. A moving phantom filled with two different radionuclides was used to simulate: (i) a great range of contrasts and (ii) the cardio/respiratory motion. Analytical and iterative reconstruction (IR) algorithms also encompassing TOF and PSF modelling were evaluated. RESULTS: Both analytic and IR algorithms provided good results in all the evaluated conditions. The amount of bias introduced by IR was found to be limited. TOF allowed faster convergence and lower noise levels. PSF achieved near full myocardial activity recovery in static conditions. Motion degraded performances, but the addition of both TOF and PSF maintained the best overall behaviour. CONCLUSIONS: IR accounting for TOF and PSF can be recommended for the quantification of dynamic cardiac PET studies as they improve the results compared to analytic and standard IR.

Physical performance of the new hybrid PET∕CT Discovery-690.

PURPOSE: The aim of this work was the assessment of the physical performance of the new hybrid PET∕CT system: Discovery-690. METHODS: The Discovery-690 combines a lutetium-yttrium-orthosilicate (LYSO) block detector designed PET tomograph with a 64-slice CT scanner. The system is further characterized by a dedicated powerful computing platform implementing fully 3D-PET iterative reconstruction algorithms. These algorithms can account for time of flight (TOF) information and∕or a 3D model of the PET point spread function (PSF). PET physical performance was measured following NEMA NU-2-2007 procedures. Furthermore, specific tests were used: (i) to measure the energy and timing resolution of the PET system and (ii) to evaluate image quality, by using phantoms representing different clinical conditions (e.g., brain and whole body). Data processing and reconstructions were performed as required by standard procedures. Further reconstructions were carried out to evaluate the performance of the new reconstruction algorithms. In particular, four algorithms were considered for the reconstruction of the PET data: (i) HD = standard configuration, without TOF and PSF, (ii) TOF = HD + TOF, (iii) PSF = HD + PSF, and (iv) TOFPSF = HD + TOF + PSF. RESULTS: The transverse (axial) spatial resolution values were 4.70 (4.74) mm and 5.06 (5.55) mm at 1 cm and 10 cm off axis, respectively. Sensitivity (average between 0 and 10 cm) was 7.5 cps∕kBq. The noise equivalent count rate (NECR) peak was 139.1 kcps at 29.0 kBq∕ml. The scatter fraction at the NECR peak was 37%. The correction accuracy for the dead time losses and random event counts had a maximum absolute error below the NECR peak of 2.09%. The average energy and timing resolution were 12.4% and 544.3 ps, respectively. PET image quality was evaluated with the NEMA IEC Body phantom by using four reconstruction algorithms (HD, TOF, PSF, and TOFPSF), as previously described. The hot contrast (after 3 iterations and for a lesion∕background activity ratio of 4:1) for the spheres of 10, 13, 17, and 22 mm was (HD) 29.8, 45.4, 55.4, and 68.1%; (TOF) 39.9, 53.5, 62.7, and 72.2%; (PSF) 28.3, 47.3, 60.4, and 71.8%; (TOFPSF) 43.8, 62.9, 70.6, and 76.4%. The cold contrast for the spheres of 28 and 37 mm was (HD) 62.4 and 65.2%; (TOF) 77.1 and 81.4%; (PSF) 62.0 and 65.2%; (TOFPSF) 77.3 and 81.6%. Similar hot and cold contrast trends were found during the analyses of other phantoms representing different clinical conditions (brain and whole body). Nevertheless, the authors observed a predominant role of either TOF or PSF, depending on the specific characteristics and dimensions of the phantoms. CONCLUSIONS: Discovery-690 shows very good PET physical performance for all the standard NEMA NU-2-2007 measurements. Furthermore, the new reconstruction algorithms available for PET data (TOF and PSF) allow further improvements of the D-690 image quality performance both qualitatively and quantitatively.

Performance measurements for the PET/CT Discovery-600 using NEMA NU 2-2007 standards.

