1. MRI and MRA of the Carotid Arteries
Robert L. Greenman
Department of Radiology
Beth Israel Deaconess Medical Center

2. MRI of the CAROTID ARTERIES
Review Pathogenesis/Progression
Intima-Media Thickness (IMT) Studies
Plaque Constituents
Morphology
Stable vs Unstable (Vulnerable)
Survey of Methods and Results
Most Published Results - 1.5T
Recent 3T Carotid MRI Studies

3. MRI of CAROTID ARTERIES
Stroke (1999 Statistics)
Worldwide
4.4 Million Deaths/Year
5,000 Disabilities/Million Persons
United States
750,000 Strokes/Year
1/3 Stroke Patients Die
1/2 of Survivors are Disabled
Gorelick, PB, et al Statement from National Stroke
Assoc. JAMA 1999; 281:

4. MRI of CAROTID ARTERIES
Acute Ischemic Attack
Disruption of Atherosclerotic Plaques
Cause of many Embolic Strokes

5. ATHEROSCLEROSIS Intimal Disease Inflammatory Disease
Response of the Intima to Injury
Ross, R. “Atherosclerosis - An Inflammatory Disease”.
N Engl J Med 1999; 340:
Davies, MJ, Woolf, N. “Atherosclerosis: what it is and
why does it occur?. Br Heart J; 1993: 69;S 3-11

6. ARTERIAL PLAQUE COMPOSITION
Major Components
Lipids
Lipid-Containing “Foam Cells” (Macrophages)
Macrophages
Connective Tissue
Matrix Proteins - Collagen
Strengthens, Holds Plaque Together
Other Components
Calcification

7. ATHEROGENESIS Endothelial Injury/Dysfunction
Lipids are a Major Cause of Injury
Adhesion and Migration of Luekocytes
Immune/Inflammatory Response
Migration of Lipids (Normal and Oxidized)
Uptake of Lipid by Macrophages
Smooth Muscle Proliferation

8. ATHEROGENESIS Endothelial Injury/Dysfunction
Causes
Elevated and Modified LDL
Free Radicals
Cigarette Smoking
Hypertension
Diabetes
Genetic Alterations
Infectious Microorganisms

9. ATHEROGENESIS Endothelial Injury/Dysfunction
Immune/Inflammatory
Response
Increased Adhesiveness
Increased Permeability
Procoagulant Properties
Release of Growth Factors
Thickening of Artery Wall and “Remodeling”

10. ATHEROGENESIS Plaque Formation
Modified Lipids Migrate Into Intima
Ingested by Macrophages
Uptake is Unregulated
“Foam Cells”
Smooth Muscle
Proliferation and Migration
Release of Growth Factors

11. ATHEROGENESIS Plaque Formation
Foam Cells Burst - Necrotic Lipid Core
Smooth Muscle Proliferation
Release of Growth Factors

12. ATHEROGENESIS Unstable (Vulnerable) Plaque
Necrotic Lipid Core Grows Large
Fibrous Cap Wears Thin - Ruptures
Thrombus

13. CAROTID PLAQUES Unstable (Vulnerable) Plaque
Large Core
Necrotic Lipid
Intraplaque Hemorrage
Unstable Fibrous Cap

14. CAROTID IMAGING ULTRASOUND
Modality of Choice: 2D Ultrasound
B-mode Ultrasound
Noninvasive
Safe
Inexpensive
Measurements
Intima-Media Thickness (IMT)
Vessel Geometry
Lumen Diameter
Distensibility

15. CAROTID IMT MRI vs US Difficulties with Carotid US
Relative position of jawbone WRT bifurcation
Vessel tortuosity
Calcification
Large Intra- and Interobserver Variability

16. CAROTID IMAGING MRI vs US
Little MRA - Mostly MRI
Soft Tissue Contrast
Lipid, Smooth Muscle, Fibrous Tissue
MR Signal Independent of Angle
Flow Sensitive
Simultaneous Information on:
Vessel Lumen
Vessel Wall

17. FSE Black Blood Imaging

18. T2-W FSE (Dark Blood)

19. CAROTID IMT MEASUREMENTS
Longitudinal Studies
Study Progression of Atherosclerosis
Risk Factor for Stroke ??
Risk Factor for Cardiovascular Disease ??

