week 1-2 Flashcards
1
Q
most common radioisotope in NM
A
Tc-99m
2
Q
half life of Tc-99m
A
6 hours
3
Q
what type of radiation does Tc-99m emit
A
gamma ray
4
Q
half life of I-131
A
8 days
5
Q
what is I-131 used for
A
imaging and treatment of thyroid disorders and inoperable liver cancer
6
Q
what type of radiation does I-131 emit
A
gamma and beta
7
Q
what is Tc-99m used for
A
80% of the scans - bones, brain, cardiac, thyroid, lung, renal
8
Q
types of gamma camera
A
single detector
multi detector
9
Q
types of dual detector systems
A
- detectors fixed at 180deg apart
- detectors fixed at 90deg apart
- detectors at variable angle between 75 and 180deg
10
Q
what is 90deg dual detector used for
A
cardiac imaging
11
Q
what is 180deg dual detector used for
A
general SPECT
total body imaging
12
Q
advantages of a dual detector system
A
- improved resolution
- cost effectiveness
- faster patient throughput
- space constraints
13
Q
components of a gamma camera
A
- collimator
- sodium iodide crystal
- photomultiplier tube
- PHA circuit, discriminator, analyser circuits
- computers for data processing and display
14
Q
how does photomultiplier tube work
A
- gamma photon enters the NaI scintillation crystal, gets converted to light photon and enters to PMT
- PMT converts light photon into photoelectrons
- localises the position where the gamma ray interacts in the crystal
- match performance from tube to tub within a camera detector
- reduced light barrier between tubes
15
Q
types of collimators
A
- parallel-hole collimator
- converging collimator
- pin-hole collimator
- diverging collimator
16
Q
what is the converging collimator used for
A
magnification
17
Q
what is pin-hole collimator used for
A
magnification + inverted image
18
Q
what is diverging collimator used for
A
minification
19
Q
how does the diameter and length of collimator holes determine the field of view, sensitivity and spatial resolution
A
- larger holes increase sensitivity but degrades resolution
- shorter length increase fov and sensitivity but degrades spatial resolution
20
Q
performance parameter of a gamma camera
A
- spatial resolution
- non-uniformity
- count rate characteristics
- energy resolution
- sensitivity
21
Q
what is spatial resolution
A
- refers to the smallest separation between 2 radioactive point sources
- dependent on intrinsic and collimator resolution
22
Q
what is intrinsic uniformity dependent on
A
PMT balance, crystal, electronics, imaged without collimator
23
Q
what is extrinsic uniformity dependent on
A
PMT balance, crystal, electronics, collimator integrity, imaged with collimator using flood source
24
Q
how are radiopharmaceuticals different from other drugs
A
- require shielding
- most given intravenously
- short shelf-life
- strength of every dose can be checked
- given in very small amounts
- purity of every dose can be checked
25
what are the half lifes of radionuclides
therapeutic (alpha and beta) - days
diagnostic (gamma and positron) - minutes and hours
26
how can the different types radioactivity be stopped
alpha - paper / hand
beta - aluminium / plastic / glass
gamma - lead / concrete
neutron - water
27
ideal properties of radionuclide for diagnostic use
- gamma ray emission only
- gamma energy 100-250keV for imaging
- physical half-life approx 1.5times duration of test
- simple cheap production/ purification
- versatile chemistry
28
ideal properties of radionuclide for therapeutic use
- pure beta minus or alpha emitter
- particle energy suitable for purpose
- physical half-life of a few days
- simple cheap production/ purification
- versatile chemistry
29
types of localization
1. compartmentalised
2. passive diffusion
3. filtration
4. facilitated diffusion
5. active transport
6. phagocytosis
7. cell sequestration
8. capillary blockade
9. ion exchange
10. chemisorption
11. cellular migration
30
what is compartmentalised localisation
to put a radiotracer in a bounded space and distributed in an enclosed volume and sustaining the tracer for time enough to scan that bounded space
a. uniform dispersion
b. non-uniformities within the compartment
- areas of increased radiopharmaceutical concentration may reflect pathological changes in the tissue or organ
- areas of decreased radiopharmaceutical concentration is usually the outcome of blockage in the cavities
c. leakage from the compartment
d. movement within the compartment
31
what is passive diffusion
comprises motion of molecules across the membrane
a. factors that affect mobility of molecules to move across membrane: pH, ionisation, size of molecule, lipid solubility
b. characteristics of passive diffusion
- concentration gradient is required
- fast at high concentration gradient and slow at low concentration gradient
- does not need any sort of input
- non-selective process because no carriers or receptors are included
32
what is filtration
special case of diffusion involving transit of molecules through pores, or channels, driven by hydrostatic or osmotic pressure gradient
a. characteristics
- requires some sort of force or pressure gradient
- does not require the local input or other external energy
- no transporters, carriers, or other receptors involved, so filtration is non-selective, is not competitively inhibited by similar molecules, and is not subject to saturation
33
what is facilitated diffusion
carrier-mediated transport across membrane
- carrier is utilised to carry the molecule across the membrane (selective carrier membrane)
- inhibited by the presence of similar molecules
- saturation can be achieved to maximum due to limited number carriers
- passive and involves a concentration gradient, external energy not employed
34
types of impurity and how they can be detected
1. radionuclidic - radioactivity measurement (dose calibrator)
2. chemical - colorimetric
3. radiochemical - thin later chromatography
35
what is equivalent dose
parameter to accommodate the difference in biological effects of different radiation types
absorbed dose x weighting factor
36
2 effects that radiation may cause to cells
- deterministic effect
- stochastic effect
37
what is deterministic effect
- effects are due to significant cell death
- basis of radiotherapy where cancer cells are targeted
- severity is directly proportional to exposure dose
- threshold level exists
- appropriate radiation protection mechanism and occupational exposure dose limits to be put in place to reduce this effect
38
what is stochastic effect
- effects are due to significant cell damage
- probability of effect is directly proportional to exposure dose
- no threshold level for these effects
- long latent period between irradiation and occurrence of effect
39
determinants of biological effects
- rate of absorption
- area exposed
- variations in species and individual sensitivity
- variations in cell sensitivity
40
rank the tissue/organs in accordance to their sensitivity to radiation
low: muscle, joints, central nerves, fats
|
| skin, inntr-layer intestine, eyes
|
high: bone marrow, breast, lymph system, reproductive organs
41
what is the dose limit of whole body for both radiation worker and public
radiation worker: 20mSv/year
pregnant staff: 2mSv/year for the remaining duration of pregnancy after declaration
public: 1mSv/year, excluding any medical exposure
42
what is the dose limit for the extremities for both radiation workers and public
radiation workers: 500mSv/year
public: 50mSv/year
43
what are the 3 basic principles of radiation protection
Shield (shielding the source)
Time (minimize time of exposure)
Distance (inverse square law)
44
what is half-value layer (HVL)
thickness of any given material where 50% of the incident energy has been attenuated
45
types of personal radiation monitors
- film badge dosimeter
- thermoluminescent dosimeter (TLD)
- optically stimulated luminescence (OSL) dosimeter
- electronic personal dosimeters
46
3 most common types of radiation detector
- gas detectors
- scintillation counters
- solid state detectors
47
possible routes of entry of radionuclides
- ingestion
- inhalation
- skin absorption
- through cuts or wounds
48
2 types of contamination that must be controlled
- removable surface contamination
- airborne contamination
49
pregnant staff can continue working in radiological dpt as long as fetal dose is kept below
1mGy
50
1mSv of fetal dose is equivalent to
~2mSv to abdomen
