Relationship between the position of the plaque signal intensity identified by 3D-FSE T1W MR plaque imaging and development of microembolic signals on transcranial Doppler during exposure procedure of carotid arteries in endarterectomy
Yasushi Ogasawara1, Kuniaki Ogasawara1, Yuiko Sato1, Shinsuke Narumi2, Makoto Sasaki3, Masakazu Kobayashi1, Shunrou Fujiwara1, Kenji Yoshida1, Yasuo Terayama2, and Akira Ogawa1

1Department of Neurosurgery, Iwate Medical University, Morioka, Japan, 2Department of Neurology and Gerontology, Iwate Medical University, Morioka, Japan, 3Institute for Biomedical Sciences, Iwate Medical University, Morioka, Japan

Synopsis

Preoperative 2D MR carotid plaque imaging can assess plaque vulnerability. It may allow improved risk stratification for patients considered for CEA and may be associated with development of MES during CEA. On the other hand, it is unclear what position of high signal intensity in the plaque, especially at the position showing maximum stenosis or maximum signal intensity, is deeply associated with MES, and it is difficult to validate it by the 2D plaque imaging. The aim of the present study was to determine where in the plaque is deeply associated with development of MES on TCD during CEA in carotid artery stenosis, using 3D-FSE T1W plaque imaging.

Purpose

Intraplaque characteristics assessed by preoperative 2D magnetic resonance (MR) carotid plaque imaging may be associated with development of microembolic signals (MES) 1 during carotid dissection in carotid endarterectomy (CEA). On the other hand, it is unclear what position of the plaque, especially at the position showing maximum stenosis or maximum signal intensity, is deeply associated with development of MES, however, it is difficult to validate it by 2D plaque imaging. The aim of the present study was to determine what position of the plaque signal intensity identified by preoperative 3D fast spin echo (3D-FSE) T1-weighted (T1W) plaque imaging2 in carotid artery stenosis is deeply associated with development of MES on transcranial Doppler (TCD) during exposure procedure of the carotid arteries in CEA.

Methods

Sixty patients with intracranial artery (ICA) stenosis (≧70%) underwent preoperative sagittal 3D-FSE T1WI of the affected carotid bifurcation within 1 week prior to CEA using a 1.5T MR imaging scanner (Signa HDxt; GE Healthcare, Milwaukee, Wisconsin) and an 8-channel neurovascular coil. The pulse sequence parameters were as follows: flow-sensitized 3D-FSE with variable flip angles; TR/TE, 500/18.3 ms; echo-train length, 24; b-value of the flow-sensitized gradients along 3 axes, 2.2 s/mm2; FOV, 25 × 19 cm2; matrix size, 512 × 512 (after zero-fill interpolation); section interval, 0.5 mm (after zero- fill interpolation); partitions, 248; voxel size, 0.5 × 0.5 × 0.5 mm3; parallel imaging factor, 2; NEX, 1; fat suppression, chemical shift selective suppression; and acquisition time, 3 minutes 54 seconds. Motion-sensitized gradients of 2.2 s/mm2 were used as the black-blood technique. Data of 3D-FSE T1W plaque imaging were processed by using a free software package (OsiriX, Pixmeo, Geneva, Switzerland) as follows (Fig.1): curved planar reformation (CPR) image was automatically generated along the carotid artery by carefully placing reference points in the center of the vessel on each axial source image. And then, new axial images perpendicular to the center line, connecting reference points in the center of the vessel, were reformatted with 1.0 mm thickness. In each patient, a reformatted axial image with the maximal plaque size and that with maximal plaque intensity were identified. In these two images, contrast ratio (CR) of the carotid plaque was calculated by dividing plaque signal intensity by sternocleidomastoid muscle signal intensity. Then CEA under TCD monitoring of MES in the ipsilateral middle cerebral artery (MCA). TCD was performed using a PIONEER TC2020 system (EME, Uberlingen, Germany; software version 2.50, 2-MHz probe; diameter, 1.5 cm; insonation depth, 40-66 mm; scale, -100 and +150 cm/s; sample volume, 2 mm; 64-point fast Fourier transform; fast Fourier transform length, 2 mm, fast Fourier transform overlap, 60%; high-pass filter, 100 Hz; detection threshold, 9 dB; minimum increase time, 10 ms) for insonation of the MCA ipsilateral to the carotid artery undergoing CEA. TCD data were stored on a hard disk using a coding system and were later analyzed manually by a clinical neurophysiologist who was blinded to patient information. MES were identified during exposure of the carotid arteries (from skin incision until ICA clamping).

Results

CRmax_size and CRmax_intensity were significantly higher in 16 patients with MES than in 44 patients without MES (p<0.0001). For all patients, the area under the receiver operating characteristic curve (AUC) to discriminate between presence and absence of MES was significantly greater with CRmax_intensity (0.929) than with CRmax_size (0.879) (p=0.0246). For 27 patients with identification of the image with the maximal plaque size and that with the maximal plaque intensity, AUCs for CRmax_size and CRmax_intensity were 1.000. For 33 patients without this identification, the AUC was significantly greater for CRmax_intensity (0.866) than for CRmax_size (0.787) (p=0.0110).

Discussion and conclusion

Consequently, preoperative 3D-FSE T1W plaque imaging for cervical carotid artery stenosis could demonstrate the deference in the ability for development of MES on TCD during exposure procedure of the carotid arteries in CEA between the highest signal intensity in the plaque and the signal intensity at the position with showing the highest degree of stenosis. It may be important for assessment for the plaque vulnerability in cervical carotid artery stenosis to carefully choose the position to measure the signal intensity of the plaque, not only the position with showing the maximum stenosis but also that with showing the highest signal intensity.

Acknowledgements

This work was partly supported by Grant-in-Aid for Strategic Medical Science Research (S1491001, 2014-2018) from the Ministry of Education, Culture, Sports, Science and Technology of Japan; Grant-in-Aid for Scientific Research (15K10313) from Japan Society for the Promotion of Science.

References

1) Spencer MP. Transcranial Doppler monitoring and causes of stroke from carotid endarterectomy. Stroke 1997;28:685-691.

2) Narumi S, Sasaki M, Natori T, Yamaguchi Oura M, Ogasawara K, Kobayashi M, Sato Y, Ogasawara Y, Hitomi J, Terayama Y. Carotid plaque characterization using 3D T1-weighted MR imaging with histopathologic validation: a comparison with 2D technique. AJNR Am J Neuroradiol. 2015;36:751-6.

Figures

Figure 1 Curved planar reformation (CPR) image and CRmax_size and CRmax_intesity

CPR image was reformatted from volume data of 3D-FSE T1W plaque imaging and the slices perpendicular to carotid artery were reformatted for measurement. Then, CRmax_size was measured on the slice showing maximum sectional plaque size (maximum stenosis) and CRmax_intesity was done on the slice showing maximum signal intensity in all.


Figure 2 Comparisons in contrast ratio in patients between without and with microembolic signal (MES) exposure procedure of carotid arteries in endarterectomy

When the position with the maximum stenosis was corresponding to that with the maximum signal intensity (left), the cut-off value to predict the development of MES could be clearly determined. On the other hand, when the two positions did not match (middle and right), it was difficult to clearly divide the groups without and with MES.




Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
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