Shear Wave Speed Values Research Articles

Magnetic resonance shear wave elastography using transient acoustic radiation force excitations and sinusoidal displacement encoding

A magnetic resonance (MR) shear wave elastography technique that uses transient acoustic radiation force impulses from a focused ultrasound (FUS) transducer and a sinusoidal-shaped MR displacement encoding strategy is presented. Using this encoding strategy, an analytic expression for calculating the shear wave speed in a heterogeneous medium was derived. Green’s function-based simulations were used to evaluate the feasibility of calculating shear wave speed maps using the analytic expression. Accuracy of simulation technique was confirmed experimentally in a homogeneous gelatin phantom. The elastography measurement was compared to harmonic MR elastography in a homogeneous phantom experiment and the measured shear wave speed values differed by less than 14%. This new transient elastography approach was able to map the position and shape of inclusions sized from 8.5 to 14 mm in an inclusion phantom experiment. These preliminary results demonstrate the feasibility of using a straightforward analytic expression to generate shear wave speed maps from MR images where sinusoidal-shaped motion encoding gradients are used to encode the displacement-time history of a transiently propagating wave-packet. This new measurement technique may be particularly well suited for performing elastography before, during, and after MR-guided FUS therapies since the same device used for therapy is also used as an excitation source for elastography.

Diabetes Status is Associated With Plantar Soft Tissue Stiffness Measured Using Ultrasound Reverberant Shear Wave Elastography Approach.

The purpose of this study was to investigate the association between the mechanical properties of plantar soft tissue and diabetes status. 51 (M/F: 21/30) participants with prediabetes onset (fasting blood sugar [FBS] level > 100 mg/dL), age >18 years, and no lower limb amputation were recruited after ethical approval was granted from Pontificia Universidad Catolica del Peru ethical review board. Ultrasound reverberant shear wave elastography was used to assess the soft tissue stiffness at the 1st metatarsal head (MTH), 3rd MTH, and the heel at both feet. Spearman's rank-order correlation (rho) test indicated a significant (P < .05) positive correlations between FBS level and the plantar soft tissue shear wave speed at the 1st MTH: rho = 0.402 (@400 Hz), rho = 0.373 (@450 Hz), rho = 0.474 (@500 Hz), rho= 0.395 (@550 Hz), and rho = 0.326 (@600 Hz) in the left foot and rho = 0.364 (@450 Hz) in the right foot. Mann-Whitney U test indicated a significantly (P < .05) higher shear wave speed in the plantar soft tissue with the following effect sizes (r) at the 1st MTH of the left foot at all tested frequencies: r = 0.297 (@450 Hz), r = 0.345 (@500 Hz), r = 0.322 (@550 Hz), and r = 0.275 (@600 Hz), and at the 1st MTH of right foot r = 0.286 (@400 Hz) in diabetes as compared with the age and body mass index matched prediabetes group. An association between fasting blood sugar level and the stiffness of the plantar soft tissue with higher values of shear wave speed in diabetes versus prediabetes group was observed. This indicated that the proposed approach can improve the assessment of the severity of diabetic foot complications with potential implications in patient stratification.

Value of shear wave elastography in the diagnosis and evaluation of cervical cancer

The aim of the present study was to explore the value of shear wave elastography (SWE) in the differential diagnosis of cervical disease and to evaluate the infiltration of cervical cancer. A total of 40 inpatients with cervical cancer, 40 inpatients with cervical benign lesion and 40 healthy volunteers encountered between October 2014 and January 2017 were enrolled. All patients and volunteers underwent conventional ultrasound (US) and SWE examinations. The malignancy and the size (including long, tranverse and anteroposterior diameter) of the lesion were assessed on US. The elastic score, strain ratio, shear wave speed (SWS) and the size of lesions were determined on SWE. Infiltration of the uterus and vaginal vault were also evaluated on US and SWE. The SWS values of cervical cancers, cervical benign lesions and normal cervixes groups were compared. The results suggested that the optimal cut-off elasticity score for predicting cervical cancers was 3 points. The strain ratio between the cervical cancers and the cervical benign lesions exhibited a significant difference (P<0.01). The mean value of SWS for cervical cancers was significantly higher than that of cervical benign lesions and normal cervix (P<0.05). Regarding the lesion size and volume, SWE and pathological measurements were larger than those determined by US (P<0.05 for each). The lesion volume on SWE and pathological measurements exhibited no significant difference (P>0.05). Compared to the pathological diagnosis of focal infiltration of uterus and vaginal vault, the diagnostic accuracy of SWE was higher than that of US. In conclusion, SWE may be used to differentiate between cervical benign lesions and cervical cancers. The elastic score, strain ratio and SWS of cervical cancers were higher than those of cervical benign lesions. Furthermore, SWE is able to evaluate the infiltration of cervical cancer.

