3 Huda Facts Final.csv - Huda Facts Final.csv Flashcards
1
Q
Watt
A
Joule/Sec
2
Q
Lead K-edge
A
88 kev
3
Q
X-ray wavelength is on the order of:
A
an atom
4
Q
MR RF wavelength is on the order of:
A
a patient
5
Q
K shell to outer shell binding energy ratio
A
1000 to 1
6
Q
Tungsten k-edge
A
70 kev
7
Q
Extremity radiograph relies mostly of which kind of x-ray interaction with tissue:
A
PE effect due to high z of bone (prob of PE effect increases with z cubed)
8
Q
KVP for extremity radiograph
A
60 KVP
9
Q
KVP for abdomen radiogaph
A
80 KVP
10
Q
KVP for chest radiograph
A
120 KVP
11
Q
MA for chest radiograph
A
500-1000
12
Q
MA for CT
A
500-1000
13
Q
MA for Fluoro
A
5
14
Q
MAS for a chest xray
A
1
15
Q
MAS for an abdomen radiograph
A
20
16
Q
Does energy get transferred with coherent scatter?
A
No
17
Q
Another name for coherent scatter
A
Raleigh
18
Q
What percentage of X-rays are absorbed by a patient
A
67%
19
Q
What percentage of X-rays are scattered by a patient
A
23%
20
Q
What percentage of X-rays penetrate the patient and hit the detector
A
1%
21
Q
Which energy is most likely transmitted by an Ag k-edge filter in mammo (25kev k-edge)
A
24 kev
22
Q
Xray energy where PE = compton in tissue
A
25 kev
23
Q
What is the half value layer of TISSUE (not aluminum) for x-rays
A
3 cm
24
Q
What interaction is most likely in a head CT?
A
Compton
25
Air Kerma for lateral skull radiograph
1 mGy
26
Air Kerma for frontal skull radiograph
2 Gy
27
Air Kerma at the image receptor for all radiographs
3 micro Gy
28
Air Kerma at the receptor is kept constant by the:
automatic exposure control (AEC)
29
Kerma Air Product for a radiograph is about:
1 G-square centimeters
30
KAP for a small bowel follow-through is about:
10 G-square centimeters
31
KAP for a TIPS is about:
100 G-sq cm
32
Air Kerma rate for fluoro
10 mGy/min
33
Cu filter is added for:
pediatric radiography
34
What percentage increased in KAP if a patient gets fatter by 3 cm?
100% bc 3 cm of human tissue is one half value layer for radiographs
35
Which x-ray tube parameter is always increased in fat patients?
KVP (not mas)
36
Skin erythema is technically possible starting at what threshold air kerma?
2 Gy
37
Cataracts are technically possible starting at what threshold air kerma?
0.5 Gy
38
Average glandular dose for a single mammo?
3 mGy per view
39
Dose to the embryo from one abdominal radiograph?
1 mGy
40
Dose to the embryo from one abd/pel CT?
10 mGy
41
Which has highest linear energy transfer among x-rays, gamma rays, and beta particles?
All the same.
42
Effective dose for chest CT, abdomen CT, and pelvis CT?
All about 3-5 mSv
43
Effective dose for head CT?
About 2 mSv
44
Range and examples for very low dose exam?
less than 0.1 mSv - examples are extremity radiograph, chest radiograph, and skull radiograph
45
Range and examples for low dose exam?
between 0.1 and 1 mSv. Examples are lateral spine radiograph, abdominal radiograph, and extremity CT.
46
Range and examples for moderate dose exams?
Between 1 and 10 mSv. Examples are CT chest, CT abdomen, CT pelvis, small bowel follow through, and MDP bone scan.
47
Range and examples for high dose exams?
Above 10 mSV. Examples are TIPS, FDG-PET, and triple phase liver protocol CT.
48
Ubiquitous background radiation per year in the US?
1 mSV
49
Background radiation in the US due to Radon?
2 mSV
50
Average amount of radiation received by a NM tech per year?
3 mSv
51
Average amount of radiation received by both IR fellows and commercial airline pilots every year?
5 mSv
52
Cosmic radiation is higher where?
High altitudes
53
What is the scatter to primary ratio in abdominal x-rays?
