Image‐guided navigation of single‐element focused ultrasound transducer
Hyungmin Kim, Alan Chiu, Shinsuk Park, Seung‐Schik Yoo
International Journal of Imaging Systems and Technology 2012 · 10.1002/ima.22020
Abstract
The spatial specificity and controllability of focused ultrasound (FUS), in addition to its ability to modify the excitability of neural tissue, allows for the selective and reversible neuromodulation of the brain function, with great potential in neurotherapeutics. Intra-operative magnetic resonance imaging (MRI) guidance (in short, MRg) has limitations due to its complicated examination logistics, such as fixation through skull screws to mount the stereotactic frame, simultaneous sonication in the MRI environment, and restrictions in choosing MR-compatible materials. In order to overcome these limitations, an image-guidance system based on optical tracking and pre-operative imaging data is developed, separating the imaging acquisition for guidance and sonication procedure for treatment. Techniques to define the local coordinates of the focal point of sonication are presented. First, mechanical calibration detects the concentric rotational motion of a rigid-body optical tracker, attached to a straight rod mimicking the sonication path, pivoted at the virtual FUS focus. The spatial error presented in the mechanical calibration was compensated further by MRI-based calibration, which estimates the spatial offset between the navigated focal point and the ground-truth location of the sonication focus obtained from a temperature-sensitive MR sequence. MRI-based calibration offered a significant decrease in spatial errors (1.9±0.8 mm; 57% reduction) compared to the mechanical calibration method alone (4.4±0.9 mm). Using the presented method, pulse-mode FUS was applied to the motor area of the rat brain, and successfully stimulated the motor cortex. The presented techniques can be readily adapted for the transcranial application of FUS to intact human brain.
Abstract via europepmc.
Exposures
Exposure 1: 350 kHz pulsed FUS to rat motor cortex (tail area) with image-guided navigation
Target: motor cortex — “the motor area of the rat brain”
Device: other named manufacturer · SensMed · Sonomo ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 350 | ✓✓✓ |
| Pulse duration (ms) | 0.5 | ✓✓✓ |
| Pulse repetition frequency (Hz) | 1,000 | ✓✓✓ |
| Duty cycle (%) | 50pulse duration × PRF gives 50% | ✓✓✓ |
| Sonication duration (s) | 0.3 | ✓✓✓⚑ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | deratingsingle value | |
| In-situ pressure (kPa) | 500 | ✓✓✓⚑ |
| In-situ Isppa (W/cm²) | 9.1 | ✓✓✓ |
| In-situ Ispta (W/cm²) | 4.5 | ✓✓✓ |
Pulse-repetition frequency of 1 kHz, tone-burst duration of 0.5 ms, sonication duration of 300 ms and a sonication interval of 2 s, delivered to the site about 2 mm posterior to bregma on the midline.
Flags from extraction
exposures[0].in_situ.pressure_kpa— Values stated after applying an assumed 87% rodent skull attenuation from the literature (derating by the authors); free-field values for the in vivo exposure are not given.exposures[0].device.family— SensMed is not a listed family; recorded as other_manufacturer. Quote names the transducer as Sonomo, SensMed.exposures[0].timing.sonication_duration_s— Recorded in ms in the paper (300 ms), converted to 0.3 s.