Computed tomography automatic exposure control techniques in 18F-FDG oncology PET-CT scanning.
OBJECTIVE
Computed tomography (CT) automatic exposure control (AEC) systems are now used in all modern PET-CT scanners. A collaborative study was undertaken to compare AEC techniques of the three major PET-CT manufacturers for fluorine-18 fluorodeoxyglucose half-body oncology imaging.


METHODS
An audit of 70 patients was performed for half-body CT scans taken on a GE Discovery 690, Philips Gemini TF and Siemens Biograph mCT (all 64-slice CT). Patient demographic and dose information was recorded and image noise was calculated as the SD of Hounsfield units in the liver. A direct comparison of the AEC systems was made by scanning a Rando phantom on all three systems for a range of AEC settings.


RESULTS
The variation in dose and image quality with patient weight was significantly different for all three systems, with the GE system showing the largest variation in dose with weight and Philips the least. Image noise varied with patient weight in Philips and Siemens systems but was constant for all weights in GE. The z-axis mA profiles from the Rando phantom demonstrate that these differences are caused by the nature of the tube current modulation techniques applied. The mA profiles varied considerably according to the AEC settings used.


CONCLUSIONS
CT AEC techniques from the three manufacturers yield significantly different tube current modulation patterns and hence deliver different doses and levels of image quality across a range of patient weights. Users should be aware of how their system works and of steps that could be taken to optimize imaging protocols.
aDepartment of Medical Physics and Engineering, Leeds Teaching Hospital NHS Trust, Leeds bCentral Manchester University Hospitals NHS Foundation Trust, Manchester, UK.
Gareth R
GR
Iball
Deborah
D
Tout
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001331:Automation; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging / Q000295:instrumentation / Q000379:methods*; D009369:Neoplasms / Q000000981:diagnostic imaging*; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000295:instrumentation / Q000379:methods*; D011829:Radiation Dosage; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*; D055815:Young Adult
D019788:Fluorodeoxyglucose F18