Hybrid PET- and MR-driven attenuation correction for enhanced ¹⁸F-NaF and ¹⁸F-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 ¹⁸F-Sodium Fluoride (¹⁸F-NaF) to segment bones from PET data and support 5-class hybrid PET/MR-driven AC for ¹⁸F-NaF and ¹⁸F-Fluorodeoxyglucose (¹⁸F-FDG) PET/MR cardiovascular imaging. Methods: We introduce 5-class Ki/MR-AC for (i) ¹⁸F-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) ¹⁸F-FDG-only data, with a streamlined simultaneous administration of ¹⁸F-FDG and ¹⁸F-NaF at 4:1 ratio (R4:1), or (iii) for ¹⁸F-FDG-only or both ¹⁸F-FDG and ¹⁸F-NaF dual-tracer data, by administering ¹⁸F-NaF 90 minutes after an equal ¹⁸F-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 ¹⁸F-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% (¹⁸F-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 ¹⁸F-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 ¹⁸F-FDG:¹⁸F-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% (¹⁸F-FDG) and 15.5% (¹⁸F-NaF) at carotid bifurcations and 21.6% (¹⁸F-FDG) and 22.5% (¹⁸F-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 ¹⁸F-NaF and ¹⁸F-FDG contrast and quantification in bone tissues and carotid walls

Interpretation of suspect head and neck fixations seen on PET/CT in lung cancer.

International audienceSmoking is the major risk factor for lung and head and neck cancer. The purpose of the present study was to determine the clinical impact of serendipitously revealed head and neck fixation on PET/CT in patients undergoing investigation for lung cancer. The reports from PET/CT studies for patients with lung cancer from September 2005 and April 2012 were retrospectively reviewed. Head and neck incidentaloma was interpreted as suggestive of second primary malignancy. These incidental findings were compared with the final diagnosis obtained from clinical and histological investigation. Five hundred and ninety-two patients were investigated on PET/CT for lung cancer in the study period. PET/CT-positive head and neck lesions suggestive of second primary malignancy were found in 65 (11%) patients. Nasoendoscopy was performed in 23 patients and biopsy in 10. In 4 patients (17.4% of those explored), a second primary malignant lesion was proved on histology: 2 squamous cell carcinomas (larynx and oral cavity), 1 undifferentiated carcinoma (parotid), and 1 osteosarcoma (mandible). At a median 13 months' follow-up, 3 of the 4 patients with a second primary had died from disease-related causes and 1 was free of recurrence. Metastases from lung adenocarcinoma were found in 2 patients (0.34%). PET/CT detected incidental head and neck malignant tumors in at least 0.68% of lung cancer patients, but in 6.4% of those with suspect head and neck fixation

Correlation between areas of high FDG uptake on pre-treatment PET/CT and preferential sites of local relapse after chemo-radiotherapy for head and neck squamous cell carcinoma

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Recherche d’une corrélation entre les zones les plus hypermétaboliques en TEP/TDM au 18FDG préthérapeutique (hotspots) et les sites préférentiels de récidive locale après radiothérapie des cancers des VADS

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