Ultrasound Localization Microscopy Precision of Clinical 3-D Ultrasound Systems

Ultrasound localization microscopy is becoming well established in preclinical applications. For its translation into clinical practice, the localization precision achievable with commercial ultrasound scanners is crucial - especially with volume imaging, which is essential for dealing with out-of-plane motion. Here, we propose an easy-to-perform method to estimate the localization precision of 3D ultrasound scanners. With this method, we evaluated imaging sequences of the Philips Epiq 7 ultrasound device using the X5-1 and the XL14-3 matrix transducers, and also tested different localization methods. For the X5-1 transducer, the best lateral, elevational, and axial precision was 109 mu m, 95 mu m, and 55 mu m for one contrast mode, and 29 mu m, 22 mu m, and 19 mu m for the other. The higher frequency XL14-3 transducer yielded precisions of 17 mu m, 38 mu m, and 6 mu m using the harmonic imaging mode. Although the center of mass was the most robust localization method also often providing the best precision, the localization method has only minor influence on the localization precision compared to the impact by the imaging sequence and transducer. The results show that with one of the imaging modes of the X5-1 transducer, precisions comparable to the XL14-3 transducer can be achieved. However, due to localization precisions worse than 10 mu m, reconstruction of the microvasculature at the capillary level will not be possible. These results show the importance to evaluate the localization precision of imaging sequences from different ultrasound transducers or scanners in all directions before using them for in vivo measurements.