Developing an efficient phase-matched attenuation correction method for quiescent period PET in abdominal PET/MRI

Area of Science:

• Medical Imaging
• Nuclear Medicine
• Radiology

Background:

• Respiratory motion artifacts in simultaneous PET/MRI lead to misalignment between PET and MR attenuation maps (µ-maps).
• This misalignment affects organs like the liver, causing significant motion artifacts in both PET and MR images.
• Accurate attenuation correction is crucial for quantitative PET imaging, especially in abdominal PET/MRI.

Purpose of the Study:

• To develop and evaluate an efficient MR-based attenuation correction (MRAC) method for generating phase-matched µ-maps in abdominal PET/MRI.
• To address misalignments caused by respiratory motion during simultaneous PET/MRI scans.
• To improve the quantitative accuracy of quiescent period PET (PET_Q) imaging in abdominal PET/MRI.

Main Methods:

• Developed a novel MRAC method utilizing CIRcular Cartesian UnderSampling (CIRCUS) for accelerated, phase-matched MRAC (MRAC_PM-CIRCUS).
• Acquired MRAC data using CIRCUS sampling (100s free-breathing) and compared it with raster k-space sampling (MRAC_PM-Default, 100s) and ungated MRAC (MRAC_UM).
• Evaluated MRAC_PM-CIRCUS in 17 patients undergoing ⁶⁸Ga-DOTA-TOC PET/MRI, assessing effects on liver lesion uptake differences and image quality, with simulated acquisition times from 5s increments.

Main Results:

• MRAC_PM-CIRCUS achieved higher image quality than MRAC_PM-Default at equivalent acquisition times, with 30s proving sufficient for phase-matched µ-maps.
• Liver lesion uptake differences between MRAC_PM-CIRCUS (30s) and MRAC_PM-Default (100s) were minimal (0.1% ± 1.4%) and not statistically significant (P > .05).
• In contrast, MRAC_UM showed significant differences (0.6% ± 11.4%) with large variations (-37% to 20%) compared to MRAC_PM-Default (P < .05).

Conclusions:

• A 30s data acquisition using specialized CIRCUS sampling effectively generates phase-matched µ-maps for abdominal PET/MRI.
• The developed MRAC_PM-CIRCUS method significantly improves the quantitative accuracy of PET_Q by correcting for respiratory motion-induced misalignments.
• This accelerated MRAC technique enhances diagnostic performance in abdominal PET/MRI, particularly for detecting neuroendocrine tumors and liver metastases.