Improved Volumetric MR-HIFU Ablation by Robust Binary Feedback Control

Abstract

Volumetric high-intensity focused ultrasound (HIFU) guided by multiplane magnetic resonance (MR) thermometry has been shown to be a safe and efficient method to thermally ablate large tissue volumes. However, the induced temperature rise and thermal lesions show significant variability, depending on exposure parameters, such as power and timing, as well as unknown tissue parameters. In this study, a simple and robust feedback-control method that relies on rapid MR thermometry to control the HIFU exposure during heating is introduced. The binary feedback algorithm adjusts the durations of the concentric ablation circles within the target volume to reach an optimal temperature. The efficacy of the binary feedback control was evaluated by performing 90 ablations in vivo and comparing the results with simulations. Feedback control of the sonications improved the reproducibility of the induced lesion size. The standard deviation of the diameter was reduced by factors of 1.9, 7.2, 5.0, and 3.4 for 4-, 8-, 12-, and 16-mm lesions, respectively. Energy efficiency was also improved, as the binary feedback method required less energy to create the desired lesion. These results show that binary feedback improves the quality of volumetric ablation by consistently producing thermal lesions of expected size while reducing the required energy as well.

Enhancement of High-Intensity Focused Ultrasound Heating by Short-Pulse Generated Cavitation

“…The energy efficiencies calculated from the ratio of coagulation volume to total acoustic energy were 1.7 and 1.0 mm 3 /J with spot scanning and direct synthesis, respectively. Even with direct synthesis, the efficiency was 1.0 mm 3 /J, which was comparable to those in volumetric HIFU ablation studies [68][69][70], for example, the ratios of 240 equivalent minutes (EM) uterine fibroids volume to applied energy of 0.29 and 0.91 mm 3 /J with treatment cell sizes of 8 and 16 mm, respectively [70]. As a result, the spot scanning trigger pulses followed by the spot scanning heating bursts achieved an efficient heating and those followed by the heating bursts with a directly synthesized focus generated a coagulation region with high efficiency and predictability.…”

“…Methods of focal spot scanning have been investigated for highly efficient ultrasonic heating [67][68][69][70][71]. In the studies, the distribution of estimated temperature was used as a feedback information to obtain uniform thermal doses in the larger target regions than that by a conventional HIFU exposure.…”

MR-Guided HIFU Treatment of Symptomatic Uterine Fibroids Using Novel Feedback-Regulated Volumetric Ablation: Effectiveness and Clinical Practice

“…In total, the treatment time remains a limiting factor of HIFU treatment. The goal of the feedback mechanism is to ensure a sufficient sonication as well as to prevent excessive temperature increases, thus further increasing patient safety [16]. Multiplanar real-time MR thermometry makes it possible to effectively monitor the ablation volume and structures at an increased risk in the near and far field [20].…”

Reduction of peak acoustic pressure and shaping of heated region by use of multifoci sonications in MR‐guided high‐intensity focused ultrasound mediated mild hyperthermia

“…• C) has been used as a definitive treatment for accessible solid tumors not amenable to surgery, whereas mild hyperthermia (40)(41)(42)(43)(44)(45) • C) has been shown effective as an adjuvant for both radiotherapy and chemotherapy. An optimal mild hyperthermia treatment is spatially accurate, with precise and homogeneous heating limited to the target region while also limiting the likelihood of unwanted thermal or mechanical bioeffects (tissue damage, vascular shutoff).…”