Physics Flashcards
1
Q
What is the threshold for cataracts caused from an acute radiation exposure to the eye (onset > 20 years)?
A
~0.5 Gy
2
Q
What is the threshold for circulatory disease caused from an acute radiation exposure?
A
~0.5 Gy. “An approx threshold dose of 0.5 Gy has been proposed for acute, and fractionated/protracted exposures.” (ICRP)
3
Q
What is the threshold for acute dose for male infertility?
A
6 Gy
4
Q
What is the threshold dose for female infertility?
A
3 Gy
5
Q
What is the threshold dose for symptomatic spinal cord injury (myelitis)?
A
50 Gy delivered in 2 fractions
6
Q
What is the SI unit for absorbed dose?
A
Gy or Joule per kilogram (J/kg)
7
Q
What is acute radiation syndrome?
A
“Radiation sickness”- spectrum of responses involving hematopoietic, GI, CV and CNS reactions to a large radiation dose received acutely or subacutely to all or most of the body. Follows a dose dependent clinical course divided into prodromal, latent and manifest periods of illness.
8
Q
What is a deterministic effect?
A
Injury in populations of cells, characterized by a threshold dose and an increase in the severity of the reaction as the dose is increased further.
9
Q
What is Linear Energy Transfer (LET)?
A
The rate of energy loss along the track of an ionizing particle, usually expressed in keV/um.
10
Q
What is the linear-non-threshold model?
A
A dose-response model which is based on the assumption that, in the low dose range, radiation doses greater than zero will increase the risk of excess cancer and/or heritable disease in a simple proportionate manner.
11
Q
What is the SI unit for effective dose?
A
Sievert (Sv). Unit for equivalent dose, effective dose, and operational dose quantities. Doses in Gy are multipled by a quality factor to obtain Sv.
12
Q
At what threshold radiation dose do you expect to see early transient erythema?
A
2 Gy
13
Q
At what threshold radiation dose do you expect to see main erythema reaction?
A
6 Gy
14
Q
At what threshold radiation dose do you expect to see permanent epilation?
A
7 Gy
15
Q
What is the maximum dose an individual of the public may receive from the release of patients injected with radioactive materials (e.g. family member of a thyroid ablation pt)?
A
500 mrem (5 mSv or 0.005 Sv)
16
Q
What is the max dose limit for a general member of the public without a specific exposure scenario (e.g. waiting room in x-ray dept)?
A
100 mrem (1 mSv or 0.001 Sv)
17
Q
What is the physical half-life of fluoride F18?
A
109 minutes (radprimer)
18
Q
What is an Auger electron?
A
An Auger electron is an e that is emitted, rather than a photon, when lower level vacancies are filled. When an L-shell e fills a K-shell vacancy, another L-shell e can be emitted rather than a photon. The emission of an Auger e leaves 2 vacancies.
19
Q
What is KERMA?
A
- Kinetic Energy Released per unit Mass (measured Gy)
- Air Kerma is the kinetic energy transferred from uncharged particles (e.g. photons) to charged particles (e.g. electrons).
- Entrance air karma is a measure of the amount of x-ray radiation that is incident on the patient.
- AK has recently replaced exposure as the quantity that measures the amount of radiation in any x-ray beam.
20
Q
What radiation dose level is associated with Bone Marrow (hematopoietic) Syndrome?
A
Whole-body exposure to 300-800 rads (3-8 Gy)
-LD50 for humans is 3 to 4 Gy for young adults without medical intervention
21
Q
What radiation dose level is a/w GI Syndrome?
A
greater than 8 Gy (other source said >10 Gy)
-Death within 3-10 days without medical care
22
Q
What radiation dose level is a/w Neurovascular Syndrome?
A
greater than 20 Gy (other source said >50 Gy)
-Inevitable death within 3 days of exposure
23
Q
What does LD 50/60 mean?
A
The dose that would kill 50% of the exposed individuals within 60 days.
24
Q
What is the LD 50/60 for humans?
A
Somewhere between 3.5 and 7 Gy (~4 Gy) depending on the level of care.
25
What is the law of Bergondie and Tribondeau (in relation to radio sensitivity)?
A fundamental law of radiation biology that states that the radio sensitivity of cells is directly proportional to their reproductive activity and inversely proportional to the degree of differentiation. Peripheral lymphocytes are an exception.
