The first involves sheep. Researchers have found that hair sheep are a good source of blood for use in tests to diagnose infectious diseases in people.

VOA: special.2009.08.03

They use food frequency questionnaires, which I mentioned before, surveys, and then biological markers like blood tests of certain things to see how diet is related to health.

研究员还运用食物频率调查表,我之前曾提到过,各类调查以及生物标志物,像是血液检测等手段,来研究饮食与健康之间的关系

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选

So tests often use human blood instead.

VOA: special.2009.08.03

A spokesman for the group says CT scans are frequently used in hospital emergency rooms because the results can be read quicker than with other tests, like ultrasound or MRIs, that do not use radiation.

VOA: standard.2010.01.30