PURPOSE: The aim of this study was to assess the performance measurements of the new PET/CT system Discovery-600 (D-600, GEMS, Milwaukee, WI). METHODS: Performance measures were obtained with the National Electrical Manufacturers Association (NEMA) NU 2-2007 procedures. RESULTS: The transverse (axial) spatial resolution FWHMs were 4.9 (5.6) mm and 5.6 (6.4) mm at 1 and 10 cm off axis, respectively. The sensitivity (average at 0 and 10 cm) was 9.6 cps/kBq. The scatter fraction was 36.6% (low energy threshold: 425 keV). The NEC peak rate (k=1) was 75.2 kcps at 12.9 kBq/cc. The hot contrasts for 10, 13, 17, and 22 mm spheres were 41%, 51%, 62%, and 73% and the cold contrasts for 28 and 37 mm spheres were 68% and 72%. CONCLUSIONS: The Discovery-600 has good performance for the NEMA NU 2-2007 parameters, particularly in improved sensitivity compared to the scanners of the same Discovery family, D-ST and D-STE.

Number of partitions (gates) needed to obtain motion-free images in a respiratory gated 4D-PET/CT study as a function of the lesion size and motion displacement.

PURPOSE: In this study we evaluate the number of data partitions (gates) needed to sort 4D-PET and 4D-CT data to obtain motion-free images as a function of lesion size and motion displacement. METHODS: Plexiglas spheres of various diameters (8, 10, 15, 20, and 25 mm) were filled with a radioactive solution of water and 18F. A PET/CT study was acquired for each sphere in a rest condition to reconstruct a motion-free image as a reference in terms of radioactivity concentration and spatial distribution. Each sphere was then moved sinusoidally in the superior-inferior direction over different motion displacements (5, 10, 15, 20, and 25 mm) with a periodic motion of 4 s. During motion a 4D-CT scan followed by a 4D-PET scan were acquired. Each set of 4D-CT and 4D-PET data was retrospectively sorted to generate one, two, four, six, eight, ten, and 12 partitions (gates) over the whole cycle of motion. 4D-PET gates were reconstructed by using the corresponding 4D-CT gates for attenuation correction, while PET data acquired, with the sphere in the rest condition were corrected for attenuation by using the corresponding CT image set. For each series of PET images, data analysis was performed by measuring (1) the maximum value of the radioactivity concentration (RACmax) in a VOI encompassing the radioactivity distribution over the volume of motion and (2) the axial-profile of the radioactivity distribution (Ax-p). RESULTS: The results show that radioactivity concentration is strongly underestimated due to motion in most conditions considered in this study. In particular, the underestimation of RACmax for the smallest sphere varied from -10.6% to -66.3% with motion displacements ranging from 5 to 25 mm. For the largest sphere, errors ranged from -1.4% to -26.7%. The 4D-PET/CT methodology allows motion-free or nearly motion-free images to be obtained. It also permits both radioactivity concentration (RACmax) and Ax-p to be recovered with residual differences with respect to the rest condition, depending on the number of partitions used to process the data. Within the limitation of the regular sinusoidal motion, used to simulate a general breathing condition, a scheme describing the number of partitions needed to obtain nearly motion-free images with Ax-p differences of around 10% with respect to the rest data is presented as a function of the lesion size and motion displacement. Such a scheme is proposed to guide the setup of a 4D-PET/CT acquisition and processing protocol for clinical applications. CONCLUSIONS: By using the 4D-PET/CT acquisition technique, it is possible to compensate for the degradation effect of lesion motion on the reconstructed PET images.

Monte Carlo GEANT4-based application for in vivo RBE study using small animals at LNS-INFN preclinical hadrontherapy facility.

Preclinical studies represent an important step towards a deep understanding of the biological response to ionizing radiations. The effectiveness of proton therapy is higher than photons and, for clinical purposes, a fixed value of 1.1 is used for the relative biological effectiveness (RBE) of protons considered 1.1. Recent in vitro studies have reported that the RBE along the spread-out Bragg peak (SOBP) is not constant and, in particular, the RBE value increases on the distal part of SOBP. The present work has been carried-out in the perspective of a preclinical hadrontherapy facility at LNS-INFN and was focused on the experimental preparation of an in vivo study concerning the RBE variation along the SOBP. The main purpose of this work was to determine, using GEANT4-based Monte Carlo simulations, the best configuration for small animal treatments. The developed GEANT4 application simulates the proton-therapy beam line of LNS-INFN (CATANA facility) and allows to import the DICOM-CT images as targets. The RBE will be evaluated using a deterministic radiation damage like myelopathy as end-point. In fact, the dose at which the 50% of animals will show the myelopathy is supposed to be LET-dependent. In this work, we studied different treatment configurations in order to choose the best two that maximize the LET difference reducing as much as possible the dose released to healthy tissue. The results will be useful to plan hadrontherapy treatments for preclinical in vivo studies and, in particular, for the future in vivo RBE studies.

