Physics: Rapid Review, Nuclear and MRI Flashcards
1
Q
Isotope
A
Same number of protons
2
Q
Isotone
A
Same number of neutrons
3
Q
Isobar
A
Same mass number
4
Q
Isomer
A
Same number of protons and neutrons, but different energies (e.g. Tc99 and Tc99M)
5
Q
Effective half life
A
Effective half life = (1/physical half life) + (1/biological half life)
6
Q
Physical half life of Tc99m
A
6 hours
Note: Turn the 9 upside down to get 6.
7
Q
Tc99m energy
A
Low (140)
8
Q
Physical half life of I-123
A
13 hours
Note: 123 is 13.
9
Q
Physical half life of Xe-133
A
125 hours
Note: Biological half life is 30 sec (breathed out).
10
Q
Physical half life of Thallium-201
A
73 hours
11
Q
Physical half life of Indium-111
A
67 hours
Note: Indium wishes it was Ga-67.
12
Q
Physical half life of Gallium-67
A
78 hours
Note: +1 to each digit.
13
Q
Physical half life of I-131
A
8 days
Note: If you spill I-131 you’re fucked (for a week and a day).
14
Q
Physical half life of F-18
A
110 min
Note: Formula 1 is fast (110 mph).
15
Q
Physical half life of cobalt-57
A
270.9 days
Note: Almost a year (3/4 of a year). This is used for quality assurance (extrinsic field uniformity).
16
Q
Physical half life of germanium-68
A
270 days
Note: This is used for PET quality assurance.
17
Q
Physical half life of Gallium-68
A
68 minutes
Note: This is used for PET quality assurance.
18
Q
Half life of strontium-89
A
50.5 days (14 days in bone)
Note: 2 weeks in bone, but ~2 months elsewhere.
19
Q
Half life of samarium-153
A
46 hours
20
Q
Half life of radium-223
A
11 days
21
Q
Half life of Yttrium-90
A
64 hours
Note: Turn 9 upside down to get 6 (then times 10 because it’s therapeutic, so you should expect it to last longer than 6 hours).
22
Q
Half life of rubidium-82
A
75 seconds
23
Q
Half life of nitrogen-13
A
10 min
24
Q
Energy of I-123
A
Low (159)
25
Energy of Xe-133
Low (81)
26
Energy of Thallium-201
Low (167 and 135)
Note: It is actually the Hg-201 daughter xrays that are images.
27
Energy of Indium-111
Medium (173 and 247)
28
Energy of Gallium-67
- 93 (40%)
- 184 (20%)
- 300 (20%)
- 393 (5%)
Note: 90, 180, 300, 400.
29
Energy of I-131
High (365)
Note: Days in a year.
30
Energy of F-18
High (511)
31
Energy of Cobalt-57
Low (122 and 136)
32
Energy of Germanium-68
High (511)
Note: This is actually the energy of its daughter product Gallium-68.
33
Beta minus decay causes...
Emission of a beta particle (electron)
Note: This is an isobaric transition.
34
Beta plus decay causes...
Emission of a positron
35
Electron capture causes...
An electron and proton to merge and become a neutron
Note: A gamma photon can also be produced if coupled with an isomeric transition.
36
Alpha decay causes...
Emission of an alpha particle (helium nucleus, 2 protons and 2 neutrons)
37
What type of atoms undergo beta minus decay?
Lots of neutrons and not enough protons
38
What type of atoms undergo beta plus decay?
Lots of protons and not enough neutrons
39
What type of atoms undergo electron capture?
Lots of protons and not enough neutrons
40
What type of atoms undergo alpha decay?
Heavy unstable atoms
41
Which type of collimator produces a fixed image size that is independent of image distance?
Parallel hole
42
Best collimator type for thryoid scintigraphy
Pinhole
43
How does a pinhole collimator affect the image?
Magnifies and inverts the image (the closer to the collimator, the more magnification)
Note: The farther from the detector, the less magnification (no magnification if equal distance between pt-collimator and collimator-detector).
44
What collimator should you use if you want to magnify without inverting the image?
Converging
45
As the pt gets farther from a converging collimator, magnification _______
Increases (and field of view decreases)
46
What collimator should you use if you want to take a large object and make a smaller image (e.g. lung scan with a mobile gamma camera)?