Mapping Tissue Properties in Trapezius with Ultrasound Shear Wave Elastography: A Pilot Study

Ultrasound shear wave elastography (SWE) is a relatively new technology in the field of sonography. Even more so, research into musculoskeletal applications of SWE is in its infancy. Despite challenges concerning the anisotropic nature of muscle tissue, the literature suggests that SWE is a promising medium with which to examine patterns of tissue properties in morphometrically complex muscles, like trapezius. Tissue properties can provide valuable insights into muscle function and dysfunction. In our laboratory, we have characterized and quantified the comprehensive architecture of the cadaveric trapezius at the fascicular level throughout the muscle volume. These 3D anatomic data are essential for improving current B‐mode ultrasound protocols and making necessary modifications for SWE compatibility.The primary aim of this study was to test a novel SWE‐adapted ultrasound protocol for trapezius—targeting regions of contractile and connective tissues—and establish baseline patterns of tissue properties throughout the muscle.Twenty healthy adults (10F, 10M) with no history of back or neck injury, surgery, or chronic pain participated in the pilot study. We performed all imaging using the Siemens ACUSON™ S3000 ultrasound system, equipped with Virtual Touch™ IQ for SWE, and a 4–9 MHz linear array transducer (9L4, Siemens Healthcare). B‐mode and SWE images were captured in both seated and prone positions from each functional partition of trapezius: descending, transverse, and ascending. We collected shear wave speed (SWS) values from regions of interest corresponding to contractile and connective tissues on each elastogram and co‐registered them with 3D models of trapezius rendered from cadaveric data. SWS data will also be analysed with respect to participant sex, age, height, weight, and hand dominance.Preliminary results show marked differences in SWS between regions of contractile and connective tissues in trapezius, consistent with the structural patterns observed during cadaveric dissection and modeling. Of particular interest were areas in the transverse and ascending partitions with extensive regions of musculoaponeurotic junction: we observed a gradual increase in SWS of up to 200% between contractile tissue and connective tissue across the musculoaponeurotic junction. Tissue properties in the descending partition of trapezius were challenging to characterize due to substantial changes in fascicle direction, limited muscle thickness, and proximity to underlying bone.To the best of our knowledge, this study is the first to investigate patterns of soft tissue stiffness in the healthy adult trapezius, including both contractile and connective tissues. These data, in combination with the novel SWS‐adapted ultrasound protocol, offer a strong foundation on which to conduct future studies of individuals with musculoskeletal disorder in trapezius.Support or Funding InformationSupported by a Vanier Canada Graduate Scholarship and a Michael Smith Foreign Study Supplement from the Canadian Institutes of Health Research (CIHR).

Liver Shear Wave Speed and Other Quantitative Ultrasound Measures of Liver Parenchyma: Prospective Evaluation in Healthy Children and Adults.