5 to 1
54
Name 3 times when you DONT use a grid?
peds radiograph, extremity radiopgraphy, and mag mammo
55
Standard grid ratio for radiography
10 to 1
56
What do the numbers in the grid stand for?
first number is height of the septa. Second number is the space BETWEEN the septa.
57
What percentage of the primary transmission makes it through a grid?
70%
58
What percentage of scatter makes it through a grid?
10%
59
At which patient thickness do you have to start using a grid (in peds)?
12 cm
60
How much more radiation is needed to expose a traditional film without the screen?
50 x more
61
What makes a film “faster?”
thicker crystal with increased sensitivity (also increased blur from light dispersion)
62
Scintillator for FPD
CsI
63
Rank scintillator types by patient dose
CsI (lowest), BaFBr (medium), Se (highest)
64
Rank scintillator types by image sharpness
BaFBr (lowest), CsI (moderate), Se (best)
65
How many shades of gray does one byte code for?
256 (2 to the 8th power)
66
What are the only two imaging modalities that make use of only 1 byte (8bits = 256 shades of gray) per pixel?
NM and US (shitty images)
67
All of modalities make use of 2 bytes (16 bits = 512 shades of gray) per pixel
radiography, mammo, CT etc.
68
How big is a chest Xray file?
10 MB
69
How big is a mammo image file
15 MB
70
How big is a CT image (one slice) image file?
0.5 MB
71
How many pixels do you need on a monitor to read mammo?
5 MP
72
How man pixels do you need on a monitor to read x-ray?
3 MP
73
How many pixels do you need on a monitor to read CT?
2 MP
74
Who monitors monitors?
Society for Motion Picture and Television Engineers
75
Does analog or digital radiography have more quantum mottle?
same
76
How many line pairs can you see if the sampling frequency is 1/6
3. Sampling frequency of 1/6 means 6 pixels for mm. If you divide pixels per mm, you get the number of line pairs visible.
77
What is the y axis of a ROC
Sensitivity or true positives
78
What is the x axis of a ROC
1-specificity or false positives
79
What is the relationship between geometric magnification and motion blur?
independent
80
Rank human cells, bacteria, and viruses in order of least to most susceptible to radiation?
human cells most then bacteria then viruses. Viruses are super resistant to radiation.
81
What is the latency period for the onset of radiation induced leukemia?
Years
82
What is the latency period for the onset of radiation induced solid cancer?
Decades
83
What is the background incidence of cancer in the US without additional exposure to radiation from medical exams?
40% of Americans get cancer
84
What is the risk of a 25 year old getting radiation induced cancer from 10 mSV of radiation?
0.10%
85
Has there been a study of human offspring having genetic effects of radiation?
No. Only animals. not even A bomb survivors.
86
What percent of human births have a genetic defect?
4%
87
What is the doubling dose for genetic defects?
1Gy (rate goes from 4% of births to 8%)
88
Deterministic effects for an embryo are VERY unlikely below what amount of radiation?
100 mGy
89
What is the rate of pediatric cancer in the US?
1 in 500
90
What is the doubling dose for pediatric cancers?
25 mGy. Rate goes from 1 in 500 to 2 in 500.
91
What is the downside to the ionization chamber method of detecting radiation?
Accurate but insensitive (needs billions of photons)
92
Ring radiation detector is what?
Thermoluminescent dosimeter (LiF)
93
Who regulates what radiology equipment can be sold in the US?
FDA
94
Who regulates dose limits for radiology equipment?
States
95
Regulatory dose limits exclude:
Medical exposures
96
Regulatory effective dose limits for radiation workers tries to reduce stochastic or deterministic risk?
Stochastic (cancer)
97
Eye dose limit
150 msv/year
98
Extremity limit
500 msv/year
99
Public dose limit
1 msv/year
100
Fetal dose limit per month
0.5 msv/month
101
Fetal dose limit for whole pregnancy
5 Msv after declaring
102
Who regulates radiopharmaceuticals?
NRC or agreement states
103
State regulation for required lead thickness in apron?
0.25 mm lead
104
How thick is lead usually in apron?
0.5 mm
105
How much does 0.5 mm of lead attenuate?
90%
106
Which tech gets the most annual radiation?
NM
107
Room shielding design?
