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NMED 260 - Instrumentation 1 > Gamma Cameras > Flashcards

Gamma Cameras Flashcards

1
Q

What are the four desirable scintillator properties?

A
  1. highest possible intensity for a given amount of energy absorbed
  2. transparent to its own light
  3. decay time should be short so photocathode can differentiate between 2 sep. events
  4. must be adequate to cause all the energy of the even to be deposited into the detector
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2
Q

why is transparency important?

A

if the scintillator is transparent to its own light, photons will reach the PMT with minimum loss of intensity

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3
Q

what is intensity?

A

it describes the number of light photons

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4
Q

how does radiation interact with scintillators?

A

Compton, photoelectric effect and pair production

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5
Q

what are the four steps to processing detection?

A
  1. interaction
  2. light production
  3. photoelectron released
  4. multiplication of electrons to form pulse
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6
Q

what is the preferred type of interaction?

A

photoelectric for complete gamma absorption

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7
Q

how does light production occur?

A

when the excited atoms in the scintillator returns to ground state

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8
Q

light intensity is _______ to the amount of energy absorbed.

A

proportional

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9
Q

where does the exponential amplification of electrons occur?

A

in the PMT

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10
Q

what causes the exponential amplification?

A

a series of charged plates to accelerate the electrons to produce secondary electrons

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11
Q

what are dynodes?

A

the series of charged plates

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12
Q

how is a pulse created?

A

by the collection of electrons at the anode

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13
Q

what is a voltage pulse?

A

a burst of electrons collected at the anode

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14
Q

describe the relationship between voltage pulse height and the number of electrons collected at the anode.

A

number of electrons collected there is PROPORTIONAL to the voltage pulse height

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15
Q

which pulse does the amplifier manipulate?

A

the z pulse

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16
Q

what does the z pulse represent?

A

size of the pulse in volts
aka the result of the energy absorbed within the crystal

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17
Q

what is a collimator?

A

1/2 inch to 2 inch piece of lead that is meant to attenuate gamma coming towards the crystal from a bad angle

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18
Q

what does absorptive collimation describe?

A

how the collimator only allows the photons travelling in an appropriate direction to interact with the crystal

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19
Q

larger holes in the collimator = _____ permissive = ____ resolution, _____ sensitivity

A

larger holes = more permissive = less resolution = high sensitivity

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20
Q

smaller holes in the collimator = _____ permissive = ____ resolution, _____ sensitivity

A

smaller holes = less permissive = higher resolution = lower sensitivity

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21
Q

what is the physical characteristics on a parallel hole collimator dependent on?

A
  • energy of radionuclide
  • required performance (reso vs. sensitivity)
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22
Q

when do you use a DIVERGING collimator?

A

when you need to increase the FOV of small diameter crystals for large organs

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23
Q

what type of collimators MAGNIFY?

A

1) pinhole
2) converging

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24
Q

what will pinhole collimators do?

A

1) magnify
2) reverse the image

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25
Q

what is the slant hole collimator?

A

a variation of the parallel-hole collimator on a 30 degree slant

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26
Q

fan beam collimators consist of: one axis is a _____ collimator, and the other axis is a _____ collimator

A

parallel-hole collimator + converging collimator

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27
Q

what would a fan beam collimator be used for?

A

SPECT studies

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28
Q

what is the role of the console?

A

to accept and analyze information from the head

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29
Q

what is the role of the camera head?

A

detection and determination of the position of activity in the organ of interest

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30
Q

more PMT = ______ spatial resolution and linearity

A

more PMT = better spatial resolution and linearity

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31
Q

what are the three common shapes of PMTs?

A
  1. circular
  2. hexagonal
  3. square
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32
Q

what type of positioning logic does an analog system use?

A

coordinate system

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33
Q

what is a coordinate system?

A

when the origin is (0,0) and it’s the centre of the crystal

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34
Q

what is the role of an amplifier?

A

shaping and increasing the pulse size

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35
Q

what are 3 parameters that determine collimator spatial resolution?

A
  1. hole length
  2. hole diameter
  3. distance between source and collimator
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36
Q

_____ length and _____ diameter holes produce better spatial resolution. why?

A

longer length + smaller diameter
- because they limit the nonperpendicular photon angles accepted

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37
Q

what are the two methods used to determine the centroid?

A

coordination system + PMT output to be digitized by ADC

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38
Q

what does normalization do?

A

it keeps the image size constant regardless of the photon energy and helps maintain good spatial resolution

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39
Q

which pulse is analyzed by the PHA?

A

z pulse

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40
Q

what information does the X and Y signal give?

A

it will determine the spatial location of the interaction within the crystal

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41
Q

what program control is only used for calibration?

A

spectrum display

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42
Q

which program control is used for positioning?

A

persistence scope

43
Q

is the persistence scope affected by the settings on the console?

A

it is NOT

44
Q

which scintillation camera correction is required because of NONUNIFORM RESPONSES OF THE PMTS?

A

energy correction

45
Q

what can be found between the detector and the pmt?

A

a light pipe

46
Q

what is a light pipe?

A

transparent material that allows scintillation light to SPREAD AS IT EXITS THE CRYSTAL

47
Q

what is spatial linearity?

A

accuracy of the positioning of detected events

48
Q

why do you need to do a spatial linearity correction?

A

because of the nonlinearity of PMT responses and the mispositioning of events

49
Q

what is uniformity?

A

the ability of the camera to reproduce a uniform radioactive distribution

50
Q

what does uniformity correction do?

A

it decreases the variability in count densities to an acceptable level

51
Q

what causes an energy spectrum to shift?