OBJECTIVE. The purpose of this study was to use 2D ultrasound shear wave elastography (SWE) to define expected ranges for liver shear wave speed and shear wave dispersion in children and adults without a known history of liver disease. The study also sought to define liver attenuation in adults. SUBJECTS AND METHODS. This was an institutional review board-approved prospective study of 128 children (younger than 18 years old) and 32 adults without liver disease who underwent 2D SWE of the liver with a Canon Aplio i800 ultrasound system (i8CX1 transducer). Ten shear wave speed and shear wave dispersion measurements were obtained. In adults, five attenuation measurements were also obtained. Pearson correlation and t tests were used to define relationships between shear wave speed and dispersion values and predictor variables. Multivariable logistic regression with forward selection was used to generate models. RESULTS. Median age was 5.04 years old for the pediatric participants and 48.92 years old for the adult participants. Mean median shear wave speed and shear wave dispersion were 1.29 ± 0.13 m/s and 11.43 ± 1.75 (m/s)/kHz, respectively, for the pediatric participants and 1.32 ± 0.13 m/s and 10.24 ± 1.65 (m/s)/kHz, respectively, for the adults. Mean median attenuation in adults was 0.52 ± 0.11 dB/cm/MHz. On multivariable modeling, height was the only significant predictor of shear wave speed in children (0.0012 m/s per cm, p < 0.0001) and abdominal wall thickness was the only predictor of shear wave speed in adults (0.12 m/s per cm, p = 0.0008). CONCLUSION. Liver shear wave speed and shear wave dispersion data for children and adults without liver disease provides data against which results from patients with liver disease can be compared. Liver shear wave speed increases during childhood associated with increases in height and shear wave speed increases in adulthood with increasing abdominal wall thickness.

Two-Dimensional Shear Wave Elastography in the Assessment of Salivary Gland Involvement in Primary Sjögren's Syndrome.

The aim of this study was to investigate the diagnostic performance of two-dimensional (2D) shear wave elastography (SWE) in the assessment of salivary gland involvement in primary Sjögren's syndrome (pSS). Fifty-three patients with pSS and 30 healthy volunteers were included. The echogenicity of all submandibular and parotid glands was evaluated with B-mode ultrasound, and their elasticity was assessed with 2D SWE. The mean and standard deviation of the shear wave speed and elasticity modes on 2D SWE were calculated. The mean shear wave speed and elasticity mode values for the submandibular and parotid glands were significantly higher in the patients with pSS (P < .05). The mean elasticity of the shear wave speed mode was best able to differentiate the parotid glands of patients with pSS from those of healthy volunteers at a cutoff value of 2.48 m/s, whereas the mean elasticity of the elasticity mode was best able to differentiate the submandibular glands of patients with pSS from those of healthy volunteers at a cutoff value of 21 kPa. Two-dimensional SWE is an effective technique for assessment of the parenchyma of the salivary glands in patients with pSS and predicts interstitial fibrosis and the severity of histologic damage.

US Time-Harmonic Elastography for the Early Detection of Glomerulonephritis.

Background Glomerulonephritis refers to renal diseases characterized by glomerular and tubulointerstitial fibrosis. Multifrequency US time-harmonic elastography enables the noninvasive quantification of tissue elasticity. Purpose To assess the diagnostic performance of US time-harmonic elastography for the early detection of glomerulonephritis. Materials and Methods From August 2016 through May 2017, study participants with biopsy-proven glomerulonephritis were prospectively examined with US time-harmonic elastography. Participants were subdivided according to chronic kidney disease (CKD) stage. All participants underwent elastography of both kidneys to generate full-field-of-view maps of renal shear wave speed (SWS). SWS was determined separately for the whole renal parenchyma, cortex, and medulla and was correlated with quantitative B-mode findings such as renal length and parenchymal thickness. Diagnostic performance of renal elastography was assessed with receiver operating characteristic curve analysis. Results Fifty-three participants with glomerulonephritis (mean age ± standard deviation, 49 years ± 14) and 30 healthy volunteers (mean age, 37 years ± 11) were evaluated. Age-adjusted renal SWS was lower in participants with glomerulonephritis than in healthy volunteers in the parenchyma, cortex, and medulla, with mean values of 1.55 m/sec (95% confidence interval [CI]: 1.51 m/sec, 1.59 m/sec) and 1.69 m/sec (95% CI: 1.64 m/sec, 1.74 m/sec; P < .001), respectively, in parenchyma, 1.80 m/sec (95% CI: 1.75 m/sec, 1.84 m/sec) and 2.08 m/sec (95% CI: 2.02 m/sec, 2.13 m/sec; P < .001) in cortex, and 1.25 m/sec (95% CI: 1.21 m/sec, 1.29 m/sec) and 1.33 (95% CI: 1.27 m/sec, 1.38 m/sec; P = .03) in medulla. Age-adjusted renal cortex SWS was lower in participants with glomerulonephritis and stage 1 CKD (preserved renal function) than in healthy volunteers (mean, 1.88 [95% CI: 1.81, 1.96] vs 2.08 [95% CI: 2.02, 2.13]; P < .001). In participants with CKD, renal cortex SWS values showed a positive association with estimated glomerular filtration rate (n = 39; r = 0.56; P < .001). Exploratory diagnostic performance of US time-harmonic elastography (area under the receiver operating characteristic curve [AUC], 0.89; 95% CI: 0.82, 0.97) outperformed that of B-mode parameters such as parenchymal thickness (AUC, 0.64; 95% CI: 0.51, 0.77; P < .001) and renal length (AUC, 0.55; 95% CI: 0.40, 0.68; P < .001) in identifying glomerulonephritis. Conclusion US time-harmonic elastography depicts abnormal renal stiffness in glomerulonephritis, particularly among patients with early disease and preserved renal function. Advanced chronic kidney disease is associated with further cortical softening. Time-harmonic elastography outperforms B-mode-based size quantification. © RSNA, 2019 Online supplemental material is available for this article.

