2015 Physics

Question 1

What % are characteristic x-rays in general radiography

Answer 1

5-9 %

Question 2

Bucky factor of a typical radiographic scatter grid

Answer 2

4

Corresponds to an 8:1 grid

Question 3

Fluoroscopic skin dose versus fluorographic (angiography) skin dose?

Answer 3

100-1000 microrad

1-10 Gray

Question 4

Best NaI geometric efficiency

Answer 4

WELL COUNTER

Question 5

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

Answer 5

Tc99m MAA, Tc99m aerosol, Xenon 133

Question 6

Multiple cameras in SPECT does what?

Answer 6

Makes scan time faster. Or decreases scan time.

Question 7

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

Answer 7

Decrease resolution

Question 8

Energy equivalent of an electron?

Answer 8

511 keV.

To generate one electron pair, 33keV.

Question 9

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

Answer 9

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

Question 10

Shallow dose equivalent is best measured using

Answer 10

TLD ring (thermoluminescent dosimeter)

Question 11

Congenital malformations are most likely to occur when?

Answer 11

20-40 days (~3-6 weeks)

Question 12

Maximum dose per single mammographic x-ray

Answer 12

3mGy per image

Question 13

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

Answer 13

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

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

Question 14

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

Answer 14

5,000 mrem (50 mSv)
100 mrem (1 mSv)

Question 15

Wavelength of x-rays in nanometers?

Answer 15

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

Question 16

What is the fatal cancer risk per Sv?

Answer 16

4% - (more accurately, 4.1%)

Question 17

What is the maximum resolution for CR in mammo?

Answer 17

10 lp/mm

Question 18

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

Answer 18

1/(2x)

Question 19

What are the spatial resolutions for SPECT and PET respectively?

Answer 19

10mm and 5mm

Question 20

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

Answer 20

5mSv

Question 21

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….

Answer 21

10 dB/cm

Question 22

Spatial resolution is determined by

Answer 22

Sampling pitch (pitch = 1/sampling frequency)

Question 23

Increasing screen thickness has what effect?

Answer 23

no effect on quantum mottle (noise)

Question 24

PET sensitivity increases with what?

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

Answer 24

detector efficiency squared

Question 25

NM converging collimator has ____efficiency and _____ resolution

Answer 25

increased , decreased

Question 26

WHat pixel size is sufficient for digital mammos?

Answer 26

0.05mm

Question 27

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

Answer 27

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

Question 28

Digital fluoro uses what flat panel detector?

Answer 28

Scintillator

Question 29

Quantum Detective Efficiency is defined as

Answer 29

% of incident x-ray photons that are converted

Question 30

Effective dose is represented by - Rad - Sv - Gy

Answer 30

Sv

Question 31

Which of the following is true of flat panel detectors?

Answer 31

Decreases pt dose

Question 32

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

Answer 32

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

Question 33

MRI slice selection acheived by

Answer 33

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

Question 34

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)

Answer 34

3 ppm | Huda says 4 ppm

Question 35

Gadolinium is how many times more ferromagnetic?

Answer 35

500 | Huda says 700

Question 36

Diffusion weighting is an indicator of what?

Answer 36

tissue integrity - isotropy

Question 37

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

Answer 37

sqrt N

Question 38

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

Answer 38

Ionization gas chamber

Question 39

Barium enema effective dose (mSv)?

Answer 39

Huda says 5-15. | others say 2-7 and 8

Question 40

% of nuc med photons reaching the detector?

Answer 40

10%

Question 41

Which of the following is NOT a digital detector?

Answer 41

Photomultiplier tube

Question 42

What is the min requirement for a monitor brightness?

Answer 42

160 candelas/m^2

Question 43

Unsaturated protons flowing in blood can cause

Answer 43

increased signal

Question 44

Tc99 mode of decay

Answer 44

isomeric transition

Question 45

what is the max time alternating gradient?

Answer 45

3 T/s

Question 46

What number takes into account physical decay and biologic excretion

Answer 46

Effective half life

Question 47

Tc99m MAA has the highest dose effect on which organ?

Answer 47

lungs

Question 48

What is the risk of inducing childhood cancer per Gy?

Answer 48

6% additional risk per Gray

Question 49

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

Answer 49

150mSv

Question 50

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

Answer 50

0.1%

Question 51

Evaluation of low contrast lesions is limited by ...

Answer 51

contrast to noise ratio

Question 52

What is not taken into account in the S factor?

