• Pixel Size – test verifies the expected pixel size based on the display field of view and the reconstruction matrix size from the measured set of four calibration pins positioned at a known physical location as specified in the Catphan section CTP401.
• CT Linearity (Sensitometry) – Mean CT values are calculated for each reference material in the phantom test section. The measured CT numbers for test materials are fit to the linear attenuation coefficients using a linear least squares for energies from 40 to 100 keV. The variance representing the lowest variance was designated as the scanner’s effective energy. The linear attenuation coefficients for this effective energy are used to determine the contrast scale from the calculated linearity slope.[3].
• Slice Thickness – is determined from the average full-width at half-maximum (FWHM) of the CT number profile for each wire ramp. The expected slice width is compared with all four measured ramps values. A trigonometric conversion is calculated based on the know ramp angle to yield the slice width. This test provides information on the position of the phantom and the vertical and horizontal tilt values. A rotation of the phantom about an axis perpendicular to the ramps is also computed. Since there are two pairs of ramps orientated along the orthogonal directions, phantom rotations about both the vertical and horizontal axes can be estimated [4].
• Localizer and Table Incrementation Accuracy – can be evaluated from the slice width section when the ramps are paired at opposing angles. The slice width test outputs a parameter called Table Position Offset, which an offset in the z-axis relative to the center of the opposing wire (or test section). Verification of the scanner table incrementation accuracy can be checked by incrementing the table by 30 mm and then returning the table to the starting position and scanning the slice width module. The reported table position offset values should be the same.
• Spatial Resolution (MTF) – The modulation transfer function (MTF) is calculated from the discrete Fourier Transform of the average vertical and horizontal LSF’s of the point spread function from the bead or wire test section. The program reports the 50%, 10% and 2% MTF cutoff values [5].
• Noise and Mean CT Number – is calculated from several regions of interest (ROI) positioned over a water/uniformity phantom section. The number, size and location of these ROI’s are variable, but typically five are defined: one at the phantom center and the other four along the axes at the same radius covering a 15 x 15 pixel area.
• Uniformity – Vertical and horizontal profiles 10 pixel wide are generated and averaged through the phantom’s center. The fractional uniformity of the profile is calculated as the percentage of the pixels within an acceptable range determined by + 2 times the central noise or + 10H, whichever is smaller.
• Contrast Detail (Low Contrast Resolution) – Theoretical Contrast-Detail data is calculated based on the measured noise of the water/uniformity test section. Note: low contrast modules (CTP263 and CTP515) are not used in this measurement. This represents a conservative estimate of the minimum contrast level required such that a cylindrical object of a given diameter should be detected [6] .

Software Information