Collimators Used in Modern Medical Imaging (Part 1) [L25]

[@saifimansoori7225]

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[@omidgharibi4354]

Answer to the question (19:35): The half-life for Re-188 is about 17 hours. After 10mins, more than 99% of initial activity still remains. So, we can assume the activity unchanged. Now we can easily multiply the activity by the sensitivity of collimator to obtain the total counts per second of Re-188: Total counts/sec = 10 MBq * 0.9 * 10^-4 = 900. Now we can calculate the number of 155 keV gamma rays counted per second which is 15.6% of the total counts: 900 * 15.6% = 140.4. If we continue counting for 10 mins, we will count a total of 140.4 * 10 * 60 = 84240 gamma rays with 155 keV of energy.

[@reyhanenosrati]

Great lecture! Thank you very much for sharing!!! a minor comment (10:15): I believe intrinsic resolution is not degraded with increasing gamma ray energy. Intrinsic resolution is actually improved with gamma ray energy because at lower energies greater statistical fluctuations occur in production of photons in the crystal. for energies above 250keV this effect becomes much smaller because of multiple Compton scattering.