Doctor of Philosophy, Stanford University, BIOE-PHD (2021)
Master of Science, Stanford University, BIOE-MS (2015)
BSE, University of Pennsylvania, Bioengineering (2013)
Kim Pauly, Postdoctoral Faculty Sponsor
Transcranial focused ultrasound phase correction using the hybrid angular spectrum method.
2021; 11 (1): 6532
The InSightec Exablate system is the standard of care used for transcranial focused ultrasound ablation treatments in the United States. The system calculates phase corrections that account for aberrations caused by the human skull. This work investigates whether skull aberration correction can be improved by comparing the standard of care InSightec ray tracing method with the hybrid angular spectrum (HAS) method and the gold standard hydrophone method. Three degassed ex vivo human skulls were sonicated with a 670kHz hemispherical phased array transducer (InSightec Exablate 4000). Phase corrections were calculated using four different methods (straight ray tracing, InSightec ray tracing, HAS, and hydrophone) and were used to drive the transducer. 3D raster scans of the beam profiles were acquired using a hydrophone mounted on a 3-axis positioner system. Focal spots were evaluated using six metrics: pressure at the target, peak pressure, intensity at the target, peak intensity, positioning error, and focal spot volume. For three skulls, the InSightec ray tracing method achieved 52±21% normalized target intensity (normalized to hydrophone), 76±17% normalized peak intensity, and 0.72±0.47mm positioning error. The HAS method achieved 74±9% normalized target intensity, 81±9% normalized peak intensity, and 0.35±0.09mm positioning error. The InSightec-to-HAS improvement in focal spot targeting provides promise in improving treatment outcomes. These improvements to skull aberration correction are also highly relevant for the applications of focused ultrasound neuromodulation and blood brain barrier opening, which are currently being translated for human use.
View details for DOI 10.1038/s41598-021-85535-5
View details for PubMedID 33753771
Acoustic Attenuation: Multifrequency Measurement and Relationship To CT and MR Imaging.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control
Transcranial magnetic resonance guided focused ultrasound (tcMRgFUS) is gaining significant acceptance as a non-invasive treatment for motion disorders and shows promise for novel applications such as blood brain barrier opening for tumor treatment. A typical procedure relies on CT derived acoustic property maps to simulate the transfer of ultrasound through the skull. Accurate estimates of the acoustic attenuation in the skull are essential to accurate simulations, but there is no consensus about how attenuation should be estimated from CT images and there is interest in exploring MR as a predictor of attenuation in the skull. In this study we measure the acoustic attenuation at 0.5, 1, and 2.25 MHz in 89 samples taken from two ex-vivo human skulls. CT scans acquired with a variety of x-ray energies, reconstruction kernels, and reconstruction algorithms and MR images acquired with ultra short and zero echo time sequences are used to estimate the average Hounsfield unit value, MR magnitude, and T2* value in each sample. The measurements are used to develop a model of attenuation as a function of frequency and each individual imaging parameter.
View details for DOI 10.1109/TUFFC.2020.3039743
View details for PubMedID 33226938
Anatomic and Thermometric Analysis of Cranial Nerve Palsy after Laser Amygdalohippocampotomy for Mesial Temporal Lobe Epilepsy.
Operative neurosurgery (Hagerstown, Md.)
BACKGROUND: Laser interstitial thermal therapy (LITT) is a minimally invasive therapy for treating medication-resistant mesial temporal lobe epilepsy. Cranial nerve (CN) palsy has been reported as a procedural complication, but the mechanism of this complication is not understood.OBJECTIVE: To identify the cause of postoperative CN palsy after LITT.METHODS: Four medial temporal lobe epilepsy patients with CN palsy after LITT were identified for comparison with 22 consecutive patients with no palsy. We evaluated individual variation in the distance between CN III and the uncus, and CN IV and the parahippocampal gyrus using preoperative T1- and T2-weighted magnetic resonance (MR) images. Intraoperative MR thermometry was used to estimate temperature changes.RESULTS: CN III (n=2) and CN IV palsies (n=2) were reported. On preoperative imaging, the majority of identified CN III (54%) and CN IV (43%) were located within 1 to 2 mm of the uncus and parahippocampal gyrus tissue border, respectively. Affected CN III and CN IV were more likely to be found<1 mm of the tissue border (PCNIII=.03, PCNIV<.01; chi-squared test). Retrospective assessment of thermal profile during ablation showed higher temperature rise along the mesial temporal lobe tissue border in affected CNs than unaffected CNs after controlling for distance (12.9°C vs 5.8°C; P=.03; 2-sample t-test).CONCLUSION: CN palsy after LITT likely results from direct heating of the respective CN running at extreme proximity to the mesial temporal lobe. Low-temperature thresholds set at the border of the mesial temporal lobe in patients whose CNs are at close proximity may reduce this risk.
View details for DOI 10.1093/ons/opz279
View details for PubMedID 31555820
A rapid beam simulation framework for transcranial focused ultrasound.
2019; 9 (1): 7965
Transcranial focused ultrasound is a non-invasive therapeutic modality that can be used to treat essential tremor. Beams of energy are focused into a small spot in the thalamus, resulting in tissue heating and ablation. Here, we report on a rapid 3D numeric simulation framework that can be used to predict focal spot characteristics prior to the application of ultrasound. By comparing with magnetic resonance proton resonance frequency shift thermometry (MR thermometry) data acquired during treatments of essential tremor, we verified that our simulation framework can be used to predict focal spot position, and with patient-specific calibration, predict focal spot temperature rise. Preliminary data suggests that lateral smearing of the focal spot can be simulated. The framework may also be relevant for other therapeutic ultrasound applications such as blood brain barrier opening and neuromodulation.
View details for DOI 10.1038/s41598-019-43775-6
View details for PubMedID 31138821
Measurements of the Relationship Between CT Hounsfield Units and Acoustic Velocity and How It Changes With Photon Energy and Reconstruction Method
IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL
2018; 65 (7): 1111–24
Transcranial magnetic resonance-guided focused ultrasound continues to gain traction as a noninvasive treatment option for a variety of pathologies. Focusing ultrasound through the skull can be accomplished by adding a phase correction to each element of a hemispherical transducer array. The phase corrections are determined with acoustic simulations that rely on speed of sound estimates derived from CT scans. While several studies have investigated the relationship between acoustic velocity and CT Hounsfield units (HUs), these studies have largely ignored the impact of X-ray energy, reconstruction method, and reconstruction kernel on the measured HU, and therefore the estimated velocity, and none have measured the relationship directly. In this paper, 91 ex vivo human skull fragments from two skulls are imaged by 80 CT scans with a variety of energies and reconstruction methods. The average HU from each fragment is found for each scan and correlated with the speed of sound measured using a through transmission technique in that fragment. As measured by the -squared value, the results show that CT is able to account for 23%-53% of the variation in velocity in the human skull. Both the X-ray energy and the reconstruction technique significantly alter the -squared value and the linear relationship between HU and speed of sound in bone. Accounting for these variations will lead to more accurate phase corrections and more efficient transmission of acoustic energy through the skull.
View details for DOI 10.1109/TUFFC.2018.2827899
View details for Web of Science ID 000436933000004
View details for PubMedID 29993366