Abstract

PurposeUltrasound methods for kidney stone imaging suffer from poor sensitivity and size overestimation. The study objective was to demonstrate feasibility of non-linear ultrasound beamforming methods for stone imaging, including plane wave synthetic focusing (PWSF), short-lag spatial coherence (SLSC) imaging, mid-lag spatial coherence (MLSC) imaging with incoherent compounding, and aperture domain model image reconstruction (ADMIRE).Materials and methodsThe ultrasound techniques were evaluated in an in vitro kidney stone model and in a pilot study of 5 human stone formers (n = 6 stones). Stone contrast, contrast-to-noise ratio (CNR), sizing, posterior shadow contrast, and shadow width sizing were compared among the different techniques and to B-mode. CT imaging within 60 days was considered the gold standard stone size. Paired t-tests using Bonferroni correction were performed to evaluate comparing each technique with B-mode.ResultsMean CT measured stone size was 6.0mm (range 2.9–12.2mm) with mean skin-to-stone distance 10.2cm (range 5.4–16.3cm). Compared to B-mode, stone contrast was best with ADMIRE (mean +12.2dB), while SLSC and MLSC showed statistically improved CNR. Sizing was best with ADMIRE (mean +1.3mm error), however this was not significantly improved over B-mode (+2.4mm). PWSF performed similarly to B-mode for stone contrast, CNR, SNR, and stone sizing. In the in vitro model, the shadow contrast was highest with ADMIRE (mean 10.5 dB vs 3.1 dB with B-mode). Shadow sizing was best with SLSC (mean error +0.9mm ± 2.9), however the difference compared to B-mode was not significant.ConclusionsThe detection and sizing of stones are feasible with advanced beamforming methods with ultrasound. ADMIRE, SLSC, and MLSC hold promise for improving stone detection, shadow contrast, and sizing.

Highlights

  • Kidney stones are highly and increasingly prevalent.[1]

  • Compared to B-mode, stone contrast was best with aperture domain model image reconstruction (ADMIRE), while shortlag spatial coherence (SLSC) and mid-lag spatial coherence (MLSC) showed statistically improved contrast-to-noise ratio (CNR)

  • Shadow sizing was best with SLSC, the difference compared to B-mode was not significant

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Summary

Introduction

Kidney stones are highly and increasingly prevalent.[1]. Diagnostic imaging is the primary means for the diagnosis, surveillance, and management of kidney stones.[2, 3] Ultrasound has several advantages over gold standard computerized tomography (CT) including its portability, accessibility, and avoidance of ionizing radiation exposure.[2]. Among pediatric populations and pregnant women with kidney stones, several guideline panels recommend ultrasound as the first-line imaging modality for stone disease.[3,4,5] Despite the advantages with ultrasound, it suffers from poorer sensitivity (24–69%), diminished specificity (82–91%), and overestimation of stone size of approximately 2-3mm compared to CT. [6,7,8,9,10,11,12] It is not surprising that the role of ultrasound is currently limited to screening in the acute setting and surveillance.[2,3,4, 13,14,15] Improving the detection and sizing tasks would provide kidney stone patients more of the benefits inherent to ultrasound imaging

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