Physical, Biological and Effective Half Life

• What must be considered in a medical context regarding half-lives?

  Multiple half-life definitions
• What is the physical half-life of a radioisotope?

  The time for radioactive nuclei to halve
• What is the physical half-life denoted as?

  $T_P$
• How is the biological half-life defined?

  The time for a substance's concentration to halve
• What does the biological half-life account for?

  Excretion and respiration processes
• What factors influence the biological half-life?

  Health and metabolism of the patient
• What is the eyective half-life?

  The combined half-life of physical and biological
• How is the eyective half-life calculated?

  Using the equation $\frac{1}{T_E} =$$\frac{1}{T_P} +$$\frac{1}{T_B}$
• What is true about the eyective half-life compared to the physical and biological half-lives?

  It is always shorter than the shortest half-life
• What happens if the physical half-life is short?

  The eyective half-life is even shorter
• What happens if the biological half-life is short?

  The eyective half-life is even shorter
• What is the biological half-life of iodine-131?

  138 days
• What is the physical half-life of iodine-131?

  8.05 days
• How do you calculate the eyective half-life for iodine-131?

  Use $\frac{1}{T_E} =$$\frac{1}{8.05} +$$\frac{1}{138}$
• What is the eyective half-life of iodine-131 after calculation?

  7.60 days
• What should you remember when checking your eyective half-life answer?

  It should be the shortest of the three half-lives