Interaction of X-rays with Matter and Imaging Gocha Khelashvili Assistant Research Professor of Physics Illinois Institute of Technology Research Medical Physicist EXELAR Medical Corporation

The Plan X-ray Interactions with Matter Used at Imaging Energies Photoelectric Effect Coherent Scattering Incoherent Scattering Pair and Triplet Production Refraction Small- and Ultra-small Angle Scattering Radiography How does it work? Imaging Parameters and Sources of X-ray contrast Drawbacks of Radiography Diffraction Enhanced Imaging (DEI) Drawbacks of DEI Multiple Image Radiography (MIR-Planar Mode) Sources of X-ray contrast MIR parameters and images MIR Model Based on Discrete Scatterers Multiple scattering series approach and MIR transport equation Solution of MIR transport equation Imaging Parameters Summary

Photoelectric Effect

Thompson (Classical) Scattering

Thompson (Classical) Scattering

Rayleigh Scattering (Coherent Scattering)

Rayleigh Scattering (Coherent Scattering)

Compton Scattering (Incoherent Scattering)

Compton Scattering (Incoherent Scattering)

Effects of Binding Energy in Compton (Incoherent) Scattering

Effects of Binding Energy in Compton (Incoherent) Scattering

Pair Production

Pair Production in Nuclear Coulomb Force Field

Pair Production in Nuclear Coulomb Force Field

Pair Production in the Electric Field (Triplet Production)

Radiography Setup

Radiography Setup and Imaging Principles Radiology Setup Object Double Crystal Monochromator Si(333) Incident X-ray beam Area Detector Attenuation Law Image Image Contrast

Drawbacks of Radiography Incoherently Scattered Beam Detector Pixel Object Pixel Attenuated Beam (by absorption) Image Contrast

DEI Setup and Imaging Principles Area Detector Object Double Crystal Monochromator Si(333) Analyzer Crystal Si(333) Incident X-ray beam

Formation of DE Images Incoherently Scattered Beam is Blocked by Crystal Detector Pixel Object Pixel Enhanced Attenuated Beam

Physics of DEI Data from NSLS X27 Relative Intensity I/Io Pisano, Johnston(UNC); Sayers(NCSU); Zhong (BNL); Thomlinson (ESRF); Chapman(IIT) Low Angle Side High Angle Side 1.00 0.80 0.60 Relative Intensity I/Io 0.40 0.20 0.00 -10 -5 5 10 Analyzer Angle (mradians) Data from NSLS X27

Calculation of DEI Images Low Angle Side High Angle Side 1.00 0.80 0.60 Relative Intensity I/Io 0.40 0.20 0.00 -10 -5 5 10 Analyzer Angle (mrad)

Comparison - Conventional and DEI ACR - Phantom 6 1 0 - 0 5 4 DEI Map Conventional On the left is a road map to the test object or phantom This object is imaged with a conventional x-ray machine and the image is graded by how many of the features can be seen in the images. This number determines if a machine can be used to image women. The middle image is a conventional image or radiograph of this phantom; approximately 70% of the features are visible. The right image is our “DEI” image. This image was taken at the same dose at the middle image and shows all of the intentional features along with some things which are “impossible” with conventional radiography… tape, scratches, air bubbles...

DEI image of ACR phantom - smallest calcifications Data from NSLS X27

Cancer in Breast Tissue Pisano, Johnston(UNC); Sayers(NCSU); Zhong (BNL); Thomlinson (ESRF); Chapman(IIT) This is a sample of excised breast tissue in which there is a type of cancer called infiltrating ductal carcinoma. This is the most common type of breast cancer. This sample shows this cancer in a conventional radiograph as the lighter or white region. Our DEI images show this region in a clearer crisper way in the absorption image in the middle And shows features which are not seen in radiography at all in the refraction image. Note the three dimensional character of the refraction image…this is an intrinsically edge enhanced image which finds boundaries of materials very well. The refraction image shows the fibrosis associated with cancer much farther away than either the conventional radiography or even our DEI absorption image. This image and sample has been investigated in detail by a pathologist and our MD and shows features never before seen in radiography. Conventional DEI - Absorption DEI - Refraction BNL Sept 1997

Drawbacks of DEI Detector Pixel Object Pixel

Experimental Evidence of Problems in DEI

Experimental Results Rod, off-center Background Thick Paper -1 -0.6 -0.2 0.2 0.6 1 x 10 -5 Rod, off-center Thick Paper 200 400 600 Background Rod and Paper

Refraction images Profiles MIR DEI Position (pixels) no paper thick paper thin paper no paper 50 100 150 200 0.2 0.4 0.6 0.8 1 Position (pixels) MIR DEI

Generalization to CT Reconstruction

A Physical Model of MIR Object Voxel Khelashvili, Brankov (IIT), Chapman (U.Sask), Anastasio, Yang (IIT), Zang (BNL), Wernick (IIT) Phys. Med. Biol. 51 (2006) 221-236 Object Voxel

Multiple Ultra-Small Angle Scattering Radiation Transport Theory Approach

MIR Radiation Transfer Equation

Ultra-Small Angle Approximation

General Solution

Phase Function

Phase Function

Plane Wave Solution

Plane Wave Solution

Imaging Parameters

Experimental Conformation Lucite container – wedge shaped. Polymethylmethacrylate (PMMA) microspheres in glycerin.

Experimental Conformation

labDEI System X-ray Source Detector Analyzer Pre-mono & Mono Morrison, Nesch, Torres, Khelashvili (IIT), Hasnah (U. Qatar) Chapman (U.Sask) Detector Analyzer Pre-mono & Mono X-ray Source

Lab DEI System tissue images Morrison, Nesch, Torres, Khelashvili, Chapman (IIT) Muehleman (Rush Medical College) 1cm cartilage bone

Summary First reliable Theoretical Model of DEI – MIR has been developed that Model can be used to simulate experiments starting from source, through crystals (this was known), through object (was unknown), through analyzer crystal (partially known – dynamical theory of diffraction – but crystal and beam specific calculations need to be done). Monte – Carlo simulation of DEI/MIR imaging system (G.Khelashvili – U. Saskatchewan / Nesch LLC) CT reconstructions – some steps are already taken in this direction – J. Brankov at all “A computed tomography implementation of multiple-image radiography” Med. Phys. 33 (2006) 278-289 CSRRI (IIT) / Nesch LLC – are developing in-lab research DEI instrument

Acknowledgements L.D. Chapman (Anatomy and Cell Biology, University of Saskatchewan, Canada) J. Brankov, M. Wernick, Y. Yang, M. Anastasio (Biomed. Engineering, IIT) T. Morrison (CSRRI, IIT) and I. Nesch (Nesch LLC) C. Muehleman (Department of Anatomy and Cell Biology, Rush Medical College)