ABSTRACT
CONTENTS 1.1 Introduction ............................................................................................... 2 1.2 Computed Tomography ........................................................................... 4
1.2.1 Scout Images ................................................................................ 10 1.2.2 Axial Sequences .......................................................................... 10 1.2.3 Spiral Sequences.......................................................................... 11 1.2.4 CT Fluoroscopy ........................................................................... 14 1.2.5 Multislice CT Scanners............................................................... 14 1.2.6 Image Quality .............................................................................. 16
1.3 Magnetic Resonance Imaging ............................................................... 17 1.3.1 Signal Generation........................................................................ 19 1.3.2 Signal Detection: Relaxation ..................................................... 20 1.3.3 Longitudinal Relaxation ............................................................ 20 1.3.4 Transverse Relaxation ................................................................ 21 1.3.5 Selective Excitation ..................................................................... 21 1.3.6 Spatial Encoding ......................................................................... 22 1.3.7 Image Reconstruction ................................................................ 23
1.4 Gamma Cameras and Single Photon Emission Tomography .......... 25 1.4.1 Collimator .................................................................................... 28 1.4.2 Crystals ......................................................................................... 29 1.4.3 Photomultiplier Tubes and Other Components ..................... 29 1.4.4 Image Acquisition Modes .......................................................... 30
1.4.4.1 Planar Imaging ............................................................. 30 1.4.4.2 SPECT Imaging ............................................................ 30
1.5 Positron Emission Tomography ............................................................ 32 1.5.1 Positron Emission and Annihilation ....................................... 33 1.5.2 Coincidence Detection ............................................................... 35 1.5.3 Photon Detection and Event Registration ............................... 36 1.5.4 Axial Sampling in PET ............................................................... 37 1.5.5 Spatial Resolution in PET........................................................... 37 1.5.6 Quantization in PET ................................................................... 39 1.5.7 Normalization ............................................................................. 40 1.5.8 Attenuation Correction .............................................................. 41 1.5.9 Absolute Quantification ............................................................. 42
In this chapter, we discuss the major medical imaging modalities used in diagnostic imaging. These modalities generate an image of the body either through the detection of photons or the use of electromagnetic waves. Let us recall the dual nature of light. The duality theory asserts that light has the properties of both waves and particles. This duality is also applicable to the photons that are involved in our imaging modalities. Figure 1.1 shows the positions of these imaging modalities in the electromagnetic
1.5.10 Scan modes in PET ..................................................................... 43 1.5.11 Static Scan .................................................................................... 43 1.5.12 Dynamic Scan.............................................................................. 44
Problems ............................................................................................................ 45 References .......................................................................................................... 46
spectrum. The relation between the frequency (or wavelength) and energy of the photon is given by
E hv= (1.1) where E is the energy, h = × −4.136 10 15 eV* is the Planck’s constant, and v is the frequency. The frequency of the wave is given by v c= /λ, where c ms= −299792458 1 is the speed of the light in vacuum, and λ is the wavelength. This means that the product of the wavelength and frequency is always constant and is equal to the speed of light in vacuum. For example, the frequency and the wavelength of a 20 keV x-ray photon can be calculated using the following script:
Note that our function mipconstants returns some fundamental constants, taken from reference [1], used in physics. Any of the three characteristics of the photons can be computed using these relations. For other constants, the reader can refer to the function itself.
