Medical Physics Lecture 1 & 2 PDF

Medical physics I Al-Karkh University of science Lecture 1 & 2 Medical Physics: Medical Physics is defined as the application of physics to the needs of medicine The field of medical physics overlaps the two very large fi...

Medical physics I Al-Karkh University of science Lecture 1 & 2 Medical Physics: Medical Physics is defined as the application of physics to the needs of medicine The field of medical physics overlaps the two very large fields of medicine and physics. The term medical physics refers to two major areas: - 1. The applications of physics to the function of the human body in health and disease. 2. The applications of physics in the practice of medicine. The first of these could be called the physics of physiology; the second includes such things as the physics of the stethoscope, the tapping of the chest (percussion), and the medical applications of lasers, ultrasound, radiation, and so forth. The word physical appears in a number of medical contexts. Only a generation ago in England a professor of physics was actually a professor of medicine. The words physicist and physician have a common root in the Greek word physiké (science of nature). The branch of medicine referred to as physical medicine deals with the diagnosis and treatment of disease and injury by means of physical agents such as manipulation, massage, exercise, heat, and water. Physical therapy is the treatment of disease or bodily weakness by physical means such as massage and gymnastic rather than by drugs. The field of medical physics has several subdivisions: - 1. Most medical physicists in the United States work in the field of radiological physics. This involves the applications of physics to radiological problems page1 Assistant prof. Dr. Ashraf.M. Alattar Medical physics I Al-Karkh University of science and includes the use of radiation in the diagnosis and treatment of disease as well as the use of radionuclides in medicine (nuclear medicine). 2. Another major subdivision of medical physics involves radiation protection of patients, workers, and the general public. In the United States this field is often called health physics. Health physics also includes radiation protection outside of the hospital such as around nuclear power plants and in industry. 3. Very often an applied field of physics is called engineering. Thus, medical physics could be called medical engineering. However, for practical purposes if you meet an individual who refers to himself as a medical physicist it is highly probable that he is working in the area of radiological physics; a person who refers to himself as a medical engineer or biomedical engineer is likely to be working on medical instrumentation, usually of an electronic nature. In addition, the medical physicist usually has a bachelor's degree in physics, while the medical engineer usually has a bachelor's degree in some field of engineering-usually electrical engineering. 4. In some areas, such as the applications of ultrasound in medicine and the use of computers in medicine, you are likely to find medical physicists and medical engineers in nearly equal numbers. (The word medical is sometimes replaced with the word clinical if the job is closely connected with patient problems in hospitals, i.e., clinical engineering or clinical physics). 5. Although the terms medical engineering and biomedical engineering are essentially synonymous, the word bioengineering has a much broader meaning. Bioengineering involves the application of any engineering to any biological area. Bioengineering includes medical engineering as an important category, but if also includes other fields such as agricultural engineering. Designing cow barns and manure spreaders are bioengineering problems! Aims of the Medical physics page2 Assistant prof. Dr. Ashraf.M. Alattar Medical physics I Al-Karkh University of science Application of the concepts and methods of physics to understanding the function of human body in health and disease 1.Physics of the body is to understanding physical aspect of the body such as ; forces on and in the body, work, energy, power of the body, heat ,blood flow, respiration, electricity, circulation and hearing. 2. Application of physics in medicine Medical physics Techniques are used for i. Diagnostic: Stethoscope Manometer (blood pressure) Sphygmomanometer Electrocardiograph(ECG), X-Ray, Electroencephalograph(EEG), Electromyography (EMG), thyroid function using I¹³¹ Computer tomography (CT scan ), Ultrasound, tuning Fork, Magnetic Resonance Imaging (MRI), Flow meter, Spirometer to study the function lungs, Audiometer, Optics, Laser, Gamma camera to study the function of kidney, liver, and lungs. ii. Therapy Radiotherapy Cobalt sixty( Co sixty ) High voltage page3 Assistant prof. Dr. Ashraf.M. Alattar Medical physics I Al-Karkh University of science Ultrasound infrared Radio frequency Heating Laser iii. Patient monitoring ECG, spirometer, blood pressure, and thermometer. Forces on and in the Body Medical physics: Medical physics (also called biomedical physics) applied physics in medicine is, generally speaking, the application of physics concepts, theories and methods to medicine or healthcare. Medical Physicists are often found in the following healthcare specialties: diagnostic and intervention radiology, nuclear medicine, and radiation oncology. Forces on and in the Body: Forces Fundamental Forces Gravitational force: Between objects Electromagnetic forces: Between electric charges page4 Assistant prof. Dr. Ashraf.M. Alattar Medical physics I Al-Karkh University of science Nuclear force: Between subatomic particles Weak forces: Arise in certain radioactive decay processes Note: These are all field forces. A force is that which causes an acceleration. Formulated by Sir Isaac Newton (1642 –1727) Classes of Forces Contact forces involve physical contact between two objects. Examples a, b, c Field forces act through empty space. The force controls all motion in the world, the important force in the body is the muscular forces that cause the blood to circulate and the lungs to take in air and other. The physicists consider the very fundamental forces described as: Gravitational force Electrical force Nuclear force (strong and weaker nuclear force) Only the gravitational and electrical forces are importance in our study of the forces affecting the human body. The electrical force important at molecular and cellular levels, e.g. affecting the binding together