Physics 2 Flashcards
(300 cards)
0
Q
Elements that have the same atomic mass (A) but different atomic number (Z)?
A
IsobArs
1
Q
Elements that have the same atomic number (Z) but different atomic mass (A- protons and neutrons)?
A
Isotopes (have same number of protons but different number of neutrons)
2
Q
What elements have the same atomic number and mass but different energy states?
A
Isomers
3
Q
What elements have the same number of neutrons but a different number of protons?
A
IsotoNes
4
Q
The general threshold for ionization is?
A
10 eV
5
Q
In what stage of fetal development can I-131 not be given?
A
10 weeks
6
Q
An isotope has?
A
The same number of protons but different number of neurtrons
7
Q
Isobar?
A
Same mass number (A) but different number of neutrons/protons
Ex: I131, Xe131, Cs 131
8
Q
Isotone?
A
Same number of neutrons, different protons
9
Q
Isomer?
A
Have same composition but have different energy states
10
Q
What determines what an element is ?
A
Z-number, the number of protons
Z is protons (ZIP)
11
Q
What is gamma decay (Isomeric transformation)?
A
nucleus in an excited state gives off gamma photon and is transformed to more stable state. Does not lose neutrons, protons.
12
Q
Beta (-) Decay?
A
Too many neutrons therefore a neutron forms an electron, proton, and an antineutrino (this has only energy, not mass or charge)
The Z = Z+1
A= unchanged due to loss of neutron and gain of proton
Element changes X->Y
13
Q
What radiotracer is produced by beta- decay?
A
Tc99 from Mo99
14
Q
What is electron capture?
A
Electron is pulled into the nucleus where it combines with a proton to form a neutron. A neutrino is ejected.
Atomic mass (A) is unchanged
Z-> Z-1
X-> Y
EC is more common in heavier elements, B+ is more common in lighter elements
15
Q
Internal conversion?
A
Nucleus releases energy displacing an electron (typically in a K or L shell)
This can be filled producing characteristic or Auger electrons
16
Q
B+ decay?
A
Proton is transformed into a neutron, positron and a neutrino (positron and neutrino are ejected from nucleus)
Then…
Positron (positive electron) is emitted from the nucleus and combines with an electron forming two 511 kev photons = annhilation
these travel in opposite directions
17
Q
Alpha decay?
A
Nucleus ejects an alpha particle (2 protons and neutrons, 4He nucleus)
18
Q
1 Ci = ? Nw
A
3.7 x 10 ^10
1 mCi = 37 MBq
19
Q
How is half life calculated in regards to the decay constant?
How can residual activity be calculated after a specific period of time?
A
Decay constant = ln2/T1/2
ln2=0.693
Nt (remaining sample) = No (Original at time 0)/2^n
n= number of half lives
20
Q
what is secular equilibrium?
A
Decay of parent is so long that it is negligible (takes 5-6 half lives of the daughter to reach quilibrium)
Ac= Ap
21
Q
What is transient equilibrium?
A
parent (longer half-life) decays with time, the activity of the child surpasses the parent and then reaches its maximum -> then both decay in constant equilibrium with each other
22
Q
What occurs when the half life of the child is longer than the parent?
A
No equilibrium
23
Q
What is the K-Shell binding energy of tungston?
A
69.5 kev
24
What is the dominant interaction in mammography?
Mamms- photoelectric effect
25
The probability of Compton scatter increases with?
increase in the density of the attenuating material
CS is proportional to the density of the material
26
There is a sharp increase in the photoelectric absorption at?
photon energies just above the K-Shell binding energy
27
Biological damage with ionizing radiation is primarily caused by?
Ionization of water molecules
28
Beam hardening?
Removes low energy xrays from a polyenergetic beam
29
The probability of photoelectric absorption is proportional to?
(Z^3)/E^3
Proportional to Z and indirectly proportional to the energy cubed of the incoming photon
PE occurs when Z is high and photon energy is low
30
What is the primary interaction on a Tungston target?
excitiation, which results in the production of heat (no electron is ejected)
31
The energy of an xray is equal to?
The difference in binding energies of two electrons shells (when the outer shell electron falls to the higher energy shell)
If xray is not produced but energy is transferred to second electron which is also ejected, this is an Auger electron emitted (occurs in low Z) material
32
What is a Bragg peak?
