Christopher Parham

Design and implementation of a compact low-dose diffraction enhanced medical imaging system.

RATIONALE AND OBJECTIVES Diffraction-enhanced imaging (DEI) is a new x-ray imaging modality that differs from conventional radiography in its use of three physical mechanisms to generate contrast. DEI is able to generate contrast from x-ray absorption, refraction, and ultra-small-angle scatter rejection (extinction) to produce high-contrast images with a much lower radiation dose compared to conventional radiography. MATERIALS AND METHODS A prototype DEI system was constructed using a 1-kW tungsten x-ray tube and a single silicon monochromator and analyzer crystal. The monochromator crystal was aligned to reflect the combined Kalpha1 (59.32 keV) and Kalpha2 (57.98 keV) characteristic emission lines of tungsten using a tube voltage of 160 kV. System performance and demonstration of contrast were evaluated using a nylon monofilament refraction phantom, full-thickness breast specimens, a human thumb, and a live mouse. RESULTS Images acquired using this system successfully demonstrated all three DEI contrast mechanisms. Flux measurements acquired using this 1-kW prototype system demonstrated that this design can be scaled to use a more powerful 60-kW x-ray tube to generate similar images with an image time of approximately 30 seconds. This single-crystal pair design can be further modified to allow for an array of crystals to reduce clinical image times to <3 seconds. CONCLUSIONS This paper describes the design, construction, and performance of a new DEI system using a commercially available tungsten anode x-ray tube and includes the first high-quality low-dose diffraction-enhanced images of full-thickness human tissue specimens.

Improved image contrast of calcifications in breast tissue specimens using diffraction enhanced imaging

The contrast of calcifications in images of breast tissue specimens using a synchrotron-based diffraction enhanced imaging (DEI) apparatus has been measured and is compared to the contrast in images acquired using a conventional synchrotron-based radiographic imaging modality. DEI is an imaging modality which derives image contrast from x-ray absorption, refraction and small-angle scatter-rejection (extinction), unlike conventional radiographic techniques, which can only derive contrast from absorption. DEI is accomplished by inserting an analyser crystal in the beam path between the sample and the detector. Two of the three breast tissue specimens contained calcifications associated with cancer, while a third contained benign calcifications. Results of the image analysis indicate that the DEI contrast of images taken with the analyser crystal tuned to the peak of its rocking curve, was as much as 19 times that of the conventional radiograph, with an average of 5.5 for all calcifications. This improved image contrast for even near-pixel-size calcifications suggests potential utility for DEI in breast imaging.

Diffraction-Enhanced Imaging of Musculoskeletal Tissues Using a Conventional X-Ray Tube

RATIONALE AND OBJECTIVES In conventional projection radiography, cartilage and other soft tissues do not produce enough radiographic contrast to be distinguishable from each other. Diffraction-enhanced imaging (DEI) uses a monochromatic x-ray beam and a silicon crystal analyzer to produce images in which attenuation contrast is greatly enhanced and x-ray refraction at tissue boundaries can be detected. The aim of this study was to test the efficacy of conventional x-ray tube-based DEI for the detection of soft tissues in experimental samples. MATERIALS AND METHODS Cadaveric human tali (normal and degenerated) and a knee and thumb were imaged with DEI using a conventional x-ray tube and DEI setup that included a double-silicon crystal monochromator and a silicon crystal analyzer positioned between the imaged object and the detector. RESULTS Diffraction-enhanced images of the cadaveric tali allowed the visualization of cartilage and its specific level of degeneration for each specimen. There was a significant correlation between the grade of cartilage integrity as assessed on the tube diffraction-enhanced images and on their respective histologic sections (r = 0.97, P = .01). Images of the intact knee showed the articular cartilage edge of the femoral condyle, even when superimposed by the tibia. In the thumb image, it was possible to visualize articular cartilage, tendons, and other soft tissues. CONCLUSION DEI based on a conventional x-ray tube allows the visualization of skeletal and soft tissues simultaneously. Although more in-depth testing and optimization of the DEI setup must be carried out, these data demonstrate a proof of principle for further development of the technology for future clinical imaging.

Characterization of diffraction-enhanced imaging contrast in breast cancer

Diffraction-enhanced imaging (DEI) is a new x-ray imaging modality that has been shown to enhance contrast between normal and cancerous breast tissues. In this study, diffraction-enhanced imaging in computed tomography (DEI-CT) mode was used to quantitatively characterize the refraction contrasts of the organized structures associated with invasive human breast cancer. Using a high-sensitivity Si (3 3 3) reflection, the individual features of breast cancer, including masses, calcifications and spiculations, were observed. DEI-CT yields 14, 5 and 7 times higher CT numbers and 10, 9 and 6 times higher signal-to-noise ratios (SNR) for masses, calcifications and spiculations, respectively, as compared to conventional CT of the same specimen performed using the same detector, x-ray energy and dose. Furthermore, DEI-CT at ten times lower dose yields better SNR than conventional CT. In light of the recent development of a compact DEI prototype using an x-ray tube as its source, these results, acquired at a clinically relevant x-ray energy for which a pre-clinical DEI prototype currently exists, suggest the potential of clinical implementation of mammography with DEI-CT to provide high-contrast, high-resolution images of breast cancer (Parham 2006 PhD Dissertation University of North Carolina at Chapel Hill).

