Abstract
Introduction: Pre-clinical Glioblastoma multiforme (GBM) research replicates the brain environment via an orthotopic model with tumour cells implanted into the mouse brain [1]. Sensitive and non-invasive imaging techniques are an essential tool for monitoring tumour growth and the response to treatment. Dual energy X-ray analysis (DEXA) exploits the energy dependence of the attenuation coefficient. Dual energy CT data is transformed into maps representing the electron volume density and an effective atomic number attributed to the photoelectric effect [3]. Synchrotron CT [2] is employed to study soft tissue structures within the mouse brain and we investigate whether DEXA offers additional information for resolving GBM from healthy tissue.
Method: Healthy ex-vivo mice and mice that were 2 week post surgical implantation of 50 uL GBM cells [4], were euthanised, frozen [5] and subject to synchrotron CT. Studies were repeated for two scan geometries with narrow and wide air gap between sample and image receptor.
Results: Synchrotron CT is capable of delivering good image quality with 20-50 um pixel size and slice thickness. The combination of a beam with high spatial coherence and a detection system with excellent spatial resolution introduces a further contrast enhancement from refraction, also called phase-contrast, manifest as edge enhancement along boundaries with steep gradients in electron density.
Conclusion: Reconstruction by filtered backprojection amplifies the image receptor dark signal to produce ghostly ring artefacts nearer the CT rotation axis. DEXA requires spatial co-registration [6] to account for beam displacement between different energies. Image quality is enhanced by 5 m air gap, rejecting coherent scatter and reducing soft tissue attenuation coefficients [7] by a few percent. DEXA finds near uniform electron density and resolves small compositional differences between brain tissues. Results show indirect evidence of GBM and surgery as the surrounding healthy brain tissues become displaced and distorted by the mass effect.