IN VIVO MRI OF THROMBI IN ADVANCED ATHEROSCLEROTIC

CAROTID ARTERYVincent Cappendijk1

Kitty Cleutjens1

Sylvia Heeneman1

Geert Willem Schurink1

Rob Welten2

Fons Kessels1

Mat Daemen1

Jos van Engelshoven1

Eline Kooi1

1University Hospital of Maastricht, Cardiovascular Research Institute Maastricht (CARIM), 2Atrium Hospital Heerlen,

Netherlands

Background (1)• Atherosclerosis is a major source of morbidity and mortality

-61,800,000 Americans have one or more types of

cardiovascular disease (CVD)

-Mortality CVD: 958,775 yearly

-Costs: 329.2 billion DollarSource: American Heart Association Website

Background (2)• Plaque composition rather than plaque size

(degree of stenosis) is the predictor of risk on thrombo-embolic events

• High-resolution multi-contrast MRI can subjectively detect atherosclerotic plaque components in vivo1,2

• Thrombus, a component in advanced (high-risk) lesions is still difficult to detect

1 Yuan et al. Radiology 2001; 221: 2852 Fayad et al. Circulation Research 2001; 89: 305

From low-risk to high-risk plaque

From fatty streak to ruptured lesion

Berliner et al. Circulation. 1995;91:2488-2496

Thrombus detection with MRIPDw FSE

T2w FSE

T1w FSE

MPRAGE

Calcified

low low low -

Lipid normal /high

low low -

Fibrous normal /high

high normal/high

-

Thrombus

normal /high

variable high high

Yuan et al, Fayad et al, Zhao et al, von Ingersleben et al, Shinnar et al, Moody et al.

Aim of the present study

• Identification of thrombus in the carotid artery with high-resolution MRI and T1w Turbo Field Echo technique (T1w TFE or MPRAGE)

• Compare this technique with T1w Fast Spin Echo (FSE)

• Determine the performance and agreement of two observers for both techniques

Subjects & Methods (1)

• 11 symptomatic patients with a carotid stenosis of more than 70%

• Pre-operative MRI scan (mean 5 +/- 4 days)

• Pathology is gold standard

• High MR signal relative to muscle tissue = positive test result

Subjects & Methods (2)

• MRI slices were matched with the corresponding histological slices by Reader 1 (bifurcation, ink, gross morphological features)

╸╹

Subjects & Methods (3)• Reader 2 scored the same by Reader 1 marked locations (unaware of the results of Reader 1)

Histology:

• Gross assignment of major plaque components (fibrous tissue, lipid core, calcification, thrombus)

• Only areas with pre-dominantly one of these tissue types were marked

MRI Protocol (1)

Hardware: 1.5 T Philips Intera whole body scanner(Gyroscan NT, release 8.1)Small diameter receiver surface coil (47 mm)

MRI Protocol (2) Technique turbo field echo fast spin echo

TR / TE 10.3 / 4.0 ms 570 / 14 ms

(double inversion pulse)

FA 15º 90º

TI 900 ms 255 ms

In-plane resolution 0.39x0.39 mm 0.39x0.39 mm

Acquisitions 6 2

Slices 3 mm 3 mm

Scan time (9 slices) 3 minutes 7 minutes

T1w 3D TFE T1w 2D FSE

Results (1)Detection rate of thrombus T1w TFE

 

Histology Thrombus + Thrombus –

MRI Reader 1 Reader 2 Reader 1 Reader 2

Thrombus + 40 35 8 4

Thrombus - 3 8 43 47

43 51

Results (2)Detection rate of thrombus T1w FSE

 

Histology Thrombus + Thrombus –

MRI Reader 1 Reader 2 Reader 1 Reader 2

Thrombus + 34 31 22 18

Thrombus - 9 12 29 33

43 51

Results (3)Detection rate of thrombus

T1w TFE T1w FSE

Reader 1 93% (95% C.I.: 81-99%) 79% (95% C.I.: 64-90%)

Reader 2 82% (95% C.I.: 67-92%) 72% (95% C.I.: 56-85%)

Kappa 0.73 0.29

Results (4)False positive results

•FSE had far more false positive results than TFE (32 vs 9;i.e. the different false positives for both readers together)

•The 9 false positives of TFE were all fibrous tissue,located within the thickened vessel wall but outside themain plaque area

•Most areas with fibrous tissue were scored correctlyin TFE (20/29)

Example of a true positive resultT1w 3D TFE

T1w FSEHistology: Internal carotidartery containing thrombus

Example of false positive T1w FSE

Carotid bifurcation; The arrows indicate two areas of histological proved fibrous tissue in the internal and external carotid artery. These areas have high signal intensity in FSE, but not in TFE

T1w 3D TFET1w FSE

Discussion

• FSE has far more false positive results than TFE

-this might be due to a T2* effect

• The 9 false positives in TFE were all located within the thickened vessel wall but outside the main plaque area. However, most areas with histological tissue were scored correctly in TFE (20/29)

-possibly not only high signal intensity but also its location determines if its thrombus

Conclusions

• Thrombus can be accurately detected with T1w TFEhigh-resolution MRI

• FSE performed significantly worse

• Two readers could detect more than 80% of histological proven thrombi using T1w TFE (Kappa=0.73)