First clinical utility of sensing Ultrasound Localization Microscopy (sULM): identifying renal pseudotumors.

Rationale: Renal pseudotumors, which mimic tumors on imaging, pose diagnostic challenges that can lead to unnecessary interventions. Sensing ultrasound localization microscopy (sULM) is an advanced imaging technique that uses ultrasound imaging and microbubbles as sensors to visualize kidney functional units. This study aims to investigate whether sULM could differentiate between renal pseudotumors and tumors based on the presence of glomeruli. Methods: Eleven patients (6 tumors, 6 pseudotumors - 1 patient with 2 pseudotumors) were included. Data on patient demographics, tumor characteristics, and sULM metrics were collected. Glomeruli were quantified and compared among tumors, pseudotumors, and renal cortex using sULM. Additional metrics, i.e., normalized speed and dispersity, were also analyzed. Results: Renal tumors exhibited fewer detected glomeruli paths (mean: 10 ± 6 /cm² [range: 4-20]) compared to pseudotumors (26 ± 5 /cm² [19-32], p < 0.001) and normal renal cortex (26 ± 6 /cm² [15-35], p < 0.01). Tumors displayed lower dispersity (0.13 ± 0.06 arbitrary units [a.u.] [0.07-0.20]) than both the renal cortex (0.3 ± 0.1 a.u. [0.1-0.4], p = 0.0012) and pseudotumors (0.22 ± 0.05 a.u. [0.16-0.25], p = 0.0389), and lower normalized speeds of 0.08 ± 0.04 without units (w.u.) [range: 0.03-0.17] compared to the renal cortex (0.18 ± 0.07 w.u. [0.11-0.28], p = 0.0014) and pseudotumors (0.14 ± 0.02 w.u. [0.12-0.16], p = 0.0497). sULM could effectively differentiate renal pseudotumors from tumors based on glomerular detection and metrics estimation. Conclusion: This initial exploration into the clinical utility of sULM suggests it could provide a noninvasive tool to support patient management, particularly for individuals with contraindications to conventional imaging methods. Further studies are needed to confirm these preliminary findings.