Diverging collimator
47
Using longer septa in a collimator...
- Lowers sensitivity (increases noise)
- Increases spatial resolution
48
Using thinner septa in a collimator...
- Increases blur (increased penetration)
- Increases sensitivity (more photons reach detector)
49
Wider collimator holes result in...
- Higher sensitivity (more photons reach detector)
- Lower spatial resolution
50
Frequency for nuclear quality assurance on constancy
Daily (using a reference source)
Note: Should be within 5% of computed activity.
51
Frequency for nuclear quality assurance on linearity
Quarterly (using a large activity of Tc-99m, about 200 mCi, and decaying it to less than the smallest activity you would measure for use)
52
Frequency for nuclear quality assurance on accuracy
Annually (using standard energy sources)
53
What are the standard energy sources used to check for nuclear imaging accuracy?
- Co-57 (low energy)
- Cs-137 (medium)
- Co-60 (high energy)
54
Frequency for nuclear quality assurance on geometry
Once during installation and again any time you move the device (using different volumes of liquid Tc-99m)
55
Best detector to survey for low level radioactivity?
Geiger-Muller counter (very sensitive, but horrible for high radiation fields)
56
What types of radiation can be detected with a Geiger-Muller counter?
Ionizing radiation (alpha, beta, and gamma)
57
What type of detector should be used to survey high level radiation?
Ionization chamber (stable across a wide voltage range)
58
How should you wear a personal thermo-luminescent dosimeter?
Wear the ring on a finger with the label facing the palm (should be worn under gloves if using gloves)
59
What are the major types of survey meters?
- Geiger-Muller counter
- Ionizing chamber
60
What type of radioactivity detector should be used for "wipe test" or urine/blood samples?
Well counter
61
Where would you look up notices, instructions, and reports to workers for nuclear medicine?
10 code of federal regulations, part 19
62
Where would you look up standards for protection against radiation?
10 code of federal regulations, part 20
63
Where would you look up information about the medicinal use of by-product material?
10 code of federal regulations, part 35
64
What is considered a major spill for Tc-99m?
> 100 mCi
65
What is considered a major spill for Thallium-201
> 100 mCi
66
What is considered a major spill for Indium-111
> 10 mCi
67
What is considered a major spill for I-123?
> 10 mCi
68
What is considered a major spill for Ga-67?
> 10 mCi
69
What is considered a major spill for I-131?
> 1 mCi
70
What is the protocol for a major spill?
- Clear area
- Cover spill with absorbent paper (do NOT clean it up)
- Clearly indicate boundaries of spill area (limit movement of contaminated persons)
- Shield source if possible
- Notify radiation safety officer immediately
- Decontaminate persons
71
What is the annual radioactive dose limit to a member of the general public?
100 mrem
72
What is the radioactive dose limit for an unrestricted area?
2 mrem/hour
73
What is the definition of a restricted area in nuclear medicine?
Any area that receives a dose greater than 2 mrem/hour
74
Where should you place "radiation area" signage?
Anywhere that you could get 5 mrem (o.oo5 rem or 0.05 mSv) in 1 hour at 30 cm
75
Where should you place "high radiation area" signage?
Anywhere you could get 100 mrem/0.1 rem (1 mSv) in 1 hour at 30 cm
76
Where should you place "very high radiation area" signage?
Anywhere you could get 500 rads (5 gray) in 1 hour at 1 meter
77
What is the NRC occupational exposure dose limit for total body dose per year?
5000 mrem/5 rem (50 mSv)
78
What is the NRC occupational exposure dose limit for dose to the ocular lens per year?
15 rem (150 mSv)
79
What is the NRC occupational exposure dose limit for total equivalent organ dose?
50 rem (500 mSv)
80
What is the NRC occupational exposure dose limit for total dose to embryo-fetus over entire 9 months of pregnancy?
500 mrem/0.5 rem (5 mSv)
Note: If the fetus has already gotten 5 mSv at the time of pregnancy declaration you can get 0.5 mSv more for the remainder of the pregnancy.
81
1 rad = ? rem
1 rad = 1 rem
82
1 rem = ? Gy
1 rad/rem = 0.01 Gy
83
1 mSv = ? mrem = ? rem
1 mSv = 100 mrem = 0.1 rem
84
5 rem = ? mSv
5 rem = 50 mSv = 0.05 Sv
85
At what dose does a mistake become a reportable event in nuclear medicine?
