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Core Rad Physics > 2015 Physics > Flashcards

2015 Physics Flashcards

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1
Q

What % are characteristic x-rays in general radiography

A

5-9 %

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2
Q

Bucky factor of a typical radiographic scatter grid

A

4

Corresponds to an 8:1 grid

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3
Q

Fluoroscopic skin dose versus fluorographic (angiography) skin dose?

A

100-1000 microrad

1-10 Gray

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4
Q

Best NaI geometric efficiency

A

WELL COUNTER

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5
Q

List the following in decreasing order of half life: Tc99m MAA, Tc99m aerosol, Xenon 133

A

Tc99m MAA, Tc99m aerosol, Xenon 133

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6
Q

Multiple cameras in SPECT does what?

A

Makes scan time faster. Or decreases scan time.

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7
Q

If positron travel increases on PET, what does this do to the image?

A

Decrease resolution

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8
Q

Energy equivalent of an electron?

A

511 keV.

To generate one electron pair, 33keV.

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9
Q

Disadvantages to using BGO in PET? (Bismuth Germanium Oxide)

A

Poorer energy resolution or decreased energy resolution. BGO crystals detect a wider range of energies.

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10
Q

Shallow dose equivalent is best measured using

A

TLD ring (thermoluminescent dosimeter)

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11
Q

Congenital malformations are most likely to occur when?

A

20-40 days (~3-6 weeks)

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12
Q

Maximum dose per single mammographic x-ray

A

3mGy per image

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13
Q

100 microRad at 1 meter from source. What is the dose if you move to 4 meters from the source?

A

Equation is Dose2 = Dose1 (Dist1/(Dist2^2))

100/(4^2) = 100/16 = 6.25 micro Rad

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14
Q

Max annual dose is ____ for rad occupational workers, and ____ for nonoccupational.

A 
5,000 mrem (50 mSv)
100 mrem (1 mSv)
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15
Q

Wavelength of x-rays in nanometers?

A

0.1 - 5 nm - (0.1 - 10 nm is more correct answer)

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16
Q

What is the fatal cancer risk per Sv?

A

4% - (more accurately, 4.1%)

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17
Q

What is the maximum resolution for CR in mammo?

A

10 lp/mm

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18
Q

What is nyquist frequency if “pixel pitch” is x?

A

1/(2x)

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19
Q

What are the spatial resolutions for SPECT and PET respectively?

A

10mm and 5mm

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20
Q

What is the overall average effective dose for the most common NM studies?

A

5mSv

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21
Q

What is the attenuation of US when using a 10MHz probe? (soft tissue attenuation coefficient = 0.5 dB/cm per MHz) —This q may be missing info….

A

10 dB/cm

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22
Q

Spatial resolution is determined by

A

Sampling pitch (pitch = 1/sampling frequency)

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23
Q

Increasing screen thickness has what effect?

A

no effect on quantum mottle (noise)

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24
Q

PET sensitivity increases with what?

  • increased septal thickness
  • decrease in septal atomic number
  • NaI detector
  • detector efficientcy squared
  • decreased detector efficiency
A

detector efficiency squared

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25
Q

NM converging collimator has ____efficiency and _____ resolution

A

increased , decreased

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26
Q

WHat pixel size is sufficient for digital mammos?

A

0.05mm

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27
Q

What is the number of fatal cancers per 1 million women exposed to 1 mSv in mammo?

A

2
Other references: 1.3 - 1.7 fatal cases per 100,000.
8 deaths per 4mSv

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28
Q

Digital fluoro uses what flat panel detector?

A

Scintillator

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29
Q

Quantum Detective Efficiency is defined as

A

% of incident x-ray photons that are converted

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30
Q

Effective dose is represented by

  • Rad
  • Sv
  • Gy
A

Sv

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31
Q

Which of the following is true of flat panel detectors?

A

Decreases pt dose

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32
Q

What pixel density monitor will display a CR image at full resolution?

A

3 MP.
(CT/MR/NM require 2MP.
CR/FLuoro: 3 MP.
Mammo: 5 MP.)

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33
Q

MRI slice selection acheived by

A

Frequency encoding gradient, phase encoding gradient, Field strength gradient (z axis is selected by field strength)

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34
Q

Number of spin orientations in the alternative energy state when placed in a MRI magnetic field? (in MRI, how many protons spin up vs down)

A

3 ppm

Huda says 4 ppm

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35
Q

Gadolinium is how many times more ferromagnetic?

A

500

Huda says 700

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36
Q

Diffusion weighting is an indicator of what?

A

tissue integrity - isotropy

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37
Q

SNR has what relationship to N? (N=number of acquisition for MRI)

A

sqrt N

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38
Q

WHat type of detector is used in the x-ray machine photo-timer?

A

Ionization gas chamber

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39
Q

Barium enema effective dose (mSv)?

A

Huda says 5-15.

others say 2-7 and 8

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40
Q

% of nuc med photons reaching the detector?

A

10%

41
Q

Which of the following is NOT a digital detector?

A

Photomultiplier tube

42
Q

What is the min requirement for a monitor brightness?

A

160 candelas/m^2

43
Q

Unsaturated protons flowing in blood can cause

A

increased signal

44
Q

Tc99 mode of decay

A

isomeric transition

45
Q

what is the max time alternating gradient?

