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The figure shows a patient undergoing a scan in a cylindrical device. The P E T system uses two gamma ray photons produced by positron electron annihilation. These gamma rays are emitted in opposite directions.
A PET system takes advantage of the two identical γ size 12{γ} {} -ray photons produced by positron-electron annihilation. These γ size 12{γ} {} rays are emitted in opposite directions, so that the line along which each pair is emitted is determined. Various events detected by several pairs of detectors are then analyzed by the computer to form an accurate image.

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.

Simplified MRI

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 γ size 12{γ} {} -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 β + size 12{β rSup { size 8{+{}} } } {} emitters and detects the two annihilation γ size 12{γ} {} 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?

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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?

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Problems&Exercises

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

5.701 MeV

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

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

42 99 Mo 57 43 99 Tc 56 + β + v ¯ e

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(a) Two annihilation γ size 12{γ} {} 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?

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[link] indicates that 7.50 mCi of 99m Tc size 12{"" lSup { size 8{"99m"} } "Tc"} {} is used in a brain scan. What is the mass of technetium?

1 . 43 × 10 9 g size 12{1 "." "43" times "10" rSup { size 8{ - 9} } `g} {}

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The activities of 131 I size 12{"" lSup { size 8{"131"} } I} {} and 123 I size 12{"" lSup { size 8{"123"} } I} {} used in thyroid scans are given in [link] to be 50 and 70 μ Ci , respectively. Find and compare the masses of 131 I and 123 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.

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

(b) What mass of 24 Na size 12{"" lSup { size 8{"24"} } "Na"} {} produces the needed 5.0-mCi activity, given its half-life is 15.0 h?

(a) 6.958 MeV

(b) 5 . 7 × 10 10 g size 12{5 "." 7 times "10" rSup { size 8{ - "10"} } `g} {}

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Questions & Answers

kinetic functional force
Moyagabo Reply
what is a principal wave?
Haider Reply
A wave the movement of particles on rest position transferring energy from one place to another
Gabche
not wave. i need to know principal wave or waves.
Haider
principle wave is a superposition of wave when two or more waves meet at a point , whose amplitude is the algebraic sum of the amplitude of the waves
arshad
kindly define principal wave not principle wave (principle of super position) if u can understand my question
Haider
what is a model?
Ella Reply
hi
Muhanned
why are electros emitted only when the frequency of the incident radiation is greater than a certain value
ANSELEM Reply
b/c u have to know that for emission of electron need specific amount of energy which are gain by electron for emission . if incident rays have that amount of energy electron can be emitted, otherwise no way.
Nazir
search photoelectric effect on Google
Nazir
what is ohm's law
Pamilerin Reply
states that electric current in a given metallic conductor is directly proportional to the potential difference applied between its end, provided that the temperature of the conductor and other physical factors such as length and cross-sectional area remains constant. mathematically V=IR
ANIEFIOK
hi
Gundala
A body travelling at a velocity of 30ms^-1 in a straight line is brought to rest by application of brakes. if it covers a distance of 100m during this period, find the retardation.
Pamilerin Reply
just use v^2-u^2=2as
Gundala
how often does electrolyte emits?
alhassan
just use +€^3.7°√π%-4¢•∆¥%
v^2-u^2=2as v=0,u=30,s=100 -30^2=2a*100 -900=200a a=-900/200 a=-4.5m/s^2
akinyemi
what is distribution of trade
Grace Reply
what's acceleration
Joshua Reply
The change in position of an object with respect to time
Mfizi
Acceleration is velocity all over time
Pamilerin
hi
Stephen
It's not It's the change of velocity relative to time
Laura
Velocity is the change of position relative to time
Laura
acceleration it is the rate of change in velocity with time
Stephen
acceleration is change in velocity per rate of time
Noara
what is ohm's law
Stephen
Ohm's law is related to resistance by which volatge is the multiplication of current and resistance ( U=RI)
Laura
acceleration is the rate of change. of displacement with time.
Radical
the rate of change of velocity is called acceleration
Asma
how i don understand
Willam Reply
how do I access the Multiple Choice Questions? the button never works and the essay one doesn't either
Savannah Reply
How do you determine the magnitude of force
Peace Reply
mass × acceleration OR Work done ÷ distance
Seema
Which eye defect is corrected by a lens having different curvatures in two perpendicular directions?
Valentina Reply
acute astigmatism?
the difference between virtual work and virtual displacement
Noman Reply
How do you calculate uncertainties
Ancilla Reply
What is Elasticity
Salim Reply
the property of a body to regain it's original shape is called elasticity. or. the property of a body which can be stretch is called elasticity.
Nazir
Practice Key Terms 6

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Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
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