Pt received at least 5 rem of whole body radioactive dose that they shouldnt have gotten
OR
Pt received at least 50 rem single organ dose that they shouldn't have gotten
Note: If there was a mistake, but less than these limits it is considered a recordable event (only locally recorded for local institutional review)
86
When must you call the NRC after a reportable event?
Within 24 hours
87
When must you send a written letter to the NRC after a reportable event?
Within 15 days
88
When must you notify the referring physician after a reportable event?
Within 24 hours
89
Who should notify the pt after a reportable event?
Nuclear medicine radiologist or referring physician
90
What mistakes may qualify as reportable events (if the dose is high enough)?
- Wrong dose (at least 20% more than it should have been)
- Wrong drug
- Wrong route
- Wrong pt
91
How soon after receipt of a radioactive package must the initial survey be done?
Within 3 working hours
92
When is a radioactive package considered beyond allowable limits?
> 6600 dpm/300 cm^2 (need to contact the shipper and the NRC)
Note: This is during the initial survey (using a Geiger-Muller counter at the package surface and 1 meter away as well as a wipe test of all surfaces).
93
What radioactive package label indicates that no special handling is required?
White 1 label
94
What is the dose limit for a white 1 label package?
Must be < 0.5 mrem/hour at surface (and 0 mrem/hour at 1 meter)
95
What is the dose limit for a yellow 1 label package?
Must be < 50 mrem/hour at surface (and < 1 mrem/hour at 1 meter)
96
What is the dose limit for a yellow 2 label package?
Must be < 200 mrem/hour at surface (and < 10 mrem/hour at 1 meter)
97
What is the transportation index for a white 1 label package?
no transportation index (rate at 1 meter is so low)
98
What is the transportation index for a yellow 1 label package?
TI < 1.0 mrem per hour
99
What is the transportation index for a yellow 2 label package?
TI > 1.0 mrem per hour
100
What is a common carrier
A truck that carries regular packages and radioactive material
101
Transportation index should not exceed ______ for common carriers
10 mrem/hour
102
Surface rate should not exceed ______ for common carriers
200 mrem
103
The sum of multiple radioactive packages traveling together should not exceed _____
50 mrem
104
What is the allowable limit of Tc-99m radionuclide purity?
0.15 microcuries of Mo per 1 millicurie of Tc
Note: This is tested in a dose calibrator with lead shields.
105
What energy photons are you looking for when testing for Tc-99m radionuclide purity?
700 keV (photons from Molybdenum breakthrough)
106
What is the allowable limit for Tc-99m chemical purity?
< 10 micrograms Al per 1 mL Tc-99m
Note: This is tested with pH paper.
107
What are the types of Tc-99m purity?
- Radionuclide purity (molybdenum breakthrough, tested with dose callibrator)
- Chemical purity (aluminum breakthrough, tested with pH paper)
- Radiochemical purity (free Tc contamination, tested with thin layer chromatography)
108
What is the allowable limit for radiochemical purity of Tc-99m?
- 91% (for most)
- 92% (for Tc-99m sulfur colloid)
- 95% (for Tc-99m TcO4)
109
If a Tc-99m dose containing free Tc is given, what will show up on scans?
- Gastric uptake
- Salivary gland uptake
- Thyroid uptake
110
When is transient equilibrium obtained for a Tc-Mo generator?
4 daughter half lives (24 hours)
111
What appears hotter on non-attenuation corrected images?
- Skin
- Lungs
112
Does PET imaging use a collimator
2D PET uses septa collimator (to reject scatter photons)
3D PET does not use a collimator (fast coincidence detector)
113
Which is more sensitive: 2D or 3D PET?
3D PET is more sensitive
Note: Lack of septa collimator results in more true, scattered, and random coincidences.
114
Which has a larger field of view for true coincidences: 2D or 3D PET?
3D PET has a larger field of view
115
Which requires more radiotracer: 2D or 3D PET?
