Principles of CT and MR imaging
The formation of CT images involves measurement of the X-ray transmission profile through a patient over a large number of views. Each profile is acquired by means of a fan-shaped X-ray beam that penetrates the body. The X-rays exiting the scanned patient
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Principles of CT and MR imaging Christian Bracco, Daniele Regge, Michele Stasi, Michela Gabelloni, and Emanuele Neri
Contents 8.1 Physical Principles of CT 8.1.1 Hounsfield Unit
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8.2 The CT Imaging System 8.2.1 Current Acquisition Configuration 8.2.2 Gantry Technology 8.2.3 Tube Technology 8.2.4 Detector Technology 8.2.5 Scintillators for CT 8.2.6 Photovoltaic Detector Array (PDA) 8.2.7 Anti-Scatter Grids 8.2.8 Multi Detector CT 8.2.9 Adjustable Parameters for CT Image Acquisition 8.2.10 Pitch 8.2.11 Image Reconstruction
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8.3 CT Dose Index 8.3.1 Dose in CT, CTDI, CTDIw, DLP, and SSDE
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8.4 Physical Principles of MRI 8.4.1 The Source of the MR Signal 8.4.2 Signal Formation 8.4.3 Signal Localization and Image Formation 8.4.4 Weightings and Image Contrast 8.4.5 Sequences 8.4.6 MRI Hardware 8.4.7 MR Safety
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References
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C. Bracco · M. Stasi Department of Medical Physics, Institute for Cancer research and Treatment, Candiolo, Turin, Italy D. Regge Department of Surgical Sciences, University Hospital “Città della Salute e della Scienza”, University of Turin, Turin, Italy Department of Radiology, Institute for Cancer Research and Treatment, Candiolo, Turin, Italy M. Gabelloni · E. Neri (*) Diagnostic and Interventional Radiology, Department of Translational Research and Advanced Technologies in Medicine and Surgery, University of Pisa, Pisa, Italy e-mail: [email protected]
Learning Objectives
• To understand the physical principles of interaction between X-rays and tissue • To learn the basic principles of image formation in X-ray computed tomography • To learn the basic principle of radiation dose estimation and measurements • To learn the basic principles of MRI: magnetic field, sequences, signal parameters, and coils • To learn the safety risks in MRI
© Springer Nature Switzerland AG 2019 D. Volterrani et al. (eds.), Nuclear Medicine Textbook, https://doi.org/10.1007/978-3-319-95564-3_8
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Physical Principles of CT
substances except water and air might show variations in HU values when they are evaluated at different tube voltages. The formation of CT images involves measurement of the Usually, for each tube voltage, the CT vendors carry out an X-ray transmission profile through a patient over a large adequate calibration of the HU scale by acquiring images of number of views. Each profile is acquired by means of a fan- air- and water-filled phantoms. shaped X-ray beam that penetrates the body. The X-rays exiting the scanned patient’s body are recorded by a detector arc, generally consisting of 800–1000 detector elements, Key Learning Points referred to as a detector row. Each projection of detector’s • The image signal relies on the photoelectric effect, record (transmission profile) is a view at one position (angle) whereas Compton scatter degrades the image
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