Gestational age-related changes in shear wave speed of the uterine cervix in normal pregnancy at 12-35 weeks' gestation.

Background This study aimed to analyze age-related changes in shear wave speed (SWS) of the normal uterine cervix. Methods We studied 362 women with a normal singleton pregnancy at 12-35 weeks' gestation. The SWS of the cervix was measured using transvaginal ultrasonography at the internal os region of the anterior cervix (IOA), posterior cervix (IOP) and cervical canal (IOC), and at the external os region of the anterior cervix (EOA), posterior cervix (EOP) and cervical canal (EOC). The following parameters were analyzed: (1) time trend of SWS of the individual sampling points, (2) comparison of SWS in the internal cervical region and SWS in the external cervical region, and (3) comparison of SWS between the internal and external cervical regions. Statistical analyses were performed using mixed-effects models. Results The SWS of IOP decreased in bilinear regression, with a critical change in the rate at 22 weeks, whereas the SWS of the remaining points decreased linearly. The estimated values of SWS of IOP at 84, 154 and 251 days were higher than those of IOA and IOC (P<0.001). The estimated values of SWS of IOP at 84 and 154 days were higher than those of EOP (P<0.001). Significant differences between IOP and EOP were shown until 244 days (P<0.05). The estimated value of SWS of IOC at 84 days was higher than that of EOC (P<0.001). Significant differences between IOC and EOC were shown until 210 days (P<0.05). Conclusion The SWS of the uterine cervix in pregnancy decreases with advancing gestation. The SWS of IOP had the highest value among the sampling points with unique characteristics.

RSNA/QIBA efforts to standardize shear wave speed as a biomarker for liver fibrosis staging

Commercial shear elasticity systems have been available to clinicians for several years for characterizing liver stiffness. The Radiological Society of North America (RSNA) established a Quantitative Imaging Biomarker Alliance (QIBA) committee on Ultrasound Shear Wave Speed to help achieve better consistency between the shear wave speed and elastic modulus values reported by different manufacturer systems. An inter-laboratory study of shear wave speed estimation was conducted at academic, industry and clinical laboratories using commercial ultrasound and magnetic resonance elastography systems in elastic (Phase I) and viscoelastic (Phase II) homogeneous, isotropic tissue-mimicking phantoms. In the elastic phantoms, shear wave speeds from different systems were within ±5% of the grand mean of all system measurements. Different appraisers and replicate measurements at a given site were not sources of significant variability in shear wave speed measurements. In the viscoelastic phantoms, shear wave speeds from different systems were within ±15% of the grand mean of all systems, with the stiffest phantoms at the deepest focal depth (7 cm) having the greatest measurement variance. Magnetic resonance elastography measurements at 140 Hz in the viscoelastic phantoms were consistent to within ±5% of thosemade with the ultrasound shear elasticity systems, while measurements made at 60 Hz had a mean bias of -2.6% relative to ultrasound systems. A method for reporting group shear wave velocities using both displacement and velocity data, along with shear wave phase velocity analysis, has been developed as a common calibration approach for the phantoms. An open-source repository of research scanner shear wave sequences and processing code has been created to allow manufacturers to have a calibration standard to assess compliance with the QIBA US shear wave speed profile and to achieve more consistent results to facilitate more rapid clinical adoption of this technology to evaluate liver fibrosis.

