292 resultados para VOLUME TOMOGRAPHY


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The "Yearbook of Private International Law" provides all about the conflict of laws developments of 2012 and 2013 in one book: Volume XIV (2012/2013) includes contributions on the proposed codification of the General Part of Private International Law in Europe, on the reform of the Chinese legal system as well as on defamation and violation of personality rights (the latter in a whole section). Furthermore, the book deals with the application of EU legislation on jurisdiction and enforcement of judgements, the recognition of judgements overturned by another judgement, and the conflict of decisions in international arbitration. Reports and court decisions from the Netherlands, Turkey, India, Finland, Croatia and Switzerland and a summary of two dissertations on the role of sovereignty and choice of courts agreements complete the book.

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This paper describes a realistic simulator for the Computed Tomography (CT) scan process for motion analysis. In fact, we are currently developing a new framework to find small motion from the CT scan. In order to prove the fidelity of this framework, or potentially any other algorithm, we present in this paper a simulator to simulate the whole CT acquisition process with a priori known parameters. In other words, it is a digital phantom for the motion analysis that can be used to compare the results of any related algorithm with the ground-truth realistic analytical model. Such a simulator can be used by the community to test different algorithms in the biomedical imaging domain. The most important features of this simulator are its different considerations to simulate the best the real acquisition process and its generality.

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Acoustic waveform inversions are an increasingly popular tool for extracting subsurface information from seismic data. They are computationally much more efficient than elastic inversions. Naturally, an inherent disadvantage is that any elastic effects present in the recorded data are ignored in acoustic inversions. We investigate the extent to which elastic effects influence seismic crosshole data. Our numerical modeling studies reveal that in the presence of high contrast interfaces, at which P-to-S conversions occur, elastic effects can dominate the seismic sections, even for experiments involving pressure sources and pressure receivers. Comparisons of waveform inversion results using a purely acoustic algorithm on synthetic data that is either acoustic or elastic, show that subsurface models comprising small low-to-medium contrast (?30%) structures can be successfully resolved in the acoustic approximation. However, in the presence of extended high-contrast anomalous bodies, P-to-S-conversions may substantially degrade the quality of the tomographic images. In particular, extended low-velocity zones are difficult to image. Likewise, relatively small low-velocity features are unresolved, even when advanced a priori information is included. One option for mitigating elastic effects is data windowing, which suppresses later arriving seismic arrivals, such as shear waves. Our tests of this approach found it to be inappropriate because elastic effects are also included in earlier arriving wavetrains. Furthermore, data windowing removes later arriving P-wave phases that may provide critical constraints on the tomograms. Finally, we investigated the extent to which acoustic inversions of elastic data are useful for time-lapse analyses of high contrast engineered structures, for which accurate reconstruction of the subsurface structure is not as critical as imaging differential changes between sequential experiments. Based on a realistic scenario for monitoring a radioactive waste repository, we demonstrated that acoustic inversions of elastic data yield substantial distortions of the tomograms and also unreliable information on trends in the velocity changes.

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After cemented total hip arthroplasty (THA) there may be failure at either the cement-stem or the cement-bone interface. This results from the occurrence of abnormally high shear and compressive stresses within the cement and excessive relative micromovement. We therefore evaluated micromovement and stress at the cement-bone and cement-stem interfaces for a titanium and a chromium-cobalt stem. The behaviour of both implants was similar and no substantial differences were found in the size and distribution of micromovement on either interface with respect to the stiffness of the stem. Micromovement was minimal with a cement mantle 3 to 4 mm thick but then increased with greater thickness of the cement. Abnormally high micromovement occurred when the cement was thinner than 2 mm and the stem was made of titanium. The relative decrease in surface roughness augmented slipping but decreased debonding at the cement-bone interface. Shear stress at this site did not vary significantly for the different coefficients of cement-bone friction while compressive and hoop stresses within the cement increased slightly.

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This work aimed at assessing the doses delivered in Switzerland to paediatric patients during computed tomography (CT) examinations of the brain, chest and abdomen, and at establishing diagnostic reference levels (DRLs) for various age groups. Forms were sent to the ten centres performing CT on children, addressing the demographics, the indication and the scanning parameters: number of series, kilovoltage, tube current, rotation time, reconstruction slice thickness and pitch, volume CT dose index (CTDI(vol)) and dose length product (DLP). Per age group, the proposed DRLs for brain, chest and abdomen are, respectively, in terms of CTDI(vol): 20, 30, 40, 60 mGy; 5, 8, 10, 12 mGy; 7, 9, 13, 16 mGy; and in terms of DLP: 270, 420, 560, 1,000 mGy cm; 110, 200, 220, 460 mGy cm; 130, 300, 380, 500 mGy cm. An optimisation process should be initiated to reduce the spread in dose recorded in this study. A major element of this process should be the use of DRLs.

