[1] Univ Stellenbosch, Tygerberg Hosp, Dept Med Imaging & Clin Oncol, Div Radiodiagnosis, Cape Town, South Africa
[2] MRC, Biostat Unit, Cape Town, South Africa
[3] Tygerberg Childrens Hosp, Dept Paediat & Child Hlth, Cape Town, South Africa
[4] Univ Stellenbosch, Cape Town, South Africa
[5] New Groote Schuur Hosp, Dept Radiat Med, Div Radiol, Cape Town, South Africa
[6] Univ Cape Town, ZA-7925 Cape Town, South Africa
[7] Univ Cape Town, Dept Paediat & Child Hlth, Red Cross War Mem Childrens Hosp, ZA-7925 Cape Town, South Africa
[8] Univ Cape Town, MRC Unit Child & Adolescent Hlth, ZA-7925 Cape Town, South Africa