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.

ARFI shear-wave elastography with simulation of acute urinary tract obstruction in an ex vivo porcine kidney model.

A total of 20 heparinized pig kidneys were investigated at 10 intrapelvic hydrostatic pressure steps (0-90 mmHg). SWE (ARFI; Virtual TouchTM IQ, Siemens) measurements were taken at three different measuring regions and in two measuring sequences using a linear ultrasonography probe (9L4, Siemens). Median values of 10 shear-wave speed (SWS) measurements were calculated for each pressure step. Logarithmic transformed median SWS values were analyzed in a linear mixed model. SWS increased significantly with increasing intrapelvic pressure. Median SWS for all kidneys in both measuring sequences and all measuring regions was 1.47 m/s (interquartile range [IQR], 0.38 m/s) at 0 mmHg, 1.94 m/s (IQR, 0.42 m/s) at 30 mmHg, 2.07 m/s (IQR, 0.43 m/s) at 60 mmHg, 2.24 m/s (IQR, 0.49 m/s) at 90 mmHg. The correlation between pelvic pressure increase and median SWS values for the central parenchyma was significantly higher compared with the peripheral parenchyma. Acutely increased renal pelvic pressure correlates with increasing SWS values in ARFI elastography in an ex vivo porcine kidney model.

Ultrasound Shear Wave Elastography: Variations of Liver Fibrosis Assessment as a Function of Depth, Force and Distance from Central Axis of the Transducer with a Comparison of Different Systems

We evaluated variation in fibrosis staging caused by depth, pre-load force and measurement off-axis distance on different ultrasound shear wave elastography (SWE) systems prospectively in 20 patients with diffuse liver disease. Shear wave speed (SWS) was measured with transient elastography, acoustic radiation force impulse (ARFI) and 2-D shear wave elastography (SWE). ARFI and 2-D-SWE measurements were obtained at different depths (3, 5 and 7 cm), with different pre-load forces (4, 7 and 10N and variable) and at 0, 2 and 4cm off the central axis of the transducer. A single, blinded pathologist staged fibrosis using the METAVIR system (F0-F4). Area under the receiver operating characteristic curve was charted to differentiate significant fibrosis (F ≥ 2). Depth was the only factor found to influence ARFI-derived values; no acquisition factors were found to affect 2-D-SWE SWS values. ARFI and 2-D-SWE for diagnosis of significant fibrosis at a depth of 7cm along the central axis had good diagnostic performance (areas under the receiver operating characteristic curve: 0.92 and 0.82, respectively), comparable to that of transient elastography. Further investigation of this finding will likely be of interest.

Evaluation of shear wave elastography for differential diagnosis of breast lesions: A new qualitative analysis versus conventional quantitative analysis.

To evaluate a special kind of ultrasound (US) shear wave elastography for differential diagnosis of breast lesions, using a new qualitative analysis (i.e. the elasticity score in the travel time map) compared with conventional quantitative analysis. From June 2014 to July 2015, 266 pathologically proven breast lesions were enrolled in this study. The maximum, mean, median, minimum, and standard deviation of shear wave speed (SWS) values (m/s) were assessed. The elasticity score, a new qualitative feature, was evaluated in the travel time map. The area under the receiver operating characteristic (AUROC) curves were plotted to evaluate the diagnostic performance of both qualitative and quantitative analyses for differentiation of breast lesions. Among all quantitative parameters, SWS-max showed the highest AUROC (0.805; 95% CI: 0.752, 0.851) compared with SWS-mean (0.786; 95% CI:0.732, 0.834; P = 0.094), SWS-median (0.775; 95% CI:0.720, 0.824; P = 0.046), SWS-min (0.675; 95% CI:0.615, 0.731; P = 0.000), and SWS-SD (0.768; 95% CI:0.712, 0.817; P = 0.074). The AUROC of qualitative analysis in this study obtained the best diagnostic performance (0.871; 95% CI: 0.825, 0.909, compared with the best parameter of SWS-max in quantitative analysis, P = 0.011). The new qualitative analysis of shear wave travel time showed the superior diagnostic performance in the differentiation of breast lesions in comparison with conventional quantitative analysis.

