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PHYS > Section 7 > Flashcards

Section 7 Flashcards

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
Q

What are the deteriments of image quality?

A
  • Spatial resolution
  • Contrast resolution
    -Sensitivity
  • Motion
26
Q

Spatial resolution

A

Better SR means finer details of an object but we have low dose rate and have a short scan time

27
Q

Contrast in NM comes from

A

functional distribution of radioactive material

28
Q

Detection of scattered radiation

A

may decrease contrast - use PHA for energy discrimination

29
Q

Sensitivity is how

A

much radioactivity required for the production of an image - expressed in keps/MBq

30
Q

Decrease in sensitivity =

A

increase in radioactivity and dose

31
Q

Gating (switching) can be used

A

to measure only at specific points in a cycle

32
Q

SPL measures

A

where the gamma ray hit the scintillator/detector

33
Q

What does the height of the PMT pulse indicate?

A

Greater the height indicates how close gamma absorption was

34
Q

PMT detects

A

gamma rays

34
Q

PMT correlation works out

A

where they hit the detector

35
Q

Collimator works out

A

which direction gamma rays came from and we make sure they came in a straight line

PHYS (8 decks)

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