Radiation imaging

Question 1

Radiation imaging

Answer 1

uses low-level radioactive chemicals → designed to absorbed by different types of tissues
- detection of hotspots

Question 2

radiographic imaging

Answer 2

• externally produced radation passes through tissue

Question 3

non- radioactive imaging

Answer 3

diagnostic ultrasound imaging
- high frequency sound send into body, detecetion of refelcet sound waves
MRI
- nuclear magnetic resonance NMR, to image nuclei of atoms inside body → magnetic nuclei absorb & re-emit elecromagnetic radiation in a magnetic field

Question 4

Basic principles of radiation imaging

Answer 4

1. radioactive trager injected into blood
2. radiation is detected and converted into electrical impulses
3. electrical impulses are converted into images

Question 5

radioactive tracer

Answer 5

chemical compound, atoms replaced by a radioisotope
→ can be used to explore specific chemical reactions/ bodily functions
e.g. glucose in tumor diagnostics

Question 6

radiation theroy

• radioactive emission
• protons and neutros
• energy states

Answer 6

• radioactive emission = spotaneous disintegration of atoms → atoms decay over time → eject particles
• protons & neutrons experience short range nuclear forces → interplay of these forces induced different arrangement of particles within the nucleus
• energy states: ground state (most stable) & excited state (precedes radiactive decay)

Question 7

radiation emittion

Answer 7

alpha radiation: alpha particles, (+)charge, 2 protons and 2 neutrons, penetration: not even paper (big particles)
beta radiation: (-) charged electrons or (+) charged particles, penetration: not through wood
gamma radiation: pure electromagnetic radiation with zero mass & charge, penetrate through all (concrete)

Question 8

Notation

Answer 8

• nucleons: protons and neutrons
• Atomic mass A (above): total number of nucleons
• Atomic number Z (lower): total number of protons

Question 9

radioactive elements

Answer 9

Elements with an atomic number Z >83 are radioactive an spontaneously decay into other elements

Question 10

Atomic mass units AMU

Answer 10

mass of nuclear particels expressed in AMU using carbon 12 as reference

• gram atomic mass: weight in grams of isotope equivalent to atomic mass
• avogadro’s number 6.023 x 10^23 atoms/gm

Question 11

alpha-decay

Answer 11

• kinetic energy is liberated
• mass equates to energy
• mass of atom is less than sum of individual components
• mass defect is manifestes as the energy required to bind nucleus together

Question 12

beta- decay

Answer 12

negatron decay (beta - )
- nucleus same number of nucleons, but total atomic number increases by 1
- neutron transformed → 1 proton + 1 electron
- energy carried away by neutrino (zero change)
positron decay (beta+)
- decreasing the atomic number by 1

Question 13

radioactive deay characteristics

Answer 13

• unaffected by changes in pressure, temperature, chemical combination
• rate of decay (lamda) constant → same number of disintegrations per time
• half life T1/2 → time required for half of the nuclei to decay (see notes for equation)

Question 14

gamma decay

Answer 14

• accompanies beta decay → protons and neutrons left in high energy state
• photons of energy emitted to achieve a more stable configuration

Question 15

nuclear instrumentation

Answer 15

• scintillation
• photomultiplier
• collimator

Question 16

scintillation

Answer 16

flash of light, which is emitted when a substance is struck by an emitted particle/gamma ray
→ amount of light emitted is proportional to the energy of the colliding particle

Question 17

photomultiplier

- oscilloscope

Answer 17

measures light intesitiy & converts it to electrical impulse
- electrical impulses are amplified and processed to provide information about incident radiation
→ using an oscilloscope
this gives information about: energy/intensity of the incident radiation, acitivty of a specific radionuclide
- no spatial/positional information

Question 18

work flow nuclear instrumentation

Answer 18

indicent photon into scintillator → produciton of light photon → light photon detected by photocathode → photoelectric effect (photon into electron) → ejection of electron through focusing electrode into multiple dynode → amplification
at the dynode every incident of electron is doubled → incident photons are rare

Question 19

collimator

Answer 19

filters a stream of rays → those travelling parallel to specific direction allowed through
- Pinhole collimator: allows only one point of entry → very time intensive
→ multihole is preferred

Question 20

anhnihilation

Answer 20

• positrons emitted though decay only travel short distances (1-2mm) in tissues
• annihilation creates a pair of photons (gamma ray) that travel 180° to one another

Question 21

Basic concept of PET system

Answer 21

• annihilation of positron and electreon → postronium → decay into gamma ray
• simultaneous detection of gamma rays of the two detectors means that this two gamma rays are coinciding → computer tomography produces an image

Question 22

error sources

Answer 22

• true conincidence: no error
• scattering process: one gamma ray is scattered → location of event interpreted somewhere else
• concurrent events: two events simultaneously → solution: exclude all simultanoues events
• secondary photon: three gamma rays

Question 23

combined MRI/PET imaging

Answer 23

• whole body PET using F-FDG (fluodeoxyglucose) → does not provide spatial resoltution → MRI
• PET provides functional information & MRI provides anatomical information