الفهرس 
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Abstract
Abstract
The aim of the study is to optimize the radiation dose that received by
oncology patients who receive F18-FDG PET-CT imaging while maintaining image quality. For PET data; several phantom studies with fillable spheres have been conducted at two different ratios 4:1and 10:1. The phantom studies were than classified into three groups: one for NEMA phantom was positioned contiguously to Jaszczak phantom and the other two studies each phantom acquired separately. In each study, the spheres were centered in the field of view and only one bed position was acquired for 3 min. but for CT data; the standard IQ and Rando phantoms were used in performance characterization and image quality assessment of the Ingenuity TOF PET/CT system released by Philips Healthcare.
Image acquisition was varied based on different combinations of milli-amperage time product (30-150 mAs), tube voltage (80,100, 120 kV), Field of View, FOV (250, 350, and 450 mm) and slice thickness (1, 2, and 4 mm). At low dose, four different options of dose right index (DRI) were selected (i.e. 0, 2, 4 and 7) while at high dose protocol the DRI values chosen were 0, 5, 10 and 20 in conjunction with the adopted iterative reconstruction algorithm level 4 (iDose4).
Image quality parameters were used to assess several characteristics of the system performance. PET results showed that no significant change in SUVmax, SUVmean value for various sphere volume with the time of bed position reduction (CV% was approximately within 10% error).but CT results, The system showed acceptable results in terms of image uniformity (± 5 HU), linearity of different tissue densities, spatial resolution measurements including modulation transfer function and full width at half maximum, single slice profile and low contrast detectability. The combined DR and iDose4 reconstruction demonstrated an image
noise reduction up to 22% for bone, 107.8% for soft tissue, 50.7% for lung and 52.7% for liver using low dose CT whereas reductions of 112.9%, 310%, 174.4% and 239% for bone, soft tissue, lung and liver respectively using high dose imaging protocol.
Reduction of the imaging time from 3 min/bed to 0.5 min could reduce the imaging time or the injected dose by a factor of 6. The CT component of the Ingenuity TOF PET/CT imaging systems has acceptable performance characteristics and should be able to provide clinical images of high diagnostic quality. The beam modulation technique and the iterative dose reduction efficient in significantly reducing doses especially in different tissues densities. However, there is still much room for improvement in areas with bone tissues.