A radioactive material is injected inside a body tissue to be used for imaging a
ID: 1548709 • Letter: A
Question
A radioactive material is injected inside a body tissue to be used for imaging applications. The biological half life of the material inside the body is 20 hours If the effective half life is4 hours then find the physical half life of the radioactive materials in days hours and in seconds. The physical half life of a radioactive material is 40 minutes. With what rate (biological half life) the body should excrete the materials so that its effective half life is one fifth of its biological half life. The physical half-life of a radioactive tracer is 20 hours while its biological half- life is 15 hours. The radiologist found that the current effective half-life is too long and needs to be reduced. By how much the biological half life should increase such that the effective half-life reduces 3 times while the physical half life remain the same. The activity of certain mass of radioactive Tc-99 is 200 mCi at 3:00 pm. If its activity reduced to 160 milli Curie (mCi) by 5 pm, then how much mass of Tc-99 is lost. Decay constant of Tc-99 is 1.92 times 10^-3 minute. How long will take for Tc-99 to lose half of its mass present at 3:00 pm? T_1 time constant of an MRI signal is 10 mil How long will it take for 80% of the magnetization to come back into the original z-direction? What percent of the protons' spin phased in x-y plane will de-phase in a time double than the T_2 time constant? For Graduates only: An RF signal of frequency 9 times 10^6 Hz is needed in an MRI imaging when an external field of 2.5 T is applied. What gradient magnetic field should be applied to make resonance with an RF signal of frequency 9.5 times 10^6 Hz.Explanation / Answer
(a) biological half life time= Tb=20 h
effective half life time=Te=4 h
we need the physical half life time Tp
1/Te= 1/Tb + 1/Tp
1/4= 1/20+ 1/Tp
1/4- 1/20= 1/Tp
Tp= 5 hours.
so physical half life time=Tp= 5 hours.
(b) physical half life time= Tb=40 mi
effective half life time =1/5 biological effective half life time
Te= 1/5 Tb
1/Te= 1/Tb + 1/Tp
1/[(1/5) Tb]= 1/Tb+ 1/40
5/Tb-1/Tb= 1/40
4/Tb=1/40
Tb= 40*4
Tb=160 minutes
Tb=2 hours and 40 minutes
so Biolgical half life time=Tp= 2 hours and 40 mins.