Biomedical subjects

Shyam Bharat

Publications and source records attributed to Shyam Bharat.

3 recordsLinked to original sources

PubMed2006

Contrast-transfer improvement for electrode displacement elastography.

Electrode displacement elastography is a strain imaging method that can be used for in-vivo imaging of radiofrequency ablation-induced lesions in abdominal organs such as the liver and kidney. In this technique, tissue motion or deformation is introduced by displacing the same electrode used to create the lesion. Minute displacements (on the order of a fraction of a millimetre) are applied to the thermal lesion through the electrode, resulting in localized tissue deformation. Ultrasound echo signals acquired before and after the electrode-induced displacements are then utilized to generate strain images. However, these local strains depend on the modulus distribution of the tissue region being imaged. Therefore, a quantitative evaluation of the conversion efficiency from modulus contrast to strain contrast in electrode-displacement elastograms is warranted. The contrast-transfer efficiency is defined as the ratio (in dB) of the observed elastographic strain contrast and the underlying true modulus contrast. It represents a measure of the efficiency with which elastograms depict the underlying modulus distribution in tissue. In this paper, we develop a contrast-transfer efficiency formalism for electrode displacement elastography (referred to as contrast-transfer improvement). Changes in the contrast-transfer improvement as a function of the underlying true modulus contrast and the depth of the inclusion in the simulated phantom are studied. We present finite element analyses obtained using a two-dimensional mechanical deformation and tissue motion model. The results obtained using finite element analyses are corroborated using experimental analysis and an ultrasound simulation program so as to incorporate noise artifacts.

Algorithms↗

PubMed2006

Elastographic measurements of in-vivo radiofrequency ablation lesions of the kidney.

BACKGROUND AND PURPOSE: Elastography may prove useful for monitoring radiofrequency ablative (RFA) therapy because heat-ablated tissues are more elastic than untreated tissues. Herein, we report our initial evaluations of the reliability of elastography for delineating thermal-lesion boundaries at the time of RFA of porcine kidneys. MATERIALS AND METHODS: In-vivo RFA was performed on 20 kidneys from 10 40-kg female pigs. Elastography was performed at the time of surgery and after 48 hours. The imaging plane was perpendicular to the axis of the RF electrode so that the ablated region was around the center of the plane. Measurements of the sections representing the same image plane used for elastography were taken at pathologic examination and compared with the measurements obtained from the elastograms. RESULTS: We found a statistically significant correlation between elastography and pathology measurements with respect to the area and volume estimates (r = 0.9302 and r = 0.953, respectively). Overall, elastography slightly underestimated the lesion size, as judged by the digitalized pathologic images, a finding consistent with previous reports. CONCLUSION: We found a correlation between the area and volume estimates of thermal lesions that were based on elastographic images and the measurements from gross pathologic dimensions. A significant limitation of renal RFA is the inaccuracy of current imaging modalities to provide real-time monitoring, and elastography may prove to be reliable for delineating the resulting thermal lesions.

Animals↗

PubMed2005

Monitoring stiffness changes in lesions after radiofrequency ablation at different temperatures and durations of ablation.

The variations in the stiffness or stiffness contrast of lesions resulting from radiofrequency (RF) ablation of canine liver tissue at different temperatures and for different ablation durations at a specified temperature are analyzed. Tissue stiffness, in general, increases with temperature; however, an anomaly exists around 80 degrees C, where the stiffness of the lesion is lower than that of the lesion ablated at 70 degrees C. On the other hand, the stiffness increases monotonically with the duration of ablation. Plots illustrating the ratio of mean strains in normal canine liver tissue to mean strains in ablated thermal lesions demonstrate the variation in the stiffness contrast of the thermal lesions. The contrast-to-noise ratio (CNRe) of the lesions, which serves as an indicator of the detectability of the lesions under the different experimental imaging conditions described above, is also presented. The results presented in this paper show that the elastographic depiction of stiffer thermal lesions is better, in terms of the CNRe parameter. An important criterion in the elastographic depiction of RF-ablated regions of tissue is the trade-off between ablation temperature and duration of ablation. Tissue necrosis can occur either by ablating tissue to high temperatures for short durations or to lower temperatures for longer durations. In this paper, we attempt to characterize the elastographic depiction of thermal lesions under these different experimental conditions. This paper provides results that may be utilized by practitioners of RF ablation to decide the ablation temperature and duration, on the basis of the strain images of normal liver tissue and ablated thermal lesions discussed in this paper.

Animals↗