Using deconvolution to improve PET spatial resolution in OSEM iterative reconstruction.

OBJECTIVES: A novel approach to the PET image reconstruction is presented, based on the inclusion of image deconvolution during conventional OSEM reconstruction. Deconvolution is here used to provide a recovered PET image to be included as "a priori" information to guide OSEM toward an improved solution. METHODS: Deconvolution was implemented using the Lucy-Richardson (LR) algorithm: Two different deconvolution schemes were tested, modifying the conventional OSEM iterative formulation: 1) We built a regularizing penalty function on the recovered PET image obtained by deconvolution and included it in the OSEM iteration. 2) After each conventional global OSEM iteration, we deconvolved the resulting PET image and used this "recovered" version as the initialization image for the next OSEM iteration. Tests were performed on both simulated and acquired data. RESULTS: Compared to the conventional OSEM, both these strategies, applied to simulated and acquired data, showed an improvement in image spatial resolution with better behavior in the second case. In this way, small lesions, present on data, could be better discriminated in terms of contrast. CONCLUSIONS: Application of this approach to both simulated and acquired data suggests its efficacy in obtaining PET images of enhanced quality.

Early diagnosis of Alzheimer's disease using a grid implementation of statistical parametric mapping analysis.

A quantitative statistical analysis of perfusional medical images may provide powerful support to the early diagnosis for Alzheimer's Disease (AD). A Statistical Parametric Mapping algorithm (SPM), based on the comparison of the candidate with normal cases, has been validated by the neurological research community to quantify ipometabolic patterns in brain PET/SPECT studies. Since suitable "normal patient" PET/SPECT images are rare and usually sparse and scattered across hospitals and research institutions, the Data Grid distributed analysis paradigm ("move code rather than input data") is well suited for implementing a remote statistical analysis use case, described in the present paper. Different Grid environments (LCG, AliEn) and their services have been used to implement the above-described use case and tackle the challenging problems related to the SPM-based early AD diagnosis.

Synthesis optimization of 2-(4-N-[11C]methylaminophenyl)-6-hydroxybenzothiazole ([11C]PIB), ß-amyloid PET imaging tracer for Alzheimer's disease diagnosis.

[11C]PIB is the most used amyloid plaques-specific positron-emitting radiotracers. The radiosynthesis of this compound, carried out by methylation of its precursor with [11C]methyl triflate in 2-butanone, has been improved optimizing the initial concentration and the purification method. Two HPLC methods were compared: good radiochemical yields, specific activities, and chemical purity above 98% were achieved by using as eluant acetonitrile/citrate and formulation in 10% ethanol.

Remote effects of subcortical cerebrovascular lesions: a SPECT cerebral perfusion study.

The remote effects of small unilateral cerebrovascular lesions confined to subcortical structures were evaluated by single photon emission computerized tomography (SPECT) and a CBF tracer, I-123 HIPDM. A CBF study was performed in 34 patients presenting with subcortical stroke either in the acute or in the chronic stages. Twenty-one of the 34 patients showed areas of cortical hypoperfusion ipsilateral to the subcortical lesion. In 14 patients, asymmetry of perfusion was also observed at the cerebellar level, perfusion being significantly reduced in the cerebellar hemisphere contralateral to the lesion. There was no correlation between the degree and extension of these remote effects and the type of stroke (ischemic or hemorrhagic), the patency of cerebral arteries, or the size and site of the lesion by transmissive computerized tomography (TCT). Subcortical hematomas showed a correlation between occurrence of remote effects and time interval from the onset of stroke, occurring more frequently in the acute phase. A correlation was observed between cortical and cerebellar remote effects and the severity of clinical presentation. The causes of remote effects are still unclear and have been extensively debated. Our data indicate that there is a relationship of remote effect to the neurological status. It is possible to show, by noninvasive, low-cost methods, remote CBF effects after stroke that may contribute to the assessment of brain functional impairment.

