A Basic Positron Emission Tomography System Constructed to Locate a Radioactive Source in a Bi-dimensional Space

A simple Positron Emission Tomography (PET) prototype has been constructed to fully characterize its basic working principles. The PET prototype was created by coupling plastic scintillator crystals to photomultipliers or PMT''s which are placed at opposing positions to detect two gamma rays emitted from a radioactive source, of which is placed in the geometric center of the PET set-up. The prototype consists of four detectors placed geometrically in a 20 cm diameter circle, and a radioactive source in the center. By moving the radioactive source centimeters from the center the system one is able to detect the displacement by measuring the time of flight difference between any two PMT''s and, with this information, the system can calculate the virtual position in a graphical interface. In this way, the prototype reproduces the main principles of a PET system. It is capable to determine the real position of the source with intervals of 4 cm in 2 lines of detection taking less than 2 min.     

CT全肝灌注的临床应用及进展

随着影像技术的发展和后处理功能的完善,肝灌注成像以研究组织、器官血流动力学变化已成为影像界关注的热点,然而CT灌注成像在肝脏等实质性器官中的应用尚处于探索阶段。肝脏具有双重血供,在各种病理生理情况下,肝脏动静脉之间及门静脉之间的血流动力学发生着复杂的变化。CT被认为是诊断肝脏病变最有价值的影像学方法,CT灌注成像能反映组织器官微循环内的血流动力学变化,是一种快速、准确、无创的功能成像方法。肝脏灌注CT检查可以同时获得形态和功能两方面的信息,使我们有可能早于形态学变化之前发现肝脏病变,有助于肝脏疾病的早期诊断和治疗,并能评价各种治疗手段对肝脏血流动力学变化的影响。本文针对全肝灌注CT扫描在临床的应用进行综述。     

MCA供血区急性脑梗死SWI图像与脑血管反应性的相关性

目的:分析大脑中动脉供血区(MCA)急性脑梗死患者的磁敏感加权成像(SWI),探讨梗死侧侧脑室旁深部髓质静脉(DMV)数量与脑血管反应性(CVR)的相关性。方法:回顾性纳入首次发生患侧MCA供血区卒中患者109例,并已完成TCD CO_2负荷实验和SWI等检查。根据SWI图像将DMV数量分为3级,5条为1级;5-10条为2级;10条为3级,分析DMV分级与CVR的关系。结果:根据排除标准共纳入MCA供血区急性脑梗死患者53例,DMV 1级、2级和3级分别有29、18、6例患者,MCA平均CVR为0.40±0.18。DMV 1级CVR为(0.45±0.22)、2级为(0.35±0.15)和3级为(0.20±0.11),3组患者间CVR存在明显差异(P0.05),且DMV 3级组较DMV 1级组、2级组显著降低(P0.05);Spearman相关分析表明,DMV分级与CVR间存在明显的负性相关关系(P0.001)。结论:MCA供血区脑梗死患者DMV分级与患侧MCA CVR呈负相关关系。     

In Vivo Nano-imaging of Membrane Dynamics in Metastatic Tumor Cells Using Quantum Dots

Changes in membrane morphology and membrane protein dynamics based on its fluidity are critical for cancer metastasis. However, this subject has remained unclear, because the spatial precision of previous in vivo imaging has been limited to the micrometer level and single molecule imaging is impossible. Here, we have imaged the membrane dynamics of tumor cells in mice with a spatial precision of 7–9 nm under a confocal microscope. A metastasis-promoting factor on the cell membrane, protease-activated receptor 1 (PAR1), was labeled with quantum dots conjugated with an anti-PAR1 antibody. Movements of cancer cells and PAR1 during metastasis were clearly observed in vivo. Images used to assess PAR1 dynamics were taken of representative cells for four stages of metastasis; i.e. cancer cells far from blood vessels in tumor, near the vessel, in the bloodstream, and adherent to the inner vascular surface in the normal tissues near tumor were photographed. The diffusion constant of PAR1 in static cells far from tumor blood vessels was smaller than in moving cells near the vessels and in the bloodstream. The diffusion constant of cells adhering to the inner vascular surface in the normal tissues was also very small. Cells formed membrane protrusion during migration. The PAR1 diffusion constant on these pseudopodia was greater than in other membrane regions in the same cell. Thus, the dynamics of PAR1 movement showed that membrane fluidity increases during intravasation, reaches a peak in the vessel, decreases during extravasation, and is also higher at locally formed pseudopodia.     

Conjugates of Gd(III) Complexes to Di- and Tri-hydroxy Substituted Cholanoic Acids: Regioselective Oxidation with Hydroxysteroid Dehydrogenases

The preparative-scale oxidation of Gd(III) complexes of ligands containing 7,12-dihydroxy and 12-hydroxy substituted cholanoic moieties to the corresponding 12-oxo derivatives was accomplished by means of 12 &#102 -hydroxysteroid dehydrogenase. The enzymatic transformation appeared preferable to the chemical one because it was highly regioselective and environmentally benign. Other dehydrogenases, namely 3 &#102 - and 7 &#102 -hydroxysteroid dehydrogenases, also proved to be capable of catalysing the regioselective oxidation of the hydroxy groups of a Gd(III) complex containing a subunit of 3,7,12-trihydroxycholanoic acid. The above complexes are of interest as contrast agents for in vivo magnetic resonance imaging.     

