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Medical Physics 2nd Semester > Nuclear Medicine Midterm > Flashcards

Nuclear Medicine Midterm Flashcards

This is NOT everything that will be on the exam. Instead it's some useful stuff to have memorized.

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1
Q

What is the proper name for an electron ejected from an atom by a gamma ray emitted from the nucleus of the same atom?

A

Conversion electrons

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2
Q

What is the difference between isotopes, isotones, isobars and isomers?

A

Isotopes: Same # of protons

Isotones: Same # of neutrons

Isobars: Same A value

Isomers: Everything is same except energy

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3
Q

Conventional and SI units for dose?

A

Conventional: 1 rad = 100 erg/gm

SI: 1 Gy = 100 rad

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4
Q

True or false, for “Nuclear Medicine” radiations, D(rad) = X(R)?

A

True

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5
Q

What are the units of LET?

A

Energy deposited/distance. Often described as,

keV/µ

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6
Q

What is the number that expresses differences among different radiations in producing biological effects?

A

Relative Biological Effectiveness (RBE)

RBE = Dstandard radiation/Dtest radiation

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7
Q

Units of dose equivalent?

A

H = wrD

Conventional: 1 rem = 100 erg/gm

SI: 1 Sv = 100 rem = 1 J/kg

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8
Q

Units of effective dose?

A

E = ΣwTHT

Conventional: 1 rem = 100 erg/gm

SI: 1 Sv = 100 rem

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9
Q

What number is used to describe the relative sensitivity of tissue to radiogenic cancer or hereditary damage?

A

Tissue weighting factor (wT)

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10
Q

Above what Z value are all isotopes radioactive?

A

Z >= 90

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11
Q

What the is process called in which an emitted gamma ray ejects an orbital electron?

A

Internal Conversion (it’s essentially the nucleus equivalent of Auger electrons)

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12
Q

Which of the following reactions are isobaric?

A) Alpha decay
B) Negatron decay

C) Electron capture
D) Positron Decay

A

B,C and D

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13
Q

What is the mathematical definition fo activity?

A

A = (lambda)N

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14
Q

Equation for effective half-life

A

Te = TpTb/(Tp+Tb)

Where Tp is physical half-life and Tb is biological half-life

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15
Q

Average life equation

A

(tau) = 1/(lambda)

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16
Q

Condition for secular equilibrium to occur

A

Tp >> Td

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17
Q

Formulas for standard deviation and percent standard deviation/variance.

A

SD = sqrt(N)

%SD or V = 100%/sqrt(N) = sqrt(N)/N

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18
Q

What variable is often taken to express the “noise” of an imagine?

A

%SD

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19
Q

If you take a 512x512 image, then convert it to 256x256 but retain all the data,

What happens to the pixel size?

What happens to the counts per pixel?

What happens to noise?

A

Pixel size is doubled

Counts per pixel is quadrupled

Noise is halved

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20
Q

What is the pixel dimension requirement for the Nyquist criterion?

A

Dimension of each pixel ~ 1/3 FWHM

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21
Q

What is the ideal pixel setup in the Nyquist crierion?

A

Use the coarsest matrix (ie largest pixels) that are compatible with the practically achievable spatial resolution.

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22
Q

Typical speed of a whole body scan?

A

5-15 cm/min

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23
Q

Difference between Un-gated and gate dynamic imaging?

A

Un-gated: images or frames acquired sequentially from beginning to end of acquisition. No summation of frames.

Gates: images or frames at different points of recurring process. 1 temporally summed image per time point.

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24
Q

Definition of count rate,

Standard deviation of count rate,

Standard deviation of NET count rate.

A

R = N/(delta)t

SDR = sqrt(R)

SDRn = sqrt(Rg/(delta)tg + Rb/(delta)tb​)

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25
Q

Detection efficiency = gp x (epsilon) x Escape Fraction x fp

About what is the value of the detection efficiency? What contirbutes the most loss?

A

D ~ 0.001 - 0.01

Geometric efficiency

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26
Q

Name one use for each of the following ionization detectors.

Ionization Chamber

Proportional Counter

Geiger counter

Solid-state ionization detector

A

Ionization Chamber - calibration chamber, dose calibrator

Proportional Counter - research

Geiger counter - survey meter

Solid-state ionization detector - intraoperative probe or gamma cameras

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27
Q

How often are accuracy and constancy quality control checked for?

A

Daily and/or after servicing

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28
Q

How often is linearity checked for? What are the two methods used to check linearity?

A

Quarterly and/or after servicing

Decay method using Tc-99m or Shield method

29
Q

How often should any geometry quality control be performed?

What are the two types of geometry quality controls?

A

At installation

Volume and Position

30
Q

Be able to identify this entire image and the parts,

A
31
Q

Definition of FWHM of a photopeak

A

(delta E at half maximum) / Ephoto peak

32
Q

Which is better energy resolution, lower or higher?

A

Lower. You always want lower energy resolution. Remember it’s a percentage, lower percent means less spread.

33
Q

Range of photopeak energy window

A

20% energy window

34
Q

Magnification per dynode in a PMT

A

3x more electrons per dynode hit

35
Q

True or false

Diagnostic use of radiopharmeceuticals is very low dose rate and very low risk

A

True

0.05% increase risk of cancer per rem.

Only threat is for pregnant women, 50% increase risk per rem

36
Q

Relationship between potential energy and binding energy

A

PE = -BE

37
Q

What is the defining characteristic as to how much damage a type of radiation causes?

