Real‐time 3D target tracking in MRI guided focused ultrasound ablations in moving tissues

Abstract

Magnetic resonance imaging-guided high intensity focused ultrasound is a promising method for the noninvasive ablation of pathological tissue in abdominal organs such as liver and kidney. Due to the high perfusion rates of these organs, sustained sonications are required to achieve a sufficiently high temperature elevation to induce necrosis. However, the constant displacement of the target due to the respiratory cycle render continuous ablations challenging, since dynamic repositioning of the focal point is required. This study demonstrates subsecond 3D high intensity focused ultrasound-beam steering under magnetic resonance-guidance for the real-time compensation of respiratory motion. The target is observed in 3D space by coupling rapid 2D magnetic resonance-imaging with prospective slice tracking based on pencil-beam navigator echoes. The magnetic resonance-data is processed in real-time by a computationally efficient reconstruction pipeline, which provides the position, the temperature and the thermal dose on-the-fly, and which feeds corrections into the high intensity focused ultrasound-ablator. The effect of the residual update latency is reduced by using a 3D Kalman-predictor for trajectory anticipation. The suggested method is characterized with phantom experiments and verified in vivo on porcine kidney. The results show that for update frequencies of more than 10 Hz and latencies of less then 114 msec, temperature elevations can be achieved, which are comparable to static experiments. Magn Reson Med 64:1704-1712,

Spectrally selective pencil‐beam navigator for motion compensation of MR‐guided high‐intensity focused ultrasound therapy of abdominal organs

“…17. The remaining periodic phase fluctuations due to respiratory motion were corrected using a multibaseline approach where the look-up table was indexed according to the kidney displacement estimate obtained by the navigator as explained by Ries et al (17). The calculation of the PRF-based temperature maps and the employed corrections are described in detail by Roujol et al (14).…”

“…The time needed for acquisition (after passage of the k-space center) and data transport (64 ms), image reconstruction and motion estimation (40 ms), and HIFU focal point update (10 ms) resulted in a focal point position update latency of 114 ms. Details on the employed beam steering strategy, including the required calculations and their timings, are given by Ries et al (17).…”

Three-dimensional MRI-linac intra-fraction guidance using multiple orthogonal cine-MRI planes

“…Yun et al (2012a) describes how the auto-contouring algorithm of Yun et al (2012b) can be extended with an artificial neural network-based motion prediction algorithm. Ries et al (2010) performed 3D target tracking by combining 2D-plane imaging with prospective slice tracking based on pencil-beam navigator sequences. The effect of the update latency was reduced using a Kalman predictor for trajectory anticipation.…”

Effects of Respiratory Liver Motion on Heating for Gated and Model-Based Motion-Compensated High-Intensity Focused Ultrasound Ablation

“…High-intensity focused ultrasound (HIFU) ablation is being increasingly studied as a non-invasive treatment option for liver cancer [1][2][3]. However, liver respiratory motion can be up to a few centimetres under normal free-breathing conditions [4,5].…”