Three‐dimensional spatial and temporal temperature control with MR thermometry‐guided focused ultrasound (MRgHIFU)

Abstract

High-intensity focused ultrasound (HIFU) is an efficient noninvasive technique for local heating. Using MRI thermal maps, a proportional, integral, and derivative (PID) automatic temperature control was previously applied at the focal point, or at several points within a plane perpendicular to the beam axis using a multispiral focal point trajectory. This study presents a flexible and rapid method to extend the spatial PID temperature control to three dimensions during each MR dynamic. The temperature in the complete volume is regulated by taking into account the overlap effect of nearby sonication points, which tends to enlarge the heated area along the beam axis. Volumetric temperature control in vitro in gel and in vivo in rabbit leg muscle was shown to provide temperature control with a precision close to that of the temperature MRI measurements. High-intensity focused ultrasound (HIFU) is an efficient noninvasive technique to produce local heating deep inside the human body (1,2). MRI provides excellent visualization of anatomical structures and tumors for treatment planning (3). In addition, MRI can provide continuous temperature mapping based on the proton resonance frequency (PRF) shift of water with a good spatial and temporal resolution (4,5) for real-time therapy control. New MRI developments in high-field, rapid imaging and magnet field stability have contributed to the performance of MRI temperature mapping. In parallel, major improvement in ultrasound technology have been made in the field of phased-array MR-compatible transducers (6). These recent developments offer the possibility to treat several points simultaneously and in a minimal amount of time.Automatic control of the temperature (7) or the thermal dose effect (8) during HIFU heating has been shown to be feasible. Using rapid temperature MRI methods and realtime data processing, an automatic proportional, integral, and derivative (PID) temperature feedback loop has been presented to control the temperature in a single point, the HIFU focal spot (9). This temperature control method has been extended to several points (10) using a multispiral trajectory of the HIFU focal point within a single plane perpendicular to the beam axis. In the latter method, the energy deposition during the next multispiral trajectory is calculated upon completion of the previous one. The resulting volume treated in three dimensions is deduced from numerical simulations. The focal point trajectory remains in a plane perpendicular to the beam axis since the overlap of the acoustic field for each focal point location presents difficulties for volumetric temperature control along the beam axis.Here, a novel method is proposed for volumetric temperature regulation with temperature control for each voxel of the predefined volume by taking into account beam overlap for the different sonication points. The optimum focal point locations and HIFU intensities are determined following each volumetric temperature map, leading to a rapid and flexible method. The new method was ...

Planning, optimisation and evaluation of hyperthermia treatments

“…Treatment optimisation to improve clinical outcome is an important application, but because of the uncertainties in tissue properties treatment limiting hot spots might still occur after pre-treatment optimisation. Some research groups explore the possibility to combine treatment planning with MRI feedback [81][82][83], but this requires MR-compatibility of the heating system. Therefore also on-line adaptive use of treatment planning is currently investigated [84][85][86].…”

Enhancement of Apoptosis by Titanium Alloy Internal Fixations During Microwave Treatments for Fractures: An Animal Study

“…Histological examinations of the skeletal muscles in pigs have showed that the minor damage can occur at 30 CEM 43 [25]. A thermal dose scale of 240 CEM 43 has been established for the leg muscles of rabbits and pigs and this dose is an irreversible lethal dose to the tissue cells [26][27][28]. In the implanted group, the results revealed that the temperature increases in the muscles in front of the titanium alloy implants were less than 41°C.…”

Coagulation of human prostate volumes with MRI-controlled transurethral ultrasound therapy: Results in gel phantoms

“…Recent studies have demonstrated for different resolutions and FOVs that increased TE (18-34 ms) can be achieved with multislice coverage (4-6 slices) and short acquisition times (∼0.5-3 s) using segmented echo-planar imaging (EPI) approaches. [51][52][53] Nonetheless, the MR thermometry sequence implemented for this study enabled us to implement multiplanar temperature control for transurethral ultrasound therapy and achieve successful treatments of whole-prostate volumes with geometries that are representative of what would be encountered clinically. This study highlighted the important roles of frequency and power for transurethral ultrasound therapy.…”