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Review Of Radiologic Physics > 9 Nuclear Medicine > Flashcards

9 Nuclear Medicine Flashcards

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1
Q

Isobars

A

–Nuclides having the same mass number A.

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2
Q

Isotopes

A

–Nuclides having the same atomic number (protons).

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3
Q

Isotones

A

–Nuclides having the same number of neutrons.

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4
Q

Isomer

A

–An isomer is the excited state of a nucleus.

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5
Q

The stable low mass number

A

–Nuclides have approximately equal numbers of neutrons (N) and protons (Z).

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6
Q

The stable high mass number

A

–Nuclides have more neutrons than protons.

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7
Q

Radionuclides

A

–Unstable nuclides.

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8
Q

Radioactive decay

A

–The transformation of an unstable nuclide.

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9
Q

A gamma-ray

A

– Electromagnetic radiation originating in a nuclear transformation.

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10
Q

Internal conversion electron

A

–The excess energy may be transferred to an orbital electron, which is then emitted from the atom as an internal conversion electron.
–After an isomeric transition, both parent and daughter nuclei have the same mass number and atomic number.

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11
Q

Metastable

A

–Isomeric states that have long lifetimes.

–To be called metastable, the half-life must be longer than 10−9 second.

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12
Q

Alpha decay,

A

–A radionuclide emits an alpha particle consisting of two neutrons and two protons.
–Alpha decay is most common in atoms with a high atomic number (Z>82).
–Energies of alpha particles are generally between 4 and 7 MeV.

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13
Q

Beta minus decay

A

–A neutron inside the nucleus is converted into a proton.
–This occurs in nuclei with an excess of neutrons (i.e., too few protons).
–The excess energy is released as an energetic electron, called a beta particle.
–The atomic number increases by one, but the mass number remains constant.

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14
Q

Antineutrinos

A neutrino

A

–Antineutrinos have no rest mass or electric charge and rarely interact with matter.

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15
Q

Average beta particle energy

A

–∼Emax/3.

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16
Q

Beta plus decay (positron emission)

A

–A proton inside the nucleus is converted into a neutron.
–The excess energy is emitted as a positively charged electron called a positron.
–Beta plus decay (positron emission) occurs in neutron-deficient nuclei (i.e., too many protons).
–Beta plus decay also results in the emission of a neutrino.
–The atomic number decreases by one and the mass number stays the
same.

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17
Q

Activity

A

–The number of transformations per unit time.
–The SI unit of activity is the becquerel (Bq).
–One becquerel is one transformation per second.
–N × λ, where N is the number of atoms in the sample.

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18
Q

Physical half-life (T1/2)

A

–The time required for a half of the radionuclide present to decay.

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19
Q

Transient equilibrium

A

– The parent radionuclide is short lived.

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20
Q

Secular equilibrium

A

– The parent is long lived.

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21
Q

Converging collimators

A

– Produce a magnified image, and FOV decreases with distance.

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22
Q

Diverging collimators

A

– Project an image size that is smaller than the object size, and FOV increases with distance.

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23
Q

Collimator sensitivity

A

– The fraction of gamma rays reaching it from all directions that pass through the holes.

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24
Q

High-sensitivity collimators

A

– Larger holes and lower resolution.

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25
Q

High-resolution collimators

A

– Smaller holes and lower sensitivity.

26
Q

The detection efficiency

A

– The percentage of incident gamma rays absorbed in the scintillator.

27
Q

A photopeak

A

– When an incident gamma ray is completely absorbed (photoelectric effect).

28
Q

Scatter events

A

– The NaI crystals occur where the energy of a Compton electron is absorbed in the crystal but the Compton scattered photon escapes.

29
Q

Energy resolution.

A

–Photopeak width is measured as the full width half maximum (FWHM).

30
Q

A pulse height analyzer (PHA)

A

– An electronic device used to determine which portion of the detected spectrum is used to create images.
–PHA analysis maximizes the number of photopeak events while minimizing the detected photons that would degrade image quality (i.e., Compton scatter).

31
Q

A long persistence screen

A

– Each count remains on the screen for a prolonged period can be used to help patient positioning.

32
Q

A true coincidence

A

–The simultaneous detection of two 511-keV annihilation photons

33
Q

Attenuation in PET

A

– It is depth independent and depends only on the total thickness of tissue traveled.

