Section 7 Flashcards

(36 cards)

1
Q

Gamma rays and xrays are both

A

high energy electromagnetic radiation (photons)

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2
Q

What is the difference between xrays and gamma rays?

A

Xrays produced by electrons in atoms
Gamma produced by nucleus

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3
Q

What are parallels of DR & NM?

A

Detecting nonvisible radiation; see visible structures in body & give diagnostic info abt patients

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4
Q

How is NM different from DR?

A

NM has source in the patient and uses gamma rays

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5
Q

Xrays are an __ source and show __

A

External source and show anatomy

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6
Q

Gamma rays are ___ source and show ___

A

Internal source and show biofunctionality

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7
Q

What is the most common isotope used in NM procedures?

A

Technicium 99

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8
Q

Gamma energy is determined by

A

the radioisotope, as the energy of the decay is the same - there is no kVp adjustment

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9
Q

Radiopharmaceutical is a

A

radioactive isotope attached to a pharmaceutical molecule

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10
Q

Why do we need a detector for gamma rays?

A

To measure how much gamma radiation; spatial position of source & energy of the radiation

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11
Q

Since gamma rays cannot be switched of, what factors must we consider?

A
  • Low Dose Rate
  • Small signals from scintillator
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12
Q

Photomultiplier tube uses

A

photoelectric effect to turn light into electrical signal

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13
Q

Describe the key properties of NM detectors

A

PMT, PMT correlation and scintillator

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14
Q

Describe the gamma camera

A

Detect scintillations (flashes of light) produced when gamma rays, resulting from radioactive decay of single photon emitting radioisotopes, interact with a sodium iodide crystal at the front of the camera.

Collimator acts as a lens for our camera - enables the parallel rays to be detected and non-parallel rays to be absorbed

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15
Q

Describe the PMT correlation

A
  1. Gamma rays hit the scintillator
  2. Multiple visible photons are produced
  3. Nearby PMT get high signal and distant PMT have a weak signal
  4. SPL works out where gamma rays hits scintillator
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16
Q

SPL =

A

Spatial Position Logic

17
Q

A collimator enables the

A

gamma source location to be determined

18
Q

What are the collimator walls called?

A

Septa and are thin as possible to minimise absorption

19
Q

Small Collimator holes =

A

High resolution

20
Q

Large collimator holes=

A

Low resolution

21
Q

Larger septa depth =

A

High resolution

22
Q

Smaller septa depth =

A

Low resolution

23
Q

Increase in resolution means __ sensitivity?

A

decrease in sensitivity

24
Q

Pulse Height Analysis is where

A

we reject scattered photons

25
What are the deteriments of image quality?
- Spatial resolution - Contrast resolution -Sensitivity - Motion
26
Spatial resolution
Better SR means finer details of an object but we have low dose rate and have a short scan time
27
Contrast in NM comes from
functional distribution of radioactive material
28
Detection of scattered radiation
may decrease contrast - use PHA for energy discrimination
29
Sensitivity is how
much radioactivity required for the production of an image - expressed in keps/MBq
30
Decrease in sensitivity =
increase in radioactivity and dose
31
Gating (switching) can be used
to measure only at specific points in a cycle
32
SPL measures
where the gamma ray hit the scintillator/detector
33
What does the height of the PMT pulse indicate?
Greater the height indicates how close gamma absorption was
34
PMT detects
gamma rays
34
PMT correlation works out
where they hit the detector
35
Collimator works out
which direction gamma rays came from and we make sure they came in a straight line