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Andrew R. Kemper - One of the best experts on this subject based on the ideXlab platform.

  • Effects of postmortem time and storage fluid on the material properties of bovine Liver Parenchyma in tension.
    Journal of the mechanical behavior of biomedical materials, 2018
    Co-Authors: Kristin M. Dunford, Tanya Leroith, Andrew R. Kemper
    Abstract:

    Abstract In motor vehicle collisions (MVCs), Liver injuries are one of the most frequently reported types of abdominal organ trauma. Although finite element models are utilized to evaluate the risk of sustaining an abdominal organ injury in MVCs, these models must be validated based on biomechanical data in order to accurately assess injury risk. Given that previous studies that have quantified the tensile failure properties of human Liver Parenchyma have been limited to testing at 48 h postmortem, it is currently unknown how the material properties change between time of death and 48 h postmortem. Therefore, the objective of this study was to quantify the effects of postmortem degradation on the tensile material properties of bovine Liver Parenchyma with increasing postmortem time when stored in DMEM or saline. A total of 148 uniaxial tension tests were successfully conducted on Parenchyma samples of fourteen bovine Livers acquired immediately after death. Liver tissue was submerged in DMEM or saline and kept cool during sample preparation and storage. Twelve Livers were stored as large blocks of tissue, while two Livers were stored as small blocks and slices. Tension tests were performed on multiple dog-bone samples from each Liver at three time points: ~6 h, ~24 h, and ~48 h postmortem. The data were then analyzed using a Linear Mixed Effect Model to determine if there were significant changes in the failure stress, failure strain, and modulus with respect to postmortem time. The results of the current study showed that the failure strain of bovine Liver Parenchyma decreased significantly between 6 h and 48 h after death when stored as large blocks in saline and refrigerated. Conversely, neither the failure stress nor failure strain changed significantly with respect to postmortem time when stored as large blocks in DMEM. The modulus did not change significantly with respect to postmortem time for tissue stored as large blocks in either saline or DMEM. Cellular disruption increased with postmortem time for tissue stored as large blocks, with tissue stored in saline showing the greatest increase at each time point. In addition, preliminary results indicated that reducing the tissue storage size had a negative effect on the material properties and cellular architecture. Overall, this study illustrated that the effects of postmortem Liver degradation varied with respect to the preservation fluid, storage time, and storage block size.

  • Modeling the biomechanical and injury response of human Liver Parenchyma under tensile loading
    Journal of the mechanical behavior of biomedical materials, 2014
    Co-Authors: Costin D. Untaroiu, Sundeep Krishna Siripurapu, Andrew R. Kemper
    Abstract:

    The rapid advancement in computational power has made human finite element (FE) models one of the most efficient tools for assessing the risk of abdominal injuries in a crash event. In this study, specimen-specific FE models were employed to quantify material and failure properties of human Liver Parenchyma using a FE optimization approach. Uniaxial tensile tests were performed on 34 Parenchyma coupon specimens prepared from two fresh human Livers. Each specimen was tested to failure at one of four loading rates (0.01s(-1), 0.1s(-1), 1s(-1), and 10s(-1)) to investigate the effects of rate dependency on the biomechanical and failure response of Liver Parenchyma. Each test was simulated by prescribing the end displacements of specimen-specific FE models based on the corresponding test data. The parameters of a first-order Ogden material model were identified for each specimen by a FE optimization approach while simulating the pre-tear loading region. The mean material model parameters were then determined for each loading rate from the characteristic averages of the stress-strain curves, and a stochastic optimization approach was utilized to determine the standard deviations of the material model parameters. A hyperelastic material model using a tabulated formulation for rate effects showed good predictions in terms of tensile material properties of human Liver Parenchyma. Furthermore, the tissue tearing was numerically simulated using a cohesive zone modeling (CZM) approach. A layer of cohesive elements was added at the failure location, and the CZM parameters were identified by fitting the post-tear force-time history recorded in each test. The results show that the proposed approach is able to capture both the biomechanical and failure response, and accurately model the overall force-deflection response of Liver Parenchyma over a large range of tensile loadings rates. Language: en