26
Cells are most radiosensitive in:
a) G0
b) G1
c) G2
d) M
```
Mitosis phase (Radprimer)
Cells are most sensitive to the effects of radiation during M or mitotic phase and the gap between S and G2. Cells are less sensitive during G1 and the least sensitive during S.
```
27
Cells are least radiosensitive in what phase?
S phase
28
The lowest acute whole body radiation exposure for which survival is unlikely is:
a) 1 Gy
b) 2 Gy
c) 4 Gy
d) 10 Gy
d) 10 Gy
29
The most common method of cell death following irradiation is:
a) Mitotic death
b) Division delay
c) Slow death
d) Apoptosis
a) Mitotic death
| Apoptosis is also a/w radiation, however mitotic death is more common
30
A patient is brought to the hospital after exposure to 4 Gy of radiation. They will most likely suffer from:
a) Bone Marrow Syndrome
b) GI Syndrome
c) CNS Syndrome
a) BM Syndrome (>2 Gy exposure). GI Syndrome occurs at 8 Gy. CNS Syndrome occurs at 20 Gy
31
Temporary sterility in the male requires a gonadal dose of about __ Gy
2 Gy
32
Permanent sterility in the male requires a gonadal dose of about __ Gy
5 Gy
33
Temporary sterility in the female requires a gonadal dose of about __ Gy
1.5 Gy
34
Permanent sterility in the female requires a gonadal dose of about __ Gy
4 Gy
35
NCRP 160 estimates that the average US population dose from medical exposure is about ____ of that from background sources:
a) 1/10
b) 1/2
c) equal
d) 2 times
e) 10 times
c) Equal
36
Which of the following would decrease the risk of skin injury?
a) Increasing the mA
b) Increasing the patient thickness
c) Increasing the kV
d) Increasing the fluoroscopy time
c) increasing the kV
37
What are stochastic (probabilistic) effects?
Stochastic or probabilistic effects are effects that are more likely to occur with increasing dose (proportional to dose). E.g. genetic effects and cancer.
38
What are non-stochastic (deterministic) effects?
Deterministic effects have a dose threshold above which the effect will occur and below which the effect will not occur. E.g. skin erythema, cataracts and infertility.
39
What is the threshold dose for wet desquamation and/or dermal necrosis?
18 Gy
40
The NCRP states that only when the dose to the fetus exceeds __ Gy are the risk of fetal effects significantly increased.
0. 15 Gy (150 mGy);
| - (typical single CT exam is usually
41
What is Rayleigh scattering (coherent or classical scatter)?
-Coherent scatter occurs when a low-energy x-ray photon is scattered from an atom without any energy loss.
-The wavelength of the scattered photon is the same as the wavelength of the incident photon.
-Does not result in any energy deposition in the pt
-
42
What is the Photoelectric Effect?
- Occurs b/w tightly bound (inner shell) electrons and incident x-ray photons. The x-ray photon is totally absorbed by an inner shell electron and that electron is ejected from the atom.
- Outer shell electrons fill the inner shell electron vacancies, with the excess energy emitted as a characteristic x-ray or Auger electron.
43
What is an Auger electron?
When a core electron is removed, leaving a vacancy, an electron from a higher energy level may fall into the vacancy, resulting in a release of energy. Although most of the time this energy is released in the form of an emitted photon, the energy can also be transferred to another electron, which is ejected from the atom. This second ejected electron is called an Auger electron.
44
What is the binding energy for a Tungsten K shell electron?
70 keV
45
What is the K edge?
The binding energy of the K-shell electrons (e.g. 70 keV for Tungsten, 33 keV for iodine)
46
Does the probability of the photoelectric effect increase or decrease as the photon energy (E) increases above the K edge?
- The probability of PE decreases rapidly as the photon energy increases above the K edge.
- Above the K edge, photoelectric interactions are proportional to 1/E^3.
47
Does photoelectric absorption increase or decrease with atomic number?
It increases with atomic number and is proportional to Z^3.
48
What is Compton scatter?
- Incident photons interact with outer shell electrons
- A Compton interaction results in a scattered photon that has less energy than the incident photon and generally travels in a different direction.
- A scattered (ejected or recoil) electron carries the energy lost by the incident photon as kinetic energy.
49
How is the probability of Compton interactions related to the photon energy?
Inversely proportional (1/E)
50
What is the linear attenuation coefficient (u)?
The linear attenuation coefficient is the fraction of incident photons removed from the beam in traveling unit distance (measured in cm^-1). E.g. u = 0.1 cm^-1 means that 10% of the photons are removed per 1 cm.