2D PET requires more radiotracer
116
In obese pts, SUVs are ______
Overestimated
117
If scan time is delayed, SUVs will be ______
Overestimated (higher FDG values)
118
High blood glucose results in _______ SUVs
Lower SUVs (underestimated)
119
IV dose extravasation will result in ________ SUVs
Lower SUVs (underestimated)
120
More iterations during iterative reconstruction results in _____ SUVs
Higher SUVs (overestimated)
121
Dose units for exposure
C/Kg (Charge created in the air/mass of that air)
122
Dose units for absorbed dose
J/Kg (energy deposited per unit kg of material)
Note: Commonly used units are Gray and Rads.
123
1 Gy = ? rads
1 Gy = 100 rads
124
What is equivalent dose?
The absorbed dose adjusted for the type of radiation (alpha particles do more damage than electrons)
125
What is the weight factor for alpha particles used to calculate equivalent doses?
20
Note: For xrays and gamma rays its 1 (absorbed dose = equivalent dose).
126
What are the units for effective dose?
Sv
127
What is effecive dose?
The equivalent dose adjusted for how radiosensitive the tissues are that absorbed the dose (best measure of cancer risk)
128
What is the threshold for stochastic effects of radioation?
There is no threshold for stochastic effects
129
Is severity of stochastic effects dose related?
No (but probability of stochastic effects increases with increasing dose)
130
What are the stochastic effects of radiation?
- Cancer risk
- Heritable effects
131
What is the air kerma?
A measure of the absorbed dose in air during fluoroscopy (Gy/min)
Note: This only accounts for the primary interaction of photons on tissue atoms (not the secondary production of scatter electrons, which also contribute to overall dose).
132
If distance doubles, the air kerma...
Decreases by a factor of 4 (inverse square law)
133
The air kerma tells you...
Deterministic effect risk
134
What is the kerma area product?
The kerma area times the cross sectional area exposed
135
The kerma area product tells you...
Stochastic effect risk
136
If distance doubles, kerma air product...
Stays the same (kerma air product is independent of distance)
137
How does collimation affect kerma air product?
Collimation decreases KAP (decreased cross sectional area exposed)
138
What is the cumulative air kerma?
A total of all the air kerma values for individual exposures
Note: This is described at a specific interventional reference point (15 cm towards the xray tube).
139
What is the CT dose index?
The radiation dose of a CT exam, normalized to beam width (based on dose absorbed by a CT phantom)
140
How big is the CT phantom for CTDI measurement?
32 cm in diameter
141
If the pt is more obese than the CT phantom, CTDI will be _______
Overestimated (obese pts receive less radiation per Kg)
142
The CTDI for a pediatric pt will be ______ if the standard CT phantom is used
Underestimated (pediatric pts would receive more radiation per Kg than the phantom)
143
How do you calculate a weighted CTDI?
(1/3 central CTDI) + (2/3 peripheral CTDI)
Note: The CT phantom has 4 peripheral ionization chambers and 1 central chamber.
144
How do you calculate the volume CTDI?
Weighted CTDI divided by CT pitch
145
What is the ACR reference dose for a head CT?
Volume CTDI of 75 mGy
146
What is the ACR reference dose for an adult abdominal CT?
Volume CTDI of 25 mGy
147
The ACR sets the reference dose for CT scans at...
The 75th percentile
148
What is the ACR reference dose for a pediatric abdominal CT?
Volume CTDI of 20 mGy (5 year old)
149
How do you calculate the dose product length for CT?
Volume CTDI times the length of the scan (in cm)
150
How do you calculate the effective dose for CT?
dose length product x k (a body part constant)
151
Direct vs indirect radiation
Direct radiation acts on DNA (uncommon in xray imaging)
Indirect radiation acts on water in the cytoplasm, creating free radicals that damage DNA (more common in xray imaging)
152
Radiation dose needed to induce acute radiation syndrome in bone marrow
> 2 Gy (latent period of 1-6 weeks)
Note: It is possible to survive.
153
Radiation dose needed to induce acute radiation syndrome in the GI tract
> 8 Gy (latent period of 5-7 days)
Note: Death occurs within 2 weeks.
154
Radiation dose needed to induce acute radiation syndrome in the CNS
> 20-50 Gy (latent period of 4-6 hours)
Note: Death occurs within 3 days.
