Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
24 Cards in this Set
- Front
- Back
|
Definition of collimator
|
Shielding device used to limit angle of entry of radiation.
Eliminates all gamma rays except those of interest |
|
|
3 types spatial resolution
|
Intrinsic- w/o collimator
Extrinsic- collimator resolution Scatter resolution- radiation outside FOV |
|
|
Resolution is measured in?
|
mm; used to differentiate objects
|
|
|
Sensitivity is?
|
amt of photons that interact w/ crystal and are converted to light
|
|
|
sensitivity is measured in?
|
cps/uCi
|
|
|
What affects intrinsic resolution? (4)
|
gamma energies
#PMT's Window size crystal placement |
|
|
What increases extrinsic resolution? 3
|
1. Inc. length of collimators
2. decrease diameter of holes 3. dec. source to collimator distance |
|
|
Sensitivity depends on what factors? 4
|
1. detection effeciency of crystal
2. Dead time 3. Collimator variables:A.. Photon energy B. Crystal thickness |
|
|
Purpose of septa?
|
Lead walls b/w holes thast absorb gammas not of interest
|
|
|
4 shapes of Septa? Which most common?
|
Circular -worst
Triangular Square Hexagonal- most common |
|
|
higher resolution, less sensitivty found in (thicker,thinner) and (longer or shorter) septa?
|
Thicker, longer-
count rate inversly propt'l to hole length |
|
|
What size collimator holes have these factors?
more photons absorbed by septa, less counts, less sensitivity, higher resolution |
Small holes
|
|
|
What are the energy parameters of low, medium and high energy collimators
|
low: 50-190kev; 201Tl, 99mTc, 123I, 133Xe
med: 190-300kev; 67Ga High: 300-400kev; 131I |
|
|
2 types of collimators
|
Single hole
Multi hole |
|
|
3 types single hole collimators
|
flat field
straight bore pinhole |
|
|
3 types of multi hole collimators
|
Parallel- most common (constant FOV for any distance)
Diverging Converging |
|
|
Parallel hole collimators classified based on ?
|
Energy of RN
Resolution & Sensitivity |
|
|
Converging collmiators AKA focusing collimator what is the focal point distance?
|
50cm in front of organ, image is magnified
|
|
|
In a diverging collimator the image is? (magnified or minified)
|
Minified
|
|
|
Which single hole collimator provides the best resolution for small objects at short distances?
|
Pinhole
|
|
|
What organ is scanned using a pinhole collimator?
|
Thyroid
|
|
|
When the distance of the organ to pinhole= distance of the pinhole to detector the image is? (magnified, minified, or same)
|
Same
|
|
|
2 ways to build collimators
|
Single solid lead
Glued lead strips |
|
|
3 defects with glued strips in collimators
|
gaps
misalignment septal tears |
