Non-invasive Imaging of Carotid Artery Atherosclerosis

Transcription

1 Non-invasive Imaging of Carotid Artery Atherosclerosis 최연현 성균관의대삼성서울병원영상의학과

2 Noninvasive Techniques US with Doppler CT MRI

3 Ultrasonography

4 Techniques of Carotid US US Anatomy (ICA vs ECA) Gray scale and color Doppler exam Transducer selection (4-7 vs MHz) Artifacts New techniques

5 경동맥협착의 Doppler 진단 Criteria: Parameters ICA 의 peak systolic velocity ICA 의 end diastolic velocity ICA/CCA 의 peak systolic velocity ratio Proximal ICA(stenotic lesion)/distal ICA peak systolic velocity ratio

6 Duplex Criteria: Comparison of Recommended Values Study Severity PSV EDV VICA/VCCA Ratio Moneta > 70% (to 4.2) Carpenter > 70% Neale > 70% NA Hood > 70% NA Browman > 70% NA NA Moneta > 60% Carpenter > 60% Derdeyn > 60% NA NA

7 Duplex Criteria: for 50% and 70% Stenosis. (Robinson et al. AJR,1988) Dm PSV EDV VICA/VCCA Stenosis 50% > 150 >50 >2 70% > 230 >75 >3 Ratio

8 경동맥협착의 Doppler 진단 Criteria CCA 의 peak velocity 는근위부와원위부에서측정할때차이 (23 cm/sec 범위 ) Stenosis > 90-95%: PSV< 25 cm/sec

9

10 Pitfalls Hypertension or hypotension Severe stenosis of distal ICA Stenosis of contralateral ICA Tandem lesions Ulceration of plaque Vessel tortuosity

11 Intimomedial Thickness Measurement

12 US quanfication of carotid atheroma Manual or semi-automated method Thickness, area, and volume measurement of plaques IMT measurement Objectiveness? (operator-dependent)

13

14 Carotid IMT and Brain Infarction Touboul et al. Circulation 2000;102: pts with brain infarction and 463 controls Mean IMT was higher in pts with brain infarction (0.797 mm vs mm, p <0.0001) Odds ratio per SD increase (0.150) = 1.82 (95% conf. Level = 1.54~2.15)

15 Enhanced CT

16 Maximum Intensity Projection

17 Noncalcified Coronary Artery Plaque

18 Plaque Characterization: ICUS vs CT Schroeder Leber Soft HU HU Intermed HU Calcified HU HU Schroeder et al. J Am Coll Cardiol 2001;37:1430 Leber et al. J Am Coll Cardiol. 2004;43:1241

19 Plaque Quantification HanWonhee

20

21 MR Angiography: Techniques Noncontrast: time-of-flight, phase contrast, true FISP (b-ffe, FIESTA) Longer time, motion artifact, flow sensitive Contrast-enhanced MRA High SI, quick, less artifacts, depiction of vessel origins from the aortic arch

22 CE-MRA vs TOF MRA

23 Sonography in Imaging Atheroma Fibrofatty, fibrocalcific, calcific type Inhomogeneous atheroma: calcifications, cholesterol crystals, hemorrhage Plaque cap rupture: irregular surface, ulcer

24 US Assessment of Plaque Composition

25 Ulcerated Plaques

26 Inhomogeneous Plaque

27 MRI for Carotid Atheroma Excellent tissue contrast (fat, fibrous tissue, collagen, thrombus) Noninvasive More accurate and objective estimation of stenosis degree than US

28 MRI Techniques T1-weighed spin echo imaging (precontrast axial, again with fat-saturation, postcontrast axial) Double inversion-recovery SE imaging (axial) T2-weighted spin echo imaging (axial) Proton-WI (axial) 3D Time-of-flight MRA (source and 3D images) Two 3-inch phased-array coils, bilateral application Field of view: 8x8 cm or cm Slice thickness = 2-3 mm, matrix, NEX = 1 or 2

29 Atheromatous Core Mostly composed of cholesterol and cholesterol esters in solid (crystal) and smectic (liquid-crystaline) state Short T2 of core due to Micellar structure of lipoproteins Denaturation by oxidation Exchange btw CEs and water molecules T2WI

