Nuclear Med extra flashcards

Question 1

Definition Becquerel

Answer 1

number of nuclei decaying per second

Question 2

Particles and mass: describe mass of positrons and photons

Answer 2

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

Question 3

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

Answer 3

-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)

Question 4

Effective doses for: VQ scans, bone scans

Answer 4

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

-Bone: effective dose 6mSv

Question 5

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

Answer 5

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

Question 6

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

Answer 6

Transmutation

Question 7

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

Answer 7

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

Question 8

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

Answer 8

-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

Question 9

What is the half life of Nitrogen 13?

Answer 9

10 mins

Question 10

What is the half life of Carbon 11?

Answer 10

20 mins

Question 11

What is the half life of Oxygen 15?

Answer 11

2 mins

Question 12

What is the half life of Iodine 131?

Answer 12

8 days

Question 13

What is the half life of Iodine 123

Answer 13

13h

Question 14

What is the half life of Xenon 133

Answer 14

5 days

Question 15

What is the half life of thallium 201

Answer 15

3 days

Question 16

Name nuclides produced in a cyclotron

Answer 16

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

Question 17

Name a nuclide produced in a generator

Answer 17

99mTc

Question 18

Name a nuclide produced in a nuclear reactor

Answer 18

125 I

Question 19

Name nuclides that are fission products

Answer 19

131 I, 133 Xe

Question 20

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

Answer 20

75%

Question 21

Do gamma cameras only detect gamma rays?

Answer 21

-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.

Question 22

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

Answer 22

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

Question 23

Gamma camera: what is the typical sensitivity of collimators?

Answer 23

1%

Question 24

What is the HVL of lead for Tc-99?

Answer 24

0.3mm thick

Question 25

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

Answer 25

5000 light photons

Question 26

How does increasing PHA affect sensitivity/spatial resolution?

Answer 26

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

Question 27

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

Answer 27

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

Question 28

What is the greatest limiting factor of gamma camera images?

Answer 28

Noise

Question 29

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

Answer 29

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

Question 30

What reconstruction algorithm is used in SPECT?

Answer 30

-FBP

Question 31

How does SPECT work?

Answer 31

-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.

Question 32

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

Answer 32

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

Question 33

Describe how PET works

Answer 33

-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

Question 34

What kind of detectors are used in PET?

Answer 34

-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.

Question 35

Why is CT done alongside PET?

Answer 35

-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.

Question 36

What is the resolution of PET?

Answer 36

-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.

Question 37

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

Answer 37

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.

Question 38

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

Answer 38

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

Question 39

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

Answer 39

-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

Question 40

Can a Geiger Muller Counter be used for monitoring dose?

Answer 40

-Used for quality control, NOT for monitoring dose.