155
Next step: possible acute radiation syndrome with no vomiting or skin redness (whole body dose < 1 Gy)
Surveillance for 5 weeks
156
Next step: possible acute radiation syndrome with vomiting 2-3 hours after exposure or skin redness 12-24 hours after exposure (whole body dose 1-2 Gy)
Consider general hospital (at mimimum surveillance for 3 weeks)
157
Next step: possible acute radiation syndrome with vomiting 1-2 hours after exposure or skin redness 8-15 hours after exposure (whole body dose 2-4 Gy)
Hospitalize in a burn center
158
Next step: possible acute radiation syndrome with vomiting within 1 hour after exposure or skin redness 1-6 hours after exposure (whole body dose > 4 Gy)
Hospitalize in a specialized radiation center
159
What is the radiation dose and onset for early transient erythema?
2 Gy skin dose (onset in hours)
160
What is the radiation dose and onset for severe "robust" erythema?
6 Gy skin dose (onset in 1 week)
161
What is the radiation dose and onset for telangiectasia?
10 Gy skin dose (onset in 52 weeks)
162
What is the radiation dose and onset for dry desquamation?
13 Gy skin dose (onset in 4 weeks)
163
What is the radiation dose and onset for moist desquamation/ulceration?
18 Gy skin dose (onset in 4 weeks)
164
What is the radiation dose and onset for secondary ulceration?
24 Gy skin dose (onset in > 6 weeks)
165
What is the radiation dose and onset for temporary epilation?
3 Gy (onset in 21 days)
166
What is the radiation dose and onset for permanent epilation?
7 Gy (onset in 21 days)
167
What is the cell cycle stage most sensitive to radiation?
M phase
Note: M > G2 > G1 > S (S phase is the least).
168
What is the most radiosensitive part of the GI tract?
Small bowel
169
What is the most radiosensitive blood cell type?
Lymphocytes
Note: A dose of 0.25 Gy is enough to depress the amount of lymphocytes circulating in blood.
170
What is the effect of a radiation dose < 50 mGy to a 0-2 week old embryo?
Probably nothing (small chance of spontaneous abortion)
171
What is the effect of a radiation dose < 50 mGy to a > 2 week old embryo/fetus?
Probably nothing (dose is small)
172
What is the effect of a radiation dose 50-100 mGy to a 0-2 week old embryo?
Nothin or spontaneous abortion ("all or nothing")
173
What is the effect of a radiation dose 50-100 mGy to a > 25 week old embryo/fetus?
Probably no teratogenic effects
174
What is the gestational age at highest risk of teratogenic effects of radiation?
8-15 weeks (this is when neuronal development occurs)
175
Elective abortion should be considered after the embryo/fetus has been exposed to how much radiation?
> 100 mGy
176
Which MRI signal relies on free induction decay (rather than creating an echo)?
T2*
177
How can you identify a spin echo sequence by the pulse sequence diagram?
There will be a 180 degree RF pulse at time = 1/2 TE
178
How can you recognize a gradient echo sequence by the pulse sequence diagram?
There will be no 180 degree RF pulse
179
How can you recognize a fast spin echo sequence by the pulse sequence diagram?
There will be multiple back to back 180 degree RF pulses (after the initial 90 degree RF pulse)
180
How can you recognize an inversion recovery sequence by the pulse sequence diagram?
There will be a 180 degree RF pulse before the initial 90 degree RF pulse
181
What type of sequence is this?
Spin echo
Note: 90 degree RF followed by 180 degree RF.
182
What type of sequence is this?
Fast spin echo
Note: Multiple 180 degree RFs after initial 90 degree RF.
183
What type of sequence is this?
Inversion recovery
Note: 180 degree RF before initial 90 degree RF.
184
What type of sequence is this?
Gradient echo (GRE)
Note: No 180 degree RF pulse.
185
T1 is determined by...
Spin-lattice interactions (and is equal to the time to reach 63% recovery of longitudinal magnetization)
186
T2 is determined by...
Spin-spin interactions (and is equal to the time to reach 37% decay of in phase)
187
T2* is determined by...
Spin-spin interactions PLUS the non-uniformity of the magnetic field
188
T1 shortening appears _______ on the image
Bright
189
T2 shortening appears ______ on the image
Dark
190
What should TR/TE be for T1 weighting?
Short TR
Short TE
191
What should TR/TE be for T2 weighting?
Long TR
Long TE
192
What should TR/TE be for PD weighting?