Computation of mass-density images from x-ray refraction-angle images

In this paper, we investigate the possibility of computing quantitatively accurate images of mass density variations in soft tissue. This is a challenging task, because density variations in soft tissue, such as the breast, can be very subtle. Beginning from an image of refraction angle created by either diffraction-enhanced imaging (DEI) or multiple-image radiography (MIR), we estimate the mass-density image using a constrained least squares (CLS) method. The CLS algorithm yields accurate density estimates while effectively suppressing noise. Our method improves on an analytical method proposed by Hasnah et al (2005 Med. Phys. 32 549-52), which can produce significant artefacts when even a modest level of noise is present. We present a quantitative evaluation study to determine the accuracy with which mass density can be determined in the presence of noise. Based on computer simulations, we find that the mass-density estimation error can be as low as a few per cent for typical density variations found in the breast. Example images computed from less-noisy real data are also shown to illustrate the feasibility of the technique. We anticipate that density imaging may have application in assessment of water content of cartilage resulting from osteoarthritis, in evaluation of bone density, and in mammographic interpretation.

Digital mammography, Sestamibi breast scintigraphy, and positron emission tomography breast imaging

Digital mammography allows for the separate optimization of image acquisition and display. Through this technology, and the application of image processing and computer aided diagnosis, breast cancer detection and breast lesion diagnosis might be improved. Besides the obvious data storage, retrieval, and transmission advantages that digital mammography will allow, additional advances such as tomosynthesis, dual energy mammography and digital subtraction mammography are in development. The possible future utility of Sestamibi breast scintigraphy and breast imaging with positron emission tomography is also discussed.

Diffraction enhanced imaging of a rat model of gastric acid aspiration pneumonitis.

RATIONALE AND OBJECTIVES Diffraction-enhanced imaging (DEI) is a type of phase contrast x-ray imaging that has improved image contrast at a lower dose than conventional radiography for many imaging applications, but no studies have been done to determine if DEI might be useful for diagnosing lung injury. The goals of this study were to determine if DEI could differentiate between healthy and injured lungs for a rat model of gastric aspiration and to compare diffraction-enhanced images with chest radiographs. MATERIALS AND METHODS Radiographs and diffraction-enhanced chest images of adult Sprague Dawley rats were obtained before and 4 hours after the aspiration of 0.4 mL/kg of 0.1 mol/L hydrochloric acid. Lung damage was confirmed with histopathology. RESULTS The radiographs and diffraction-enhanced peak images revealed regions of atelectasis in the injured rat lung. The diffraction-enhanced peak images revealed the full extent of the lung with improved clarity relative to the chest radiographs, especially in the portion of the lower lobe that extended behind the diaphragm on the anteroposterior projection. CONCLUSIONS For a rat model of gastric acid aspiration, DEI is capable of distinguishing between a healthy and an injured lung and more clearly than radiography reveals the full extent of the lung and the lung damage.

DIFFRACTION ENHANCED IMAGING OF SOFT TISSUES

Z. ZHONG , D. CHAPMAN, D. CONNOR , A. DILMANIAN, N. GMUR , M. HASNAH, R. E. JOHNSTON, M. Z. KISS, J. LI , C. MUEHLEMAN-, O. OLTULU, C. PARHAM, E. PISANO, L. RIGON , D. SAYERS, W. THOMLINSON, M. YAFFE, AND H. ZHONG 1 2 NSLS, Brookbaven National Lab., Upton, NY 11973, USA Biological, Chemical and Physical Sci., Illinois lnst. Tech., Chicago, IL 60616, USA Dept. Physics, North Carolina State Univ., Raleigh, NC 27695, USA Medical Dept., Brookhaven National Lab., Upton, NY 11973, USA Dept. Biochemistry, Anatomy, Rush Med. College, Chicago, IL 60612, USA Biomed. Eng., Radiology, Univ. North Carolina, Chapel Hill, NC 27599, USA Dept. Physics, Univ. of Trieste and INFN, Sezione di Trieste, Italy ESRF, F-38043, Grenoble Cedex, France 11 Med. Imaging and Med. Biophysics, Univ. Toronto, Ontario, M4N3M5, Canada Dept. Mechanical Engineering, Univ. Akron, Akron, OH 44325-3903, USA

Preliminary performance measurements from a second generation diffraction enhanced imaging system

Purpose: The goal of this study was to begin quantifying the performance of a second generation diffraction enhanced imaging (DEI) system designed to reduce imaging time from our first generation system. Background: DEI, a phase contrast x-ray imaging modality, generates images with enhanced soft tissue contrast at a lower dose than conventional radiography. Our group has previously reported on an x-ray tube-based DEI system, but a substantial gap remained between the imaging time of that system and that of a clinical DEI system. Method: A high power, rotating anode x-ray tube was integrated into this second generation DEI system along with an image intensifier to improve photon counting efficiency. Images of phantoms were acquired using a tube power of 10 kW (125 kVp, 80 mA) at the silicon [333] reflection with the analyzer crystal at its half-reflectivity point. Results: Our preliminary results show comparable image contrast to the first generation DEI system. Imaging time was reduced by a factor four and x-ray-on time was reduced by a factor of sixty from the initial prototype system. Conclusions: These early results from our second generation diffraction enhanced imaging system show significant reduction in imaging time with preservation of DEI contrast.

Application of the multiple image radiography method to breast imaging

The Multiple Image Radiography (MIR) method is new imaging modality that extends the capability of conventional absorption based radiography by adding the additional contrast mechanisms of x-ray refraction and ultra-small angle scatter. In order to design a clinically based MIR system, the MIR specific x-ray properties in breast tissue must be analyzed to determine which are diagnostically useful. Developing MIR as an imaging modality also requires developing new phantoms that incorporate x-ray refraction and ultra-small angle scatter in addition to traditional x-ray absorption. Three breast cancer specimens were imaged using MIR to demonstrate its MIR specific x-ray properties. An uncompressed anthropomorphic breast phantom with an imbedded low absorption contrast acrylic sphere was imaged to provide a physical model of how the unique properties of MIR can be utilized to improve upon conventional mammography and illustrate how these can be used to design a clinically useful imaging system.