BME 595 - Medical Imaging Applications Part 2: INTRODUCTION TO MRI Lecture 2 Basics of Magnetic...

BME 595 - Medical Imaging ApplicationsPart 2: INTRODUCTION TO MRI

Lecture 2 Basics of Magnetic Resonance Imaging

Feb. 23, 2005

James D. Christensen, Ph.D.IU School of Medicine

Department of RadiologyResearch II building, E002C

jadchris@iupui.edu317-274-3815

References

Online resources for introductory review of MRI physics:Robert Cox’s book chapters online

http://afni.nimh.nih.gov/afni/edu/See “Background Information on MRI” section

Mark Cohen’s intro Basic MR Physics slideshttp://porkpie.loni.ucla.edu/BMD_HTML/SharedCode/MiscShared.html

Douglas Noll’s Primer on MRI and Functional MRIhttp://www.bme.umich.edu/~dnoll/primer2.pdf

Joseph Hornak’s Web Tutorial, The Basics of MRIhttp://www.cis.rit.edu/htbooks/mri/mri-main.htm

Books covering basics of MRI physics:E. Mark Haacke, et al. Magnetic Resonance Imaging: Physical Principles and Sequence

Design, 1999.

D. Shaw. Fourier Transform NMR Spectroscopy, 1976.

R. N. Bracewell. The Fourier Transform and its Applications, 1965.

Fourier Transform

Discrete case

Fourier Transform Pairs

Convolution Theorem

Signal Detection:Real & Image Components

X channel (0 phase - Real)

Y channel (90 phase - Imaginary)

Single-Channel Detection

X channel (0 phase - Real) Y channel (90 phase - Imaginary)

Problem: positive & negative frequencies cannot be distinguished!

Quadrature Detection

+ and - frequencies can be distinguished. The entire bandwidth can be utilized

Signal ADC With sufficient sampling rate

Signal ADC Insufficient sampling rate causes aliasing

K-Space EncodingUsing an Applied Gradient

Where ρ is the spin density and k is the spatial frequency

Frequency-Encoding2-Spin Example

Dirac Delta function (line with width=0)

Phase-Encoding

2D K-Space -> Image Space

Slice Selection

Slice Selection

Slice Selection

Slice Selection

Oblique Slice Selection

Spin-Echo Pulse Sequence

Homework