Stiffness Maps Research Articles

Assessment of liver fibrosis with liver and spleen magnetic resonance elastography, serum markers in chronic liver disease

The accurate assessment of liver fibrosis is essential for patients with chronic liver disease. A liver biopsy is an invasive procedure that has many potential defects and complications. Therefore, noninvasive assessment techniques are of considerable value for clinical diagnosis. Liver and spleen magnetic resonance elastography (MRE) and serum markers have been proposed for quantitative and noninvasive assessment of liver fibrosis. This study aims to compare the diagnostic performance of liver and spleen stiffness measured by MRE, fibrosis index based on the 4 factors (FIB-4), aspartate aminotransferase-to-platelet ratio index (APRI), and their combined models for staging hepatic fibrosis. One hundred and twenty patients with chronic liver disease underwent MRE scans. Liver and spleen stiffness were measured by the MRE stiffness maps. Serum markers were collected to calculate FIB-4 and APRI. Liver biopsies were used to identify pathologic grading. Spearman's rank correlation analysis evaluated the correlation between the parameters and fibrosis stages. Receiver operating characteristic (ROC) analysis evaluated the performance of the four individual parameters, a liver and spleen stiffness combined model, and an all-parameters combined model in assessing liver fibrosis. Liver stiffness, spleen stiffness, FIB-4, and APRI were all correlated with fibrosis stage (r=0.87, 0.64, 0.65, and 0.51, respectively, all P<0.001). Among the 4 individual diagnostic markers, liver stiffness showed the highest values in staging F1-4, F2-4, F3-4 and F4 (AUC =0.89, 0. 97, 0.95, and 0.95, all P<0.001). The AUCs of the liver and spleen stiffness combined model in the F1-4, F2-4, F3-4, and F4 staging groups were 0.89, 0.97, 0.95, and 0.96, respectively (all P<0.001). The corresponding AUCs of the all-parameters combined model were 0.90, 0.97, 0.95, and 0.96 (all P<0.001). The AUCs of the liver and spleen stiffness combined model were significantly higher than those of APRI, FIB-4 in the F2-4, F3-4, and F4 staging groups (all P<0.05). Both combined models were not significantly different from liver stiffness in staging liver fibrosis (all P>0.05). Liver stiffness measured with MRE had better diagnostic performance than spleen stiffness, APRI, and FIB-4 for fibrosis staging. The combined models did not significantly improve the diagnostic value compared with liver stiffness in staging fibrosis.

Direct measure of crystalline domain size, distribution, and orientation in polyethylene fibers

High performance ultra high molecular weight polyethylene (UHMWPE) fibers are primarily composed of extended chain (shish) and lamellae (kebab) crystalline domains. Characterization of these architectures commonly utilizes x-ray scattering techniques, which rely upon models to transform from inverse scattering space to real space. Scattering models for lamellae and straight chain crystalline domains were developed and intended for use in ideal scattering scenarios; ie. purely extended chain or purely lamellae. Simultaneous implementation of both models with real (non-ideal) fibers takes for granted the validity of either model in the presence of the other crystalline feature. In this work, we utilize atomic force microscopy (AFM) to directly couple real space stiffness measurements to the analysis of scattering data. The validity of scattering models is tested against real space image analysis and conclusions are drawn regarding the analysis of scattering data to quantify crystalline domain sizes. We find that the lamellae long spacing estimated from scattering data is consistent with real space image analysis. Whereas significant differences are observed for the analysis of lamellae diameter. The characteristic size of extended chain crystalline domains is measured via the streak analysis method on both SAXS 2D scattering data and the Fast Fourier Transform (FFT) of AFM stiffness maps. The streak analysis results in comparable length scales when applied to SAXS and FFT AFM images. A comparison of the streak analysis with novel filtered AFM images suggest that the streak analysis is capturing continuity of straight chain crystalline domains.

Immune checkpoint blockade (ICB) response evaluation with MRI/MR elastography (MRE) in surgical and nonsurgical patients with HCC.