Sharp increase in ionization potential of a charged particle near the end of the charged particles range (in diagnostic xrays this is at the entrance skin location- maximal dose is delivered to skin surface and with falloff in dose deposition with increasing depth)
33
What is LET proportional to?
particle charge
It is inversely proportional to particle velocity
alpha- high LET, therefore path length is equal to range
34
What is Bremsstrahlung radiation?
charged particle changes directions and gives off electromagnetic radiation in the form of an xray (energy of emitted xray is equal to kinetic energy lost by charged particle)
35
Bremsstrahlung is proportional to?
Energy of charged particle and Z number of absorber
Ex: Low Z such as plastic is used for beta emitting isotopes to minimize bremsstrahlung
36
What interaction occurs in compton scatter?
incoming photon interacts with outer shell (or free electron), dislodging it.
37
The probability of compton scatter is independent of absorber atomic number (Z)? T or F
True
But compton scatter is proportional to material physical density (which is proportional to linear attenuation coefficient)
38
What is the dominant photon interaction above 25-30 kev?
Compton
39
T or F: filters made from higher atomic number material attenuate higher energy xrays
True
40
The law of Bergondie and Tribondeau describes?
Radiosensitivity of cells is proportional to the how often the cells divide and inversely proportional to the degree of differentiation
41
What cell cycle are cells most sensitive in?
M phase > G2 phase >> S (least sensitive)
42
The majority of radiation tissue damage is caused by?
The electron
43
Treshold dose for cataracts?
0.5 Gy- timeline of dose (chronic or acute does not matter)
150 mSv/year
44
What is the dose level in a high radiation area and very high radiation area?
What is the dose level in a radiation area?
High- 1 mSv/1 hour at 30 cm
Very high- 5 Gy/ 1 hour at 1 meter
Radiation area- 0.05 mSv/hour at 30 cm
45
During which phase of development is the fetus most likely to have a malformation due to radiation exposure?
2-8 weeks, organogenesis
46
The dose limit in an unrestricted area is?
0.02 mSv/hour
47
The annual dose limit to an occupational radiation worker is?
50 mSv
48
A dose of 15 Gy to a single field is a ?
Sentinel event
49
A medical event must be reported to the NRC?
Within one calendar day of the discovery of the event
50
What is the dose limit to the lens of the eye in the general public?
15 mSv/yr
51
What is the average lifetime risk of developing cancer?
5%/Sv
52
Threshold below which no deterministic effects have been seen?
0.1 Gy
53
What is an absorbed fraction?
The dose emitted by the source organ that is absorbed by the target organ
54
What forms of radiation are considered non-penetrating?
Alpha, beta, auger- radiation stays in source organ
55
What is S value and what does it depend on?
mean doses per unit cumulated activity
Mass of target organ (inversely proportional) , radiation emitted from source organ, energy of emissions absorbed by the target organ
56
What types of radiation source should be shielded with plastic?
Beta ( -) -> decrease bremsstrahlung
Gamma- shield with lead
57
Steps for handling spills?
Inform -> contain -> decontaminate
58
Ideal pH of radiopharmaceutical?
7.4
59
Maximum amount of Mo breakthrough?
0.15 microcurie/mCi of Tc99- (0.15 kBq/1 Mbq)
60
Dose calibrators are?
Ionization chambers
61
Annual dose limit to a member of the public?
1 mSv
62
Phosphor screen (intensifier screen) in screen film radiography is used to?
Increase conversion of light to xrays or vice versa
Film speed can be increased by increasing the thickness of the phosphor (but there is increased lateral dispersion decreasing spatial resolution)
63
The dynamic range or latitude is narrower for film screen or digital?
Film screen (can overexpose or under expose easily)
Digital has a much wider dynamic range- can lead to dose creep
64
Bit depth determines?
The number of possible pixels
65
What is the difference between direct and indirect radiography systems?
Indirect first convert xray to visible light
Direct- convert xray directly to measurable charge separation and voltage production
66
Benefit of amorphous selenium in direct detector over indirect?
Better spatial resolution due to less lateral dispersion of charge and lower patient dose due to thick layer of amorphous selenium which absorbs xrays more effectively
67
What are the two methods of indirect radiography for converting xrays to visible light?
