Increased sensitivity through use of overlapping 180° orbits in clinical myocardial perfusion imaging

Clinical cardiac imaging is hindered by noise due to limited activity and imaging time. Use of 90° dual-detector systems with 90° gantry rotation may provide the best sensitivity/resolution for cardiac imaging, but this option is not readily available to those using a triple-detector system with detectors at 120° intervals. This study utilizes a cardiac/chest phantom to compare several triple-detector orbits, with assessment of sensitivity and resolution. A 180° rotation with reconstruction of two of the three heads was evaluated, resulting in overlapping 180° orbits; use of a starting angle of 165° for the first head placed the overlapping portion of the orbits over the LAO myocardial region, where camera-cardiac distance is most favorable. Use of this overlapping orbit yielded resolution equivalent to a conventional (single-head) 180° rotation. Sensitivity was 87%–90% of that of a 90° dual-detector system, and 16%–20% better than the common practice of using a 120° orbit with reconstruction of 1 /12 heads to achieve 180° of data. Use of 360° acquisition with reconstruction of all three heads provided the greatest sensitivity, though at the expense of some loss in image quality. Thus, for those centers performing cardiac imaging using a triple-detector system, use of overlapping 180° orbits is the preferred acquisition choice.     

Regional brain kinetics of 6-fluoro-(β-11C)-L-dopa and (β-11C)-L-dopa following COMT inhibition. A study in vivo using positron emission tomography

Summary The regional brain kinetics of (-11C)-L-dopa and 6-fluoro-(-11C)-L-dopa was measured in six Rhesus monkeys using positron emission tomography (PET). Radioactivity accumulated specifically in the striatal region and the increase in L-dopa-derived radioactivity utilization with time was calculated using surrounding brain as a reference area, this being devoid of dopaminergic activity. The rate constant for selective striatal utilization i.e. grossly decarboxylation was 0.0110 ± 0.0007 (S.D) and 0.0057 ± 0.0006 min1 for (-11C)-L-dopa and 6-fluoro-(-11C)-L-dopa, respectively. After pre-treatment of the monkeys with the peripherally and centrally active catecholamine-O-methyl transferase (COMT) inhibitor Ro 40-7592 10 mg/kg, the decarboxylation rate remained unchanged (0.0112 ± 0.0015 min-1) for (11C)-L-dopa, whereas an increase in rate was measured for 6-fluoro-(-11C)L-dopa (0.0092 ± 0.0015 min–1). Differences in the distribution of radiolabelled metabolites i.e. the corresponding O-methyl-L-dopa in the reference area is most probably the reason for the difference in calculated decarboxylation rate seen between the radiotracers. The higher decarboxylation rate measured for 6-fluoro-(-11C)-L-dopa after blockade of COMT shows that the radiolabelled metabolites i.e. 6-fluoro-O-methyl-(-11C)-L-dopa significantly contributes to background radioactivity.     

Assessment of the scatter fraction evaluation methodology using Monte Carlo simulation techniques

To evaluate scatter fraction and scatter pair spatial distribution, experimental methods are generally used. These methods make use of a line source, placed along the FOV axis, inserted in a cylindrical phantom filled with air or water. The accuracy of these experimental methodologies can be tested by the use of a Monte Carlo method. In fact, the simulation allows the shape of the scatter event projection and the scatter fraction to be defined. An example of this application is the simulation package PETSI (PET SImulation). In this paper the comparison between the predicted scatter fraction and the experimentally evaluated one, obtained using an ECAT III PT 911/02 double ring whole body scanner are presented. PETSI permits additional data to be obtained: a) the true and scatter component of the energy spectrum; b) the spatial distribution, in the FOV plane, of the detected scatter events at different energy thresholds; c) the scatter to total detected events ratio; d) the predicted scatter fraction at both energy thresholds and FOV diameters. This information is very useful for optimizing both energy threshold and FOV size and to improve the accuracy of the currently used methods for the scatter fraction evaluation. Preliminary results of the predicted scatter fraction in a uniform phantom are presented.This article was presented at the 1st EEC workshop on accuracy determination in PET, January 19–20th. 1989 Pisa, Italy (COMAC-BME Concerted Project Characterization and Standardization of PET Instrumentation)     

Sarcoma of follicular dendritic cells in the dorsal mediastinum

Follicular dendritic cell sarcomas (FDCSs) are very rare and usually originate in lymph nodes. We report an exceedingly rare case with localization in the dorsal mediastinum and, for the first time, provide positron emission tomography (PET) data for this tumor. This report describes the case of a 76-year-old man with a clinically aggressive tumor in the dorsal mediastinum. Computed tomography scan revealed displacement of soft tissue and lymph nodes. PET showed that the tumor had a high proliferation rate. Investigation of the successfully removed tumor mass revealed reactivity of the tumor cells for follicular dendritic cell markers and desmosomes linking adjacent tumor cells at the ultrastructural level. Marked atypia, a high mitotic rate, and areas of coagulative necrosis were found. The tumor in our case revealed the typical features and thus was classified as FDCS. In contrast to previous reports in the literature, preoperative imaging, histology, and immunohistochemistry studies indicated at least an intermediate degree of malignancy. Nevertheless, the patient made a good postoperative recovery and remained apparently disease-free 2 years later.     