480 Background: Currently, there is a lack of imaging biomarkers of immunotherapy outcome in hepatocellular carcinoma (HCC). The study aim was to determine if HCC enhancement on MRI and stiffness change measured by magnetic resonance elastography (MRE) can predict immunotherapy response. Methods: This was a prospective, Institutional Review Board approved study of 38 patients with HCC treated with immune checkpoint blockade (ICB) therapy. All patients had liver MRI/MRE and HCC biopsy at baseline, and MRI/MRE with biopsy or resection after 6 weeks therapy. HCC stiffness (kPa) was measured on MRE elastograms (liver stiffness maps). HCC enhancement and change in stiffness were compared with treatment response to ICB in 1) non-surgical patients (pembrolizumab), and 2) surgical patients (nivolumab +/- ipilimumab). For non-surgical patients, treatment response was defined as overall survival &gt;1 year. For surgical patients, treatment response was defined as &lt;50% viable tumor at time of resection. Analysis was performed using descriptive statistics and Spearman correlation; p-value &lt;0.05 was considered statistically significant. Results: Twenty-five patients were evaluable. Median age was 67 years (32, 78). Etiology of liver disease was NASH (n=8), HCV (n=8), HBV (n=2) and unknown (n=7). Treatment response occurred in 11/25 (44%) patients. Median HCC size and change in size were 4.7 cm (1.2, 14.0) and –0.32 cm, respectively. Median baseline HCC stiffness and change in stiffness were 5 kPa (2.2, 12.4) and –0.1 kPa (–2.2, 1.5), respectively. Median change in HCC size for responders and non-responders was –1.2 cm (–4.8, 0.4) and 0 cm (–1.5, 1.1), respectively (p = 0.02). Treatment response was associated with absence of portal venous phase capsular enhancement and increase in HCC stiffness, (p&lt;0.001). Conclusions: Capsular enhancement and MRE stiffness change may be useful biomarkers of immune cell activated response to ICB therapy.

Characterizing Hydrogen Microbubble Stiffness Properties Using Atomic Force Microscopy

In the past decades, bubbles have been gaining extensive attentions for their wide range of applications, especially those at the micro-scale. Research on the bubbles’ mechanical properties is necessary for better implementations. Precise measurement of the microbubbles’ mechanical properties (e.g. stiffness and adhesion) relies largely on delicate manipulation technologies in aqueous environment. As a consequence, atomic force microscopy (AFM) has been widely adopted in this field. Bubble stiffness is an important indicator to reflect the stability. Existing studies mainly focused on statistic property of the microbubbles’ stiffness, which may omit delicate specific characteristics of a single microbubble. In this letter, as an instance, AFM-based stiffness measurement of a single hydrogen microbubble has been carried out. The electrochemistry method was adopted to generate stable hydrogen microbubbles. By using force volume mode of a commercial AFM, the temperature-dependent stiffness property of the microbubble was studied. Furthermore, stiffness map of a single microbubble was captured, which shows location-dependent anisotropic characteristic, contradicting the preassumption that stiffness of bubbles should be isotropic. To explain this phenomenon, the contact condition between the AFM tip and the bubble surface is considered as the key reason that induces the anisotropic observation, and a corresponding model is established to verify this hypothesis.

High-Resolution Ex Vivo Elastography to Characterize Tumor Stromal Heterogeneity In Situ in Pancreatic Adenocarcinoma.

Tumor stiffening in pancreatic adenocarcinoma (PDAC) has been linked to cancer progression and lack of therapy response, yet current elastography tools cannot map stiffness in a whole tumor field-of-view with biologically relevant spatial resolution. Therefore, this study was developed to assess stiffness heterogeneity and geometrical patterns across whole PDAC xenograft ex vivo tumors. The ex vivo elastography (EVE) mapping system was capable of creating stiffness map at 300-micron spatial resolution under a 5-20 mm field of view relevant to whole tumor assessment. The stiffness value at each location was determined by compression testing and an absolute tumor Young's modulus map was calculated based on the calibration between the system and ultrasound elastography (R2 = 0.95). Two PDAC tumor lines AsPC-1 and BxPC-3 implanted in xenograft models were assessed to show tumor stiffness and its linear relationship to collagen content (R2 = 0.59). EVE was able to capture stiffness heterogeneity ranging between 5 and 100kPa in pancreatic tumors with collagen content up to 25%. More importantly, data shows the inverse relationship of local stiffness to local drug distribution (R2 = 0.66) and vessel patency (R2 = 0.61) in both PDAC tumor lines. The results suggested that elastography could be utilized to predict drug penetration in PDAC tumors or assess response to biological modifying adjunct therapies. This study presents the first attempt to map out stiffness on a biologically relevant spatial scale across whole PDAC tumor slices with spatial resolution in the hundreds of microns.

