Nuclear Medicine Midterm Flashcards
This is NOT everything that will be on the exam. Instead it's some useful stuff to have memorized.
What is the proper name for an electron ejected from an atom by a gamma ray emitted from the nucleus of the same atom?
Conversion electrons
What is the difference between isotopes, isotones, isobars and isomers?
Isotopes: Same # of protons
Isotones: Same # of neutrons
Isobars: Same A value
Isomers: Everything is same except energy
Conventional and SI units for dose?
Conventional: 1 rad = 100 erg/gm
SI: 1 Gy = 100 rad
True or false, for “Nuclear Medicine” radiations, D(rad) = X(R)?
True
What are the units of LET?
Energy deposited/distance. Often described as,
keV/µ
What is the number that expresses differences among different radiations in producing biological effects?
Relative Biological Effectiveness (RBE)
RBE = Dstandard radiation/Dtest radiation
Units of dose equivalent?
H = wrD
Conventional: 1 rem = 100 erg/gm
SI: 1 Sv = 100 rem = 1 J/kg
Units of effective dose?
E = ΣwTHT
Conventional: 1 rem = 100 erg/gm
SI: 1 Sv = 100 rem
What number is used to describe the relative sensitivity of tissue to radiogenic cancer or hereditary damage?
Tissue weighting factor (wT)
Above what Z value are all isotopes radioactive?
Z >= 90
What the is process called in which an emitted gamma ray ejects an orbital electron?
Internal Conversion (it’s essentially the nucleus equivalent of Auger electrons)
Which of the following reactions are isobaric?
A) Alpha decay
B) Negatron decay
C) Electron capture
D) Positron Decay
B,C and D
What is the mathematical definition fo activity?
A = (lambda)N
Equation for effective half-life
Te = TpTb/(Tp+Tb)
Where Tp is physical half-life and Tb is biological half-life
Average life equation
(tau) = 1/(lambda)
Condition for secular equilibrium to occur
Tp >> Td
Formulas for standard deviation and percent standard deviation/variance.
SD = sqrt(N)
%SD or V = 100%/sqrt(N) = sqrt(N)/N
What variable is often taken to express the “noise” of an imagine?
%SD
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?
Pixel size is doubled
Counts per pixel is quadrupled
Noise is halved
What is the pixel dimension requirement for the Nyquist criterion?
Dimension of each pixel ~ 1/3 FWHM
What is the ideal pixel setup in the Nyquist crierion?
Use the coarsest matrix (ie largest pixels) that are compatible with the practically achievable spatial resolution.
Typical speed of a whole body scan?
5-15 cm/min
Difference between Un-gated and gate dynamic imaging?
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.
Definition of count rate,
Standard deviation of count rate,
Standard deviation of NET count rate.
R = N/(delta)t
SDR = sqrt(R)
SDRn = sqrt(Rg/(delta)tg + Rb/(delta)tb)
Detection efficiency = gp x (epsilon) x Escape Fraction x fp
About what is the value of the detection efficiency? What contirbutes the most loss?
D ~ 0.001 - 0.01
Geometric efficiency
Name one use for each of the following ionization detectors.
Ionization Chamber
Proportional Counter
Geiger counter
Solid-state ionization detector
Ionization Chamber - calibration chamber, dose calibrator
Proportional Counter - research
Geiger counter - survey meter
Solid-state ionization detector - intraoperative probe or gamma cameras
How often are accuracy and constancy quality control checked for?
Daily and/or after servicing
How often is linearity checked for? What are the two methods used to check linearity?
Quarterly and/or after servicing
Decay method using Tc-99m or Shield method
How often should any geometry quality control be performed?
What are the two types of geometry quality controls?
At installation
Volume and Position
Be able to identify this entire image and the parts,
Definition of FWHM of a photopeak
(delta E at half maximum) / Ephoto peak
Which is better energy resolution, lower or higher?
Lower. You always want lower energy resolution. Remember it’s a percentage, lower percent means less spread.