2mm Pb thickness in the wall usually 2 meters high starting at the floor
108
Scattered x-ray intensity at 1 meter from the patient
1000 x less
109
What is the average monthly badge reading for radiology residents?
< 0.1 mSv per month
110
What does .DAM refer to?
Initiative to reduce dose called: “dont order tests that don’t affect management”
111
What is the dose limits for a medical imaging exam?
There are no dose limits
112
Average T1 time for human tissue?
~500 ms
113
Average T2 time for human tissue?
~50 ms
114
Average T2* time for human tissue?
~5 ms
115
Which water molecules have longer T1 time in human tissue?
Water in solids and free water - both T1 dark.
116
Which water molecules have shorter T1 time in human tissue?
Water that is structured such as proteinaceous water.
117
Larmor frequency at 1 T
42 MHz
118
What happens to T1 when spin-lattice interactions are increased?
Reduced
119
Does T1 change with different flip angles?
No, they are independent
120
What kinds of nuclei are used in MRI or NMR?
Those with odd mass numbers.
121
How are T1 and Bo related?
If you double Bo, T1 increases by root 2.
122
How are T2 and Bo related?
Not related.
123
What is the likely T2 value for protons in bone?
Very short. (dark)
124
Can T1 be less than T2 for a given tissue?
No. It’s impossible.
125
What are the units of magnetic field gradients?
Tesla per meter
126
In a 128 x 256 MRI grid, how many phase encoding steps?
128
127
In a 128 x 256 MRI grid, what does the 256 refer to?
Number of times an individual echo is parsed up or “sampled” by the receiver coil. This is the number of pixels in the frequency encoding direction.
128
Center of an MRI image shows?
Low spatial frequency. (contrast)
129
Periphery of an MRI image shows?
High spatial frequency. (resolution)
130
How does K space matrix size compare to MR image matrix size?
Same.
131
What will most likely reduce T1 weighting in a spin echo image?
Increasing TR.
132
What will most likely reduce T2 signal in a spin echo image?
Decreasing TE.
133
How does SNR increase with every additional NEX?
by root 2
134
What is the upside to GRE?
fast. Short TR.
135
What is the downside to GRE?
Worse SNR because signal is degraded by T2* effects, which remain present due to lack of 180 refocusing pulse.
136
STIR TI is about?
150ms
137
FLAIR TI is about?
2400
138
What kind of MRI sequence will produce the strongest echo?
SE>GE and shortest TE possible to reduce dephasing.
139
How many pixels would most likely be in a single echo within 128 x 196 SE image?
196. For any given echo (and therefore a single line of K space), the number of pixels is determined by the numbers of samples taken - i.e., the number of data points along the frequency encoding direction.
140
Iron based MR contrast agents are?
supra-paramagnetic
141
How does heat dissipate between the focal spot and the anode body?
Conduction
142
How does heat dissipate between the anode body and the tube housing?
Radiation
143
How does heat dissipate between the tube housing and the atmosphere?
Convection
144
What is the usual anode angle?
~15 degrees.
145
Three ways to decrease heel effect?
Increase anode angle, decrease FOV AKA cassette size, increase SID.
146
Why use a large focal spot of 1.2 mm in PA and lateral chest XR?
Increasing focal spot size allows for more power and therefore quicker acquisition which is important to reduce respiratory motion.
147
What increases when KVP increases?
Both scatter and penetration.
148
If you increase mAs by 2 how much do you decrease mottle?
root 2
149
In fluoro what is the typical SID?
100 cm
150
Why keep the II or FPD close to the patient?
To reduce dose AND to reduce variable geometric magnification in the patient.
151
Typical SID for PA and lateral CXR?
72 inches
152
Use a grid in portable CXR?
no
153
Use a grid in portable abdominal XR?
yes. Reduce grid ratio from 10:1 to 5:1.
154
What is the problem in a CXR obtained at an exposure index of 100?
Way too much mottle. Huda would be furious that yo missed his lung nodule because your contrast to noise ratio would be lower. Not that contrast would not change; only mottle.
155
Why do we see mach band artifact?
Lateral inhibition of the retina.
156
If you see an XR and there are parts with fine exposure and parts with shitty exposure, whats the problem?
