Technical Note: A simple method for measuring the slice sensitivity profile of iteratively reconstructed CT images...

Area of Science:

• Medical Imaging Physics
• Radiological Physics
• Image Reconstruction Algorithms

Background:

• The American Association of Physicists in Medicine (AAPM) Task Group 233 (TG233) established a method for measuring the slice sensitivity profile (SSP) in computed tomography (CT) images reconstructed with iterative reconstruction (IR) algorithms.
• The TG233 method involves a slanted phantom plane edge to create an oversampled edge-spread function (ESF).

Purpose of the Study:

• To investigate the validity of a non-slanted edge method for obtaining a fine-sampled ESF directly from CT images.
• To determine if a simpler, non-slanted approach can accurately measure SSPs, particularly for IR algorithms.

Main Methods:

• A non-slanted edge method was proposed, positioning the phantom edge perpendicular to the z-axis and reconstructing images with a 1-mm slice thickness and 0.1-mm increment.
• The SSP was calculated by differentiating the ESF generated from the mean CT values plotted against slice position.
• Methodology was validated by comparing SSPs from the non-slanted edge method, the TG 233-recommended slanted edge method, and a standard coin method using filtered back projection (FBP) and two IR algorithms.

Main Results:

• For FBP images, the non-slanted edge method demonstrated good agreement with both the coin and slanted edge methods.
• For IR algorithms, SSP measurements using the non-slanted edge method showed strong agreement with those obtained via the slanted edge method.

Conclusions:

• The non-slanted edge method for SSP measurement in CT images is valid.
• The proposed method offers simplicity and practicality, enabling routine and accurate SSP determination for both FBP and IR algorithms.