Journal of X-Ray Science and Technology 11 (2003) 1–11 1 IOS Press A study on the section sensitivity profile in multi-row-detector spiral CT Ge Wang a , Mark Madsen a , Katherine Redford a , Shiying Zhao b and Michael W. Vannier a a CT/Micro-CT Laboratory, Department of Radiology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242, USA b Department of Mathematics & Computer Science, University of Missouri – St. Louis, 8001 Natural Bridge Road, St. Louis, MO 63121-4499, USA Tel.: +1 319 356 2930; Fax: +1 319 356 2220; E-mail: ge-wang@uiowa.edu Abstract. The section sensitivity profile (SSP) was well understood in the case of single-row-detector spiral CT. With the introduction of multi-row-detector spiral CT and the transition into cone-beam spiral CT, a revisit to the SSP issue becomes necessary. In this paper, the SSP of multi-row-detector spiral CT is formulated for the half-scan interpolation method at any transverse position. Based on the SSP formula, numerical simulation is performed to quantify the characteristics of the SSP with the number of detector rows up to 40. It is shown that the SSP varies as a function of the pitch and the number of detector rows. Given an appropriate selection of the pitch and the number of detector rows, the SSP does not change very much over the field of view in terms of the mean, the slice thickness, and the skewness of the SSP. Although in general applications the SSP at the gantry iso-center can be used as the representative of the SSP family, for more accurate analyses the spatial variation of the SSP must be taken into account. Keywords: Multi-row-detector spiral/helical CT, half-scan interpolation, section sensitivity profile (SSP),image quality, pitch effect, moment analysis 1. Introduction The newest technology in medical X-ray CT is multi-row-detector spiral/helical CT [1–3]. A multi- row-detector scanner features several adjacent parallel rows of detectors, allowing simultaneous acqui- sition of data from multiple transverse slices. The tendency toward increasing the number of detector rows continues, and eventually cone-beam spiral CT, which uses a truly 2D detector array, will become a reality [4–7]. Mutli-row-detector/cone-beam spiral CT is advantageous for larger scanning range in shorter time with higher longitudinal image resolution, and has important medical and other applications. The image quality of multi-row-detector spiral CT has yet to be fully explored, especially when the number of detector rows is large [1–3]. A key aspect of image quality is the slice sensitivity profile (SSP) [8–10]. The SSP can be defined as the longitudinal profile of the point spread function (PSF). The slice thickness is derived from the SSP as the measure of longitudinal image resolution. The asymmetric geometry of spiral CT raw data interpolation, both in single- and multi-row-detector cases, makes the SSP dependent upon the position in the field of view. Although the SSP and its spatial variation was investigated in the single-row-detector case [8–10], the SSP issue has not been systematically addressed in the multi-row-detector case. 0895-3996/03/$8.00  2003 – IOS Press. All rights reserved