Long TR
Short TE
Note: Long TR minimizes T1 weighting and short TE minimizes T2 weighting.
193
What is considered a short TR for spin echo?
250-700 ms
194
What is considered a long TR for spin echo?
> 2000 ms
195
What is considered a short TE for spin echo?
10-25 ms
196
What is considered a long TE for spin echo?
> 60 ms
197
What is considered a short TR for gradient echo?
< 50 ms
198
What is considered a long TR for gradient echo?
> 100 ms
199
What is considered a short TE for gradient echo?
1-5 ms
200
What is considered a long TE for gradient echo?
> 10 ms
201
How do you calculate the table time for a standard sequence?
TR x phase matrix x NEX
NEX: # of excitations (per TR)
202
How do you calculate the table time for a 3D sequence?
TR x phase matrix x NEX x # of slices
NEX: # of excitations (per TR)
203
How can you estimate the table time for a fast spin echo sequence?
1/echotrain length
204
How can you make MRI slices thinner?
- Increase the slice selection gradient (make it steeper)
- Decrease the transmit bandwidth
205
How will decreasing the slice slection gradient affect slice thickness?
Thicker slices
206
How is MRI signal to noise ratio affected by making the slices thicker?
Increased signal to noise ratio
207
How is MRI signal to noise ratio affected by a larger field of view?
Increased signal to noise ratio
208
How is MRI signal to noise ratio affected by a larger matrix?
Decreased signal to noise ratio
209
How is MRI signal to noise ratio affected by a greater magnetic field strength?
Increased signal to noise ratio
210
How is MRI signal to noise ratio affected by a greater receiver bandwidth?
Decreased signal to noise ratio
211
How is MRI signal to noise ratio affected by a greater transmit bandwidth?
Increased signal to noise ratio
212
How is MRI signal to noise ratio affected by more excitations per slice?
Increased signal to noise ratio
213
How is MRI signal to noise ratio affected by utilizing partial K space sampling?
Decreased signal to noise ratio
214
How is MRI spatial resolution affected by thicker slices?
Decreased spatial resolution
215
How is MRI spatial resolution affected by a larger field of view?
Decreased spatial resolution
216
How is MRI spatial resolution affected by a larger matrix?
Increased spatial resolution
217
How is MRI spatial resolution affected by a greater magnetic field strength?
No effect on spatial resolution
218
How is MRI spatial resolution affected by a greater receiver bandwidth?
No effect on spatial resolution
219
How is MRI spatial resolution affected by a greater transmit bandwidth?
Decreased spatial resolution
220
How is MRI spatial resolution affected by more excitations per slice?
No effect on spatial resolution
221
How is MRI spatial resolution affected by utlizing partial K space sampling?
No effect on spatial resolution
222
How is the duration of an MRI exam affected by thicker slices?
No effect on table time
223
How is the duration of an MRI exam affected by a larger field of view?
No effect on table time
224
How is the duration of an MRI exam affected by a larger matrix?
Increased table time
225
How is the duration of an MRI exam affected by a greater magnetic field strength?
No effect on table time
226
How is the duration of an MRI exam affected by a greater receiver bandwidth?
Decreased table time
227
How is the duration of an MRI exam affected by a greater transmit bandwidth?
No effect on table time
228
How is the duration of an MRI exam affected by more excitations per slice?
Increased table time
229
How is the duration of an MRI exam affected by utilizing partial k space sampling?
Decreased table time
230
What does a smaller receiver bandwidth do?
Increases signal to noise ratio
231
What does a smaller transmit bandwidth do?
- Decreases signal to noise ratio
- Makes slices thinner
232
How are thinner MRI slices a tradeoff?
Improved spatial resolution, but more noise (lower SNR)
233
What artifacts are made worse by higher magnetic fields?
- Type 1 chemical shift artifact
- Susceptibility artifacts (e.g. metal)
234
What artifacts are minimized by using a thicker receiver bandwidth?
- Type 1 chemical shift artifact
- Susceptibility artifacts (e.g. metal)
235
Why is increasing the number of excitations per TR a tradeoff?
Improved SNR, but increased table time
236
What is the best sequence for signal to noise ratio?
PD
237
What are the out of phase and in phase times for a 1.5 T MRI?
