# what is the radioactivity measured in mCi, of the sample?

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(a) In a sample of 1000 atoms,if 50 atoms decay in 5seconds, what is the radioactivity measured in mCi, of the sample?

b) in order to produce a level of radioactivity of 1mCi, how many nuclei of 99mTc (

?

= 3.22X10^(-5)s^(-) ) must be present? What mass of the radionuclide does this correspond to?(Avogadro’s number is 6.02X10^(23).

c) A radioactive sample of 99mTc contains 10mCi activity at 9 am.What is the radioactivity of the sample at 3pm on the same day.

2) In a nuclear medicine scan using 99mTc, the image SNR for a 30-min scan was 50:1 for an injected radioactive dose of 1 mCi (3.7X10^(7) disintegrations per second). Imaging began immediately after injection.

a) if the injected dose were doubled to 2mCi, what would be the image SNR for a 30-min scan?

b) if the scan time were doubled to 60min with an initial dose of 1mCi, what would be the image SNR?

3) Assuming that there are 6.7X10^(22) protons in 1cm^(3) of water, what is the magnetization contained within this volume at a magnetic field strength of 1.5T?

4) Calculate the effects of the following pulse sequences on thermal equilibrium magnetization. The final answer should include x,y, and z components of magnetization.

a) 90x (a pulse with tip angle 90 degrees , applied about the x axis).

b)80x.

c) 90x 90y (the second 90 degrees pulse is applied immediately after the first).

d)80x80y