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排序方式: 共有224条查询结果,搜索用时 31 毫秒
1.
Anastasiia Panfilova Sarah E. Shelton Cristina Caresio Ruud J.G. van Sloun Filippo Molinari Hessel Wijkstra Paul A. Dayton Massimo Mischi 《Ultrasound in medicine & biology》2019,45(2):539-548
Dynamic contrast-enhanced ultrasound (DCE-US) has been proposed as a powerful tool for cancer diagnosis by estimation of perfusion and dispersion parameters reflecting angiogenic vascular changes. This work was aimed at identifying which vascular features are reflected by the estimated perfusion and dispersion parameters through comparison with acoustic angiography (AA). AA is a high-resolution technique that allows quantification of vascular morphology. Three-dimensional AA and 2-D DCE-US bolus acquisitions were used to monitor the growth of fibrosarcoma tumors in nine rats. AA-derived vascular properties were analyzed along with DCE-US perfusion and dispersion to investigate the differences between tumor and control and their evolution in time. AA-derived microvascular density and DCE-US perfusion exhibited good agreement, confirmed by their spatial distributions. No vascular feature was correlated with dispersion. Yet, dispersion provided better cancer classification than perfusion. We therefore hypothesize that dispersion characterizes vessels that are smaller than those visible with AA. 相似文献
2.
Objective:To assess the sensitivity and the specifity of predicting idiopathic AF with P wave dura-tion and P wave dispersion. Methods: The maximum P wave duration and P wave dispersion in 36 patients with idio-pathic AF were measured and compared with those of sex-and age-matched healthy subjects. Results:The maxi-mum P wave duration and P wave dispersion were higher in patients with idiopathic Af than in control group. Themaximum P wave duration >110ms or P wave dispersion >40ms was used to differentiate patients from healthy 相似文献
3.
Materials are distributed throughout the body of mammals by fractal networks of branching tubes. Based on the scaling laws of the fractal structure, the vascular tree is reduced to an equivalent one-dimensional, tube model. A dispersion–convection partial differential equation with constant coefficients describes the heterogeneous concentration profile of an intravascular tracer in the vascular tree. A simple model for the mammalian circulatory system is built in entirely physiological terms consisting of a ring shaped, one-dimensional tube which corresponds to the arterial, venular, and pulmonary trees, successively. The model incorporates the blood flow heterogeneity of the mammalian circulatory system. Model predictions are fitted to published concentration-time data of indocyanine green injected in humans and dogs. Close agreement was found with parameter values within the expected physiological range. © 2003 Biomedical Engineering Society.
PAC2003: 8710+e, 8719Hh, 8719Uv 相似文献
4.
目的 :探讨AMI早期QT间期离散度、JT间期离散度与严重心律失常的关系。方法 :测定 46例AMI患者心梗发生后第 3d的QT间期离散度 (QTd)和JT间期离度 (JTd)。并与30例正常人的对照组比较。结果 :AMI组QTd、JTd、QTcd较对照组显著增大 (P <0 0 1 )。住院期间严重室性心律失常发生组 (1 8例 )的QTd、JTd、QTcd较无严重室性心律失常组 (2 8例 )明显增大 (P <0 0 1 ) ,且发生室颤的 9例患者QTd、JTd、QTcd比无室颤的明显增大 (P <0 0 1 )。结论 :早期测定AMI患者QTd、JTd、QTcd对患者近期严重室性心律失常的发生有预测意义 相似文献
5.
利巴韦林分散片的制备及稳定性评价 总被引:2,自引:0,他引:2
目的研究利巴韦林分散片的处方和制备工艺。方法对按笔者自我设计配方制备的4种利巴韦林分散片,采用高效液相色谱法测定溶出度及进行稳定性评价。结果以处方3工艺制成的片剂,质量可控,稳定性较好。结论处方3工艺成熟,质量稳定,是一种易于服用、奏效快的新制剂。 相似文献
6.
Amphiphilic amino acid copolymers as stabilizers for the preparation of nanocrystal dispersion 总被引:2,自引:0,他引:2
Jonghwi Lee Soo-Jeong Lee Ji-Yeun Choi Ji Youn Yoo Cheol-Hee Ahn 《European journal of pharmaceutical sciences》2005,24(5):441-449
The recent advance of particle size engineering in nanometer ranges has widened the formulation opportunities of relatively water-insoluble drugs. However, the ‘nanoformulation’ suffers from a lack of systematic understanding about the requirements of polymeric stabilizers. Furthermore, the polymers that can be used for the preparation of nanocrystals are so limited that finding a proper stabilizer for a given formulation is often difficult. In this study, amino acid copolymers whose properties can systematically be tailored are developed, and their morphological and compositional effects are investigated. Copolymers containing lysine (K) as their hydrophilic segments, and phenylalanine (F) or leucine (L) as their hydrophobic segments successfully produce stable nanocrystals (200–300 nm) in water, while copolymers of K and alanine (A) could not generate nanosized particles. Not the morphology but the hydrophobicity of copolymers seems to be a critical parameter in the preparation of drug nanocrystals by wet comminution. The effective stabilization performance of copolymers requires the hydrophobic moiety content to be higher than 15 mol%. Comminution for only 5 min is long enough for nanocrystal preparation, and the crystallinity of drug is found intact after the processing. 相似文献
7.