The MUSHA Hand II: A Multi-Functional Hand for Robot-Assisted Laparoscopic Surgery

Although substantial progresses have been made in robot-assisted laparoscopic surgery, the graspers for existing surgical systems generally remain nonsensorized forceps design with limited functions. This article presents the design, development, and preliminary evaluation of the MUSHA Hand II, a multifunctional hand with force sensors for robot-assisted laparoscopic surgery. The proposed hand has three snake-like underactuated fingers that can be folded into a $\phi$ 12 mm cylindrical form. Each finger has a three-axis force sensor, to provide force information. After been deployed into an abdominal cavity, the hand can be configured to either grasper mode, retractor mode, or palpation mode for different tasks. Underactuated finger design enhances the adaptivity in grasping and the compliance in interaction with the environment. In addition, fingertip force sensors can be utilized for palpation to obtain a real-time stiffness map of organs. Using the da Vinci Research Kit as a robotic testbed, the functionality of the hand has been demonstrated and experiments have been conducted, including robotic palpation and organ manipulation. The results suggest that the hand can effectively enhance the functionality of a robotic surgical system and overcome the limits on force sensing introduced by the use of robots in laparoscopic surgery.

Comparison between ROI-based and volumetric measurements in quantifying heterogeneity of liver stiffness using MR elastography.

This study was conducted to quantify the heterogeneity of liver stiffness (LS) on MR elastography (MRE) by comparing ROI-based and volumetric measurements. LS was measured by ROI-based and volumetric segmentation of the liver parenchyma. Mean LS (MLS) was calculated and used to assign stages of fibrosis. Volumetric measurements of stiffness maps were used to determine the percentage of liver volume above/below MLS and presence of LS heterogeneity. Heterogeneous stiffness was defined when the first and second most predominant stages were more than one category apart. MLS values by each method were compared using the Wilcoxon signed-rank test. We included 128 patients with suspected liver fibrosis (mean age 54.4 ± 14.8 years). MLS was 2.7 ± 1.0 kPa for ROI measurements and 2.6 ± 0.9 kPa for the volumetric method (p = 0.001). Of 59 patients with normal stage (F0), 31 patients (52.5%) had > 20% of liver volume with abnormal LS (F1-F4). Heterogeneous LS was reported in 18 patients (14%). MLS measurement may not represent the entire spectrum of hepatic fibrosis. Volumetric segmentation may potentially improve the detection of heterogeneous fibrosis and the accuracy of LS measurement. • Heterogeneity of hepatic fibrosis may occur in patients with chronic liver disease. • MR elastography is used to assess hepatic fibrosis by measuring liver stiffness. • Measuring liver stiffness by the ROI method and reporting a mean value may fail to detect heterogeneity of hepatic fibrosis. Volumetric assessment of liver stiffness by MR elastography may detect heterogeneity of parenchymal involvement.

Ultrasound elastography: A novel user-independent quasi-static method

Quasi-static ultrasound elastography is a popular clinical ultrasound modality which can give measures of the relative stiffness of a region of interest [1]. Tumours have been well documented to have different mechanical properties than the surrounding healthy tissue [2]. Ultrasound elastography techniques take advantage of this contrast to create stiffness maps of soft tissue called elastograms, with these, the tumours can be easily distinguished from the healthy tissue [1]. Current quasi-static methods require the user to manually palpate the region of interest with the ultrasound probe, which can lead to user-user variability when imaging [3]. We propose a novel, user-independent method where external palpation is provided by means of a stepper motor via the perineum. A tissue-mimicking agar phantom of the prostate was created and imaged using a transrectal probe. An elastography algorithm was then developed using MATLAB and inclusions of varying stiffness and sizes were successfully delineated from the surrounding soft tissue.

Atherosclerotic plaque mechanical characterization coupled with vector Doppler imaging in atherosclerotic carotid arteries in-vivo.

