Zabel Physical Aspects of Diagnostics

2. completely revised Auflage 2023
ISBN: 978-3-11-075712-5
Verlag: De Gruyter
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, Band Volume 2, 444 Seiten

Reihe: Medical Physics

The updated edition of the second of three volumes on Medical Physics presents modern physical methods for medical diagnostics. It provides a solid background on imaging techniques that use non-ionizing probes (ultrasound, endoscopy including CLE and OCT, MRI) and imaging techniques that use ionizing radiation (X-ray radiography, CT, SPECT, PET). Radiation sources, interactions of radiation with matter and radiation protection for x-rays, -rays, protons and neutrons are presented. Some of these topics are also relevant to the therapeutic applications presented in Volume 3. NEW: highlighted boxes emphasize specifi c topics; math boxes explain more advanced mathematical issues; each chapter concludes with a summary of the key concepts, questions, a self-assessment of the acquired competence and exercises. The appendix provides answers to questions and solutions to exercises.

Zielgruppe

R&D laboratories in bio-medical engineering, researchers and stud

Autoren/Hrsg.

Zabel, Hartmut

Fachgebiete

• Medizin | Veterinärmedizin Medizin | Public Health | Pharmazie | Zahnmedizin Klinische und Innere Medizin Medizinische Diagnose und Diagnostik
• Technische Wissenschaften Sonstige Technologien | Angewandte Technik Medizintechnik, Biomedizintechnik
• Medizin | Veterinärmedizin Medizin | Public Health | Pharmazie | Zahnmedizin Medizin, Gesundheitswesen Medizintechnik, Biomedizintechnik, Medizinische Werkstoffe
• Naturwissenschaften Physik Angewandte Physik Medizinische Physik

Leseproben

Part A: Diagnostics without ionizing radiation
1 Sonography
Physical parameters of sound and ultrasound Sound velocity in air 330 m/s Sound velocity in water 1500 m/s Sound velocity in tissue 1540 m/s Sound velocity in bones 3600 m/s Typical ultrasound frequency 10 MHz Typical ultrasound wavelength 0.5 mm Typical pulse repeat frequencies 1–5 kHz Typical ultrasound half-value thickness in tissue 4 cm Typical lateral resolution 1 mm Typical axial resolution 0.5 mm Typical frame rate 20–30 Hz Typical power deposited 50 mW Near field at 1 MHz 35 mm 1.1 Introduction and overview
Sonography works with ultrasound waves. Medical sonography is an imaging modality that uses ultrasound (US) for taking static images of organs and tissues, dynamic images of heart and lung movement, and kinetic images of blood flow. A well-known and common example of sonography is imaging fetuses as part of prenatal checkups. Sonography is not limited to medicine. Many other fields use US techniques such as submarine navigation, seafloor mapping, food control, security screening, surface cleaning, nondestructive material testing, and ultrasonic welding of plastics. US imaging is much more practical to handle by a physician than any radiation-based imaging modality. It can be applied locally at the bedside or the site of an accident and does not require special safety procedures for the patient or the examining staff. Direct communication with the patient is possible during the examination, which is a significant advantage compared to other imaging modalities such as magnetic resonance imaging (MRI), computed tomography (CT), or positron emission tomography. Conversely, conventional US images have lower resolution and require considerable experience to interpret them correctly for useful diagnostics. US imaging for medical diagnostics are mainly in the following areas: Cardiovascular system Abdominal organs Urology/prostate Obstetrics/gynecology Ophthalmology Mammography After discovering the piezoelectric effect by Paul-Jacques Curie1 and Pierre Curie2 in 1880, Langevin3 first used it to produce ultrasonic waves, mainly for industrial and military applications. It was not until the 1940s to 1950s of the twentieth century that US was applied for medical investigations. In the 1960s, the first handheld contact B-mode scanner was produced and commercialized. The basic properties and terms of sound waves are presented and defined in Section 12.2 of Volume 1: pressure amplitude, sound velocity, particle velocity, acoustic impedance, sound intensity, reflection, and transmission at interfaces. It is recommended to refresh these terms before continuing with the following discussions. Table 1.1 reviews the most important relationships. The frequencies used for sonography are much beyond audible sound, i.e., more than 20 kHz. In fact, most sonographic systems use frequencies in the range of 2–20 MHz. Although these have much higher frequencies than considered in Chapter 12 of Volume 1, the physics of sound waves is the same. Tab. 1.1:Review of important relationships in sonography. Sound velocity vs=?k=B? Wave amplitude ?0=u0/? Pressure amplitude p0=-B?0k Acoustic impedance Z=?vs Particle velocity amplitude u0=p0/Z Time average intensity =12Zu02=12p02Z 1.2 Ultrasound transducer
1.2.1 Piezoelectric effect For generating and detecting US waves, a piezoelectric head is used, also called a transducer. In general, transducers are devices that convert one form of energy into another. In the present case, US transducers convert electrical energy into vibrational energy of a crystal lattice using the piezoelectric effect. The exploitation of the piezoelectric effect requires a single crystal with appropriate properties. Piezoelectric crystals are ionic and insulating materials with high electrical polarizability that is strongly coupled to the crystal lattice. Mechanical compressive or tensile strain generates electrical potentials, and vice versa, electric potentials are converted into elastic strain. In either case, a polarization of electric dipole moments in the crystal is induced via strain or electrical potential. The direct piezoelectrical effect relates the polarization P of these electric dipole moments to the stress s applied, as illustrated in Fig. 1.1: Fig. 1.1: Working principle of the direct piezoelectric effect. Application of compressive or tensile stress induces an electric polarization and a voltage change. Conversely, the application of a voltage changes the length of the piezoelectric crystal. (1.1)P=g·s, where g is the piezoelectric coefficient with the unit g=m/V. The converse piezoelectric effect relates the length change ?l of the crystal to the applied voltage change ?U: (1.2)?l=g·?U Note that the expansion of the crystal does not depend on its size but only on the voltage applied. The magnitude of the piezoelectric coefficient g is on the order of 500 pC/N or 0.5 nm/V. The piezoelectric coefficient  g is actually a tensor, but for simplicity, we keep it here as a scalar. A more complete discussion can be found in the review [1]. The piezoelectric transduction can be utilized in a static or dynamic mode up to high frequencies. Piezoelectric crystals have numerous applications in physics and technology as actuators, sensors, and for nano-positioning. For instance, the sensing head of scanning tunneling microscopes and atomic force microscopes is driven by piezoelectric crystals. What are piezoelectric materials made of? There is a large variety of piezoelectric materials [1, 2]. The most common ones are crystals of insulating ceramic materials, which lack inversion symmetry. The best-known example is the piezoelectric compound PbTiO3 (short notation, PT) or the Zr-doped version Pb(Zr1–xTix)O3 (short notation, PZT). The movement of Zr4+/Ti4+ ions in and out of the oxygen plane (see Fig. 1.2) by application of an electrical field or by stress induces an electrical dipole moment. Therefore, these piezoelectric materials can either be used as actuators by applying a voltage or as...

