Physics

Question 1

Signature Peak Rh

Answer 1

23

Question 2

Signature Peak Mo

Answer 2

20

Question 3

Signature Peak Silver

Answer 3

25

Question 4

Signature Peak Tungsten

Answer 4

70

Question 5

K edge of Iodine

Answer 5

33

Question 6

K edge of Barium

Answer 6

37

Question 7

Smaller focal spot in mammo will have what effect on motion artifact?

Answer 7

increased artifact (longer exposure time)

Question 8

What causes “ring artifact” on CT?

Answer 8

Seen in 3rd generation CT when there are defective detector elements.

Question 9

What is the basic idea behind a fast spin echo sequence?

Answer 9

Multiple refocusing pulses are used to sample multiple lines of k-space after 1 exitation pulse.

Question 10

In a spin echo sequence, what effect with shortening the echo time have?

Answer 10

decreases T2 weighting

Question 11

Effective radiation dose of chest radiograph

Answer 11

0.1 mSv

Question 12

effective radiation dose mammography

Answer 12

0.4 mSv

Question 13

Effective radiation dose CT head

Answer 13

2 mSv

Question 14

effective radiation dose CT Chest

Answer 14

7 mSv

Question 15

effective radiation dose CT Abd pelv w/o and with and without

Answer 15

10 mSv and 20 mSv

Question 16

mSv and cancer risk according to FDA…

Answer 16

10 mSv increases fatal cancer risk by 1/2000

overall fatal cancer death is 400/2000 (20%)

adding 10 mSv changes fatal cancer to 401/2000

Question 17

What is the symbol for bulk magnetic moment?

Answer 17

M

Question 18

What direction is the z axis/ longitudinal?

Answer 18

crainiocaudal

Question 19

larmor frequency equation

Answer 19

(42. 6 MHz/T) x B
synonyms: precession freq, resonance freq

Question 20

T2 is which relaxation?

Answer 20

transverse

Question 21

T1 is which relaxation?

Answer 21

longitudinal

Question 22

T1 = time required for ____% recovery of M_z?

Answer 22

63%

Question 23

T2= _____% remaining spin-spin, transverse mag

Answer 23

37%

Question 24

Fat is ___ on T1 and ____ on T2

Answer 24

short

think of short and fat winnie the pooh

Question 25

free induction decay is given by a rate given by which relaxation time?

Answer 25

T2\* Free induction decay is synomym for T2\* decay

Question 26

Which relaxation time is the shortest between T1, T2, and T2\*

Answer 26

T2\* slowest T1

Question 27

PD weighting has \_\_\_TR and ___ TE?

Answer 27

Long TR and short TE high signal low contrast all the tissues are participating ALL hydrogens

Question 28

Type 1 chemical shift artifact

Answer 28

frequency-encoding gradient causes water and fat in a single voxel to map onto different pixels difference gets bigger with higher telsa

Question 29

how does higher bandwidth affect chemical shift?

Answer 29

increased bandwidth decreases the appearance of type 1 chemical shift artifact (you are assigning more Hz per pixel)

Question 30

How to do calculate how long it takes to fill out K-space?

Answer 30

repetitions x # slices x TR x # phase enchoding steps synonyms for repitions+ # signal averages (NSA) and # of excitations (NEX) - for turbo spin echo you divide by the turbo factor - Single-shot fast spine echo (SSFSE)= all rows of k-space in one TR (pretending that all the echos are the same) good for fetal MRI

Question 32

BLADE faster or slower? when is it good?

Answer 32

slower but good with motion because you are sampling the center of K-space multiple times

Question 33

half fourier methods compare to full k-space sampling in what way?

Answer 33

lower SNR faster aquisition

Question 34

How do you increase SNR?

Answer 34

increase static magnetic field (b₀) increase voxel size 3. increase reciever bandwidth

Question 35

Three types of fat suppression?

Answer 35

Inversion recovery chemical fat suppression (chemical shift spectral sensitive fat suppresion) DIXON

Question 36

pros and cons of chemical fat suppression

Answer 36

pros: unaffect tissue contrast works with gad cons: fails with field inhomogeneity (based on chemical shift)- happens with large or oddly shaped anatomy saturation pulse increases aquisition time

Question 37

DIXON fat suppression

Answer 37

you take in and out of phase and subtract to figure out fat pros: works with gad cons: susceptible to B-field inhomogeneity, better than chemical fat suppression longer TR needed in and out phase aquired together

Question 38

Inversion recovery fat suppression pros and cons

Answer 38

pros: reobust to b-field inhomogeneity cons: also suppresses gad

Question 39

Features of main black blood methods. (T2 spin echo, inversion recovery, double inversion recovery)

Answer 39

T2 Spin echo- blood isn't pitch black Inversion recovery- dark blood Double inversion recovery- bright myocardium, dark blood

Question 40

specific absorption rate (SAR) in MRI is...

Answer 40

watts (W) per kilogram (kg) 1 W/kg -\> 1 deg C change/ hr to decrease SAR- decrease number of RF pulses, lengthen out TR SAR limit is 4 W/kg over 15 min interval

Question 41

"Effective mA or mAs" = ?

Answer 41

The term "effective mA" or "effective mAs" is used in helical CT scanning and is the mAs/pitch. **As the pitch increases** with all other settings remaining constant, the number of x-ray photons contributing to the slice data will **decrease (effective mAs).** The effective mAs **determines the dose** to the slice (CTDIvol) **and signal to noise.**

Question 42

What effects SAR? What's the max SAR you can give someone?

Answer 42

SAR= Specific absorption rate SAR = duty rate x magnet strength**²** x alpha² (flip angle) max SAR you can give someone is **4 W/kg** in the body, 1.5 W everyone else

Question 43

What is the primary source of acoutstic noise in MRI?

Answer 43

Magnetic field gradients.

Question 44

What sequence is most likely to bother your ears?

Answer 44

DWI | (EPI/echo planar imaging)