Final answer:
The correct reagent for a gallbladder ejection fraction test is 99mTc-HIDA, as it is specifically absorbed by the gallbladder and visualized via cholescintigraphy.
Step-by-step explanation:
The reagent used in a gallbladder ejection fraction test is 99mTc-HIDA, also known as hydroxy iminodiacetic acid. This radioactive material is ideal for gallbladder scans because it is taken up by the gallbladder, allowing medical professionals to measure gallbladder function through a process referred to as cholescintigraphy.
Other reagents listed, such as 99mTc-sulfur colloid and 99mTc-sestamibi, are used for different types of nuclear medicine scans, but not specifically for gallbladder ejection fraction tests.