Methods used in clinical practice to diagnose and monitor atherosclerosis present limitations. Imaging the mechanical properties of the arterial wall has demonstrated the potential evaluate plaque vulnerability and assess the risk for stroke. Adaptive Pulse Wave Imaging (PWI) is a non-invasive ultrasound imaging technique, which automatically detects points of spatial mechanical inhomogeneity along the imaged artery and provides piecewise stiffness characterization. The aims of the present study are to: 1) demonstrate the initial feasibility of adaptive PWI to image the mechanical properties of an atherosclerotic plaque 2) demonstrate the feasibility to combine adaptive PWI with vector Doppler in a single imaging modality in order to simultaneously obtain information plaque mechanical properties and plaque hemodynamics. The common carotid arteries of 1 healthy subject and 2 carotid artery disease patients were scanned in vivo. One of the patients underwent carotid endarterectomy and a plaque sample was retrieved. In this patient, a higher compliance value of the stenotic segment was estimated by Adaptive PWI as compared with the adjacent arterial wall, and the healthy carotid artery. This was corroborated by histological staining of the plaque sample, which revealed the presence of a large necrotic core and a thrombus, characteristics associated with reduced stiffness. Moreover, the same sequence demonstrated the feasibility to obtain both stiffness maps and vector flow information, showing promise in atherosclerosis diagnosis and patient care.

Posture-related stiffness mapping of paraspinal muscles.

The paraspinal compartment acts as a bone-muscle composite beam of the spine. The elastic properties of the paraspinal muscles play a critical role in spine stabilization. These properties depend on the subjects' posture, and they may be drastically altered by low back pain. Supersonic shear wave elastography can be used to provide quantitative stiffness maps (elastograms), which characterize the elastic properties of the probed tissue. The aim of this study was to challenge shear wave elastography sensitivity to postural stiffness changes in healthy paraspinal muscles. The stiffness of the main paraspinal muscles (longissimus, iliocostalis, multifidus) was measured by shear wave elastography at the lumbosacral level (L3 and S1) for six static postures performed by volunteers. Passive postures (rest, passive flexion, passive extension) were performed in a first shear wave elastography session, and active postures (upright, bending forward, bending backward) with rest posture for reference were performed in a second session. Measurements were repeated three times for each posture. Sixteen healthy young adults were enrolled in the study. Non-parametric paired tests, multiple analyses of covariance, and intra-class correlations were implemented for analysis. Shear wave elastography showed good to excellent reliability, except in the multifidus at S1, during bending forward, and in the multifidus at L3, during bending backward. Yet, during bending forward, only poor quality was recorded for nine volunteers in the longissimus. Significant intra- and inter-muscular changes were observed with posture. Stiffness significantly increased for the upright position and bending forward with respect to the reference values recorded in passive postures. In conclusion, shear wave elastography allows reliable assessment of the stiffness of the paraspinal muscles except in the multifidus at S1 and longissimus, during bending forward, and in the multifidus at L3, during bending backward. It reveals a different biomechanical behaviour for the multifidus, the longissimus, and the iliocostalis.

Magnetic Resonance Elastography in Primary Sclerosing Cholangitis: Interobserver Agreement for Liver Stiffness Measurement with Manual and Automated Methods

Primary sclerosing cholangitis, a chronic liver disease causes heterogeneous parenchymal changes and fibrosis. Liver stiffness measurement (LSM) with magnetic resonance Elastography (MRE) may be affected by this heterogeneous distribution. We evaluated interobserver agreement of LSM in primary sclerosing cholangitis (PSC) with manual and automated methods to study the influence of heterogeneous changes. A total of 79 consecutive patients with PSC who had a liver MRI and MRE formed the study group. Three readers with 1-3 years' experience in MRE and a MRE expert (11 years' experience) independently performed LSM. Each reader manually drew free hand (fROI) and average (aROI) on stiffness maps. Automatic liver elasticity calculation (ALEC) was used to generate automated LSM. The expert fROI was the reference standard. Correlation analysis and absolute intra-class correlation coefficient (ICC) analysis was performed. LSM data of 79 livers and 315 sections were evaluated. There was excellent ICC between expert and reader fROIs (0.989, 95% confidence interval, and 0.985-0.993) and aROIs (0.971, 95% confidence interval, and 0.953-0.983) and ALEC (0.972, 0.957-0.982) with fROI performing better. The areas measured with fROIs and ALEC had moderate ICC with Expert fROI (0.64 and 0.56, respectively) whereas aROI area had a poor ICC of 0.12. Comparison of multiple methods showed significant differences in LSM between expert fROI and aROI of two readers and no significant differences for fROIs of all three readers. LSM with MRE in PSC patients shows excellent interobserver agreement with both fROI and aROI methods with better performance with fROI. fROI may therefore be preferred for LSM measurements in PSC.

Normative values for magnetic resonance elastography-based liver stiffness in a healthy population.

