2. Why Medical Imaging?
• Motivation: Need to “see” inside the body
• Options:
✓ Open the body and take a look (most invasive)
✓ Endoscopic cameras (minimally invasive)
✓ Medical imaging (noninvasive)
• Goal: To assist with identifying and/or diagnosing medical conditions
3. Medical Imaging Theory
Every medical imaging
system can be thought of
as a black box that
transmits energy into the
body and then receives
energy out of the body
and does something with
that energy to make an
image.
❑ What kind of energy?
❑ What are the effects on the body?
❑ What are the effects on the image?
4. Timeline of Medical Imaging
• 1895 – First X-ray image (Roentgen)
• 1950s – Ultrasound Imaging (Ludwig, Wild, etc.)
• 1971 – Magnetic Resonance Imaging, i.e. MRI (Damadian)
• 1972 – X-ray computed tomography, i.e. CT (Hounsfield & Cormack)
5. Visualizing the
heart with…
• Here are the four
primary imaging
methods that can be
used to see the heart.
• Each one of these
images have advantages
and disadvantages.
6. Imaging System Resolution
• Temporal resolution ➔ how fast
an image can be recorded?
(Ultrasound is the best temporal
resolution)
• Spatial resolution ➔ how blurry
an image will be? ➔ The ability
to resolve two points in space.
• The worst spatial resolution = x-
ray
• The best spatial resolution = MRI
7. Visualizing the
heart with…
• The worst spatial resolution
= x-ray ➔ it looks more
blurry.
• The best spatial resolution =
MRI ➔ we can see borders
between different chambers.
• Ultrasound is the best
temporal resolution ➔ we
can see things in real time.
9. Outline
• What are x-rays?
• How are they created?
• How do they interact with our body?
• Safety requirements
• Example of Uses
• Advantages and disadvantages
10. Cost Comparison
• Q: What is the cheapest medical imaging modality available for
doctors to visualize internal structures non-invasively?
• A: X-rays are the cheapest and most widely used form of medical
imaging.
11. The Genesis of Projection X-Rays
• 1895: First discovered by Professor Wilhelm Roentgen
➔ Soon afterward, Roentgen used x-rays to image his wife’s hand.
• 1896: First diagnostic x-ray used to show the fractured wrist of Eddie McCarthy.
• 1901: Roentgen won the first Nobel Prize in Physics for this discovery.
12. Electromagnetic (EM) Radiation
• X-rays are a form of electromagnetic radiation.
• EM radiation is energy that exhibits wave-like behavior as it travels through
space.
• EM radiation is carried by “particles” known as photons.
14. Atomic Structure
• Atom contains three main components: electrons
(gray), protons (red), and neutrons (blue).
• Electrons orbit the nucleus of the atom and are
negatively charged.
• Protons form part of the nucleus and are positively
charged. The total number of protons defines the
type of atom (or element).
• Neutrons form the remainder of the nucleus.
Which element is represented here??
15.
16. Electron Structure
• Electrons orbit the nucleus in different
shells (e.g., K, L, M)
• The K shell is closest to the nucleus.
17. Ionization
• Ionization ➔ The process of
knocking an electron out of an
atom (e.g. with EM radiation) to
form an ion.
• Each one of dots or represent
electrons orbiting nucleus of the
atom ➔ then comes EM radiation
➔ then knock the element out of
its shell ➔ becomes free electron.
• What is the charge of this ion?
18. Ionization Energy
• Mininum energy required to ionize an atom.
❑ The msaller atoms are
really close to that
positively charged
nucleus and they want
to remain neutral.
❑The smaller atoms
have a higher
ionization energy than
the larger atom.
19. X-ray interactions with matter
• X-rays interact
with electrons
by knocking
them out of
the atom (i.e.
ionizing
radiation).
X-ray interact with matter in 3 primary ways :
20. Compton Scattering
• X-rays scatter with
longer wavelengths than
the incident x-ray.
• Shift in wavelength
increases with scattering
angle, according to the
Compton formula:
21. Where do x-rays come from?
• X-rays come from an x-
ray tube.
• X-ray tubes are typically
made of glass and have
some heated filaments.
22. X-ray Tube
• X-ray tube has cathode and some electrical wires to heat up the electrons on the
cathode then smash into the anode ➔ generate some x-rays by generating the
EM radiation from the high-speed electrons then slam to anode plate.
28. Jones Fracture
• Avulsion of the 5th proximal metatarsal.
• Occurs due to a sudden force under the foot, such as when landing
from a high jump on to another player’s foot when playing basketball.
30. Dental Radiography
• Used to diagnose cavities, hidden molars, etc.
• The x-rays are coming from outside of your mouth and the film in
inside your mouth.
32. Adverse Effects of Ionizing Radiation
• A single ionizing radiation emission can ionize many atoms along its
path.
• An ion’s electrical charge can lead to unnatural chemical reactions
inside cells.
❑ Broken DNA chains
❑ Apoptosis (cell death)
❑ Mutations (can cause cancer)
• X-rays are used sparingly today because of these risks.
33. Radiation Dose and Dose Rate (1)
Risk of harm
depends on the
dose and the
dose rate (the
time the body
is exposed to
radiation).
37. Geiger Counter
• How do we know how
much dose we’re getting?
• Geiger Counter ➔
Registers how much the
gas it contains get ionized
by incoming particles of
radiation and converts
that information into an
electronic signal.
39. X-ray Pros and Cons
Advantages :
• Relatively inexpensive
• Can identify bone structures
Disadvantages :
• Poor soft tissue contrast
• Birth defects (if used to image pregnant women)
• Radiation poisoning at high dose with long exposure times-induced
cancers
• Effects are negligible when imaging for bone fractures because the
required radiation doses are low with short exposure times.
