01-BasicPhysics2011-UniversityofMinnesota.pdfVIP

Radiology Physics OR: “I DIDN’T SIGN UP TO LEARN THIS STUFF” ? Chris Ober, DVM, PhD, DACVR ? 7 February 2011 Just take a deep breath… Why worry about physics? ? Know what the system can give you ? Know what the system CAN’T give you ? Recognize errors and know how to correct them ? Understand the importance of radiation safety ? It’s on the test, so I might as well teach it Books to Consider ? Thrall. Textbook of Veterinary Diagnostic Radiology. 4th or 5th ed. 2002 or 2007. ? Morgan Silverman. Techniques of Veterinary Radiography. 4th ed. 1984. ? *Bushberg, Seibert, et al. The Essential Physics of Medical Imaging. 2nd ed. 2002. * Masochists only The Game Plan ? X-rays ? Generation of X-rays ? Interaction of X-rays with matter ? Accessory equipment 1st Period ? X-rays ? Generation of X-rays ? Interaction of X-rays with matter ? Accessory equipment What are X-rays? ? Type of electromagnetic radiation – Can act as wave or particle (photon) – No mass, no charge – Travel at speed of light What are X-rays? ? Shorter wavelength than visible light ? Higher energy than visible light ? High energy makes them Ionizing Radiation Ionizing Radiation ? Radiation that is capable of generating ions ? Can cause disruption of molecular bonds ? Thus important in radiation safety and radiation therapy ? Note: X-rays and gamma rays are different only in source – X: outside nucleus, interaction of highspeed particles – Gamma: within nucleus due to spontaneous decay 2nd Period ? X-rays ? Generation of X-rays ? Interaction of X-rays with matter ? Accessory equipment What We Need ? Interaction of high-speed charged particles ? Particles: electron source ? High speed: method of accelerating electrons ? Interaction: target for electrons to crash into The X-ray Tube The X-ray Tube The X-ray Tube ? Cathode – Negatively charged – Filament made of tungsten – Set into focusing cup ? Thermionic Emission – Current thru filament – Heat generated – Electrons released (boiled off) in cloud around filam