30 Regions with Fibers Collagen, elastin, proteoglycan Moderately high SI areas on T2WI

31 MRI Appearance of Plaque Components on Various Imaging Sequences Plaque Components T2WI T1WI T1WI, Proton WI TOF CE on Fat- Post- Suppr. Contrast Recent Hemorrhage Variable H-to-M H Variable H No Lipid-rich Necrotic Core Variable (L) H M-to-H H M No Fibrous Tissue Variable M M H M-to-L Yes Calcification L L L L L No Tissue contrast is relative to SI of muscle

32 Stable Plaque T2WI Pathology

33 Lipid-rich Plaque FISSURE T1WI Proton-WI T2WI TOF

34 Fibrous Cap on MRI LeeSG

35 Intact plaque cap with intraplaque hemorrhage (fibrin) TOF Cap T1FS Fibrin

36 Contrast-enhancement in fibrous component Pre Post

37 Increased neovasculature within plaque may contribute to plaque instability. Contrast-enhancement represents neovasculature in the histopathology (sensitivity 76%, specificity 79% by Yuan). Contrast-enhancement improves differentiation of tissue types (fibrous tissue, necrotic core, calcifications).

38 Plaque Characterization by Contrast-enhancement Pre Post Chinyongil

39 MRI Accuracy Ex vivo T2WI: Accurate for fibrocalcific plaques (90% sensitivity, 100% specificity) -Serfaty et al In vivo multispectral MRI for lipid-rich cores and intraplaque hemorrahge: overall accuracy 87%, sensitivity 85%, specificity 92% -Yuan et al

40 Fibrous Cap Rupture at MRI and Recent TIA or Stroke (Yuan, Circulation 2002) Intact thick FC (n = 11) % Symptomatic Likelihood to have TIA/stroke 9 1X Odds Ratio Intact thin FC (n = 12) Ruptured FC (n = 30) 50 10X (95% CI = 1.0, 104) 70 23X (95% CI = 3, 210) 6 18

41 Lipid lowering drugs Direct effects on Endothelial cell function Inflamm. cell activity VSMC proliferation Platelet aggregation Thrombus formation

42 Effects of Lipid-Lowering Therapy on Carotid Plaques at MRI Significant reduction in vessel wall thickness and area at 12 m and after (Corti, 2001) Pts with 10-y intensive therapy had a smaller core lipid area and lipid composition than control group (Zhao 2001)

43 Changes in Carotid Plaques after Statin Therapy: MRI Evaluation 45 pts with 30-70% stenosis PreTx (Simbastatin 20 mg) and F-up MRI (19 ± 7.5 m) Decreased mean total chol., LDL, & CRP compared with control group: Total Chol = 188 ± 26 vs 158 ± 50, p<.001 LDL = 125 ± 23 vs 110± 42, p <.001 CRP = 0.41 ± 0.59 vs 0.10 ± 1.3, p<0.01

44 Results Stabilization of plaque components on MRI in 16% (7/45) Decreased plaque thickness: 4.2 mm± 1.0 vs 3.4 mm ± 1.3, p < 0.001

45 Increased Fibrotic Component on T2WI at 20 m f-up YoonJY

46 Improved Wall Thickness, at 1 y (0.5 mm) YoonYCh

47 Contrast Agents for MR Imaging of Atherosclerosis Ultrasmall superparamagnetic particles of iron oxide (USPIO) Fibrin-specific polypeptide (EPIX) Plaque detection by Gadofluorine (Schering)

48 USPIO in Watanabe Hyperlipidemic Rabbits (5 ds) Watanabe Control Watanabe USPIO USPIO No USPIO

49 Gadofluorine M Courtesy of Dr Whal Lee, SNUH

50 Fibrin-specific polypeptide (20 h post EP-1873, EPIX) Botnar, Circulation 2004

51 Summary Noninvasive imaging studies may eliminate the need of DSA in assessment of stenosis degree. CT angiography and high-resolution MRI/MRA can be useful in further evaluation of intracranial/extracranial carotid arteries and coronary arteries in selected patients High-resolution MRI can identify vulnerable carotid plaques and allows early intervention on unstable plaques.