20. CAROTID IMT MEASUREMENTS
IMT and Brain Infarction
Touboul, et al. Circulation 102: , 2000

21. CAROTID IMT MEASUREMENTS
IMT of Common Carotid Artery
Some Studies Suggest IMT Related to
Cardiovascular Risk Factors
Prevalence of Atherosclerosis of
Peripheral
Coronary
Femoral

22. CAROTID IMT MEASUREMENTS
Increased IMT Associated with
Age
Howard, et al
Hypertension
Zanchetti, et al
Diabetes
Kawamori, et al
Hyperlipidemia
Poli, et al
Increased IMT Associated with CAD
Crouse, et al. Circulation: 92: , 1995

23. CAROTID IMT MEASUREMENTS
Study: Risk Factors that Predict Stroke/MI
Iglesias, et al.
(Subset “Rotterdam Study”)
374 Subjects - Stroke or MI
1496 Controls
Mean Follow-up: 4.2 years
Results/Conclusions
Significant association between Carotid IMT and Stroke and MI
Predictive Value Low When Combined With Other Clinical Observations
Iglesias, et al. Stroke: 32: , 2001

24. CAROTID IMT MRI vs US MRI Studies of IMT Measurement Results
Crowe, et al. JMRI: 21: , 2005
2D US vs 3D MRI (Black-Blood TSE)
10 Healthy Subjects, 5 Hypertensive Patients
Results
Bland-Altman Analysis
Mean Diff. MRI & US - 1.2%
Significant Difference in IMT (P<0.05) Between Hypertensive &Non-Hypertensive for Both Methods

25. CAROTID IMT MRI vs US Wall Thickness Measurements
3D-TSE MRI vs US
Crowe, et al, 2005 JMRI;21:

26. CAROTID IMT MRI vs US Crowe, et al, 2005 JMRI;21:282-289
Wall Thickness Measurements
3D-TSE MRI vs US
Crowe, et al, 2005 JMRI;21:

27. CAROTID IMT MRI vs US Correlation Study DIR Black Blood MRI vs US
17 Patients
Intermediate/High Framingham Cardiovascular Risk Score
Results
Significant Correlation
R = 0.72, p < 0.05
Mani, et al. J Cardiovasc Magn R 8:

28. CAROTID CE-MRA Identifies Luminal Narrowing Not Plaque Size
100% Sensitivity
92% Specificity
Compare to Conventional MRA
Wutke, et al. Stroke 33:
Not Plaque Size
Vessel May Remodel
Can Overestimate Extent of Stenosis

29. Image of the entire vascular region from the aortic arch to the intracranial vessels
Wutke, R. et al. Stroke 2002;33:
Copyright ©2002 American Heart Association

30. MRI of CAROTID PLAQUES Non-Invasive MRI Signal Intensities
Based on Tissue Biochemical Environment
Soft Tissue Contrast
Lipid vs Smooth Muscle, Fibrous Tissue
Vessel wall/Lumen Contrast
Flexibility in Achieving Desired Contrast

31. MRI of CAROTID PLAQUES Dark Blood Sequences Bright Blood Sequences
T2-Weighted
T1-Weighted
PD- Weighting (Proton Density)
Bright Blood Sequences
2D and 3D Time-of-Flight (TOF)
Others
Magnetization Transfer (MT)
Diffusion Sensitive

32. MRI of CAROTID PLAQUES MRI Contrast of Atherosclerotic Plaque
Yuan, C, et al. Radiology 2001; 221:

33. MRI of CAROTID PLAQUES MRI Contrast Mechanisms Identification of:
Lipid Core
Calcium Deposits
Fibrous Connective Tissue
Intraplaque Hemorrhage

34. 1.5T MRI STUDIES Multiple Weightings – T2W, T1W, PDW
Shinnar, et al. Arterioscler Thromb Vasc Biol 1999;19:
Yuan, et al. Radiology 2001; 221:
Fibrous Cap Thickness Measurement
Hatsukami, et al. Circulation 2000;102:
Contrast Enhanced
Yuan, et al. J Magn Reson Imaging 2002; 15:62-67

