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Magnetic Resonance Imaging Gerald R. Aben, MD, FACR Associate Professor Radiology College of Osteopathic Medicine
6/12/2012 1 DEPARTMENT OF RADIOLOGY
MRI
6/12/2012 2 DEPARTMENT OF RADIOLOGY
Magnetic Resonance Imaging • Tube shaped machine
• Uses a magnetic field and radio frequency waves • Body chemical composition and tissue structure contribute to form image contrast
• Computer generated image
• Special terms • High signal (white or bright), Low signal (dark grey or dark), Isointense (equal density)
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Magnetic Resonance Imaging • Advantages:
• No ionizing radiation (no x-rays)
• Sensitive to slight chemical difference
• Three dimensional study
• Capable of showing fine anatomic structure
• Angiography can be done non-invasively
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3-T MRI scanning
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MRI with Patient
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MRI Principles
• Hydrogen ions in the magnetic field of the MRI machine align with a small net dipole(1)
• Application of a radio frequency causes ions to move to a higher energy state(2-3) (Blue arrow) 6/12/2012 DEPARTMENT OF RADIOLOGY 7
MRI Principles
• When the frequency is removed the ions begin to return to prior state releasing energy(4 – 5)
• Resulting radiofrequency is measured and localized to create an image(Changing bl )
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MRI Sequences
• T1- Weighted – short TR short TE – Fat Bright
• T2- Weighted – long TR, long TE – Water Bright
• Proton Density- Weighted or balanced imaging – long TR, Short TE
6/12/2012 DEPARTMENT OF RADIOLOGY 9
MRI Image Parameters
Parameters T1
Weighted Image
Proton Density-Weighted
Image
T2 Weighted
Image
TR (msec) ≤500 ≥2000 ≥ 2000
TE (msec) ≤ 25 ≤ 40 ≥ 75
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TR = Time of repetition of the radio-frequency pulse TE = Time of echo, the time of collecting the signals
T1-Weighted
Proton Density-Weighted (balanced)
T2-Weighted
CSF Dark gray or Black Dark gray “White” or
light
White Matter
“White” or light Dark gray Dark gray
Gray Matter Gray Light gray Dark gray
Signal Intensity of Certain Tissues
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MRI Normal Brain Midline T1
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Corpus Callosum
Vermis
Cerebellum
Scalp
CSF
Brain MRI Normal Axial T1
• Ventricles
• White Matter
• Grey Matter
• Scalp fat
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Brain MRI Normal Flair
• T-2 Sequence
• Special technique suppresses CSF signal
• Allows better evaluation of areas adjacent to CSF spaces
• Excellent for evaluation of Multiple Sclerosis
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Brain MRI Normal T2
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Brain Coronal T1
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Lumbar Spine MRI
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T1 Proton Density T2
Arrow at disk herniation
MRI Thoracic Spine
• Intramedullary Spinal Cord Lesion
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MRI Thorax
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Cardiac MRI
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MRI Abdomen
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MR Angiogram Cerebral
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MRI into the Future
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Cardiac Function and Perfusion • Advanced Cardiac evaluation
– Perfusion
– Function
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CAD Enhanced Prostate MRI
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Courtesy of Dr. Kevin DeMarco
1024 MR Angiography Exceeds DSA resolution (no contrast) 8-Channel head coil
Increased Resolution MRA
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Courtesy of Jim Potchen, MD
Nerve Track Imaging
6/12/2012 DEPARTMENT OF RADIOLOGY 28
Brain Functional Imaging-Listening to Brahms
Music Therapy Professor Musically Naive Engineer Courtesy of Jim Potchen, MD
6/12/2012 DEPARTMENT OF RADIOLOGY 29
Brain Functional Imaging Listening to Someone Reading Prose
Music Professor
Engineer Courtesy of Jim Potchen, MD
6/12/2012 DEPARTMENT OF RADIOLOGY 30
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