Reducing beam hardening effects and metal artefacts in spectral CT using Medipix3RX

Kishore Rajendran ,J P Ronaldson,J L Mohr,Joseph L Healy ,Niels J A De Ruiter ,Nanette Schleich ,N Anderson ,S J Nik,Alexander I Chernoglazov ,Ali Atharifard ,Alex M T Opie ,Christopher Bateman ,Michael F Walsh ,Tim B F Woodfield ,P H Butler ,V B H Mandalika ,M.n Clyne ,Aamir Raja ,Raj Kumar Panta ,Seamus Tredinnick ,Steven P Gieseg ,Philip J Bones ,Derek J Smithies ,Stephen T Bell ,Nick Cook ,Anthony Butler ,Raphaël Grasset ,Peter Renaud ,Christoph Bartneck ,R Doesburg ,Mark Billinghurst

doi:10.1088/1748-0221/9/03/p03015

Abstract

This paper discusses methods for reducing beam hardening effects and metal artefacts using spectral x-ray information in biomaterial samples. A small-animal spectral scanner was operated in the 15 to 80 keV x-ray energy range for this study. We use the photon-processing features of a CdTe-Medipix3RX ASIC in charge summing mode to reduce beam hardening and associated artefacts. We present spectral data collected for metal alloy samples, its analysis using algebraic 3D reconstruction software and volume visualisation using a custom volume rendering software. The cupping effect and streak artefacts are quantified in the spectral datasets. The results show reduction in beam hardening effects and metal artefacts in the narrow high energy range acquired using the spectroscopic detector. A post-reconstruction comparison between CdTe-Medipix3RX and Si-Medipix3.1 is discussed. The raw data and processed data are made available (http://hdl.handle.net/10092/8851) for testing with other software routines.

Highlights

Data acquisition from discrete energy ranges at a single exposure [12, 13]
The gray level inhomogeneities are reflected in the Contrast to Noise Ratio (CNR)
The CNR between metal and polymethyl methacrylate (PMMA) regions is relatively high in the last two energy ranges while the high variance in the metal region affects the global contrast in the energy ranges corresponding to [15, 80] keV and [35, 80] keV

Summary

Introduction

The ASIC was designed to count photon events and categorise them based on energy thresholds specified by the user This feature primarily enables the capture of spectral signatures for multiple materials which can be used for material discrimination. Charge sharing occurs when the charge carriers from a single photon event spread across the boundaries of multiple pixels and are counted as separate low energy events thereby distorting the spatial and spectral resolution. To overcome this problem, the new Medipix3RX enables a fully operational Charge Summing Mode (CSM) [12]. Porous scaffolds of these metals are usually implanted in bone to study bone ingrowth [19, 20] and were chosen for this study due to its clinical relevance

Methods

Results

Conclusion