LECTURE-1
INTRODUCTION
OF MEDICAL PHYSICS
Sherif H. El-Gohary , Phd
Assistant Professor, Biomedical Engineering Engineering
Sh.ElGohary@eng1.cu.edu.eg
MEDICAL PHYSICS
WHAT IS MEDICAL PHYSICS?
Application of the concepts and methods of
physics to the diagnosis and treatment of
human disease
Medical Physicist
Physics
Medicine
AIMS OF THE MEDICAL PHYSICS
Application of the concepts and
methods of physics to understanding the
function of human body in health and
disease
MEDICAL PHYSICS
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. MEDICAL PHYSICS DISCIPLINES
• Diagnostic Medical Physics
• Therapeutic Medical Physics
• Nuclear Medical Physics
• Medical Health Physics
Radiation Safety
3.APPLICATION OF PHYSICS IN MEDICINE
Medical physics Techniques are used for
a. Diagnostic :
•
Stethoscope
•
Manometer (blood pressure )
•
Sphygmomanometer
•
Electrocardiograph(ECG),
•
X- Ray,
•
Electroencephalograph(EEG),
•
Electromyography (EMG)
DIAGNOSTIC MEDICAL PHYSICS
DIAGNOSTIC MEDICAL PHYSICS
• Computer tomography (CT scan ) ,
• Ultrasound
• 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 .
B. THERAPY
• Radiotherapy
• Ultrasound
• infrared
• Radio frequency
• Heating
• Laser
THERAPEUTIC MEDICAL PHYSICS
1-PHYSICAL UNITS (SI UNIT)
SI units(Standard units):
Two types of SI units
1.Physical unit
a. MKS system
M = meter
K = Kilogram
S
= Second
b. CGS system
C = centimeter
G = gram
S = second
2 .PHYSIOLOGICAL UNIT
In medicine it is often convenient to measure quantities in
nonstandard units.
For example :the physical units of pressure is Newtons
per square meter ,
Physiological unit of blood pressure is expressed in
millimeter of mercury (mm Hg)
Another example of pulse rate measures in
pulse per minute
NUCLEAR MEDICAL PHYSICS
Brain perfusion
neurotransmission
MEDICAL HEALTH PHYSICS
Radiation Protection
Radiation Safety Officer
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
Listen Up!
WHAT IS SOUND?
• A vibration is the complete back and forth motion of an object.
• Beating a drum causes the drum skin to vibrate, which causes
the air around it to vibrate.
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
WHAT ARE SOUND WAVES?
•A sound wave is a longitudinal wave that is caused by
vibrations and that travels through a medium.
• In a longitudinal wave, the particles of a medium
vibrate in the same direction that the wave travels.
•As the wave passes through a medium, its particles
compress together and then spread out.
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
WHAT ARE SOUND WAVES?
•Longitudinal waves are also called compression waves.
They are made up of compressions and rarefactions.
•A compression is the part of a longitudinal wave where
particles are close together.
•A rarefaction is the part of a longitudinal wave where
particles are spread apart.
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
HOW DO SOUND WAVES TRAVEL?
• Sound waves travel in all directions away from their
source.
• They can only travel through a medium.
• All matter—solids, liquids, and gases—is composed of
particles. The particles in matter make up the medium
through which waves can travel.
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
HOW DO SOUND WAVES TRAVEL?
• The particles of a medium only vibrate back and forth
along the path of the sound waves.
• Most sounds travel through air, but some travel
through other materials, such as water, glass, and
metal.
• In a vacuum there are no particles to vibrate, so no
sound can be made.
• Sound must travel through a medium to be detected.
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
HOW DO HUMANS HEAR SOUND?
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
HOW DO HUMANS HEAR SOUND?
•Humans detect sounds with their ears, which act
like funnels for sound waves.
•The ear directs sound vibrations from the
environment to the three tiny bones in the
middle ear.
•These bones carry vibrations from the eardrum
to the oval window, which leads to the inner ear.
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
HOW DO HUMANS HEAR SOUND?
•Vibrations travel through fluid to the cochlea,
which has thousands of nerve cells.
•Each nerve cell has tiny surface hairs that bend
with the vibrations to send electrical signals to
the brain, which interprets the signals as sound.
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
HOW DO HUMANS HEAR SOUND?
Describe how sound gets interpreted by the brain.
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
INTRODUCTION
• Sound : It is the audible waves of frequency between 20 Hz
and 20 kHz.
• Infrasound : refers to the sound of frequency below the
normal hearing range (<20 Hz) and subsonic (0 to
20Hz),which cannot be heard.
