Experimental determination of section sensitivity profiles and image noisein electron beam computed tomography

To determine the effect of continuous-volume scanning (CVS) on z-axis resol ution, section sensitivity profiles were measured on an electron beam compu ted tomography (CT) scanner and compared with those obtained using the step -volume scanning (SVS) mode. A steel bead was imaged using different scan p arameters, and the mean CT number over the bead was plotted against the z-a xis position to determine section sensitivity profiles. From these profiles , full width at half maximum (FWHM), full width at tenth maximum (FWTM), an d full width at tenth area (FWTA) were calculated. A uniform water phantom was imaged to measure noise. To determine the visual significance of change s in the section sensitivity profile, a section thickness and contiguity ph antom was imaged. All section sensitivity profiles measured had an FWHM val ue within 0.5 mm of the nominal scan width. The FWTM and FWTA values increa sed with the CVS mode compared with the SVS mode. This broadening of the se ction sensitivity profiles was most significant with larger collimator widt hs. However, use of smaller collimator widths increased image noise. When a ll other parameters remained constant, increasing the exposure time to redu ce image noise did not affect the section sensitivity profile. The CVS mode produced wider section sensitivity profiles than the SVS mode. This effect was minimized when the smallest collimator width was used, but at the expe nse of increased image noise. (C) 1999 American Association of Physicists i n Medicine. [S0094-2405(99)02202-6].