51
What does Half-Value Layer (HVL) mean?
The HVL quantifies the ability of an x-ray beam to penetrate tissue. The HVL is the thickness of material that attenuates an x-ray beam by 50%
52
What is the mathematical relation between HVL and linear attenuation coefficient?
HVL = 0.693 / u (linear attenuation coefficient)
53
Name 3 ways to increase x-ray beam quality.
1) Increasing the x-ray tube voltage (kV) is the most direct way
2) Reducing the voltage waveform ripple
3) Increasing x-ray tube filtration increases the beam quality, as low-energy photons are preferentially removed
54
What is the SI unit for radiation exposure?
coulombs per kilogram (C/kg) or roentgens (R) in non-SI units
55
What is the atomic number and K-shell binding energy of Tungsten?
Z=74
| 70 keV
56
What is the atomic number and K-shell binding energy of Barium?
Z=56
| 37 keV
57
What is the atomic number and K-shell binding energy of Lead?
Z=82
| 88 keV
58
What is the atomic number and K-shell binding energy of Iodine?
Z=53
| 33 keV
59
What is the typical binding energy for an outer shell electron?
0.005 keV
60
For soft tissue, at what photon energy level are the photoelectric and Compton effects equal?
25 keV. In tissue, PE dominates at energies lower than 25 keV and Compton scatter dominates at energies greater than 25 keV
61
For bone, at what photon energy level are the PE and Compton effects equal?
40 keV
62
What is the Bucky factor?
The Bucky factor is the ratio of radiation incident on the grid to the transmitted radiation. It is the increase in patient dose due to the use of a grid. Typical values range between 2 and 6.
63
How is the grid ratio calculated?
- It is the ratio between the strip height (h) along the x-ray beam direction to the gap (D) between the lead strips; so the grid ratio = h/D
- typical range from 4 to 16
64
How does increasing the grid ratio affect image contrast?
Increases image contrast, but also increased tube loading and patient exposure
65
What is the Heel Effect?
The Heel Effect is caused by the anode angle. X-rays (bremsstrahlung) are produced under the surface of the anode disc. X-ray photons on the anode side of the beam have a longer path to the surface of the anode than photons on the cathode side of the beam and thus the beam will be more attenuated and less intense on the anode side of the beam.
66
Patients with a history of allergies and those with features of atopy, such as asthma, dermatitis, and urticaria, have an approximately ______ increased risk of severe reaction to contrast media
3 to 6 fold
67
Serious anaphylactic reactions to contrast media are caused by which type of hypersensitivity
Type 1 (anaphylactic) hypersensitivity reaction
68
What is the standard dose of Epinephrine for treating severe allergic reactions to contrast?
- IM: 0.3 mg (0.3 mL of 1:1000 dilution), repeat to total dose of 1 mg;
- or IV: 0.3 mg (1–3 mL of 1:10,000 dilution) slow infusion, repeat to total dose of 1 mg
69
What is the dose for Atropine for tx of moderate to severe vasovagal reaction (pt unresponsive)?
IV: 0.6–1.0-mg slow infusion followed by saline
| flush, repeat to total dose of 3 mg
70
What is the tx for hypertensive crisis related to contrast dye?
- IV labetalol: 20-mg slow infusion over 2 min, double the dose every 10 min (eg, 40 mg 10 min later, then 80 mg 10 min after that)
- Sublingual nitroglycerin tablet, 0.4 mg; repeat every 5–10 min; IV furosemide, 20–40 mg, slow infusion over 2 min
71
For an elective CT scan, what is the typical pre-medication for contrast allergy?
- Prednisone, 50 mg by mouth at 13, 7, and 1 h before injection of contrast agent.
- Diphenhydramine, 50 mg IV, IM, or by mouth 1 h before injection of contrast material
72
For an emergent CT scan, what is the typical pre-medication for contrast allergy?
- IV methylprednisolone 40 mg, or IV hydrocortisone 200 mg every 4 h until study performed
- Diphenhydramine 50 mg IV 1 h before injection of contrast material
73
What type of radiation plays the predominant role in x-ray spectra used for imaging?
Bremsstrahlung radiation
74
What is the typical target material used for mammography tubes?
Molybdenum
75
What is the typical energy range for characteristic x-rays produced by molybdenum targets for mammography?
17 to 19.5 keV
76
What type of radiation plays the predominant role in mammography?
