dorisfung,
i only know that we can take vhs to dr.tsang by this week, so haven't try this before. but, next wed, i will go to dr.tsang's clinic again. this time i will take a vhs. may be i can tell u after my next visit.
by the way, i know dr.tsang will not be in HK by mid-Dec. so, i have mark down all questions which i want to ask. so that, i won't have to wait dr.tsang's advice until Jan.