Phosphors and scintillators (NaI or CsI)- scintillators are more efficient at ocnversion
68
What is the purpose of thin film transistors (TFT)?
measure stored charge in direct and indirect systems
Have a fill factor, which has decreased detector efficiency in scintillators
69
In indirect detectos, what contributes to the greatest loss of spatial resolution?
lateral dispersion
70
What is the advantage of TFT to measure charge vs. Charge coupled device (CCD)?
No need for input demagnificaiton (CCD measures xrays directly, but small FOV)
71
In film screen, what stores the latent image?
Silver Halide
72
Contrast in screen film depends on?
Silver halide crystals - small uniform = high contrast
Large, irregular- low contrast
contrast is inversely proportional to latitude
73
In digital radiography, how does one correct for bad pixel or row?
Interpolation algorithm
74
How is the number of shades of gray determined?
2^n
75
modulation transfer function is a measure of _______ in radiography?
Resolution
76
T or F: focal spot size affects patient dose.
False, change in focal spot size does not significantly alter patient dose
77
MQSA-how many fibers, specks and masses must be visualized?
4 fibers, 3 specks, 3 masses
78
Weekly MR QC?
center frequency, setup and scanning, table position, geometric accuracy, high and low contrast resolution, artifact analysis, film quality control and visual checklist
annual- field homogeneity, slice thickness accuracy, slice position accuracy, radiofrequency coil checks, softcopy displays (monitors)
79
What effects the signal to noise ratio?
SNR increases with increased voxel volume, inversely proportional to the receiver bandwidth
Increases with the number of excitations
Increases with increase in TR and decrease in TE
80
Susceptibility artifact is ____________ by decreasing the receiver bandwidth?
increased by decreasing the receiver bandwidth
81
The center of K-space contains information about?
Low spatial frequencies, determines contrast
82
The periphery of K-Space?
contains higher spatial frequencies, pertains to details/blurring
83
Under-sampling of the periphery of k-space/ high spatial frequencies will result in?
Gibbs/Truncation artifact
84
True or False? The dose area product remains constant regardless of distance from patient?
True
85
In high level activated control, what is the maximum air kerma permitted 30 cm from image receptor?
176 mGy/min
lower level dose is 87 mGy/min
86
Compared to a single fluoroscopic image, cine images are approximately __________ the dose?
10 times the dose
87
How does noise in last image hold compare to noise in live fluoroscopic examination?
last image hold has less noise due to average multiple images together
88
Filtered backprojection filters the?
projected data
89
The system MTF is______?
The MTF PRODUCT of all components
90
What is the attenuation of the ultrasound beam in soft tissue?
0.5 dB/cm/mHz
91
What is a diffuse reflector vs. specular?
Specular- larrge smooth surface
Diffuse- irregular surface
92
Ultrasound Nyquist frequency =
NF = PRF/2
93
Color doppler is a measurement of ________ velocity?
Average
94
Which doppler function is independent of doppler angle?
power
color and spectral are dependent on angle
95
What is the geometric efficiency of a radionucleide calibrator?
100% but intrinsic efficiency is much less because it is a gas calibrator
Can differentiate between different energies (not just events)
96
What results in increased intrinsic efficiency?
Increased density and thickness of detector, increased Z number
97
Non-circular orbits of SPECT cameras results in?
better spatial resolution than circular orbits (camera can be closer to patient)
98
What is the Chang attenuation correction factor for Tc99 in SPECT imaging?
In Tc99 there is an assumed correction factor of 15%/cm
Chang attenuation factor correction applies to a uniform attenuation medium and uniform source of radioactivity
Chang is an improvement on the conjugate views attenuation correction
99
What are the methods of attenuation correction with SPECT?
Scanning Line Source
and
CT attenuation correction
100
What is the blurring function that occurs in filtered back projection and how is it fixed?
blurring function = 1/r (r=distance to center)
Fixed with ramp filter
101
MR pixel size is inversely proportional to?
product of gradient amplitude and duration
- The larger the gradient, the smaller the pixel
102
A increase in the receiver bandwidth results in a ___________ in the signal to noise?
Decrease
Increasing sampling time results in a narrower bandwidth and increased signal to noise
103
A higher slice select gradient results in ________ slices
Thinner
104
As voxel volume increases, spatial resolution ________?
decreases - smaller voxels help discern two objects which may be close together- if the are in the same voxel, they cannot be differentiated from each other
105
Proton density has?
Long TR, Short TE
106
A wide receiver bandwidth reduces what artifact?
Chemical Shift - Type I
107
How is susceptibility artifact reduced?
