Myocardial perfusion imaging (MPI) is one of the most commonly performed procedu

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 Bq  

Related Questions

Navigate

• Browse (All)
• Browse M
• Subjects

---