Faulty grid.
157
Tube current in contact mammo?
100 MA.
158
Tube current in mag mammo?
25 MA.
159
mAs for contact mammo?
100 mAs
160
mAs for mag mammo?
75 mAs.
161
To change contrast in mammo is it effective to change KVP?
Not really. Better to change your target/filter.
162
How does breast compression affect X-ray penetration?
Increases penetration because breast tissues is spread apart.
163
Higher/lower/or comparable radiation in digital mammo versus screen film?
Comprable.
164
Higher/lower/or comprable radiation in BTS versus FF mammo?
Comprable.
165
What should the luminance be for a mammo monitor?
600 cd/ sq meter
166
What is the problem with increasing SID to reduce geometric blur?
Takes longer resulting in motion artifact.
167
What is the half value layer of normal breast tissue at mammo level xrays?
1 cm (compared to 3 cm for diagnostic radiography)
168
What is the HVL of aluminum for mammo?
0.5 mm Al (compared to 3 mm Al for diagnostic radiography)
169
What is the angular movement and number of images in BTS?
15 degrees, 15 images.
170
What improves in BTS compared to FFDM?
Contrast. Resolution and dose DO NOT CHANGE.
171
What are the only machines in radiology that are not regulated at the state level after they have been sold?
Mammo machines continue to be regulated at the federal level.
172
What is the MQSA regulation for resolution for SF mammo?
12 lp/mm
173
MQSA phantom specs?
4.2 cm breast, 50% glandularity.
174
Use a grid in fluoro?
yes
175
Grid ratio in fluoro?
10:1 (same as XR)
176
In fluoro, what is the temporal resolution equal to?
The time for one frame to be acquired. (~33ms)
177
What are the two advantages of pulsed fluoro?
reduces motion blur and increases contrast
178
What does the FDA require on all digital fluoro machines?
last image hold
179
Detector element for image intensifier (II)?
CsI
180
How will replacing analog with digital fluoroscopy (alone) affect patient dose?
No change.
181
What is different about GU fluoro machine compared to GI fluoro machine?
GU has the detector under the table.
182
What is your KVP for iodine studies in fluoro?
70kvp
183
What is your KVP for barium studies in fluoro?
110 kip
184
Does the tube current change between iodine and barium studies in fluoro?
no. both 5 ma.
185
When does the alarm go off in fluoro?
at 5 min.
186
When you electronically mag something, what increases?
spatial resolution.
187
When is the automatic brightness control (ABC) in effect?
Electronic mag modes ONLY
188
What happens to AK with electronic mag?
Increases
189
What happens with KAP with electronic mag?
Unchanged.
190
What happens with AK with collimation?
Unchanged.
191
What happens with KAP with collimation?
Decreases.
192
In fluoro, what increases when collimation increases?
Contrast
193
How many dose rate control buttons are there on a fluoro machine?
3
194
How many photospot images equals the dose of 1 minute of fluoro?
10
195
What is the number of images acquired at the 5 minute warning?
5000 (1000 per minute)
196
Why do fluoro images look shitty?
Lots of mottle bc low MA (5 ma compared to 500-1000 for xr and IR)
197
What is the spatial resolution of the II WITHOUT THE TV?
5 lp/mm (better than digital chest). The TV is the limiting factor.
198
Name four types of artifacts that occur when using an II?
vignetting, s-distortion, image saturation, and pincushion.
199
What are two requirements of High Level Control?
Audible and visual indicators
200
Is there automatic brightness control (ABC) on flat panel detectors (FPD?)
No. Electronic mag does not require an increase in AK!
201
Do you get saturation artifact with FPD?
No.
202
Do you get image lag in FPD?
Yes.
203
When you take a photo spot as opposed to a fluoro image, why does the image quality improve?
Less mottle. Higher mas.
204
DSA tube current?
500 ma (approximately the same as XR, much higher than 5 ma in fluoro)
205
What is the usual SID for angioraphy? What does this require for short operators?
100 cm (step stool)
206
In fluoro/angio, does an air gap increase or decrease OPERATOR dose?
Increases. This is why you keep the II and FPD right next to the patient.
207
What is the fraction of total KAP attributable to fluoro time in IR?
Only 1/3. The rest is from diagnostic images.