Answer 52

tissue weighting factor

Question 53

What causes a linear defect in nuclear medicine imaging?

Answer 53

cracked crystal

Question 54

What is the most common source of nuclear medicine artifacts?

Answer 54

patient motion

Question 55

What is the best measure of CT absorbed dose?

Answer 55

``` Currently best answer would be DLP. Next best would be CTDI. CTDI100 CTDI FDA MSAD ```

Question 56

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

Answer 56

decreased dose

Question 57

Degrees of angular rotation in tomosynthesis in mammo

Answer 57

15

Question 58

Unit for S factor

Answer 58

mGy/Bq-s

Question 59

Effective dose for abdominal CT

Answer 59

4 mSv

Question 60

Percentage of x rays transmitted through a patient on chest radiograph

Answer 60

10%

Question 61

Difference in HU between gray and white matter

Answer 61

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

Question 62

Dose for development of acute cataract formation

Answer 62

2500 mGy (other sources: 2Gy threshold)

Question 63

Typical mammo grid ratio

Answer 63

5:1

Question 64

Resolution for general computed radiography

Answer 64

3 line pair/mm | if 3 is not an answer choice, go up to the next one

Question 65

Noise of CT (%)

Answer 65

0.3%

Question 66

Film latitude for CXR

Answer 66

10,000:1

Question 67

Shades of Gray on a typical display

Answer 67

1024

Question 68

Most common reciprocating grid

Answer 68

10:1

Question 69

Storage for DSA

Answer 69

2MB

Question 70

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

Answer 70

invert the magnetization vector

Question 71

Reverberation artifact

Answer 71

wrong echo location

Question 72

What is the most common cause of ghosting artifact on MRI

Answer 72

patient motion

Question 73

In CT, current and scan time is proportional to:

Answer 73

effective dose. (not mA-s)

Question 74

Effectiveness of x ray production of high atomic number target

Answer 74

1%

Question 75

Energy of x ray in mammo should be

Answer 75

20 keV

Question 76

If the radiation dose is doubled, the quantum mottle

Answer 76

decreases by 40%

Question 77

Maximum organ dose in NM

Answer 77

50Gy

Question 78

To double MRI SNR, RF bandwidth has to:

Answer 78

quartered or decreased by a factor of 4. | SNR=k*(voxel volume)*(sqrt(N/rf bandwidth))

Question 79

What is the storage phosphor used in digital radiography?

Answer 79

barium fluorohalide

Question 80

Sum of all organ doses is

Answer 80

effective dose

Question 81

0.5 mm lead apron attenuates what percent of x ray beams

Answer 81

1%

Question 82

How do you fix wraparound artifact?

Answer 82

increase sampling rate

Question 83

How many mammos must interpreting physicians read?

Answer 83

240 in 6 months, | or 960 in 24 months

Question 84

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

Answer 84

Partial volume effect

Question 85

What are the units of US intensity?

Answer 85

mW/cm^2

Question 86

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

Answer 86

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

Question 87

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

Answer 87

600, 1540 cm/sec | air 300; lung 600; fat 1460; soft tissue 1540; bone 3300

Question 88

What is the max RF dose for whole body MRI?

Answer 88

4 Watts/kg | (head is 3 W/kg. extremity is 8 W/kg

Question 89

Structures in the center of K-space demonstrate

Answer 89

low spatial frequency

Question 90

Which of the following does NOT increase MR SNR? - Decreased slice thickness - Increased pixel size - increased acquisitions

Answer 90

Decreased slice thickness

Question 91

GRE images have all of the following EXCEPT? - decreased field inhomogeneities - low flip angle - short T1

Answer 91

Decreased field inhomogeneities.

Question 92

Doubling the slice thickness in MRI increases the SNR by

Answer 92

DOUBLE

Question 93

CT pitch is defined as

Answer 93

Table movement of one tube revolution / collimator width.

Question 94

Mammo rhodium filter will filter what energy levels?

Answer 94

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

Question 95

What is no longer required by law? - automatic collimation - other options

Answer 95

automatic collimation (good guessing)

Question 96

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

Answer 96

0.3rad (3 mGy)

Question 97

Head CT effective dose? (in mSv)

Answer 97

2.0 mSv

Question 98

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

Answer 98

Tungsten (for gen radiography) | Molybdenum for Mammo

Question 99

Single exposure tube rating is based on ___ - Anode heat capacity - Tube heat capacity - X ray unit heat capacity

Answer 99

Anode heat capacity | AKA anode heat loading