Utilizing an Agar/Silica Phantom for Magnetic Resonance Imaging-guided Focused Ultrasound Evaluation: Lesion...

In preclinical research, agar-based tissue-mimicking phantoms have proven to be valuable tools for magnetic resonance imaging (MRI)-guided focused ultrasound (MRgFUS) evaluations. This study evaluates an agar-based silica-doped phantom for MRgFUS, examining main properties, MRI appearance, and thermal lesion formation in comparison with excised porcine tissue.

The proposed agar/silica phantom was subjected to various single and grid sonication protocols in a 3T MRI scanner, with thermal effects monitored intraprocedurally through magnetic resonance thermometry and postsonication through T2-Weighted (T2-W) Turbo Spin Echo (TSE) imaging. The accuracy of lesion formation according to planned patterns and lesion visibility on T2-W TSE images were assessed. To establish the lesion detection threshold, phantom exposure was gradually increased, with identical sonication protocols repeated to assess repeatability. Grid sonications were also conducted on excised porcine tissue for comparison.

The phantom facilitated lesion formation across various patterns and depths without significant shifting effects, exhibiting lesions with excellent contrast on T2-W images and adaptability to variations in power and pulse duration settings. In contrast, excised tissue exhibited abnormal temperature fluctuations during grid sonications and lesion shifting. The minimum focal temperature required to generate a measurable lesion on T2-W images was 39°C (thermal dose threshold of 1.49 × 10^-4 CEM43°C), with lesion sizes increasing proportionally to energy levels. A comparison of thermal profiling in repeated sonications demonstrated good repeatability.

This study confirms that the agar/silica phantom provides a reliable, reproducible platform for MRgFUS assessment, improving lesion visualization, and calibration for preclinical studies.