MR-PET co-registration in upper abdominal imaging: quantitative comparison of two different T1-weighted gradient echo sequences: initial observations.

Purpose: The purpose of this study is to quantitatively compare the accuracy of spatial registration of Cartesian breath-hold 3D-GRE and non-respiratory-triggered free-breathing radial 3D-GRE images with PET data acquisition on whole-body hybrid MR-PET system.

Materials And Methods: Eight patients (six men and two women; mean age, 56.6 ± 5.5 years) with nine ablated hepatocellular carcinomas constituted our study population. Spatial coordinates (x, y, z) of the estimated isocenters of the ablated areas were independently determined by two radiologists. Both T1-weighted sequences were performed in the axial plane. Distance between the isocenter of the lesion on PET images and on both T1-weighted images was measured, and misregistration was calculated. Statistical analysis was performed using Student t test.

Results: Misalignment values of the hepatic ablation zones between PET and MR images were calculated at 4.94 ± 1.35 mm (reader 1) and 4.89 ± 2.21 mm (reader 2) for Cartesian 3D-GRE sequence, and 2.48 ± 0.65 mm (reader 1) and 2.72 ± 0.44 mm (reader 2) for the radial 3D-GRE sequence, with p values of 0.0011 and 0.0133, respectively.

Conclusion: Radial 3D-GRE offers improved registration accuracy with PET, supporting the use of this T1-weighted sequence in upper abdominal MR-PET studies.