Radiology Steps in radiation production Kilovoltage and voltage

Radiation Physics National Board “interest” X-ray production –Technical Term – –Thermionic emission –*Steps in X-ray production

X-ray Beam Quality The beam of radiation we use in dentistry may be described in two ways: 1.Quality = penetrating ability - energy of the photon beam 2.Quantity = amount - # of photons in beam

Voltage Determines the speed of electrons that travel from cathode to anode. When voltage is increased, the speed of the electrons is increased. When the speed of the electrons is increased, the electrons strike the target with greater force and energy. Resulting in a penetrating x-ray beam with a short wavelength. Measured in volts or kilovolts (kV’s) This is adjusted according to individual diagnostic needs of the patient.

Kilovoltage Kilovoltage is controlled by the kilovoltage peak dial, or kVp. (Only on some machines) Determines the wavelength (quality) or speed and energy of the wave. Density= overall darkness or blackness of an image. Adjustment in the kVp = a change in the density.

Kilovoltage Quality = penetrating ability kVp is the electrical force needed to move the electrons from the –cathode to the +anode kVp setting is the only factor influencing the penetrating ability (quality, power) of beam

Increased kVp - shorter wavelength, more penetrating- also more xrays produced

Decreased kVp -longer wavelength, less penetrating, fewer xrays produced

Soft xrays Hard xrays

kVp = Low contrast Greys Long scale contrast kVp = High contrast Black and white Short scale contrast

Kilovoltage Peak Rule If kVp increased by 15, decrease time by 1/2 If kVp decreased by 15, increase time by 2 5 kV rule Need to increase kVp by 5 to see a change in density