Increase receiver bandwidth
Increase Matrix
Decrease Slice thickness
Use lower strength magnet
In EPI= use parallel imaging
108
How many phase encoding sequences does the 3D MRI have?
2 phase encoding steps and 1 frequency encoding step
109
How is aliasing in MRI fixed?
Larger FOV
Saturation bands on anatomy outside FOV
110
What is ghosting?
Errors in gradient performance that result in image shift
or patient motion/flow artifact
Nyquist ghosting - typically in echo planar imaging
111
How is ghosting or motion reduced?
Switch frequency and phase encoding directions
Gating sequences to reduce motion
Reduce Eddy Currents- Nyquist Ghosting
Use motion reducing sequences- propeller/blade
112
Gibbs/Truncation artifact correction?
Increase matrix size
| occurs at sharp or distinct boundaries between tissue
113
What are the two types of chemical shift artifact?
Type I- shift in the fat and soft tissue (appears as bright band and dark band)- due to small receiver bandwidth
Type II-India ink artifact (boundaries with large differences in fat/water content cancel out)
114
What is the appearance of a spike in K-space?
How is it fixed?
Alternating light and dark bands over image
Caused by loose wires/vibrating metals, etc.- which should be fixed
115
What causes zipper artifact?
Erroneous RF signal in scanning room
116
What id dielectric effect?
Loss of signal centrally, typically in a large patient
Remedy- dielectric pads on surface of patient
117
What is the predominant effect of RF exposure?
Tissue Heating
118
What increases the MRI specific absorption rate?
Square of magnetic field strength and flip angle
RF pulses per cycle
119
How is SAR decreased?
Smaller flip angle, longer TR, fewer slices per TR, decrease echo train length
120
What is the SAR limit?
1 degree celsius increase in whole body temperature
or
4 W/kg per 15 minutes for average adult
121
When is peripheral nerve stimulation most likely to happen?
High gradients- like EPI
122
What are the acoustic dose limits in MRI
140 dB and 99 dBA
123
What are the types of direct and indirect detectors in radiography?
Indirect- PSP (photostimulable phosphor) - more blue from lateral dispersion
Indirect-Scintillator (CsI)- has columns therefore less blur from lateral dispersion
Direct- amorphous selenium photoconductor- directly reads charge, little to no lateral dispersion
124
Shades of gray?
2^n (n= bits)
125
What are the conversion steps from taking an imaging to viewing an image in regards to analog/digital?
Analog-> digital for processing -> digital for storage -> analog for viewing
126
How many bits are in a byte?
8
127
What are important disadvantages of analog compared to digital?
Analog is susceptible to distortion of signal- amplification of inaccuracies, attenuation loses and electrical noise
Advantage of analog- less time
128
What ensures an accurate ADC (analog to digital conversion)?
Nyquist limit must be met - minimum sampling rate limit
There is degradation in the sampling and quantization steps when converting to digital
129
What determines the ability of an analog to digital converter?
The number of bits
analog signal with large signal to noise ration requires an ADC with a lot of bits for conversion
130
What is typical luminescence for radiography and mammography?
Radiography- 200 cd/m^2
Mammography- 600 cd/m^2
131
How many bits/pixel are used in mammography and general radiogrpahy?
Mammogrpahy- 16 bits
Radiography- 10 bits
132
High KV gives ______ contrast?
low
Incrased KeV = increased Compton scatter therefore decreasing contrast
133
What does a wide CT window provide?
Low contrast, wide range (lung windows)
Narrow window- high contrast
134
What affects quantum mottle/noise?
Number of photons- controlled by mA (tube current)
135
A receiver operating curve plots sensitivity vs?
1 - specificity or false positive fraction
136
What percentage of electrons/energy make xrays in X-ray tube?
1%, the rest is heat
137
What increases the heel effect?
Smaller anode angle
Increased Cassette size
Decreased source to image distance
138
Breast Compression minimizes?
focal spot blur
scatter
Dose
Tissue overlap
139
What is the receptor air kerma in radiography?
3 microGy
Mammography - 100 microGy
140
A grid most likely affects?
Contrast (removes scatter, therefore increasing contrast)
141
What is the bucky factor?
The increase in the amount of radiation when a grid is used
142
Binning of data in fluoroscopy results in?
reduction in data, quantum mottle/noise, and spatial resolution
143
Which has a larger dynamic range- image intensifier or flat panel detector?
