title: Optimization of the CT acquisition protocol to reduce patient dose without compromising the diagnostic quality for PET-CT:  a phantom study.
abstract: OBJECTIVE
  We conducted a phantom study to optimize the computed tomography (CT) acquisition protocol, to reduce patient dose without compromising the diagnostic quality of PET-CT study.
  
  
  METHODS
  We conducted 42 PET-CT phantom studies. The jaszczak phantom was filled with 18F-fluorodeoxyglucose activity (1.4, 4, 6, 8, 10, and 12 mCi, on different settings) and PET-CT was acquired at different tube currents of 16, 25, 30, 35, 40, 45, and 50 mAs, keeping all the other parameters constant. Two nuclear medicine physicians qualitatively evaluated 252 images for their diagnostic quality (contrast, resolution, and number of lesion detected). The images were also evaluated qualitatively for noise on CT (the physical measure of image quality) and standardized uptake value (mean) on PET images. The weighted CT dose index (CTDIw) was measured for calculating the changes in the radiation dose with the change in tube current.
  
  
  RESULTS
  The 42 images provided same diagnostic information in CT images at different tube currents. However, there was a gradual increase in noise in the image acquired at lower values of the tube current, in mAs. The modulation of CT tube current had no effect on the PET images as well as the PET-CT images. Standardized uptake value mean values were also not affected with lowering of tube current. On reducing the tube current from 50 to 16 mAs, a reduction in the radiation dose (CTDIw) to almost 68% was achieved.
  
  
  CONCLUSIONS
  It is possible to reduce the tube current of the CT tube of PET-CT to a much lower level, without any loss of diagnostic information of a PET-CT image. Moreover, this can significantly reduce the radiation dose.
authors: Department of Nuclear Medicine, All India Institute of Medical Sciences, New Delhi, India.
authors: Sunil
authors: S
authors: Kumar
authors: Anil Kumar
authors: AK
authors: Pandey
authors: Punit
authors: P
authors: Sharma
authors: Arun
authors: A
authors: Malhotra
authors: Rakesh
authors: R
authors: Kumar
mesh_terms: D000328:Adult; D000368:Aged; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000592:standards*; D008875:Middle Aged; D064847:Multimodal Imaging / Q000379:methods*; D049268:Positron-Emission Tomography; D011446:Prospective Studies; D011829:Radiation Dosage; D019275:Radiopharmaceuticals; D036542:Tomography, Spiral Computed / Q000379:methods; D014057:Tomography, X-Ray Computed
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18