208
How big is the spacer cone under the C arm that prevents SOD from getting too small?
Approximately 30 cm.
209
Which action is the most helpful for reducing operator dose in IR?
shielding. way more effective than decreasing time or or increasing distance.
210
By how much would effective dose go up in Pb aprons were not used in IR?
> 1000 x
211
How many kinds of coils are there in an MRI magnet?
3. Superconducting coil that creates the main magnetic field. Gradient coils for localization. Transmit/receive RF coils or excitation and FID signal collection.
212
When you apply the slice select gradient, is the magnetic field higher at the head or feet?
feet
213
Which MRI image acquisition requires the best field uniformity?
MRS
214
What are two types of gradient coils?
Saddle and Helmholtz
215
What is a quadrature coil?
A type of RF coil.
216
Contrast enhanced MRA is what type of sequence?
3D GRE
217
What are three factors that decrease signal in TOF?
turbulence, slow flow, and in plane flow.
218
What is the net phase when a bipolar gradient is applied to stationary tissue and what sequence does this occur in?
No signal. Phase contrast imaging.
219
What should be done to maximize tissue saturation in TOF MRA?
Decrease TR.
220
What are the 3 types of images acquired from a phase contrast technique?
Phase, MIPS, and Magnitude
221
In DWI the dephasing and rephasing gradients occur when?
On either side of the 180 degree refocussing pulse.
222
Which MRI sequence is the fastest? FSE, GRE, or EPI?
EPI.
223
What is the weighting of an EPI image?
Mostly T2* (no refocusing 180 pulse)
224
About how long does it take to acquire images of the head (10 slices) using EPI?
1 second. Approximately 10 slice per second.
225
Approximate spatial resolution of MRI?
0.3 lp/mm
226
Approximate spatial resolution of CT?
0.7 lp/mm
227
Approximate spatial resolution of DSA?
3 lp/mm
228
How much would tripling each voxel dimension increase SNR?
x 27
229
When in increase your receiver bandwidth what are you actually doing?
Increasing readout (frequency-encoded) gradient. This will decrease SNR.
230
When B ranges between 1 and 1.1 T what is the likely receiver bandwidth?
4 MHZ because the Larmor Frequency of 1 T is 40 MHZ
231
What does increasing the readout bandwidth decrease?
chemical shift AND susceptibility
232
Using a multichannel receiver coil will have what effect on acquisition time?
Decreases it. Makes the scan faster.
233
What are two effects of increasing the main magnetic field Bo?
Increased SNR. Increased T1 for all tissues. T2 is independent of Bo.
234
How to fix Gibbs artifact?
Increase the MATRIX SIZE.
235
Most common patient safety issue in MRI?
Burns. These constitute 70% of FDA reports.
236
Which coil uses the most power in MRI?
Body. Biggest.
237
What is the limit for whole body heating in normal mode for MRI?
Up to 0.5 degrees C
238
What is the limit for whole body heating in 1st level (supervised) mode?
Up to 1 degree C
239
What is the limit for whole body heating in 2nd level (IRB approved mode?
No limit. Above 1 degree C.
240
Noise from gradient coils should be kept below which level?
100 dB
241
What zone do you code a patient in?
Zone 2. Remove the patient from the scanner all the way to Zone 2.
242
What shape is the MR safe sign?
Square.
243
What shape is the MR conditional sign?
Triangle.
244
What shape it the MR not safe sign?
Circle
245
What should MRI patients be advised to wear to protect their ears?
Both ear plugs and ear protectors.
246
Fan v. cone angle of a CT beam
Fan angle is in the axial plane of the patient. Cone angle extends along the z axis of the patient.
247
1 line of a sonogram is called?
A projection
248
1 line of a projection is called?
A ray
249
Does a smoothing filter affect contrast?
Technically no. It just decreases noise and therefore increases CNR.
250
Does an edge enhancing filter affect contrast?
Technically no. It increases SR but unfortunately also increases noise.
251
What are two examples of edge enhancing filters?
Bone and lung kernels.
252
Which is better: statistical iterative reconstruction of model-based iterative reconstruction?
Model-based.
253
What is the equation for Hounsfield Units
1000 x (Attenuation in question - Attenuation of Water) / Attenuation of Water
254
A 10 HU changes represents what change in attenuation?
