Stacy Kopso, M.Ed., RT(R)(M) X-ray Production Stacy Kopso, M.Ed., RT(R)(M)

X-ray Production When the exposure button is pressed, the projectile electron collide with the atom of the anode target and loose energy X-rays are produced through two processes

Bremsstrahlung Occurs when an incident electron interacts w/ the force field of the target’s(tungsten) atomic nucleus Projectile electron undergoes three processes Slows down Changes direction Loses some of its energy

An incident electron interacts w/ the force field of the target’s (tungsten) atomic nucleus and changes direction

Bremsstrahlung The process results in the emission of a bremsstrahlung x-ray photon 85% of the xray beam consists of this interaction 1/3 of the kVp selected

Bremsstrahlung The Brem photon energy is equal to the amount of energy lost by the projectile electron Small amount of electron energy loss Low energy photon- long wavelength Large amount of electron energy loss High energy photon- short wavelength The greater the direction change, the greater the energy loss

Characteristic Radiation Projectile electron interacts with the tungsten atom by ejecting an inner shell (K)electron and ionizing the atom The K shell vacancy is filled by an outer shell electron The process of filling the K-shell vacancy results in the emission of a characteristic xray photon

Characteristic Binding energies of shells K= 69 keV(kiloelectron volt) L=12 keV M=3keV N=1keV If an L shell fills the K shell the K-Characteristic photon has an energy range of 57keV (69-12) If an M shell fills the K shell the K-Characteristic photon has an energy range of 66keV (69-3)

Characteristic Energy of the x-ray photon is equal to the difference between the binding energies of the orbital shell (k shell and one that filled vacancy) Depends on; energy level of incoming electron binding energy of electron that is knocked out shell of orbital electron that drops into vacancy

Characteristic Only K-shell (characteristic x-rays) are diagnostically useful Characteristic x-rays produced from L-shell and farther from the nucleus, possess too little energy to be diagnostically useful(skin entrance dose or absorbed by filtration)

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Beam Characteristics Beam Quality Beam Quantity Penetrating ability Energy kVp, filtration Primary factor-kVp Directly proportional to kVp High quality=hard beam (high kVp) Low quality=soft beam (low kVp) Amount/number Intensity mAs, kVp, distance, filtration Primary factor-mAs Directly proportional to mAs Squared for kVp kVp doubled-intensity increases by factor of 4 Pt dose-expressed in Roentgen

Beam Quality Penetrating ability/energy High quality=hard beam (high kVp) Low quality=soft beam (low kVp) Filtration Removes the lower energy photons making the quality higher. Does not change the energy of the beam Half value layer Filtration is measured in half-value layer Thickness of absorbing material (AL) necessary to reduce the energy of the beam to ½ its original intensity The only technical factors that affect HVL are kVp and filtration

How many half value layers will it take to reduce an x-ray beam whose intensity is 78 R/min to an intensity of less than 10R/min???? 3

Beam Quantity Amount/Intensity/Number kVp 15% rule mAs Direct although not proportional Double the intensity, increase the kVp by just 15% 60 kVp to 69 kVp mAs Directly proportional Double the intensity, double mAs 30mAs to 60 mAs

Beam Quantity Filtration Distance Increase filtration Decrease quantity Remove low energy photons Distance Increase distance=decrease in quantity Inverse Square law

Inverse Square Law Used to calculate a change in beam intensity with changes in SID The intensity of the beam is inversely proportional to the square of the distance Distance is ½ = 4x more intensity Distance is doubled = 1/4 intensity Formula I 1 /I2 = (d2 /d1 )2

Inverse Square Law An exposure taken at 40 inches yields an intensity of 200mR. What is the intensity if the distance is increased to 80inches? I 1 /I2 = (d2 /d1 )2 50mR

Direct Square Law Density maintenance Used to maintain radiographic density with changes in SID mAs 1 / mAs 2 = (SID 1 / SID2)2 A satisfactory radiograph is produced using exposure factors of 75kVp and 10mAs at a distance of 40 inches. What new mAs would be required to produce a similar density if the distance is increased to 80 inches? 40mAs

Quality or Quantity???? Directly proportional to kVp Directly proportional to mAs Amount/number Intensity Penetrating ability Energy Primary factor mAs Affected by kVp and filtration Affected by mAs, kVp, distance and filtration

X-ray beam Primary beam Remnant beam Useful radiation that consists of the xray photons directed through the xray tube window port Incident photons Remnant beam The portion of the attenuated xray beam that emerges from the patient and interacts with image receptor Exit radiation

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Emission Spectrum Graphically illustrates the x-ray beam so you can visually see the nature of the beam and the effects of different influencing factors on them

Emission Spectrum The xray beam is the result of 2 different anode target interactions Characteristic and Bremsstrahlung Characteristic photons have a discrete emission spectrum Brems have a continuous emission spectrum

Characteristic Discrete Emission Spectrum Photons are named for the shell being filled K,L,M etc Bar represents each level according to their energy Only K and L are labeled because they are the only shells with enough energy to have diagnostic value Height of bar is the number of photons

Characteristic Discrete Emission Spectrum Y-axis X-axis K characteristic photons have an energy ranges of 57keV to 69keV L characteristic photons have an energy ranges of 9keV to 12kEv

Bremsstrahlung Continuous Emission Spectrum Energy depends on strength of attraction to the nucleus Energy range of 0 to the maximum kVp selected on the control panel Most are 1/3 of the kVp selected Bell shaped graph

Bremsstrahlung Continuous Emission Spectrum 1/3 of kVp kVp selected Y-axis X-axis Bell curve for tungsten target

Combine the Two X-ray Emission Spectrum

Emission Spectrum Factors that change the appearance of the x-ray emission spectrum mA kVp Tube filtration Generator type Target material Quantity Vertical axis Quality Horizontal axis

Change in mAs Quantity changes An increase in mAs will cause the amplitude of the curve to rise (proportional to the quantity of radiation)

Change in kVp Quality & Quantity changes Increase in kVp will cause the amplitude to rise and the peak of the curve shift to the right

Added Filtration Quality & Quantity changes An increase in filtration will cause the amplitude to decrease and shift the peak of the curve to the right

Change in generator Quantity & Quality change As the efficiency of the generator type increases, so does the x-ray quantity & quality.

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