Fully integrated 3D high-resolution multicontrast abdominal PET-MR with high scan efficiency.

Area of Science:

• Medical Imaging
• Radiology
• Biophysics

Background:

• Standard abdominal PET-MR scans suffer from resolution limits and misalignment due to breath-holding. Free-breathing PET acquisitions with breath-hold MR data introduce artifacts. Respiratory motion significantly impacts image quality in simultaneous PET-MR examinations.
• Current methods for simultaneous PET-MR imaging often compromise image resolution and accuracy due to respiratory motion. This limits the diagnostic potential of combined PET-MR scans, particularly in abdominal oncology.

Purpose of the Study:

• To develop and evaluate a novel 3D free-breathing simultaneous PET-MR acquisition technique. The goal is to achieve high isotropic resolution anatomical MR and metabolic PET imaging with respiratory motion compensation and high scan efficiency.
• To enhance the quality of both MR and PET images by integrating respiratory motion information into the reconstruction process. This aims to improve diagnostic accuracy and reduce scan times in oncology patients.

Main Methods:

• A 3D free-breathing simultaneous PET-MR acquisition protocol was implemented. This protocol yields T1- and T2-weighted MR images with 1.5 mm³ isotropic resolution. Nonrigid respiratory motion information and respiratory-resolved attenuation-correction maps were derived without increasing scan time.
• The acquired motion information was utilized in motion-compensated image reconstructions for both MR and PET data. This approach aims to correct for involuntary patient motion during the scan, thereby improving image fidelity and reducing artifacts.

Main Results:

• The method accurately provided respiratory motion information (1.3 ± 0.1 mm). Anatomical feature sharpness in MR images improved by 19 ± 13% with a 54 ± 26% shorter scan time compared to gated MR. Simultaneously acquired PET images showed improved uptake values (75 ± 94%) and resolution (16 ± 27%).
• Evaluation in 11 oncology patients demonstrated the effectiveness of the motion-compensated approach. Significant improvements in both MR image sharpness and PET data quantification were observed, highlighting the clinical utility of the technique.

Conclusions:

• The proposed simultaneous PET-MR method enables motion-compensated, high-quality 3D imaging. It offers a comprehensive and highly efficient examination for oncology patients. This technique overcomes limitations of previous methods, providing superior anatomical and metabolic information.
• This advanced PET-MR technique significantly enhances image quality and scan efficiency by effectively managing respiratory motion. It represents a substantial advancement in simultaneous PET-MR imaging, offering improved diagnostic capabilities for oncological applications.