Errors introduced by tissue heterogeneity in estimation of local cerebral glucose utilization with current kinetic models of the [18F]fluorodeoxyglucose method.

The effects of tissue heterogeneity on the estimation of regional cerebral glucose utilization (rCMRglc) in normal humans with [18F]2-fluoro-2-deoxy-D-glucose ([18F]FDG) and positron emission tomography (PET) were compared with respect to the various kinetic models of the [18F]FDG method. The kinetic models were conventional homogeneous tissue models of the [18F]FDG method, with (4K Model) and without (3K Model) a rate constant to account for an apparent loss of [18F]2-fluoro-2-deoxy-D-glucose-6-phosphate ([18F]FDG-6-P), and a tissue heterogeneity model (TH Model). When either of the kinetic models designed for homogeneous tissues was applied to heterogeneous tissues, estimates of the rate constant for efflux of [18F]FDG from the tissue (k2*) and of the rate constant for phosphorylation of [18F]FDG (k3*) decreased as the duration of the experimental period was increased. When the 4K Model was used, estimates of the rate constant for the apparent dephosphorylation of [18F]FDG-6-P (k4*) were significantly greater than zero and fell with increasing duration of the experimental period. Although the TH Model included no term to describe an apparent dephosphorylation of [18F]FDG-6-P, the fit of the TH Model to the time course of total tissue radioactivity was at least as good as and often better than the fit of the 4K Model in the 120-min period following the pulse of [18F]FDG. Hence, the high estimates of k4* found in PET studies of less than or equal to 120 min can be explained as the consequence of measuring radioactivity in a heterogeneous tissue and applying a model designed for a homogeneous tissue; there remains no evidence of significant dephosphorylation of [18F]FDG-6-P in this time period. Furthermore, use of the 4K Model led to an overestimation of rCMRglc; whole-brain glucose utilization calculated with the 4K Model was greater than 20% higher than values usually obtained in normal humans by the model-independent Kety-Schmidt technique. rCMRglc was accurately estimated by the TH Model and, in experimental periods sufficiently long to minimize the effects of tissue heterogeneity, also by the original 3K Model of the deoxyglucose method.

Metabolic impairment in human amnesia: a PET study of memory networks.

Human amnesia is a clinical syndrome exhibiting the failure to recall past events and to learn new information. Its "pure" form, characterized by a selective impairment of long-term memory without any disorder of general intelligence or other cognitive functions, has been associated with lesions localized within Papez's circuit and some connected areas. Thus, amnesia could be due to a functional disconnection between components of this or other neural structures involved in long-term learning and retention. To test this hypothesis, we measured regional cerebral metabolism with 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) and positron emission tomography (PET) in 11 patients with "pure" amnesia. A significant bilateral reduction in metabolism in a number of interconnected cerebral regions (hippocampal formation, thalamus, cingulate gyrus, and frontal basal cortex) was found in the amnesic patients in comparison with normal controls. The metabolic impairment did not correspond to alterations in structural anatomy as assessed by magnetic resonance imaging (MRI). These results are the first in vivo evidence for the role of a functional network as a basis of human memory.

Assessment and comparison of three scatter correction techniques in single photon emission computed tomography.

The detection of scattered radiation is recognized as one of the major sources of error in single photon emission computed tomography (SPECT). In this work three scatter correction techniques have been assessed and compared. Scatter coefficients and parameters characteristic of each technique have been calculated through Monte Carlo simulations and experimentally measured for various source geometries. Their dependence on the source/matter distribution and their spatial non-stationarity have been described. Each of the three scatter correction methods has then been tested on several SPECT phantom studies. The three methods provided comparable results. Following scatter compensation, both image quality and quantitative accuracy improved. In particular a slight improvement in spatial resolution and a statistically significant increase in cold lesion contrast, hot lesion recovery coefficient, and signal/noise ratio have been demonstrated with all methods.

