Abstract
Image quality is a key issue in radiology, particularly in a clinical setting where it is important to achieve accurate diagnoses while minimizing radiation dose. Some computed tomography (CT) manufacturers have introduced algorithms that claim significant dose reduction. In this study, we assessed CT image quality produced by two reconstruction algorithms provided with GE Healthcare's Discovery 690 Elite positron emission tomography (PET) CT scanner. Image quality was measured for images obtained at various doses with both conventional filtered back‐projection (FBP) and adaptive statistical iterative reconstruction (ASIR) algorithms. A standard CT dose index (CTDI) phantom and a pencil ionization chamber were used to measure the CT dose at 120 kVp and an exposure of 260 mAs. Image quality was assessed using two phantoms. CT images of both phantoms were acquired at tube voltage (kV) of 120 with exposures ranging from 25 mAs to 400 mAs. Images were reconstructed using FBP and ASIR ranging from 10% to 100%, then analyzed for noise, low‐contrast detectability, contrast‐to‐noise ratio (CNR), and modulation transfer function (MTF). Noise was 4.6 HU in water phantom images acquired at 260 mAs/FBP 120 kV and 130 mAs/50% ASIR 120 kV. The large objects (frequency<7 lp/cm) retained fairly acceptable image quality at 130 mAs/50% ASIR, compared to 260 mAs/FBP. The application of ASIR for small objects (frequency>7 lp/cm) showed poor visibility compared to FBP at 260 mAs and even worse for images acquired at less than 130 mAs. ASIR blending more than 50% at low dose tends to reduce contrast of small objects (frequency>7 lp/cm). We concluded that dose reduction and ASIR should be applied with close attention if the objects to be detected or diagnosed are small (frequency>7 lp/cm). Further investigations are required to correlate the small objects (frequency>7 lp/cm) to patient anatomy and clinical diagnosis.PACS number(s): 87.57.‐s, 87.57.C, 87.57.cf, 87.57.cj, 87.57.cm, 87.57.cp, 87.57.N, 87.57.nf, 87.57.np, 87.57.nt, 87.57.Q, 87.59.‐e, 87.59.B
Highlights
420 Hussain et al.: Effect of adaptive statistical iterative reconstruction (ASIR) on image qualitytradeoff between radiation dose and image quality
The CTDIw was calculated as 21.7 mGy, which was within the tolerance values permitted by the American College of Radiology (ACR) (35 mGy for an adult abdomen)
We have studied the effect of ASIR on phantom image quality and verified the findings on patient images
Summary
420 Hussain et al.: Effect of ASIR on image quality. tradeoff between radiation dose and image quality. We have to acquire the images using minimum radiation possible to minimize the risk. Reducing the radiation dose carries a risk of compromising image quality due to increased noise. Since CT images were first used in a clinical setting, the standard method of image reconstruction has been filtered backprojection (FBP).(1) This is simple back-projection of the X-ray signal into the image matrix and a filter applied to make the objects sharper. Some CT manufacturers have introduced algorithms that utilize iterative reconstructions and they claim to reduce the patient radiation dose while preserving image quality. The concept of iterative reconstruction has existed since the 1960s, but it was hard to implement clinically due to modest computational power. The power of today’s computers has brought iterative reconstruction to the forefront once again
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