Evaluation of Atlas-Based Attenuation Correction for Integrated PET/MR in Human Brain: Application of a Head Atlas and Comparison to True CT-Based Attenuation Correction.
Attenuation correction (AC) for integrated PET/MR imaging in the human brain is still an open problem. In this study, we evaluated a simplified atlas-based AC (Atlas-AC) by comparing (18)F-FDG PET data corrected using either Atlas-AC or true CT data (CT-AC).


METHODS
We enrolled 8 patients (median age, 63 y). All patients underwent clinically indicated whole-body (18)F-FDG PET/CT for staging, restaging, or follow-up of malignant disease. All patients volunteered for an additional PET/MR of the head (additional tracer was not injected). For each patient, 2 AC maps were generated: an Atlas-AC map registered to a patient-specific liver accelerated volume acquisition-Flex MR sequence and using a vendor-provided head atlas generated from multiple CT head images and a CT-based AC map. For comparative AC, the CT-AC map generated from PET/CT was superimposed on the Atlas-AC map. PET images were reconstructed from the list-mode raw data from the PET/MR imaging scanner using each AC map. All PET images were normalized to the SPM5 PET template, and (18)F-FDG accumulation was quantified in 67 volumes of interest (VOIs; automated anatomic labeling atlas). Relative difference (%diff) between images based on Atlas-AC and CT-AC was calculated, and averaged difference images were generated. (18)F-FDG uptake in all VOIs was compared using Bland-Altman analysis.


RESULTS
The range of error in all 536 VOIs was -3.0%-7.3%. Whole-brain (18)F-FDG uptake based on Atlas-AC was slightly underestimated (%diff = 2.19% ± 1.40%). The underestimation was most pronounced in the regions below the anterior/posterior commissure line, such as the cerebellum, temporal lobe, and central structures (%diff = 3.69% ± 1.43%, 3.25% ± 1.42%, and 3.05% ± 1.18%), suggesting that Atlas-AC tends to underestimate the attenuation values of the skull base bone.


CONCLUSIONS
When compared with the gold-standard CT-AC, errors introduced using Atlas-AC did not exceed 8% in any brain region investigated. Underestimation of (18)F-FDG uptake was minor (<4%) but significant in regions near the skull base.
Department of Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland University of Zurich, Zurich, Switzerland Department of Radiology, Nippon Medical School, Tokyo, Japan tetsuro.sekine@gmail.com.
Tetsuro
T
Sekine
Department of Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland University of Zurich, Zurich, Switzerland.
Alfred
A
Buck
Department of Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland University of Zurich, Zurich, Switzerland GE Healthcare, Waukesha, Wisconsin.
Gaspar
G
Delso
Department of Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland University of Zurich, Zurich, Switzerland.
Edwin E G W
EE
Ter Voert
Department of Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland University of Zurich, Zurich, Switzerland Department of Neuroradiology, University Hospital Zurich, Zurich, Switzerland; and.
Martin
M
Huellner
Department of Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland University of Zurich, Zurich, Switzerland Division of Diagnostic and Interventional Radiology, Department of Medical Radiology, University Hospital Zurich, Zurich, Switzerland.
Patrick
P
Veit-Haibach
Department of Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland University of Zurich, Zurich, Switzerland.
Geoffrey
G
Warnock
D000328:Adult; D000368:Aged; D001271:Atlases as Topic; D001921:Brain / Q000033:anatomy & histology* / Q000000981:diagnostic imaging* / Q000473:pathology; D005260:Female; D019788:Fluorodeoxyglucose F18; D006257:Head / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008099:Liver / Q000000981:diagnostic imaging; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals; D012015:Reference Standards; D019291:Skull Base / Q000000981:diagnostic imaging / Q000473:pathology; D014057:Tomography, X-Ray Computed / Q000379:methods*
D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18
18F-FDG; PET/MR; atlas-based; attenuation correction; brain