DETERMINATION OF SPIRAL CT SLICE SENSITIVITY PROFILES USING A POINT RESPONSE PHANTOM

Objective: This study was done to compare the slice sensitivity profiles (SSP) for combinations of collimation, pitch, and table speed for spiral CT using a point response phantom. The goal was to determine the optimal combination of parameters to reduce partial volume averaging without compromising z-axis coverage. Materials and Methods: A copper ball bearing measuring 0.4 mm was embedded in a closed-cell air-foam background to create a point response input phantom. The phantom was scanned at pitches from 0.1 to 2.0 for collimations of 5, 8, and 10 mm. The full width half maximums (FWHMs) and full width tenth maximums (FWTMs) were estimated from SSP curves generated by plotting the maximum pixel value in HU for each reconstructed image against table position. FWHMs and FWTMs were compared separately for constant collimation and increasing table speed and for constant table speed and decreasing collimation using either a two-tailed z-test or chi-square test. Results: Differences between FWHMs and between FWTMs for comparisons made between different collimations at constant table speeds of 8 and 10 mm/s were significantly different (p < 0.0001). Differences between FWHMs and between FWTMs showed a linear trend, increasing with increasing pitch for constant collimation (p < 0.0013). Conclusion: Scanning at narrower collimation but higher pitch provides a narrower SSP when scanning at equivalent table speeds without compromising z-axis coverage.