INTRODUCTIONChronic liver disease resulting in fibrosis, and ultimately cirrhosis, is a significant cause of morbidity and mortality worldwide. None of the conventional imaging techniques are able to detect early fibrosis and compare its grade with the histopathologic scale. Liver biopsy, as the diagnostic standard for liver fibrosis, also has limitations and is not well accepted by patients. Magnetic resonance elastography is a well-established technique for evaluating liver stiffness and may replace invasive procedures. Detection of liver fibrosis in its early stages, however, requires a detailed knowledge of normal liver stiffness.OBJECTIVESThis study aimed to determine normal liver stiffness values in healthy volunteers.PATIENTS AND METHODSA total of 102 volunteers (mean age, 21.6 years; range, 20–28 years) with no history of gastrointestinal, hepatobiliary, or cardiovascular disease were enrolled in the study. Liver stiffness was evaluated by magnetic resonance elastography with a 1.5T clinical magnetic resonance scanner. Images of the induced transverse wave propagation were obtained and converted to tissue stiffness maps (elastograms).RESULTSThe mean (SD) liver stiffness for the entire group of volunteers was 2.14 (0.28) kPa (range, 1.37–2.66 kPa). For women, the mean (SD) stiffness value was 2.14 (0.30) kPa (range, 1.37–2.66 kPa), and for men, 2.14 (0.25) kPa (range, 1.54–2.54 kPa).CONCLUSIONSLiver stiffness in a healthy adult cohort did not exceed 2.7 kPa and is not influenced by sex, body mass index, or fat content.

Immunotherapy response evaluation with MR elastography (MRE) in advanced HCC.

230 Background: To determine changes in MRE HCC stiffness as predictor of immunotherapy response in patients with advanced HCC. Methods: This was a prospective, Institutional Review Board approved study of 15 patients with biopsy proven advanced HCC (not amenable to curative therapy), who were to be treated with Pembrolizumab. Eligible patients were &gt; 18 years old with radiographic disease progression/intolerance to sorafenib. All patients had liver MRI with MR Elastography (MRE) and liver biopsy at baseline and at 9 weeks of therapy. HCC stiffness (kilopascals, kPa) was measured on liver MRE elastograms (stiffness maps). Change in HCC stiffness on MRE was compared with overall survival, time to disease progression, and total number of lymphocytes on targeted liver biopsy. Data cutoff date was September 1st 2018. Analysis was performed using descriptive statistics including Spearman correlation ( R), Cox regression, Wilcoxon rank sum test and Fisher’s exact test. Results: Of the initial 15 patients, 4 withdrew from therapy, 1 patient did not undergo MRE scan, and 1 patient had MRE failure. The final 9 patients included 6 men. Median age was 70 years (range, 54-78). Etiology of liver disease was HCV (n = 4) and NASH (n = 5). HCC was moderately differentiated in 8 of 9 patients and well-differentiated in 1 patient. Median overall survival and time to progression were 52 weeks (range, 16-112) and 18 weeks (range, 9-48), respectively. Average non-tumorous liver stiffness was 3.2 kPa (range, 2.1-4.3). No significant change in non-tumor liver stiffness was seen at 9 weeks (p = 0.12). Median baseline tumor stiffness was 4.5 kPa (range, 2.4-7.5). Increase in HCC stiffness at 9 weeks was seen in 5 patients, decrease in 3 patients and no change in 1. Change in HCC stiffness at 9 weeks correlated significantly with overall survival ( R = 0.83), and time to progression ( R = 0.96), (p &lt; 0.05). Nine patients had liver biopsy at baseline and 7 had biopsy at 9 weeks. HCC T lymphocytes on biopsy (n/mm2) significantly correlated with HCC stiffness ( R = 0.79), (p &lt; 0.01). Conclusions: Our pilot data suggests early change in tumor stiffness may help predict better immunotherapy response in patients with advanced HCC.

