Myocardial perfusion imaging (MPI) is one of the most commonly performed procedu
ID: 2009897 • Letter: M
Question
Myocardial perfusion imaging (MPI) is one of the most commonly performed procedures in SPECT. In this procedure a patient would intravenously receive a 99mTc labeled agent. When we consider radioactivity in the body it is eliminated in two ways: (1) by its physical decay constant p, and (2) by its biological elimination decay constant b. Therefore, we must define the effective decay constant as e = p+b.
a) Considering both half-lives, derive an expression describing the activity of 99mTc as a function of time given an initial activity of the radionuclide ingested by the individual.
b) If the physical half-life of 99mTc is 6 hours and the biological half-life of the 99mTc labeled compound is 12 hours. What is the effective decay constant in hr^-1.
c) If a patient is injected with 25 mCi(1Ci = 3.7×1010Bq), how much activity will there be remaining after 24 hours? What fraction is this of the initial activity?
Any help would be greatly appreciated!!!! =)
Explanation / Answer
a) Given the effective decay constant of 99m Tc is e = p + b initial activity of radioactive nucleus is A o = e N o activity of nucleus is A = e N = e N o e -e t b) physical half-life of 99mTc is 6 hours biological half-life of the 99mTc is 12 hours. e = p + b 1 / t e = 1/ t p + 1 / t b = 1 / 6 + 1/ 12 te = 4 hr effective decay constant e = 0.693 / 4 hr = 0.17324 h r -1 c) initial activity of the sample is A o = 25 mCi = 25 *10-3 * 3.7*1010 Bq = 9.25*108 Bq activity of the sample after 24 hours is A = A o e -e t = ( 9.25*108 Bq ) ( e 0.17324*24 ) =( 9.25*108 Bq ) ( 0.015642) = 1.4469*107 BqRelated Questions
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