OOP: 2.2 ms
IP: 4.4 ms
OR
OOP: 6.6 ms
IP: 8.8 ms
238
What are the out of phase and in phase times for a 3.0 T MRI?
OOP: 1.1 ms
IP: 2.2 ms
OR
OOP: 3.3 ms
IP: 4.4 ms
239
fMRI depends on...
T2* effects (uses blood oxygen level dependent imaging)
240
What MRI sequence is used for cardiac "bright blood"?
Gradient echo
241
What MRI sequence is used for cardiac "black blood"?
Double inversion spin echo
242
What MRI sequence is used to null myocardium for cardiac MRIs?
Inversion recovery
Note: The inversion time is chosen to match the patients myocardium.
243
What is the only macrolytic, non-ionic commonly used MRI contrast agent?
Gadobutrol (AKA Gadavist)
Note: All the other main MRI contrast agents are linear, ionic.
244
Which major MRI contrast agent has the highest risk of nephrogenic systemic fibrosis?
Gadopentetate (AKA Magnevist)
245
Which MRI contrast agent has a 50% hepatocyte uptake?
Gadoxetate (AKA Eovist)
Note: Gadobenate (AKA Multihance) has 5% hepatocyte uptake.
246
How should you minimize fat signal on post gadolinium MRI sequences?
Fat saturation
Note: Do NOT use STIR (the fat inversion time is too similar to gad and you will null contrast signal).
247
How does gadolinium work as an MRI contrast agent?
Increasing spin-lattice interactions (shortens T1)
248
When should you be worried about nephrogenic systemic fibrosis due to gadolinium?
- Renal failure (GFR < 30)
- Pro-inflammatory states (acute illness)
- Using an older contrast agent like Gadodiamide (AKA Omniscan)
249
What are the high energy radionuclides?
- I-131
- F-18 (511 keV)
- Germanium-68/Gallium-68 (511 keV, used for QA)
250
Which MRI artifacts mostly occur in the phase encoding direction?
- Aliasing
- Gibbs/truncation artifact
- Motion artifact
- Zipper artifact
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Which MRI artifacts mostly occur in the frequency encoding direction?
Type 1 chemical shift artifact
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Which MRI artifacts occur in the phase encoding AND frequency encoding directions?
- Type 2 chemical shift (AKA india ink)
- Gibbs artifact (AKA truncation), though this is mostly in the phase encoding direction
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In what direction does this artifact occur?
Phase encoding direction
Note: This is aliasing.
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How can you fix this artifact?
- Increase the field of view
- Change the phase encoding direction
Note: This is aliasing (due to a small field of view in the phase encoding direction).
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In what direction does this artifact occur?
Frequency encoding direction only
Note: This is type 1 chemical shift artifact.
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How can you minimize this artifact?
- Bigger pixels
- Fat suppression
- Increase receiver bandwidth
- Use a weaker magnet
Note: This is type 1 chemical shift artifact (due to differences in resonant frequencies at the interface between fat-water).
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In what direction does this artifact occur?
Both the phase and frequency encoding direction
Note: This is the type 2 chemical shift (India ink) artifact.
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How can you minimize this artifact?
- Adjust the TE
- Perform spin echo sequence instead
Note: This is the type 2 chemical shift/India ink artifact (due to differences in resonant requencies that oppose each other at specific TE intervals).
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This artifact only occurs on what type of sequences?
Gradient echo sequences
Note: This is the type 2 chemical shift (India ink) artifact.
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What type of artifact is this?
Gibbs (AKA truncation) artifact
Note: This is due to a limited field of view.
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In what direction does this artifact occur?
Most often the phase encoding direction (but can also occur in the frequency encoding direction)
Note: This is the Gibbs/truncation artifact (due to limited sampling of free induction decay).
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How can you minimize this artifact?
- Use a bigger matrix
- Decrease bandwidth
- Decrease pixel size
Note: This is the Gibbs/truncation artifact (due to a limited sampling of free induction decay).
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How can you minimize this artifact?
Decrease pixel size (increase phase encoding steps or decrease field of view)
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The center of K space contains...
Information about gross form and contrast
Note: The periphery of k space contains information about spatial resolution.
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In which direction does this artifact occur?
Phase encoding direction
Note: This is motion artifact.
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How can you minimize this artfact?
