X-RAY PRODUCTION

• BREMSTRAHLUNG RADIATION

• CHARACTERISTIC RADIATION

MAXIMUM ENERGY OF AN X-RAY IN THE BEAM

kVp OF OPERATIONkVp OF OPERATION

kVkVpeakpeak

ONE PHOTON ENERGY

keV

kilo-electron-volt

GREATEST # OF PHOTONS IS EMITTED WITH ENERGY:

APPROX. 1/3 OF MAX PHOTON ENERGY

FOUR PRINCIPAL FACTORS INFLUENCING THE SHAPE OF AN X-RAY 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

CURRENTINTENSITY

ENERGY – NO CHANGE

2 * mA = 2 * number of photons4 * mA = 4 * number of photons

Tube voltage (kVp) CHANGE

kVp

INTENSITY

ENERGY –

15% INCREASE OF KVP = 2 * mAs

FILTRATION CHANGE

FILTRATION

INTENSITY

ENERGY –

VOLTAGE WAVEFORM CHANGE

VOLTAGE WAVEFORM

INTENSITY

ENERGY

PATIENT DOSE

SINGLE PHASE THREE PHASE>>

RADIOLOGIC QUANTITIES SI UNITS

• EXPOSURE ---AIR KERMA (Gya)

• ABSORBED DOSE---GRAY (Gyt)

• EFFECTIVE DOSE---SEIVERT (Sv)

• RADIOACTIVITY---BECQUEREL (Bq)

RADIOLOGIC QUANTITIES CUSTOMARY UNITS

• EXPOSURE ---ROENTGEN (R)

• ABSORBED DOSE---rad (rad)

• EFFECTIVE DOSE---rem (rem)

• RADIOACTIVITY---curie

EXPOSURE ( INTENSITY)THE TOTAL ELECTRICAL CHARGE PER UNIT MASS THAT X-RAY AND GAMMA RAY PHOTONS GENERATE IN DRY AIR.

                  

1R=2.58 x 10-4 C/kg

1 AIR KERMA=100R

ABSORBED DOSETHE AMOUNT OF ENERGY PER UNIT MASS ABSORBED BY THE IRRADIATED OBJECT

rad= RADIATION ABSORBED DOSE

1 GRAY=100 rad

EFFECTIVE DOSEPROVIDES A MEASURE OF THE OVERALL RISK OF EXPOSURE TO IONIZING RADIATION. UNIT OF OCCUPATIONAL EXPOSURE DOSE.

1 Sv = 100 rem

The SI derived unit of activity, usually meaning radioactivity. "Radioactivity" is caused when atoms disintegrate, ejecting energetic particles

RADIOACTIVITY

The SI derived unit of activity, usually meaning radioactivity. "Radioactivity" is caused when atoms disintegrate, ejecting energetic particles. One becquerel is the radiation caused by one disintegration per secondThe unit is named for a French physicist, Antoine-Henri Becquerel (1852-1908), the discoverer of radioactivity

One curie was originally defined as the radioactivity of one gram of pure radium. In 1953 scientists agreed that the curie would represent exactly 3.7 x 1010 atomic disintegrations per secondThe unit is named for Pierre and Marie Curie, the discoverers of radium and polonium.