34
Q

Time of flight (TOF) PET

A

–Measuring the difference in arrival times of the two annihilation photons from an annihilation.
–TOF information can be used in the reconstruction process to improve image quality including improved spatial resolution as well as enhanced lesion contrast.
–TOF PET can identify the location of an annihilation event with an uncertainty that corresponds to a Full Width Half Maximum of ∼7.5 cm.

35
Q

Radionuclide purity

A

–The presence of unwanted radionuclides in the sample.

36
Q

Contaminant radionuclides

A

– Identified by their (distinctive) photopeak energies using gamma ray spectroscopy.

37
Q

Chromatography

A

– Separates compounds that are soluble in saline.

38
Q

Chemical purity

A

–The amount of unwanted chemical contaminants in the agent.

39
Q

Sterility

A

– The radiopharmaceutical is free of any microbial contamination.
–Even if a preparation is sterile, it may still contain pyrogens, which may cause a reaction if administered to a patient.
–Sterility and pyrogenicity tests should be performed before the agent is administered to a patient.

40
Q

The photopeak window of the PHA

A

–Evaluated by using a source that radiates the whole crystal.
–Irradiation of the whole crystal may be achieved using a sheet source, or a point source at a distance.
–The photopeak window is checked daily.

41
Q

Field uniformity

A

–The ability of the scintillation camera to reproduce a uniform distribution of activity.
–Differences in the PMT response and transmission of light in the crystal contribute to nonuniformity.
–Checked daily by placing a large-area disc made of 57Co in front of the camera.

42
Q

Contrast

A

–The difference in intensity (counts) in any abnormality compared to the intensity in the surrounding normal anatomy (background).
–Contrast is affected by septal penetration and scatter.

43
Q

Subject contrast

A

–The difference in activities in the abnormality and surrounding normal anatomy.

44
Q

Image contrast

A

–The corresponding difference in image counts in the abnormality and normal anatomy.

45
Q

The target to background ratio

A

–The ratio of organ-specific uptake to unwanted uptake in other tissues.

46
Q

Nuclear medicine resolutionis

A

–The ability to distinguish two adjacent radioactive sources.

47
Q

System resolution (R)

A

–The intrinsic resolution of the scintillation camera (Ri) and resolution of the collimator (Rc).
–R = (R2i + R2c )0.5.

48
Q

Noise

A

–Any unwanted counts in a nuclear medicine image that can interfere with the detection of abnormalities.

49
Q

Quantum mottle

A

–Random noise results from statistical variation in pixel counts.

50
Q

Quantum mottle can be reduced

A

–Increasing the number of counts in the image.
–Increasing image counts include increasing the administered activity, imaging time, or using a higher-sensitivity collimator.

51
Q

Biologic half-life (Tb)

A

–The biologic clearance.

52
Q

The effective half-life (Te)

A

– Radionuclide in any organ encompasses both radioactive decay and biologic clearance.
–It must always be shorter than the physical or biologic half-life.
–1/Te = 1/Tb + 1/T1.

53
Q

Cumulative activity

A

–The total number of nuclear transformations in an organ is called cumulative activity (A∞).

54
Q

For exponential decay, cumulative activity A∞

A

–1.44 × A × Te where A is the initial activity in the organ and Te is the effective half-life.

55
Q

S factor

A

–The radiation dose to any organ or tissue is obtained by dividing the total energy absorbed in the organ by the organ mass.
–Dividing the absorbed energy by the target organ mass gives the S factor.

56
Q

Energy absorbed in a target organ per nuclear emission in the source organ depends on three factors.

A

–The first is the number of emissions per transformation.
–The second is the energy associated with each emission.
–The third is the fraction of emitted energy deposited in the target organ.

57
Q

The dose to a target organ

A

–From activity in one source organ, is obtained by multiplying the source organ cumulative (A∞) and the source to target S factor.
–Organ dose D = A∞× Ssource→target.

58
Q

Equilibrium is always established

A

Equilibrium is always established after four daughter half-lives.

59
Q

The limit for 99Mo breakthrough

A

The limit for 99Mo breakthrough is 0.15 μCi 99Mo per mCi 99mTc.

60
Q

Typical full width half maximum width of an image of a line source obtained using a scintillation camera using a low-energy high-resolution (LEHR) collimator

A

Eight mm.

61
Q

The representative adult effective dose for a 99mTc labeled radiopharmaceutical

A

Five mSv.

62
Q

The representative adult effective dose for a PET study

A

Ten mSv.

Review Of Radiologic Physics (11 decks)

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