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FRCR physics > Nuclear Med extra flashcards > Flashcards

Nuclear Med extra flashcards

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1
Q

Definition Becquerel

A

number of nuclei decaying per second

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2
Q

Particles and mass: describe mass of positrons and photons

A

-Positrons have very little mass (esp compared to protons), they are equal to electrons in mass.
-Photon: can be considered to have no mass.

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3
Q

Tc99m: radiation emitted, A and Z number, origin particle

A

-Mass number 99
-Atomic number: 43
-Is created from Mo-99 when it undergoes Beta minus decay
-Tc 99 has a half life of 200k (so it isn’t technically stable)

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4
Q

Effective doses for: VQ scans, bone scans

A

-Lung ventilation: 0.1-0.6mSv
-Lung perfusion: 1mSv
Total imaging for V/Q: under 1.6mSv

-Bone: effective dose 6mSv

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5
Q

Bone scan: what radionuclide is used? How much activity administered? How long have to wait post injection to look for mets

A

-Effective dose is 6mSv
-99mTc-MDP is used
-Activity: 555-750 Mbq
-For mets: time to scan following injection time is 3-4 h.

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6
Q

What do we call the process of new element formation (post alpha decay)

A

Transmutation

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7
Q

Shielding: what can you use for gamma, x-rays, apha and beta

A

-Gamma: concrete, barium plaster, lead
-X-ray: lead aprons
-Alpha: sheet of paper
-Beta: plastic

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8
Q

18-F: what is it normally attached to? Half life and where is it made?

A

-18-F: attached to FDG (fluorodeoxyglucose) to produce 18-FDG and is metabolised by tissues with a high metabolic activity
and glucose update —> used in diagnosis, staging and monitoring of cancer.
-Fluorine-18: Most common used radionuclide
-Half life: 110 minutes
-Radionuclides have short half lives, produced in cyclotrons

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9
Q

What is the half life of Nitrogen 13?

A

10 mins

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10
Q

What is the half life of Carbon 11?

A

20 mins

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11
Q

What is the half life of Oxygen 15?

A

2 mins

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12
Q

What is the half life of Iodine 131?

A

8 days

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13
Q

What is the half life of Iodine 123

A

13h

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14
Q

What is the half life of Xenon 133

A

5 days

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15
Q

What is the half life of thallium 201

A

3 days

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16
Q

Name nuclides produced in a cyclotron

A

fluoride18, 67 Ga, 111ln, 123 I, 201 TI

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17
Q

Name a nuclide produced in a generator

A

99mTc

18
Q

Name a nuclide produced in a nuclear reactor

A

125 I

19
Q

Name nuclides that are fission products

A

131 I, 133 Xe

20
Q

By how much can lead glass sleeves used for syringes can reduce the radiation?

A

75%

21
Q

Do gamma cameras only detect gamma rays?

A

-Can detect more than gamma rays - anything’s that has radiation will stimulate the crystal but the PHA will limit their inclusion in the image if they are not of the expected energy.

22
Q

Gamma camera: what is the crystal made of? How does thickness affect resolution and sensitivity

A

-Large NaI crystal is typically 9-12mm thick.
-Spatial resolution is increased using a thinner crystal
-Typical SR is 5mm
-Thicker crystal: improves sensitivity

23
Q

Gamma camera: what is the typical sensitivity of collimators?

A

1%

24
Q

What is the HVL of lead for Tc-99?

A

0.3mm thick

25
Q

PMTs: a flash of 1 gamma photon usually releases X light photons

A

5000 light photons

26
Q

How does increasing PHA affect sensitivity/spatial resolution?

A

-increasing the PHA increases sensitivity but reduces spatial resolution due to increased scatter of image.

27
Q

T/f only ever used 1 PHA window
What is the window width normally set at?

A

-False
-Can use multiple PHA windows (eg when more than one gamma ray is emitted in In-III)
-Window is usually set at +/- 10%

28
Q

What is the greatest limiting factor of gamma camera images?

A

Noise

29
Q

SPECT: what is the SR and how does this compare to PET?

A

-15-20mm
(SR of PET is 4.5mm in centre and 5mm in periphery)

30
Q

What reconstruction algorithm is used in SPECT?

A

-FBP

31
Q

How does SPECT work?

A

-Measures gamma rays released from decay of radio-isotopes (same ones detected in regular gamma imaging).
-Multiple axial sections are created simultaneously from one gamma camera
-Camera seaming stationary for up to 30 secs and images are collected in 6 degree increments.
-Can have up to 3 cameras detecting simultaneously —> obtain scan faster which reduces the effect of patient movement or increases count rate for same scan time. Both lead to improved resolution of the image.

32
Q

SPECT: what is the max accepted variation in count rate?

A

-Quality control: max accepted variation in count rate is 2%

33
Q

Describe how PET works

A

-F-18 decays by releasing a positron - this is due to neutron deficit in the atom (Beta plus decay).
-Distribution of the radiotracer is determined by the detection of coincident gamma rays
-PET scanners consist of a stationary ring of detectors that surround the patient

34
Q

What kind of detectors are used in PET?

A

-Scintillation detectors: most common detector used in PET to detect coincident gamma rays
-Bismuth germinate: short decay time (300 nanoseconds): allows for rapid measurements and very little dead time.

35
Q

Why is CT done alongside PET?

A

-Structures with little/no FDG update will not be seen on PET scan normal tissues are not clearly represented, this is why PET
is often fused with CT.
-CT allows for anatomical correlation and attenuation corrections to be made on PET images.
-Scan acquisition time: usually 30 mins.

36
Q

What is the resolution of PET?

A

-8-10mm
-Negative PET scan cannot reliably exclude serious pathology in lesions smaller than this
-Lesions below this size with a high metabolic activity can still be detected.

37
Q

Proton rich or proton poor nuclides result in PET emission? How are the photons made?

A

Proton rich radionuclides
-Achieve stability by converting a proton into a neutron, with the positive charge being carried away from the nucleus by a
positron
-After a few mm, the positron combines (annihilates) with an electron outside the radioactive nucleus and releases 2 photons
at 180 degree trajectories, each with an energy of approx 511 keV. The positrons do not have that energy.

38
Q

What are the most radiosensitive and resistant phases of the cell cycle?

A

-Most radioresistant phase of the cell cycle is: S phase
-Most radiosensitive phase: Late G2 and M phases

39
Q

Describe a Geiger Muller counter (outside, sensor, walls, anode)

A

-Gas filled radiation detector
-Sensor: inert gas-filled tube (helium, neon or argon) that briefly conducts an electrical current when a particle or photon of radiation temporarily ionises the gas.
-Walls: metal or coated to form cathode.
-Anode: thin central wire

40
Q

Can a Geiger Muller Counter be used for monitoring dose?

A

-Used for quality control, NOT for monitoring dose.

FRCR physics (13 decks)

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