MR Imaging of Atherosclerosis: MR Imaging of Atherosclerosis: The Seattle ExperienceThe Seattle Experience

University of Washington

Chun Yuan, Ph.D.Thomas S. Hatsukami, M.D.

Human Carotid Plaque

The First High Resolution Carotid 1.5 T MRI by Yuan et al

June 1998

The First High Resolution Carotid ImagingThe First High Resolution Carotid Imaging by a 3T MRIby a 3T MRI

Fine structures like plaque cap now can be imaged.

May 2003

1.5 T; 2 NEX; resolution 0.63x0.63 mm 3 T; 2 NEX; resolution 0.63x0.63 mm

3 T; 1 NEX; resolution 0.27x0.55 mm1.5 T; 1 NEX; resolution 0.27x0.55 mm

Comparing 1.5 and 3T Comparing 1.5 and 3T without Software Enhancementwithout Software Enhancement

GE 3T and 1.5T Scanners with Identical Phased-array Design

Carotid Artery Carotid Artery AtherosclerosisAtherosclerosis

• Stroke/TIA• Location• Carotid endarterectomy

(CEA)• Access to plaque specimen• In vivo and Ex vivo studies• Histology

Carotid MRI HardwareCarotid MRI Hardware

Phased array coilsPhased array coils• Designed / built in-house• Flexible• Bi-lateral• Significant SNR improvement

Head holderHead holder• Restricts motion• Consistent positioning• Patient comfort

- Hayes, et al., JMRI 6:109-112, 1996.Pathway Medical Technologies, Redmond, WA

Imaging Protocol: Imaging Protocol: Multi-Contrast WeightingMulti-Contrast Weighting

• DIR/MDIR technique• Bright/black blood • Spatial resolution

• 0.31 x 0.31 x 2 mm

• Total scan time • 30 minutes

• Serial scan capability

TOF T1W

PDW T2W

Quantitative AnalysisQuantitative Analysis

• Quantitative Vascular Analysis System (QVAS)

PD

T1

TOF

Fibrous cap

Lipid core

Calcium Media/adventitia

Lumen

Hemorrhage

Kerwin WS, et al. Proceedings of MICCAI 4th International Conference, 786-794, 2001.

QVAS: Morphological IndexesQVAS: Morphological Indexes

• Vessel lumen and wall area/volume• Wall thickness • Eccentricity and lesion distribution

Han C, et al. IEEE Transactions on Image Processing, 10(6): 865-873, 2001.

Inter-scan and Inter-rater VariabilityInter-scan and Inter-rater Variability

V1

V2

Blood Vessel Volume MeasurementBlood Vessel Volume Measurement

• Precision of MRI for Measuring Plaque Volume• 3.8 – 4.6% for T1W,

PDW, & T2W imaging• Possible to detect a >

13% change in plaque volume with 95% confidence

• IQ – most important factor

Hemorrhage - Recent

(Type VI)

TOF T1WI

PDWI T2WI

Mallory’s Trichrome

MRI Based Lesion TypeMRI Based Lesion Type

MRI Based Lesion TypeMRI Based Lesion Type

TOF T1WI

PDWI T2WI

H&E

Type VIII: Fibrous Lesion

Fibrous Cap CharacteristicsFibrous Cap CharacteristicsGross

SpecimenMasson’s Trichrome In Vivo 3D-MOTSA Image

1 32

3

1 = Fibrous Cap Rupture

2 = Intraplaque Hemorrhage

3 = Thick Fibrous Cap

Thick fibrous cap appears as dark band between lumen and plaque core.

Recent plaque hemorrhage appears hyperintense.

Risk of Symptoms by Cap Status on MRIRisk of Symptoms by Cap Status on MRI

95% CI

3, 210

1, 104

---

23

10

1

OR for Sx

70%

50%

9%

% w/ Sx

Ruptured Cap

Thin Cap

Thick Cap

Cap Status

p = 0.001 Mann-Whitney test for cap status vs. symptoms

DCE-MRI ProtocolDCE-MRI Protocol

• MRI: 2DSPGR (TR / TE = 100 / 3.5 msec)• Contrast agent: 20 ml Omniscan (Gadolinium-based)

administered at 2ml/sec

time~15 sec

DynamicMRI

Contrast injection

Pre-contrastMRI

Post-contrastMRI

t = 1 t = nt = 3t = 2

...

DCE- Kinetic Model ResultsDCE- Kinetic Model Results

0

5

10

15

20

25

30

0 0.5 1 1.5 2 2.5 3fVA (%) by histology

fBV

(%) b

y M

RI

R = 0.80p < 0.001

SummarySummary• High resolution MRI

• Carotid phased array

• Black/bright blood• Multi-contrast

weighting• Contrast agent

application

• High resolution MRI• Fibrous cap• Microvessels• Lipid core• Ca• Lumen surface condition• Matrix• Volume

Grant support provided by: NIH and AstraZeneca Pharmaceuticals, Pfizer, and Esperion Therapeutics

vil.rad.washington.edu

Department of Radiology Niranjan Balu Tobias SaamBaocheng Chu Dongxiang Xu William S. Kerwin Annette KampshulteZachary E. Miller Vasily Yarnykh

Department of Pathology

Russell Ross Steve SchwartzRandy Small Marina S. Ferguson

Department of E. E. Jenq Neng Hwang Ying Luo

Mountain Whisper Light Nayak Polissar

C. Yuan, T.S. Hatsukami