1%
255
If you increase KVP does a calcium kidney stone attenuate more or less photons?
Less
256
If you increase KVP does a uric acid stone attenuate more or less photons?
More
257
Are CT x-ray beam filtered?
Highly filtered to reduce beam hardening artifact
258
What is a CT detector made out of?
CsI
259
What does detector offset refer to in CT?
at 180 degrees the projection will be slightly different. this improves spatial resolution.
260
Typical thickness of a CT slice acquisition?
0.5 mm
261
Typical thickness of a CT slice on the monitor?
4-5 mm
262
Is the anode capacity for heat higher or lower than traditional XR?
higher
263
In CT xray tube output will increase more by increasing KVP or MAS?
KVP. Increase of 15% KVP will double the output. MAS rises linearly.
264
What are the 2 sizes of phantoms in CT for measuring CTDI vol?
16 cm and 32 cm.
265
What size CT phantom for head?
16 cm
266
What size CT phantom for body?
32 cm
267
What size CT phantom for the neck?
Variable.
268
What size CT phantom for peds?
Variable.
269
What are the units for KAP in fluoro?
G x sq cm
270
What are the units for CTDI in CT?
G x cm
271
Is KVP or MA adjusted by the AEC in CT?
Just the MA.
272
What is the average KVP in CT for a fat patient?
140
273
What is the average KVP in CT for a not fat patient?
120
274
What is the average KVP for CT with contrast studies using iodine?
80
275
What is the ACR dose limit for a head CT? What is the average dose for a head CT?
CTDIvol 80mGy is the limit. CTDIvol 60mGy is the average.
276
How does CT fluoro work?
continuous tube rotation.
277
How many images per second acquired in CT fluoro?
6
278
Is KVP or MAS or both reduced in CT fluoro?
Only MAS - about 20% of the diagnostic dose.
279
What is the most likely CTDIvol for an infant head CT?
Half of an adult = 30 mGy.
280
What is effective MAS?
MAS/pitch
281
What is the best possible temporal resolution of a CT scan?
0.5 x the rotation time.
282
How long does it take a modern CT to rotate one time?
300ms
283
What is the best possible temporal resolution for a dual source (not necessarily dual energy) CT scanner?
0.25 x rotation time = 75 ms.
284
What happens to CT noise with MAS and slice thickness are both doubled?
Halved bc mas decreases noise linearly and slice thickness increases noise by square root.
285
Name four things that affect SR in CT
Focal spot, detector size, reconstruction filter choice, and field of view.
286
Ring artifacts in CT imply which generation scanner?
3rd
287
Two ways to fix streak artifact from metallic implant in CT?
Use iterative reconstruction. Increase KVP.
288
When is cone beam CT used?
dentists
289
What is a Bushberg / Defrise Phantom?
Google it. Know it.
290
What causes aliasing in all modalities: CT, MRI, and US?
Undersampling.
291
In IR and fluoro where is the AK measured?
15 cm from the patient’s isocenter closer to the source. This spot is called the Interventional Reference Point (IRP)
292
Helpful approximation: what should you assume the peak skin dose is equal to in fluoro/IR?
Air Kerma at the Interventional Reference Point (IRP)
293
What is the frequency of “serious skin burns” in IR?
1 out of 10,000
294
At what peak skin dose, does the Joint Commission visit for a sentinel event?
15 G
295
What is the most likely peak skin dose during an IR procedure
1 G
296
What is the patient peak skin dose limit in IR?
No limit.
297
What is considered a “very low dose” radiology procedure. Name 3 examples.
< 0.1 mSv. Skull, chest, and extremity XR.
298
What is considered a “low dose” radiology procedure. Name 3 examples.
Between 0.1 and 1 mSv. Abdominal and spine XR. Extremity CT.
299
What is considered a “moderate dose” radiology procedure. Name 3 examples.
Between 1 and 10 mSv. Chest CT, Abdominal CT, Small bowel follow-through fluoro, MDP bone scan.
300
What is considered a “high dose” radiology procedure. Name 3 examples.
Greater than 10 mSV. TIPS, FDG-PET, triple phase liver CT.
