![]() Scattered photons can travel back towards the tube, pass through the patient and hit the detector from any odd angle, or scatter again withinĮach time a photon ejects an electron - ionizes an atom - this creates free radicals that can damage DNA and wreak havoc. The photon then scatters in a different direction with a bit less energy, and the free electron goesĪbout doing damage. Ionizes an electron but does not use up all of its energy. The second major effect is Compton (incoherent) scatter, where a photon hits an atom and ![]() Move around and ionize neighboring atoms, there are no scatter photons. The first is the photoelectric effect, where a photon uses up all of its energy to eject an electron from an atom while the electron will Again, without going into the gory detail here, we need to know that there are two major ways in which diagnostic x-rays Note that the average energy of the beam is much less than the peak energy a rule of thumb is that it would be 1/3 of the maximum energy. Because of tube filtration, the very low energy photons are removed and do not reach the patient. Each element will have one or a couple relevant characteristic x-rays, which are produced at a higher rate compared to theīremsstrahlung at any frequency (but with a very narrow peak). Characteristic x-rays are due to electron ejection events the hole is filled by another electron, which emitsĪn x-ray at a specific frequency. The most photons produced occurs at ~0 keVĪnd almost no photons are produced at keV = kV. Bremsstrahlung radiation is a continuum with maximal energy at a keV = tube kV. While I will not go into detail here, know that there are two contributions to the x-ray spectrum produced by the tube: Bremsstrahlung radiationĪnd characteristic x-rays. Additionally, higher velocity electrons will produce more photons, Kilovolts) affects the velocity of the electrons as they strike the anode this affects the energy of the photons The voltage across the x-ray tube (measured in and often referred to as kV, or MA will increase the number of electrons that strike the anode, with a consequent linear increase in the number Milliamperes) across the tube determines how many electrons are released to strike the anode. ![]() The current (measured in and often referred to as mA, or There are two primary means by which we can change the x-ray beam produced by the tube:Īltering the current (mA) and altering the volage (kV). High-energy photons (produced by bombarding an metallic anode with electrons). Muscle, bone, and iodinated contrast - we need to understand how x-rays interact with matter. In order to understand the means by which we see contrast in an x-ray image - i.e. This contrast does not take into account the effects of scatter. Right: Simulated image contrast with fat, muscle, and iodinated contrast in a vessel. Middle: X-ray intensity passing through the patient (white = strongest radiation, black = weakest). Orange, transmitted beam spectrum (scaled to have the same intensity). Left: X-ray spectra Blue, Tube beam spectrum. Your browser does not support the HTML Canvas. Soft tissue Transmission % (Attenuation %) Of a tungsten anode with 2.5 mm Al filtration. The x-ray tube is a (very) gross approximation Is a first-order approximation and does not take into account secondary scatter events. Dose is the dose to the patient for the same image noise note that this dose Air kerma (K ar) reflects the change in photon flux necessary to obtain the sameĮxposure (image noise). ![]() You can also alter the body part thickness. This simulator illustrates the effects of changing tube voltage in fluoroscopy or radiography on patientĭose and image contrast. | Mammography | Things to Remember | Go Home X-Ray Interaction with Matter | Attenuation and Dose | Tissue Contrast ![]()
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