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Generalized Born methods are currently among the solvation models most commonly used for biological applications. We reformulate the generalized Born molecular volume method initially described by (Lee et al, 2003, J Phys Chem, 116, 10606; Lee et al, 2003, J Comp Chem, 24, 1348) using fast Fourier transform convolution integrals. Changes in the initial method are discussed and analyzed. Finally, the method is extensively checked with snapshots from common molecular modeling applications: binding free energy computations and docking. Biologically relevant test systems are chosen, including 855-36091 atoms. It is clearly demonstrated that, precision-wise, the proposed method performs as good as the original, and could better benefit from hardware accelerated boards.

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The noise power spectrum (NPS) is the reference metric for understanding the noise content in computed tomography (CT) images. To evaluate the noise properties of clinical multidetector (MDCT) scanners, local 2D and 3D NPSs were computed for different acquisition reconstruction parameters.A 64- and a 128-MDCT scanners were employed. Measurements were performed on a water phantom in axial and helical acquisition modes. CT dose index was identical for both installations. Influence of parameters such as the pitch, the reconstruction filter (soft, standard and bone) and the reconstruction algorithm (filtered-back projection (FBP), adaptive statistical iterative reconstruction (ASIR)) were investigated. Images were also reconstructed in the coronal plane using a reformat process. Then 2D and 3D NPS methods were computed.In axial acquisition mode, the 2D axial NPS showed an important magnitude variation as a function of the z-direction when measured at the phantom center. In helical mode, a directional dependency with lobular shape was observed while the magnitude of the NPS was kept constant. Important effects of the reconstruction filter, pitch and reconstruction algorithm were observed on 3D NPS results for both MDCTs. With ASIR, a reduction of the NPS magnitude and a shift of the NPS peak to the low frequency range were visible. 2D coronal NPS obtained from the reformat images was impacted by the interpolation when compared to 2D coronal NPS obtained from 3D measurements.The noise properties of volume measured in last generation MDCTs was studied using local 3D NPS metric. However, impact of the non-stationarity noise effect may need further investigations.

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PURPOSE: To compare volume-targeted and whole-heart coronary magnetic resonance angiography (MRA) after the administration of an intravascular contrast agent. MATERIALS AND METHODS: Six healthy adult subjects underwent a navigator-gated and -corrected (NAV) free breathing volume-targeted cardiac-triggered inversion recovery (IR) 3D steady-state free precession (SSFP) coronary MRA sequence (t-CMRA) (spatial resolution = 1 x 1 x 3 mm(3)) and high spatial resolution IR 3D SSFP whole-heart coronary MRA (WH-CMRA) (spatial resolution = 1 x 1 x 2 mm(3)) after the administration of an intravascular contrast agent B-22956. Subjective and objective image quality parameters including maximal visible vessel length, vessel sharpness, and visibility of coronary side branches were evaluated for both t-CMRA and WH-CMRA. RESULTS: No significant differences (P = NS) in image quality were observed between contrast-enhanced t-CMRA and WH-CMRA. However, using an intravascular contrast agent, significantly longer vessel segments were measured on WH-CMRA vs. t-CMRA (right coronary artery [RCA] 13.5 +/- 0.7 cm vs. 12.5 +/- 0.2 cm; P < 0.05; and left circumflex coronary artery [LCX] 11.9 +/- 2.2 cm vs. 6.9 +/- 2.4 cm; P < 0.05). Significantly more side branches (13.3 +/- 1.2 vs. 8.7 +/- 1.2; P < 0.05) were visible for the left anterior descending coronary artery (LAD) on WH-CMRA vs. t-CMRA. Scanning time and navigator efficiency were similar for both techniques (t-CMRA: 6.05 min; 49% vs. WH-CMRA: 5.51 min; 54%, both P = NS). CONCLUSION: Both WH-CMRA and t-CMRA using SSFP are useful techniques for coronary MRA after the injection of an intravascular blood-pool agent. However, the vessel conspicuity for high spatial resolution WH-CMRA is not inferior to t-CMRA, while visible vessel length and the number of visible smaller-diameter vessels and side-branches are improved.

