Yotaro Ishihara MS, Presenter: Employee, General Electric Company

Yasuhiro Imai MS, Abstract Co-Author: Employee, General Electric Company

Kosuke Sasaki MS, Abstract Co-Author: Employee, General Electric Company

Masatake Nukui MS, Abstract Co-Author: Employee, General Electric Company

Minoru Yamada MS, Abstract Co-Author: Nothing to Disclose

Masahiro Jinzaki MD, Abstract Co-Author: Nothing to Disclose

Sachio Kuribayashi MD, Abstract Co-Author: Research grant, General Electric Company

00030490-DMT et al, Abstract Co-Author: Nothing to Disclose

An experimental fine pitch detector multislice CT (FDCT) using an ultrasmall focal spot x-ray tube and a density-doubled matrix detector had already demonstrated its high contrast resolution. We investigated the detectability of small object especially in low frequency area with both the experimental FDCT and the commercial MSCT.

To look at low contrast detectability, we scanned the low contrast part of ACR phantom (ACR CT accreditation phantom, American College of Radiology, VA) with both the experimental FDCT and a commercial MSCT (LightSpeed VCT, GE Healthcare, WI). The low contrast part of ACR phantom has 6 parts of different diameter (25mm, 6mm, 5mm, 4mm, 3mm and 2mm) and all the difference from the background material is 0.6% (6HU). And we scanned a 20cm water phantom to measure image SD and wiener spectrum (WS), and 0.05mm tungsten wire phantom for the measurements of measured transfer functions (MTF). Radiation dose and image thickness of these measurements were all the same in each system. With the MTF and the WS values, we also calculated the Noise Equivalent Quanta (NEQ) of the experimental FDCT and the commercial MSCT in order to compare their detectability in each frequency range. To get the NEQ value, we divided the second power of the MTF by the WS, and calculated its ratio (MSCT/FDCT). When the ratio is less than 1.0, the experimental FDCT has the better NEQ value than the commercial MSCT.

Low contrast resolution of 2mm, 0.6% (6HU) could be visualized with both the experimental FDCT and the commercial MSCT. Image SD of the experimental FDCT was 5.2 (HU), 20% worse than the commercial MSCT. NEQ value ratio gradually decreased from around 1.0 to around 0.6 where the frequency range was from 0 (1/mm) to 0.7 (1/mm) and close to 0 where the frequency range was over 0.7 (1/mm). This means FDCT has better detectability than the commercial MSCT not only in high frequent area but also in low frequent area.

The experimental FDCT has better detectability than the commercial MSCT in every frequent area despite degradation of noise intensity. And it indicates that high contrast resolution can compensate low contrast resolution because of the graininess.

Improvement of detectability can improve diagnostic ability without increasing radiation dose.

Ishihara, Y, Imai, Y, Sasaki, K, Nukui, M, Yamada, M, Jinzaki, M, Kuribayashi, S, et al, 0, Detectability of an Experimental Fine Pitch Detector Multislice CT Scanner.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8005442.html