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Hiroki Hori, Toshio Yamaguchi, Yoshiyuki Konishi, Takaomi Taira, and Yoshihiro Muragaki

OBJECTIVE

This study evaluated changes of fractional anisotropy (FA) in the ventral intermediate nucleus (VIM) of the thalamus after transcranial MR-guided focused ultrasound (TcMRgFUS) thalamotomy and their associations with clinical outcome.

METHODS

Clinical and radiological data of 12 patients with medically refractory essential tremor (mean age 76.5 years) who underwent TcMRgFUS thalamotomy with VIM targeting were analyzed retrospectively. The Clinical Rating Scale for Tremor (CRST) score was calculated before and at 1 year after treatment. Measurements of the relative FA (rFA) values, defined as ratio of the FA value in the targeted VIM to the FA value in the contralateral VIM, were performed before thalamotomy, and 1 day and 1 year thereafter.

RESULTS

TcMRgFUS thalamotomy was well tolerated and no long-term complications were noted. At 1-year follow-up, 8 patients demonstrated relief of tremor (improvement group), whereas in 4 others persistent tremor was noted (recurrence group). In the entire cohort, mean rFA values in the targeted VIM before treatment, and at 1 day and 1 year after treatment, were 1.12 ± 0.15, 0.44 ± 0.13, and 0.82 ± 0.22, respectively (p < 0.001). rFA values were consistently higher in the recurrence group compared with the improvement group, and the difference reached statistical significance at 1 day (p < 0.05) and 1 year (p < 0.01) after treatment. There was a statistically significant (p < 0.01) positive correlation between rFA values in the targeted VIM at 1 day after thalamotomy and CRST score at 1 year after treatment. Receiver operating characteristic curve analysis revealed that the optimal cutoff value of rFA at 1 day after thalamotomy for prediction of symptomatic improvement at 1-year follow-up is 0.54.

CONCLUSIONS

TcMRgFUS thalamotomy results in significant decrease of rFA in the targeted VIM, at both 1 day and 1 year after treatment. Relative FA values at 1 day after treatment showed significant correlation with CRST score at 1-year follow-up. Therefore, FA may be considered a possible imaging biomarker for early prediction of clinical outcome after TcMRgFUS thalamotomy for essential tremor.

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Yongqin Xiong, Jianfeng He, and Xin Lou

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Shiro Horisawa, Toshio Yamaguchi, Keiichi Abe, Hiroki Hori, Masatake Sumi, Yoshiyuki Konishi, and Takaomi Taira

Musician’s dystonia (MD) is a type of focal hand dystonia that develops only while playing musical instruments and interferes with skilled and fine movements. Lesioning of the ventro-oral (Vo) nucleus of the thalamus (Vo-thalamotomy) using radiofrequency can cause dramatic improvement in MD symptoms. Focused ultrasound (FUS) can make intracranial focal lesions without an incision. The authors used MRI-guided FUS (MRgFUS) to create a lesion on the Vo nucleus to treat a patient with MD. Tubiana’s MD scale (TMDS) was used to evaluate the condition of musical play ranging from 1 to 5 (1: worst, 5: best). The patient was a 35-year-old right-handed man with involuntary flexion of the right second, third, and fourth fingers, which occurred while playing a classical guitar. Immediately after therapeutic sonications of FUS Vo-thalamotomy, there was dramatic improvement in the MD symptoms. The TMDS scores before; at 0 and 1 week after; and at 1, 3, 6, and 12 months after MRgFUS Vo-thalamotomy were 1, 4, 4, 5, 5, 5, and 5, respectively. No complications were observed. Focused ultrasound Vo-thalamotomy can be an effective treatment for MD.

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Kazuaki Yamamoto, Hisashi Ito, Shigeru Fukutake, Takashi Odo, Tetsumasa Kamei, Toshio Yamaguchi, and Takaomi Taira

Transcranial MR-guided focused ultrasound (MRgFUS) therapy is a less invasive form of stereotactic treatment for tremors and other movement disorders. Its stereotactic accuracy is ensured by stability of the stereotactic frame and MR table. The authors report a case wherein the patient’s movement was detected, and the MR images were repeated to continue the treatment.

A 72-year-old man with essential tremor underwent unilateral ventralis intermedius thalamotomy using MRgFUS. The stereotactic frame was correctly fixed to the patient’s skull and the table. During the seventh sonication, the patient pressed the emergency button and vomited several times. Before the eighth sonication, the patient’s movement was detected and was verified on coronal images. The MR images were repeated, and the treatment was successfully completed with significant improvement in the tremors. After treatment, it was discovered that the MR table was laterally unstable due to the absence of ball bearings, which should be present on both sides of the guide rail of the MR table. The ball bearings were attached to the reverse side of the table, and the table was stabilized. Stereotactic accuracy of MRgFUS is not only ensured by rigid fixation of the stereotactic frame, but also by stability of the MR table.

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Hiroki Hori, Hirokazu Iwamuro, Masayuki Nakano, Takahiro Ouchi, Takashi Kawahara, Takaomi Taira, Keiichi Abe, Ken Iijima, and Toshio Yamaguchi

OBJECTIVE

In transcranial magnetic resonance imaging–guided focused ultrasound (TcMRgFUS), a high skull density ratio (SDR) is advantageous to achieve a sufficiently high temperature at the target. However, it is not easy to estimate the temperature rise because the SDR shows different values depending on the reconstruction filter used. The resolution characteristic of a computed tomography (CT) image depends on a modulation transfer function (MTF) defined by the reconstruction filter. Differences in MTF induce unstable SDRs. The purpose of this study was both to standardize SDR by developing a method to correct the MTF and to enable effective patient screening prior to TcMRgFUS treatment and more accurate predictions of focal temperature.

METHODS

CT images of a skull phantom and five subjects were obtained using eight different reconstruction filters. A frequency filter (FF) was calculated using the MTF of each reconstruction filter, and the validity of SDR standardization was evaluated by comparing the variation in SDR before and after FF correction. Subsequently, FF processing was similarly performed using the CT images of 18 patients who had undergone TcMRgFUS, and statistical analyses were performed comparing the relationship between the SDRs before and after correction and the maximum temperature in the target during TcMRgFUS treatment.

RESULTS

The FF was calculated for each reconstruction filter based on one manufacturer's BONE filter. In the CT images of the skull phantom, the SDR before FF correction with five of the other seven reconstruction filters was significantly smaller than that with the BONE filter (p < 0.01). After FF correction, however, a significant difference was recognized under only one condition. In the CT images of the five subjects, variation of the SDR due to imaging conditions was significantly improved after the FF correction. In 18 cases treated with TcMRgFUS, there was no correlation between SDR before FF correction and maximum temperature (rs = 0.31, p > 0.05); however, a strong positive correlation was observed after FF correction (rs = 0.71, p < 0.01).

CONCLUSIONS

After FF correction, the difference in SDR due to the reconstruction filter used is smaller, and the correlation with temperature is stronger. Therefore, the SDR can be standardized by applying the FF, and the maximum temperature during treatment may be predicted more accurately.