Shielded transceiver RF coil array for simultaneous PET-MRI

Solis, Elizabeth; Tomasi, Dardo; Junnarkar, S.; Schlyer, David; Vaska, P.; Pratte, J.‐F.; O’Connor, P.; Rodrı́guez, A. O.

doi:10.1590/s0103-97332008000200013

Cited by 6 publications

(5 citation statements)

References 8 publications

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“…One reason why we did not install metallic shielding around the PET detector is that we wanted to obtain MR images with minimal attenuation of the RF power. Thus, the continuous shielded metallic enclosure in our previous PET/MRI work in 4 T MRI caused a significant reduction in the SNR, and required us to increase the power levels of the RF amplifiers (Solis et al 2008). The challenge is to shield the RF excitation pulses generated by the MRI coil from the PET detector electronics that are sited within 20 mm radially from the coil.…”

Section: Discussionmentioning

confidence: 99%

Small animal simultaneous PET/MRI: initial experiences in a 9.4 T microMRI

Maramraju¹,

Smith²,

Junnarkar³

et al. 2011

Phys. Med. Biol.

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We developed a non-magnetic positron-emission tomography (PET) device based on the rat conscious animal PET that operates in a small-animal magnetic resonance imaging (MRI) scanner, thereby enabling us to carry out simultaneous PET/MRI studies. The PET detector comprises 12 detector blocks, each being a 4 × 8 array of lutetium oxyorthosilicate crystals (2.22 × 2.22 × 5 mm(3)) coupled to a matching non-magnetic avalanche photodiode array. The detector blocks, housed in a plastic case, form a 38 mm inner diameter ring with an 18 mm axial extent. Custom-built MRI coils fit inside the positron-emission tomography (PET) device, operating in transceiver mode. The PET insert is integrated with a Bruker 9.4 T 210 mm clear-bore diameter MRI scanner. We acquired simultaneous PET/MR images of phantoms, of in vivo rat brain, and of cardiac-gated mouse heart using [(11)C]raclopride and 2-deoxy-2-[(18)F]fluoro-D-glucose PET radiotracers. There was minor interference between the PET electronics and the MRI during simultaneous operation, and small effects on the signal-to-noise ratio in the MR images in the presence of the PET, but no noticeable visual artifacts. Gradient echo and high-duty-cycle spin echo radio frequency (RF) pulses resulted in a 7% and a 28% loss in PET counts, respectively, due to high PET counts during the RF pulses that had to be gated out. The calibration of the activity concentration of PET data during MR pulsing is reproducible within less than 6%. Our initial results demonstrate the feasibility of performing simultaneous PET and MRI studies in adult rats and mice using the same PET insert in a small-bore 9.4 T MRI.

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Section: Discussionmentioning

confidence: 99%

Small animal simultaneous PET/MRI: initial experiences in a 9.4 T microMRI

Maramraju¹,

Smith²,

Junnarkar³

et al. 2011

Phys. Med. Biol.

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“…Compared to PMTs typically used for PET scintillation light detection, semiconductor-based avalanche photo-diodes (APDs) and silicon photo-multipliers (SiPMs) can be operated within strong magnetic fields, thereby making APDs and SiPMs very suitable for PET detectors to be operated within or in close proximity to an MRI bore (Vandenberghe and Marsden 2015 ). Since their introduction, numerous PET detector systems for PET–MRI based on APD (Judenhofer et al 2007 , Solis et al 2008 , Catana et al 2008 , Delso et al 2011 , Maramraju et al 2011 , Vaska et al 2011 , Kolb et al 2012 ) or SiPM technology (Hong et al 2012 , Yamamoto et al 2012 , Yoon et al 2012 , Hong et al 2013 , Levin et al 2013 , Weissler et al 2014 , Olcott et al 2015 , Weissler et al 2015a ) have been presented. In this case, the analogue APD/SiPM signals are either transmitted via copper-based, shielded cables or optical fibres from the MRI bore to the PET electronics residing outside the MRI bore to be digitized and processed (Judenhofer et al 2007 , Maramraju et al 2011 , Hong et al 2012 , Kolb et al 2012 , Yamamoto et al 2012 , Yoon et al 2012 , Hong et al 2013 , Olcott et al 2015 ), or are digitized within the MRI bore, requiring more electronics to be moved towards or housed within the MRI (General Electric ( 2014 ), Solis et al 2008 , Maramraju et al 2011 , Vaska et al 2011 , Weissler et al 2014 , 2015a )(Vandenberghe and Marsden ( 2015 ), p. R140–1).…”

