Physical Aspects of Organs and Imaging

Hartmut Zabel

• Editorial: De Gruyter
• Año: 2017
• ISBN:
  9783110372854
• Edición: 1
• Categoría: Medizin
• Categoría: Biotechnologie in der Medizin

Medical Physics covers the applied branch of physics concerned with the application of concepts and methods of physics to diagnostics and therapeutics of human diseases. The first part, Physical and Physiological Aspects of the Body, covers those body systems that have a strong physical component, such as body mechanics, energy household, action potential, signal transmission in neurons, respiratory and circulatory system as well as visual and sound perception. The second part of this volume, Imaging Modalities without Ionizing Radiation, introduces sonography, endoscopy, and magnetic resonance imaging.

The second volume complements the imaging modalities with the use of ionizing radiation: x-ray radiography, scintigraphy, SPECT, and PET. This first part is followed by chapters on radiation treatment of tumors, in particular x-ray radiotherapy, proton and neutron radiation therapy, and brachytherapy. The last part treats aspects of diagnostics and therapeutics beyond radiology, including laser applications, multifunctional nanoparticles and prosthetics.

This first volume

- connects the basic principles of physics with the functionality of the body and with physical methods used for diagnostics and therapeutics.
- covers the first part of the entire field, including the physics of the body and imaging methods without the use of ionizing radiation.
- provides an introduction for Bachelor students to the main concepts of Medical Physics during their first semesters guiding them to further specialized and advanced literature.
- contains many questions & answers related to the content of each chapter.
- is also available as a set together with Volume 2.

Contents
Part A: Physical and physiological aspects of the body
Brief overview of body parts and functions
Body mechanics and muscles
Elastomechanics: bones and fractures
Energy household of the body
Resting potential and action potential
Signal transmission in neurons
Electrophysical aspects of the heart
The circulatory system
The respiratory system
Kidneys
Basic mechanism of vision
Sound and sound perception

Part B: Imaging modalities without ionizing radiation
Sonography
Endoscopy
Magnetic resonance imaging
Questions & answers

Part A:Physical and physiological aspects of the body

1Brief overview of body parts and functions

1.1Introduction

Body parts and functions are, as we know, controlled by chemical and biochemical processes. It may be less evident that our body also strictly follows physical principles. This becomes obvious when inspecting different parts of our body. Any movement requires forces, torques, and mechanical stability. The energy household of the body follows the principles of thermodynamics. The sensory system including hearing and sight is based on the principles of acoustics and optics, respectively. The respiratory system, blood circulation, and kidneys all obey the laws of diffusion, hydrostatics, and hydrodynamics. Signal propagation along nerve fibers can be described by electrical circuitry, etc. Part A of this book comprising Chapters 2–12 is dedicated to the physiology of some organs, sensors and systems, with special emphasis on their connection to basic physical principles. This can and will not replace textbooks on physiology but it will provide a solid background for the comprehension of the remaining Part B of Volume 1 and Parts A–C of Volume 2, dealing with imaging, radiotherapy, and prosthetics. Before starting with the kinematics of the body in Chapter 2, we briefly review the basic building blocks, some organs, and systems of the human body.

1.2Overview

1.2.1Cells

The human body consists of about 60 × 1012 cells. They form the building blocks of the body like bricks of a house. The cross section of a cell is shown in Fig. 1.1. All cells contain double-stranded helical nucleic acid chains known as deoxyribonucleic acid (DNA). Each DNA molecule contains a sequence of paired nucleobases, which read like letters of the genetic code. About 20 000 genes in the DNA encode about 2 × 106 proteins in the human body that do their daily job. They build ion channels and molecular motors, they form receptors, enzymes and hormones, they take care of oxygen transport, strengthen tissues and bones in the body, regulate water and ion concentrations, and are responsible for many more tasks. Proteins are big; some contain more than 100 000 atoms. Furthermore, they are folded up from a chain of amino acids into complex quaternary structures. So far only a few proteins have been described with atomic resolution. Although almost all cells contain the complete and identical genetic information, they specialize in different tasks. Muscle cells develop a surprising tensile force, liver cells are specialized in performing important tasks for the metabolism of food, and nerve cells can transmit electrical signals as fast as 100 m/s. This specialization and combined action of certain tasks is only possible through a high degree of self-organization and communication among the cells. Comparing cells with bricks is, after all, a gross oversimplification. When we build a complex system, then we indeed start with simple building blocks that fit together to form something more complex. In contrast, in organisms the complexity does not start at the cell level but already at the molecular level of DNA, ribosomes, lysosomes and many more. This incredible complexity organizes life. First, cells organize to form tissues: epithelial tissue, connective tissue, muscular tissue, and nervous tissue. Tissues, in turn, assemble to form organs with characteristic and distinct shapes and functions like the liver and the kidneys. Several organs work together in a system, such as the digestive system that involves ten different organs. The body contains eleven distinguishable systems: (1) cardiovascular/circulatory system; (2) respiratory system; (3) digestive system/excretory system; (4) endocrine system; (5) lymphatic system/immune system; (6) sensory system; (7) locomotor system; (8) nervous system; (9) renal system/urinary system; (10) integumentary system; (11) reproductive system. All eleven systems interact and are responsible for the life of the human body. These interactions take place under the promise of constancy in a variable environment. For instance, core body temperature, arterial blood pressure, and blood partial oxygen/carbon dioxide pressures are kept constant by an active negative feedback system, like a thermostat. This control mechanism is known as homeostatic control or homeostasis. Body temperature homeostasis is further discussed in Chapter 4.

Fig. 1.1: Schematic of a human cell. The cell membrane separates the cytoplasm from the extracellular space. The cytoplasm contains among many other parts the genetic information inside the nucleus and the mitochondria with its own genetic information, acting as a powerhouse for the cell functions. The cell membrane is a double lipid layer that is perforated by a number of ion channels for maintaining an electrical potential across the cell membrane, or rather changing it by depolarization upon a stimulus (adapted from OpenStax Anatomy and Physiology, 2016, © Creative Commons).

1.2.2Circulation

For maintaining all body functions, blood circulation is essential. No blood circulation, no life. As the name implies, blood circulation is a closed ci...