Metabolic dysfunction-associated steatotic liver disease requires reliable, noninvasive assessment of fibrosis. Ultrasound shear wave elastography (SWE) is widely used, but measurement quality often declines with higher body mass index (BMI). A prospective, single-centre trial tested whether increasing the push pulse mechanical index (MI) above current limits can improve SWE quality without harming the liver. Healthy adults stratified by BMI underwent conventional SWE at MI 1.4 and increased push MI (IPMI) SWE at MI 2.5 on a modified system, with liver function tests (LFTs) collected up to seven days.
Safety With Elevated Acoustic Output
The protocol raised MI only for push pulses and kept tracking-pulse MI, thermal index and derated spatial peak temporal average intensity within regulatory limits. Safety was assessed by changes in aspartate aminotransferase (AST), alanine transaminase (ALT) and alkaline phosphatase (ALP) against stringent non-inferiority margins (AST 7.5 U/L, ALT 12 U/L, ALP 17.5 U/L). Among 22 analysable participants, upper 95% confidence limits for biomarker change on day 1, day 2 and day 7 remained below these margins, indicating no evidence of liver injury.
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Mean [95% CI] day-1 changes were AST −0.86 U/L [−2.34, 0.61], ALT 0.32 U/L [−1.04, 1.68] and ALP 1.73 U/L [−1.02, 4.47]. Results at later time points were similarly within bounds in paired tests and linear mixed-effects models. No serious adverse events were attributed to IPMI SWE. Two participants reported mild, transient abdominal sensations that resolved before follow-up and were deemed unlikely to be related. Transducer performance remained within predefined limits.
Image Quality and Efficiency
Image quality was measured by the interquartile range to median (IQRM) ratio of shear wave speed. IPMI SWE reduced IQRM by 0.019, a 29.2% relative decrease [95% CI 7.7%–50.9%], with statistical significance (p=0.01). Improvements were seen across BMI categories, including normal weight, overweight and obesity classes, with consistently lower IQRM values under IPMI. Representative cases showed more homogeneous elastograms and a higher proportion of diagnostic frames with IPMI when conventional acquisitions displayed signal loss.
Workflow signals also favoured IPMI. The attempts needed to obtain ten diagnostic measurements decreased from 11.41 to 10.73 on average, a difference of 0.68 that approached significance (p=0.058). IPMI required fewer measurements in 6 of 22 cases overall and in 4 of 10 cases with BMI ≥30.0 kg/m², with none requiring more. Completion-curve analysis indicated a higher probability of finishing the exam for a given number of attempts with IPMI.
Shear wave speeds were consistent between techniques: 1.34 ± 0.21 m/s for conventional SWE and 1.36 ± 0.20 m/s for IPMI (mean difference 0.02 m/s [95% CI −0.04, 0.07]). Values aligned with expectations for a healthy cohort and did not suggest a technique-driven bias.
Cohort and Protocol Summary
Twenty-four volunteers were enrolled between July 2023 and April 2024, two withdrew before imaging, leaving 22 for analysis across BMI strata: normal (n=6), overweight (n=6), class 1 obesity (n=7) and class 2 obesity (n=3). Participants fasted for at least four hours. Experienced sonographers acquired up to 20 attempts per mode to achieve ten diagnostic measurements from the right hepatic lobe through an intercostal window during breath hold. Regions of interest were placed about 2 cm below the capsule, avoiding vessels and focal lesions, with on-system adequacy checks.
For IPMI, push MI was 2.5 with frame rate adjusted to match the soft-tissue thermal index of conventional imaging (0.98), implying an expected temperature rise of about 1°C. Push frequency was 2.3 MHz for both modes. LFTs were obtained within 48 hours before imaging and at 1, 2 and 7 days after. The analysis plan focused on non-inferiority of LFT changes on day 7 and included secondary outcomes of IQRM reduction and measurement attempts. Statistical methods comprised paired non-inferiority tests, paired t-tests, Wilcoxon signed-rank tests and mixed-effects modelling. Data capture and analysis were conducted on a secure platform, sponsorship provided equipment and financial support without analytic control.
Raising push pulse MI to 2.5 improved SWE exam quality, with a 29.2% reduction in measurement variability and signals of greater efficiency, while serial LFTs showed no evidence of liver injury within stringent non-inferiority thresholds. Findings support further development and evaluation of IPMI SWE, particularly for individuals in whom higher BMI degrades elastography performance, with future work directed to broader safety, accuracy against reference standards and assessment in patients with liver fibrosis.
Source: Radiology Advances
Image Credit: Freepik
