Simultaneous measurements using multi-slice dual layer DOI-PET/MRI system: First small animal studies

Abstract

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Objectives: Simultaneous measurement of PET and MRI is a promising strategy for direct comparison of functional and anatomical information in molecular imaging. Our objective is to evaluate the developed multi-slice dual layer depth-of-interaction (DOI) PET/MRI system by in vivo rat brain imaging.

Methods: The PET part has transaxial filed-of-view (FOV) of 4cm in diameter and axial FOV of 0.7cm with dual-layer DOI detection capability. The spatial resolution was less than 3mm FWHM in both directions. The MRI part used 0.15T permanent magnet with RF coil of 3cm in diameter. The PET detector ring was placed inside the permanent magnet while the RF coil was placed inside the PET’s FOV. Using this system, normal rat brains were imaged with approximately 37MBq of ¹⁸F-FDG and ¹⁸F-NaF under pentobarbitone anesthesia. After tracer injection, simultaneous measurements of PET (list mode acquisition) and MRI (3D Spin Echo Sequence, TR/TE=100/16msec) were performed at appropriate time points. PET and MRI images were co-registered for fusion images.

Results: Simultaneous PET/MRI images of rat brain were obtained successfully without noticeable distortion in either image set. ¹⁸F-FDG image showed high uptake in the harderian glands and striatums, and ¹⁸F-NaF image showed high uptake in the skull, consistent with known distribution. High resolution PET/MRI images enabled us to form fusion images having both functional and anatomical information.

Conclusions: Simultaneous PET/MRI imaging system was quite useful for animal studies. This system will be used for quantitative measurements for small animals.