X-RAY EMISSION
SPECTRUM
X-RAY PRODUCTION
BREMSTRAHLUNG RADIATION
CHARACTERISTIC RADIATION
BREMS
BREMS EMISSIONCONTINUOUS
CHARACTERISTIC EMISSIONDISCRETE (EACH)
GREATEST # OF
PHOTONS IS EMITTED
WITH ENERGY:
APPROX. 1/3 OF MAX
PHOTON ENERGY
FOUR PRINCIPAL FACTORS
INFLUENCING THE SHAPE OF AN XRAY EMISSION SPECTRUM:
ELCTRONS TRAVELING FROM CATHODE TO
ANODE HAVE DIFFERENT ENERGIES– NOT JUST
PEAK ENERGY
THE TARGET IS RELATIVELY THICK– CAUSING
MULTIPLE INTERACTIONS.
LOW ENERGY X-RAYS ARE MORE LIKELY
ABSORBED IN THE TARGET
EXTERNAL FILTRATION REMOVES LOW
ENERGY PHOTONS
FACTORS AFFECTING THE X-RAY
EMISSION SPECTRUM
TUBE CURRENT
TUBE VOLTAGE
ADDED FILTRATION
TARGET MATERIAL
VOLTAGE WAVEFORM
CURRENT CHANGE
INTENSITY
CURRENT
ENERGY – NO CHANGE
2 * mA = 2 * number of photons
4 * mA = 4 * number of photons
mAs DOES NOT AFFECT
ENERGY OF THE X-RAYS
PENETRATING POWER OF THE XRAY BEAM
SPEED OF THE X-RAY PHOTONS!!!!
Why changing
mA or time
Avoiding motion – mA
time
Pediatric technique modification
Reducing noise - mAs
NOISE
MOTION
Tube voltage (kVp)
CHANGE
INTENSITY kVp
ENERGY –
15% INCREASE OF KVP = 2 * mAs
kVp AFFECTS:
ENERGY OF THE X-RAYS
PENETRATING POWER OF THE XRAY BEAM
INTENSITY ( NUMBER) OF X-RAY
PHOTONS
IT DOES NOT CHANGE THE SPEED
OF THE X-RAY PHOTONS!!!!
kVp IN CT
80-140
TOO LOW – NOISE
(NOT ENOUGH PENETRATION OF THE PATIENT )
PHOTON STARVATION!!!!!
FILTRATION CHANGE
INTENSITY
FILTRATION
ENERGY –
FILTRATION AFFECTS:
AVERAGE ENERGY OF THE X-RAY BEAM
PENETRATING POWER OF THE X-RAY
BEAM
INTENSITY ( NUMBER) OF X-RAY
PHOTONS
IT DOES NOT CHANGE THE SPEED OF
THE X-RAY PHOTONS!!!!
FILTRATION MATERIAL
ALUMINIUM ( SPECIAL FILTER IN CT)
BOWTIE
TO MAKE THE BEAM HARDER AND
MORE MONOENERGETIC
TARGET CHANGE
INTENSITY
ENERGY
TARGET MATERIAL
Z#
CHARACTERISTIC
RADIATION
CHANGE
TARGET MATERIAL
COMPOSITION IN CT
TUNGSTEN + RHENIUM
VOLTAGE WAVEFORM
CHANGE
INTENSITY
VOLTAGE WAVEFORM
ENERGY
OPERATION ON 3-PHASE EQUIPMENT = 12% * SINGLE PHASE
PATIENT DOSE
SINGLE PHASE
>
THREE PHASE