Fourier-Domain Shift Matching: A Robust Time-of-Flight Approach for Shear Wave Speed Estimation.

Our primary objective of this work was to design and test a new time-of-flight (TOF) method that allows measurements of shear wave speed (SWS) following impulsive excitation in soft tissues. Particularly, under the assumption of the local plane shear wave, this work named the Fourier-domain shift matching (FDSM) method, estimates SWS by aligning a series of shear waveforms either temporally or spatially using a solution space deduced by characteristic curves of the well-known 1-D wave equation. The proposed SWS estimation method was tested using computer-simulated data, and tissue-mimicking phantom and ex vivo tissue experiments. Its performance was then compared with three other known TOF methods: lateral time-to-peak (TTP) method with robust random sampling consensus (RANSAC) fitting method, Radon sum transformation method, and a modified cross correlation method. Hereafter, these three TOF methods are referred to as the TTP-RANSAC, Radon sum, and X-corr methods, respectively. In addition to an adapted form of the 2-D Fourier transform (2-D FT)-based method in which the (group) SWS was approximated by averaging phase SWS values was considered for comparison. Based on data evaluated, we found that the overall performance of the above-mentioned temporal implementation of the proposed FDSM method was most similar to the established Radon sum method (correlation = 0.99, scale factor = 1.03, and mean difference = 0.07 m/s), and the 2-D FT (correlation = 0.98, scale factor = 1.00, and mean difference = 0.10 m/s) at high signal quality. However, results obtained from the 2-D FT method diverged (correlation = 0.201) from these of the proposed temporal implementation in the presence of diminished signal quality, whereas the agreement between the Radon sum approach and the proposed temporal implementation largely remained the same (correlation = 0.98).

Measurement of shear wave speed dispersion in the placenta by transient elastography: A preliminary ex vivo study.

BackgroundPlacental elasticity may be modified in women with placental insufficiency. Shear wave elastography (SWE) can measure this, using acoustic radiation force, but the safety of its use in pregnant women has not yet been demonstrated. Transient elastography (TE) is a safer alternative, but has not yet been applied to the placenta. Moreover, the dispersion of shear wave speed (SWS) as a function of frequency has received relatively little study for placental tissue, although it might improve the accuracy of biomechanical assessment.ObjectiveTo explore the feasibility and reproducibility of TE for placental analysis, to compare the values of SWS and Young’s modulus (YM) from TE and SWE, and to analyze SWS dispersion as a function of frequency ex vivo in normal placentas.Materials and methodsTen normal placentas were analyzed ex vivo by an Aixplorer ultrasound system as shear waves were generated by a vibrating plate and by using an Aixplorer system.The frequency analysis provided the value of the exponent n from a fractional rheological model applied to the TE method. We calculated intra- and interobserver agreement for SWS and YM with 95% prediction intervals, created Bland-Altman plots with 95% limits of agreement, and estimated the intraclass correlation coefficient (ICC).Main resultsThe mean SWS was 1.80 m/s +/- 0.28 (standard deviation) with the TE method at 50 Hz and 1.82 m/s +/-0.13 with SWE (P = 0.912). No differences were observed between the central and peripheral regions of placentas with either TE or SWE. With TE, the intraobserver ICC for SWS was 0.68 (0.50–0.82), and the interobserver ICC for SWS 0.65 (0.37–0.85). The mean parameter n obtained from the fractional rheological model was 1.21 +/- 0.12, with variable values of n for any given SWS.ConclusionsTE is feasible and reproducible on placentas ex vivo. The frequency analysis of SWS provides additional information about placental elasticity and appears to be able to distinguish differences between placental structures.

