Optimizing imaging protocols for overweight and obese patients: a lutetium orthosilicate PET/CT study.
High photon attenuation and scatter in obese patients affect image quality. The purpose of the current study was to optimize lutetium orthosilicate (LSO) PET image acquisition protocols in patients weighing > or =91 kg (200 lb).


METHODS
Twenty-five consecutive patients (16 male and 9 female) weighing > or =91 kg (200 lb; range, 91-168 kg [200-370 lb]) were studied with LSO PET/CT. After intravenous injection of 7.77 MBq (0.21 mCi) of 18F-FDG per kilogram of body weight, PET emission scans were acquired for 7 min/bed position. Single-minute frames were extracted from the 7 min/bed position scans to reconstruct 1-7 min/bed position scans for each patient. Three reviewers independently analyzed all 7 reconstructed whole-body images of each patient. A consensus reading followed in cases of disagreement. Thus, 175 whole-body scans (7 per patient) were analyzed for number of hypermetabolic lesions. A region-of-interest approach was used to obtain a quantitative estimate of image quality.


RESULTS
Fifty-nine hypermetabolic lesions identified on 7 min/bed position scans served as the reference standard. Interobserver concordance increased from 64% for 1 min/bed position scans to 70% for 3 min/bed position scans and 78% for 4 min/bed position scans. Concordance rates did not change for longer imaging durations. Region-of-interest analysis revealed that image noise decreased from 21% for 1 min/bed position scans to 14%, 13%, and 11% for, respectively, 4, 5, and 7 min/bed position scans. When compared with the reference standard, 14 lesions (24%) were missed on 1 min/bed position scans but only 2 (3%) on 4 min/bed position scans. Five minute/bed position scans were sufficient to detect all lesions identified on the 7 min/bed position scans.


CONCLUSIONS
Lesion detectability and reader concordance peaked for 5 min/bed position scans, with no further diagnostic gain achieved by lengthening the duration of PET emission scanning. Thus, 5 min/bed position scans are sufficient for optimal lesion detection with LSO PET/CT in obese patients.
Halpern
Benjamin S
BS
Department of Molecular and Medical Pharmacology, Ahmanson Biological Imaging Center, UCLA David Geffen School of Medicine, Los Angeles, California 90095-6942, USA.
Dahlbom
Magnus
M
Auerbach
Martin A
MA
Schiepers
Christiaan
C
Fueger
Barbara J
BJ
Weber
Wolfgang A
WA
Silverman
Daniel H S
DH
Ratib
Osman
O
Czernin
Johannes
J
D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008187:Lutetium; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000150:complications* / Q000175:diagnosis*; D009765:Obesity / Q000150:complications* / Q000175:diagnosis*; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D017640:Silicates; D013382:Subtraction Technique; D014057:Tomography, X-Ray Computed / Q000379:methods*
D019275:Radiopharmaceuticals; D017640:Silicates; C477682:lutetium orthosilicate; D019788:Fluorodeoxyglucose F18; D008187:Lutetium