Transcript Lecture 1

MEDICAL IMAGING
Dr. Hugh Blanton
ENTC 4390
Lecture 1
EM Introduction
Mass
• MassMeasure of the resistance of a
body to acceleration.

• eg. F ( Newtons)  ma
• Newton’s 2nd Law
Dr. Blanton - ENTC 4337 - Lab 2
3
Mass
• kg (kilograms) is a lot of mass in the
nuclear physics world.
• Define
• 1 atomic mass unit (amu) = 1/12 mass of 1
atom of Carbon 12
27
• 1.6604310
kg
Dr. Blanton - ENTC 4337 - Lab 2
4
Energy
• Energy The ability to do work.

• E( joules)  F (newton)  r (meters)
• For electrical forces:
• E ( joules)  q(coulombs)  V (volts)
Dr. Blanton - ENTC 4337 - Lab 2
5
Electron-Volt
• For 1 electron moving in a 1V
potential difference,
•

18
E  1.6 10
1  1.6 10
18
J
• Define this as 1 electron-Volt (eV)
Dr. Blanton - ENTC 4337 - Lab 2
6
Conservation of Mass
2


m
• E ( J )  m(kg)c 
2
s


2
• c is the speed of light
•
2.997925 10 8 m
Dr. Blanton - ENTC 4337 - Lab 2
s
7

27
• 1 amu  1.6604310
2.99792510 
8
27
1 amu  1.4923210
Dr. Blanton - ENTC 4337 - Lab 2
8
EM Radiation
• Two ways to transfer energy from
one body to another:
• particle—kinetic energy
• wave—propagation of a disturbance.
• EM radiation has properties of both of
these—the wave/particle duality.
Dr. Blanton - ENTC 4337 - Lab 2
10
Waves
• Longitudinal waves—disturbance in
the direction of propagation.
• eg. sound
Animation courtesy of Dr. Dan Russell, Kettering University
Dr. Blanton - ENTC 4337 - Lab 2
11
• Transverse waves—disturbance
perpendicular to direction of
propagation.
• eg. waves in the ocean
Animation courtesy of Dr. Dan Russell, Kettering University
Dr. Blanton - ENTC 4337 - Lab 2
12
• Regardless of the type of wave, they
can be characterized by:
•
•
•
•
•
wavelength l
frequency (f)
phase f
velocity n
amplitude
n  fl
Dr. Blanton - ENTC 4337 - Lab 2
13
• Wave characteristics of EM radiation:
• EM radiation can be seen to be a transverse
wave of particular oscillations of electric and
magnetic
fields.

E
oscillatory
electric field
(force)
l
perpendicular
magnetic field
(force)
wavelength
c  310 8 m

H
wave frequency (cycles per second)  n 
Dr. Blanton - ENTC 4337 - Lab 2
14
c
l
s
• EM radiation has wave
characteristics such as:
• reflection
• refraction
• interference
Dr. Blanton - ENTC 4337 - Lab 2
15
Dr. Blanton - ENTC 4337 - Lab 2
16
• Particle characteristics of EM radiation:
• Particles of EM radiation are called quanta or
photons.
• Photons can be thought of as wave packets of
electric and magnetic fields

E
oscillatory
electric field
(force)
perpendicular
magnetic field
(force)
l
wavelength
c  310 8 m

H
Photon Energy  E  hn 
Dr. Blanton - ENTC 4337 - Lab 2
hc
l
17
s
• h is Planck’s constant
h  6.62 1034 J  s  4.131018 keV  s
E keV  
hc
l


 1.24 10 9 / l
Dr. Blanton - ENTC 4337 - Lab 2
18
Example
• What is the frequency and l for 100
keV photons?
EkeV   100 keV


E keV   100 keV  1.24 109 / l

1.24 10 
l
 1.24 10
9
14
100 keV
1.24 10 9
l
 1.24 10 14
100 keV


Dr. Blanton - ENTC 4337 - Lab 2
19
• What is the frequency and l for 100
keV photons?
EkeV   100 keV
E  hf
E
100 keV
20
f  

0
.
24

10
h 4.13 10 18 keV  s 
f  2.4 1019 Hz
Dr. Blanton - ENTC 4337 - Lab 2
20
EM Radiation
Low E, long l—Acts like wave.
High E, short l—Acts like particles.
Dr. Blanton - ENTC 4337 - Lab 2
21
• Scientists have observed that
electromagnetic radiation has a dual
"personality."
• Besides acting like waves.
• It acts like a stream of particles (called "photons")
that have no mass.
• The photons with the highest energy
correspond to the shortest wavelengths.
Dr. Blanton - ENTC 4337 - Lab 2
22
• Electromagnetic waves are produced by
the motion of electrically charged particles.
• These waves are also called "electromagnetic
radiation" because they radiate from the
electrically charged particles.
• They travel through empty space as well as
through air and other substances.
Dr. Blanton - ENTC 4337 - Lab 2
23