Über Autor(innen)

Hartmut Zabel received his doctorate in 1978 from the LM University of Munich in the field of physics on a topic in condensed matter physics. He then spent a year as a postdoctoral fellow at the University of Houston, Texas, and joined the faculty of the University of Illinois at Urbana-Champaign in 1979 as Assistant Professor, where he was promoted to Associate Professor in 1983 and Full Professor of Physics in 1986. In 1989 he received a call to the Ruhr University Bochum and held the chair for experimental physics/condensed matter physics from 1989 to 2012. He maintained his connection to the University of Illinois as Adjunct Professor of Physics. After his retirement in 2012, he was first a Senior Professor at the Ruhr University and from 2014 to 2018 Distinguished Guest Professor at the Johann Gutenberg University in Mainz. In addition, he was a guest researcher at various universities and institutions, i.a. at Brookhaven National Laboratory (USA), Risø National Laboratory (Denmark), University of Kyoto, National Institute of Science and Technology, Gaithersburg-Washington, KTH Stockholm, and Uppsala University (Sweden). He was also member and chairperson of various scientific committees and advisory bodies, including those at the Paul Scherrer Institute in Switzerland, the Institut Laue-Langevin (Grenoble, France), Argonne National Laboratory, and the Helmholtz Center Berlin. In 1996 he was elected a Fellow of the American Physical Society, in 2001 he received an honorary doctorate from the KTH in Stockholm, In addition to his scientific work at the University of Illinois and the Ruhr University Bochum with over 500 publications in peer-reviewed scientific journals on the structure, dynamics, magnetism and superconductivity of solids, he was supervisor and co-supervisor of more than 50 doctoral students in Urbana, Bochum and Mainz, organizer and co -organizer of numerous international workshops and conferences, editor and co-editor of five books, and guest lecturer at many summer schools in Europe. i.a. he was a guest lecturer in the European Graduate School "HERCULES" in Grenoble for the last 30 years, lecturing on the topic of scattering experiments with synchrotron radiation and neutrons. At the beginning of 2000, the medical department at the Ruhr University Bochum developed a new study concept based on the model of the University Hospital Charité in Berlin: problem-oriented learning (POL). As a representative of the physics department, Hartmut Zabel was involved in the curriculum development. In addition to the standard physics course for medical students, he also supervised the physics-related seminars in the POL teaching format. Finally, he developed a new lecture series on "Medical Physics" for physics students and initiated a master course "Medical Physics" at the Ruhr University Bochum, which was later established and certified.