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1.
Stephan E. Maier Harvey E. Cline Ferenc A. Jolesz 《Magnetic resonance in medicine》1995,34(5):706-712
Three dimensional (3D) phase contrast angiograms contain velocity data, which is discarded after the reconstruction of the projections. In extension to earlier work on velocity quantification with ungated 2D phase data, this paper shows that a useful estimate of the average velocity and flow rate can be extracted from ungated 3D phase contrast angiograms. Simulations and experiments in a phantom and in vivo were performed. For pulsatile flow and strong spin saturation, an over-estimation of the flow rate at the net in-flow end of the imaging volume and underestimation at the net out-flow end was observed. Imaging at lower RF tip angles yielded flow rates close to the correct value within the entire imaging volume. In contrast to ungated 2D experiments, the flow rates determined by repeated 3D experiments showed no variation. 相似文献
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4.
Ferenc Pongrácz Zoltán Bárdosi 《International journal of computer assisted radiology and surgery》2006,1(3):149-156
Purpose To develop an easy-to-use, dentition planning method which is based on three-dimensional (3D) computer planning technology to replace conventional plaster-cast occlusion planning techniques.
Methods The optimal dental occlusion is defined according to the condition of centric occlusion, i.e. after bringing occlusal surfaces of mandibular and opposing maxillary arches into identical 3D position. This identical position of occlusal surfaces represents the common reference frame for the 3D manipulation of all graphical elements. The planning procedure involves the following steps: (1) the optimal occlusal surface is approximated as triangle and localized both on the maxilla and mandible; (2) the original volumetric model is resampled according to the occlusal orientations; (3) the program reads in the models of ideal upper and lower dental arches from files, reshapes those to the patient anatomy and visualizes the local alignment on separate panels for mesiodistal and faciolingual inclinations. The final goal of the proposed method is to combine the requirements of functional and aesthetic designs and create an input for orthodontics, implantology and maxillofacial surgery.
Results In the present study the optimal dental occlusion is created by image resampling after bringing the occlusal surfaces of mandibular and opposing maxillary arches into identical 3D position. This identical position of occlusal surfaces represents the common reference frame for manipulation of all graphical elements.
Conclusions The proposed graphical environment was able to fit the elements of the ideal dentition curve to patient computed tomography under predefined centric occlusion. Rotation and scaling transformations of teeth were possible in the reformatted volumetric views about any of the axes of the teeth’s own reference space. 相似文献
5.
Summary Results of re-operations of 99 adult patients with recurrent supratentorial lobar glioblastomas (60 patients) and anaplastic
astrocytomas (39 patients) have been reviewed. In all cases both surgical interventions were performed at the same institute.
Age of patients with glioblastoma varied between 19 and 64 and with anaplastic astrocytoma between 21 and 68 years, with a
mean value of 48 and 36 years, respectively. The median interval between the first and second operations was 47 weeks for
patients with glioblastoma and 83 weeks with anaplastic astrocytoma. The mortality rate of the re-operations was 3%. Following
re-operation radio-and/or chemotherapy was applied in most of the cases. Median survival time after re-operation was 18.5
weeks in patients with glioblastoma and 55 weeks with anaplastic astrocytoma. Survival curves were calculated according to
Kaplan-Meier method and for statistical evaluation the generalized Wilcoxon test and multiple linear regression method were
used.
Histologically lower grade tumour at the first operation and longer interval between the two operations proved to influence
positively and differentiation of the primary tumour negatively the survival time. 相似文献
6.
M Nehéz G W Fischer H Scheufler R Schmidt T Sipos I Dési 《Ecotoxicology and environmental safety》1992,24(1):13-16
The organophosphorus herbicide buminafos (O,O-dibutyl-(1-butylaminocyclohexyl)-phosphonate) was tested for its acute toxic, cytogenetic, and embryotoxic activity on different strains of mice. The oral LD50 value for male NMRI mice was determined to be 3500 mg/kg. Single oral doses of 175, 1000, and 2000 mg/kg did not cause any significant enhancement in the percentage of chromosome aberrations in bone marrow cells of male NMRI mice. After oral administration of 500 and 1000 mg/kg buminafos to pregnant Halle:DBA and Halle:AB mice at Days 6-15 of gestation no embryotoxic effects were observed. The cytogenetic inactivity of buminafos in the bone marrow chromosome assay corresponds to negative findings in other mutagenicity tests. 相似文献
7.
Stephan E Maier Sridhar Vajapeyam Hatsuho Mamata Carl-Fredrik Westin Ferenc A Jolesz Robert V Mulkern 《Magnetic resonance in medicine》2004,51(2):321-330
Several studies have shown that in tissues over an extended range of b-factors, the signal decay deviates significantly from the basic monoexponential model. The true nature of this departure has to date not been identified. For the current study, line scan diffusion images of brain suitable for biexponential diffusion tensor analysis were acquired in normal subjects on a clinical MR system. For each of six noncollinear directions, 32 images with b-factors ranging from 5 to 5000 s/mm2 were collected. Biexponential fits yielded parameter maps for a fast and a slow diffusion component. A subset of the diffusion data, consisting of the images obtained at the conventional range of b-factors between 5 and 972 s/mm2, was used for monoexponential diffusion tensor analysis. Fractional anisotropy (FA) of the fast-diffusion component and the monoexponential fit exhibited no significant difference. FA of the slow-diffusion biexponential component was significantly higher, particularly in areas of lower fiber density. The principal diffusion directions for the two biexponential components and the monoexponential solution were largely the same and in agreement with known fiber tracts. The second and third diffusion eigenvector directions also appeared to be aligned, but they exhibited significant deviations in localized areas. 相似文献
8.
