Highlights
- •Automatic Exposure Control (AEC) reduces dose delivered in chest paediatric MDCT.
- •Application of AEC results in a deterioration of image quality indices.
- •Iterative reconstruction (IR) compensates for the deterioration of image quality indices.
- •IR changes the amplitude and the spatial frequency in Noise Power Spectrum curves.
- •AEC/IR reduce the dose by 43–91% while maintaining diagnostic image quality.
Abstract
Purpose
To evaluate the impact of Automatic Exposure Control (AEC) on radiation dose and image
quality in paediatric chest scans (MDCT), with or without iterative reconstruction
(IR).
Methods
Three anthropomorphic phantoms representing children aged one, five and 10-year-old
were explored using AEC system (CARE Dose 4D) with five modulation strength options.
For each phantom, six acquisitions were carried out: one with fixed mAs (without AEC)
and five each with different modulation strength. Raw data were reconstructed with
Filtered Back Projection (FBP) and with two distinct levels of IR using soft and strong
kernels. Dose reduction and image quality indices (Noise, SNR, CNR) were measured
in lung and soft tissues. Noise Power Spectrum (NPS) was evaluated with a Catphan
600 phantom.
Results
The use of AEC produced a significant dose reduction (p < 0.01) for all anthropomorphic sizes employed. According to the modulation strength
applied, dose delivered was reduced from 43% to 91%. This pattern led to significantly
increased noise (p < 0.01) and reduced SNR and CNR (p < 0.01). However, IR was able to improve these indices. The use of AEC/IR preserved
image quality indices with a lower dose delivered. Doses were reduced from 39% to
58% for the one-year-old phantom, from 46% to 63% for the five-year-old phantom, and
from 58% to 74% for the 10-year-old phantom. In addition, AEC/IR changed the patterns
of NPS curves in amplitude and in spatial frequency.
Conclusions
In chest paediatric MDCT, the use of AEC with IR allows one to obtain a significant
dose reduction while maintaining constant image quality indices.
Abbreviations:
AEC (Automatic Exposure Control), CNR (contrast-to-noise ratio), CTDIvol (volume CT dose index), DRLs (Diagnostic Reference Levels), FBP (Filtered Back Projection), IR (iterative reconstruction), mAseff (effective or modulated mAs), mAsfix (fixed mAs), mAsmod (modulated mAs), mAsref (image quality reference mAs), MDCT (Multi Detector Computed Tomography), NPS (Noise Power Spectrum), ROI (Region of Interest), SAFIRE (Sinogram Affirmed Iterative Reconstruction), SNR (signal-to-noise ratio), SSDE (size-specific dose estimate)Keywords
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Article info
Publication history
Published online: April 04, 2016
Accepted:
March 16,
2016
Received in revised form:
February 23,
2016
Received:
December 9,
2015
Identification
Copyright
© 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