- Use saturation pulses
- Respiratory gating
- Faster sequences (e.g. BLADE, PROPELLER)
Note: This is the motion artifact.
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What type of artifact is this?
Cross talk artifact (due to overlapping slices)
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How can you minimize this artifact?
- Increase slice gap
- Interleave slices (do all odd slices, then all even slices)
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What are two common types of motion artifact on MRI?
- Breathing artifact (due to diaphragm motion)
- Pulsation artifact (due to blood vessel motion)
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At what angle does magic angle artifact occur?
55 degrees (between tendon and main magnetic field)
Note: You see this more with short TE sequences (not seen on T2 sequences).
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What artifact is this?
Zipper artifact (caused by poor shielding letting RF interference through)
Note: Did you leave the MRI room door open?
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How can you minimize this artfact?
- Close the MRI room door (if open)
- Remove all electronic devices from MRI room (e.g. pulse ox)
- Call the MRI tech to repair RF shielding
Note: This is zipper artifact (due to poor shielding from RF interference).
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This artifact is worse on what type of sequences?
GRE sequences
Note: This is magnetic field inhomogeneity artifact (causing geometric distortion).
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What would make this artifact worse?
- Using GRE sequences
- Using a bigger magnetic field strength
Note: This is susceptability artifact caused by metal augmenting the local magnetic field.
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How can you minimize this artifact?
- Use spin echo sequences (not GRE)
- Use lower magnetic field strength
- Use higher receiver bandwidth
- Use short echo train spacing
- Use thinner slices
Note: This is susceptability artifact caused by metal augmenting the local magnetic field.
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What is the cause of this artifact?
Large gradient changes causing geometric distortion and non-uniformity (most noticible on diffusion images)
Note: This is Eddy current artifact.
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How can you minimize this artifact?
Shimming (passive and active) to reduce magnetic field inhomogeneity
Note: This is magnetic field inhomogeneity artifact (which can cause poor fat saturation).
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How can you minimize this artifact?
Optimize the sequence of gradient pulses
Note: This is caused by eddie currents (due to large gradient changes, especially on diffusion imaging).
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What is the cause of this artifact?
Radiowaves are shortened enough by dielectric effects to match the length of a body part (creating a standing wave)
Note: This is a dielectric effect artifact.
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How can you minimize this artifact?
- Use parallel RF transmision (to create longer FR waves)
- Use dielectric pads
- Use weaker magnet (1.5 T)
Note: This is dielectric effect artifact.
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How can you fix this artifact?
Reconstruct the image again (from the dame data)
Note: This is herringbone or crisscross artifact (due to a data processing/reconstruction error).
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What are the MRI zones?
- Zone I (far from the magnet)
- Zone II (MRI screening room)
- Zone III (locked control room)
- Zone IV (MRI room)
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Which MRI zones are restricted?
Zones III and IV (screened people only)
Note: Zones I and II are unrestricted (prescreen)
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In what scenarios should you quench the MRI magnet?
- Life threatening fire in the MRI room
- Someone is pinned by a metal object
Note: A pt coding is not a reason to quench (unless they're coding because they are pinned by an oxygen tank).
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What is the 5G line?
A circle drawn around the MRI machine that indicates risk to implantable devices (e.g. pacemaker, neurostimulation, insulin pump)
Note: Inside this line magnetic forces are above 5 gauss.
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Which sequences have the highest risk of causing hearing damage?
Echo planar sequences (loud noises are due to gradient switching)
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What sequences are most likely to cause neurostimulation?
Echo planar (due to rapid gradient switching and high-bandwidth readouts)
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What is the specific absorption rate for MRI?
(B^2) x (Alpha^2) x (duty cycle)
B: Magnetic field strength
Alpha: Flip angle
Duty cycle: How short your TR is
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What is the limit for specific absorption rate?
4 W/Kg
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How will doubling the TR affect the duty cycle?
Half the duty cycle
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Can you continue breastfeeding after getting IV contrast?
No, it is recommended to stop breastfeeding (for both iodinated and gadolinium contrast)
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What radionuclides are not safe when breastfeeding?
- Tc-99m (can resume in 12-24 hours)
- I-123 (can resume in 2-3 days)
- Gallium-67 (don't resume)
- I-131 (don't resume)
