Impact of DOI detection and correction for fused images using DOI-PET/MRI system

Abstract

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Objectives: It is well known that the depth-of-interaction (DOI) information can reduce the off-center radial resolution degradation of the PET image. For a PET/MRI combined system, the DOI information may contribute to more accurate registrations in the fusion image between PET and MRI. We tried DOI correction of the simultaneously measured images of small animals using our DOI-PET/MRI system and compared without DOI information to show the impact of the DOI detection on PET/MRI combined system.

Methods: The DOI PET/MRI system consists of optical fiber based dual layer DOI MR-compatible PET (inner layer diam.:51mm, outer layer diam.:54.5mm) and a permanent magnet MRI (0.15T). Simultaneously measured PET images of rat were reconstructed with and without DOI information and fused with the simultaneously measured MRI images. The DOI correction was performed in the image base. Images of DOI layer combinations (inner-inner, inner-outer, outer-inner, outer-outer) were reconstructed with different magnification ratio to be the same image size among these images. For the images without DOI correction, a single magnification ratio was used for all DOI combinations.

Results: With the DOI correction, images with all DOI combination showed good registration in fused images. Without the DOI correction, significant registration error could be observed in some of the DOI combinations on fused images. Summed images without DOI correction also showed registration error with some spatial resolution degradation.

Conclusions: With these results, it is concluded that DOI detection in PET/MRI system will contribute to precise registration for PET and MRI images.

Research Support: Program for Promotion of Fundamental Studies in Health Sciences of the National Institute of Biomedical Innovations.