A

3 T/s

46
Q

What number takes into account physical decay and biologic excretion

A

Effective half life

47
Q

Tc99m MAA has the highest dose effect on which organ?

A

lungs

48
Q

What is the risk of inducing childhood cancer per Gy?

A

6% additional risk per Gray

49
Q

What is the exposure limit for the lens of the eye? in mSv

A

150mSv

50
Q

What percent of 90 degree scattered radiation reaches a patient standing 1 meter away?

A

0.1%

51
Q

Evaluation of low contrast lesions is limited by …

A

contrast to noise ratio

52
Q

What is not taken into account in the S factor?

A

tissue weighting factor

53
Q

What causes a linear defect in nuclear medicine imaging?

A

cracked crystal

54
Q

What is the most common source of nuclear medicine artifacts?

A

patient motion

55
Q

What is the best measure of CT absorbed dose?

A 
Currently best answer would be DLP.
Next best would be CTDI.
CTDI100
CTDI FDA
MSAD
56
Q

WHen comparing digital mammo and screen film, digital mammo has:

A

decreased dose

57
Q

Degrees of angular rotation in tomosynthesis in mammo

A

15

58
Q

Unit for S factor

A

mGy/Bq-s

59
Q

Effective dose for abdominal CT

A

4 mSv

60
Q

Percentage of x rays transmitted through a patient on chest radiograph

A

10%

61
Q

Difference in HU between gray and white matter

A

10 HU (Gray is 40HU and white is 30 HU)

62
Q

Dose for development of acute cataract formation

A

2500 mGy (other sources: 2Gy threshold)

63
Q

Typical mammo grid ratio

A

5:1

64
Q

Resolution for general computed radiography

A

3 line pair/mm

if 3 is not an answer choice, go up to the next one

65
Q

Noise of CT (%)

A

0.3%

66
Q

Film latitude for CXR

A

10,000:1

67
Q

Shades of Gray on a typical display

A

1024

68
Q

Most common reciprocating grid

A

10:1

69
Q

Storage for DSA

A

2MB

70
Q

What is the purpose of the initial 180 degree pulse for inversion recovery?

A

invert the magnetization vector

71
Q

Reverberation artifact

A

wrong echo location

72
Q

What is the most common cause of ghosting artifact on MRI

A

patient motion

73
Q

In CT, current and scan time is proportional to:

A

effective dose. (not mA-s)

74
Q

Effectiveness of x ray production of high atomic number target

A

1%

75
Q

Energy of x ray in mammo should be

A

20 keV

76
Q

If the radiation dose is doubled, the quantum mottle

A

decreases by 40%

77
Q

Maximum organ dose in NM

A

50Gy

78
Q

To double MRI SNR, RF bandwidth has to:

A

quartered or decreased by a factor of 4.

SNR=k(voxel volume)(sqrt(N/rf bandwidth))

79
Q

What is the storage phosphor used in digital radiography?

A

barium fluorohalide

80
Q

Sum of all organ doses is

A

effective dose

81
Q

0.5 mm lead apron attenuates what percent of x ray beams

A

1%

82
Q

How do you fix wraparound artifact?

A

increase sampling rate

83
Q

How many mammos must interpreting physicians read?

A

240 in 6 months,

or 960 in 24 months

84
Q

Signal detected in PET is smaller than a pixel. WHat is this artifact called when it registers as a larger signal with less activity?

A

Partial volume effect

85
Q

What are the units of US intensity?

A

mW/cm^2

86
Q

US Doppler SHift of flowing blood with 3 MHz probe at 60 degrees for venous flow?

A

100-1,000 Hz

Venous blood at <30cm/sec. shift will be between 100-1,000 Hz.

87
Q

What is the velocity of US in lung and soft tissue?

A

600, 1540 cm/sec

air 300; lung 600; fat 1460; soft tissue 1540; bone 3300

88
Q

What is the max RF dose for whole body MRI?

A

4 Watts/kg

(head is 3 W/kg. extremity is 8 W/kg

89
Q

Structures in the center of K-space demonstrate

A

low spatial frequency

90
Q

Which of the following does NOT increase MR SNR?

  • Decreased slice thickness
  • Increased pixel size
  • increased acquisitions
A

Decreased slice thickness

91
Q

GRE images have all of the following EXCEPT?

  • decreased field inhomogeneities
  • low flip angle
  • short T1
A

Decreased field inhomogeneities.

92
Q

Doubling the slice thickness in MRI increases the SNR by

A

DOUBLE

93
Q

CT pitch is defined as

A

Table movement of one tube revolution / collimator width.

94
Q

Mammo rhodium filter will filter what energy levels?

A

> 25 keV
(Rhodium filters electrons below 20keV and above 23 keV.
Silver filters electrons below 23keV and above 25keV..)

95
Q

What is no longer required by law?

  • automatic collimation
  • other options
A

automatic collimation (good guessing)

96
Q

Skin dose of AP abdominal adult radiograph (in rad)?

A

0.3rad (3 mGy)

97
Q

Head CT effective dose? (in mSv)

A

2.0 mSv

98
Q

Stem of anode in rotating anode system is made of what?

A

Tungsten (for gen radiography)

Molybdenum for Mammo

99
Q

Single exposure tube rating is based on ___

  • Anode heat capacity
  • Tube heat capacity
  • X ray unit heat capacity
A

Anode heat capacity

AKA anode heat loading

Core Rad Physics (8 decks)

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