1- Introduction to Medical Physics PDF

MEDICAL PHYSICS 1- Introduction to Medical Physics PRESENTED BY HUSSAIN HASAN MS.C. IN MEDICAL PHYSICS Terminology Terminology is the science of terms. The physics: It is the science of nature. The medical physics: – The field of medical physics overlaps the two very large...

MEDICAL PHYSICS 1- Introduction to Medical Physics PRESENTED BY HUSSAIN HASAN MS.C. IN MEDICAL PHYSICS Terminology Terminology is the science of terms. The physics: It is the science of nature. The medical physics: – 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 and this called physics of physiology. 2. The application of physics in the practice of medicine, which is, included such things as the tapping of the chest, physics of the stethoscope, medical applications of lasers, Ultrasound, radiation, and so forth.  Terminology The physical therapy: – It is the treatment of disease or bodily weakness by physical means such as massage and gymnastics rather than by drugs. Biophysics: is a relatively defined field that has very little to do with medicine, and it is involved with the physics of large biomolecules, viruses, and so forth, and it does approach medical physics in the area of transport of materials across cell membranes. Biophysicists conduct basic research that may improve the practice of medicine in the next generation, while medical physicists engage in applied research that they hope will improve the practice of medicine in the current generation.  The field of Medical Physics has several subdivisions: 1. Radiological physics. 2. Nuclear medicine. 3. Radiation protection (health physics) of t he patient, worker, and the public (inside or outside of the hospital such as around nuclear power plants and in industry. Sometimes the applied field of physics is called engineering. Medical physics is called medical engineering. The word medical is sometimes replaced with the word clinical if the job s closely connected with patient problems in hospitals (clinical engineering or clinical physics). Modeling There is three types of modeling: 1. Mechanical modeling 2. Electrical modeling 3. Mathematical modeling Model making is common in scientific activities. A famous 19th-century physicist Lord Kelvin said (I never satisfy myself until I can make a mechanical model of a thing. If I can make a mechanical model, I can understand it). An example of a model The flow of blood is represented by the flow of electricity is often used in the study of the body's circulatory system. This electrical model can simulate very well many phenomena of the cardiovascular system. Equations are mathematical models that can be used to describe and predict the behavior of some physical systems. Some of them are referred to as laws. Example: F= ma ……………………………… Newton's second law Or F= Δmv/Δt, – v: is the velocity, mv is the momentum. – Δmv / Δt: means the rate of change of momentum with time. In the medical field:  W= f(h) means the weight W is a function of the height h.  R= f(p) that the heart rate R is a function of the power produced by the body P.  Modeling A medical researcher may use a model of some function of the body to predict properties that were not originally suspected. Many functions of the body are controlled by homeostasis, which is analogous to feedback control in engineering. The two kinds of feedback: 1. Negative feedback: If the system is designed so that an increase in the amount that is feedback decreases the production and a decrease in the sample increases the production. Examples: a) The control of house temperature by a thermostat and furnace. b) To control the level of calcium in the blood by bones and kidneys. 2. Positive feedback: in which a change in the sample feedback causes a change in the same direction produces an unstable control. Measurement One of the main characteristics of science is its ability to reproducibly measure quantities of interest. The growth of science is related to the growth of the ability to measure. In the practice of medicine, body temperature and pulse rate measured during the 17th century The number and accuracy of quantitative measurements used in medicine have increased during the 19 and 20¹ centuries. Measurement The following figure illustrates a few of the common measurements used in the practice of medicine. Some of these measurements are more reproducible than others. Systems of measurement are: 1. International system (SI) units or metric units: – The basic units are the meter (m) for length, the kilogram (Kg) for mass, and the second (sec) for time. The larger or smaller units can be used (cm, mm, g, and mg) 2. English units: – The basic units are (feet, pounds, and gallons). 3. Nonstandard units: – (gram, foot, cm, liter, minute. dyne, calorie, mm of Hg. atmosphere. Fahrenheit Celsius…..). In medicine, it is often convenient to measure quantities in nonstandard units. Example: The correct units for pressure involve force per unit area (newton/m², dyne/cm², and pound/in²) Blood pressure is generally expressed in mm Hg a length of liquid which is of a column of mercury that has a pressure at its base equal to blood pressure. Measurement There are many other physical measurements involving the body and time. We can divide them into two groups: 1. Measurements of repetitive processes such as the pulse. 2. Measurements of non-repetitive processes such as how long it takes the kidneys to remove a foreign substance from the blood.  Accuracy & Precision In science, accuracy and precision have different meanings. Accuracy: Refers to how close a given measurement is to an accepted standard. Example: – A person's height measured, as 1.765 m may be accurate to 0.003 m compared to the standard meter. Precision: Refers to the reproducibility of measurement and it is not necessarily In general, it is desirable to have related to the accuracy of the both good accuracy and good measurement precision. Physical quantities Very small and very large numbers are common in physical science and are best expressed with the help of powers of 1. The powers of 10- to 10+ are as follows: Units: Some common British and SI (metric) units of length and time are: Length: – 1 foot (ft.) = 12 in = 0.305 m – 1 inch (in) = 0.083 ft. = 2.54 cm – 1 mile (mi) = 5280 ft. = 1.61 km – 1 meter = 100 cm = 39.4 in – 1 kilometer (km) = 1000 m = 0.62 mi Time: – 1 minute (min) = 60 second (s) – 1 hour (hr.) = 60 min = 3600 s – 1 day = 24 hr. Mass: – Gram (g) Kilogram (kg), Pound (lb False Positives and False Negatives When the physician decides if the patient is ill or not? After he or she has reviewed a patient's:- 1. Medical history. 2. The findings of the physical examination. 3. The results of clinical laboratory measurements. It is not surprising that sometimes wrong decisions are made. These wrong decisions are of two types: - 1. False Positives. 2. False Negatives. A false positive error occurs when a patient is diagnosed to have a particular disease when he or she does not have it. A false negative error occurs when a patient is diagnosed to be free of a particular disease when he or she does have it. Note: In some situations a diagnostic error can have a great impact on a patient's life. Diagnostic errors (false positives and false negatives) can be reduced by: 1. Research into the causes of misleading laboratory test values. 2. Development of new clinical tests and better instrumentation. Errors or uncertainties from measurements can be reduced by: 1. Using care in taking the measurement. 2. Repeating measurements. 3. Using reliable instruments. 4. Properly calibrating the instruments