of our bones and controlling the contraction of our muscles. Gravitational force, though very much weaker than the electrical force. page5 Assistant prof. Dr. Ashraf.M. Alattar Medical physics I Al-Karkh University of science How Forces Affect the Body _The muscular forces that cause the blood to circulate and lungs to take in air. -In the bones there are many crystals of bone mineral that require calcium. A calcium atom will become part of crystal if it gets close to a natural place for calcium and electrical forces are great enough to trap it. It will stay in that place until local conditions have changed and electrical forces can no longer hold it in place. This might happen if the bone crystals destroyed by cancer. (1) Gravitational force: Some Effects of Gravity on the Body One of the important medical effects of gravity is the formation of varicose veins in the legs as the venous blood travels against the force gravity on its way to the heart. Forces on the body where acceleration, the Newton's second low, force equals mass times acceleration. F = ma The force equals the change of momentum Δ(mv) over a short internal of time Δt or F = (Δ(mv) )/Δt From Newton law: There is a force of attraction between any two objects F=mg Where: g= acceleration due to gravity (m/sec2or cm /sec2). m= the mass (kg, g). f= the force (Newton, dyne). page6 Assistant prof. Dr. Ashraf.M. Alattar Medical physics I Al-Karkh University of science Our weight is due to the attraction between the earth and our bodies. The medical effect of gravitational force is the formation of varicose veins in the legs as the venous blood travels against the force of gravity on its way to the heart. Varicose veins are veins that have become enlarged and twisted. The term commonly refers to the veins on the leg, although varicose veins can occur elsewhere. Veins have pairs of leaflet valves to prevent blood from flowing backwards. Leg muscles pump the veins to return blood to the heart, against the effects of gravity. When veins become varicose, the leaflets of the valves no longer meet properly (as illustrated in figure.1), and the valves do not work. This allows blood to flow backwards and they enlarge even more. Varicose veins are most common in the superficial veins of the legs, which are subject to high pressure when standing. Besides being a cosmetic problem, varicose veins can be painful, especially when standing. page7 Assistant prof. Dr. Ashraf.M. Alattar Medical physics I Al-Karkh University of science Fig.(1) shows the cause of varicose veins 2- The electrical force: This force is more complicated than gravity since it involves attractive and repulsive forces between static electrical charges as well as magnetic produced by moving electrical charges (electric currents). The electrical forces are immense compared to gravitational force, for example the electrical force between an electron (e- ) and a proton (P+) in hydrogen atom is about 1039 times greater than the gravitational force between them , as shows in figure (2). page8 Assistant prof. Dr. Ashraf.M. Alattar Medical physics I Al-Karkh University of science Fig.(2) Represents (a) Gravitational force, and (b) Electrical force. (3) Nuclear forces: These forces counteract the enormous Coulomb’s repulsion of the positively charged “protons” and hold them together inside the nucleus. There are two types of nuclear forces: i) Strong nuclear forces: The strong nuclear force acts as the ''glue'' to hold the nucleus together against the repulsive forces produced by the protons on each other. ii) Weak nuclear forces: associated with electron decay from the nucleus (It may be related to the electrical forces). (4) Frictional forces Friction and energy loss resulting from friction appear everywhere in our everyday life. Some diseases of the body, such as arthritis, increase the friction in bone joint. Force of friction Ff is described by page9 Assistant prof. Dr. Ashraf.M. Alattar Medical physics I Al-Karkh University of science Ff = μN N : is normal force is coefficient of friction between two surfaces :μ - Friction must be overcome when joints move, but for normal joints it is very small. If a disease of the joint exists, the friction may become large. Synovial fluid in the joint is involved in lubrication. The saliva we add when we chew food acts as lubricant. 1-4.Forces, Muscles, and joints. Muscle Forces involving levers For the body to be at rest and equilibrium (static),the sum of the forces acting on it in any direction and the sum of the torques any axis must both equal zero. second, and third-class systems page10 Assistant prof. Dr. Ashraf.M. Alattar Medical physics I Al-Karkh University of science A simple example is in the case of biceps muscle and radius bone acting to support a weight W in the hand (Fig 3a),(Fig 3b) shows the forces and dimensions of a typical arm. There are only two torques: that due to the weight W, which is equal to 30W page11 Assistant prof. Dr. Ashraf.M. Alattar Medical physics I Al-Karkh University of science acting clockwise and that produced by the muscle force M, which is counterclockwise and of magnitude 4M, with the arm in equilibrium we find that We can find the force supplied by the biceps if we sum the torques about the pivot point at the joint. 4M – 30W = 0 and M = 7.5W A muscle force 7.5 times the weight, we neglected the weight of the forearm and hand. the torques about the joint we find that M remains constant as α change length of the biceps muscle changes with the angle. In general, each muscle has a minimum length to which it can be contracted and maximum length to which it stretched and still faction. At these two extremes the force the muscle can exert is essentially zero. At some point in between, the muscle can produce its maximum force The arm can be raised and held out horizontally from the shoulder by the deltoid muscle By taking the sum of the torques about shoulder joint, the tension T can be calculated. T = (2W1+4W2)/Sinα page12 Assistant prof. Dr. Ashraf.M. Alattar Medical physics I Al-Karkh University of science page13 Assistant prof. Dr. Ashraf.M. Alattar Medical physics I Al-Karkh University of science Accelerations can produce a number of effects such as 1-An apparent increase or decrease in body weight 2-Changes in internal hydrostatic pressure 3-Distortion of the elastic tissues of the body 4-the tendency of the solids with different densities suspended in a liquid to separate. page14 Assistant prof. Dr. Ashraf.M. Alattar