1. Intravascular Magnetic Resonance Imaging
Albert C. Lardo, Ph.D.
Assistant Professor of Radiology, Biomedical Engineering
and Surgery - Johns Hopkins University School of Medicine
and
Chief Scientific Officer - Surgi-Vision, Inc.
2. 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
3. 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
4. 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 (70-400µm)
5. 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).
8 cm
100-185 cm
Coaxial transmission line
DTC
Decoupling and tuning circuit
Scanner
Inner conductorOuter conductor
6. MR Signal Strength Depends on Coil
Distance from the Energy Source
Signal→
Distance →
Energy Source
CoilTissue
7. 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
InternalArtery
Distance from Coil (cm)
Chest depth (180lb male) ~300mm
Distance from Coil and Structure of Interest
Internal Coil
2 106
External Coil
10 26
8. 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 µm Resolution ~ 60 µm
20. 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
21. 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