Section: Introductionmentioning

confidence: 99%

FPGA-based RF interference reduction techniques for simultaneous PET–MRI

et al. 2016

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The combination of positron emission tomography (PET) and magnetic resonance imaging (MRI) as a multi-modal imaging technique is considered very promising and powerful with regard to in vivo disease progression examination, therapy response monitoring and drug development. However, PET–MRI system design enabling simultaneous operation with unaffected intrinsic performance of both modalities is challenging. As one of the major issues, both the PET detectors and the MRI radio-frequency (RF) subsystem are exposed to electromagnetic (EM) interference, which may lead to PET and MRI signal-to-noise ratio (SNR) deteriorations. Early digitization of electronic PET signals within the MRI bore helps to preserve PET SNR, but occurs at the expense of increased amount of PET electronics inside the MRI and associated RF field emissions. This raises the likelihood of PET-related MRI interference by coupling into the MRI RF coil unwanted spurious signals considered as RF noise, as it degrades MRI SNR and results in MR image artefacts. RF shielding of PET detectors is a commonly used technique to reduce PET-related RF interferences, but can introduce eddy current-related MRI disturbances and hinder the highest system integration. In this paper, we present RF interference reduction methods which rely on EM field coupling–decoupling principles of RF receive coils rather than suppressing emitted fields. By modifying clock frequencies and changing clock phase relations of digital circuits, the resulting RF field emission is optimised with regard to a lower field coupling into the MRI RF coil, thereby increasing the RF silence of PET detectors. Our methods are demonstrated by performing FPGA-based clock frequency and phase shifting of digital silicon photo-multipliers (dSiPMs) used in the PET modules of our MR-compatible Hyperion IID PET insert. We present simulations and magnetic-field map scans visualising the impact of altered clock phase pattern on the spatial RF field distribution, followed by MRI noise and SNR scans performed with an operating PET module using different clock frequencies and phase patterns. The methods were implemented via firmware design changes without any hardware modifications. This introduces new means of flexibility by enabling adaptive RF interference reduction optimisations in the field, e.g. when using a PET insert with different MRI systems or when different MRI RF coil types are to be operated with the same PET detector.

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“…However, the use of these methods has limitations because operations are performed using a system with a low magnetic field or because the MRI and PET images cannot be measured simultaneously. Recently, newly developed PET photodetectors composed of lutetium oxyorthosilicate and avalanche photodiodes have been shown to be viable alternatives for use in MR‐PET fusion systems (Kolb et al, ), as these new detectors are less sensitive to magnetic fields. Using these materials, advanced types of MR‐PET systems, such as integrated MR‐PET or insertable MR‐PET systems, can be developed.…”

Section: Introductionmentioning

confidence: 99%

“…While both techniques are commonly beneficial for diagnostic or research purposes, their roles are slightly different, as MRI provides high-resolution anatomical information in a noninvasive manner and PET provides functional or metabolic information using radioisotopes. Thus, several types of MR-PET fusion systems have been developed and used in small animal (Gilbert et al, 2006;Solis et al, 2008;Wehrl et al, 2011) and human brain studies (Cherry et al, 2008;Schlemmer et al, 2008;Antoch and Bockisch, 2009;Herzog et al, 2010) to simultaneously provide complementary information.…”

Section: Introductionmentioning

confidence: 99%

An optimal RF shielding method for MR‐PET fusion system with insertable PET

Han

Kim

et al. 2014

Int J Imaging Syst Tech

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An RF shielding method is proposed to preserve the resonance frequency of an RF coil regardless of the existence of a positron emission tomography (PET) detector module, so that the RF coil can effectively operate for both simultaneous MR‐PET imaging and MR stand‐alone imaging. The RF shield between the RF coil and the PET detector module was manufactured in the form of a hollow acryl cylinder wrapped with gold‐taffeta woven tape. As we adopted a double‐layer RF shield between the RF coil and the PET detector module, it was possible to maintain the resonance frequency of the RF coil and the MR image quality was similar in both cases, with and without the insertable PET detector module. Using the insertable concept of the PET system and the RF coil with an additional double‐layer RF shield, both an MR‐PET fusion system and an MR stand‐alone system were realized. © 2014 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 24, 263–269, 2014

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Shielded transceiver RF coil array for simultaneous PET-MRI

Cited by 6 publications

References 8 publications

Small animal simultaneous PET/MRI: initial experiences in a 9.4 T microMRI

Small animal simultaneous PET/MRI: initial experiences in a 9.4 T microMRI

FPGA-based RF interference reduction techniques for simultaneous PET–MRI

An optimal RF shielding method for MR‐PET fusion system with insertable PET

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