  • Effect of Strain Rate on the Material Properties of Human Liver Parenchyma in Unconfined Compression
    Journal of biomechanical engineering, 2013
    Co-Authors: Andrew R. Kemper, Anthony C. Santago, Joel D. Stitzel, Jessica L. Sparks, Stefan M. Duma
    Abstract:

    The Liver is one of the most frequently injured organs in abdominal trauma. Although motor vehicle collisions are the most common cause of Liver injuries, current anthropomorphic test devices are not equipped to predict the risk of sustaining abdominal organ injuries. Consequently, researchers rely on finite element models to assess the potential risk of injury to abdominal organs such as the Liver. These models must be validated based on appropriate biomechanical data in order to accurately assess injury risk. This study presents a total of 36 uniaxial unconfined compression tests performed on fresh human Liver Parenchyma within 48 h of death. Each specimen was tested once to failure at one of four loading rates (0.012, 0.106, 1.036, and 10.708 s-1) in order to investigate the effects of loading rate on the compressive failure properties of human Liver Parenchyma. The results of this study showed that the response of human Liver Parenchyma is both nonlinear and rate dependent. Specifically, failure stress significantly increased with increased loading rate, while failure strain significantly decreased with increased loading rate. The failure stress and failure strain for all Liver Parenchyma specimens ranged from -38.9 kPa to -145.9 kPa and from -0.48 strain to -1.15 strain, respectively. Overall, this study provides novel biomechanical data that can be used in the development of rate dependent material models and the identification of tissue-level tolerance values, which are critical to the validation of finite element models used to assess injury risk.

  • Modeling the Biomechanical and Injury Response of Human Liver Parenchyma under Tensile Loading
    2013
    Co-Authors: Costin D. Untaroiu, Andrew R. Kemper
    Abstract:

    The Liver is the most frequently injured abdominal organ in frontal vehicle collisions. To better predict the Liver biomechanical response and injury risk during numerical simulations of traffic accidents, accurate material models of the Liver should be incorporated in human finite element (FE) models. This study presents a total of 18 tension tests performed on fresh human samples of Liver Parenchyma at four loading rates. All these tests were simulated using specimen‐specific FE models. Three different approaches were employed to identify the parameters of a first‐order Ogden material model of Liver Parenchyma. The FE simulations with model parameters identified using an analytical approach or based on the displacement of optical markers showed a stiffer response and lower failure stress/strain than the FE‐based models. These variations are probably caused by mechanical inhomogeneity of the tissue and possible violations of other assumptions employed in data analysis (e.g. constant cross‐section assumption). The FE‐based optimized models matched the test data well. The material models presented in this study could be easily implemented in human FE models and used to better understand the Liver injury mechanism during vehicle collisions.

Vassilios Raptopoulos - One of the best experts on this subject based on the ideXlab platform.

  • standardisation of Liver mdct by tracking Liver Parenchyma enhancement to trigger imaging
    European Radiology, 2012
    Co-Authors: Harald Brodoefel, A Tognolini, Giulia Zamboni, S Gourtsoyianni, Cd Claussen, Vassilios Raptopoulos
    Abstract:

    To assess Parenchymal bolus-triggering in terms of Liver enhancement, lesion-to-Liver conspicuity and inter-image variability across serial follow-up MDCTs. We reviewed MDCTs of 50 patients with hepatic metastases who had a baseline CT and two follow-up examinations. In 25 consecutive patients CT data acquisition was initiated by Liver Parenchyma triggering at a 50-HU enhancement threshold. In a matched control group, imaging was performed with an empirical delay of 65 s. CT attenuation values were assessed in vessels, Liver Parenchyma and metastasis. Target lesions were classified according to five enhancement patterns. Compared with the control group, Liver enhancement was significantly higher with Parenchyma triggering (59.8 ± 7.6 HU vs. 48.8 ± 11.2 HU, P = 0.0002). The same was true for conspicuity (Liver Parenchyma – lesion attenuation) of hypo-enhancing lesions (72.2 ± 15.9 HU vs. 52.7 ± 19.4 HU, P = 0.0006). Liver triggering was associated with reduced variability for Liver enhancement among different patients (P = 0.035) and across serial follow-up examinations in individual patients (P < 0.0001). The number of patients presenting with uniform lesion enhancement pattern across serial examinations was significantly higher in the triggered group (20 vs. 11; P = 0.018). Liver Parenchyma triggering provides superior lesion conspicuity and improves standardisation of image quality across follow-up examinations with greater uniformity of enhancement patterns. • Liver Parenchyma tracking improves Liver enhancement and lesion-to-Liver conspicuity in abdominal CT • In serial CT studies this technique reduces variability of conspicuity and enhancement patterns • Higher Liver-to-lesion conspicuity is a prerequisite for reliable detection of Liver lesions • Stabilisation of enhancement permits more accurate follow-up of oncology patients

