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RA6007: Radiation Physics > Mock MCQ > Flashcards

Mock MCQ Flashcards

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1
Q

In PET, do you need more shielding than Nuclear med, or the same?

A

More shielding needed

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2
Q

name the most used isotope in PET and what it is combined with to make the radiotracer

A

F-18 and deoxyglucose

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3
Q

what does the radiotracer highlight in the scan

A

cells with high metabolic activity

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4
Q

how does Ga-68 compare to F-18 in the spatial resolution of a PET scan?

A

Ga-68 PET scans have worse spatial resolution

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5
Q

Name the image reconstruction that can be completed on PETCT scans

A

Filtered back projection and iterative reconstruction

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6
Q

What is the scintillator made of in PET? past and present?

A

past - Bismuth Germanate (BGO)
present - Gadolinium orthosilicate (GSO) or Lutetium orthosilicate (LSO)

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7
Q

Unlike SPECT, Tissue attenuation correction is not needed in PET CT, T/F?

A

False; attenuation is much easier in PET, but is still needed!!

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7
Q

does PET use a full or half-ring of detectors?

A

PET uses a full ring of detectors

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7
Q

what forms the line of response?

A

the two gamma photons released at 180 degrees to each other

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8
Q

what is advice for patietns for prior to PET?

A

no exercise, muscle activity can give false positives for high metabolic activity

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9
Q

what is the time of flight in PET?

A

time of flight is the process where the time difference between the arrival of two coincidence events at opposite detectors and allows for precise location of the annihilation interaction to be defined.

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10
Q

is there a collimator in PET?

A

No collimators in PET, there are in SPECT, this is the weakest link in the imaging chain in SPECT.

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11
Q

describe the relationship of B0 to T1 and T2 values for tissue

A

T1 is dependent on B0 (this means T1 will increase as magnetic field strength increases)
T2 is independent of B0 (T2 is unaffected by shifts in Larmour frequency)

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12
Q

at what field strength is tissue heating an issue

A

at a high magnetic field strength tissue heating becomes more of an issue

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13
Q

Do inversion recovery sequences produce T1 or T2 weighted sequences?

A

IR produces T1 weighted images, this is due to the addition of the 180 degree pulse.

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14
Q

what is the echo train length?

A

the echo train length is the number of echoes produced after a single pulse

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15
Q

what is the projectile effect?

A

the attraction of ferromagnetic objects to the scanner. this is an issue for both low and high field strength magnets

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16
Q

what is the time limiting step in the production of an MR sequence?

A

The magnetic field strength is the time-limiting factor in MRI

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17
Q

what is contained within the central lines of K-space?

A

image contrast is contained within the central lines of k space

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18
Q

what is contained within the peripheral lines of k space?

A

the spatial resolution information is located within the peripheral lines of k space

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19
Q

which sequence is most affected by the chemical shift of the second kind artefact

A

gradient echo sequence

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20
Q

name risks associated with emergency magnet quenching?

A

asphyxiation

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21
Q

what are SAR values?

A

Specific absorption rate and this is a measure of the amount of power deposited by a radiofrequency field in a certain mass of tissue

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22
Q

how to remove wrap around artefact?

A

increase the field of view

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23
Q

how can you improve signal to noise ratio in MRI

A

By using Half fourier scanning

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24
Q
A
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25
Q

what is the relationship between the aperture of the U/S probe to the length of the near field?

A

the size of the U/S probe has a direct effect on fresnel zone/near field length, double aperture size, double length of the near field!

26
Q

what two factors influence the length of the near field?

A

the aperture size and the frequency.
higher frequency, longer near field!

27
Q

is u/s faster in bone or soft tissue?

A

u/s is faster in bone

28
Q

what form of wave is ultrasound?

A

U/S is a sound wave

29
Q

can sound waves travel in a vacuum (without a medium)

A

no

30
Q

what must be matched to ensure maximum transmission of the U/S beam?

A

we must match the acoustic impedance of the two media to ensure minimum reflection and maximum transmission of the beam

31
Q

what is the typical absorption of U/S in tissue in dB/cm/MHz?

A

typical absorption of U/S in tissue = 1Db/cm/MHz.

32
Q

describe the relationship between the piezoelectric crystal and the wavelength of emitted U/S.

A

The size of the piezoelectric crystal is related to the wavelength of the U/S.
Piez. thickness = 1/2 wavelength.

33
Q

what is axial resolution in U/S?

A

Axial resolution is the spatial resolution in the plane parallel to the U/S beam

34
Q

what is lateral resolution in U/S?

A

Lateral resolution is the spatial resolution perpendicular to the U/S beam direction

35
Q

which is better, axial or lateral resolution

A

axial resolution is better than lateral resolution

36
Q

What are the differences in spatial pulse length in doppler vs imaging?

A

doppler U/S uses longer SPL than imaging U/S.

37
Q

what is the main effect of long spatial pulse length?

A

long spatial length pulse is associated with poorer spatial resolution

38
Q

what is pulse repetition frequency?

A

PRF is number of u/s pulses per second

39
Q

what is the nuclear force that binds the nucleons together tightly in the nucleus?

A

the strong nuclear force

40
Q

what letter denotes atomic number?

A

Z

41
Q

what does an alpha particle consist of?

A

2 protons and 2 neutrons

42
Q

what causes beta particle emission?

A

conversion of a neutron to a proton

43
Q

what is the main radioisotope used for nuclear medicine?

A

Technetium (Tc 99m)

44
Q

what is technetium produced in?

A

a generator

45
Q

what is technetium parent radionuclide?

A

molybdenum

46
Q

what is typical administered activity for an isotope bone scan?

A

500 MBq

47
Q

What effects does the collimator have in NM?

A

collimator impacts:
spatial resolution
sensitivity
FOV size
magnification/minification

48
Q

what is the weakest link of NM? How to counteract this best?

A

the collimator is the weakest link, we should keep the patient as close as possible to the detector to improve the extrinsic resolution

49
Q

where is molybdenum produced

A

Mo produced in a nuclear reactor and stored in a generator.

50
Q

what NM imaging is galium-67 used in?

A

lymphoma, rare use, Tc99m much more common

51
Q

what is extrinsic resolution

A

spatial resolution with the collimator (poorer)

52
Q

what is intrinsic resolution?

A

spatial resolution without the collimator, better than extrinsic

53
Q

How can Mo breakthrough be measured?

A

can be measured with a well-counter, comparing eluate activity with and without lead shielding (6mm)

54
Q

how does the collimator affect spatial resolution in NM?

A

collimator decreases spatial resolution

55
Q

can collimator in NM reduce scatter

A

the pulse height analyser is most effective at reducing compton scatter.

56
Q

can the time of flight technique be used in PET?

A

yes.

57
Q

name a dose reduction measure you can make in PET CT?

A

use a low dose CT instead of a diagnostic CT to reduce patient dose

58
Q

is PHA used in PET?

A

yes

59
Q

what is the main material used in scintillators in PET?

A

Bismuth germanate, Letium orthosilicate, gadolinium orthosilicate

60
Q

what is typical patient dose in PET CT?

A

PET alone: 8-10mSv
PET with diagnostic CT: 15mSv
PET with low-dose CT: 8-10mSv + 2mSv

61
Q

is a dual headed gamma camera used in SPECT?

A

Yes.

61
Q

can technetium be used in SPECT?

A

yes

62
Q

are collimators used in SPECT?

A

Yes, parallel-hole collimators are used in SPECT

63
Q

How is tissue attenuation correction performed in modern SPECT scanners?

A

using the attached CT scanner

RA6007: Radiation Physics (6 decks)

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