Flat panel detector
II- demonstrates vignetting, distortion, glare, and saturation
144
What is the minimum required distance between two objects to discern them in axial resolution of an ultrasound?
Minimum distance is 1/2 Spatial pulse length (SPL) or the objects will not be distinguished separately
SPL = number of wavelengths x length of each wavelength in a pulse
145
Which collimator has the worst resolution?
Diverging
146
Major advantage of 3D PET over 2D PET?
sensitivity - no collimator or septa in 3D PET
147
What is the dose limit to a member of the public who is near an individual treated with radionuclide therapy?
5 mSv (patient must be educated if dose exceeds 1 mSv)
148
An administered dose must be within ________% of the calibrated dose?
20%
149
What radionuclide requires a written directive?
I-131
Written directive must have -RN, Dose, Patient name, route of administration, Authorized User, date
Others- Zevalin
150
What is a medical event?
- The administered dose differs from the prescribed dose by more than 0.05 effective dose equivalent or 0.5 dose to organ/skin
- 0.05 mSv to fetus or breastfeeding child
- 20% difference than the prescribed dose/or a single fraction of 50% difference/or falls out of prescribed range
- Wrong drug, wrong route, wrong person, dose administered via leaking source or wrong treatment
- If administration of unintended drug results in unintended permanent side effects
151
When must a medical event be reported to the NRC?
By the next calendar day after discovery
Written report must be submitted within 15 days
Referring physician and patient should be notified within 24 hours (referring physician can inform patient or can choose not to if they feel informing the patient may be harmful)
152
How long must patient dose records be kept for -NRC?
3 years
153
Transportation of radioactive material is controlled by the?
Department of transportation
154
White level I dose on dose survey?
less than 0.5 mrem (5 microSv) on surface/hour
155
Yellow Level II dose survey?
50 mrem (0.5 mSv) per hour at surface and 1 mrem (10 microSv) at 1 meter/hour
156
Yellow level III dose monitor?
200 mrem (2 mSv) at surface/hour or 10 mrem (0.1 mSv) at 1 meter/hour
157
What is the transportation index?
number of millirems detected from the package at 1 meter/hr
-should be less than 10
If >10 must be transported in specific carrier
158
When should a package with radioactive material be received?
Within 3 hours or 3 hours of the next business day
159
How is a package received?
- Survey at 1 meter and compare to dose on transportation index
- Can the surface level
- If survey detects higher radiation- wipe test can be used- must wipe 300 cm^2 or 100 cm2 x 3 - well counter (must inform carrier if counts are over 6600/min)
-
160
Shielding radioactive material?
Beta- plastic
Positron emission- tungston
161
What is level of Moly breakthrough in 1 mCu of Tc99?
0.15 MICROCi of Mo
162
"Caution very high radiation" denotes?
100 mrem (1 mSv)
163
Unrestriceted areas dose limit?
20 mrem/hour (20 microSv)/hour
or 100 mrem (1 mSv) in one week
164
Who should wear a dosimeter?
If expected dose will be greater than the 10% occupational dose limit- a badge should be given
165
Breastfeeding cessation for thallim, gallium, and indium?
Tc99?
Th, Ga, In- At least a week
Tc99- 0-24 hours
166
What are considered major spills?
100 mCi of Tc or thallium
10 mCi of gallium and indium
1 mCi of I-131
167
Fetal abnormalities have not been reported in doses less than?
0.1 Gy (10 rad, 100 mGy)
168
Risk of radiation induced cancer in the general population?
5% per sv
169
The noise level is digital subtraction angiograms is _______ than the noise in individual images?
Higher
170
Typically, an ultrasound transducer crystal thickness is equal to______?
1/2 the wavelength (wavelength/2)
171
What is the length of the Fresnel Zone (near-field)?
d^2/ (4 x wavelength)
d= diameter of the transducer
Fresnel zone increases with increasing trasnducer size and lower wavelengths
172
What is M Mode?
Displays time dependent motion
173
What is ultrasound line density?
The number of vertical lines per FOV
174
What is the time to acquire MR images?
(TR x Number of phase encoding steps x Number of signal averages)/Echo train Length
175
Axial ultrasound resolution is determined by ______?
Pulse length
Axial resolution is decreased with increasing pulse length, decreasing frequency, and increasing wavelength
176
Ultrasound lateral resolution is determined by_______?