A

How dense and focused the dose delivery is

Ex. Alpha particles give a very concentrated dose 100 keV/micron

38
Q

True or false

Low oxygen tissue is less resistant to most radiations?

A

False. It’s more resistant

39
Q

What is used as a single-value metric of overall radiation damage comparable among different types of irradiation?

A

Effective Dose

40
Q

By definition, what is the time to decay if all radionuclei in a sample decayed at the same exact time?

A

Mean lifetime

41
Q

In secular equilibrium, about how many half-lives does it take for the daughter nuclei to have same activity as parent?

A

about 4

42
Q

In transient equilibrium, after how many half-lives will the daughter nuclei have maximum activity?

A

About 4 half-lives

This is why you elute a generator every 4 half-lives

43
Q

What is the definition of critical energy.

Extra points: what is the equation?

A

Definition: energy at which collisional energy losses = radiative

Ec = 1600mec2/Z

44
Q

In general, higher spatial frequency means ______ signal.

A

Reduced

It’s harder to pickup higher frequency signal

45
Q

Memorize the following definition equations,

Sensitivity: true-positive fraction =

Specificity: true-negative fraction =

Accuracy: Fraction of correct diagnoses =

Positive predictive value =

Negative predictive value =

A

Sensitivity = TP / (TP+FN) (Fraction of positives you’re able to call)

Specificity = TN / (TN+FP) fraction of negatives you’re able to call)

Accuracy = (TP + TN) / (TP + FP + TN + FN) (fraction of total diagnosis that were correctly made)

Positive predictive value = TP / (TP + FP) (fraction of total positive predictions that were actually positive)

Negative predictive value = TN / (TN + FN) (fraction of total negative predictions that were actually negative)

46
Q

Memorize the following graph of receiver-operator characteristic curve (ROC)

A
47
Q

% uptake formula

A

Net count rate / (Net count rate given to patient / F)

or

F(Net count rate) / (Net count rate given to patient)

Where F is the fraction of admistered activity to standard

48
Q

Know these two diagrams. They will almost definitely be on the exam.

A
49
Q

Name for performance without a collimator. What about with a collimator?

A

Without: intrinsic performance

With: extrinsic or system performance

50
Q

In terms of the crystal area, what is the clinical imaging area of a gamma camera?

A

Inner-most 75% of the crystal area

Defined as the Central Field of View CFOV

(usual FOV is the entire crystal area)

51
Q

What percent septal penetration is tolerable?

A

5%

52
Q

In general, what happens to sensitivity when going from low-energy septal rating to high energy? What about resolution?

A

Both drop

Septa get thicker and longer. Even though the holes get wider, still less photons are making it to the crystal.

53
Q

For a higher-sensitivity gamma camera, what should you do to the holes? What is the tradeoff?

A

Widen hole size

Decreases resolution

54
Q

For a higher-resolution gamma camera, what should you do to the holes? What is the tradeoff?

A

Make the holes more narrow

Reduces sensitivity

55
Q

In general, how is FWHMcollimator of a gamma camera affected when you increase the source to aperture distance.

How bout when you increase the hole width?

A

Increase source to aperture distance - increase FWHM

Increasing hole width - increase FWHM

56
Q

True or false

Increasing the PMT dimensions will over estimate the position of an event in a gamma camera?

A

False

PMT dimensions has no affect at all on position of event calculation

57
Q

Equation for integral uniformity

A

100% x (Max pixel counts - min pixel counts) / (Max pixel counts + min pixel counts)

58
Q

Procedure to find differential uniformity

A

Take the maximum value of the integral uniformity of individual 1x5 and 5x1 sets of pixels

59
Q

What is the ideal uniformity?

A

0%

60
Q

How often should you do a uniformity check with Tc-99m?

What about for other isotopes?

A

Daily

Monthly

61
Q

What is the allowed uniformity value for a Tc-99m check? what about for other isotopes.

A

< 3% for Tc-99m

< 5% for other isotopes

62
Q

How far away should you position your isotopes in uniformity and sensitivity checks from the detector? Why?

A

Atleast 3 x largest detector dimensiona way

So approximation to a point source can be made, and differences at peripheral are small

63
Q

What energy range is used for

low-energy collimators

medium-energy collimators

high-energy collimators

A

low-energy collimators: 0< 200 keV

medium-energy collimator: 200 - 300 keV

high-energy collimators: > 300 keV

64
Q

What energy rating collimator would you use for Tc-99m?

A

Low

(highest enegry photon from Tc-99m is 140 keV

65
Q

For extrinsic routine check of gamma camera uniformity, which source do you use?

100-200 µCi Co-57 point source

100-200 µCi Co-57 flood (sheet) source

10-20 mCi Co-57 point source

10-20 mCi Co-57 flood (sheet) source

A

10-20 mCi Co-57 flood (sheet) source

66
Q

When you have a pattern of a bunch of cold spots equally spaced on a gamma camera flood image, what is that most likely an issue of?

A

Software corrections being off, corrupted or outdated

67
Q

How often do you need to check flood-field uniformity of your gamma camera for Tc-99m or Co-57?

About how many counts do you want in your flood image?

A

Daily check

10-15 million counts

68
Q

How often should you check gamma camera spatial resolution using a resolution phantom (or mask)?

A

Weekly

69
Q

How many counts should you have for a uniformity correction?

What about sensitivity flood correction?

A

Uniformity - 10-15 mil

Sensitivity - 60 - 100 mil

Medical Physics 2nd Semester (7 decks)

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