The effect of applied transducer force on acoustic radiation force impulse quantification within the left lobe of the liver

3D Ultrasound Shear Wave Elastography for Musculoskeletal Tissue Assessment Under Compressive Load: A Feasibility Study

Given its real-time capability to quantify mechanical tissue properties, ultrasound shear wave elastography holds significant promise in clinical musculoskeletal imaging. However, existing shear wave elastography methods fall short in enabling full-limb analysis of 3D anatomical structures under diverse loading conditions, and may introduce measurement bias due to sonographer-applied force on the transducer. These limitations pose numerous challenges, particularly for 3D computational biomechanical tissue modeling in areas like prosthetic socket design. In this feasibility study, a clinical linear ultrasound transducer system with integrated shear wave elastography capabilities was utilized to scan both a calibrated phantom and human limbs in a water tank imaging setup. By conducting 2D and 3D scans under varying compressive loads, this study demonstrates the feasibility of volumetric ultrasound shear wave elastography of human limbs. Our preliminary results showcase a potential method for evaluating 3D spatially varying tissue properties, offering future extensions to computational biomechanical modeling of tissue for various clinical scenarios.

Impact of probe-induced abdominal compression on two-dimensional shear wave elastography measurement of split liver transplants in children

PURPOSE

To evaluate the effect of probe-induced abdominal compression of split liver transplants (SLT) in children on 2D-shear wave elastography (SWE) values.

MATERIALS AND METHODS

Data from 11 children (4.7 ± 4.8 years) who had undergone SLT and SWE were evaluated retrospectively. Elastograms were obtained with probes placed in an epigastric, midline position on the abdominal wall, with no and slight compression, using convex and linear transducers. For each identically positioned probe and condition, 12 serial elastograms were obtained and the SLT diameter was measured. Liver stiffness and degree of SLT compression were compared.

RESULTS

Slight probe pressure resulted in SLT compression, with a shorter distance between the cutis and the posterior margin of the liver transplant than in the measurement with no pressure (curved array, 5.0 ± 1.1 vs. 5.9 ± 1.3 cm, mean compression 15 %± 8 %; linear array, 4.7 ± 0.9 vs. 5.3 ± 1.0 cm, mean compression 12 %± 8 %; both p < 0.0001). The median liver stiffness was significantly greater with slight pressure than with no pressure (curved transducer, 13.38 ± 3.0 vs. 7.02 ± 1.7 kPa, p < 0.0001; linear transducer, 18.53 ± 7.1 vs. 9.03 ± 1.5 kPa, p = 0.0003).

CONCLUSION

Slight abdominal compression can significantly increase SWE values in children with left-lateral SLT. To obtain meaningful results and reduce operator dependency in free-hand examinations, probe pressure must be controlled carefully.

KEY POINTS

· Probe-induced compression can increase elastography values in split liver transplants in children. · In free-hand examination, probe pressure must be controlled carefully. · Pressure loading can be determined indirectly by the anteroposterior transplant diameter.

CITATION FORMAT

· Groth M, Fischer L, Herden U et al. Impact of probe-induced abdominal compression on two-dimensional shear wave elastography measurement of split liver transplants in children. Fortschr Röntgenstr 2023; 195: 905 - 912.

Effects of Maximal Eccentric Trunk Extensor Exercise on Lumbar Extramuscular Connective Tissue: A Matched-Pairs Ultrasound Study

Recently, it has been shown that the extramuscular connective tissue (ECT) is likely involved in delayed onset muscle soreness (DOMS). Therefore, the aim of the present study was to investigate the effects of maximal trunk extension eccentric exercise (EE) on ECT thickness, self-reported DOMS, ECT stiffness, skin temperature, and possible correlations between these outcomes. Healthy adults (n = 16, 29.34 ± 9.87 years) performed fatiguing EE of the trunk. A group of highly active individuals (TR, n = 8, > 14 h of sport per week) was compared with a group of less active individuals (UTR, n = 8, < 2 h of sport per week). Ultrasound measurements of ECT thickness, stiffness with MyotonPro and IndentoPro, skin temperature with infrared thermography, and pain on palpation (100 mm visual analog scale, VAS) as a surrogate for DOMS were recorded before (t0), immediately (t1), 24 h (t24), and 48 h (t48) after EE. ECT thickness increased after EE from t0 to t24 (5.96 mm to 7.10 mm, p = 0.007) and from t0 to t48 (5.96 mm to 7.21 mm, p < 0.001). VAS also increased from t0 to t24 (15.6 mm to 23.8 mm, p < 0.001) and from t0 to t48 (15.6 mm to 22.8 mm, p < 0.001). Skin temperature increased from t1 to t24 (31.6° Celsius to 32.7° Celsius, p = 0.032) and t1 to t48 (31.6° Celsius to 32.9° Celsius, p = 0.003), while stiffness remained unchanged (p > 0.05). Correlation analysis revealed no linear relationship between the outcomes within the 48-hour measurement period. The results may confirm previous findings of possible ECT involvement in the genesis of DOMS in the extremities also for the paraspinal ECT of trunk extensors. Subsequent work should focus on possible interventions targeting the ECT to prevent or reduce DOMS after strenuous muscle EE.

