995 resultados para pulse-echo technique


Relevância:

20.00% 20.00%

Publicador:

Resumo:

Ultrasound-guided core-needle biopsy has high sensitivity in the diagnosis of breast cancer. The present study is aimed at detailing the main steps of such procedure, including indications, advantages, limitations, follow-up and description of the technique, besides presenting a checklist including the critical steps required for an appropriate practice of the technique. In the recent years, an increasing number of patients have required breast biopsy, indicating the necessity of a proportional increase in the number of skilled professionals to carry out the procedures and histological diagnoses. A multidisciplinary approach involving the tripod clinical practice-radiology-pathology is responsible for the highest rate of accuracy of the technique and must always be adopted.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Abstract Objective: To compare the diagnostic performance of the three-dimensional turbo spin-echo (3D TSE) magnetic resonance imaging (MRI) technique with the performance of the standard two-dimensional turbo spin-echo (2D TSE) protocol at 1.5 T, in the detection of meniscal and ligament tears. Materials and Methods: Thirty-eight patients were imaged twice, first with a standard multiplanar 2D TSE MR technique, and then with a 3D TSE technique, both in the same 1.5 T MRI scanner. The patients underwent knee arthroscopy within the first three days after the MRI. Using arthroscopy as the reference standard, we determined the diagnostic performance and agreement. Results: For detecting anterior cruciate ligament tears, the 3D TSE and routine 2D TSE techniques showed similar values for sensitivity (93% and 93%, respectively) and specificity (80% and 85%, respectively). For detecting medial meniscal tears, the two techniques also had similar sensitivity (85% and 83%, respectively) and specificity (68% and 71%, respectively). In addition, for detecting lateral meniscal tears, the two techniques had similar sensitivity (58% and 54%, respectively) and specificity (82% and 92%, respectively). There was a substantial to almost perfect intraobserver and interobserver agreement when comparing the readings for both techniques. Conclusion: The 3D TSE technique has a diagnostic performance similar to that of the routine 2D TSE protocol for detecting meniscal and anterior cruciate ligament tears at 1.5 T, with the advantage of faster acquisition.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Background and Question Paired-pulse TMS (Transcranial Magnetic Stimulation) paradigms allow explore motor cortex physiology. The Triple Stimulation Technique (TST) improves conventional TMS in quantifying cortico-spinal conduction. The objective of our study was to compare both methods in paired-pulse paradigms of inhibition and of facilitation. Method We investigated paired pulse paradigms of 2 ms (short intra-cortical inhibition) and of 10 ms intervals (intra cortical facilitation) in a randomized order in 22 healthy subjects applying conventional TMS and the TST protocol. Results Paired-pulse paradigms by both TMS and the TST yielded comparable results of short intra- cortical inhibition and intra cortical facilitation. However, the coefficient of variation was significantly smaller for SICI paradigm using TST. Conclusion These results suggest no greater sensitivity of the TST for quantifying inhibition and facilitation. The utility of TST to better quantify the individual amount of inhibition in SICI paradigms and its clinical utility need further studies.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