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The atomic force microscope is a convenient tool to probe living samples at the nanometric scale. Among its numerous capabilities, the instrument can be operated as a nano-indenter to gather information about the mechanical properties of the sample. In this operating mode, the deformation of the cantilever is displayed as a function of the indentation depth of the tip into the sample. Fitting this curve with different theoretical models permits us to estimate the Young's modulus of the sample at the indentation spot. We describe what to our knowledge is a new technique to process these curves to distinguish structures of different stiffness buried into the bulk of the sample. The working principle of this new imaging technique has been verified by finite element models and successfully applied to living cells.

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BACKGROUND: Induction radiochemotherapy, followed by resection, for T4 non-small cell lung cancer, has shown promising long-term survival but may be associated with increased postoperative morbidity and death, depending on patient selection. Here, we determined the effect of induction radiochemotherapy on pulmonary function and whether postinduction pulmonary function changes predict hospital morbidity and death and long-term survival. METHODS: A consecutive prospective cohort of 72 patients with T4 N0-2 M0 non-small cell lung cancer managed by radiochemotherapy, followed by resection, is reported. All patients underwent thoracoabdominal computed tomography or fusion positron emission tomography-computed tomography, brain imaging, mediastinoscopy, echocardiography, ventilation-perfusion scintigraphy, and pulmonary function testing before and after induction therapy. Resection was performed if the postoperative forced expiratory volume in 1 second and diffusion capacity of the lung for carbon monoxide exceeded 30% predicted and if the postoperative maximum oxygen consumption exceeded 10 mL/kg/min. RESULTS: The postoperative 90-day mortality rate was 8% (lobectomy, 2%; pneumonectomy, 21%; p=0.01). All deaths after pneumonectomy occurred after right-sided procedures. The 3-year and 5-year survival was 50% (95% confidence interval, 36% to 62%) and 45% (95% confidence interval, 31% to 57%) and was significantly associated with completeness of resection (p=0.004) and resection type (pneumonectomy vs lobectomy, p=0.01). There was no correlation between postinduction pulmonary function changes and postoperative morbidity or death or long-term survival in patients managed by lobectomy or pneumonectomy. CONCLUSIONS: In properly selected patients with T4 N0-2 M0 non-small cell lung cancer, resection after induction radiochemotherapy can be performed with a reasonable postoperative mortality rate and long-term survival, provided the resection is complete and a right-sided pneumonectomy is avoided. Postinduction pulmonary function changes did not correlate with postoperative morbidity or death or with long-term outcome.

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The state of the art to describe image quality in medical imaging is to assess the performance of an observer conducting a task of clinical interest. This can be done by using a model observer leading to a figure of merit such as the signal-to-noise ratio (SNR). Using the non-prewhitening (NPW) model observer, we objectively characterised the evolution of its figure of merit in various acquisition conditions. The NPW model observer usually requires the use of the modulation transfer function (MTF) as well as noise power spectra. However, although the computation of the MTF poses no problem when dealing with the traditional filtered back-projection (FBP) algorithm, this is not the case when using iterative reconstruction (IR) algorithms, such as adaptive statistical iterative reconstruction (ASIR) or model-based iterative reconstruction (MBIR). Given that the target transfer function (TTF) had already shown it could accurately express the system resolution even with non-linear algorithms, we decided to tune the NPW model observer, replacing the standard MTF by the TTF. It was estimated using a custom-made phantom containing cylindrical inserts surrounded by water. The contrast differences between the inserts and water were plotted for each acquisition condition. Then, mathematical transformations were performed leading to the TTF. As expected, the first results showed a dependency of the image contrast and noise levels on the TTF for both ASIR and MBIR. Moreover, FBP also proved to be dependent of the contrast and noise when using the lung kernel. Those results were then introduced in the NPW model observer. We observed an enhancement of SNR every time we switched from FBP to ASIR to MBIR. IR algorithms greatly improve image quality, especially in low-dose conditions. Based on our results, the use of MBIR could lead to further dose reduction in several clinical applications.

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Recherches médiévales, 4, série Magistralia. Leçons et lectures, 1. Choix, notices et avant-propos d'Alain Corbellari