Abstract
A bright μm-sized source of hard synchrotron x-rays (critical energy Ecrit > 30 keV) based on the betatron oscillations of laser wakefield accelerated electrons has been developed. The potential of this source for medical imaging was demonstrated by performing micro-computed tomography of a human femoral trabecular bone sample, allowing full 3D reconstruction to a resolution below 50 μm. The use of a 1 cm long wakefield accelerator means that the length of the beamline (excluding the laser) is dominated by the x-ray imaging distances rather than the electron acceleration distances. The source possesses high peak brightness, which allows each image to be recorded with a single exposure and reduces the time required for a full tomographic scan. These properties make this an interesting laboratory source for many tomographic imaging applications.
Highlights
Metabolic activity and consequent rate of bone turnover
The intrinsic size of our x-ray source was smaller than a voxel and so effectively does not contribute to the final resolution
Though synchrotron-based μCT operates at much higher flux and so can be much faster, often they operate at repetition rates much higher than the detector frame rates
Summary
Metabolic activity and consequent rate of bone turnover. Trabecular microarchitecture is an important indicator of bone strength[7] and 2D histological and radiographic examination is insufficient to fully diagnose important details of the trabecular connectivity[8]. Plasma electrons trapped inside this cavity experience both longitudinal and radial focussing fields and so oscillate transversely whilst being accelerated forward These so-called betatron oscillations cause the electrons to emit synchrotron-like radiation confined to a narrow cone in the forward direction (see Methods). By using wakefield acceleration at the near-GeV level, that we can produce the required x-ray spectrum and brightness for single-shot bone imaging whilst maintaining the advantageously small x-ray source-size. The 300 TW Astra-Gemini laser pulse was focussed into a variable length helium gas cell to produce an electron beam by self-injection[19] with energies up to 1.1 GeV and > 100 pC total charge (see Methods), producing a co-propagating betatron x-ray beam-see Fig. 1a. A point projection image was produced on an x-ray CCD camera a further 120 cm away, at a geometric magnification of 2.7
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