Interpreting Modulation Transfer Function in Endoscopic Imaging: Spatial-Frequency Conversion Across Imaging Spaces...

Area of Science:

• Medical Imaging
• Optical Engineering
• Image Quality Assessment

Background:

• Endoscopes are crucial medical devices requiring objective imaging performance evaluation.
• Modulation Transfer Function (MTF) is a key metric for image resolution, but its interpretation is complicated by varying spatial frequency definitions.
• Inconsistent spatial frequency units across the imaging chain can lead to erroneous comparisons of endoscopic systems and regions of interest (ROIs).

Purpose of the Study:

• To systematically analyze spatial frequency relationships within the endoscopic imaging chain.
• To develop a practical workflow for consistent MTF analysis and interpretation.
• To account for factors like sensor sampling, processing, scaling, and geometric distortion in MTF measurements.

Main Methods:

• Developed a framework to analyze spatial frequency across the endoscopic imaging chain, from object plane to digital image.
• Incorporated ROI-specific local magnification measurements to correct for geometric distortion.
• Integrated sensor sampling, in-camera processing, and resampling into the spatial frequency conversion workflow.
• Validated the workflow with case studies comparing different ROIs and image scaling scenarios.

Main Results:

• Demonstrated that MTF comparisons can be misleading when spatial frequency is not standardized to object space.
• Showcased how off-axis ROIs may incorrectly appear superior to the image center without proper object space conversion.
• Illustrated that resampled images can show inflated MTF values if scaling differences are not addressed.
• Confirmed that the proposed workflow enables consistent MTF comparisons across diverse endoscopic configurations.

Conclusions:

• A standardized MTF analysis workflow is essential for accurate endoscopic device evaluation and quality assurance.
• Consistent reporting of spatial frequency in object space (cycles per millimeter) is critical for meaningful comparisons.
• The developed framework clarifies the combined impact of optics, sensor characteristics, and image processing on reported MTF.