Correction for oral contrast artifacts in CT attenuation-corrected PET images obtained by combined PET/CT.

Recent studies have shown increased artifacts in CT attenuation-corrected (CTAC) PET images acquired with oral contrast agents because of misclassification of contrast as bone. We have developed an algorithm, segmented contrast correction (SCC), to properly transform CT numbers in the contrast regions from CT energies (40-140 keV) to PET energy at 511 keV. METHODS: A bilinear transformation, equivalent to that supplied by the PET/CT scanner manufacturer, for the conversion of linear attenuation coefficients of normal tissues from CT to PET energies was optimized for BaSO(4) contrast agent. This transformation was validated by comparison with the linear attenuation coefficients measured for BaSO(4) at concentrations ranging from 0% to 80% at 511 keV for PET transmission images acquired with (68)Ge rod sources. In the CT images, the contrast regions were contoured to exclude bony structures and then segmented on the basis of a minimum threshold CT number (300 Hounsfield units). The CT number in each pixel identified with contrast was transformed into the corresponding effective bone CT number to produce the correct attenuation coefficient when the data were translated by the manufacturer software into PET energy during the process of CT attenuation correction. CT images were then used for attenuation correction of PET emission data. The algorithm was validated with a phantom in which a lesion was simulated within a volume of BaSO(4) contrast and in the presence of a human vertebral bony structure. Regions of interest in the lesion, bone, and contrast on emission PET images reconstructed with and without the SCC algorithm were analyzed. The results were compared with those for images obtained with (68)Ge-based transmission attenuation-corrected PET. RESULTS: The SCC algorithm was able to correct for contrast artifacts in CTAC PET images. In the phantom studies, the use of SCC resulted in an approximate 32% reduction in the apparent activity concentration in the lesion compared with data obtained from PET images without SCC and a <7.6% reduction compared with data obtained from (68)Ge-based attenuation-corrected PET images. In one clinical study, maximum standardized uptake value (SUV(max)) measurements for the lesion, bladder, and bowel were, respectively, 14.52, 13.63, and 13.34 g/mL in CTAC PET images, 59.45, 26.71, and 37.22 g/mL in (68)Ge-based attenuation-corrected PET images, and 11.05, 6.66, and 6.33 g/mL in CTAC PET images with SCC. CONCLUSION: Correction of oral contrast artifacts in PET images obtained by combined PET/CT yielded more accurate quantitation of the lesion and other, normal structures. The algorithm was tested in a clinical case, in which SUV(max) measurements showed discrepancies of 2%, 1.3%, and 5% between (68)Ge-based attenuation-corrected PET images and CTAC PET images with SCC for the lesion, bladder, and bowel, respectively. These values correspond to 6.5%, 62%, and 66% differences between CTAC-based measurements and (68)Ge-based ones.     

A Coordinate System for Tumor Identification in Positron Emission Tomography (PET) Imaging

Purpose: PET can be useful in determining the progression of malignant disease over time as well as the response to therapy. To achieve this, the physician must be able to unambiguously identify and characterize individual tumors among several different scans.Methods: We have developed a coordinate system for identifying individual tumor sites on PET scans, selecting the carina on the transmission scan as a point of origin. Using this system, each tumor is given a set of spherical coordinates that identifies its position: a rho (rho, displacement from carina), a theta (θ, angle between the A-P axis and the tumor), and a phi (φ, angle between the polar axis and the tumor). We tested this method on a patient with metastatic thyroid cancer, who underwent 18FDG and 124I-Iodide PET scans in the same week. This sytem was also used on a patient with metastatic prostate cancer, who had two FDG scans done 7 weeks apart. The patient underwent chemotherapy treatment during this period, and the scans were performed to assess therapy response.Results: The patient with thyroid cancer had a total of 90 tumors, 82 of them identified in the 18FDG scan and 35 in the 124I-Iodide scan, with 27 tumors identified in both. For rho, θ, and φ among the 27 matching pairs of tumors, the mean differences were 6.80 +/- 5 mm, 6.22 +/- 4.54 degrees, and 5.51 +/- 5.81 degrees, respectively. The disparity in coordinate values between corresponding tumors can be explained by the distinctive uptake patterns of the radiopharmaceuticals. The patient with prostate cancer had 9 tumors identifiable in both the pre- and post-therapy scans. The mean differences for rho, θ, and φ among the 9 pairs of tumors were 1.93 +/- 1.65 mm, 6.67 +/- 5.53 degrees, and 2.04 +/- 2.02 degrees, respectively. After thorough analysis, we have determined that corresponding tumors with rho < 15 mm, θ and φ < 15 degrees difference usually indicate a match.Conclusion: This coordinate system facilitates the identification and characterization of individual tumors among multiple scans, thus aiding in both the assessment of diagnostic capabilities of different tracers, and the tracking of tumors following therapy.     

