Transcript Introduction of Medical Imaging and MRI

Introduction of Medical Imaging
Chun Yuan
Organization of the Course
• 8 Lectures (1.5 hours per lecture)
– Introduction of medical imaging and MRI
– Basic concept of image formation
– Basic pulse sequences and contrast manipulation
– Image Reconstruction
– RF pulse and gradient pulse
– Fast imaging and advanced applications
– MRI hardware
– Functional MRI
Text Books
• Magnetic Resonance Imaging - Physical Principles
and Sequence Design
– ISBN:
0-471-35128-8
– Authors:
E. M. Haacke, R. W. Brown, M. R.
Thompson, and R. Venkatesan
– Publisher:
John Wiley and Sons, 1999
• Handbook of MRI Pulse Sequences
– ISBN:
– Authors:
– Publisher:
0-7803-4723-4
Bernstein, King, and Zhou
Elsevier Publishing, 2004
Credits
• Home work
– One for each day
– 60%
• Term project
– Topics will be provided
– 40%
What is Medical Imaging
• Introduce some form of radiation
– electromagnetic
– Acoustic
• Observe its interaction with tissue
– attenuation
– scattering / reflection
– Concentration
• Convert the observations into a clinically meaningful
image
– film
– computer
Electromagnetic Spectrum
Imaging Considerations
• Type of information
– anatomical - from head to toe
– functional - cardiac, brain, etc.
– quantitative vs. qualitative
• Limitations
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resolution
sensitive range (e.g. view angles)
speed
cost
invasiveness
“Classical” methods
Images that are direct manifestations of the interaction
between radiation and tissue
• Projection Radiography (Conventional X-ray)
• Ultrasound
• Conventional Nuclear Medicine
Projection Radiography
• Physical Principle: Variation in X-ray attenuation
of different tissues
• Methodology: A beam of X-rays is directed
through a patient onto a film.
• Image: An X-ray “shadow” of the patient.
• History:
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Roentgen’s discovery - 1895
Application to medicine – 1896
contrast materials - early 1900’s
angiography - 1927
Projection Radiography System
Projection Radiography Examples
Chest X-Ray
Angiogram
Mammogram
Ultrasound
• Physical Principle: Ultrasound waves scatter
and reflect within the body
• Methodology: A pulse of ultrasonic energy is
propagated into the body and backscattered
echoes record the depth of objects in the body.
• Image: A “depth map” of patient organs.
• History:
– Concept derived from W.W.II sonar
– Major clinical development - 1970’s
Ultrasound System
Ultrasound Mode
• B-mode image
– Longitudinal view of digital artery
– Frequency: 40MHz
– Resolution: up to 50mm
• Doppler
– Flow velocity in digital artery
Nuclear Medicine
• Physical Principle: Variable uptake of radioactive
materials by different organs
• Methodology: Inject patient with radiolabeled
substance and record time-space pattern of
radiation.
• Image: A map of the radioactivity of the patient.
• History:
– Therapeutic administration of radiolabeled substances
- 1950
– Scintillation camera - 1952
Nuclear Medicine System
Nuclear Medicine Example
“Computed” methods
Images that are formed using mathematical methods
and computers from indirect measurements of the
interaction between radiation and tissue
• Computed Tomography (CT)
– X-ray CT
– PET
– SPECT
• Magnetic Resonance Imaging
• (3D Ultrasound)
Computed Tomography
• Physical Principle: Projection slice theorem dictates
how to reconstruct a 2-D image from multiple 1-D
projections (Radon Transform).
• Methodology: Obtain multiple projection images and
reconstruct images using a computer.
• Image: A 2-D slice mapping the patient’s X-ray
attenuation coefficient (X-ray CT) or radioactivity (PET
and SPECT).
• History:
– X-ray CT proposed - mid 1960’s
– Early clinical use - 1972
– PET and SPECT followed X-ray CT
Computed Tomography System
X-ray CT Example
PET Example
Magnetic Resonance Imaging
• Physical Principle: Within a strong magnetic field,
paramagnetic nuclei (usually hydrogen protons) will
resonate in response to RF radiation
• Methodology: Place patient in a magnet, irradiate with
RF field, and record spatially encoded RF echoes.
• Image: A map of proton concentration through a slice
of the body.
• History:
– NMR discovered - 1940’s
– Imaging proposed in 1972
– Current generation of machines developed in 1980’s
Nobel Prize for MRI
MRI System
MRI Example
Star Artifacts in CT
Shadow Artifacts in Ultrasound
Wrap-around Artifacts in MRI