Development of a dual-detector X-ray imaging system for phase retrieval study

doi:10.1016/j.nimb.2006.11.075

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

Volume 254, Issue 2, January 2007, Pages 300-306

https://doi.org/10.1016/j.nimb.2006.11.075 Get rights and content

Abstract

Based on a recently introduced phase X-ray imaging approach, a dual-detector prototype was developed for in-line X-ray phase imaging and phase retrieval utilizing a micro-focus X-ray source and two computed radiography (CR) cassette detectors. The system was built on a horizontal optical rail to facilitate manual adjustment of the positions of the X-ray source, the sample and the detectors. The novel design of the detector-1 is essential, it detects a portion of radiation to form an attenuation image; allows the rest of radiation to reach the detector-2 to form a phase contrast image, and the two images are used to retrieve a phase map. The two detectors are balanced for optimal phase-retrieval with reasonable radiation dose to the object to be imaged. The system was examined in terms of the linearity, the fractions of the X-ray photons detected by the two detectors, respectively and the imaging quality of phantoms. Preliminary results showed that the system is capable of phase X-ray imaging and quantitative phase retrieval.

Introduction

Phase contrast X-ray imaging, quantitative X-ray phase imaging and phase retrieval have been gaining popularity in the past a few years due to their potential for clinical applications, including mammography [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13]. Based on a comprehensive X-ray phase imaging theory [5], [8], [9], a dual-detector approach has been investigated [7] for quantitative phase retrieval. With such a method, one X-ray exposure results in two images as required for quantitative phase retrieval, which reduces the radiation dose to patients, alignment errors and motion artifacts. To experimentally validate this approach, a prototype was developed and tested in our laboratory. The system adopts horizontal configuration by using an optical rail. The detector subsystem is a computed radiography (CR) system, which provides the ability of direct digitalization with high sensitivity and large dynamical range. More importantly, with a novel design, a modified CR plate allows the detection of a fraction of X-ray photons while letting other photons pass through the plate to reach another detector for forming a phase contrast image. With these images, a quantitative phase map can be retrieved.

Section snippets

Theory

A “thin sample” [5] in a X-ray imaging system can be described by its optical transmission function (OTF) T(x, y) = A(x, y)exp(iϕ(x, y)). The objective of phase retrieval is to obtain the phase map ϕ(x, y). A comprehensive theoretical formalism has been presented [5] for phase retrieval in a system configuration shown in Fig. 1(a).

Generalized to conditions of polychromatic X-ray source with finite focal spot size and real detectors with finite spatial resolution, the formula can be written as [8] $\hat{F} (I_{1}$

System configuration

The whole system, as shown in Fig. 2, was built on a 98.5-in horizontal optical rail (X95-2.5, Newport Corp., Irvine, CA), attached to which are carriers which mount the X-ray tube, the filter brace, the sample brace and two detector braces. The distance between the X-ray tube and the sample is R₁. Detector-1 is placed directly behind the sample and detector-2 is placed some distance R₂ downstream the sample. All the carriers can be easily moved to adjust R₁ and R₂ freely.

The micro-focus tube

Logarithm linearity of the CR system

The pixel values (PVs) of the digitalized X-ray image are proportional to the logarithm of the X-ray exposure X on the entrance surface of the CR cassettes. This logarithm linearity must be determined for the conversion of the CR images to radiation intensity images. From $PV = a \ln X + b,$ where a and b are constants, it is easy to find out that the ratio between any two radiation exposure values is related to the corresponding PVs through $\frac{X_{2}}{X_{1}} = \exp [\frac{{PV}_{2} - {PV}_{1}}{a}] .$

We used a mammography cassette to determine the

Conclusion

We developed and tested the performance of a dual-detector X-ray imaging prototype for the purpose of in-line X-ray phase imaging and phase retrieval. The system utilizes a micro-focus X-ray tube and two CR detectors with horizontal configuration.

In this study, we first examined the linearity of the CR system, which is crucial for conversion of the pixel values (PVs) of the CR images to X-ray intensity values and hence for quantitative phase retrieval. We found that the PVs are in good

Acknowledgement

The research is supported in part by a grant from the National Institute of Health (RO1 EB002604).

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Development of a dual-detector X-ray imaging system for phase retrieval study

Abstract

Introduction

Section snippets

Theory

System configuration

Logarithm linearity of the CR system

Conclusion

Acknowledgement

Opt. Commun.

On the possibilities of X-ray phase contrast microimaging by coherent high-energy synchrotron radiation

Rev. Sci. Instr.

Phase-contrast imaging using polychromatic hard X-rays

Nature

Contrast and resolution in imaging with a microfocus X-ray source

Rev. Sci. Instr.

Mammography with synchrotron radiation: phase-detection techniques

Radiology

A general theoretical formalism for X-ray phase contrast imaging

J. X-ray Sci. Technol.