Abstract
Abstract 4D ultrasound (4D US) is gaining relevance as a tracking method in radiation therapy (RT) with modern matrix array probes offering new possibilities for real-time target detection. However, for clinical implementation of USguided RT, image quality, volumetric framerate and artifacts caused by the probe’s presence during planning and / or setup computed tomography (CT) must be quantified. We compared three diagnostic 4D US systems with matrix array probes using a commercial wire phantom to measure spatial resolution as well as a calibration and a torso phantom to assess different image quality metrics. CT artifacts were quantified in the torso phantom by calculating the total variation and percentage of affected voxels between a reference CT scan and CT scans with probes in place. We found that state-of-the-art 4D US systems with small probes can fit inside the CT bore and cause fewer metal artifacts than larger probes. US image quality varies between systems and is task-dependent. Volume sizes and framerates are much higher than the commercial guidance solution for US-guided RT, warranting further investigation regarding clinical performance for image guidance.
Highlights
In recent years, real-time volumetric ultrasound (4D US) imaging has seen major improvements in volume rates and image quality
The aim of this study is the assessment of current diagnostic 4D ultrasound (4D US) systems with online data access regarding their suitability for motion compensation in radiation therapy (RT), including image quality, volumetric framerates and computed tomography (CT) artifacts
Global total variation (TV) increase was between 1.9% (4Vc-D) and 4.6% (X6-1), most pronounced in the regions of interest (ROIs) directly below the probe (Figure 1b) ranging from 166% (4Vc-D) to 390% (X61)
Summary
Real-time volumetric ultrasound (4D US) imaging has seen major improvements in volume rates and image quality. It is being investigated for diagnostic and interventional tasks as an image guidance method, for example for target localization in radiation therapy (RT). The commercial diagnostic 4D US systems iU22, Epiq 7 (Philips Healthcare, Best, Netherlands), Vivid 7 and E9 (GE Healthcare, Chicago, USA) can be accessed with either custom or manufacturer-provided real-time streaming interfaces and are currently under investigation for motion compensation in RT [4,5,6]
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