Geometric and dosimetric accuracy and imaging dose of the real-time tumour tracking system of a gimbal mounted linac

PurposeTo suggest a comprehensive testing scheme to evaluate the geometric and dosimetric accuracy and the imaging dose of the VERO dynamic tumour tracking (DTT) for its clinical implementation.MethodsGeometric accuracy was evaluated for gantry 0° and 90° in terms of prediction (E_P), mechanical (E_M) and tracking (E_T) errors for sinusoidal patterns with 10 and 20 mm amplitudes, 2–6 s periods and phase shift up to 1 s and for 3 patient patterns. The automatic 4D model update was investigated simulating changes in the breathing pattern during treatment.Dosimetric accuracy was evaluated with gafchromic films irradiated in static and moving phantom with and without DTT. The entrance skin dose (ESD) was assessed using a solid state detector and gafchromic films.ResultsThe RMS of E_P, E_M, and E_T were up to 0.8, 0.5 and 0.9 mm for all non phased-shifted motion patterns while for the phased-shifted ones, E_P and E_T increased to 2.2 and 2.6 mm. Up to 4 updates are necessary to restore a good correlation model, according to type of change.For 100 kVp and 1 mA s X-ray beam, the ESD per portal due to 20 s fluoroscopy was 16.6 mGy, while treatment verification at a frequency of 1 Hz contributed with 4.2 mGy/min.ConclusionsThe proposed testing scheme highlighted that the VERO DTT system tracks a moving target with high accuracy. The automatic update of the 4D model is a powerful tool to guarantee the accuracy of tracking without increasing the imaging dose.     

Polyfluorinated bis-styrylbenzenes as amyloid-β plaque binding ligands

Detection of cerebral β-amyloid (Aβ) by targeted contrast agents remains of great interest to aid the in vivo diagnosis of Alzheimer’s disease (AD). Bis-styrylbenzenes have been previously reported as potential Aβ imaging agents. To further explore their potency as ¹⁹F MRI contrast agents we synthetized several novel fluorinated bis-styrylbenzenes and studied their fluorescent properties and amyloid-β binding characteristics. The compounds showed a high affinity for Aβ plaques on murine and human brain sections. Interestingly, competitive binding experiments demonstrated that they bound to a different binding site than chrysamine G. Despite their high logP values, many bis-styrylbenzenes were able to enter the brain and label murine amyloid in vivo. Unfortunately initial post-mortem ¹⁹F NMR studies showed that these compounds as yet do not warrant further MRI studies due to the reduction of the ¹⁹F signal in the environment of the brain.     

18F-labeled benzimidazopyridine derivatives for PET imaging of tau pathology in Alzheimer’s disease

Hyperphosphorylated tau proteins are one of the neuropathological hallmarks in the Alzheimer’s disease (AD) brain. The in vivo imaging of tau aggregates with nuclear medical imaging probes is helpful for the further comprehension of and medical intervention in the AD pathology. For tau-selective PET imaging, we newly designed and synthesized ¹⁸F-labeled benzimidazopyridine (BIP) derivatives with fluoroalkylamino groups, [¹⁸F]IBIPF1 and [¹⁸F]IBIPF2, and evaluated their utilities as tau imaging probes. They both bound selectively to tau against amyloid β (Aβ) aggregates in AD brain sections in vitro, and showed good pharmacokinetics in mouse brains in vivo. Notably, [¹⁸F]IBIPF1 exhibited high tau-selectivity (Tau/Aβ ratio = 34.8), high brain uptake (6.22% ID/g at 2 min postinjection), and subsequent washout (2.77% ID/g at 30 min postinjection). In vivo analysis of radiometabolites indicated that [¹⁸F]IBIPF1 was stable against metabolism in the mouse brain. These encouraging preclinical results suggest that further structural optimization based on the BIP scaffold may lead to the development of more useful tau imaging probes.     

Syntheses and evaluation of a homologous series of aza-vesamicol as improved radioiodine-labeled probes for sigma-1 receptor imaging

Sigma-1 receptor imaging probes for determining the expression levels are desirable for diagnoses of various diseases and companion diagnoses of therapeutic agents targeting the sigma-1 receptor. In this study, we aimed to develop probes with higher affinity for the sigma-1 receptor. For this purpose, we synthesized and evaluated compounds, namely, vesamicol derivatives, in which alkyl chains of varying chain length were introduced between a piperazine ring and a benzene ring. The binding affinity of the vesamicol derivatives for the sigma-1 receptor tended to increase depending on the length of the alkyl chain between the benzene ring and the piperazine ring. The sigma-1 receptor of 2-(4-(3-phenylpropyl)piperazin-1-yl)cyclohexan-1-ol (5) (K_i?=?5.8?nM) exhibited the highest binding affinity; therefore, we introduced radioiodine into the benzene ring in 5. The radioiodine labeled probe [¹²⁵I]2-(4-(3-(4-iodophenyl)propyl)piperazin-1-yl)cyclohexan-1-ol ([¹²⁵I]10) showed high accumulation in the sigma-1 receptor expressing DU-145 cells both in vitro and in vivo. Co-injection of [¹²⁵I]10 with an excess level of a sigma receptor ligand, haloperidol, resulted in a significant decrease in the tumor accumulation in vitro and in vivo, indicating sigma receptor-mediated tumor uptake. These results provide useful information for developing sigma-1 receptor imaging probes.