| dc.description.abstract | Focused ultrasound (FUS) is a non-invasive therapeutic technology that can use ultrasonic energy to precisely target tissue deep inside the body without incisions or radiation. However, for the safety and credibility of FUS applications in the clinic, challenges of rapidly and quantitatively visualizing FUS field in free field and in in vivo brains still exist and need to be further overcome.
Firstly, good knowledge of the acoustic output of FUS transducers is essential for safety, quality assurance, research, and development of FUS treatment. Several techniques have been developed, such as hydrophones and radiation force balances. However, no portable and fast method directly provides quantitative spatially resolved beam maps at therapeutic pressure levels. This dissertation presents a rapid projection imaging method to characterize acoustic pressure fields of FUS transducers based on background-oriented schlieren (BOS) imaging. This method requires only a background pattern, a water tank, and a camera. It can rapidly provide a quantitative projected measurement of FUS pressure fields using a deep neural network with high spatial resolutions.
Secondly, magnetic resonance imaging (MRI) guidance is powerful for FUS to confirm that the FUS beam focuses on the target anatomy during ultrasound therapy. MR acoustic radiation force imaging (MR-ARFI) can detect tissue displacements by using motion encoding gradients and a series of short FUS bursts. However, MR-ARFI is not fast enough for the low duty cycle (<1%) FUS applied in nonthermal applications (e.g., neuromodulation), and a relatively long FUS pulse may induce heat deposition. This work developed a reduced-FOV 3D MR-ARFI sequence with a low-rank reconstruction for targeting transcranial focused ultrasound with a scan time of two minutes twenty seconds and a low FUS duty cycle of 0.85%. The presented work will enhance the procedure of targeting the focus, especially when it needs to be repeated many times when finding, steering, or phase-correcting the focus.
This dissertation presents advanced techniques in the visualization of therapeutic FUS to rapidly map the acoustic pressure fields of FUS transducers in the free field based on BOS imaging and target FUS beams in the in vivo brain via MR-ARFI with high resolution and accuracy. | |
