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BioMedima - Introduction to imaging modalities
- 1. Introduction to Imaging Modalities Easy resources in biomedical imaging
- 2. A biomedical image is the computerised result of an interaction between an energetic wave (radiation) and biological tissues. The basic biomedical imaging experiment is achieved in three steps: 1) an energetic wave is emitted, aiming at a subject 3) output waves are detected and processed into images 2) input waves are modified when interacting with subject’s tissues The information about subject’s internal structures resides in the different properties between entering waves and waves exiting the subject. By comparing input and output waves, features of traversed organs can be calculated and displayed. Depending on their properties (energy, frequency, wavelength...), waves will interact differently with biological tissues. Characteristics and output images of imaging systems are directly linked to the type of waves used to image the subject. Two types of energetic waves are used in biomedical imaging: - sound waves or compression waves (ultrasound imaging) - electromagnetic waves for all other modalities Authors: C. Berger The imaging experiment Imaging modalities 2010
- 3. Infra-sounds Acoustic sounds 17 10-2 10-4 10-6 20 2x104 2x106 2x108 Frequency (Hz): Wavelength (meters): 10-7 2x109 Hyper-sounds Infrasonic Sonic Ultrasonic Hypersonic { Medical diagnostic and therapy Sound waves are not electromagnetic waves but compression waves.They need a medium to propagate and can not spread in vacuum. Extension CompressionCompression Compression A vibrating system transmits vibrations to biological tissues in contact with it. Vibrations propagate within tissues being alternatively compressed and extended. Ultra-sounds Extension Tissues Authors: C. Berger Sound waves Imaging modalities 2010
- 4. Electromagnetic waves are energetic radiations composed by photons that have both particle (photons) and undulatory (wave) properties. Electromagnetic waves are composed by an electric and a magnetic fields that oscillate perpendicularly to each other. The wave propagates in a direction perpendicular to both fields. Photons Electromagnetic waves can travel through vacuum and matter. When traveling through biological tissues: - energy carried by electromagnetic waves may be transferred to atoms with which it interacts - the sped of electromagnetic waves, which is the same as the speed of light, slows down slightly P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P PP P P P P P P P P P P P P P P P P P P P P P P P P P P P Electric field Magnetic field Propagation direction 2010Authors: C. Berger Electromagnetic waves Imaging modalities 2010
- 5. Authors: C. Berger The electromagnetic spectrum Imaging modalities Wavelength (meters): Visible spectrum: { Radio 103 3x107 Microwave 10-2 3x1010 Infrared 10-5 3x1013 Visible 10-6 3x1014 Ultraviolet 10-8 3x1016 Xray 10-10 3x1018 Gamma ray 10-12 3x1020 700 nm 400 nm Frequency (Hz): Electromagnetic waves are classified according to their frequency. 2010