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: 0-7803-4723-4 Bernstein, King, and Zhou – Publisher: 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 – – 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: – Roentgen’s discovery - 1895 – Application to medicine – 1896 – contrast materials - early 1900’s – angiography - 1927

Projection Radiography System

Projection Radiography Examples Chest X-Ray Mammogram Angiogram

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