Istvn . Mrocz Kullervo Hynynen HLkon Gudbjartsson Sharon Peled Vincent Colucci Ferenc A. Jlesz 《Journal of magnetic resonance imaging : JMRI》1998,8(1):136-142
The aim of this study was to investigate a potential technique for image-guided minimally invasive neurosurgical interventions. Focused ultrasound (FUS) delivers thermal energy without an invasive probe, penetrating the dura mater, entering through the cerebrospinal fluid (CSF) space, or harming intervening brain tissue. We applied continuous on-line monitoring by MRI to demonstrate the effect of the thermal intervention on the brain tissue. For this, seven rabbits had a part of their skull removed to create access for the FUS beam into the brain through an acoustic window of 11 mm in diameter. Dura was left intact and skin was sutured. One week later, the rabbits were sonicated for 3 seconds with 21 W acoustic power, and the FUS focus was visualized with a temperature-sensitive T1-weighted MRI pulse sequence. The tissue reaction was documented over 7 days with T2-weighted images of the brain. The initial area of the central low signal intensity in the axial plane was .4 ± .3 mm2, and for the bright hyperintensity surrounding the lesion, it was 2.3 ± .6 mm2 (n = 7). In the coronal plane, the corresponding values were .4 ± .1 mm2 and 3.4 ± .9 mm2 (n = 5). The developing brain edema culminated 48 hours later and thereafter diminished during the next 5 days. Histology revealed a central necrosis in the white matter surrounded by edematous tissue with inflammatory cells. In summary, the image-guided thermal ablation technique described here produced a relatively small lesion in the white matter at the targeted location. This was accomplished without opening the dura or the need for a stereotactical device. MRI allowed on-line monitoring of the lesion setting and the deposition of thermal energy and demonstrated the tissue damage after the thermal injury. 相似文献
9.
Diazoxide is a putative mitochondrial, ATP-sensitive potassium channel opener that has been implicated in neuroprotection in cerebral ischemia. Administered as pretreatment, diazoxide can attenuate ischemia-related neuronal injury, but little is known about the potential neuroprotective properties of the drug when it is given after the onset of an ischemic insult. In a previous study, we applied diazoxide after imposing chronic cerebral hypoperfusion by means of permanent, bilateral occlusion of the common carotid arteries (2VO) in rats. We observed that ischemia-induced learning impairment assessed in the Morris water maze, and microglial activation visualized by immunocytochemistry, were prevented by diazoxide as determined at 13 weeks after 2VO. However, dimethyl sulfoxide, the organic solvent of diazoxide also prevented memory deficits, without any effect on microglial activity. Therefore, we have repeated our experiments with the use of an inorganic solvent, aqueous NaOH solution in order to clarify the effect of diazoxide independent of dimethyl sulfoxide. The present results demonstrated that diazoxide alone did not improve learning performance, but it prevented microglial activation in the hippocampus 13 weeks after the onset of 2VO. These data provide evidence that post-treatment with diazoxide is not effective in impeding a long-term memory deficiency, but it can attenuate ischemia-induced microglial activation, independently of the solvent used. 相似文献
10.
Csoma E Bácsi A Liu X Szabó J Ebbesen P Beck Z Kónya J Andirkó I Nagy E Tóth FD 《Journal of medical virology》2002,67(1):67-87
Human herpesvirus 6 (HHV-6) and human immunodeficiency virus type 1 (HIV-1) may interact during transplacental transmission of HIV-1. The placental syncytiotrophoblast layer serves as the first line of defense of the fetus against viruses. Patterns of replication of HHV-6 variant A (HHV-6A) and HIV-1 were analyzed in singly and dually infected human term syncytiotrophoblast cells cultured in vitro. For this purpose, the GS strain of HHV-6A and the Ba-L and IIIB strains of HIV-1 were used. HHV-6A replication was restricted at the level of early gene products in singly infected syncytiotrophoblasts, whereas no viral protein expression was found in cells infected with HIV-1 alone. Coinfection of syncytiotrophoblast cells with HHV-6A and HIV-1 resulted in production of infectious HIV-1. In contrast, no enhancement of HHV-6A expression was observed in cell cultures infected with both viruses. Uninfected syncytiotrophoblast cells were found to express CXCR4 and CCR3 but not CD4 or CCR5 receptors. Infection of syncytiotrophoblasts with HHV-6A did not induce CD4 expression and had no influence on chemokine receptor expression. Activation of HIV-1 from latency in coinfected cells was mediated by the immediate-early (IE)-A and IE-B gene products of HHV-6A. Open reading frames U86 and U89 of the IE-A region were able to activate HIV-1 replication in a synergistic manner. The data suggest that in vivo double infection of syncytiotrophoblast cells with HHV-6A and HIV-1 could contribute to the transplacental transmission of HIV-1 but not HHV-6A. 相似文献