Original Article
Copyright ©2013 Baishideng Publishing Group Co., Limited. All rights reserved.
World J Radiol. Nov 28, 2013; 5(11): 421-429
Published online Nov 28, 2013. doi: 10.4329/wjr.v5.i11.421
CT dose and image quality in the last three scanner generations
Andreas Christe, Johannes Heverhagen, Christoph Ozdoba, Christian Weisstanner, Stefan Ulzheimer, Lukas Ebner
Andreas Christe, Johannes Heverhagen, Lukas Ebner, Department of Radiology, University Hospital of Bern, Inselspital, 3010 Bern, Switzerland
Christoph Ozdoba, Christian Weisstanner, Department of Neuroradiology, University Hospital of Bern, Inselspital, 3010 Bern, Switzerland
Stefan Ulzheimer, Siemens AG Healthcare, An der Lände 1, 91301 Forchheim, Germany
Author contributions: Ebner L, Christe A performed the majority of the experiments; Ozdoba C, Weisstanner C coordinated the experiments with the Somatom Definition Edge Scanner and were also involved in editing the manuscript; Ulzheimer S, Heverhagen J performed the physical, mathematical and technical review and edited the manuscript; Christe A, Ebner L designed the study and wrote the manuscript.
Correspondence to: Andreas Christe, MD, Departement of Radiology, University Hospital of Bern, Inselspital, Freiburgstrasse 10, 3010 Bern, Switzerland. andreas.christe@insel.ch
Telephone: +41-31-6321965 Fax: +41-31-6324874
Received: July 17, 2013
Revised: September 24, 2013
Accepted: November 2, 2013
Published online: November 28, 2013
Processing time: 133 Days and 19.6 Hours
Abstract

AIM: To compare the computed tomography (CT) dose and image quality with the filtered back projection against the iterative reconstruction and CT with a minimal electronic noise detector.

METHODS: A lung phantom (Chest Phantom N1 by Kyoto Kagaku) was scanned with 3 different CT scanners: the Somatom Sensation, the Definition Flash and the Definition Edge (all from Siemens, Erlangen, Germany). The scan parameters were identical to the Siemens presetting for THORAX ROUTINE (scan length 35 cm and FOV 33 cm). Nine different exposition levels were examined (reference mAs/peek voltage): 100/120, 100/100, 100/80, 50/120, 50/100, 50/80, 25/120, 25/100 and 25 mAs/80 kVp. Images from the SOMATOM Sensation were reconstructed using classic filtered back projection. Iterative reconstruction (SAFIRE, level 3) was performed for the two other scanners. A Stellar detector was used with the Somatom Definition Edge. The CT doses were represented by the dose length products (DLPs) (mGycm) provided by the scanners. Signal, contrast, noise and subjective image quality were recorded by two different radiologists with 10 and 3 years of experience in chest CT radiology. To determine the average dose reduction between two scanners, the integral of the dose difference was calculated from the lowest to the highest noise level.

RESULTS: When using iterative reconstruction (IR) instead of filtered back projection (FBP), the average dose reduction was 30%, 52% and 80% for bone, soft tissue and air, respectively, for the same image quality (P < 0.0001). The recently introduced Stellar detector (Sd) lowered the radiation dose by an additional 27%, 54% and 70% for bone, soft tissue and air, respectively (P < 0.0001). The benefit of dose reduction was larger at lower dose levels. With the same radiation dose, an average of 34% (22%-37%) and 25% (13%-46%) more contrast to noise was achieved by changing from FBP to IR and from IR to Sd, respectively. For the same contrast to noise level, an average of 59% (46%-71%) and 51% (38%-68%) dose reduction was produced for IR and Sd, respectively. For the same subjective image quality, the dose could be reduced by 25% (2%-42%) and 44% (33%-54%) using IR and Sd, respectively.

CONCLUSION: This study showed an average dose reduction between 27% and 70% for the new Stellar detector, which is equivalent to using IR instead of FBP.

Keywords: Low dose computed tomography; Computed tomography image quality; Dose reduction; Computed tomography detector; Image noise; Computed tomography signal to noise

Core tip: A computed tomography dose reduction between 30% and 80% can be expected when using iterative reconstruction instead of filtered back projection. The benefit of dose reduction is larger at lower dose levels. An additional dose reduction between 27% and 70% can be obtained by applying the new Stellar detector.