Non-invasive Imaging of Carotid Artery Atherosclerosis 최연현 성균관의대삼성서울병원영상의학과
Noninvasive Techniques US with Doppler CT MRI
Ultrasonography
Techniques of Carotid US US Anatomy (ICA vs ECA) Gray scale and color Doppler exam Transducer selection (4-7 vs 10-13 MHz) Artifacts New techniques
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
Duplex Criteria: Comparison of Recommended Values Study Severity PSV EDV VICA/VCCA Ratio Moneta > 70% 325.0 130.0 4.0 (to 4.2) Carpenter > 70% 210.0 70.0 3.0 Neale > 70% 270.0 110.0 NA Hood > 70% 130.0 100.0 NA Browman > 70% 175.0 NA NA Moneta > 60% 260.0 70.0 3.2 Carpenter > 60% 170.0 40.0 2.0 Derdeyn > 60% 230.0 NA NA
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
경동맥협착의 Doppler 진단 Criteria CCA 의 peak velocity 는근위부와원위부에서측정할때차이 (23 cm/sec 범위 ) Stenosis > 90-95%: PSV< 25 cm/sec
Pitfalls Hypertension or hypotension Severe stenosis of distal ICA Stenosis of contralateral ICA Tandem lesions Ulceration of plaque Vessel tortuosity
Intimomedial Thickness Measurement
US quanfication of carotid atheroma Manual or semi-automated method Thickness, area, and volume measurement of plaques IMT measurement Objectiveness? (operator-dependent)
Carotid IMT and Brain Infarction Touboul et al. Circulation 2000;102:313 470 pts with brain infarction and 463 controls Mean IMT was higher in pts with brain infarction (0.797 mm vs 0.735 mm, p <0.0001) Odds ratio per SD increase (0.150) = 1.82 (95% conf. Level = 1.54~2.15)
Enhanced CT
Maximum Intensity Projection
Noncalcified Coronary Artery Plaque
Plaque Characterization: ICUS vs CT Schroeder Leber Soft 14 26 HU 49 22 HU Intermed 91 21 HU Calcified 416 194 HU 391 156 HU Schroeder et al. J Am Coll Cardiol 2001;37:1430 Leber et al. J Am Coll Cardiol. 2004;43:1241
Plaque Quantification HanWonhee
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
CE-MRA vs TOF MRA
Sonography in Imaging Atheroma Fibrofatty, fibrocalcific, calcific type Inhomogeneous atheroma: calcifications, cholesterol crystals, hemorrhage Plaque cap rupture: irregular surface, ulcer
US Assessment of Plaque Composition
Ulcerated Plaques
Inhomogeneous Plaque
MRI for Carotid Atheroma Excellent tissue contrast (fat, fibrous tissue, collagen, thrombus) Noninvasive More accurate and objective estimation of stenosis degree than US
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 10 10 cm Slice thickness = 2-3 mm, 256 192 matrix, NEX = 1 or 2
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
Regions with Fibers Collagen, elastin, proteoglycan Moderately high SI areas on T2WI
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
Stable Plaque T2WI Pathology
Lipid-rich Plaque FISSURE T1WI Proton-WI T2WI TOF
Fibrous Cap on MRI LeeSG
Intact plaque cap with intraplaque hemorrhage (fibrin) TOF Cap T1FS Fibrin
Contrast-enhancement in fibrous component Pre Post
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).
Plaque Characterization by Contrast-enhancement Pre Post Chinyongil
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
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
Lipid lowering drugs Direct effects on Endothelial cell function Inflamm. cell activity VSMC proliferation Platelet aggregation Thrombus formation
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)
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
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
Increased Fibrotic Component on T2WI at 20 m f-up YoonJY
Improved Wall Thickness, at 1 y (0.5 mm) YoonYCh
Contrast Agents for MR Imaging of Atherosclerosis Ultrasmall superparamagnetic particles of iron oxide (USPIO) Fibrin-specific polypeptide (EPIX) Plaque detection by Gadofluorine (Schering)
USPIO in Watanabe Hyperlipidemic Rabbits (5 ds) Watanabe Control Watanabe USPIO USPIO No USPIO
Gadofluorine M Courtesy of Dr Whal Lee, SNUH
Fibrin-specific polypeptide (20 h post EP-1873, EPIX) Botnar, Circulation 2004
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.