37 research outputs found
Hybrid PET- and MR-driven attenuation correction for enhanced šâ¸F-NaF and šâ¸F-FDG quantification in cardiovascular PET/MR imaging
Background: The standard MR Dixon-based attenuation correction (AC) method in positron emission tomography/magnetic resonance (PET/MR) imaging segments only the air, lung, fat and soft-tissues (4-class), thus neglecting the highly attenuating bone tissues and affecting quantification in bones and adjacent vessels. We sought to address this limitation by utilizing the distinctively high bone uptake rate constant Ki expected from šâ¸F-Sodium Fluoride (šâ¸F-NaF) to segment bones from PET data and support 5-class hybrid PET/MR-driven AC for šâ¸F-NaF and šâ¸F-Fluorodeoxyglucose (šâ¸F-FDG) PET/MR cardiovascular imaging.
Methods: We introduce 5-class Ki/MR-AC for (i) šâ¸F-NaF studies where the bones are segmented from Patlak Ki images and added as the 5th tissue class to the MR Dixon 4-class AC map. Furthermore, we propose two alternative dual-tracer protocols to permit 5-class Ki/MR-AC for (ii) šâ¸F-FDG-only data, with a streamlined simultaneous administration of šâ¸F-FDG and šâ¸F-NaF at 4:1 ratio (R4:1), or (iii) for šâ¸F-FDG-only or both šâ¸F-FDG and šâ¸F-NaF dual-tracer data, by administering šâ¸F-NaF 90 minutes after an equal šâ¸F-FDG dosage (R1:1). The Ki-driven bone segmentation was validated against computed tomography (CT)-based segmentation in rabbits, followed by PET/MR validation on 108 vertebral bone and carotid wall regions in 16 human volunteers with and without prior indication of carotid atherosclerosis disease (CAD).
Results: In rabbits, we observed similar (< 1.2% mean difference) vertebral bone šâ¸F-NaF SUVmean scores when applying 5-class AC with Ki-segmented bone (5-class Ki/CT-AC) vs CT-segmented bone (5-class CT-AC) tissue. Considering the PET data corrected with continuous CT-AC maps as gold-standard, the percentage SUVmean bias was reduced by 17.6% (šâ¸F-NaF) and 15.4% (R4:1) with 5-class Ki/CT-AC vs 4-class CT-AC. In humans without prior CAD indication, we reported 17.7% and 20% higher šâ¸F-NaF target-to-background ratio (TBR) at carotid bifurcations wall and vertebral bones, respectively, with 5- vs 4-class AC. In the R4:1 human cohort, the mean šâ¸F-FDG:šâ¸F-NaF TBR increased by 12.2% at carotid bifurcations wall and 19.9% at vertebral bones. For the R1:1 cohort of subjects without CAD indication, mean TBR increased by 15.3% (šâ¸F-FDG) and 15.5% (šâ¸F-NaF) at carotid bifurcations and 21.6% (šâ¸F-FDG) and 22.5% (šâ¸F-NaF) at vertebral bones. Similar TBR enhancements were observed when applying the proposed AC method to human subjects with prior CAD indication.
Conclusions: Ki-driven bone segmentation and 5-class hybrid PET/MR-driven AC is feasible and can significantly enhance šâ¸F-NaF and šâ¸F-FDG contrast and quantification in bone tissues and carotid walls