Radiography Flashcards
1
Q
Explain how xrays are produced.
A
energy conversion when a fast-moving stream of electrons suddenly decelerate in the target (anode) of an xray tube . This is called Brems radiation
2
Q
What technique is used to protect the patient’s skin from receiving unnecessary radiation?
A
filtration (usually made of aluminum)
3
Q
What is one of the most important actions xray personnel can take in order to avoid unnecessary radiation dose to the patient?
A
collimation
4
Q
explain collimation.
A
reduces the primary xray beam to the area of clinical interest AND reduces the amount of scattered radiation reaching the xray film
5
Q
explain filtration
A
material placed in the primary xray beam (usually made of aluminum), it is used to preferentially absorb or eliminate the less penetrating xrays before they reach a patient
6
Q
explain the function of the grid.
A
reduce the scattered radiation produced in the patient (part being xrayed) before it reaches the xray film ; drawback is the use of grids results in increased patient radiation dose
7
Q
Explain kVp.
A
determines the maximum photon energy (QUALITY) of the xray beam produced
8
Q
What is the optimal target-to-film distance for radiographic examinations?
A
40 inch target to film distance
9
Q
in radiography, what is the main source of scattered radiation?
A
the patient (body part being xrayed)
10
Q
What factors affect scattered radiation?
A
- kvP used
- field size (area exposed)
- part thickness (volume exposed)
- tissue density (z number)
11
Q
Explain Brems radiation (aka “breaking” radiation or brehmsstrahlung)
A
the process by which xrays are produced; energy conversion when a fast moving stream of electrons is suddenly decelerated in the target of an xray tube
12
Q
What is the cathode?
A
negative electrode or filament
13
Q
what is the anode?
A
positive electrode containing the target
i.e. electrons flow from the cathode to the anode
14
Q
what % of energy deposited in the target by electrons is converted to xrays? what happens to the rest of the energy?
A
1%; while the other 99% is converted to heat
15
Q
what directions do electrons flow in the xray tube?
A
from the cathode (filament) to the target (anode)
16
Q
Explain milliamperes (mA).
A
refers to the QUANTITY of electrons flowing per second and is related to the # of xrays produced per second
17
Q
Which factors, KvP and mA, is quantitative? how about qualitative?
A
KvP- quality of xray
mA- quantity of xray
18
Q
A tube current of 200mA produces ____ as many electrons as a current of 100mA and ___ as many xrays per second as does 100mA.
A
twice; twice
19
Q
Which principle allows high anode heating with small effective focal spots?
A
line-focus principle
20
Q
what is the relationship between the target angle and the effective focal spot?
A
as the target angle decreases, so does the effective focal spot
21
Q
what is the usual anode angle?
A
12-20 deg
22
Q
what is the focus spot? why is this important?
A
the area bombarded by the electron stream; the size of the focal spot influences resolution of the image
23
Q
Explain the “heel effect”. why is this important?
A
the result of the line focus principle that distributes radiation intensity more on the cathode side than on the anode side; results in reduced xray intensity on the anode side because of the abosrption fo the xrays in the “heel” by the target
24
Q
what does filtration effectively accomplish by reducing the # of low-energy xrays from reaching the patient?
A
- reduced scattered radiation
- improves quality of the radiograph
- the xray beam becomes less polychromatic (more monochromatic)
25
Explain Half-value layer (HVL).
defined as the thickness of absorbing material necessary to reduce the xray intensity to half its original value
26
what represents the largest contribution to unnecssary patient radiation dose?
failure to collimate an xray
27
The use of 0.5mm lead equivalent sheet of lead to protect gonads reduces gonad dose by approximately what %?
92%
28
What is the minimum depth of lead equivalent for gonad shielding?
0.5mm
29
What techniques help reduce scatter radiation?
collimation
| use of grids
30
what is the disadvantage of using a grid?
increases patient radiation dose
31
what is the general grid ratio for tube potentials below 90 kVp?
8:1
32
what is the general grid ratio for tube potentials above 90 kVp?
10:1, 12:1
33
What factors help reduce patient radiation dose?
```
collimation
use of intensifying screens
higher KvP
lower mAs
lower time exposure
```
34
What factors increase patient radiation dose?
use of grids
35
what is the intensification factor? how is it calculated?
magnitude of dose reduction obtained when using an intensifying screen; calculated by exposure without intensifying screens divided by exposure with screens
36
Examinations taken with intensifying screens reduce the radiation dose of the patient by approximately what %, compared to exams conducted without intensifying screens?