Beam width and line density
177
Lateral resolution is best in the ________?
Fresnel zone
178
Doppler shift equation?
2 x frequency (velocity/speed) x Cos theta
179
To avoid aliasing in ultrasound, the PRF must be _______?
twice the highest doppler frequncy shift
- Can also decrease frequency and increase angle
180
Acoustic impedance =
tissue density x velocity of sound in tissue
181
Ultrasound waves are _______?
Longitudinal
182
What is the ultrasound nominal frequency?
The resonant frequency the ultrasound transducer is designed to emit, but generally a range of frequencies are produced (bandwidth)
183
What ultrasound mode is used for diagnostic imaging, continuous or pulsed?
Continuous
184
What is the role of the backing layer in the ultrasound probe?
Matching layer?
Backing layer- dampens oscillation and affects duration of pulse pressure (increased dampening = shorter pulse pressures)
ML- affects bandwidth and increases efficiency of transmission
185
Most transducers have a _______ Q-factor?
Low (this is due to the large bandwidth of the transducer)
186
CT Hounsfeld Unit Calculation?
1000 x [(attenuation coefficient - attenuation coefficient of water)/attenuation coefficient of water]
187
Pixel Size?
FOV/Matrix
188
Binding energies increase with _________ atomic number?
Increasing
189
Auger electrons typically occur with ?
Low Z (atomic number elements)
190
Heavier elements typically have more?
Neutrons
191
What is the average Beta energy given off during Beta (-) decay?
1/3 Emax
192
What is the threshold for Beta + decay?
1.022 MeV= (two 511 keV)
193
What are the ways neutron deficient radionuclides decay?
Beta + and Electron capture
194
What is isobaric decay?
The mass number (total number of protons and neutrons remain the same).
195
Which radionuclides decay by electron capture?
Co-57, Ga-67, IN-111, I-123, I-125, and Tl-201
196
Decay diagrams-
Diagonal line pointing to right?
Diagonal line pointing to the left?
Right-Atomic number increases by one (beta -)
Left- Atomic number decreases by one (beta +, EC)
Vertical- gamma ray admission (isomeric conversion)
197
What radionuclides are made in cyclotron?
Ga67, In111, I123, Tl201, F18, N13, O15, Sr82
198
What radionuclides are produced by nuclear fission?
Mo9, I131, Xe133
199
How is Mo99 breakthrough measured?
Place sample in led container and then place in dose calibrator (140 keV photons will be removed by lead, therefore only Mo99 is measured)
200
Limit of Aluminum breakthrough in Tc99?
10 micrograms Al/1 mL of Tc99
201
Photoelectric effect can produce?
A characteristic xray or Auger Electron
202
Gas-filled detectors in nuclear medicine?
Ionization chamber/dose callibrators, Geiger-Mueller Counters
203
Ionization chambers are frequently run in _____ mode?
And good for ________ radiation fields?
Current- avoids dead time, so is good for use in high radiation fields
204
Dose calibrators are typically filled with?
Argon- higher Z than air, which contributes to detector efficiency
205
Geiger-Mueller Counters are _______?
Sensitive due to multiplication effect, these are good at detecting small levels of radiation
Cannot differentiate between energies
Pulse mode- paralyzed at high radiation due to dead time
206
Scintillation detectors are used in?
Gamma cameras, thyroid uptake and well counters
207
Linear attenuation coefficient?
n= mu x N x (x)
n = number of photons removed
N = number incident
Mu= linear attenuation coefficient
(X) = thickness
208
Energy resolution of a detector =?
Width of the photo-peak at half the maximum height (full width at half maximum).
209
Medium energy collimators?
Ga67 and In-111
I-131= high energy
210
The main component in the system resolution is the?
Collimator resolution
211
Thicker crystals have _____ intrinsic resolution and ________ detection efficiency than thinner ones?
worse, better
212
True or False: Both spatial resolution and efficiency vary significantly with the distance of the source to the collimator?
False, spatial resolution does vary with distance, but the efficiency does not
213
What is the advantage of SPECT over planar iamging?
Removes superimposed anatomy
214
Which ahs better spatial resolution, planar or SPECT?
Planar (has smaller object to collimator distance)
215
Ramp filter in Gamma Camera imaging?
amplifies each spatial frequency in proportion to that frequency (higher spatial frequencies are amplified more than lower)
Simple back projection has a tendency to filter out higher frequencies, which are restored with RAMP
RAMP accentuates noise at high spatial frequencies
216
What are smoothing filters used in gamma imaging?
