SHAPE Society

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

9. 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

10. Interactive Interface
Gutman, McVeigh, NHLBI

11. 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

12. IVUS versus IVMRI
Intravascular UltrasoundIntravascular Ultrasound Intravascular MRIIntravascular MRI
Explanted Human Aortic Specimen
Atalar et al.

13. Intravascular Rabbit Aortic Imaging
DIR-FSE
TE=20ms, ETL= 20, FOV=6cm
DIR-FSE
TE=26.4ms, ETL= 20, FOV=4cm
Resolution – 150µmResolution – 234µm
Yucel et al. Serfaty et al.

14. Intravascular MRI of Watanabe Rabbits
mm
B
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.

15. Intravenous Guidewire - Swine
0.16x0.16x4 mm, TR 531, TE 11, BSP, 6 NEX, 2:25
stent
iliac a.
iliac v.
Bluemke et al.

16. Cardiac Coil Ch2 Cardiac Coil Ch3Cardiac Coil Ch1
All Channels
External vs. Endovascular Coil
Iliac Imaging - Pig
Lederman et al.
DIR-FSE TR=1558ms, TE=26ms, ETL= 24, FOV=4cm
Endovascular coil
156 µm resolution

17. MR ScoutX-ray Fluoroscopy High resolution MR
Iliac wall
vein
R Iliac
DIR-FSE
TR=2000ms, TE=6.1ms,
ETL= 24, FOV=10cm, st=4 mm
Human IVMRI Iliac Imaging
Yucel et al.

18. Design
Plaque
Plaque
Vessel
0.014” MRIG
Balloon - 3%
Gd
Gd/blue-dye medium or
Gd/GFP-lentivirus medium
Xiaoming Yang, et al.
Johns Hopkins Hospital

19. Control
Gd/GFP-lentivirus
Immunohistochemistry
G
H
Xiaoming Yang, et al.
Johns Hopkins Hospital
MR imaging of Gd/GFP-lentivirus transfer
a
fed
cb

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