MedPhys
Physik für FCRC
Physik für FCRC
piezoelectric effect
- quartz produces electric when compressed or expand
- lose the prperties when heated
acustic impedance
- Impedance = density x speed of sound
- Z = p x c
- independant to frequency f
- large Z = more reflexion
- small Z = less reflexion
Acustic impredance
- Total reflexion at air, because Zair is 0, and the difference of Z is large.
transducer
- linear
- curvilinear
- phased
- annular
ultrasound: A-mode
- Amplitude Mode
B-Mode
- Brightness mode
ultrasound quality
spatial resolution
- high frequency = high axial resolution (along the axis of the beam)
- focus the beam, more scan lines = high lateral resolution
ultrasound: doppler effect
- louder, when the object is moving towards
- less louder, when object is moving away
power doppler
- amplitude is the amount of the red blood calls, not the velocity
- quantity of the blood flow
Doppler with colors
- red = flow towards the transducer
- blue = flow away the transducer
- turbulence = green / yellow
harmonic frequency
- transducer frequency is the the 1st
- it changes through the tissue, so the harmonic frequencies are produced
ultrasound m-mode
- motion mode
ultrasound artefarct: speckle
- many small structures
- textured appearance
ultrasound artefarct: reverberation
- strong the reflector near the surface
- series of delayed echoes
ultrasound artefarct: double reflection
- diaphragma as a mirror
ultrasound artefarct:shadowing
- bowel gas, stone, bone
ultrasound artefarct: enhancement
- cyst, bladder
ultrasound artefarct:refraction
different velocity through the tissus
at the border
ultrasound artefarct: aliasing
- caused by under sampling
- colour change, and wrapped around
ultrasound contrast agent
- air-filledd (vascular, thrombosis)
- perfluorocarbon (liver, spleen, metastase)
- gold (combined with antibodies)
Nucleus
protons and neutrons
Atomic mass (A)
protons + neutrons
Atomic number
number of protons
nuclides
same protons = same element
Isotope
same chemical properties, but different physical properties
electron orbit
K: 2
outer orbit shell
valence
determines the chemical, electrical and thermal properties of the element
ion
electrons <> protons
electron excitation
gains energy and moves to higher energy outer shell
Binding energy E and atomic number Z of
Iodine?
Barium?
Tungsten?
Lead?
energy to remove the electron from the an atom
high, as Z=atomic number is high
high for electron in the inner shell, closer to the nucleus
Binding energy = E
energy to remove an electron from the shel
E increase = atomic numbre Z increase
E increase = K shell, near to the nucleus
Electromagnetic radiation (EMR)
speed of light in vacuum
3 x 108 m/s
magnetic and electric components
wave and particle component
X-Ray
EMR from the electron
Gamma ray
from the nucleus
EMR
the wave model
f = 1 Hz = 1/s
in different media f constant----- speed changes
EMR
the particle model
photon
Wave equation
v = f x λ
velocity = frequency x wavelength
Planck-Einstein equation
E = h x f
Photon energy = Planck constant x frequency
E=h x c /λ = 1,24 /λ
photon fluence
number of photons in a slice of the beam
energy fluence
energy of all the photons in a fluence
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Cartes-fiches
Nucleus
protons and neutrons
Atomic mass (A)
protons + neutrons
Atomic number
number of protons
nuclides
same protons = same element
Isotope
same chemical properties, but different physical properties
electron orbit
K: 2
outer orbit shell
valence
determines the chemical, electrical and thermal properties of the element
ion
electrons <> protons
electron excitation
gains energy and moves to higher energy outer shell
Binding energy E and atomic number Z of
Iodine?
Barium?
Tungsten?
Lead?
energy to remove the electron from the an atom
high, as Z=atomic number is high
high for electron in the inner shell, closer to the nucleus
Binding energy = E
energy to remove an electron from the shel
E increase = atomic numbre Z increase
E increase = K shell, near to the nucleus
Electromagnetic radiation (EMR)
speed of light in vacuum
3 x 108 m/s
magnetic and electric components
wave and particle component
X-Ray
EMR from the electron
Gamma ray
from the nucleus
EMR
the wave model
f = 1 Hz = 1/s
in different media f constant----- speed changes
EMR
the particle model
photon
Wave equation
v = f x λ
velocity = frequency x wavelength
Planck-Einstein equation
E = h x f
Photon energy = Planck constant x frequency
E=h x c /λ = 1,24 /λ
photon fluence
number of photons in a slice of the beam
energy fluence
energy of all the photons in a fluence
beam intensity
energy fluence per time unit
Production of characteristic radiation
hit the inner electron
the outer electron falls down
emission of a photon with energy = binding energy inner electron - bindung energy outer electron
determined by atomic number and unaffected by tube voltage
characteristic radiation of tungsten
Z = 74
Ek = 70 keV
EL = 12 keV
Kalpha= Ek- EL = 70 -12 = 58 keV
Bremsstrahlung
80% X-ray = Bremsstrahlung
K-shell, near the nucleus
continuous spectrum
beam intensity
area under the curve
increase with the kV = increase the photon energy
increasing mA (tube current) = no shape change
increase target number = increase the photon energy
Linear attentuation coefficient (µ)
µ = 0.693 /HVL (1/m)
fractional reduction of the energy per unit thickness
depends on the density of material
increase= density increase
= atomic number increase
= photon energy decreases
Mass attentuation coefficient (mac)
mac = µ / density (cm2/g)
fractional reduction per unit mass
depends on energy and atomic number
beam hardening
become homogenous with high energy photons because low energy photon are more attenuated.
Photoelectric Absorption.
the photon completely disappears; its energy is transferred to one of the orbital electrons of the atom (K-shell).
Electron trops down from L to K-shell.
Photoelectric Absorption = Z3 / E3 (Z: atomic number; E =photon energy)
Increase with Z3
Decrease with the photon energy.
important, whenn Z is high, and the photon energy is low.
compton scatter
Photon hits the free electron in the outer shell.
new photon with lower energy and new direction, and electron with more energy.
80% in radiology are compton scatter, 20% are scattered.
important, whenn Z is low, and the photon energy is high.
scatter angle
angle between the incoming photon and the scatter photon.
0° = maximum energy for scatter photon, electrons travel 90° and has minimum energy
180° = photon backward with minimum energy, electron travel 0° forward with the maximum energy
scatter angle up = the energy of the scatter photon down
Elastic scattering (Raleigh)
incoming photon is less energic to the binding electron.
photon deflected without energy loss.
high Z and low energy.
Pair production
photonw with high energy > 1.02 MeV (2*511 keV)
nucleus = production of positron and electron
E = mc2 (m: mass, c: speed of light)
Total infiltration
at least 2,5 mm Aluminium
Filter material
Al = 1,5 mm (Z= 13)
Copper = 0.1 - 0.3 mm (Z=29)
Filtration effects
-Beam hardening
-Increase the HVL
-Reduction of the number of photon
-shift to the the right
-no change in maximum photon energy
K-edge filter
Remove both high and low energy photon.
not in mammography
Luminescence
1. Fluorescence
2.Phosphorescence
Fluorescence
The photon excites an electron into one of the many higher energy vibrational states.
Some energy is transferred into vibrational energy and then the excited electron relaxes into the ground state, releasing a photon of lower energy then the photon initially absorbed.
phosphorescence
electron from the valence band to the conduction band
stuck in the conduction band until more energy by heat or light, then fall down the valence band with emmission of light.
1. heat = lithium fluoride
2. light = barium fluorohalide