95%
37
What is the notable exception to the 40-inch target to film distance for optimal radiographic examinations?
chest radiography, where a 72-inch target to film distance is utilized to diminish magnification of the heart shadow on the radiograph
38
What 4 factors determine the quantity of scatter radiation?
```
kVp
part thickness
field size/area exposed
tissue density
*higher of these factors leads to greater scatter radiation
```
39
List in order of increasing density the following: water, bone, lead, muscle, aluminum, air, fat
air, fat, water, muscle, bone, aluminum, lead
40
which areas fo the body require patient shielding?
fetus, gonads, lens of the eye, thyroid gland, active blood forming organs such as spleen and bone marrow
41
What is attenuation?
the process by which an xray beam of radiation is reduced in intensity by absorption or scattering when passing through a material
42
explain the Compton effect.
An interaction between an incoming xray photon and an outer shell electron of an atom of the irradiated object in which the photon surrenders a portion of its kinetic energy to dislodge the electron from its orbit and then continues on its way but in a new direction; this process accounts for most of the scattered radiation produced during xray exams
43
What % of retake studies are due to error in exposure factors? What % of retake studies are due to positioning errors?
50% of retakes are due to errors in exposure factors
| 25% of retakes are due to errors in positioning
44
How does CT scan produce an image?
a fixed ring of detectors surrounds the patient, and the xray tube moves around the patient to collect views of the anatomy from many angular positions
45
Where does the majority of unnecessary radiation from CT examinations occur?
when the prepatient collimator is improperly adjusted
| there is also a predetector collimator
46
which examinations have high dose effect on the bone marrow?
lumbar spine exams
retrograde urography
abdominal angiography
chest tomography
47
which blood cell type is most affected by irradiation of the bone marrow?
lymphocytes
48
what exams are the largest contributors to the genetically significant dose?
lumbar and lumbosacral exams
49
what is the estimated mean annual genetically significant dose (GSD) to the U.S. population in 1970?
20 millirads
50
List in order the cell types of diminishing sensitivitiy.
(most sensitive) lymphocytes or WBC> RBC, granulocytes> epithelial cells> endothelial cells> connective tissue cells> bone cells> muscle cells> nerve cells> brain cells (least sensitive)
51
At what maximum dose for diagnostic radiographic exams show no indications of injury?
25 rads or less
52
What is the order of most frequently occuring radiation-induced cancers? (in descending order of susceptibility)
(most susceptible) female breast > thyroid gland >hematopoetic tissue > lungs > GI tract bones
53
what does ALARA stand for?
as low as reasonably achievable
54
true or false: there is no minimum threshold of radiation dose necessary to achieve a biological event
true
55
explain stochastic effects. give an example
the probability of an effect occuring, rather than its severity
Ex. genetic effects, carcinogenesis
56
Explain non-stochastic effects. give an example.
severity of an effect varies with radiation dose (aka deterministic)
Ex. cataracts, bone marrow cell depletion, non-malignant skin damage
57
what is the chief danger to the operator during radiographic procedures?
exposure to scattered radiation coming from the patient, and other scattered media
58
by what % is exposure reduced when an operator stands behind the protective barrier?
99.87%
59
by what % is exposure reduced from scattered radiation by wearing protective clothing?
97%
60
What does "rad" measure?
absorbed dose ("Radiation abosrbed dose")
* aka gray (Gy)- in SI units
* 1 Gy= 100 rads
61
What does "rem" measure?
dose equivalent
| *aka sievert- in SI units
62
what 3 basic principles can be used to reduce dose to X radiation?
1. time
2. distance
3. shielding
63
What is the Inverse Square Law?
I1 (D1)^2 = I2 (D2)^2
*If the distance from an Xray source is doubled, the radiation intensity is reduced to 1/4 of the intensity a the original distance
64
If the distance from an xray source is tripled, how does this affect the intensity ?
reduces the intensity to 1/9
65
What are 3 ways for energy to be lost?
1. photoelectric effect
2. compton scattering
3. pair production
66
Explain the photoelectric effect.
A collision between a photon of x-radiation and an orbital electron of an atom, where the electron is knocked out of its orbit and the photon loses all its energy
67
Explain compton scattering.
interaction of a photon of x-ray with an orbital electron of the absorber atom producing a recoil electron and a photo energy which is less than that of the incident photon
68
explain pair production.
incident photos is annihilated in the vicinity of the nucleus of the absorbing atom with subsequent production of an electron and positron pair
69
what is the half value layer?
defined as the thickness of a specified material which attentuates the xray beam so to that exposure rate is reduced to one half ; commonly expressed in mm thickness of aluminum
70
Cellular damage occurs on which order of time?
seconds/ minutes
71
Cellular death occours on which order of time?
minutes/hours
72
What is the maximum occupational exposure to an embryo during a pregnancy?
may not exceed 0.5rem (500mrems) or 5 mSv
| *may not exceed >0.05 rem in any one month what a
73
What are the units of abosrbed dose?
