MTF and FWHM analysis
Independent point-source MTF and wire-ramp FWHM / slice thickness.
1. Choose a method
Services → MTF analyzes in-plane resolution using a bead or perpendicular wire section. The default uses 2D background correction and edge-weighted FFT; MTF50/10 are independent crossings of the measured spectrum. Negative lobes and overshoot are retained. The adjacent FWHM tool measures wire-ramp width and slice thickness using Gaussian fit or half-height crossings. Each tool retains its own ROI, analysis settings, results and reset state when switching.
2. Select and adjust
For a bead or wire section, draw a square ROI of at least 8×8 pixels around one bright target and surrounding background. Center the target with sufficient background; sensitivity warnings indicate that the ROI should be enlarged and checked again. For a ramp, choose horizontal X / vertical Y and draw a narrow rectangle along one wire, including background at both ends and at least 8 pixels along the ramp. The ROI controls transverse averaging; rotated or multiple ramps are unsupported. Drag the interior to move or a corner to resize; release to calculate.
3. Read results
MTF shows X/Y curves and MTF50 / MTF10. FWHM shows half-maximum width and Slice Thickness = FWHM × tan θ. Expand Analysis & profile to choose Gaussian fitting / half-height crossings and inspect the profile. The default angle is 23°; choose 45° in Settings → Service tools → FWHM. Single-ramp results do not correct phantom tilt or substitute nominal DICOM thickness, and do not measure slice spacing. Click ! for method and quality notes. MTF units are lp/mm or lp/cm; FWHM and thickness use mm.
Limits
Return to the original slice to restore its ROI. Reset MTF clears this viewport's results. Finite target size is not corrected. Cross-slice averaging and MPR analysis are unsupported. No automatic pass/fail assessment is made.