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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- 1 / 172
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Flashcards
IRMER ( ionisating radiation medical exposures amendment)
-referral criteria
-protocols an procedures
- referrer
- practioner
- operator
Referrer
- who do the request for x-ray
- must provide clinical informations
- employer can define the person
practioner
- who justifies the x-ray
- radiologist oder radiographer
operator
- many operators possible
- check the patient ID
- press the button
- maintain the equiqument
- not healthcare person nessecerily
diagnostic reference levels (DRLs)
- typical exams for standard-size patients
- set locally, but not greater than the national DRL, unless it can be justified
- DAP, screening time an radioactivity
MARS (medicines administration of radioactive substances regulations)
- similar to IRMER, but for radioactive substances
- must have a ARSAC certificate
- ARSAC is part of HSE
- ARSAC certificate for location, substances und purpose, 5 years
CT scanner 1st generation
- rotate-translate type
- increment of 1°
- 180°
CT scanner 2nd generation
-rotate-translate
-multiple detectors
CT scanner 3rd generation
-rotate-rotate-type
-360°
CT scanner 4th generation
- outer detectors are stationary
- inner tube rotate 360°
CT scanner 5th generation
- electron beam scanner
- electrons swept around a high voltage ring to produce x-rays
- no mechanical part
CT filtration
- hardening with 0,5 mm copper = 8 mm aluminium
- bow tie filter, because less tissue of body in the periphery
CT collimation
- post-patient to reduce scatter reaching the patient
CT detectors
- small for better spatial resolution
- wide dynamic range
- old: filled with gas (xenon, krypton)
- modern: with scintillant bismuth germinate
CT voxel and pixel
- voxel is 3D
- pixelis 2 D
CT number
- average attenuation of the tissue within the voxel
- Hounsfield unit
CT window
- covers 12bit range = -1024 to + 3071
- human eye can distinguish 50 grey shades
ct back projection
- reduction of blurring
- noise is amplified
CT pitch
- 1 pitch = coverage of the whole body
- increase the table movement > 1
ct pitch
table moves faster
CT image quality
-spatial resolution is high
-noise
- quantum noise (photon)
- structural noise (reconstruction)
- electric noise (scanner)
CT quantum noise
- \(noise = {1 \over\sqrt{N} }\)
- decrease by increase the number of photons like increase mAS, kV and increase the slice width
CT structural noise
- bigger voxel = more photon = less noise
- smooth kernel reduce noise and resolution
CT artefarct: photon starvation
- through the shoulder more attenuation of tissue
- increase mAs
CT artefarct: beam hardening
- beam hardening in the center
- beam more power, so less attenuated, CT number in the center is lower = dark streak
- bow-tie filter ist needed
CT ring artefarct
- failure of a single detector
CT artefarct: partial volume effect
- high contrast can be seen on more slice and are larger than they are
- reduces the visibility of low contrast structure
- reduce slice width = reduce the artifarct
CT dose
effective dose = mSv
CT dose: affecting factors
kV:
- increase kV with decrease mAs = less dose = same quality
- increase Kv without alter mAs = more dose
mAs
- increase mAs = increase dose = less noise
pitch
- doubling the pitch = half the dose
- dose : 1/pitch
Gated Cardio-CT
retropective:
- tube is always on
- high dose
prospective:
- tube is only on when the ECG shows the heart is still
- stable heart rate
- beta-blocker
- lower dose
ultrasound
- 2-20 MHz
- mechanical wave
- Air: 330 m/s
- Water 1480 m/s
- soft tissue 1540 m/s
- high stiffness = more speed (water)
- high density = less speed (bone)
ultrasound speed
c = stiffness / density = k / p
the higher the frequency, the more the attenuation
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