Samantha L. Lipman Ned C. Rouze Mark L. Palmeri Kathryn R. Nightingale 《Ultrasound in medicine & biology》2018,44(4):897-908
Shear wave elasticity imaging (SWEI) characterizes the mechanical properties of human tissues to differentiate healthy from diseased tissue. Commercial scanners tend to reconstruct shear wave speeds for a region of interest using time-of-flight methods reporting a single shear wave speed (or elastic modulus) to the end user under the assumptions that tissue is elastic and shear wave speeds are not dependent on the frequency content of the shear waves. Human tissues, however, are known to be viscoelastic, resulting in dispersion and attenuation. Shear wave spectroscopy and spectral methods have been previously reported in the literature to quantify shear wave dispersion and attenuation, commonly making an assumption that the acoustic radiation force excitation acts as a cylindrical source with a known geometric shear wave amplitude decay. This work quantifies the bias in shear dispersion and attenuation estimates associated with making this cylindrical wave assumption when applied to shear wave sources with finite depth extents, as commonly occurs with realistic focal geometries, in elastic and viscoelastic media. Bias is quantified using analytically derived shear wave data and shear wave data generated using finite-element method models. Shear wave dispersion and attenuation bias (up to 15% for dispersion and 41% for attenuation) is greater for more tightly focused acoustic radiation force sources with smaller depths of field relative to their lateral extent (height-to-width ratios <16). Dispersion and attenuation errors associated with assuming a cylindrical geometric shear wave decay in SWEI can be appreciable and should be considered when analyzing the viscoelastic properties of tissues with acoustic radiation force source distributions with limited depths of field. 相似文献
8.
P波离散度预测扩张型心肌病伴阵发性心房颤动的临床价值 总被引:3,自引:0,他引:3
目的探讨P波离散度(Pd)预测扩张型心肌病(DCM)伴阵发性心房颤动(PAF)的价值。方法30例DCM伴阵发性Af者(A组),26例DCM无Af者(B组)。通过12导联体表心电图测定P波最大持续时间(Pmax)与最小持续时间(Pmin),计算Pd(Pd=Pmax-Pmin)。比较A组与B组的Pd与Pmax。结果A组Pd为48.44-13.8ms,Pmax为122.84-13.7ms,Pmin为76.2±12.0ms,与B组Pd30.6±10.2ms,Pmaxll0.2±10.4ms,Pmin80.8+11.5ms相比明显延长(p<0.01)。A组左房(LA)内径41.415.6mm,B组LA内径40.24-6.2mm,两组相比无显著差异(p>0.05)。为预测Af,取P波时限≥120ms,Pd≥40ms以及两者相结合,敏感性分别为86%、90%、73%,特异性分别为80%、85%、89%,阳性预测值分别为84%、87%、88%。结论Pd增加和P波宽度延长,可预测DCM并发阵发性Af的危险性。 相似文献
9.
Objectives
Short ramie fibers were selected to investigate the effect of fiber length and volume fraction on the flexural properties of ramie fiber reinforced denture base PMMA. With the aid of measured interfacial shear strength and theoretical prediction values, experimental results were well interpreted.Methods
Interfacial properties between denture base PMMA and ramie fibers were evaluated by single fiber pull-out test. Then, chopped ramie fibers were pre-stirred with PMMA powder by a mechanical blender and then mixed with MMA liquid to fabricate composites. Two crucial influencing factors, fiber volume fraction and fiber length, were studied to clarify their effects on flexural properties of composites.Results
With 1.5 mm fibers addition, flexural modulus of denture base PMMA rose from 2.50 to 3.46 GPa with 10 vol.% fibers, while flexural strength declined steadily with increment of fiber content. If fiber length was 3.0 mm, the modulus showed a growth to 3.5 GPa at 4 vol.% fiber content followed by a drop to 3.00 GPa at 10 vol.%, whereas fluctuation in strength was experienced. Experimental results were discussed by comparison with two theoretical models.Significance
Short ramie fiber reinforced denture base PMMA had higher flexural modulus than neat resin, while strength was lowered due to the weak interfacial adhesion. The potential of vegetable fibers as reinforcing agents for denture base should be further investigated by strengthening the interface between cellulose and denture base PMMA. 相似文献10.
Leyla Deger Céline Plante Louis Jacques Sophie Goudreau Stéphane Perron John Hicks Tom Kosatsky Audrey Smargiassi 《Canadian respiratory journal》2012,19(2):97-102