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

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Presentation on theme: "MRI and MRA of the Carotid Arteries Robert L. Greenman Department of Radiology Beth Israel Deaconess Medical Center."— Presentation transcript:

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

2 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 MRI of the CAROTID ARTERIES

3 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 MRI of CAROTID ARTERIES Gorelick, PB, et al Statement from National Stroke Assoc. JAMA 1999; 281:

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

5 Intimal Disease Inflammatory Disease Response of the Intima to Injury ATHEROSCLEROSIS 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 Major Components –Lipids Lipid-Containing “Foam Cells” (Macrophages) Macrophages –Connective Tissue Matrix Proteins - Collagen Strengthens, Holds Plaque Together –Other Components Calcification ARTERIAL PLAQUE COMPOSITION

7 1.Endothelial Injury/Dysfunction Lipids are a Major Cause of Injury 2.Adhesion and Migration of Luekocytes 3.Immune/Inflammatory Response 4.Migration of Lipids (Normal and Oxidized) 5.Uptake of Lipid by Macrophages 6.Smooth Muscle Proliferation ATHEROGENESIS

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

9 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 1.Large Core –Necrotic Lipid –Intraplaque Hemorrage 2.Unstable Fibrous Cap CAROTID PLAQUES Unstable (Vulnerable) Plaque

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

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

16 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 CAROTID IMAGING MRI vs US

17 FSE Black Blood Imaging

18 T2-W FSE (Dark Blood)

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

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

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

22 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 CAROTID IMT MEASUREMENTS

23 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 CAROTID IMT MEASUREMENTS Iglesias, et al. Stroke: 32: , 2001

24 MRI Studies of IMT Measurement –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 CAROTID IMT MRI vs US

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

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

27 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 CAROTID IMT MRI vs US Mani, et al. J Cardiovasc Magn R 8:

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

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

30 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 MRI of CAROTID PLAQUES

31 Dark 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 MRI of CAROTID PLAQUES

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

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

34 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: T MRI STUDIES

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

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

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

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

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

40 3D TOF (Bright Blood) –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. MRI of CAROTID PLAQUES

41 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 MRI of CAROTID PLAQUES

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

43 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 MRI of Neovasculature

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

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 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”) Vessel sharpness: “The average edge value along the calculated vessel border” … “Higher edge values correspond to better vessel definition.”

49 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 METHODS

50 2D-TOF Results

51 DIR-BB Results

52 Gradient Value Comparison

53 Carotid Edge Values

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

55 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 CONCLUSIONS

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