Download - 089 intravascular magnetic resonance imaging
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Intravascular Magnetic Resonance Imaging Albert C. Lardo, Ph.D.
Assistant Professor of Radiology, Biomedical Engineering and Surgery - Johns Hopkins University School of Medicine
andChief Scientific Officer - Surgi-Vision, Inc.
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Intravascular Coils – Two Modes
• Active visualization of catheters, guidewires and devices
• Enables MR-guided intervention
Tracking
• Very high local signal for imaging structures directly adjacent to the coil
• Enables diagnostic vascular imaging
Imaging
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External surface coils• Cardiac mechanical function• Perfusion• Metabolic Imaging• Angiography
• Plaque characterization and therapy assessment??
Problem
Spatial resolution limitation (~1 mm)
Cardiovascular MRI - From the Outside In
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Why do we need more spatial resolution?
External
Aorta ~10
Renal ~7
Iliac ~5
Coronary ~7
Artery
Distance from Coil (cm)
Chest depth (180lb male) ~300mm
Quantitative assessment of deep thoracic arteries commonly prone to atherosclerotic disease (e.g. aorta, renal, iliac, coronary)
Goal: Detection of small but potentially unstable plaques
Fibrous cap detection (70-400m)
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Intravascular MRI - From the Inside Out
MR Coil Miniaturization
Endovascular MRI – Placement of small radiofrequency receiver antennas (coils) directly into blood vessels for active tracking and high resolution imaging (Atalar et al 1996).
cm100-185 cm
Coaxial transmission line
DTC
Decoupling and tuning circuit
Scanner
Inner conductorOuter conductor
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MR Signal Strength Depends on Coil Distance from the Energy Source
Sign
al
Distance
Energy Source
CoilTissue
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Distance from coil (cm)
SNR
Internal vs. External Coil
External
Aorta ~10 0.4, 2
Renal ~7 ~0.4
Iliac ~4.5 ~0.6
Coronary ~7.5 ~0.2
InternalArteryDistance from Coil (cm)
Chest depth (180lb male) ~300mm
Distance from Coil and Structure of Interest
Internal Coil
2 106
External Coil
10 26
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Endovascular Coils - Two Designs
• High local signal and moderate resolution
• Signal falls off with distance (1/R)
• Can be made very small and flexible (>1F)
• Very high local signal and thus resolution
• Signal falls off very rapidly with distance (1/R2)
• Larger in size and less flexible
Loopless Loop
Resolution ~ 200 m Resolution ~ 60 m
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MRI Intravascular Guidewire
• Loopless antenna design• Gold plated Nitinol core• Nitinol tubing• Intravascular placement• OD = 0.032” and 0.014”• Fully tuned and decoupled
Antenna whip
Nitinol tube
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Interactive Interface
Gutman, McVeigh, NHLBI
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MR-guided Applications
• Intravascular MR imaging• MR-guided Catheterization• Real-Time Angiography• MR-guided Balloon Angioplasty• MR-guided Stent Placement• MR-guided Invasive Electrophysiology•MR-Guided Gene Therapy
Require Imaging and Tracking
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IVUS versus IVMRI
Intravascular UltrasoundIntravascular Ultrasound Intravascular MRIIntravascular MRI
Explanted Human Aortic Specimen
Atalar et al.
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Intravascular Rabbit Aortic Imaging
DIR-FSETE=20ms, ETL= 20, FOV=6cm
DIR-FSETE=26.4ms, ETL= 20, FOV=4cm
Resolution – 150mResolution – 234m
Yucel et al. Serfaty et al.
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Intravascular MRI of Watanabe Rabbits
mmB
FSE, 1200/13-msec TR/TE, Double IR blood suppression, 16 ETL, 4-cm FOV, 32 NEX,256x256 matrix
ACM
• Resolution: 150 µm
Watanabe rabbit with a 0.032” MRI-Guidewire
Serfaty et al.
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Intravenous Guidewire - Swine
0.16x0.16x4 mm, TR 531, TE 11, BSP, 6 NEX, 2:25
stent
iliac a.
iliac v.
Bluemke et al.
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Cardiac Coil Ch2 Cardiac Coil Ch3Cardiac Coil Ch1
All Channels
External vs. Endovascular CoilIliac Imaging - Pig
Lederman et al.DIR-FSE TR=1558ms, TE=26ms, ETL= 24, FOV=4cm
Endovascular coil
156 m resolution
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MR ScoutX-ray Fluoroscopy High resolution MR
Iliac wallvein
R Iliac
DIR-FSETR=2000ms, TE=6.1ms,
ETL= 24, FOV=10cm, st=4 mm
Human IVMRI Iliac Imaging
Yucel et al.
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Design
Plaq
ue
Plaq
ue
Vessel
0.014” MRIGBalloon - 3% Gd
Gd/blue-dye medium or Gd/GFP-lentivirus medium
Xiaoming Yang, et al.Johns Hopkins Hospital
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Control
Gd/GFP-lentivirus
Immunohistochemistry
G
H
Xiaoming Yang, et al.Johns Hopkins Hospital
MR imaging of Gd/GFP-lentivirus transfer
a
fed
cb
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Summary
• Intravascular MR coils and guidewires provide active device localization and high resolution imaging
• MRI guided cardiovascular intervention is feasible on currently available scanners
• Further improvements in spatial and temporal resolution, device localization and MR scanner design are required for general clinical use
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Challenges
• Further loop coil miniaturization for coronary imaging
• Effects of cardiac motion during coronary imaging
• Real-time quantitative device localization• Reduction of image acquisition time