BACKGROUND: Abdominoperineal resection (APR) following radiotherapy is associated with a high rate of perineal wound complications. The anterolateral thigh (ALT) flap, combined with the vastus lateralis (VL) muscle, can cover complex perineal and pelvic anteroposterior defects. This is used for the first time transabdominally through the pelvis and the perineum (TAPP) in the infero-posterior directions; this technique has been described and illustrated in this study. METHODS: Among over 90 patients who underwent perineal reconstruction between May 2004 and June 2011, six patients presented high-grade tumours invading perineum, pelvis and sacrum, thereby resulting in a continuous anteroposterior defect. ALT + VL TAPP reconstructions were performed after extended APR and, subsequently, sacrectomy. Patients were examined retrospectively to determine demographics, operative time, complications (general and flap-related), time to complete healing and length of hospital stay. Long-term flap coverage, flap volume stability and functional and aesthetic outcomes were assessed. RESULTS: Mean operating time of the reconstruction was 290 min. No deaths occurred. One patient presented partial flap necrosis. Another patient presented a novel wound dehiscence after flap healing, due to secondary skin dissemination of the primary tumour. Following volumetric flap analysis on serial post-operative CT scans, no significant flap atrophy was observed. All flaps fully covered the defects. No late complications such as fistulas or perineal hernias occurred. Donor-site recovery was uneventful with no functional deficits. CONCLUSIONS: The use of the ALT + VL flap transabdominally is an innovative method to reconstruct exceptionally complex perineal and pelvic defects extending up to the lower back. This flap guarantees superior bulk, obliterating all pelvic dead space, with the fascia lata (FL) supporting the pelvic floor.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Cardiovascular disease is the leading cause of death worldwide. Within this subset, coronary artery disease (CAD) is the most prevalent. Magnetic resonance angiography (MRA) is an emerging technique that provides a safe, non-invasive way of assessing CAD progression. To generate contrast between tissues, MR images are weighted according to the magnetic properties of those tissues. In cardiac MRI, T2 contrast, which is governed by the rate of transverse signal loss, is often created through the use of a T2-Preparation module. T2-Preparation, or T2-Prep, is a magnetization preparation scheme used to improve blood/myocardium contrast in cardiac MRI. T2-Prep methods generally use a non-selective +90°, 180°, 180°, -90° train of radiofrequency (RF) pulses (or variant thereof), to tip magnetization into the transverse plane, allow it to evolve, and then to restore it to the longitudinal plane. A key feature in this process is the combination of a +90° and -90° RF pulse. By changing either one of these, a mismatch occurs between signal excitation and restoration. This feature can be exploited to provide additional spectral or spatial selectivity. In this work, both of these possibilities are explored. The first - spectral selectivity - has been examined as a method of improving fat saturation in coronary MRA. The second - spatial selectivity - has been examined as a means of reducing imaging time by decreasing the field of view, and as a method of reducing artefacts originating from the tissues surrounding the heart. Two additional applications, parallel imaging and self-navigation, are also presented. This thesis is thus composed of four sections. The first, "A Fat Signal Suppression for Coronary MRA at 3T using a Water-Selective Adiabatic T2-Preparation Technique", was originally published in the journal Magnetic Resonance in Medicine (MRM) with co-authors Ruud B. van Heeswijk and Matthias Stuber. The second, "Combined T2-Preparation and 2D Pencil Beam Inner Volume Selection", again with co-authors Ruud van Heeswijk and Matthias Stuber, was also published in the journal MRM. The third, "A cylindrical, inner volume selecting 2D-T2-Prep improves GRAPPA-accelerated image quality in MRA of the right coronary artery", written with co-authors Jerome Yerly and Matthias Stuber, has been submitted to the "Journal of Cardiovascular Magnetic Resonance", and the fourth, "Combined respiratory self-navigation and 'pencil-beam' 2D-T2 -Prep for free-breathing, whole-heart coronary MRA", with co¬authors Jerome Chaptinel, Giulia Ginami, Gabriele Bonanno, Simone Coppo, Ruud van Heeswijk, Davide Piccini, and Matthias Stuber, is undergoing internal review prior to submission to the journal MRM. -- Les maladies cardiovasculaires sont la cause principale de décès dans le monde : parmi celles-ci, les maladies coronariennes sont les plus répandues. L'angiographie par résonance magnétique (ARM) est une technique émergente qui fournit une manière sûre, non invasive d'évaluer la progression de la coronaropathie. Pour obtenir un contraste entre les tissus, les images d'IRM sont pondérées en fonction des propriétés magnétiques de ces tissus. En IRM cardiaque, le contraste en T2, qui est lié à la décroissance du signal transversal, est souvent créé grâce à l'utilisàtion d'un module de préparation T2. La préparation T2, ou T2-Prep, est un système de préparation de l'aimantation qui est utilisé pour améliorer le contraste entre le sang et le myocarde lors d'une IRM cardiaque. Les méthodes de T2-Prep utilisent généralement une série non-sélective d'impulsions de radiofréquence (RF), typiquement [+ 90°, 180°, 180°, -90°] ou une variante, qui bascule l'aimantation dans le plan transversal, lui permet d'évoluer, puis la restaure dans le plan longitudinal. Un élément clé de ce processus est la combinaison des impulsions RF de +90° et -90°. En changeant l'une ou l'autre des impulsions, un décalage se produit entre l'excitation du signal et de la restauration. Cette fonction peut être exploitée pour fournir une sélectivité spectrale ou spatiale. Dans cette thèse, les deux possibilités sont explorées. La première - la sélectivité spectrale - a été examinée comme une méthode d'améliorer la saturation de la graisse dans l'IRM coronarienne. La deuxième - la sélectivité spatiale - a été étudiée comme un moyen de réduire le temps d'imagerie en diminuant le champ de vue, et comme une méthode de réduction des artefacts provenant des tissus entourant le coeur. Deux applications supplémentaires, l'imagerie parallèle et la self-navigation, sont également présentées. Cette thèse est ainsi composée de quatre sections. La première, "A Fat Signal Suppression for Coronary MRA at 3T using a Water-Selective Adiabatic T2-Preparation Technique", a été publiée dans la revue médicale Magnetic Resonance .in Medicine (MRM) avec les co-auteurs Ruud B. van Heeswijk et Matthias Stuber. La deuxième, Combined T2-Preparation and 2D Pencil Beam Inner Volume Selection", encore une fois avec les co-auteurs Ruud van Heeswijk et Matthias Stuber, a également été publiée dans le journal MRM. La troisième, "A cylindrical, inner volume selecting 2D-T2-Prep improves GRAPPA- accelerated image quality in MRA of the right coronary artery", écrite avec les co-auteurs Jérôme Yerly et Matthias Stuber, a été présentée au "Journal of Cardiovascular Magnetic Resonance", et la quatrième, "Combined respiratory self-navigation and 'pencil-beam' 2D-T2 -Prep for free-breathing, whole-heart coronary MRA", avec les co-auteurs Jérôme Chaptinel, Giulia Ginami, Gabriele Bonanno , Simone Coppo, Ruud van Heeswijk, Davide Piccini, et Matthias Stuber, subit un examen interne avant la soumission à la revue MRM.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

