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portfolio
CV
Last update: 05/01/2025
publications
Transcranial MR-Guided Histotripsy System
Published in IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control (Front Cover Article), 2021
Abstract: This study develops the first transcranial MR-guided histotripsy (tcMRgHt) system for in vivo brain treatment. A 700 kHz, 128-element MR-compatible ultrasound transducer was designed, achieving peak negative pressures of 137 MPa in free field and 72 MPa through a skull with aberration correction. The system is MR-compatible and enabled electronic focal steering. In vivo testing in pigs demonstrated successful targeted brain tissue ablation without excessive bleeding or edema. The results confirm the feasibility of using tcMRgHt for transcranial treatment in a swine model.
Recommended citation: N. Lu, et al (2021). "Transcranial MR-Guided Histotripsy System." IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 68(9).
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Transcranial magnetic resonance-guided histotripsy for brain surgery: pre-clinical investigation
Published in Ultrasound in medicine & biology, 2022
Abstract: This study evaluates the in vivo feasibility of transcranial MR-guided histotripsy (tcMRgHt) for brain surgery. Using a 700 kHz, 128-element MR-compatible transducer inside a 3T MRI scanner, histotripsy was delivered to eight pigs through an excised human calvarium after craniotomy. MRI scans before and after treatment confirmed well-confined lesions without excessive edema or hemorrhage. Histology showed precise tissue ablation, correlating with MRI findings. These results demonstrate the first in vivo feasibility of tcMRgHt in the pig brain, supporting further investigation for clinical brain surgery applications.
Recommended citation: N. Lu, et al. (2022). "Transcranial magnetic resonance-guided histotripsy for brain surgery: pre-clinical investigation." Ultrasound in medicine & biology. 48(1).
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Two-step aberration correction: application to transcranial histotripsy
Published in Physics in Medicine & Biology, 2022
Abstract: Phase aberration correction (AC) is crucial in transcranial histotripsy to correct for the skull-induced focal distortion. This paper enhances a 2-step AC method for clinical use, combining a CT-based analytical approach with a cavitation-based approach using acoustic cavitation emission (ACE). A 700 kHz, 360-element hemispherical transducer was used to generate histotripsy-induced cavitation and acquire ACE shockwaves. Testing on excised human skulls showed that the 2-step AC achieved 90 ± 7% peak focal pressure, reduced focal shift, and improved refocusing compared to individual AC methods. This real-time AC workflow enhances transcranial histotripsy for brain therapy.
Recommended citation: N. Lu, et al. (2022). "Two-step aberration correction: application to transcranial histotripsy." Physics in Medicine & Biology. 67(12).
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Accurate and Robust Eye Tracking with Ultrasound: A Computational Study
Published in 2023 IEEE International Ultrasonics Symposium (IUS), 2023
Abstract: This paper introduces an ultrasound simulation platform for generating realistic eye-tracking data, accounting for transducer design, sensor noise, occlusions, and headset slippage. Using a face/eye model with adjustable gaze and eyelid opening, synthesized data were input into a machine learning algorithm to estimate gaze and slippage. The system achieved a gaze RMSE of 0.085° without slippage and 0.756° with slippage. This end-to-end pipeline supports the optimization of wearable ultrasound devices and explores ultrasound as a complementary technology to camera-based eye tracking for AR/VR applications.
Recommended citation: N. Lu, et al. (2023). "Accurate and Robust Eye Tracking with Ultrasound: A Computational Study." 2023 IEEE International Ultrasonics Symposium (IUS) Proceedings.
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Treatment envelope of transcranial histotripsy: challenges and strategies to maximize the treatment location profile
Published in Physics in Medicine & Biology, 2024
Abstract: A 750 kHz, 360-element ultrasound array was developed for transcranial histotripsy. This study evaluates its performance using experiments and simulations in human skulls. Results show that treatment efficacy depends on skull properties, with shallow targets facing greater challenges due to attenuation and pre-focal pressure hotspots. Strategies such as array design optimization and pose adjustment are proposed to enhance treatment. These findings guide the development of next-generation histotripsy arrays for clinical applications.
Recommended citation: N. Lu, et al. (2024). "Treatment envelope of transcranial histotripsy: challenges and strategies to maximize the treatment location profile." Physics in Medicine & Biology. 69(22).
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talks
Transcranial MR-Guided Histotripsy Treatment: An In-Vivo Pig Study
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Real-time volumetric spine imaging for interventional guidance with a large-aperture array
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teaching
Teaching Assistant: Medical Imaging System
BME/EECS 516 (graduate course), University of Michigan, Department of Biomedical Engineering, 2022
Teaching assistant for ultrasound lab.
Guest Lecturer: 3D+ Imaging Sensors
EE 119/219 (undergraduate & graduate course), Stanford University, Department of Electrical Engineering, 2024
Lecture Preview
This lecture will introduce students to state-of-the-art topics in the field of ultrasound imaging. We will start with brief reviews of the ultrasound fundamentals, and then move on to discuss the hardware (transducer, array, and system), imaging sequences, and beamforming methods. We will conclude by discussing the real-world challenges, emerging applications, and advanced ultrasound techniques including ultrafast imaging, super-resolution imaging, aberration correction, etc. Live demo and hands-on experience using a commercial ultrasound system will be provided to the students. If time permits, we’ll also introduce ultrasound simulation software which can be helpful for students who are interested in ultrasound-related projects.