A computer simulation method for low-dose CT images by useof real high-dose images: a phantom studyTomomi Takenaga 1 • Shigehiko Katsuragawa 2,3 • Makoto Goto 4 • Masahiro Hatemura 4 •Yoshikazu Uchiyama 2 • Junji Shiraishi 2Received: 12 May 2015/Revised: 5 August 2015/Accepted: 6 August 2015/Published online: 20 August 2015? Japanese Society of Radiological Technology and Japan Society of Medical Physics 2015Abstract Practical simulations of low-dose CT imageshave a possibility of being helpful means for optimizationof the CT exposure dose. Because current methods reportedby several researchers are limited to specif i c vendor plat-forms and generally rely on raw sinogram data that arediff i cult to access, we have developed a new computerizedscheme for producing simulated low-dose CT images fromreal high-dose images without use of raw sinogram data orof a particular phantom. Our computerized scheme for low-dose CT simulation was based on the addition of a simu-lated noise image to a real high-dose CT image recon-structed by the f i ltered back-projection algorithm. First, asinogram was generated from the forward projection of ahigh-dose CT image. Then, an additional noise sinogramresulting from use of a reduced exposure dose was esti-mated from a predetermined noise model. Finally, a noiseCT image was reconstructed with a predetermined f i lterand was added to the real high-dose CT image to create asimulated low-dose CT image. The noise power spectrumand modulation transfer function of the simulated low-doseimages were very close to those of the real low-doseimages. In order to conf i rm the feasibility of our method,we applied this method to clinical cases which wereexamined with the high dose initially and then followedwith a low-dose CT. In conclusion, our proposed methodcould simulate the low-dose CT images from their realhigh-dose images with suff i cient accuracy and could beused for determining the optimal dose setting for variousclinical CT examinations.Keywords Low-dose CT ? Simulation ? Filtered back-projection ? NPS ? MTF1 IntroductionThe average typical effective dose in a CT examination ismuch larger than that in a general radiographic examina-tion, whereas CT examinations provide much usefulinformation for accurate diagnoses. For example, the dosefor a chest CT examination is 250–350 times larger thanthat for chest radiography [1, 2]. Therefore, it is necessaryto optimize the exposure dose in CT examinations. Becausemultiple exposures to the same patient for determining theoptimal dose in a CT examination are ethically unaccept-able, a number of studies in which low-dose CT simulationwas used have been proposed [3–8]. If low-dose CT imagesare simulated with a high degree of accuracy, we will beable to estimate a personalized exposure dose that is suit-able for each individual patient. In this study, we note that‘‘low dose’’ means a relatively low exposure dose com-pared to that of the standard diagnostic CT examination,whereas low-dose CT sometimes meant a large reductionof the exposure dose for screening CT. In a low-dose CTexamination with a reconstruction algorithm of f i lteredback-projection (FBP), the increased noise caused by thereduction of the exposure dose is added to the raw sino-gram data, and then the noise on a CT image is propagated& Tomomi Takenaga138w5004@st.kumamoto-u.ac.jp1Graduate School of Health Sciences, Kumamoto University,4-24-1 Kuhonji, Kumamoto 862-0976, Japan2Faculty of Life Sciences, Kumamoto University,4-24-1 Kuhonji, Kumamoto 862-0976, Japan3Faculty of Fukuoka Medical Technology, Teikyo University,6-22 Misakimachi, Omuta, Fukuoka 836-0037, Japan4Department of Radiology, Kumamoto University Hospital,1-1 Honjyo, Kumamoto 862-0976, JapanRadiol Phys Technol (2016) 9:44–52DOI 10.1007/s12194-015-0332-3