1. rad
| 2. gray (Gy)
74
How often should an analysis of the # of retakes be done as part of the quality assurance program?
every 3 months (QUARTERLY)
75
How long should records or written logs of maintenance and/or repairs of xray equipment be kept for?
at least 3 years
76
what % humidity should be maintained in the dark room?
between 40-60%
77
Which personnel monitoring device leaves no permanent record?
pocket ionization chamber
78
When must you notify the Department of Radiologic Health Branch about an acquisition of a xray machine?
within 30 days of acquisition
79
When do you have to report (in writing) to the Department about any change in: registrant's name, address, location of the installation, or receipt, sale, transfer, disposal, or discontinuance of use?
within 30 days
80
When do you renew a registration for xray machine?
July of every even-numbered year
81
What does "whole body dose" refer to regarding the purposes of external exposure?
means exposure to ANY of the following:
- head
- trunk (including male gonads)
- arms above the elbow
- legs above the knee
82
What personnel monitoring devices are considered acceptable?
film badge
thermoluminescent dosimeter (TLD)
*note: pocket ionization chambers or audible warning devices may be worn only IN ADDITION to the above devices
83
How sensitive are film badges to detecting radiation exposure?
can sense exposure equivalent to doses as low as 10 millirads and up to as high as 700 rads
*Note one rem is approximately one rad
84
What is the most common material used in the thermoluminescent dosimeters?
lithium fluoride
85
which personnel monitoring device is more accurate- film badge or TLD?
accuracy of TLD (+/- 9%) compared to film badges (+/- 25%)
86
what is a major disadvantage to the TLD?
once the TLD exposure has been read, it cannot be read again. Thus it does not provide a truly permanent record of exposure.
TLDs are also generally more costly than film badges
87
Where should the personnel monitoring device be worn?
positioned on the collar above the protective apron or on the top of the protective apron itself
88
What is the annual occupational dose equivalent for whole body dose?
```
5 rem (or 0.05 Sv)
*know in SI units (Sv)
```
89
What is the annual occupational dose equivalent for skin and extremities?
50 rem (or 0.5 Sv)
90
What is the annual occupational dose equivalent for lens of the eye?
15rem (or 0.15 Sv)
91
What is the occupational dose equivalent for persons under age 18?
may receive 10% of the adult occupational dose limits
92
What is the radiation dose limit for the public?
0. 1 rems (1 mSv) in a year OR
| 0. 002 rems (2 millirems) in any one hour
93
how often should film badges or TLD badges be changed?
once every month
94
When was the first case of human injury from x-ray exposure reported in scientific literaturer?
1895
95
What % of average population's exposure from manmade ionizing radiation sources comes from medical uses of radiation?
over 90%
96
What does the largest contribution to total radiation dose to the population from manmade radiation source come from?
medical radiographic examinations
97
Approximately what percentage of the exposure from diagnostic xray exams could be eliminated without decreasing patient benefit?
30%
98
what materials should tabletop and vertical cassette holders be made of?
```
aluminum
Bakelite (plastic)
carbon fiber
cardboard
*all materials must allow xrays to easily penetrate the cover
```
99
What is this? a thin, rigid light-tight x-ray holder containing intensifying screens mounted within front and back covers that are hinged together?
cassettes
100
what is an intensifying screen for?
device in cassette that converts the energy of the xray beam into visible light that then exposes the xray film
101
what does the "target" refer to?
the origin of the xray beam; xrays are produced when electrons hit a "target" made of tungsten
102
what are intensifying screens made of these days?
rare-earth (aka gadolinium oxysulfide) screens
| used to be calcium tungstate screens
103
what is the main cause for retaking a film?
improper selection of primary exposure factors (KvP and mAs)
104
what principle helps to prevent film retakes?
phototiming (the desired degree of film darkening and corresponding density and contrast can be controrlled by the use of automatic timing equipment)
105
what is the patient skin dose for CT examinations?
on the order of one to several rads
106
What are the 3 equipment provisions for MOBILE radiographic equipment?
1. dead-man type exposure switch and so that operator can stand at least 6 feet away from patient
2. source-to-skin distance at least 12 inches
3. personnel monitoring equipment required for all persons operating the mobile xray equipment
107
What are somatic dose indicators vs. genetic dose indicators?
effects of irradiation an individual receives (somatic) vs. effects exhibited in future offspring of persons who have been irradiated (genetic)
108
Are injuries to the developing fetus/embryo considerred genetic or somatic dose effects?
somatic dose
109
Give examples of somatic dose indicators.
