32.1 Medical imaging and diagnostics  (Page 3/9)

 Page 3 / 9

Phet explorations: simplified mri

Is it a tumor? Magnetic Resonance Imaging (MRI) can tell. Your head is full of tiny radio transmitters (the nuclear spins of the hydrogen nuclei of your water molecules). In an MRI unit, these little radios can be made to broadcast their positions, giving a detailed picture of the inside of your head.

Section summary

• Radiopharmaceuticals are compounds that are used for medical imaging and therapeutics.
• The process of attaching a radioactive substance is called tagging.
• [link] lists certain diagnostic uses of radiopharmaceuticals including the isotope and activity typically used in diagnostics.
• One common imaging device is the Anger camera, which consists of a lead collimator, radiation detectors, and an analysis computer.
• Tomography performed with $\gamma$ -emitting radiopharmaceuticals is called SPECT and has the advantages of x-ray CT scans coupled with organ- and function-specific drugs.
• PET is a similar technique that uses ${\beta }^{+}$ emitters and detects the two annihilation $\gamma$ rays, which aid to localize the source.

Conceptual questions

In terms of radiation dose, what is the major difference between medical diagnostic uses of radiation and medical therapeutic uses?

One of the methods used to limit radiation dose to the patient in medical imaging is to employ isotopes with short half-lives. How would this limit the dose?

Problems&Exercises

A neutron generator uses an $\alpha$ source, such as radium, to bombard beryllium, inducing the reaction ${}^{4}\text{He}+{}^{9}\text{Be}\to {}^{\text{12}}\text{C}+n$ . Such neutron sources are called RaBe sources, or PuBe sources if they use plutonium to get the $\alpha$ s. Calculate the energy output of the reaction in MeV.

5.701 MeV

Neutrons from a source (perhaps the one discussed in the preceding problem) bombard natural molybdenum, which is 24 percent ${}^{\text{98}}\text{Mo}$ . What is the energy output of the reaction ${}^{\text{98}}\text{Mo}+n\to {}^{\text{99}}\text{Mo}+\gamma$ ? The mass of ${}^{\text{98}}\text{Mo}$ is given in Appendix A: Atomic Masses , and that of ${}^{\text{99}}\text{Mo}$ is 98.907711 u.

The purpose of producing ${}^{\text{99}}\text{Mo}$ (usually by neutron activation of natural molybdenum, as in the preceding problem) is to produce ${}^{\text{99m}}\text{Tc.}$ Using the rules, verify that the ${\beta }^{-}$ decay of ${}^{\text{99}}\text{Mo}$ produces ${}^{\text{99m}}\text{Tc}$ . (Most ${}^{\text{99m}}\text{Tc}$ nuclei produced in this decay are left in a metastable excited state denoted ${}^{\text{99m}}\text{Tc}$ .)

${}_{\text{42}}^{\text{99}}{\text{Mo}}_{\text{57}}\to {}_{\text{43}}^{\text{99}}{\text{Tc}}_{\text{56}}+{\beta }^{-}+{\overline{v}}_{e}$

(a) Two annihilation $\gamma$ rays in a PET scan originate at the same point and travel to detectors on either side of the patient. If the point of origin is 9.00 cm closer to one of the detectors, what is the difference in arrival times of the photons? (This could be used to give position information, but the time difference is small enough to make it difficult.)

(b) How accurately would you need to be able to measure arrival time differences to get a position resolution of 1.00 mm?

[link] indicates that 7.50 mCi of ${}^{\text{99m}}\text{Tc}$ is used in a brain scan. What is the mass of technetium?

$1\text{.}\text{43}×{\text{10}}^{-9}\phantom{\rule{0.25em}{0ex}}\text{g}$

The activities of ${}^{\text{131}}\text{I}$ and ${}^{\text{123}}\text{I}$ used in thyroid scans are given in [link] to be 50 and $\text{70 μ}Ci$ , respectively. Find and compare the masses of ${}^{\text{131}}\text{I}$ and ${}^{\text{123}}\text{I}$ in such scans, given their respective half-lives are 8.04 d and 13.2 h. The masses are so small that the radioiodine is usually mixed with stable iodine as a carrier to ensure normal chemistry and distribution in the body.

(a) Neutron activation of sodium, which is 100% ${}^{\text{23}}\text{Na}$ , produces ${}^{\text{24}}\text{Na}$ , which is used in some heart scans, as seen in [link] . The equation for the reaction is ${}^{\text{23}}\text{Na}+n\to {}^{\text{24}}\text{Na}+\gamma$ . Find its energy output, given the mass of ${}^{\text{24}}\text{Na}$ is 23.990962 u.

(b) What mass of ${}^{\text{24}}\text{Na}$ produces the needed 5.0-mCi activity, given its half-life is 15.0 h?

(a) 6.958 MeV

(b) $5\text{.}7×{\text{10}}^{-\text{10}}\phantom{\rule{0.25em}{0ex}}\text{g}$

Physics is a physical science that deals with the study of matter in relation to energy
what is physics
physics is a physical science that deals with the study of matter in relation to energy
Osayuwa
a15kg powerexerted by the foresafter 3second
what is displacement
movement in a direction
Jason
hello
Hosea
Explain why magnetic damping might not be effective on an object made of several thin conducting layers separated by insulation? can someone please explain this i need it for my final exam
Hi
saeid
hi
Yimam
What is thê principle behind movement of thê taps control
while
Hosea
what is atomic mass
this is the mass of an atom of an element in ratio with the mass of carbon-atom
Chukwuka
show me how to get the accuracies of the values of the resistors for the two circuits i.e for series and parallel sides
Explain why it is difficult to have an ideal machine in real life situations.
tell me
Promise
what's the s . i unit for couple?
Promise
its s.i unit is Nm
Covenant
Force×perpendicular distance N×m=Nm
Oluwakayode
İt iş diffucult to have idêal machine because of FRİCTİON definitely reduce thê efficiency
Oluwakayode
if the classica theory of specific heat is valid,what would be the thermal energy of one kmol of copper at the debye temperature (for copper is 340k)
can i get all formulas of physics
yes
haider
just broswe
Osayuwa
just browse
Osayuwa
what affects fluid
pressure
Oluwakayode
Dimension for force MLT-2
what is the dimensions of Force?
how do you calculate the 5% uncertainty of 4cm?
4cm/100×5= 0.2cm
haider