Which dose for what image? Iterative reconstruction for CT scan

Abstract

Purpose: To evaluate the potential of iterative reconstruction for reducing the dose given to the patient during abdominal CT scanning.

Materials and methods: A double abdominal CT scan acquisition (Somatom Definition AS+ Siemens) performed without contrast administration at -30% and at -70% of the doses (mAs) was compared to the standard acquisition in 10 patients. The raw data were reconstructed by filtered back projection (FBP) and using the SAFIRE iterative reconstruction method (five levels of iteration). The signal, noise, signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR) were compared for three regions of interest, including the kidney, psoas and abdominal fat.

Results: The signal in each region of interest was not modified based on the type of reconstruction. The noise level decreased significantly during the passage from the FBP to SAFIRE, as well as with the increase in the SAFIRE level. The SNR and CNR therefore increased with the use of iterative reconstructions. The increase in noise observed between the acquisition at -30% and that at -70% was compensated by the use of higher SAFIRE levels.

Conclusion: Iterative reconstructions can be used to improve the SNR and CNR at a constant dose or to reduce the dose by keeping the same SNR and CNR on abdominal CT images.

Keywords: CT scan; Dose; Irradiation; Iterative reconstruction; X-rays.