N-acetylcysteine prevents vasospasm after subarachnoid hemorrhage

BackgroundThis study investigated the ability of NAC to prevent cerebral vasospasm in a rabbit model of SAH.MethodsTwenty-one, male New Zealand white rabbits were randomly divided into 3 groups of 7 rabbits each: group 1 (control), group 2 (SAH only), group 3 (SAH + NAC treatment). NAC (150 mg/kg, single dose, IP) was administered just before SAH and continued until 72 hours after SAH in group 3.Animals were killed 72 hours after SAH. Tissue MDA levels, SOD, and GSH-Px activities were measured, and basilar artery cross-sectional areas, arterial wall thickness, and endothelial apoptosis in a cross section of basillary artery were determined in all groups.ResultsIntraperitoneal administration of NAC was found to be markedly effective against developing a cerebral vasospasm following a SAH in rabbits. It could significantly reduce elevated lipid peroxidation and increase the level of tissue GSH-Px and SOD enzymatic activities. Also, NAC treatment was found to be effective in increasing the luminal area and reducing wall thickness of the basilar artery. The morphology of arteries in the NAC treatment group was well protected. NAC markedly reduced apoptotic index and protects the endothelial integrity.ConclusionsThis study demonstrates, for the first time, that NAC treatment attenuates cerebral vasospasm in a rabbit SAH model. NAC treatment has significant neuroprotective effect and markedly prevents cerebral vasospasm after SAH. In conclusion, the NAC treatment might be beneficial in preventing cerebral vasospasm after SAH, thus showing potential for clinical implications.     

Neuron-specific enolase levels as a marker for possible neuronal damage in idiopathic intracranial hypertension

Although formerly considered as a “benign” disease, the presence of some important problems such as vision loss, resistance to appropriate medical treatment and relapses suggests that neuronal damage might play a role in the pathophysiology of IIH. In order to demonstrate possible neuronal damage/dysfunction participating in IIH pathophysiology, we aimed to investigate the relationship between serum neuron-specific enolase (NSE) levels and clinical features in patients with idiopathic intracranial hypertension (IIH). Thirty-six patients with IIH, diagnosed according to the revised criteria, and 40 age, gender and body mass index-matched healthy controls were enrolled in this study after their consent. Serum samples were evaluated for NSE via enzyme-linked immunosorbent assay method. NSE levels were higher in the IIH group (23.7 ± 14.53 ng/ml) compared to the control group (22.7 ± 13.11 ng/ml), but the difference was not statistically significant (p = 0.824). There were also no statistically significant differences in NSE levels in IIH patients regarding the presence of visual loss, relapse, oligoclonal bands and papilledema. We could not demonstrate any correlations between NSE levels and age, body mass index, cerebrospinal fluid opening pressure and disease duration. The present study is the first to analyze NSE levels in IIH patients and showed no significant difference between patients and controls, and also between different clinical subgroups of IIH patients.     

Knockdown of CTRP6 inhibits high glucose-induced oxidative stress,inflammation and extracellular matrix accumulation in mesangial cells through regulating the Akt/NF-κB pathway

C1qTNF-related protein 6 (CTRP6) is a member of the CTRP family and exerts a key role in the progression of diabetes mellitus. However, the role of CTRP6 in diabetic nephropathy remains unknown. The present study was designed to examine the roles of CTRP6 in diabetic nephropathy and explore the potential molecular mechanisms. Our results showed that the expression level of CTRP6 was significantly increased in high glucose (HG)-stimulated glomerular mesangial cells (MCs). The following loss/gain-of-function assays demonstrated that CTRP6 knockdown significantly inhibited HG-induced reactive oxygen species (ROS) production in MCs. CTRP6 knockdown caused significant decreases in tumour necrosis factor-α (TNF-α), interleukin (IL)-1β and IL-6 production levels in HG-induced MCs. Moreover, knockdown of CTRP6 inhibited HG-stimulated extracellular matrix (ECM) accumulation in MCs characterized by decreased expression and production levels of fibronectin (FN) and collagen IV (Col IV). Furthermore, CTRP6 knockdown suppressed HG-induced the activation of Akt/NF-κB pathway in MCs, while overexpression of CTRP6 exhibited the opposite effects. Treatment with LY294002, an inhibitor of Akt, reversed the induction effects of CTRP6 overexpression on ROS production, inflammation and ECM accumulation in MCs. In conclusion, these findings demonstrated that CTRP6 knockdown inhibits HG-induced ROS production, inflammation and ECM accumulation in MCs, which were mediated by the inactivation of the Akt/NF-κB pathway. The roles of CTRP6 in diabetic nephropathy provided evidence for its therapeutic potential for the treatment of diabetic nephropathy.     