301
Name 3 things that are considered when converting the CT DLP into an effective dose (mSV)
Body region, physical size of the organs involved, patient age.
302
What is the approximate dose the embryo from a CT abd/pelvis on a pregnant woman?
10-20 mSV. For context, there is NO risk of deterministic effects on the fetus before a cumulative dose of 100mSV; however, there is an increased stochastic risk to the fetus starting around 25 msV.
303
Average CTDIvol and effective dose for a head CT?
60mGy for CTDI. 2mSv for effective dose.
304
Average CTDIvol and effective dose for a chest CT
10mGy for CTDI. 6mSv for effective dose.
305
Which of the following has the lowest dose? Head ct, chest ct, abdomen ct, or pelvis ct?
head ct. Only 2 mSv. The rest are about 5 mSv.
306
Approximate fetal dose for a single abdominal radiograph?
1 mGy (no deterministic effects below 100 mGy)
307
Compared to a 25 year-old how much more/less stochastic risk does an infant have for the same amount of radiation?
3 x more stochastic risk
308
Compared to a 25 year-old how much more/less stochastic risk does an old person have for the same amount of radiation?
3 x less stochastic risk
309
Screening mammo is in which dose category? Very low, low, moderate, or high?
Low (0.1 to 1 mSv)
310
About how much dose to the fetus per minute when performing fluoro on mother?
2 mGy/min
311
What is the stochastic risk of cancer from 10mSV of effective dose in a 25 year old?
0.1 percent. Risk of cancer rises from 40% to 40.1%.
312
Creation method for radionuclides that decay via B-?
Either reactors or fission
313
Difference between reactor and fission products?
Reactor products are NOT carrier free. Fission products are carrier free.
314
Do cyclotrons add charge or subtract charge?
Add. Products have an extra proton. They get stable by releasing a positron or capturing an electron.
315
1 mCi is how many Bq?
37 MBq
316
Half life activity equation using decay constant
T(1/2) x 0.69 = decay constant
317
Long parent half life and short daughter half life is called what?
Secular equilibrium
318
Equilibrium occurs after how many half lives?
4
319
How would a radionuclide produced in a cyclotron most likely decay
Beta positive decay
320
How would a radionuclide made in a reactor likely decay?
Beta negative decay.
321
What is the energy resolution for I123 if the photo peak width is 16 kev
10%
322
Who regulates administered radionuclides?
NRS or agreement states
323
What is the most likely photo peak width for Tc 99m gamma rays?
14 kev
324
What is another name for a low energy collimator?
Foil collimator. Used for Tc 99m as well as I 123.
325
What goes down far from the NM collimator? Spatial resolution, SNR, or Contrast?
Spatial Resolution
326
How many counts are acquired in uniformity correction flood images?
100 million (happens quarterly and typically scheduled for overnight)
327
What two variables have the most impact on the quality of a nuclear medicine study?
collimator selection and # of counts
328
Which type of collimator will result in the WORST spatial resolution?
Diverging.
329
What kind of collimator do you use for a MDP bone scan planar acquisition?
LEHR
330
About how many minutes does it take to acquire ALL of the photons from a MDP bone scan?
15m
331
Name one type of iterative reconstruction?
OSEM (Ordered subset expectation maximization)
332
In NM what is a high pass filter?
Same thing as high spatial frequency filter = high resolution filter. SR increases. Sensitivity decreases.
333
In MRI what part of k space does a high pass filter remove?
Center of K space. You still have good spatial resolution but you lose contrast.
334
In MRI what part of k space does a low pass filter remove?
Periphery. You lose spatial resolution, but you still have contrast.
335
In SPECT what determines resolution perfomance?
lead collimator height and distance between collimators
336
Approximate pixel size (mm) for chest X-ray?
0.1 mm
337
Approximate pixel size (mm) for NM spect?
2 mm
338
What accounts for improved image quality in PET compared to SPECT?
More counts. Less mottle.
339
Two ways to know you are looking at an attenuation correction image in PET?
bright lungs and NO dark line around the periphery of the body.
340
Two ways to know you are looking at a non-attenuation correction image in PET?
dark lungs and dark periphery of the body.
341
What do you use Phosphorus 32 for?
Treating polycythemia vera. Pure alpha emitter.
