Kranion, an open-source environment for planning transcranial focused ultrasound surgery: technical note

Abstract

Transcranial focused ultrasound (FUS) ablation is an emerging incision-less treatment for neurological disorders. The factors affecting FUS treatment efficiency are not well understood. Kranion is open-source software that allows the user to simulate the planning stages of FUS treatment and to “replay” previous treatments for off-line analysis. This study aimed to investigate the relationship between skull parameters and treatment efficiency and to create a metric to estimate temperature rise during FUS. CT images from 28 patients were analyzed to validate the use of Kranion. For stereotactic targets within each patient, individual transducer element incident angles, skull density ratio, and skull thickness measurements were recorded. A penetration metric (the “beam index”) was calculated by combining the energy loss from incident angles and the skull thickness. Kranion accurately estimated the patient’s skull and treatment parameters. The authors observed significant changes in incident angles with different targets in the brain. Using the beam index as a predictor of temperature rise in a linear-mixed-effects model, they were able to predict the average temperature rise at the focal point during ablation with < 21% error (55°C ± 3.8°C) in 75% of sonications, and with < 44% (55°C ± 7.9°C) in 97% of sonications. This research suggests that the beam index can improve the prediction of temperature rise during FUS. Additional work is required to study the relationship between temperature rise and lesion shape and clinical outcomes.

Comparison Between Ray-Tracing and Full-Wave Simulation for Transcranial Ultrasound Focusing on a Clinical System Using the Transfer Matrix Formalism

“…Jones et al report that the reconstructed images with the fullwave simulation corrections significantly reduced the PSLR, the shift of the detected emission position, the signal-to-noise ratio and the volume at -3dB as compared to images reconstructed with the ray-tracing correction. More recently, Paeng et al [58] compared the performance of the manufacturer's correction with Kranion, an open-source raytracing algorithm for transcranial aberration correction [18] where the skull is modeled as a single layer. On average, the correction from Insightec improves the restored pressure by more than 10% as compared to Kranion.…”

“…On average, the correction from Insightec improves the restored pressure by more than 10% as compared to Kranion. Since the Insightec ray-tracing algorithm is proprietary, it is difficult to compare it to other ray-tracing techniques previously published [18], [19], [76], and similarly, comparing different full-wave simulation algorithms [42], [48], [57], [76] without having access to the details of the code is limited. Nevertheless, the manufacturer ray-tracing simulation performed beyond our expectations.…”

“…acoustic stars [16], [17]) to non-invasive based on numerical simulations of the ultrasonic propagation through the skull bone with either ray-tracing [10], [18]- [20] angular spectrum [21]- [24], finite difference [25]- [32] or pseudo-spectral schemes [33]- [37]; or a combination of numerical phase estimation adjusted with echoes from injected micro-bubbles [38]. For all numerical methods, the acoustic properties such as density, speed of sound and attenuation are derived from CT or MR imaging of the skull bone [25], [39]- [42].…”

Focusing in on the Future of Focused Ultrasound as a Translational Tool

“…One such software is Kranion [ 23 ]. Kranion allows users to plan tFUS treatment and estimate thermal rise.…”

Technical Principles and Clinical Workflow of Transcranial MR-Guided Focused Ultrasound

“…These regions, along with sensitive neurovascular structures, can be blocked as “no-pass zones” using the MRgFUS system software, which turns off the number of active transducer elements to minimize energy deposition in these regions. Numerical simulations of transskull ultrasound propagation may provide the opportunity to investigate treatment feasibility preoperatively [37-39].…”