• Ultrasound : It ranges above 20 kHz ,which is also cannot be
heard
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
INTRODUCTION
• Bats and dolphins are animals that use ultrasound as SONAR
(Sound Navigation and Ranging) for both hunting and navigation.
• It is believed that they can make a picture in their brains from the
ultrasound echoes they pick up.
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
INTRODUCTION
Ultrasound
- Sound
waves with frequencies above the normal
human range of hearing.
Sounds in the range from 20-100kHz
Infrasound
- Sounds with frequencies below the normal human
range of hearing.
Sounds in the 20-200 Hz range
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
TWO TYPES OF WAVE TRAVEL
Particles in a medium vibrate about their mean positions,
transferring energy but not matter.
longitudinal wave – vibration along the direction of energy transfer
transverse wave – vibration perpendicular to the direction of energy
transfer
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
LONGITUDINAL WAVES
It can be thought of as ‘density waves’ in a material
medium (solid, liquid or gas).
‘pressure’ or ‘compression’ waves, because
compressions alternate with rarefactions.
• slinky spring
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
In sound waves, also known as acoustic waves, the local oscillations
always move in the same direction as the wave
The ‘hot’ colors occur wherever particles are close together
and the ‘cold’ colors occur wherever they are far apart.
The colors therefore represent the density of air
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
TRANSVERSE WAVES
Wave particles vibrate
in an up-and-down motion.
• Crests
Highest part of a wave
• Troughs
The low points of the wave
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
GRAPHING A SOUND WAVE.
Sound as a pressure wave
The variation of pressure with distance is a useful way
to represent a sound wave graphically.
But remember – sound is actually a longitudinal wave.
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
DETECTORS OF SOUND
• Ear – structure, range of hearing, locating a
sound source by comparing arrival times
• Microphone
• Sound level meter
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
MEASURE THE SPEED OF SOUND
… with a double beam oscilloscope
…or use echoes from an exterior school wall.
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
GENERAL MODEL FOR RADIATION
SOURCE
MEDIUM
DETECTOR
Journey: may involve transmission, reflection, refraction,
partial absorption
detector: absorption at the journey’s end
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
GENERAL PROPERTIES OF SOUND
• Sound waves require a medium for their transmission. .
Matter must be present for sound to travel.
1. A sound wave is a mechanical disturbance in a gas, liquid
or solid cause local pressure increase (i.e. compression )and
pressure decrease (rarefaction).
2. Sound wave spread outward as a longitudinal wave i.e. the
pressure changes occur in the same direction that the
wave travels.
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
GENERAL PROPERTIES OF SOUND
• Velocity of the sound is given by :
V =f * λ
• f= frequency of vibration of the sound wave.
• λ =wave length of the sound wave.
• The velocity of the sound differs from the medium to
medium, Why?
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
VELOCITY OF ULTRASOUND IN SEVERAL
MATERIALS OF MEDICAL INTEREST
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
VELOCITY OF ULTRASOUND IN SEVERAL
MATERIALS OF MEDICAL INTEREST
• Note that the velocity of ultrasound in bone is twice that
in soft tissue and the velocity in soft tissue is five times
that in air.
• The velocity of ultrasound does not depend on frequency,
it is determined by the medium.
• i.e..
Speed in gas < speed in liquid <
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
speed in solid
REFLECTION
Sound
Source
Incident
Transmitted
Reflected
MEDIUM 1
MEDIUM 2
Acoustic Interface
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
REFLECTION
Soft Tissue (1540 m/s)
Fat (1459 m/s)
Acoustic interface / Acoustic Mismatch
Soft Tissue (1540 m/s)
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
Bone (4080 m/s)
TWO TYPES OF ULTRASOUND
• The two types of ultrasound employed in diagnostic are:
1. Continuous wave
2. Pulsed wave.
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
TWO TYPES OF ULTRASOUND
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
ACOUSTIC IMPEDANCE
• Acoustic impedance (Z) is used to describe the reflection of
sound at an interface.
• It is a function of the density of the medium and its
compressibility, which is measured by the velocity of sound in
the medium.
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
ACOUSTIC IMPEDANCE
• Mathematically, acoustic impedance is described by:
Z = ρV
• Where
• ρ : is the density of the medium (Kg/m3)
• V : is the velocity of the sound in the medium (m/ s)
.∙. Acoustic impedance therefore has unit (Kg/m2.s)
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123
Sherif El-Gohary, Ph.D.
Medical Physics HEMN123