It has been carried out an investigation of ethanol electro-oxidation on Ti/IrO2 electrodes. The experimental results show a high selectivity towards acetaldehyde formation thus, offering potential advantages in cost and availability of raw material. It has been observed that the electrode is partially blocked by a film formed after the oxidation of the starting material which can be removed by pulse technique between RDO and RDH onset. The mechanism and the selectivity of the product formed is presented.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Diffusion coefficients provide uniquely detailed and easily interpreted information on molecular organization and phase structure. They are quite sensitive to structural changes, and to binding and association phenomena, in particular for liquid colloidal or macromolecular systems. This paper describes the principles of diffusion measurements in liquids by pulsed magnetic field gradient spin-echo (PFG-SE) NMR spectroscopy. The important PFG-SE technique known as DOSY is presented and discussed. This is a noninvasive technique that can provide individual multicomponent translational diffusion coefficients with good precision in a few minutes, without the need for radioactive isotopic labelling.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

In this work, using the EPR spectroscopy, we analysed the thermal stability of some organic-mineral compounds found in a Gleysoil from Rio Janeiro. It was observed a complete disappearance of the EPR signal around 600 °C for the < 2 µm fraction and a residual EPR signal of semiquinone free radical for the 2-20 µm and 20-53 µm fractions at the same temperature. Also, the experiments showed that the 2-20 µm fraction had a larger concentration of semiquinone free radical per g of carbon and a smaller line width indicated a larger humification of this fraction. This is an evidence that the soil organic matter of this fraction (2-20 µm) is more stable than the other ones.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The present experiment describes the preparation, characterization of n-butyl(pyridil)cobaloxime complex and its electrochemical property. The infrared and uv-visible absorption spectra were used to characterize the complex obtained. The infrared spectrum of the compound showed characteristics bands that indicated the formation of the Co-C chemical bond formation. The electronic absorption spectrum in acetonitrile showed transition bands attributed to p-p*, metal-to-ligand charge transfer, d-d transitions and charge transfer Co-C. The electrochemical property was investigated by the pulse differential voltammetry technique. Two oxidation processes: Co(I)/Co(II) at -423 mV and Co(II)/Co(III) at 752 mV were observed.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

We study how the combination of long and short laser pulses can be used to induce torsion in an axially chiral biphenyl derivative (3,5-difluoro-3 ,5 -dibromo-4 -cyanobiphenyl). A long, with respect to the molecular rotational periods, elliptically polarized laser pulse produces 3D alignment of the molecules, and a linearly polarized short pulse initiates torsion about the stereogenic axis. The torsional motion is monitored in real-time by measuring the dihedral angle using femtosecond time-resolved Coulomb explosion imaging. Within the first 4 picoseconds (ps), torsion occurs with a period of 1.25 ps and an amplitude of 3◦ in excellent agreement with theoretical calculations. At larger times, the quantum states of the molecules describing the torsional motion dephase and an almost isotropic distribution of the dihedral angle is measured.We demonstrate an original application of covariance analysis of two-dimensional ion images to reveal strong correlations between specific ejected ionic fragments from Coulomb explosion. This technique strengthens our interpretation of the experimental data

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The design and use of a novel apparatus for a variant of vacuum distillation is described. Relative to a conventional device, the apparatus/technique described permits superior recovery of multigram quantities of moderately volatile liquids from vacuum distillations.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Digitoitu 22. 5. 2008.