Abstract
We present a numerical tool to compare directly the contrast-to-noise-ratio (CNR) of the attenuation- and differential phase-contrast signals available from grating-based X-ray imaging for single radiographs. The attenuation projection is differentiated to bring it into a modality comparable to the differential phase projection using a Gaussian derivative filter. A Relative Contrast Gain (RCG) is then defined as the ratio of the CNR of image values in a region of interest (ROI) in the differential phase projection to the CNR of image values in the same ROI in the differential attenuation projection. We apply the method on experimental data of human breast tissue acquired using a grating interferometer to compare the two contrast modes for two regions of interest differing in the type of tissue. Our results indicate that the proposed method can be used as a local estimate of the spatial distribution of the ratio δ/β, i.e., real and imaginary part of the complex refractive index, across a sample.
Highlights
Traditional X-ray imaging uses attenuation to produce image contrast
Among the many different methods for obtaining X-ray phase-contrast images that have been reported so far, one that seems promising for clinical applications is grating-based imaging using a Talbot interferometer. [5,6,7,8,9,10,11] This approach produces differential phase contrast (DPC), i.e. it yields phase contrast in the form of the derivative of the total phase shift produced by a sample
It is defined as the ratio of the contrast-to-noise ratio (CNR) in a DPC projection to the CNR in an attenuation projection and it is meant as a analysis tool that can be applied on real data
Summary
In recent decades the possibility of using the refractive properties of a sample for imaging has been investigated, [1,2,3] leading to the field of X-ray phase-contrast imaging It has been demonstrated on multiple occasions that X-ray phase-contrast is superior to attenuation contrast under certain conditions. In this paper we introduce a quantity, the “Relative Contrast Gain” (RCG), which provides an estimate of the expected performance of a differential phase-contrast image compared to an attenuation projection. It is defined as the ratio of the contrast-to-noise ratio (CNR) in a DPC projection to the CNR in an attenuation projection and it is meant as a analysis tool that can be applied on real data. In contrast to the approach of Engel et al, here we propose to solve the problem of comparing the two image modalities by differentiating the attenuation image along the same direction as the derivative of the phase
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