# Passive antennas for improved image quality in transcranial MR-guided focused ultrasound

> **NIH NIH R21** · VANDERBILT UNIVERSITY MEDICAL CENTER · 2021 · $203,523

## Abstract

Project Summary/Abstract
Transcranial MR-guided focused ultrasound (tcMRgFUS) neurosurgery is a non-invasive treatment for
essential tremor, neuropathic pain, and many emerging applications. tcMRgFUS systems have a water bath
that couples acoustic energy into the head and is circulated to cool the scalp between sonications. The water
bath, however, also acts as a high permittivity dielectric with a much shorter RF wavelength than free space. At
the same time, the transducer bowl is electrically conductive, so when the electromagnetic waves generated by
the MRI scanner for imaging enter the bath, they travel through the bath in the transducer bowl and reflect off
the bowl’s inner surface above the head. The reflected waves then cancel with the incoming waves which
causes a dark band with very low MR signal in the images, and generally low signal throughout the brain. The
low signal limits the types of scans that can be used to guide and assess tcMRgFUS treatment, especially spin
echo scans such as diffusion which could enable earlier lesion and tractography-based assessment. To
address this problem, we propose to develop a novel passive reflecting antenna that will sit in the water bath
above the head, and will create its own wave reflection that can be controlled so as to add constructively with
the incoming wave, thereby restoring the MR signal to levels commensurate with imaging outside the
transducer. The wires will require no electrical connections and can be made very thin to avoid disturbing the
ultrasound beam. We also propose to develop a complementary ring of passive loop coils that would sit
outside the bottom of the transducer and further increase the fields in the brain. We will use electromagnetic
simulations of a tcMRgFUS system in an MRI scanner to optimize the antennas and loop coils, design
mechanical holders for them that do not disturb the ultrasound beams and do not require modifying the
transducer, and then evaluate them in MR imaging of healthy volunteers in a clinical tcMRgFUS system.

## Key facts

- **NIH application ID:** 10148771
- **Project number:** 5R21EB029639-02
- **Recipient organization:** VANDERBILT UNIVERSITY MEDICAL CENTER
- **Principal Investigator:** Xinqiang Yan
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $203,523
- **Award type:** 5
- **Project period:** 2020-05-01 → 2023-01-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10148771

## Citation

> US National Institutes of Health, RePORTER application 10148771, Passive antennas for improved image quality in transcranial MR-guided focused ultrasound (5R21EB029639-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10148771. Licensed CC0.

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