A

whether the event is directly under the PMT or between PMTs

52
Q

what will happen if you keep the photo peak centred?

A

increase in energy resolution of the system

53
Q

what are the 4 parameters that affects the collimator’s sensitivity?

A
  1. hole length
  2. hole diameter
  3. hole geometry
  4. septal thickness
54
Q

_____ hole length + _____ hole diameter = greater sensitivity

A

shorter hole length + larger hole diameter = greater sensitivity

55
Q

does changing the distance between the source and the collimator have an effect on sensitivity?

A

nope.

56
Q

what causes the “pincushion effect”?

A

malpositioning of the events (when X and Y aren’t normalized)

57
Q

what does the pincushion effect cause?

A

poor field uniformity

58
Q

what is the spatial linearity correction?

A

usage of a table of position-based correction factors

59
Q

who is responsible for energy/linearity corrections?

A

factory or service personnel

60
Q

who is responsible for camera maintenance?

A

service personnel

61
Q

what is responsible for autotuning?

A

gamma cameras

62
Q

who is responsible for the uniformity correction map?

A

technologist

63
Q

what is the range of temperature that imaging rooms are recommended to be at?

A

20-21 degrees

64
Q

what are some other special considerations for imaging rooms?

A
  • air filters should be cleaned regularly
  • humidistat to monitor moisture
  • having a battery backup
  • location of the gamma camera
65
Q

sudden changes in temperature can damage the crystal. what is the temperature range stated in Prekeges?

A

more than 12 degrees celsius per hour will damage the crystal

66
Q

is it analog or digital signals that are able to be manipulated, analyzed and eventually stored?

A

digital signals

67
Q

is it analog or digital signals that are dependent on continuously variable voltages?

A

analog signals

68
Q

is it analog or digital signals that are dependent on discrete voltages?

A

digital signals

69
Q

is it analog or digital signals that are based on binary information?

A

digital signals

70
Q

where does the analogy to digital energy conversion occur?

A

right after the PMT

71
Q

what are signal weights?

A

signals created based on responses from PMTs closest to the detection event

72
Q

what are position calculations?

A

when the PMT signals are modified by their position, the location of the event is determined with spatial resolution accuracy of about 3.5 mm

73
Q

what is energy summation?

A

adding of the digitized signals from each PMT in the area of interaction
= determines the energy of that event

74
Q

what are the cons of analog signals?

A
  • increased dead time
  • decreased efficiency
  • affected by electronic noise
  • no image manipulation
75
Q

what are the pro(s) of analogy signals?

A

it preserves all data

76
Q

what are the cons of digital signals?

A
  • lose some data in conversion
  • down time increases if problem occurs
77
Q

what are the pros of digital signals?

A

+ decreased dead time
+ increased efficiency – quicker access and transfer of data

78
Q

what is the difference between “binary” and “decimal”?

A

binary = system that has 2 possible digits (0,1)
decimal = system that has 10 possible digits (0-9)

79
Q

you read binary left to right. t/f

A

false.
right to left

80
Q

what is a “BIT”?

A

single position of binary number representation

81
Q

What is a “BYTE”?

A

1 byte = 8 bits

82
Q

what is a “WORD”?

A

group of bits that a computer can process at one time

83
Q

how many bits make up a word? bytes?

A

16 bits
2 bytes (1 byte = 8 bits)

84
Q

the diameter of the crystal is equal to the ______ of X and Y signals.

A

maximum range of X + Y = diameter of crystal

85
Q

specific area on crystal = specific (A).
each (A) is assigned to a specific (B) in computer memory.

A

(A) = pixel
(B) = location

86
Q

is it analog or digital that consists of a grid/matrix of pixels?

A

digital image

87
Q

what is a pixel value?

A

it gives the location information dependent on the number of counts or other quantity associated with that pixel

88
Q

X (+/-) & Y (+/-) position signals are analyzed using ADCs.

A

X- and Y-

89
Q

what is the flow in a ramp conversion?

A

input pulse —> charge deposited in capacitor (ADC input) —> discharges through resistors + during discharge, gate pulse activates clock oscillator —> production of a train of pulses counted

90
Q

the number of clock pulses is dependent on?

A

the initial amount of charge deposited – amplitude of input pulse

91
Q

is the digital signal or analog signal expressed in binary?

A

digital signal

92
Q

what does successive approximation describing?

A

a trial and error technique that the ADC compares the signal to preset values in succession and transmits the results in digital form

93
Q

when does the successive approximation process start?

A

by turning on the most significant bit

94
Q

when will a bit be turned off during the successive approximation process?

A

if the value represented is GREATER than the input value

95
Q

What is the flash/parallel approximation process?

A

comparing signals to preset values at the same time and transmitting the results in digital form

96
Q

what is the unit of division in the ADC?

A

1 bit therefore, 1-bit = dividing into two equal parts
2 bits = dividing into four equal parts

97
Q

more bits an ADC = better the _______.

A

accuracy

98
Q

What is the LUT? (Lookup table)

A

single digital array consisting of shades of grey with values ranging from zero to high values

99
Q

what shade is zero on the LUT?

A

white

100
Q

what shade is the highest value on the LUT?

A

black

101
Q

what is the LUT used for?

A

to correlate image density to counts per pixel

102
Q

more bits to an ADC = _____ to digitize a signal

A

more bits = more time

103
Q

faster sampling rates = more _____

A

faster sampling rate = more accurate but need more storage space

104
Q

loss of information could occur due to slower sampling rate. t/f

A

true

NMED 260 - Instrumentation 1 (3 decks)

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