Embedded microchannel arrays for contrast agent transport in silicone MRI phantoms

Abstract

Clinically relevant MRI phantoms play a key role in the development of imaging techniques and surgical practice, using tissue mimicking materials to replicate the architectures and signal response for a specific anatomical region. Tailoring the physical and chemical properties of these materials to match the magnetic resonance relaxation times, T₁ and T₂, of native tissues is fundamental for the development of pathophysiological assessments (e.g. dementia), and monitoring the progression and treatment of disease (e.g. cancer and arthritis). The detection of tumours with MRI relies on the accumulation of contrast agents in the extravascular and extracellular space, producing higher signal intensities than the surrounding healthy tissue. This plays a pivotal role in evaluating pharmokinetic parameters in patients, however, is not yet replicated in MRI phantoms. To realistically reproduce anatomical size-scales, sub-voxel features are required within macro-scale phantoms such as micro-channels to form perfusion phantoms. In this work, we used replica lithography and sacrificial wax moulding to embed microchannel arrays (D: 500-1000 um) into a silicone phantom to simulate the perfusion of a gadolinium contrast agent, imaged using a 7 Tesla pre-clinical MRI scanner. We attempted to simulate interstitial tissue accumulation and characterise the signal enhancement of an adjacent poly(ethylene glycol) diacrylate phase in response to contrast agent permeation. We mimicked the arterial bolus and demonstrated contrast agent accumulation, with full- and partial-volume voxel (1x1x1 mm) assessment reflecting the spatial movement of gadolinium. Fabricating sub-voxel features remains technically challenging, however, combined with permeable secondary phases, they may replicate the role of capillary networks in contrast agent exchange within tumours.