Butterworth, Hanning
217
Chang Method of Attenuation Correction in Gamma Imaging?
Best for uniform structure with uniform attenuation (ex: brain)
218
What is the advantage of TOF PET?
the difference in time in which each 511 kev photon interacted with the detector is recorded
219
Effective milliampere-second?
(tube current x rotation time)/pitch
220
abortion to avoid possible radiation-induced congenital anomalies considered only for doses?
> 0.1 Gy (100 mGy)
221
No congenital abnormalities have been noted below?
10 mGy
222
What are the gamma camera QC and when are they preformed?
Uniformity- daily
Spatial resolution and Linearity- weekly
Annual tests: energy resolution, count rate response, sensitivity, collimator integrity, formatter performance, whole body accessory
223
SPECT QC?
– Uniformity and center of rotation checks weekly
| – Gantry and table alignment quarterly
224
Dose Calibrator QC values must be within?
10%
225
Hot sink disposal limits?
liquid waste,
226
What is the LD 100/30 and 50/30 for a general population?
LD100/ 0 whole body dose in humans, ~550 R/ 5.5 Gy
| LD50/ 0 whole body dose in humans, ~ 50 R / .5 Gy
227
What is the only isotope not found on a wipe test?
Xe-133 is only commonly used isotope not found on a wipe test
228
How often are leak surveys preformed?
Q 6 months
229
After decontamination, what is an acceptable radiation limit?
0.02 mSv/hr- general dose okay for public
230
Beam hardening artifact in CT- correction?
Increase KvP
Decrease slice thickness
Increase filtration- bow tie filter
231
CT metal artifact remedy?
MAR software
| Gantry angulation
232
CT out of field artifact correction (Ex: arms)?
Larger FOV
Tape patient tissues
Raise Arms above head
233
How is CT aliasing fixed?
Increase scan time
Complete arc scan
234
How is CT noise/photon starvation remedied?
KvP increase
mAs increase
Slice thickness increase
235
CT ring artifact cause?
Detector out of calibration
236
What is the highest decimal number for a X-bit binary number?
(2^X)-1
237
A Bequerel is?
Disintegration/second
238
8 bits gives how many shades of gray?
256
239
Radiation weighting factors are conservative estimates of?
Radiation Biological Effect
240
The amplitude of alternating voltage can be increased or decreased using?
a transformer
241
What is the activity of a radionuclide given a number of atoms and half-life calculated?
Activity = decay constant x Number of disintegrating atoms
= 0.693/half-life x number of disintegrating atoms
242
What is the cut-off for compton scatter (above what kev?)
25 keV
243
Optical densities are ________?
What is the optical density equation?
Addative
The optical density equation is- OD = log 10 (incident/transmitted)
244
The purpose of automatic exposure control is to ?
maintain the same dose or dose index to the image receptor regardless of kvP or thickness
245
What is a typical focal spot size and mA in magnification mammography?
0.1 mm, 30 mA
246
Mammographic filters remove?
Both high and low energy xrays
247
Each increment in the mammographic AEC density control should increase mA and dose by?
12-15%
248
Why is spatial resolution degraded in tomosynthesis?
long exposure times
249
The noise content of fluoroscopy in an image intensifier is determined by?
Xray photons absorbed at the input phosphor
250
T or F: The resolution of a flat-panel intensifier in fluoroscopy does not change with input field size?
What limits the spatial resolution of the FP system?
True
Limited by: fixed pixel size
251
Typical size of a digital chest or abdomen radiograph is _____ MB?
10
252
What is low pass spatial filtering in digital image processing
Method of noise reduction in which a portion of the average value of the surrounding pixels is added to each pixel
253
What is unshapness masking in digital image processing?
Subtraction of smoothed version of image which is then added to to a replicate original
254
Histogram equilization in digital image processing is?
Elimination of black and white pixels that contribute little diagnostic value, expands remainder of data
255
In digital imaging processing, what is background subtratction?
digitally reduced effect of scatter to increase image contrast
256
The maximum allowable CTDI to a pediatric abdomen ?
25 mGy (justification required for >20)
257
What is a typical CTDI for a head scan?
60 mGy
258
White streaks in CT (shoulders/pelvis) are due to?
