Magnetic Resonance Imaging Gerald R. Aben, MD, FACR Associate Professor Radiology College of Osteopathic Medicine

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MRI

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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

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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

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Brain Functional Imaging-Listening to Brahms

Music Therapy Professor Musically Naive Engineer Courtesy of Jim Potchen, MD

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Brain Functional Imaging Listening to Someone Reading Prose

Music Professor

Engineer Courtesy of Jim Potchen, MD

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