[1] Univ Aberdeen, Dept Gen Practice & Primary Care, Aberdeen AB9 2AY, Scotland
[2] Univ Aberdeen, Dept Radiol, Aberdeen AB9 2AY, Scotland
[3] Med Coll Georgia, Dept Med, Augusta, GA 30912 USA
[4] Aberdeen Royal Hosp NHS Trust, Aberdeen Matern Hosp, Aberdeen, Scotland
[5] Grampian Healthcare NHS Trust, Dept Radiol, Aberdeen, Scotland