Prospective comparison of 2D-shearwave elastography in both liver lobes in healthy subjects and in patients with chronic liver disease

Background/aims: 2D-shearwave elastography is an established method for liver stiffness measurement (LSM). However, the success rate of LSM using the recommended standard technique in the right lobe is limited by several factors. We aimed to compare LSM in the right and left liver lobe in order to evaluate whether LSM in the left lobe could be an alternative if measurements in the right lobe are not feasible. Methods: A total of 116 subjects, 58 healthy volunteers and 58 patients with chronic liver disease (CLD), were prospectively included. LSM were performed in the right lobe and in the left lobe, both in neutral and in inspiration position. Results: LSM in the left lobe (8.39(±4.83)kPa) was significantly (p < .001) higher than LSM in the right lobe (6.27(±2.45)kPa). LSM in inspiration position (8.60(±4.33) kPa) was significantly (p = .009) higher than LSM in neutral position (7.70(±3.01)kPa). LSM in the left lobe overestimated the grade of fibrosis in 50.0% of the patients with CLD. However, correlation between LSM values right and left was strong (r = 0.856) and additional use of LSM in the left lobe increased the success rate from 106/116 (91.4%) to 112/116 (96.6%; p = .098). High skin-to-liver-capsule-distance and presence of ascites were independent risk factors for non-successful LSM. Conclusions: Despite significantly higher values, LSM in the left lobe may be an alternative if LSM in the right lobe is not feasible, and cirrhosis can be ruled out with high probability if LSM is within the normal range.

Full noncontact laser ultrasound: first human data

Full noncontact laser ultrasound (LUS) imaging has several distinct advantages over current medical ultrasound (US) technologies: elimination of the coupling mediums (gel/water), operator-independent image quality, improved repeatability, and volumetric imaging. Current light-based ultrasound utilizing tissue-penetrating photoacoustics (PA) generally uses traditional piezoelectric transducers in contact with the imaged tissue or carries an optical fiber detector close to the imaging site. Unlike PA, the LUS design presented here minimizes the optical penetration and specifically restricts optical-to-acoustic energy transduction at the tissue surface, maximizing the generated acoustic source amplitude. With an appropriate optical design and interferometry, any exposed tissue surfaces can become viable acoustic sources and detectors. LUS operates analogously to conventional ultrasound but uses light instead of piezoelectric elements. Here, we present full noncontact LUS results, imaging targets at ~5 cm depths and at a meter-scale standoff from the target surface. Experimental results demonstrating volumetric imaging and the first LUS images on humans are presented, all at eye- and skin-safe optical exposure levels. The progression of LUS imaging from tissue-mimicking phantoms, to excised animal tissue, to humans in vivo is shown, with validation from conventional ultrasound images. The LUS system design insights and results presented here inspire further LUS development and are a significant step toward the clinical implementation of LUS.

Toward Standardized Acoustic Radiation Force (ARF)-Based Ultrasound Elasticity Measurements With Robotic Force Control

OBJECTIVE

Acoustic radiation force (ARF)-based approaches to measure tissue elasticity require transmission of a focused high-energy acoustic pulse from a stationary ultrasound probe and ultrasound-based tracking of the resulting tissue displacements to obtain stiffness images or shear wave speed estimates. The method has established benefits in biomedical applications such as tumor detection and tissue fibrosis staging. One limitation, however, is the dependence on applied probe pressure, which is difficult to control manually and prohibits standardization of quantitative measurements. To overcome this limitation, we built a robot prototype that controls probe contact forces for shear wave speed quantification.

METHODS

The robot was evaluated with controlled force increments applied to a tissue-mimicking phantom and in vivo abdominal tissue from three human volunteers.

RESULTS

The root-mean-square error between the desired and measured forces was 0.07 N in the phantom and higher for the fatty layer of in vivo abdominal tissue. The mean shear wave speeds increased from 3.7 to 4.5 m/s in the phantom and 1.0 to 3.0 m/s in the in vivo fat for compressive forces ranging from 2.5 to 30 N. The standard deviation of shear wave speeds obtained with the robotic approach were low in most cases ( 0.2 m/s) and comparable to that obtained with a semiquantitative landmark-based method.

CONCLUSION

Results are promising for the introduction of robotic systems to control the applied probe pressure for ARF-based measurements of tissue elasticity.

SIGNIFICANCE

This approach has potential benefits in longitudinal studies of disease progression, comparative studies between patients, and large-scale multidimensional elasticity imaging.