Iterative Reconstruction as a Method for Optimisation of Computed Tomography Procedures

BACKGROUND: Computed tomography (CT) is still commonly regarded as a method that causes a high radiation exposure. For that reason, producers intensively try to find new solutions for dose reduction while maintaining a high diagnostic value of images. One of the recent strategies focuses on CT image reconstruction. Iterative reconstruction (IR) is an alternative for filtered back projection (FBP) that is commonly used today. The aim of the article is to demonstrate and compare the effects of two IR algorithms on dose value and image details. MATERIAL/METHODS: Investigations were performed on two 128 multi-detector (MDCT) CT scanners: – iCT (Philips Healthcare with iDose(4)); – Definitions AS+ (Siemens Medical Solutions with SAFIRE system). The measurements involved: – image quality indicators for the CATPHAN 600 phantom; – dosimetric indicators of exposure (DLP i CTDI(vol)). RESULTS: The signal-to-noise ratios (SNR) in the images reconstructed with IR and FBP were analysed, and the SNR(IR)/SNR(FBP) ratios were calculated and correlated with CTDI(vol) values. The effects of IR and FBP algorithms on low-contrast resolution were also compared in relation to CTDI(vol) values. The smallest diameter of supra-slice objects in the Catphan phantom were taken into consideration. Both iterative algorithms definitely improved the visibility of low-contrast objects in comparison to a standard algorithm (FBP) with similar exposure parameters. These algorithms allow an 80% reduction of the CTDI(vol) value while maintaining an acceptable visibility of low-contrast objects. However, the results obtained with each of the studied iterative algorithms differ.