Focused Ultrasound Lab

• This project proposed an effective and practical reconstruction pipeline to achieve motion-robust, multi-slice, real-time MR thermometry for monitoring thermal therapy in abdominal organs.
• The application includes a fast spiral MRI pulse sequence and a real-time reconstruction pipeline based on multi-baseline proton resonance frequency shift (PRFS) method with visualization of temperature imaging.
• The pipeline supports multi-slice acquisition with minimal reconstruction lag. Simulations with a virtual motion phantom were performed to investigate the influence of the number of baselines and respiratory rate on the accuracy of temperature measurement.

The result of healthy volunteer experiments without heating (volunteer #1). (a) A coronal slice is acquired and shows the left and right kidney organs which are indicated with blue dashed lines. PRFS temperature maps show that a (c) multi-baseline PRFS reconstruction allows stable and homogeneous temperature measurements, compared to a (b) single baseline

Motion phantom

• In this project, we developed a low-cost and simple MR-compatible respiratory motion simulator to support proof-of-concept studies of MR monitoring approaches with respiratory-induced abdominal organ motion.
• The phantom motion system integrates pneumatic control via an actuator subsystem located outside the MRI and coupled via plastic tubing to a compressible bag for distention and retraction within the MRI safe motion subsystem and phantom positioned within the MRI scanner.

Publication

• K. Kim, P. Jones, C. Diederich, E. Ozhinsky. Technical Note: Low-cost MR-compatible pneumatic respiratory organ simulator for development of MR-guided thermal therapy. Medical Physics, 00:1-7, 2022.
• K. Kim, C. Diederich, K. Narsinh, E. Ozhinsky. Motion-robust, multi-slice, real-time MR Thermometry for MR-guided thermal therapy in abdominal organs. International Journal of Hyperthermia, 40(1):2151649, 2023.

• This project proposed electronic beam steering, multi-focal patterns, and sector vortex beamforming approaches in conjunction with partial array activation.
• Turning off a percentage of the outer array to increase the f-number increased the focal size with a decrease in focal gain.
• Sonications with the vortex mode number 4 provided the focused pressure fields around the axis of the beam and the heated volume was enlarged, for higher mode numbers and for lower number of active elements.
• We developed an acoustic and thermal simulation framework to calculate the 3D acoustic intensity and temperature distribution resulting from the proposed beamforming and scanning strategies.
• This project demonstrated the feasibility of large volume hyperthermia beam patterns using the ExAblate body system.

Publication

• K Kim, M Zubair, M Adams, CJ Diederich, E Ozhinsky, Sonication strategies toward volumetric ultrasound hyperthermia treatment using the ExAblate body MRgFUS system, International Journal of Hyperthermia, 38 (1), 1590-1600, 2021

• Feasibility of prostate hyperthermia with endorectal ultrasound applicators has been demonstrated in clinical trials
• This project presents a real-time MR thermometry-guided system for hyperthermia delivery within constrained regions with the ExAblate prostate array and validated it in phantom experiments.
• We developed real-time MR Thermometry platform to control the focus and power output of the ultrasound beam, ensuring constant and uniform heating within the region of treatment.

Publication

• E Ozhinsky, V Salgaonkar, C Diederich, V Rieke, MR thermometry-guided ultrasound hyperthermia of user-defined regions using the ExAblate prostate ablation array, Journal of Therapeutic Ultrasound, 6, 2018 

• Proton resonant frequency shift (PRF) thermometry fails to detect temperature change in tissues with high lipid content, such as bone marrow.
• Current clinical protocols rely on measurement of temperature change of adjacent muscle
• Poor accuracy of temperature measurement, sub-optimal ablation
• Here, we developed T2-based thermometry to monitor the temperature in bone marrow during focused ultrasound ablation.
• We measured a T2 elevation of 269 ms. Assuming the T2/temp coefficient of 7 ms/°C, this corresponds to a temperature rise of 38°C. The ex-vivo experiment shows that it takes 10-15 minutes for the marrow to return to the baseline temperature.
• The in-vivo experiment showed excellent correspondence between the area of T2 elevation in marrow during the ablation and the resulting non-enhancing area in the post-contrast images.

Publication

• E Ozhinsky, M Han, M Bucknor, R Krug, V Rieke. T2-based temperature monitoring in bone marrow for MR-guided focused ultrasound. Journal of Therapeutic Ultrasound, 17;4:26, 2016.

• Desmoid tumors are benign but locally aggressive soft tissue tumors that arise from fibroblast cells.

• The gold-standard assessment of the reduction of viable tumor volume post-treatment is non-perfused volume (NPV). Evaluation of NPV is typically performed with post-treatment gadolinium enhanced MR imaging. As gadolinium cannot be repeatedly administered during treatments, there is a need for alternative non-contrast monitoring of the tissue to prevent over and under treatment.

• The objective of this study was to develop an alternative method of non-contrast monitoring of tissue ablation during focused ultrasound treatment.

• Double-echo and multi-echo images were acquired before, during and after the MRgFUS treatment. T2 maps were generated with an exponential fit and T2 maps were compared to post-treatment post-contrast images. T2 mapping showed excellent qualitative agreement with the post-contrast NPV.

• This study showed that T2 mapping may be used to visualize the extent of ablation with focused ultrasound and can be used as a predictor of NPV prior to the administration of contrast.

Publication

• S Morochnik, E Ozhinsky, V Rieke, M Bucknor, T2 mapping as a predictor of nonperfused volume in MRgFUS treatment of desmoid tumors, International Journal of Hyperthermia, 35(1):1271-1276, 2019.

• The goal of this study was to investigate near-field heating in patients treated with the InSightec fibroid system.
• Accurate measurement of near-field heating in adipose tissue: shorter treatments and preventing injury in healthy tissues

Publication

• E Ozhinsky, MP Kohi, P Ghanouni, V Rieke, T2-based temperature monitoring in abdominal fat during MR-guided focused ultrasound treatment of patients with uterine fibroids, Journal of Therapeutic Ultrasound, 3:15, 2015.