1. injuries to the superficial tissue
2. cancer
3. cataract formation
4. impaired fertility
5. life-span shortening
6. injuries to the developing fetus/embryo
110
What dose of acute radiation exposure may cause temporary sterility in female ovaries?
300 rads
111
What dose of acute radiation exposure may cause temporary sterility in male testes?
30 rads
112
which radiographic examinations produce the highest gonad exposures?
barium enema
IVP (Intravenous pyelogram)
lumbar spine
hips and upper femur exam
113
Biological effects of radiation are influenced by what?
1. dose rate to the tissue exposed
2. total dose received by the tissue exposed
3. type of cell irradiated (but not cell size!)
114
According to what hypothesis do we follow that says that any dose, no matter how small is considered to have some degree of effect?
non-threshold, linear hypothesis
115
What does the Law of Bergonie and Trribondeau state?
The radiosensitivity of tissues depends on:
1. # of undifferentiated cells
2. degree of mitotic activity in the tissue
3. length of time the cells stay in active proliferation
(NOT cell size)
116
What does the radiosensitivity of tissues depend on?
(aka Law of Bergonie and Trribondeau)
1. # of undifferentiated cells
2. degree of mitotic activity in the tissue
3. length of time the cells stay in active proliferation
(NOT cell size)
117
Which biological tissues are especially radiosensitive?
blood-forming organs (spleen, red bone marrrow)
GI tissue
developing embryo/fetus (1st trimester)
118
Radiation exposure at what doses have been shown to have no indications of acute injurious effect?
25 rads or less
119
Radiation exposure at what doses have been shown to cause radiation-induced cataract formation?
order of several hundred rads
120
What is the most frequently occurring radiation-induced cancer?
```
#1 is female breast
#2 is thyroid gland
#3 is hemopoetic tisue
```
121
What absorbed dose to the fetus could result in spontaneous abortion?
50 rads
122
What radiation dose has been shown to cause deleterious effects to the embryo?
as little as 10 rads
123
When must thryoid shields be worn?
when the wearer is in close proximity to the patient during fluoroscopy
124
What are accepted personnel monitoring devices?
```
film badge
thermoluminescent dosimeter (TLD)
```
125
Which personnel monitoring devices may only be worn iN ADDITION to the other accepted devices?
pocket chamber or dosimeter
| audible warning device
126
Radiation dose to an embryo/fetus may not exceed what?
5 mSv (0.5 rem)
127
What other classifications of personnel must be monitored regardless of the exposure they are likely to receive?
1. persons who enter a high radiation area
| 2. persons who operate mobile xray equpment
128
what is considered a high radiation area?
any area accessible to individuals in which there exists radiation levels that could result in an individual receiving a dose equivalent in excess of 1mSv (0.1 rem) in one hour at 30cm from the radiation source
129
When must overexposure of a film badge dosimeter or other personnel monitoring device be reported to the Radiologic Health branch?
within 30 days
130
When must immediate notification to the RHB be reported?
If an individual has received 5x annual maximum exposure:
1. total effective dose equivalent of 0.25Sv or more
2. eye dose equivalent of 0.75 Sv or more
3. skin or extremities dose equivalent of 2.5 Sv or more
131
When must 24-hour notification be reported to the RHB?
if an individual has received within 24 hours the annual dose limits:
1. total body dose 0.05Sv
2. eye dose 0.15 Sv
3. skin and extremities dose 0.5 Sv
132
What is the S.I. unit for absorbed dose?
```
Gray
1 gray (Gy)= 100 rads
```
133
What is the S.I. unit for dose equivalent?
Sievert
| 1 Sv= 100 rems
134
When is the "safer" times to perform x-ray exams on females who could be pregnant?
10-14 days after the onset of menses
135
What is the max. dose to an embryo/fetus during the ENTIRE pregnancy?
5 mSv (0.5 rem)
136
What is the max. dose to an embryo/fetus in any month of pregnancy (once the pregnancy becomes known) ?
0.05 rem
137
When is the embryo-fetus most sensitive to rradiation?
1st trimester
138
photographic material is sensitive to what?
temperature- store in the range of 60-70 deg F
| pressure damage- store films standing on edge; never flat
139
What does the BEIR (Biological Effects of Ionizing Radiations) report estimate?
the increased risk of mortality from all radiation-induced cancers to an individual in the U.S. population
