Method to calculate frequency characteristics of reconstruction filter kernel in X-ray computed tomography

Area of Science:

• Medical Imaging
• Image Reconstruction
• Filter Kernel Analysis

Background:

• Computed tomography (CT) image reconstruction relies on filtered back projection (FBP) algorithms.
• Image quality in FBP is critically dependent on the reconstruction filter kernel, whose specifics are often undisclosed.
• The frequency response of the filter kernel is theoretically linked to the modulation transfer function (MTF) of the reconstruction algorithm (MTF_A).

Purpose of the Study:

• To propose and validate a method for determining the frequency response of CT reconstruction filter kernels.
• To assess the inherent image quality performance of CT scanners through filter kernel analysis.

Main Methods:

• Derived filter kernels from two clinical CT scanners.
• Obtained the modulation transfer function (MTF) and separated it into system MTF and algorithm MTF (MTF_A).
• Calculated filter kernel frequency response using the relationship between the filter kernel and MTF_A.
• Verified the results by measuring the noise power spectrum (NPS) and calculating the filter kernel using the filter kernel-NPS relationship.

Main Results:

• Calculated filter kernels using two distinct methods showed strong agreement across both CT scanners.
• The proposed method for determining filter kernel frequency response was validated.
• The effectiveness of the developed method was confirmed.

Conclusions:

• The proposed method successfully determines the frequency response of CT reconstruction filter kernels.
• This approach allows for the clarification of inherent image quality performance of CT scanners.
• The findings validate a novel approach to understanding CT image reconstruction parameters.