35. MRI of CAROTID PLAQUES T2-Weighting Delineates Lipid Core and Thrombus
Yuan, C, et al. Radiology 2001; 221:

36. MRI of CAROTID PLAQUES Multiple-Weighting Study
Mitsumori, L, et al. JMRI :

37. MRI of CAROTID PLAQUES Multiple-Weighting Study Lipid Core/Fibrous Cap
Mitsumori, L, et al. JMRI :

38. MRI of CAROTID PLAQUES Multiple-Weighting Study
Pitfall of DIR-BB FSE studies
Mitsumori, L, et al. JMRI :

39. MRI of CAROTID PLAQUES Multiple-Weighting Study Calcification
Mitsumori, L, et al. JMRI :

40. MRI of CAROTID PLAQUES 3D TOF (Bright Blood) Imaging Parameters:
Bright Lumen/Dark Fibrous Tissue
Identify Unstable Fibrous Caps in vivo
Imaging Parameters:
TR = 23 ms
TE = 3.8 ms
2 Signal Averages
Scan Time = Min.

41. MRI of CAROTID PLAQUES 3D TOF (Bright Blood) Spatial Resolution
Slice Thickness = 2 mm
Acquisition Matrix:
Size = 256 x 256
Voxel Size = 0.5 x 0.5 x 2 mm
Zero Filled:
Matrix = 512 x 512
Zero Filled Voxel Size = 0.25 x 0.25 x 2 mm

42. MRI of CAROTID PLAQUES 3D TOF (Bright Blood)
Unstable Fibrous Cap Detection
Yuan, C, et al. Radiology 2001; 221:

43. MRI of Neovasculature Neovasculature in Plaques Associated with
Infiltration of Inflammatory Cells
Plaque Destabilization
Involved In Recruitment of Leukocytes
Inflammatory Cells Present at Rupture Sites
Measurement of Neovasculature may Identify Vulnerable Plaques
Contrast-Enhanced MRI

44. MRI of Neovasculature MRI of Neovasculature
Kerwin, et al. Circulation 107:

45. 1.5T to 3.0T Comparisons All Studies Evaluated Black-Blood
Anumula, et al, Acad Radiol; :
Compared Multi-coil Arrays
Univ. Pennsylvania (FW Wehrli)
Yarnykh, et al, JMRI; :
Compared Multicontrast
Univ. Washington (C. Yuan)
Koktzoglou, et al,JMRI; :
Compared Multi-slice
Northwestern & Mt Sinai (L Debiao, ZA Fayad)
Greenman, et al. MRI 2007 In Press
Vessel Wall Sharpness with Field Strength and Spatial Resolution

46. 1.5T to 3.0T Comparisons Conclusions of studies 3.0T Improves
SNR
CNR
SNR can be traded for higher spatial resolution

47. Purpose Apply Edge Detection to Evaluate effect of
Spatial Resolution
Static Field Strength
Carotid Imaging Methods:
2D-TOF (GRE)
2D Black-Blood (Double-IR FSE)

48. Edge Detection
Have Been Used to Evaluate and Compare Vessel Edge Definition
Coronary Arteries (Bright Blood)
Compare Results of Acquisition Schemes
Deriche Algorithm
First-order derivative
Create derivative or “edge” images
Vessel sharpness: “The average edge value along the calculated
vessel border” … “Higher edge values correspond to better
vessel definition.”
Botnar, et al, Circulation 1999;99:
Weber, et al, JMRI 2004;20:
Deriche, R, IEEE Trans PAMI. 1990;12:78-87
(“Fast algorithms for low-level vision”)

49. METHODS Compared Spatial Resolution/Field Strength:
0.27 mm X 0.27 mm X 2.0 mm
1.5T and 3.0T; n = 12 (1.5T-H, 3.0T-H)
0.55 mm x 0.55 mm x 2.0 mm (Zero-Filled 2X)
1.5T only; n= 5 (1.5T-L)
2D DIR Black Blood FSE
2D Gradient Echo Time-of-Flight

50. 2D-TOF Results

51. DIR-BB Results

52. Gradient Value Comparison

53. Carotid Edge Values

54. MRI of CAROTID PLAQUES Identify Stable/Unstable Plaques
Follow Progression of Plaque Development
Monitor Therapies

55. CONCLUSIONS
3.0 Tesla MRI Offers Improved Signal-to-Noise Ratio – Resolution
IMT Measurements
May Be Able To Identify Unstable Plaques
Improved Accuracy: Measurement Cap Thickness
May Improve Monitoring of Interventional Therapies