year 4 day 1 - sylabus, IV rok, IV rok CM UMK, Radiologia, 2014-15

//-->.pos {position:absolute; z-index: 0; left: 0px; top: 0px;}10/14/2012Day 1Dr. Zbigniew Serafin, MD, PhDserafin@cm.umk.plDiagnostic imagingradiographyfluoroscopyinvasive angiographyCTMRIultrasoundnuclear imaging (scintigraphy, PET, SPECT)coronarography, ventriculography, electrophysiology,echocardiographymolecular imagingoptical iamginginterventional radiology2organ-basedapproachmodality-basedapproachneuroimagingcardiovascular imagingMSK imagingGI imaginguroimagingrespiratory imagingradiographyCTMRIultrasoundinterventionalnuclear imaging3110/14/20121895 – invention of X-rays by W.K. Roentgen1895 – first X-ray of the human1896 – first radiation in juries1896 – Becquerel discovers radioactivity1905 – the first English book on Chest Radiography is published1918 – Eastman introduces radiographic film1934 – Joliot and Curie discover artificial radionuclides1950's – development of the image intensifier and X-ray television1956 – medical use of ultrasound starts in Poland.1962 – emission reconstruction tomography (later SPECT and PET)1972 – invention of CT by Hounsfield at EMI1977 – first human MRI images.1980's – Fuji develops CR technology.1984 – MRI cleared for commercial use by FDA4November 8, 1895Roentgen’s experimental apparatus (Crookes tube)that led to the discovery of the new radiation.Roentgen demonstrated that the radiation wasnot due to charged particles, but due to an as yetunknown source, hence “x” radiation or “x-rays.”“x-5http://www.learningradiology.com6210/14/2012Bertha Roentgen (1895)„Über eine neue Art von Strahlen”http://www.learningradiology.com7Radiationemission or emission and propagationof energy in the form of particles orwaves.Ionizing radiationradiation having sufficient energy toionize an atom8Interaction of X-rays with matter = sources of attenuationThe attenuation that results due to the interaction between penetratingradiation and matter is not a simple process. A single interaction eventbetween a primary x-ray photon and a particle of matter does not usuallyresult in the photon changing to some other form of energy and effectivelydisappearing. Several interaction events are usually involved and the totalattenuation is the sum of the attenuation due to different types ofinteractions.These interactions includethe photoelectric effect, scattering,and pair production9310/14/2012Photoelectricabsorption of x-rays occurs when the x-ray photon isabsorbed, resulting in the ejection of electrons from the outer shell of theatom, and hence the ionization of the atom. Subsequently, the ionizedatom returns to the neutral state with the emission of an x-raycharacteristic of the atom. This subsequent emission of lower energyphotons is generally absorbed and does not contribute to (or hinder) theimage making process. Photoelectron absorption is the dominant processfor x-ray absorption up to energies of about 500 KeV. Photoelectronabsorption is also dominant for atoms of high atomic numbers.Photoelectric effect is a low-energy phenomenon and is themost important for imageacquisition and radiation safety10Compton scatteringoccurs when the incident x-ray photon is deflectedfrom its original path by an interaction with an electron. The electron gainsenergy and is ejected from its orbital position. The x-ray photon losesenergy due to the interaction but continues to travel through the materialalong an altered path. Since the scattered x-ray photon has less energy, it,therefore, has a longer wavelength than the incident photon. The event isalso known as incoherent scattering because the photon energy changeresulting from an interaction is not always orderly and consistent.Compton scattering is the mostprobable interaction of gammarays and high energy X-rays withatoms in living beings. Thephenomenon responds for theimage noise and health hazardrelated to imaging.11Thomson scattering(Rayleigh, coherent, or classical scattering), occurswhen the x-ray photon interacts with the whole atom so that the photon isscattered with no change in internal energy to the scattering atom, nor tothe x-ray photon. Thomson scattering is never more than a minorcontributor to the absorption coefficient. The scattering occurs without theloss of energy. Scattering is mainly in the forward direction.Thomson scattering is related to 5-10%of all tissue interactions with X-rays.12410/14/2012Pair productioncan occur when the x-ray photon energy is greater than1.02 MeV, but really only becomes significant at energies around 10 MeV.Pair production occurs when an electron and positron are created with theannihilation of the x-ray photon. Positrons are very short lived anddisappear (positron annihilation) with the formation of two photons of 0.51MeV energy. Pair production is of particular importance when high-energyphotons pass through materials of a high atomic number.Pair production is used in PETimaging.13X-rays are produced when energetic electrons strike a metal target. The X-ray sourceconsists of an evacuated tube containing a cathode, from which the electrons are emitted,and an anode, which supports the target material where the X-rays are produced. Onlyabout 1 per cent of the energy used is emitted as X-rays – the remainder is dissipated asheat in the anode. In most systems the anode is rotated so that the electrons strike only asmall portion at any one time and the rest of the anode can cool. The X-rays are emittedfrom the tube via a radio-translucent exit window.Basic X-ray productionelectron source – cathodetarget – anodeevacuated path for the e-s totravel through – x-ray tube insertexternal energy source toaccelerate the e-s – generator14Electron interactions with the anode produce:1. Heat – the kinetic energy (KE) of the electron deposits its energy in theform of heat (~99%)2. X-rays productionBremsstrahlung– continuous energy spectrumcharacteristic X-rays – discrete energies155

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