342
What are the only two imaging modalities in which you code 1 pixel with 1 byte
ultrasound and nm. the rest of the modalities code 1 pixel with 2 bytes (=16 bits)
343
What is another name for the gamma camera?
anger camera
344
What is mistuning or detuning in NM?
When the energy window is mis-aligned so that the photons you are interested in (e.g. 140 for Tc99m study) are not being counted.
345
What is the photo peak for Co 57 and when is it used?
120 kev. for daily uniformity checks on anger cameras.
346
What is the degree of variability allowed for gamma cameras during daily uniformity testing with Co 57?
2-3 percent
347
Where is SR and linearity measured during weekly checks on anger cameras?
Right up against the anger/gamma camera. Because spatial resolution falls off rapidly with distance from the camera, these weekly checks always overestimate the system SR.
348
Without doing calculations, what is the approximate wavelength of a ultrasound wave using a 15 MHz transducer?
~0.1 mm
349
Speed of sound in bone
4000 m/s
350
What kind of reflection is useful in diagnostic ultrasound?
specular. non-specular aka diffuse is garbage.
351
When does scatter happen in ultrasound?
when the interface being interrogated by the ultrasound beam is much smaller than the beam wavelength.
352
In ultrasound how much attenuation does a 10 dB drop result in?
10 percent.
353
In ultrasound how much attenuation does a 20 dB drop result in?
1%
354
What is the approximate mHz of an abdominal ultrasound transducer?
3 MHZ
355
What is the approximate mHz of a breast transducer?
10-15 MHZ
356
Name three high ultrasound attenuators
Air, lung, bone
357
In human tissue, what is the change in decibel with depth?
0.5 db/cm /mHZ
358
What is the unit of acoustic impedence?
Rayl
359
Transducer thickness is equal to?
1/2 wavelength
360
What has the highest acoustic impedence?
PZT (what the transducer crystals are made out of) is higher than bone.
361
Does lung attenuate ultrasound beams a lot or a little?
a lot despite having low impedence.
362
Roughly how many PZT elements are there in a clinical ultrasound probe?
About 100
363
What’s the most likely number of lines in a single ultrasound image?
About 100
364
How are elements fired in a phased array ultrasound transducer?
All at once
365
Ultrasound is:
“always focused”
366
What is the reduction in US frame rate from using 5 focal zones?
Five times slower
367
What is the advantage of a 1.5D ultrasound array?
Better elevational resolution
368
What feature of phased array probes gives you better lateral resolution?
The ability to set multiple focal zones
369
What do phased arrays vary to steer and focus the ultrasound beam?
Time delays
370
3 ways to increase line density?
Decrease the frame rate, field of view, or depth.
371
What is the product of lines per frame and image frame rate?
Pulse repetition period
372
On an ultrasound machine, does gain affect depth?
No
373
To avoid aliasing in ultrasound the PRF must be at least what?
2x the doppler shift
374
A fetus kicking during an ultrasound exam will cause what kind of artifact?
Flash artifact. Apparently this can be corrected for using something called a “wall filter”
375
What is “continuous doppler?”
The machine use you during a code to listen for someone’s pulse. No images provided, only audible response to blood flow.
376
How does increasing the spatial pulse length affect axial resolution?
Inversely related. High SPL, worse axial resolution.
377
Axial resolution is about what?
1/2 the SPL
378
Is lateral resolution better than worse than axial resolution in ultrasound?
4x worse than axial resolution regardless of transducer frequency.
379
In ultrasound, does spatial compounding affect noise?
Yes, it decreases noise.
380
In ultrasound, does spatial compounding affect contrast?
No.
381
Which ultrasound resolution is changed by adjusting the frame rate? Axial, elevational, or lateral?
Lateral.
382
Name three assumptions the ultrasound machine makes that accounts for artifacts?
Sound waves travel in straight lines. Only one reflection per beam. Speed of sound in tissue is uniform.
383
In what category of dose does ERCP belong?
Moderate = between 1 and 10 mSv.
384
Compare the receptor air kerma between a chest X-ray and a mammogram and explain why there is a difference?
3 microG for CXR. 100 microG for mammo. Need less mottle in mammo to detect subtle differences. Can tolerate higher mottle in xr.
