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Study on the radiofrequency transparency of electrically floating and ground PET inserts in a 3 T clinical MRI system

https://repo.qst.go.jp/records/86384
https://repo.qst.go.jp/records/86384
95cc1ca7-9a5f-4dec-a835-10465c7654bd
Item type 学術雑誌論文 / Journal Article(1)
公開日 2022-06-27
タイトル
タイトル Study on the radiofrequency transparency of electrically floating and ground PET inserts in a 3 T clinical MRI system
言語
言語 eng
資源タイプ
資源タイプ識別子 http://purl.org/coar/resource_type/c_6501
資源タイプ journal article
アクセス権
アクセス権 metadata only access
アクセス権URI http://purl.org/coar/access_right/c_14cb
著者 Hossain, Akram

× Hossain, Akram

WEKO 1056107

Hossain, Akram

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Takayuki, Obata

× Takayuki, Obata

WEKO 1056108

Takayuki, Obata

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Fumihiko, Nishikido

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WEKO 1056109

Fumihiko, Nishikido

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Taiga, Yamaya

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WEKO 1056110

Taiga, Yamaya

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Hossain, Akram

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WEKO 1056111

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Takayuki, Obata

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WEKO 1056112

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Fumihiko, Nishikido

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WEKO 1056113

en Fumihiko, Nishikido

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Taiga, Yamaya

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WEKO 1056114

en Taiga, Yamaya

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抄録
内容記述タイプ Abstract
内容記述 Purpose
The positron emission tomography (PET) insert for a magnetic resonance imaging (MRI) system that implements the radiofrequency (RF) built-in body coil of the MRI system as a transmitter is designed to be RF-transparent, as the coil resides outside the RF-shielded PET ring. This approach reduces the design complexities (e.g., large PET ring diameter) related to implementing a transmit coil inside the PET ring. However, achieving the required field transmission into the imaging region of interest (ROI) becomes challenging because of the RF shield of the PET insert. In this study, a modularly RF-shielded PET insert is used to investigate the RF transparency considering two electrical configurations of the RF shield, namely the electrical floating and ground configurations. The purpose is to find the differences, advantages and disadvantages of these two configurations.

Methods
Eight copper-shielded PET detector modules (intermodular gap: 3 mm) were oriented cylindrically with an inner diameter of 234 mm. Each PET module included four-layer Lutetium-yttrium oxyorthosilicate scintillation crystal blocks and front-end readout electronics. RF-shielded twisted-pair cables were used to connect the front-end electronics with the power sources and PET data acquisition systems located outside the MRI room. In the ground configuration, both the detector and cable shields were connected to the RF ground of the MRI system. In the floating configuration, only the RF shields of the PET modules were isolated from the RF ground. Experiments were conducted using two cylindrical homogeneous phantoms in a 3 T clinical MRI system, in which the built-in body RF coil (a cylindrical volume coil of diameter 700 mm and length 540 mm) was implemented as a transceiver.

Results
For both PET configurations, the RF and MR imaging performances were lower than those for the MRI-only case, and the MRI system provided specific absorption ratio (SAR) values that were almost double. The RF homogeneity and field strength, and the signal-to-noise ratio (SNR) of the MR images were mostly higher for the floating PET configuration than they were for the ground PET configuration. However, for a shorter axial field-of-view (FOV) of 125 mm, both configurations offered almost the same performance with high RF homogeneities (e.g., 76 ± 10%). Moreover, for both PET configurations, 56 ± 6% larger RF pulse amplitudes were required for MR imaging purposes. The increased power is mostly absorbed in the conductive shields in the form of shielding RF eddy currents; as a result, the SAR values only in the phantoms were estimated to be close to the MRI-only values.

Conclusions
The floating PET configuration showed higher RF transparency under all experimental setups. For a relatively short axial FOV of 125 mm, the ground configuration also performed well which indicated that an RF-penetrable PET insert with the conventional design (e.g., the ground configuration) might also become possible. However, some design modifications (e.g., a wider intermodular gap and using the RF receiver coil inside the PET insert) should improve the RF performance to the level of the MRI-only case.
書誌情報 MEDICAL PHYSICS

巻 49, 号 5, p. 2965-2978, 発行日 2022-05
出版者
出版者 John Wiley & Sons, Inc
ISSN
収録物識別子タイプ ISSN
収録物識別子 0094-2405
DOI
識別子タイプ DOI
関連識別子 10.1002/mp.15588
関連サイト
識別子タイプ DOI
関連識別子 https://doi.org/10.1002/mp.15588
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