Hippocampal theta rhythms from a computational perspective: code generation, mood regulation and navigation.

In this paper three computer models are summarized discussing different functions of the cortico-hippocampal system. Mood regulation, rhythm and code generation and navigation are integrated into a coherent conceptual framework around the concepts of structural hierarchy and circular causality. First, a model of spatio-temporal code generation is reviewed in which the hippocampal population theta rhythm plays an important role. Next, generation and pharmcological modulation of this rhythm is examined using a computer model of multiple cell populations forming a feed-back loop within the hippocampus and between the septum and the hippocampus. Last, an abstract, but biologically motivated model of navigation is described which achieves a near optimal mode of navigation by composing hierarchical levels of the cortico-hippocampal system. The connections among the different hierarchical structures of the cortico-hippocampal organization and their functional roles are discussed.     

Attenuation correction of PET images with respiration-averaged CT images in PET/CT.

Attenuation correction (AC) of PET images with helical CT (HCT) in PET/CT matches only the spatial resolution of CT and PET, not the temporal resolution. We therefore proposed the use of respiration-averaged CT (ACT) to match the temporal resolution of CT and PET and evaluated the improvement of tumor quantification in PET images of the thorax with ACT. METHODS: First, we examined 100 consecutive clinical PET/CT studies for the frequency and magnitude of misalignment at the diaphragm position between the HCT and the PET data. Patients were injected with 555-740 MBq of (18)F-FDG and scanned 1 h after injection. The HCT data were acquired at the following settings: 120 kV, 300 mA, pitch of 1.35:1, collimation of 8 x 1.25 mm, and rotation cycle of 0.5 s. Patients were instructed to hold their breath at midexpiration during HCT of the thorax. The PET acquisition was 3 min per bed. Second, we retrospectively analyzed studies of 8 patients (1 with esophageal cancer and 7 with lung cancer). Each study included regular PET/CT followed by 4-dimensional (4D) CT for radiation treatment planning. We compared the results of AC of the PET data with HCT and ACT. There were 13 tumors in these 8 patients. The 4D CT data were acquired at the following settings: 120 kV, 50-150 mA, cine duration of 1 breathing cycle plus 1 s, collimation of 8 x 1.25 mm, and rotation cycle of 0.5 s. The acquisition was taken when the patient was in the free-breathing state. We averaged the 10 phases of the 4D CT data to obtain ACT for AC of the PET data. Both the ACT and the HCT data were used for AC of the same PET data. RESULTS: There was a misalignment between the HCT and the PET data in 50 of 100 patient studies. In 34 studies, the misalignment was greater than 2 cm. In a comparison of HCT and ACT, 5 tumors had differences in standardized uptake values (SUV) between HCT-and ACT-attenuation-corrected PET of less than 20%, and 4 tumors had differences in SUV of more than 50%. The latter 4 tumors were found in the patient with esophageal cancer and in 2 of the patients with lung cancer. The PET data from these 3 patients had a misalignment of 2-4.5 cm relative to the HCT data. Breathing artifacts were significantly reduced by ACT. Seven of the 8 patients had a lower diaphragm position on HCT than on ACT, suggesting that the patients tended to hold a deeper breath during HCT than during ACT. CONCLUSION: The high rate of misalignment suggested a potential mismatch between the HCT and the PET data with the limited-breath-hold CT protocol. In the comparison of HCT and ACT, significant differences (>50%) in SUV were attributable to different breathing states between HCT and PET. The PET data corrected by ACT did not show breathing artifacts, suggesting that ACT may be more accurate than HCT for AC of the PET data.     

Hierarchial thermodynamic approach to the brain

A thermodynamic approach to understanding the brain is presented. Thermodynamics may be extended to "higher than molecule" levels. The role of the concept of entropy in thermodynamic-based nonthermodynamic systems has been discussed. Static and dynamic structures, cooperative and competitive mechanisms and some of their neurobiological applications are discussed. Postsynaptic membrane noises, dynamic synaptic activity, synaptogenesis, plasticity, retinotopy and perception have been considered as self-organizing neural structures appearing at different hierarchical levels.     

矽肺的X线诊断(附20例分析)

目的评价胸片在矽肺诊断的应用价值。材料与方法回顾性分析20例经职业病防治所确诊为矽肺的X线资料。结果矽肺胸部X线表现为双肺弥漫分布斑点、小结节影,其特征性改变为矽结节。矽结节常融合成块,易合并结核、肺气肿、气胸、胸膜炎等。结论胸部X线片对矽肺的并发症及诊断有一定价值。