Non-invasive Imaging of Carotid Artery Atherosclerosis2005/08/05  · MRI Appearance of Plaque...

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

경동맥 협착의 Doppler 진단Criteria: Parameters

• ICA의 peak systolic velocity

• ICA의 end diastolic velocity

• ICA/CCA의 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 Ratio

50% > 150 >50 >2

70% > 230 >75 >3

경동맥 협착의Doppler 진단 Criteria

• CCA의 peak velocity는 근위부와원위부에서 측정할 때 차이(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 1010 cm

• Slice thickness = 2-3 mm, 256192 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,

Fat-

Suppr.

Proton

WI

TOF CE on

Post-

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

T1WI Proton-WI T2WI

FISSURE

TOF

Lipid-rich Plaque

LeeSG

Fibrous Cap on MRI

Intact plaque cap with intraplaque

hemorrhage (fibrin)

Cap

Fibrin

TOF T1FS

Pre Post

Contrast-enhancement in fibrous

component

• 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)

%

Symptomatic

Likelihood to

have

TIA/stroke

Odds Ratio

Intact thick FC

(n = 11)

9 1X

Intact thin FC

(n = 12)

50 10X

(95% CI =

1.0, 104)

6

Ruptured FC

(n = 30)

70 23X

(95% CI = 3,

210)

18

Lipid lowering drugs

Direct effects on

• Endothelial cell function

• Inflamm. cell activity

• VSMC proliferation

• Platelet aggregation

• Thrombus formation

Effects of Lipid-Lowering Therapy onCarotid 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)

USPIO USPIO No USPIO

Watanabe Control Watanabe

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.