  • Standardisation of Liver MDCT by tracking Liver Parenchyma enhancement to trigger imaging
    European radiology, 2011
    Co-Authors: Harald Brodoefel, A Tognolini, Giulia Zamboni, S Gourtsoyianni, Cd Claussen, Vassilios Raptopoulos
    Abstract:

    To assess Parenchymal bolus-triggering in terms of Liver enhancement, lesion-to-Liver conspicuity and inter-image variability across serial follow-up MDCTs. We reviewed MDCTs of 50 patients with hepatic metastases who had a baseline CT and two follow-up examinations. In 25 consecutive patients CT data acquisition was initiated by Liver Parenchyma triggering at a 50-HU enhancement threshold. In a matched control group, imaging was performed with an empirical delay of 65 s. CT attenuation values were assessed in vessels, Liver Parenchyma and metastasis. Target lesions were classified according to five enhancement patterns. Compared with the control group, Liver enhancement was significantly higher with Parenchyma triggering (59.8 ± 7.6 HU vs. 48.8 ± 11.2 HU, P = 0.0002). The same was true for conspicuity (Liver Parenchyma – lesion attenuation) of hypo-enhancing lesions (72.2 ± 15.9 HU vs. 52.7 ± 19.4 HU, P = 0.0006). Liver triggering was associated with reduced variability for Liver enhancement among different patients (P = 0.035) and across serial follow-up examinations in individual patients (P 

A Tognolini - One of the best experts on this subject based on the ideXlab platform.

  • standardisation of Liver mdct by tracking Liver Parenchyma enhancement to trigger imaging
    European Radiology, 2012
    Co-Authors: Harald Brodoefel, A Tognolini, Giulia Zamboni, S Gourtsoyianni, Cd Claussen, Vassilios Raptopoulos
    Abstract:

    To assess Parenchymal bolus-triggering in terms of Liver enhancement, lesion-to-Liver conspicuity and inter-image variability across serial follow-up MDCTs. We reviewed MDCTs of 50 patients with hepatic metastases who had a baseline CT and two follow-up examinations. In 25 consecutive patients CT data acquisition was initiated by Liver Parenchyma triggering at a 50-HU enhancement threshold. In a matched control group, imaging was performed with an empirical delay of 65 s. CT attenuation values were assessed in vessels, Liver Parenchyma and metastasis. Target lesions were classified according to five enhancement patterns. Compared with the control group, Liver enhancement was significantly higher with Parenchyma triggering (59.8 ± 7.6 HU vs. 48.8 ± 11.2 HU, P = 0.0002). The same was true for conspicuity (Liver Parenchyma – lesion attenuation) of hypo-enhancing lesions (72.2 ± 15.9 HU vs. 52.7 ± 19.4 HU, P = 0.0006). Liver triggering was associated with reduced variability for Liver enhancement among different patients (P = 0.035) and across serial follow-up examinations in individual patients (P < 0.0001). The number of patients presenting with uniform lesion enhancement pattern across serial examinations was significantly higher in the triggered group (20 vs. 11; P = 0.018). Liver Parenchyma triggering provides superior lesion conspicuity and improves standardisation of image quality across follow-up examinations with greater uniformity of enhancement patterns. • Liver Parenchyma tracking improves Liver enhancement and lesion-to-Liver conspicuity in abdominal CT • In serial CT studies this technique reduces variability of conspicuity and enhancement patterns • Higher Liver-to-lesion conspicuity is a prerequisite for reliable detection of Liver lesions • Stabilisation of enhancement permits more accurate follow-up of oncology patients

