# 32.1 Medical imaging and diagnostics  (Page 3/9)

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

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Luke
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the basic formula is uncertainty in momentum multiplied buy uncertainty In position is greater than or equal to 4×pi/2. same formula for energy and time
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what is the dimension of strain
Is there a formula for time of free fall given that the body has initial velocity? In other words, formula for time that takes a downward-shot projectile to hit the ground. Thanks!
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Maxamed
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50 N... (50 *1.732)N
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Is earth is an inertial frame?
The abacus (plural abaci or abacuses), also called a counting frame, is a calculating tool that was in use in Europe, China and Russia, centuries before the adoption of the written Hindu–Arabic numeral system
Sahim
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Is earth inertia frame?
Sahim
only the center
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What is an abucus?
Irungu
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prakash
a load of 20N on a wire of cross sectional area 8×10^-7m produces an extension of 10.4m. calculate the young modules of the material of the wire is of length 5m
Young's modulus = stress/strain strain = extension/length (x/l) stress = force/area (F/A) stress/strain is F l/A x
El
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Ebenezer
Ebenezer
two bodies x and y start from rest and move with uniform acceleration of a and 4a respectively. if the bodies cover the same distance in terms of tx and ty what is the ratio of tx to ty
what is cesium atoms?
The atoms which form the element Cesium are known as Cesium atoms.
Naman
A material that combines with and removes trace gases from vacuum tubes.
Shankar
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Varun
Heat capacity can be defined as the amount of thermal energy required to warm the sample by 1°C. entropy is the disorder of the system. heat capacity is high when the disorder is high.
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What is realm
The quantum realm, also called the quantum scale, is a term of art inphysics referring to scales where quantum mechanical effects become important when studied as an isolated system. Typically, this means distances of 100 nanometers (10−9meters) or less or at very low temperature.
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what is mean by Newtonian principle of Relativity? definition and explanation with example