Somatotopic organization along the central sulcus, for pain localization in humans, as revealed by positron emission tomography

Regional cerebral blood flow was measured with positron emission tomography (PET) in six healthy volunteers at rest and during experimentally induced, sustained cutaneous pain on the dorsum of the right hand or on the dorsum of the right foot. Pain was inflicted by intracutaneous injection of capsaicin, providing a mainly C-fibre nociceptive stimulus. Statistical analysis showed significant activations along the central sulcus (SI) area when comparing pain in the hand to pain in the foot. Separate comparison of both pain states to a baseline revealed different locations along the central sulcus for hand pain and foot pain. The encountered differences are consistent with what is previously known about the somatotopics of non-painful stimuli. When comparing painful stimuli to baseline, the contralateral anterior cingulate gyrus, the ipsilateral anterior insular cortex and the ipsilateral prefrontal cortex were implicated. The results are consistent with an involvement of SI in the spatial discrimination of acute cutaneous pain. Received: 17 October 1996 / Accepted: 12 May 1997     

Estrogen receptor genotype modulates myocardial perfusion in young men

Most of the effects of estrogens are mediated by estrogen receptors. Vascular endothelial cells and smooth muscle cells express estrogen receptor (ESR1) in both genders. A long genotype group of a common thymine-adenine (TA) dinucleotide repeat polymorphism in the regulatory region of this gene has previously been related to coronary artery disease. The present study examined whether coronary blood flow is affected by this genotype. A total of 49 healthy men were genotyped by PCR and divided into three groups according to median number of the ESR1 promoter TA repeat (=19), i.e., in the short allele genotype group both alleles were of fewer than 19 repeats whereas in the long allele group both alleles were 19 repeats or more. The intermediate group comprised men who had one short and one long allele. Myocardial blood flow was measured by positron emission tomography using [¹⁵O]water, performed at rest and during adenosine stimulation. Men with long alleles had lower adenosine-stimulated coronary flow than those with short alleles and those with one short and one long allelle. Our results suggest that adenosine-stimulated myocardial perfusion is lower in subjects with ESR1 long alleles than the other TA repeat genotypes.     

阈值校正方式对PET脑显像统计参数图分析显示结果的影响

目的 探讨各种阈值校正方法对统计参数图(SPM)软件统计比较结果显示的影响.方法 利用Hoffman标准脑模型制作缺损模型PET成像与正常模型PET成像,进行统计参数图的统计比较.并选取脑梗死患者与健康检查者进行统计参数图的统计比较.结果 校正与非校正产生的结果有差异,其中族错误率(FWE)校正(P=5×10-2)得到的统计分析结果激活区最少及最小,其次是错误发现率(FDR)校正(P=5×10-2),非校正方式(P=1×10-3)得到的激活区最多及最大.但FDR校正效果不稳定,有时不如不校正.结论 统计参数图软件中FWE校正方法可明显降低假阳性,得到的结果可信度稳定地高于非校正方法.     

The effect of the muscarinic antagonist scopolamine on regional cerebral blood flow during the performance of a memory task

Scopolamine, a muscarinic antagonist, impairs memory performance in both humans and animals. In this study, repeated measurements of regional cerebral blood flow (rCBF) were made in normal volunteers whilst performing auditory verbal memory tasks, before and after the administration of scopolamine (0.4 mg s.c.) or placebo. Compared to placebo, scopolamine increased blood flow in the lateral occipital cortex bilaterally and the left orbitofrontal region. Scopolamine decreased rCBF in the region of the right thalamus, the precuneus and the right and left lateral premotor areas. Scopolamine attenuated memory-task-induced increases of rCBF in the left and right prefrontal cortex and the right anterior cingulate region. These data suggest that acute blockade of cholinergic neurotransmission affects diverse brain areas, including components of the visual and motor systems, and, in addition, modulates memory task activations at distinct points in a distributed network for memory function.     

Dopamine receptor properties in Parkinson''s disease and Huntington''s chorea evaluated by positron emission tomography using 11C-N-methyl-spiperone

Dopaminergic receptor properties in the striatum of patients with Parkinson's disease (PD) and Huntington's chorea (HD) were studied by positron emission tomography (PET), using 11C-N-methyl-spiperone as a dopamine D2 receptor ligand. The time-dependent regional radioactive uptake in the caudate nucleus and the putamen was measured and fitted to a 3-compartment pharmacokinetic model. The rate constant k3 for specific binding to the receptor compartment in the striatum was determined in relation to the binding in regions with a low density of specific binding sites, such as the cerebellum and the frontal cortex . k3, which is a measure of the receptor density, was reduced in one patient with HD but less affected in PD in comparison with healthy controls. The pattern of k3 values calculated from the 6 PD patients is discussed in relation to any side-to-side differences in dopamine receptor densities in hemiparkinsonism and to possible "hypersensitivity" of dopamine receptors in the early stage of the disease and down-regulation in more advanced disease.     

The Bücherer-Strecker synthesis of d- and l-(1-11C)tyrosine and the in vivo study of l-(1-11C)tyrosine in human brain using positron emission tomography

The synthesis of d-and l-(1-¹¹C)tyrosine, starting with ¹¹C-cyanide, is reported. dl-(1-¹¹C)Tyrosine was prepared by the Bücherer-Strecker reaction, from carrier added ¹¹C-cyanide with an incorporation of 80% in 20 min. The isolation of the pure d- and l-amino acid isomers from the enantiomeric mixture was accomplished within 15 min by preparative HPLC using a chiral stationary phase and a phosphate buffer as the mobile phase. Typically, the total synthesis time was 50 min (including purification) from end of trapping of ¹¹C-cyanide, with a radiochemical yield of d- and l-amino acid of 40%–60%. The d- and l-(1-¹¹C)tyrosine were both obtained optically pure, with a carrier added specific activity of 0.3–0.5 Ci/mmol and a radiochemical purity better than 99%. The ¹¹C labelled l-tyrosine was used in an in vivo study in the human brain using positron emission tomography (PET).