MTF and FWHM analysis
Independent point-source MTF and wire-ramp FWHM / slice thickness.
On this page
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 rectangle around one bright target, with at least 8 pixels on each axis. The rectangle selects the target; the program determines its integration and background support. A square is not required. Enable Show actual sampling region to inspect it and avoid multiple bright targets in one selection. 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. Set ROI precisely accepts width and height separately.
3. Read results
MTF shows X/Y curves and MTF50 / MTF10 without diagnostic annotations below the values. The calculation method appears below the chart. With Gaussian equivalent enabled, MTF50 ≈ 0.54866 × MTF10. Calculation details lists the method, integration support, background ring, version and time. Calculation failures show their reason. FWHM displays width and Slice Thickness = FWHM × tan θ; expand Method and profile to choose Gaussian fit or half-height crossings. The default angle is 23°, with 45° available in Service tools settings. A single ramp does not correct phantom tilt or measure slice spacing. MTF units are lp/mm or lp/cm; FWHM and thickness use mm.
Important
Limits
Return to the original slice to restore its ROI. Clear MTF results 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.
Save and recalculate
Workspaces retain completed MTF/FWHM ROIs, curves, results and calculation parameters. Reopening preserves saved values; select Recalculate to apply current settings. Units and precision only affect formatting. The information button lists the method, sampling dimensions, version and time. In Show actual sampling support, cyan marks the integration boundary and light dashes mark the inner and outer background boundaries. Default integration uses 110% of the adaptive reference support and partly overlaps the background ring; this percentage does not describe the drawn ROI size. Bounds are hidden while editing. Historical results without sampling bounds acquire them after recalculation.