Quantitative assessment of cervical softening during pregnancy in the Rhesus macaque with shear wave elasticity imaging

Abnormal parturition, e.g. pre- or post-term birth, is associated with maternal and neonatal morbidity and increased economic burden. This could potentially be prevented by accurate detection of abnormal softening of the uterine cervix. Shear wave elasticity imaging (SWEI) techniques that quantify tissue softness, such as shear wave speed (SWS) measurement, are promising for evaluation of the cervix. Still, interpretation of results can be complicated by biological variability (i.e. spatial variations of cervix stiffness, parity), as well as by experimental factors (i.e. type of transducer, posture during scanning). Here we investigated the ability of SWEI to detect cervical softening, as well as sources of SWS variability that can affect this task, in the pregnant and nonpregnant Rhesus macaque. Specifically, we evaluated SWS differences when imaging the cervix transabdominally with a typical linear array abdominal transducer, and transrectally with a prototype intracavitary linear array transducer. Linear mixed effects (LME) models were used to model SWS as a function of menstrual cycle day (in nonpregnant animals) and gestational age (in pregnant animals). Other variables included parity, shear wave direction, and cervix side (anterior versus posterior). In the nonpregnant cervix, the LME model indicated that SWS increased by 2% (95% confidence interval 0–3%) per day, starting eight days before menstruation. During pregnancy, SWS significantly decreased at a rate of 6% (95% CI 5–7%) per week (intracavitary approach) and 3% (95% CI 2–4%) per week (transabdominal approach), and interactions between the scanning approach and other fixed effects were also significant. These results suggest that, while absolute SWS values are influenced by factors such as scanning approach and SWEI implementation, these sources of variability do not compromise the sensitivity of SWEI to cervical softening. Our results also highlight the importance of standardizing SWEI approaches to improve their accuracy for cervical assessment.

Point shear wave elastography (pSWE) using Acoustic Radiation Force Impulse (ARFI) imaging: a feasibility study and norm values for renal parenchymal stiffness in healthy children and adolescents.

To evaluate the applicability of point shear wave elastography (pSWE) for measuring renal parenchymal stiffnessin healthy children and adolescents and to establish norm values for shear wave speed (SWS) using two ARFI methodsand ultrasound probes. We prospectively investigated 264 children (43.9% males). pSWE(Virtual TouchTM Quantification and Virtual TouchTM Imaging Quantification (VTQ and VTIQ; Siemens, Germany)) wasperformed in the renal cortex of 528 healthy kidneys using a 1-6 MHz convex and a 4-9 MHz linear ultrasound probe inventrolateral and dorsal examinations. Feasibility and reproducibility of pSWE measurements were evaluated. SWS valueswere analysed with regard to age, body dimensions, kidney volume and measuring depth. pSWE measurementswere successful in >95% of subjects using the low and in <60% using the high-frequency probe. Mean SWS values (m/s)differed by method and probe: 2.10±0.43 (VTQ1-6MHz, convex, ventrolateral), 2.30±0.37 (VTQ1-6MHz, convex, dorsal), 1.58±0.44 (VTQ4-9MHz, linear, dorsal) and 1.96±0.27 (VTIQ4-9MHz, linear, dorsal). SWS was positively correlated withage, weight and body height, but independent of sex, BMI, or kidney volume and depth. pSWE (VTQ) is afeasible method to evaluate renal parenchymal stiffness in children of all ages. SWS values are age and weight dependentand differ significantly between high- and low-frequency probes. High-frequency probes and VTIQ should only be used inchildren <10 years.

Characterization of glioblastoma in an orthotopic mouse model with magnetic resonance elastography.