Destructive and Nondestructive Evaluation of Dry Spots in Thick Glass Fiber Reinforced Composites

This article reports on the destructive and nondestructive evaluation of dry spots or patches in thick unidirectional glass/epoxy laminates. Dry spots in composites can act as weak regions potentially resulting in catastrophic failure if undetected. Composite samples with dry spots were fabricated and nondestructive evaluation was first carried out using non-contact air coupled ultrasonics. Two types of dryness were investigated: surface and mid-plane dryness. Both types were tested using two ultrasonic testing methods. The ultrasonic velocity was used to determine stiffness and dryness fraction maps. The results showed that the dryness could be detected and characterized using the ultrasonic nondestructive evaluation. To validate the results, a destructive analysis was carried out by cutting the sample into small pieces and burning them to obtain the weight of matrix and fibers. This was further used in micromechanics models to obtain void and dryness fractions. Both model and ultrasonic results show that dry spots result in spatial gradient of mechanical properties around the dry spot. Nondestructive characterization of dryness helps in deciding if the part must be scrapped or repaired based on the severity in terms of loss of stiffness.

Fast tomoelastography of the mouse brain by multifrequency single-shot MR elastography.

To introduce in vivo multifrequency single-shot magnetic resonance elastography for full-FOV stiffness mapping of the mouse brain and to compare in vivo stiffness of neural tissues with different white-to-gray matter ratios. Viscous phantoms and 10 C57BL-6 mice were investigated by 7T small-animal MRI using a single-shot spin-echo planar imaging magnetic resonance elastography sequence with motion-encoding gradients positioned before the refocusing pulse. Wave images were acquired over 10 minutes for 6 mechanical vibration frequencies between 900 and 1400 Hz. Stiffness maps of shear wave speed (SWS) were computed using tomoelastography data processing and compared with algebraic Helmholtz inversion (AHI) for signal-to-noise ratio (SNR) analysis. Different brain regions were analyzed including cerebral cortex, corpus callosum, hippocampus, and diencephalon. In phantoms, algebraic Helmholtz inversion-based SWS was systematically biased by noise and discretization, whereas tomoelastography-derived SWS was consistent over the full SNR range analyzed. Mean in vivo SWS of the whole brain was 3.76 ± 0.33 m/s with significant regional variation (hippocampus = 4.91 ± 0.49 m/s, diencephalon = 4.78 ± 0.78 m/s, cerebral cortex = 3.53 ± 0.29 m/s, and corpus callosum = 2.89 ± 0.17 m/s). Tomoelastography retrieves mouse brain stiffness within shorter scan times and with greater detail resolution than classical algebraic Helmholtz inversion-based magnetic resonance elastography. The range of SWS values obtained here indicates that mouse white matter is softer than gray matter at the frequencies investigated.

An inverse problem approach to stiffness mapping for early detection of breast cancer: tissue phantom experiments

ABSTRACTEarly detection of breast cancer will continue to be crucial in improving patient survival rates. Our ultimate goal is to develop an electro-mechanical device to automate and refine the manual breast exam process, and use inverse techniques to generate a tissue stiffness map of the breast tissue. We have previously presented computational simulations of the stiffness mapping approach, which employs static indentations of the tissue and measurements of surface displacements. In this paper, we report on experimental validation of the technique with tissue phantom experiments. We tested 12 tissue phantom samples without simulated tumours and 14 tissue phantom samples with simulated tumours. Our stiffness mapping approach correctly identified all 26 samples.

Preliminary Evaluation of an Online Estimation Method for Organ Geometry and Tissue Stiffness

During open surgeries, surgeons use tactile palpation to form an understanding of the anatomy, including any underlying anatomical structures such as arteries or tumors. This letter explores methods for restoring this capability in the context of minimally invasive robot-assisted surgery. Previous works have demonstrated the ability of robots to use discrete palpation to characterize organ shape and, when followed with offline data processing, to produce a stiffness map of the organ. In our earlier work, we presented an offline estimation technique, independent of palpation strategy, to estimate organ shape and stiffness using Gaussian processes. This study extends our prior work by demonstrating a fast online technique for estimation of organ shape and stiffness. Our goal is to provide near video-frame-rate updates of the organ geometry and tissue stiffness during force controlled exploration. Two different palpation modes are experimentally explored: autonomous palpation and constrained semiautonomous teleoperation. We report the experimental evaluation of our approach for stiffness estimation using autonomous palpation. And we demonstrate the feasibility of using our method during interactive teleoperation in a simulated surgical scenario. We believe that future use of the online stiffness and geometry information based on our proposed method can help surgeons in improving their understanding of the surgical scene and its correlation to preoperative imaging, thereby increasing safety and improving surgical outcomes.

Real-Time Vision-Based Stiffness Mapping †.

