1MRC/UCT Medical Imaging Research Unit, Department of Human Biology, University of Cape Town, Cape Town, South Africa, 2Scientific and Statistical Computing Core, National Institutes of Health, Bethesda, MD, United States, 3African Institute for Mathematical Sciences, Muizenberg, South Africa, 4Children’s Infectious Diseases Clinical Research Unit, Department of Pediatrics and Child Health, Stellenbosch University, Cape Town, South Africa, 5Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States