  • Standardisation of Liver MDCT by tracking Liver Parenchyma enhancement to trigger imaging
    European radiology, 2011
    Co-Authors: Harald Brodoefel, A Tognolini, Giulia Zamboni, S Gourtsoyianni, Cd Claussen, Vassilios Raptopoulos
    Abstract:

    To assess Parenchymal bolus-triggering in terms of Liver enhancement, lesion-to-Liver conspicuity and inter-image variability across serial follow-up MDCTs. We reviewed MDCTs of 50 patients with hepatic metastases who had a baseline CT and two follow-up examinations. In 25 consecutive patients CT data acquisition was initiated by Liver Parenchyma triggering at a 50-HU enhancement threshold. In a matched control group, imaging was performed with an empirical delay of 65 s. CT attenuation values were assessed in vessels, Liver Parenchyma and metastasis. Target lesions were classified according to five enhancement patterns. Compared with the control group, Liver enhancement was significantly higher with Parenchyma triggering (59.8 ± 7.6 HU vs. 48.8 ± 11.2 HU, P = 0.0002). The same was true for conspicuity (Liver Parenchyma – lesion attenuation) of hypo-enhancing lesions (72.2 ± 15.9 HU vs. 52.7 ± 19.4 HU, P = 0.0006). Liver triggering was associated with reduced variability for Liver enhancement among different patients (P = 0.035) and across serial follow-up examinations in individual patients (P 

Harald Brodoefel - One of the best experts on this subject based on the ideXlab platform.

  • standardisation of Liver mdct by tracking Liver Parenchyma enhancement to trigger imaging
    European Radiology, 2012
    Co-Authors: Harald Brodoefel, A Tognolini, Giulia Zamboni, S Gourtsoyianni, Cd Claussen, Vassilios Raptopoulos
    Abstract:

    To assess Parenchymal bolus-triggering in terms of Liver enhancement, lesion-to-Liver conspicuity and inter-image variability across serial follow-up MDCTs. We reviewed MDCTs of 50 patients with hepatic metastases who had a baseline CT and two follow-up examinations. In 25 consecutive patients CT data acquisition was initiated by Liver Parenchyma triggering at a 50-HU enhancement threshold. In a matched control group, imaging was performed with an empirical delay of 65 s. CT attenuation values were assessed in vessels, Liver Parenchyma and metastasis. Target lesions were classified according to five enhancement patterns. Compared with the control group, Liver enhancement was significantly higher with Parenchyma triggering (59.8 ± 7.6 HU vs. 48.8 ± 11.2 HU, P = 0.0002). The same was true for conspicuity (Liver Parenchyma – lesion attenuation) of hypo-enhancing lesions (72.2 ± 15.9 HU vs. 52.7 ± 19.4 HU, P = 0.0006). Liver triggering was associated with reduced variability for Liver enhancement among different patients (P = 0.035) and across serial follow-up examinations in individual patients (P < 0.0001). The number of patients presenting with uniform lesion enhancement pattern across serial examinations was significantly higher in the triggered group (20 vs. 11; P = 0.018). Liver Parenchyma triggering provides superior lesion conspicuity and improves standardisation of image quality across follow-up examinations with greater uniformity of enhancement patterns. • Liver Parenchyma tracking improves Liver enhancement and lesion-to-Liver conspicuity in abdominal CT • In serial CT studies this technique reduces variability of conspicuity and enhancement patterns • Higher Liver-to-lesion conspicuity is a prerequisite for reliable detection of Liver lesions • Stabilisation of enhancement permits more accurate follow-up of oncology patients

  • Standardisation of Liver MDCT by tracking Liver Parenchyma enhancement to trigger imaging
    European radiology, 2011
    Co-Authors: Harald Brodoefel, A Tognolini, Giulia Zamboni, S Gourtsoyianni, Cd Claussen, Vassilios Raptopoulos
    Abstract:

