A capsule containing radiolabelled 75SeHCAT (with 370 kBq of Selenium-75 and less than 0.1 mg<unk>  is taken orally with water, to ensure passage of the capsule into the gastrointestinal tract. The physical half life of 75Se is approximately 118 days; activity is adjusted to a standard reference date. Patients may be given instructions to fast prior to capsule administration; there is significant variation in clinical practice in this regard. The effective dose of radiation for an adult given 370 kBq of<unk>  is 0.26 mSv. (For comparison, the radiation exposure from an abdominal CT scan is quoted at 5.3 mSv and annual background exposure in the UK 1-3 mSv.) Measurements were originally performed with a whole-body counter but are usually performed now with an uncollimated gamma camera. The patient is scanned supine or prone with anterior and posterior acquisition from head to thigh 1 to 3 hours after taking the capsule. Scanning is repeated after 7 days. Background values are subtracted and care must be taken to avoid external sources of radiation in a nuclear medicine department. From these measurements, the percent retention of<unk>  at 7 days is calculated. A 7-day<unk>  retention value greater than 15% is considered to be normal, with values less than 15% signifying excessive bile acid loss, as found in bile acid malabsorption. With more frequent measurements, it is possible to calculate<unk>  retention whole-body half-life; this is not routinely measured in a clinical setting. A half-life of greater than 2.8 days has been quoted as normal.
SeHCAT
BDPC
PHTPP
DDAIP
DKMS
E-med
Phosmet
MOPP 