ABSTRACT
X-rays and gamma rays are carried by wave packets called photons and dier only by the source of radiation. X-rays are created by the interaction of an energetic electron with a target surface, and gamma rays are created by certain types of nuclear disintegrations. ey are dened as ionizing radiation because they can cause a breaking of chemical bonds of molecules or the loss of electrons in single atoms. ey are a form of electromagnetic radiation, similar to light and radio waves except that they are of shorter wavelength and higher energy than light photons or radio wave photons. e energy of a photon is related to wavelength by νλ = c, where ν is the frequency in Hz, λ is the wavelength in meters, and c is the velocity of light in m/s. e energy of a single photon is E = hν, where E is the energy in joules, J, and h is Planck’s constant of 6.63 × 10−34 Js, where s is the time in seconds. e charge of an electron is 1.60 × 10−19 C, where C is in coulombs. Combining these relationships, we nd that
18.5.4 Scintillator Diode 465 18.5.5 ermoluminescent Detector 466
18.6 Basic Clinical X-Ray System 466 18.6.1 X-Ray-Generating Systems 466 18.6.2 Mechanical Components 466 18.6.3 Automatic Exposure Control 467
18.7 Fluoroscopy 467 18.7.1 Intensier/TV 467 18.7.2 Image Storage: Digital Subtraction Angiography 468 18.7.3 Image and Information Communication Systems 468
18.8 Computed Tomography 468 18.8.1 Simple Tomography 468 18.8.2 Picture of the Universe 469 18.8.3 Fan Beams and Detector Arrays 469 18.8.4 Spot Filming 469 18.8.5 Contrast Agents 470
18.9 Magnetic Resonance Imaging 471 18.9.1 Nuclear Magnetic Resonance 471 18.9.2 Image Generation 471
18.10 Ultrasound 472 18.10.1 Acoustic Impedance and Reection 472 18.10.2 Ultrasonic Imaging 473
18.11 Quality Assurance 473 18.11.1 Need for Quality Assurance 473 18.11.2 Phantoms and Test Objects 473 18.11.3 Test Instruments and Test Tools 474 18.11.4 Test Procedures 474
References 475
the energy of a photon accelerated through an electric eld of e volts can also be dened in electron volts, eV, where 1 eV = 1.60 × 10−19 J and the energy and wavelength are related, E = hc/λ J or E = hc/λ (1.60 × 10−19 eV), or, more simply, in the units usually encountered, E = 1.240 keV/λ where λ is in nm (10−9 m).