A procedure for patient repositioning and compensation for misalignment between transmission and emission data in PET heart studies.

A procedure for patient repositioning and compensation for misalignment between transmission and emission data in positron emission tomography (PET) heart studies has been developed. Following the transmission scan (TR1), patients are moved from the scanner bed for the administration of the tracer, and repositioned when ready for the emission scan (EM1). A short postinjection transmission scan (TR2) is performed at the end of the EM1 study. TR1 and TR2 images are compared to recognize misalignment between transmission and emission studies. TR1 sinograms are compensated for misalignment to allow for a proper attenuation correction. The procedure has been tested on phantom and [18F]FDG PET heart studies. Misalignments down to 2.5 mm translation and 1 degree rotation in the transaxial plane and 4 mm in the axial direction can be recognized and compensated for. The procedure is suitable for clinical purposes, allowing reduction of patient time on the scanner bed, increased patient comfort and significant increase of patient throughput.

Evaluation in dogs and humans of three potential technetium-99m myocardial perfusion agents.

The biodistribution of the three cationic 99mTc complexes [99mTc(TMP)6]+, [99mTc(POM-POM)3]+, and [99mTc(TBIN)6]+--where TMP represents trimethylphosphite, POM-POM represents 1,2-bis(dimethyoxyphosphino)ethane, and TBIN represents t-butylisonitrile--have been evaluated in humans and dogs. Each agent was studied in three normal volunteers at rest, while [99mTc(POM-POM)3]+ and [99mTc(TBIN)6]+ were each studied in one normal volunteer at exercise. Even though all three agents yield good myocardial images in dogs, none appear suitable for clinical use as myocardial perfusion imaging radiopharmaceuticals. In humans, [99mTc(TMP)6]+ and [99mTc(POM-POM)3]+ clear very slowly from the blood and provide myocardial images only several hours after injection. [99mTc(TBIN)6]+ clears rapidly from the blood, but accumulation in the lung obscures the myocardial image for the first hour after injection; at later times, activity in the liver and spleen masks the apical wall. These results correlate with the blood-binding properties of the three complexes. [99mTc(TMP)6]+ and [99mTc(POM-POM)3]+ bind tightly to the plasma of human blood, but not to the plasma of dog blood; [99mTc(TBIN)6]+ does not bind tightly to the plasma of either dog or human blood. Among the Tc(I) complexes studied to date in humans, [99mTc(TBIN)6]+ appears to be unique in biodistribution pattern, blood-binding properties, and the fact that exercise improves the ultimate myocardial image. All the Tc(I) complexes appear to undergo myocardial accumulation by a mechanism different from that utilized by Tc(III) complexes. Animal studies alone are not adequate to evaluate the potential utility of 99mTc cationic complexes for myocardial perfusion studies.

Comparison of dual-head coincidence PET versus ring PET in tumor patients.

UNLABELLED: This study compared the multiring detector (Ring-PET) and the dual-head coincidence imaging system (DH-PET) for staging/ restaging neoplastic patients before or after surgery or radiochemotherapy. METHODS: Seventy patients with suspected tumor recurrence or metastatic dissemination received an intravenous dose of 18F-fluorodeoxyglucose (FDG) under overnight fasting and were studied in sequence with a dedicated positron emission tomograph with Ring-PET and a DH-PET. Ring-PET studies were performed 45-75 min postinjection and were followed by a DH-PET scan approximately 3 h postinjection. Number and location of the hypermetabolic lesions detected on DH-PET and Ring-PET reconstructed images were blindly assessed by three independent observers. RESULTS: DH-PET identified all 14 head lesions detected by Ring-PET, 53 of 63 thoracic lesions and 36 of 45 abdominal lesions. Of the 19 lesions not identified by DH-PET, 6 were smaller than 10 mm, 8 were between 10 and 15 mm and 1 was 18 mm; dimensions of 4 bone lesions were not available. A concordant restaging, based on location and number of lesions detected, was found in all 14 patients with head tumors, in 28 of 30 patients with thoracic tumors and in 24 of 26 patients with abdominal tumors. CONCLUSION: We found a good agreement between Ring-PET and DH-PET assessment of oncologic patients in detecting hypermetabolic lesions > or = 10-15 mm.

