Imaging Technologies II Flashcards
Definition of a particles
2 protons, 2 neutrons (He nucleus)
Definition of B- particles
An electron
Definition of B+/positrons
antiparticle of electron
Definition of isomeric transition
Nuclear process where a nucleus with excess energy following the emission of an a/b particle emits energy without changing the mass/atomic no
Definition of half life
The time then for half the nuclei to decay
Definition of nuclear magnetic resonance
When nuclei absorb energy from a radiofrequency waves applied at a specific frequency in a magnetic field
Definition of resonance frequency
Natural frequency of a system, frequency needed for most efficient energy transfer
Types of radioactive emissions
a particles b particles (b-) positrons y radiation xrays
Alpha decay
Natural radioactive elements heavier than Pb
Unstable radionuclide ejects a (helium nucleus)
Beta minus decay
Electron created in transformation = b-
v= antineutrino created in transformation
Atomic no increases by 1
Neutron no decreases by 1
Mass no, unchanged
Beta plus decay
Positron created in transformation = b+
v= neutrino created in transformation
Atomic no decreases by 1
Neutron no increases by 1
Mass no, unchanged
Positron annihilation and detection
Tracer decays and emits positron
Annihilation occurs with e-, releases 2 y photons at 180
Detected with 511keV
Isomeric transition
Nucleus with excess energy emits y after loss of a/b-/b+
99m 43 Tc emits y without changing atomic mass/no
Decay kinetics
Rate of decay = dN/dt = -lambda N
Lambda= decay constant
N= no of nuclei
1st order process
Half life
Time taken for half the nuclei to decay
T1/2 = In2/lambda
Penetrating ability of a, b, y, xray
a stopped by tissue
b stopped by perspex
y, xray stopped by lead
Imaging in nuclear medicine
Radioactive iodine image of thyroid
Widespread availability of 99m Tc, y
Gamma camera, image y emitting radioisotopes
How do positron emission tomography machines work (PET)
Ring of detectors to count coincidental y photons released from positron releasing F18
How do single photon emission tomography machines work (SPECT)
Similar to CT, rotate y camera around patient
Positron emitting tracers
Short half lives
Cyclotron needed for production
Wide range of clinical, research applications
Oncology currently use 18FDG
Nuclear magnetic resonance
When nuclei absorb energy from a radio frequency wave applied at a specific frequency in a magnetic field
Resonance
Natural frequency of a system, most efficient energy transfer occurs here
NMR requires radio waves of the right frequency
How does NMR work?
Sample placed in strong magnetic field
Irradiated with radio waves at resonance frequency
Radiowaves reemitted by sample, signal analysed
Why is NMR good?
Standard method for chemical analysis and non destructive testing
MRI involves localising the signal with magnetic field gradients to form image
Why is the hydrogen nucleus important
H1, simplest isotope, highest NMR sensitivity, high abundance in body
MRI uses H in H2O, as a result won’t show bone
Components of an MRI machine
Magnet
Gradient coils
RF coils
Foundations for ultrasound imagine
Hydrophone invented to locate icebergs
Patent for metal defect detections
Used for human imaging
Ultrasound imaging modes
2B/B mode imaging
Obstetric ultrasound
3D imaging
How does ultrasound imaging work?
Emit short ultrasound pulse, listen to what is reflected back
Detects waves reflected from tissue structures
Tissue properties determine amount of reflected energy, absorbed by it
How to work out the distance from the transducer to the tissue?
154000 x T / 2
What is A mode scanning
1D imaging
What is M mode imaging
Repeated A scans of a moving target
Good for measuring tissue motion
What is B mode scanning
2D imaging
Move A mode transducer to different positions
Create 2D image from 1D lines
Needs beam with good lateral resolution
Developments in image display
Analogies can converter
Maximum brightness stored, doesn’t depend on exposure time
Displayed on TV at it forms
3D ultrasound technology, matrix array transducers
Phased array with elements in matrix
Steer and focus in all directions
Volume made from multiple lines
Easier to understand
Modern ultrasound systems
More compact, faster
Onboard image analysis