Characteristic x-rays
77
In spin echo imaging, a T1 weighted sequence tends to have _____ TR and _____ TE (short or long)
Short TR and short TE
78
In spin echo imaging, a T2-weighted sequence tends to have _____ TR and _____ TE (short or long)
Long TR and long TE
79
A proton density sequence is obtained with: ____ TR and ___ TE
Long TR and short TE
80
In plain film radiography, what is an intensifying screen?
A screen between the patient and the film. It is a material that has a much higher absorption efficiency for x-ray photons and that converts the x-ray photon energy to visible, and sometimes UV light - parts of the electromagnetic spectrum to which the film is substantially more sensitive.
81
What is the larmor frequency of a proton (H1) at 3T? at 1.5 T?
128 MHz at 3 T
| 64 MHz at 1.5 T
82
What does increasing the object-to-collimator distance do to the system spatial resolution of a gamma camera?
a) degrades resolution
b) improves resolution
c) no effect on resolution
a) An increase in object-to-collimator distance degrades the system spatial resolution. This is an important factor to remember when positioning patients for imaging. The closer the detector is to the patient, the better the resolution of the images obtained.
83
Which of the following is a proper gadolinium dose calculation for a routine neuro MRI examination?
a) 10 mmol/kg
b) 5 mmol/kg
c) 1 mmol/kg
d) 0.1 mmol/kg
e) 0.01 mmol/kg
d) 0.1 mmol/kg
84
For CT angiogram of the head and neck, appropriate scan delay after beginning the contrast injection is:
a) 0 sec
b) 5 sec
c) 10 sec
d) 30 sec
e) 60 sec
d) 30 sec
85
A breast-feeding mother must undergo a gadolinium infused MRI for evaluation of a pelvic mass. After careful consideration, the best recommendation regarding breast-feeding and gadolinium use is:
a) The mother should stop breast-feeding for 48 hours and then resume breast-feeding as usual
b) The mother should stop breast-feeding for 24 hours and then resume breast-feeding as usual
c) The mother should stop breast-feeding for six hours and then resume breast-feeding as usual
d) The mother should pump her milk for 24 hours, store it for later use, and then resume breast-feeding as usual
e) The mother need not modify her breast-feeding practice
e) The mother need not modify her breast-feeding practice.
86
What is the annual effective dose limit for a radiation worker?
5 year cumulative dose limit?
Max limit in 1 year?
- 20 mSv per year
- 5 year cumulative dose limit of 100 mSv
- Max of 50 mSv in 1 year
87
What is the annual effective dose limit in a member of the public?
5 year cumulative dose limit?
- 1 mSv
| - 5 mSv
88
What is "Equivalent Dose"?
| What is it measured in?
- Equivalent dose (HT) is the absorbed dose (DT) multiplied by a radiation weighting factor (WR) (varies by alpha particle, beta, gamma ray, etc.).
- Measured in Sv.
89
What is "Effective Dose"?
| What is it measure in?
The effective dose is calculated by multiplying the equivalent dose (HT) by a tissue weighting factor (WT).
-Measured in Sv
90
What is considered long TE and long TR?
- Long TR >1500 ms
- Long TE >90 ms
- divide by 3 to get short TR and TE (TR 500, TE 30)
- intermediate weighting is in between
- PD weighting is short TE, long TR
- T2WI is long TE and long TR
- T1WI is short TE and short TR
91
In a standard MRI, the center of k space represents what?
Contrast. Periphery of k space is for edge sharpness (spatial resolution).
92
T1 relaxation describes which of the following?
a) Recovery of longitudinal magnetization after an rf-pulse
b) Decay of longitudinal magnetization after an rf-pulse
c) Decay of transverse magnetization after an rf-pulse
d) Recovery of transverse magnetization after an rf-pulse
a) T1 relaxation describes the recovery longitudinal magnetization after an rf-pulse.
- After 1 T1 period, 63% of magnetization has recovered due to interactions with surrounding lattice (spin lattice relaxation); Mz(t) = M0 x (1-e^[-t/T1]). Longitudinal magnetization has completely recovered (> 99%) after 5 T1 times. T1 times are usually 5-10 longer than T2 times. Different tissues have different T1 properties: Fat has a short T1 time, whereas water has a long T1 time.
93
Annual dose limit to the extremity?
500 mSv
94
Annual dose limit to a Fetus of declared pregnant worker
5 mSv during gestation
