Clinical Evaluation of Real-Time Optical-Tracking Navigation and Live Time-Intensity Curves to Provide Feedback During Blinded 4D Contrast-Enhanced Ultrasound Imaging

TL;DR

This study evaluates a real-time optical-tracking system for 4D contrast-enhanced ultrasound imaging, demonstrating improved operator positioning and image re-alignment to enhance quantification and repeatability.

Contribution

The paper introduces an in-house developed optical-tracking system that provides real-time feedback and image re-alignment during contrast-enhanced ultrasound imaging.

Findings

Tracking helps maintain steady transducer position during lengthy acquisitions.

Tracking feedback reduces displacement compared to blind acquisition.

Image re-alignment improves perfusion parameter repeatability.

Abstract

Current commercial matrix transducers for 3D DCE-US do not display side-by-side B-mode and contrast-mode images when capturing volumetric data, thus leaving the operator with no position feedback during lengthy acquisitions. The purpose of this study was to investigate the use of transducer tracking to provide positioning feedback and to re-align images to improve quantification. An interventional tracking system was developed in house using an infrared camera and a 3D-printed tracking target attached to a X6-1 matrix transducer. The system displays a virtual probe on a separate screen and allows to capture a reference position to provide operator feedback when no B-mode image is available. To test this set-up, five experienced operators were asked to locate an image landmark within a volunteer liver in B-mode images using the X6-1 connected to an EPIQ7 system. Operators were then asked to maintain the transducer position for 4 minutes under three feedback methods: i) B-mode, ii) display of real-time virtual transducer, iii) blind. The magnitude of displacement over the cine was computed as an estimate of the imaging position error. We also investigated whether transducer coordinates can be used to re-align images due to motion and improve contrast ultrasound perfusion repeatability. A total of 8 patient data were obtained under an IRB for this. Results suggest that tracking can assist operators maintain a steady position during a lengthy acquisition. With blinded acquisition, an average displacement of 4.58 mm (S.D. 2.65 mm) was noted. In contrast, the average displacement for tracking-feedback was comparable to B-mode at 3.48 mm (S.D. 0.8 mm). We also observed that perfusion parameters had better repeatability after re-alignment.