High-resolution technetium-99m-HMPAO SPECT in patients with probable Alzheimer's disease: comparison with fluorine-18-FDG PET.

UNLABELLED: SPECT studies of regional cerebral perfusion with a high-resolution system were compared to PET studies of regional cerebral glucose utilization (rCMRglc) in 21 patients with probable Alzheimer's disease (AD). Ten normal subjects were also evaluated with SPECT and 10 with PET. METHODS: rCMRglc (for PET) and counts (for SPECT) in the associative cortices were normalized to the average rCMRglc, and counts in the calcarine cortex and basal ganglia were considered as a "reference area" to obtain a ratio. The ratio differences between patients and controls were tested with ANOVA performed separately for PET and SPECT. RESULTS: The difference between probable AD patients and controls was significant for both PET (p < 0.00001) and SPECT (p < 0.005); this difference was significant for the frontal, temporal and parietal cortices (p < 0.0001) for PET, and for the temporal (p < 0.005) and parietal (p < 0.001) cortices for SPECT. Temporo-parietal defects were detected in all subjects with PET and in 90% with SPECT. CONCLUSION: PET and SPECT are able to detect characteristic temporo-parietal abnormalities in probable AD. However, the presence of abnormalities in other associative areas is better evaluated with PET.

Time dependence of residual tissue viability after myocardial infarction assessed by [18F]fluorodeoxyglucose and positron emission tomography.

Areas of myocardial infarction may retain glycolytic activity and this finding is indicative of tissue viability and predictive of functional recovery after revascularization. In order to assess the relation between the time elapsed from the occurrence of acute myocardial infarction and persistence of myocardial metabolic activity in the infarcted tissue, we prospectively studied 65 patients with previous myocardial infarction diagnosed clinically and by electrocardiographic (Q wave) and enzymatic criteria. All patients underwent coronary angiography and contrast left ventriculography, evaluation of regional myocardial glucose metabolism (in the fasting state) by positron emission tomography (PET) with 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG), and assessment of myocardial perfusion by single photon emission computed tomography (SPECT) with technetium-99m methoxyisobutyl isonitrile (99mTc-MIBI). Based on the regional metabolic and perfusion findings, patients were divided into 2 groups, depending on the absence (group 1, 26 patients) or presence (group 2, 39 patients) of [18F]FDG uptake in the underperfused regions. Areas of underperfusion at rest, consistent with the clinically identified myocardial infarction site, were observed in all patients. Severity of coronary artery disease, presence of collaterals, number of hypocontractile segments, and wall motion score did not differ significantly in the 2 groups. The time elapsed from the infarction was significantly greater (1,860 +/- 1,333 days) in group 1 than in group 2 (92 +/- 115 days; p < 0.0001). Exercise caused an increase in severity and/or extent of resting perfusion abnormalities in a greater proportion of patients of group 1 (53% vs 23%).(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative radionuclide angiocardiography using gold-195m.

A limitation of first-pass radionuclide angiocardiography is the limited repeatability because of the relatively long half-life of technetium-99m (Tc-99m). The feasibility, reproducibility and validity of multiple sequential quantitative first-pass studies were assessed in humans using the short-lived isotope gold-195m (Au-195m) (half-life of 30.6 seconds, 262 keV), which can be directly obtained from a generator made of its parent isotope, mercury-195m (half-life of 41.6 hours). Thirty-three subjects (13 normal volunteers and 20 cardiac patients) were studied using a large-field gamma camera equipped with a medium-energy collimator. After Au-195m intravenous injections, repeat first-pass studies were performed in the left anterior oblique projection. A left anterior oblique study was then obtained after i.v. injection of Tc-99m. Left ventricular ejection fraction calculations were performed separately by 2 observers. Reproducibility of Au-195m first-pass studies was excellent. The correlation coefficients for left ventricular ejection fraction from the first and the second Au-195m injections were 0.93 and 0.98 for observers 1 and 2, respectively. The correlation coefficients between Au-195m and Tc-99m first-pass studies were 0.95 and 0.98, respectively.