Range of photopeak energy window
20% energy window
Magnification per dynode in a PMT
3x more electrons per dynode hit
True or false
Diagnostic use of radiopharmeceuticals is very low dose rate and very low risk
True
0.05% increase risk of cancer per rem.
Only threat is for pregnant women, 50% increase risk per rem
Relationship between potential energy and binding energy
PE = -BE
What is the defining characteristic as to how much damage a type of radiation causes?
How dense and focused the dose delivery is
Ex. Alpha particles give a very concentrated dose 100 keV/micron
True or false
Low oxygen tissue is less resistant to most radiations?
False. It’s more resistant
What is used as a single-value metric of overall radiation damage comparable among different types of irradiation?
Effective Dose
By definition, what is the time to decay if all radionuclei in a sample decayed at the same exact time?
Mean lifetime
In secular equilibrium, about how many half-lives does it take for the daughter nuclei to have same activity as parent?
about 4
In transient equilibrium, after how many half-lives will the daughter nuclei have maximum activity?
About 4 half-lives
This is why you elute a generator every 4 half-lives
What is the definition of critical energy.
Extra points: what is the equation?
Definition: energy at which collisional energy losses = radiative
Ec = 1600mec2/Z
In general, higher spatial frequency means ______ signal.
Reduced
It’s harder to pickup higher frequency signal
Memorize the following definition equations,
Sensitivity: true-positive fraction =
Specificity: true-negative fraction =
Accuracy: Fraction of correct diagnoses =
Positive predictive value =
Negative predictive value =
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)
Memorize the following graph of receiver-operator characteristic curve (ROC)
% uptake formula
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
Know these two diagrams. They will almost definitely be on the exam.
Name for performance without a collimator. What about with a collimator?
Without: intrinsic performance
With: extrinsic or system performance
In terms of the crystal area, what is the clinical imaging area of a gamma camera?
Inner-most 75% of the crystal area
Defined as the Central Field of View CFOV
(usual FOV is the entire crystal area)
What percent septal penetration is tolerable?
5%
In general, what happens to sensitivity when going from low-energy septal rating to high energy? What about resolution?
Both drop
Septa get thicker and longer. Even though the holes get wider, still less photons are making it to the crystal.
For a higher-sensitivity gamma camera, what should you do to the holes? What is the tradeoff?
Widen hole size
Decreases resolution
For a higher-resolution gamma camera, what should you do to the holes? What is the tradeoff?
Make the holes more narrow
Reduces sensitivity
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?
Increase source to aperture distance - increase FWHM
Increasing hole width - increase FWHM
True or false
Increasing the PMT dimensions will over estimate the position of an event in a gamma camera?
False
PMT dimensions has no affect at all on position of event calculation
Equation for integral uniformity
100% x (Max pixel counts - min pixel counts) / (Max pixel counts + min pixel counts)
Procedure to find differential uniformity
Take the maximum value of the integral uniformity of individual 1x5 and 5x1 sets of pixels
What is the ideal uniformity?
0%
How often should you do a uniformity check with Tc-99m?
What about for other isotopes?
Daily
Monthly
What is the allowed uniformity value for a Tc-99m check? what about for other isotopes.
< 3% for Tc-99m
< 5% for other isotopes
How far away should you position your isotopes in uniformity and sensitivity checks from the detector? Why?
Atleast 3 x largest detector dimensiona way
So approximation to a point source can be made, and differences at peripheral are small
What energy range is used for
low-energy collimators
medium-energy collimators
high-energy collimators
low-energy collimators: 0< 200 keV
medium-energy collimator: 200 - 300 keV
high-energy collimators: > 300 keV
What energy rating collimator would you use for Tc-99m?
Low
(highest enegry photon from Tc-99m is 140 keV
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
10-20 mCi Co-57 flood (sheet) source
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?
Software corrections being off, corrupted or outdated
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?
Daily check
10-15 million counts
How often should you check gamma camera spatial resolution using a resolution phantom (or mask)?
Weekly
How many counts should you have for a uniformity correction?
What about sensitivity flood correction?
Uniformity - 10-15 mil
Sensitivity - 60 - 100 mil
