Development and validation of an intrinsic landmark-based gating protocol applicable for functional and molecular ultrasound imaging

Abstract

Objectives To implement a retrospective intrinsic landmarkbased (ILB) gating protocol for contrast-enhanced ultrasound (CEUS) and to compare its efficiency to non-gated, manually gated and extrinsically gated CEUS. Methods CEUS of the liver was performed in healthy mice (n05) and in NEMO knockout mice with dysplastic livers (n05). In healthy animals, first-pass kinetics of non-specific microbubbles was recorded. Knockout mice were analysed regarding retention of VEGFR2-specific microbubbles. For retrospective gating, a landmark which showed respiratory movement was encircled as a region of interest (ROI). During inspiration, the signal intensity within the ROI altered, which served as gating signal. To evaluate the accuracy, non-gated, extrinsically gated and ILB-gated time-intensity curves were created. For each curve, descriptive parameters were calculated and compared to the gold standard (manual frame-by-frame gating). Results No significant differences in the variation of ILB- and extrinsically gated time-intensity curves fromthe gold standard were observed. Non-gated data showed significantly higher variations. Also the variation of molecular ultrasound data was significantly lower for ILB-gated compared to non-gated data. Conclusion ILB gating is a robust and easy method to improve data accuracy in functional and molecular ultrasound liver imaging. This technique can presumably be translated to contrast-enhanced ultrasound examinations in humans. Key Points ̇ Quantitative analysis of the uptake of contrast agents during ultrasound is complex. ̇ Intrinsic landmark-based gating (ILB) offers a simple implementable method for motion correction. ̇ Results using ILB-gating are comparable to extrinsic gating using external biomonitoring devices. ̇ Functional and molecular imaging of mobile organs will benefit from ILB gating. © European Society of Radiology 2012.