Glioblastoma (GBM) is the most common primary brain tumor. It is highly malignant and has a correspondingly poor prognosis. Diagnosis and monitoring are mainly accomplished with MRI, but remain challenging in some cases. Therefore, complementary methods for tumor detection and characterization would be beneficial. Using magnetic resonance elastography (MRE), we performed a longitudinal study of the biomechanical properties of intracranially implanted GBM in mice and compared the results to histopathology. The biomechanical parameters of viscoelastic modulus, shear wave speed and phase angle were significantly lower in tumors compared with healthy brain tissue and decreased over time with tumor progression. Moreover, some MRE parameters revealed sub-regions at later tumor stages, which were not easily detectable on anatomical MRI images. Comparison with histopathology showed that softer tumor regions contained necrosis and patches of viable tumor cells. In contrast, areas of densely packed tumor cells and blood vessels identified with histology coincided with higher values of viscoelastic modulus and shear wave speed. Interestingly, the phase angle was independent from these anatomical variations. In summary, MRE depicted longitudinal and morphological changes in GBM and may prove valuable for tumor characterization in patients.

Ultrasound-Based Shear Wave Elastography in the Assessment of Patients with Diabetic Kidney Disease

In previous studies of acoustic radiation force impulse (ARFI) elastography, using Virtual Touch tissue quantification (VTQ) (Siemens Acuson S2000), it was reported that the measurement of renal shear wave speed in patients with chronic kidney disease (CKD) is not influenced exclusively by renal fibrosis. The purpose of the present study was to analyze the role of VTQ in patients with diabetic kidney disease, considered the main cause of CKD. The study group included 164 patients: 80 patients with diabetic kidney disease (DKD) and 84 without renal disease or diabetes mellitus. In each subject in lateral decubitus, five valid VTQ measurements were performed in each kidney and a median value was calculated, the result being expressed in meters/second. The following means of the median values were obtained In DKD patients, the means of the median values were for VTQ right kidney, 2.21 ± 0.71 m/s, and for VTQ left kidney, 2.13 ± 0.72 m/s, whereas in the normal controls statistically significant higher values were obtained: 2.58 ± 0.78 m/s for VTQ right kidney (p = 0.0017) and 2.46 ± 0.81 m/s for VTQ left kidney (p = 0.006). Patients with an estimated glomerular filtration rate (eGFR) >60 mL/min (DKD stages 1 and 2 together with normal controls) had a significantly higher kidney shear wave speed compared with patients with an eGFR <60 mL/min (2.53 m/s vs. 2.09 m/s, p < 0.05). In the DKD group, there was a significant correlation between eGFR and VTQ levels for the right kidney (r = 0.28, p = 0.04). There was no correlation of VTQ values with proteinuria level, stage of diabetic retinopathy or glycated hemoglobin. Our study indicates that shear wave speed values in patients with diabetic kidney disease and eGFRs <60 mL/min are significantly lower compared with those of patients with eGFRs >60 mL/min (either normal controls or diabetic patients with DKD stages 1 and 2), and values decrease with the decrease in eGFR. However, proteinuria, diabetic retinopathy and glycated hemoglobin have no influence on VTQ.

Comparison of Virtual Touch Tissue Imaging & Quantification (VTIQ) and Toshiba shear wave elastography (T-SWE) in diagnosis of thyroid nodules: Initial experience.

The aim of this study was to compare the diagnostic performance of two different 2D shear wave speed imaging techniques of Virtual Touch Tissue Imaging & Quantification (VTIQ) and Toshiba shear wave elastography (T-SWE) in predicting malignant thyroid nodules (TNs). 75 TNs in 75 patients which were subject to both VTIQ and T-SWE examinations were enrolled and analyzed. Shear wave speed (SWS) values on VTIQ and T-SWE were computed (SWS_max, min, mean and median). Area under the receiver operating characteristic (AUROC) curve was obtained to assess the diagnostic performance. The AUROC for VTIQ was the highest with SWS_min whereas for T-SWE was SWS_max (0.774 versus 0.851; p > 0.05). The AUROC, sensitivity and negative predictive value (NPV) corresponding to SWS_max for VTIQ were significantly lower than those for T-SWE (0.717 versus 0.851, 61.5% versus 92.3% and 78.7% versus 94.3%; all p < 0.05). However, no significant differences were found between AUROC with SWS_min, SWS_mean, or SWS_median for VTIQ and SWS_max for T-SWE (all p > 0.05). In general, VTIQ is equal to T-SWE for diagnosis of TNs. In the clinical practice, the selection of SWS_max should be avoided in VTIQ whereas should be selected in T-SWE.