NEMA characterization of the SAFIR prototype PET insert

Area of Science:

• Preclinical imaging
• Medical physics
• Nuclear medicine

Background:

• The SAFIR prototype is a preclinical Positron Emission Tomography (PET) insert designed for simultaneous dynamic imaging with a 7 T Bruker Magnetic Resonance Imaging (MRI) scanner.
• It features a coincidence resolving time of 194 ps (FWHM) and an energy resolution of 13.8% (FWHM), enabling precise quantitative imaging at high activities (up to 500 MBq).
• This capability is crucial for studying rapid biological processes within short time frames (< 5 s).

Purpose of the Study:

• To evaluate the performance of the SAFIR prototype PET insert according to the NEMA NU 4-2008 standard.
• To assess its suitability for dynamic imaging of small rodents within a 7 T MRI scanner.
• To validate its quantitative imaging capabilities at high radiotracer activities.

Main Methods:

• Performance evaluation was conducted using the NEMA NU 4-2008 standard with the PET insert inside the MRI scanner, without acquiring MRI data.
• Measurements were performed using specific energy windows (391-601 keV) and coincidence time windows (500 ps).
• Reconstruction methods included Filtered Backprojection 3D Reprojection (FBP3DRP) and Maximum Likelihood Expectation Maximization (MLEM).

Main Results:

• Spatial resolution improved from 2.6 mm (FWHM) with FBP3DRP to 1.2 mm (FWHM) with MLEM at a 5 mm radial offset.
• Peak sensitivity was measured at 1.06% at the scanner's center.
• High Noise Equivalent Count Rates (NECR) were achieved (799 kcps for mouse phantom at 537 MBq, 121 kcps for rat phantom at 624 MBq), with NECR peaks not yet reached.

Conclusions:

• The SAFIR prototype insert meets all initial design requirements for preclinical PET imaging.
• It is capable of acquiring dynamic images of small rodents at high activities (≥ 500 MBq).
• The insert demonstrates high sensitivity and excellent count-rate performance, suitable for advanced research applications.