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21.
Jonathan Ophir S. Kaisar Alam Brian S. Garra Faouzi Kallel Elisa E. Konofagou Thomas Krouskop Christopher R. B. Merritt Raffaella Righetti Remi Souchon Seshadri Srinivasan Tomy Varghese 《Journal of Medical Ultrasonics》2002,29(4):155-171
Elastography is a method that can ultimately generate several new kinds of images, called elastograms. As such, all the properties
of elastograms are different from the familiar properties of sonograms. While sonograms convey information related to the
local acoustic backscatter energy from tissue components, elastograms relate to its local strains, Young's moduli or Poisson's
ratios. In general, these elasticity parameters are not directly correlated with sonographic parameters, i.e. elastography
conveys new information about internal tissue structure and behavior under load that is not otherwise obtainable. In this
paper we summarize our work in the field of elastography over the past decade. We present some relevant background material
from the field of biomechanics. We then discuss the basic principles and limitations that are involved in the production of
elastograms of biological tissues. Results from biological tissues in vitro and in vivo are shown to demonstrate this point.
We conclude with some observations regarding the potential of elastography for medical diagnosis. 相似文献
22.
胃癌癌前病变癌变机制及其逆转的研究进展 总被引:23,自引:7,他引:16
王冠庭 《世界华人消化杂志》2000,8(1):1-4
胃癌癌前病变与胃癌的发生关系,日益受到重视,近几年来特别强调幽门螺杆菌为引起慢性萎缩性胃炎与胃癌的重要危险因子.因此,许多学者进一步深入研究幽门螺杆菌感染对发生胃癌的危险性,胃癌癌前病变发生癌变的机制以及如何使其逆转,是预防和降低胃癌发病的重要课题. 相似文献
23.
颜光涛 《军医进修学院学报》2010,31(1):1-3,38
对瘦素与肿瘤的最新研究进展进行综述,并阐明瘦素参与调节肿瘤发生、发展的可能机制,它可能有望成为早期诊治肿瘤的一个关键点。 相似文献
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26.
In conventional elastography, internal tissue deformations, induced by external compression applied to the tissue surface, are estimated by cross-correlation analysis of echo signals obtained before and after compression. Conventionally, strains are estimated by computing the gradient of estimated displacement. However, gradient-based algorithms are highly susceptible to noise and decorrelation, which could limit their utility. We previously developed strain estimators based on a frequency-domain (spectral) formulation that were shown to be more robust but less precise compared to conventional strain estimators, In this paper, we introduce a novel spectral strain estimator that estimates local strain by maximizing the correlation between the spectra of pre- and postcompression echo signals using iterative frequency-scaling of the latter; we also discuss a variation of this algorithm that may be computationally more efficient but less precise. The adaptive spectral strain estimator combines the advantages of time- and frequency-domain methods and has outperformed conventional estimators in experiments and 2-D finite-element simulations. 相似文献
27.
Spatial-angular compounding is a new technique that enables the reduction of noise artifacts in ultrasound elastography. Previous results using spatial angular compounding, however, were based on the use of the tissue incompressibility assumption. Compounded elastograms were obtained from a spatially-weighted average of local strain estimated from radiofrequency echo signals acquired at different insonification angles. In this paper, we present a new method for reducing the noise artifacts in the axial strain elastogram utilizing a least-squares approach on the angular displacement estimates that does not use the incompressibility assumption. This method produces axial strain elastograms with higher image quality, compared to noncompounded axial strain elastograms, and is referred to as the least-squares angular-compounding approach for elastography. To distinguish between these two angular compounding methods, the spatial-angular compounding with angular weighting based on the tissue incompressibility assumption is referred to as weighted compounding. In this paper, we compare the performance of the two angular-compounding techniques for elastography using beam steering on a linear-array transducer. Quantitative experimental results demonstrate that least-squares compounding provides comparable but smaller improvements in both the elastographic signal-to-noise ratio and the contrast-to-noise ratio, as compared to the weighted-compounding method. Ultrasound simulation results suggest that the least-squares compounding method performs better and provide accurate and robust results when compared to the weighted compounding method, in the case where the incompressibility assumption does not hold. 相似文献
28.
Chalmers RM; Howard RS; Wiles CM; Hirsch NP; Miller DH; Williams A; Spencer GT 《QJM : monthly journal of the Association of Physicians》1996,89(6):469-476
Twenty-nine patients with a neuronopathic or neuropathic disorder were
referred for assessment of respiratory insufficiency between 1978 and 1994.
Diagnoses included spinal muscular atrophy (6), chronic idiopathic
demyelinating neuropathy (4), Vialetto-van Laere syndrome (3), hereditary
motor and sensory neuropathy (3) and a miscellaneous group (5). We also
describe seven patients with Guillain-Barre syndrome (GBS) who required
long-term ventilatory support for over 6 months to 7 years after the
initial illness. Respiratory insufficiency occurred as a consequence of
respiratory muscle weakness, impaired bulbar function and restrictive lung
defects. In some groups presentation was with progressive nocturnal
hypoventilation culminating in acute respiratory failure. Five patients
with GBS or chronic idiopathic demyelinating neuropathy were weaned from
ventilatory support up to 18 months after the initial illness. The
remaining 24 patients required continuous or nocturnal ventilatory support
using intermittent positive-pressure ventilation (13), negative pressure
ventilation (4), nasal-mask-delivered intermittent positive-pressure
ventilation (4), nasal-mask-delivered continuous positive-pressure
ventilation (3), mouthpiece-assisted ventilation by day (2) and rocking bed
(1). None have been weaned from support after a period of ventilation
ranging from one month to 10 years. Eight patients have subsequently died.
相似文献
29.
J. Neil Waddell MDipTech PGDipCDTech HDE ; Alan GT Payne BDS MDent DDSc FCD ; Michael V. Swain BSc PhD ; Jules A. Kieser BDS PhD DSc FLS FDSRCSEd 《Clinical implant dentistry and related research》2010,12(1):26-38
Background: Soldered or cast bars are used as a standard of care in attachment systems supporting maxillary and mandibular implant overdentures. When failures of these bars occur, currently there is a lack of evidence in relation to their specific etiology, location, or nature. Purpose: To investigate the failure process of a case series of six failed soldered bars, four intact soldered bars, and one intact cast milled bar, which had been supporting implant overdentures. Materials and Methods: A total of 11 different overdenture bars were removed from patients with different configuration of opposing arches. A failed bar (FB) group (n = 6) had failed soldered overdenture bars, which were recovered from patients following up to 2 years of wear before requiring prosthodontic maintenance and repair. An intact bar (IB) group (n = 5) had both soldered bars and a single cast milled bar, which had been worn by patients for 2 to 5 years prior to receiving other aspects of prosthodontic maintenance. All bars were examined using scanning electron microscopy to establish the possible mode of failure (FB) or to identify evidence of potential failure in the future (IB). Results: Evidence of a progressive failure mode of corrosion fatigue and creep were observed on all the FB and IB usually around the solder areas and nonoxidizing gold cylinder. Fatigue and creep were also observed in all the IB. Where the level of corrosion was substantial, there was no evidence of wear from the matrices of the attachment system. Evidence of an instantaneous failure mode, ductile and brittle overload, was observed on the fracture surfaces of all the FB, within the solder and the nonoxidizing gold cylinders, at the solder/cylinder interface. Conclusion: Corrosion, followed by corrosion fatigue, appears to be a key factor in the onset of the failure process for overdenture bars in this case series of both maxillary and mandibular overdentures. Limited sample size and lack of standardization identify trends only but prevent broad interpretation of the findings. 相似文献