    To assess Parenchymal bolus-triggering in terms of Liver enhancement, lesion-to-Liver conspicuity and inter-image variability across serial follow-up MDCTs. We reviewed MDCTs of 50 patients with hepatic metastases who had a baseline CT and two follow-up examinations. In 25 consecutive patients CT data acquisition was initiated by Liver Parenchyma triggering at a 50-HU enhancement threshold. In a matched control group, imaging was performed with an empirical delay of 65 s. CT attenuation values were assessed in vessels, Liver Parenchyma and metastasis. Target lesions were classified according to five enhancement patterns. Compared with the control group, Liver enhancement was significantly higher with Parenchyma triggering (59.8 ± 7.6 HU vs. 48.8 ± 11.2 HU, P = 0.0002). The same was true for conspicuity (Liver Parenchyma – lesion attenuation) of hypo-enhancing lesions (72.2 ± 15.9 HU vs. 52.7 ± 19.4 HU, P = 0.0006). Liver triggering was associated with reduced variability for Liver enhancement among different patients (P = 0.035) and across serial follow-up examinations in individual patients (P 

Giulia Zamboni - One of the best experts on this subject based on the ideXlab platform.

  • standardisation of Liver mdct by tracking Liver Parenchyma enhancement to trigger imaging
    European Radiology, 2012
    Co-Authors: Harald Brodoefel, A Tognolini, Giulia Zamboni, S Gourtsoyianni, Cd Claussen, Vassilios Raptopoulos
    Abstract:

    To assess Parenchymal bolus-triggering in terms of Liver enhancement, lesion-to-Liver conspicuity and inter-image variability across serial follow-up MDCTs. We reviewed MDCTs of 50 patients with hepatic metastases who had a baseline CT and two follow-up examinations. In 25 consecutive patients CT data acquisition was initiated by Liver Parenchyma triggering at a 50-HU enhancement threshold. In a matched control group, imaging was performed with an empirical delay of 65 s. CT attenuation values were assessed in vessels, Liver Parenchyma and metastasis. Target lesions were classified according to five enhancement patterns. Compared with the control group, Liver enhancement was significantly higher with Parenchyma triggering (59.8 ± 7.6 HU vs. 48.8 ± 11.2 HU, P = 0.0002). The same was true for conspicuity (Liver Parenchyma – lesion attenuation) of hypo-enhancing lesions (72.2 ± 15.9 HU vs. 52.7 ± 19.4 HU, P = 0.0006). Liver triggering was associated with reduced variability for Liver enhancement among different patients (P = 0.035) and across serial follow-up examinations in individual patients (P < 0.0001). The number of patients presenting with uniform lesion enhancement pattern across serial examinations was significantly higher in the triggered group (20 vs. 11; P = 0.018). Liver Parenchyma triggering provides superior lesion conspicuity and improves standardisation of image quality across follow-up examinations with greater uniformity of enhancement patterns. • Liver Parenchyma tracking improves Liver enhancement and lesion-to-Liver conspicuity in abdominal CT • In serial CT studies this technique reduces variability of conspicuity and enhancement patterns • Higher Liver-to-lesion conspicuity is a prerequisite for reliable detection of Liver lesions • Stabilisation of enhancement permits more accurate follow-up of oncology patients

  • Standardisation of Liver MDCT by tracking Liver Parenchyma enhancement to trigger imaging
    European radiology, 2011
    Co-Authors: Harald Brodoefel, A Tognolini, Giulia Zamboni, S Gourtsoyianni, Cd Claussen, Vassilios Raptopoulos
    Abstract:

    To assess Parenchymal bolus-triggering in terms of Liver enhancement, lesion-to-Liver conspicuity and inter-image variability across serial follow-up MDCTs. We reviewed MDCTs of 50 patients with hepatic metastases who had a baseline CT and two follow-up examinations. In 25 consecutive patients CT data acquisition was initiated by Liver Parenchyma triggering at a 50-HU enhancement threshold. In a matched control group, imaging was performed with an empirical delay of 65 s. CT attenuation values were assessed in vessels, Liver Parenchyma and metastasis. Target lesions were classified according to five enhancement patterns. Compared with the control group, Liver enhancement was significantly higher with Parenchyma triggering (59.8 ± 7.6 HU vs. 48.8 ± 11.2 HU, P = 0.0002). The same was true for conspicuity (Liver Parenchyma – lesion attenuation) of hypo-enhancing lesions (72.2 ± 15.9 HU vs. 52.7 ± 19.4 HU, P = 0.0006). Liver triggering was associated with reduced variability for Liver enhancement among different patients (P = 0.035) and across serial follow-up examinations in individual patients (P