Photon starvation (detectors are below threshold for response)
259
In ultrsound, harmonic imaging?
Decreases clutter and improves lateral resolution at depth
260
What is a thermal index of 1 in ultrasound?
What is a safe thermal index?
TI of 1 - operating at power level that can raise tissue temperature by 1 degree C
Safe TI typically
261
What remains constant in ultrasound?
Frequency
262
Ultrasound axial resolution is?
1/2 x spatial pulse length
spatial pulse length = wave length x number of waves in a pulse
263
In Doppler ultrasound, the maximum velocity is _______?
Vmax = C x PRF/ (4 x operating frequency x cos doppler angle)
264
Elevational or slice thickness in ultrasound is determined by?
the transducer element width
265
In room shielding, the U factor is?
Fraction of operating time that the beam is directed toward the barrier
266
What will a narrow CT window do to noise?
Increase the display noise
267
Which of the following do not affect the hounsfeld unit?
- Linear attenuation coefficient
- mAS
- Iodine concentration
- Density
- kvP
mAs
268
What is typically increased in a flat panel CT detector vs. CT ring detector?
Contrast -to-noise
269
How often is the breast phantom used?
Weekly to evaluate system resolution
270
Collimation in fluoroscopy will have what effect on skin dose and effective dose?
No change on skin dose, but will result in lower effective dose
271
The difference in image intensifier vs. FPD fluoroscopy is ______?
Contrast resolution
272
What is the high-dose rate limit for fluoroscopy?
176 mGy/min (20 R/min)
273
How is dose in fluoroscopy measured?
Total air kerma at a reference point indicator
| this is an approximate of skin dose and IS NOT SKIN DOSE
274
In IR, how si the visibility of iodine contrast improved?
Addition of Cu filter, which maximizes the number of photons just above k-edge of iodine- 33.4
275
What is the maximum number of electrons in the outer shell of any atom?
8
276
What is the transportation index is measured in?
mR/h
277
Center of rotation correction is a quality assurance test of SPECT that ______?
A test of integrity of the location of the point source image on the detector head as a function of gantry angle
COR variation should be less than 2 mm
278
Why is a NaI detector detector doped with thallium?
It creates imperfections that capture electrons, which emit light, which is subsequently amplified by PMT
279
What precaution should be taken for whole body doses greater than 2 Gy?
Antibiotics
280
Doppler shift is greatest?
if beam is parallel to direction of flow (0 degrees)
281
What is the limit for normal dose fluoroscopy?
88 mGy/min
282
Energy resolution in nuclear medicine?
Energy resolution = change in energy (FWHM)/ photopeak energy
283
The output of an X-ray tube is proportional to?
mAs x kVp ^2
284
What is a F-Factor?
Converts Roentgens (ionization of air) to absorbed dose in tissue (rads)
285
How many pixels are required to form a line pair?
two
286
How is the CTDI volume obtained?
CTDIw x 1/pitch
pitch = table movement/slice thickness x scan field
287
What is the maximum dose of X-ray tube leakage at 1 hour?
100 mR in one hour
288
Radiation doses at 1 meter are typically _____ % of primary?
1%
289
Typical doses to fetus for maternal CT of abdomen are?
10-50 mGy
290
What is the ultrasound dose limit _______ W/cm^2?
0.72
291
How is integral uniformity of a gamma camera calculated?
(Max counts per pixel-minimum counts per pixel)/ (max + min) x 100
292
Radiation survery of unrestricted area is preformed _____?
Restricted?
Weekly
Daily
293
MQSA- Darkroom cleanliness?
Daily
294
Compression testing, dark room fog, screen film contact, fixer retnetion- MQSA?
Semianually
295
Processor QC- MQSA?
Daily
296
MQSA- screen cleanliness and phantom?
Weekly
297
Viewbox cleanliness and Repeat analysis- MQSA?
Quarterly
298
How is voxel size calculated for MRI?
The voxel size for a 2D MR image is calculated with the following formula: (FOV/phase encoding steps) × (FOV/frequency encoding steps) × (slice thickness).
For a 3D MR image, the final term is (FOV/phase encoding steps in the z- axis) instead of (slice thickness).
299
High risk gadolinium agents?
“High- risk” agents as defined by the FDA and ACR include: (1) gadodiamide [Omniscan], (2) gadoversetamide [OptiMARK], and (3) gadopentetate dimeglumine [Magnevist].