This paper presents new findings concerning a hand-held stiffness probe for the medical diagnosis of abnormalities during palpation of soft-tissue. Palpation is recognized by the medical community as an essential and low-cost method to detect and diagnose disease in soft-tissue. However, differences are often subtle and clinicians need to train for many years before they can conduct a reliable diagnosis. The probe presented here fills this gap providing a means to easily obtain stiffness values of soft tissue during a palpation procedure. Our stiffness sensor is equipped with a multi degree of freedom (DoF) Aurora magnetic tracker, allowing us to track and record the 3D position of the probe whilst examining a tissue area, and generate a 3D stiffness map in real-time. The stiffness probe was integrated in a robotic arm and tested in an artificial environment representing a good model of soft tissue organs; the results show that the sensor can accurately measure and map the stiffness of a silicon phantom embedded with areas of varying stiffness.

Magnetic resonance elastography of the lumbar back muscles: A preliminary study.

Back pain is associated with increased lumbar paraspinal muscle (LPM) stiffness identified by manual palpation and strain elastography. Recently, magnetic resonance elastography (MRE) has allowed the stiffness of muscle to be characterized noninvasively in vivo, providing quantitative 3D stiffness maps (elastograms). The aim of this study was to characterize the stiffness (shear modulus, SM) of the LPM (multifidus and erector spinae) using MRE. MRE of the lumbar region was performed on seven adults in supine position. MRE was acquired in three muscular states: relaxed with outstretched legs, stretched with passive pelvis flexion, and contracted with outstretched legs and tightened trunk muscles. The mean SM was measured within a region of interest manually defined in the multifidus, erector spinae, and the entire paraspinal compartment. The intermuscular difference and the effects of stretching and contraction were assessed by ANOVA and t-tests. At rest, the mean SM of the paraspinal compartment was 1.6 ± 0.2 kPa. It increased significantly with stretching to 1.65 ± 0.3 kPa, and with contraction to 2.0 ± 0.7 kPa. Irrespective of muscular state, the erector spinae was significantly stiffer than the multifidus. The multifidus underwent proportionally higher stiffness changes from rest to contraction and stretching. MRE can be used to measure the stiffness of the LPM in different muscular states. We hypothesize that, irrespective of posture, the erector spinae behaves as semi-rigid beam, and ensures permanent stiffness of the spine. The multifidus behaves as an adaptable muscle that provides segmental flexibility to the spine and tunes the spine stiffness. Clin. Anat. 31:514-520, 2018. © 2018 Wiley Periodicals, Inc.

Cardiac MR elastography using reduced-FOV, single-shot, spin-echo EPI.

PurposeTo implement a reduced field of view (rFOV) technique for cardiac MR elastography (MRE) and to demonstrate the improvement in image quality of both magnitude images and post‐processed MRE stiffness maps compared to the conventional full field of view (full‐FOV) acquisition.MethodsWith Institutional Review Board approval, 17 healthy volunteers underwent both full‐FOV and rFOV cardiac MRE scans using 140‐Hz vibrations. Two cardiac radiologists blindly compared the magnitude images and stiffness maps and graded the images based on several image quality attributes using a 5‐point ordinal scale. Fisher's combined probability test was performed to assess the overall evaluation. The octahedral shear strain‐based signal‐to‐noise ratio (OSS‐SNR) and median stiffness over the left ventricular myocardium were also compared.ResultsOne volunteer was excluded because of an inconsistent imaging resolution during the exam. In the remaining 16 volunteers (9 males, 7 females), the rFOV scans outperformed the full‐FOV scans in terms of subjective image quality and ghosting artifacts in the magnitude images and stiffness maps, as well as the overall preference. The quantitative measurements showed that rFOV had significantly higher OSS‐SNR (median: 1.4 [95% confidence interval (CI): 1.2–1.5] vs. 2.1 [95% CI: 1.8–2.4]), P < 0.05) compared to full‐FOV. Although no significant change was found in the median myocardial stiffness between the 2 scans, we observed a decrease in the stiffness variation within the myocardium from 2.1 kPa (95% CI: [1.9, 2.3]) to 1.9 kPa (95% CI: [1.7, 2.0]) for full‐FOV and rFOV, respectively (P < 0.05) in a subgroup of 7 subjects with ghosting present in the myocardium.ConclusionThis pilot volunteer study demonstrated that rFOV cardiac MRE has the capability to reduce ghosting and to improve image quality in both MRE magnitude images and stiffness maps. Magn Reson Med 80:231–238, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.