Renal Volume Estimation Using Freehand Ultrasound Scans: An Ex Vivo Demonstration

Renal volume has the potential to serve as a robust biomarker for tracking the onset and progression of renal diseases and also for quantifying renal function. We propose a method to estimate renal volumes using freehand ultrasound scans at the point of care. A conventional ultrasound probe was augmented with an Intel RealSense D435 i camera. Visual inertial simultaneous localization and mapping was used to localize the probe in free space. The acquired 2-D ultrasound images, segmented by trained clinicians, were combined with the estimated poses of the probe to yield accurate volumes. The method was tested on two ex vivo sheep kidneys embedded in gelatin phantoms. Four different scanning protocols were tested: transverse linear, transverse fan, longitudinal linear and longitudinal fan. The estimated renal volumes were compared with those obtained using the water displacement method, the ellipsoidal method and computed tomography imaging. The water displacement method yielded mean volumes of 66.00 and 66.20 mL for kidneys 1 and 2, respectively (ground truth). Freehand ultrasound scans produced mean volumes of 64.08 mL (2.90% error) and 65.25 mL (1.40% error); the ellipsoidal method yielded volumes of 57.49 mL (12.90% error) and 60.15 mL (9.13% error); and computed tomography yielded a volume of 63.00 mL (4.54% error).