Callaghan was responsible for the launch of 7T MRI at University College London. Her research considers advanced, microstructure brain imaging as a means to understand the structure and function of brains. She makes use of quantitative imaging to understand tissue microstructure through measurements of iron levels and myelination. In particular, 7T MRI offers hope to interrogate the neural circuitry that is involved with human cognition. She is interested in inter-individual ageing and in-vivo histology using MRI.