The performances evaluation of 32-channel coil system for extracranial and intracranial artery wall imaging at 3T
Xiaoqing Hu1, Lei Zhang1, Xiao Chen1, Xiaoliang Zhang2,3, Xin Liu1, Hairong Zheng1, Yiu-Cho Chung1, and Ye Li1

1Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, CAS, Shenzhen, China, People's Republic of, 2Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States, 3UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, CA, United States

Synopsis

Atherosclerosis is a major cause of ischemic stroke. The high resolution magnetic resonance imaging (MRI) of vessel wall can detect nonstenotic atherosclerotic plaque missed by luminal angiography. To develop a multi-channel radiofrequency (RF) coil system with high spatial resolution and large longitudinal coverage for the intracranial and extracranial arteries vessel wall imaging in one setting. The high resolution images with 0.6 mm3 are obtained with the proposed “24+8” channel coil system from a patient in vivo.

Purpose

Atherosclerosis is a major cause of ischemic stroke [1-2]. The high resolution magnetic resonance imaging (MRI) of vessel wall can detect nonstenotic atherosclerotic plaque missed by luminal angiography. This work aims to develop a multi-channel radiofrequency (RF) coil system with high spatial resolution capability and large longitudinal coverage for the intracranial and extracranial artery wall imaging in one setting.

Methods and Materials

A “24+8” channel coil system for simultaneous imaging of extracranial and intracranial arterial wall is developed by combining the designed 24-channel head coil [3] with a separate 8-channel carotid coil as shown in Fig. 1. The “24+8” channel coil system is compared with the “12+4+8” configuration [4] (12-channel head coil combing with 4-channel neck coil and 8-channel carotid coil) for their SNR distribution. Phantom study: A cylindrical phantom (filled with 1.24g/L NiSO4•6H2O and 2.62g/L NaCl, from Siemens) measuring 160mm in diameter and 320mm in length is used to evaluate the coil system's sensitivity over an area of interest large enough to cover the head and neck. A gradient echo (GRE) sequence with the following parameters is used for image acquisitions: TR = 300ms, TE = 10ms, bandwidth = 130Hz/pixel, FOV = 320×320mm2, slice thickness = 3mm, acquisition matrix = 256×256, flip angle = 60 degree. Sagittal and coronal images are acquired. Noise images are acquired by setting transmit voltage to zero on the scanner. The covariance root sum of squares (Cov-SoS) [5] method was used to reconstruct the images. The SNR map was calculated based on reference [5]. In-vivo study: A patient previously diagnosed to have both intracranial and extracranial atherosclerosis is recruited and scanned with the proposed “24+8” channel coil system to validate its ability to image vessel walls. A T1w-SPACE sequence, modified to support DANTE with improved CSF signal suppression, is used. The 3D imaging volume covers the area from the extracranial to intracranial arteries. Imaging parameters are: FOV = 159×212mm2, ETL = 35, ESP = 4.34ms, resolution matrix = 256×336, TR/TE = 1140/27ms, bandwidth = 531Hz/ pixel, averages = 1.4 (21), iPAT = 2, partition = 72, total time = 7m36s.

Results

Figure 2 (A1-A4) shows how the SNR varies with the imaging volume in the proposed “24+8” channel coil system and the “12+4+8” configuration. Their SNR variation over the 320mm region is also shown in Fig. 2 (A5-A6). In the head region, the SNR of the proposed “24+8” channel coil system is significantly higher than that of the “12+4+8” configuration. In the carotid region, the SNR of the proposed “24+8” channel coil system is almost identical to that of the “12+4+8” configuration. The curve reconstruction results of pre-contrast left and right intracranial and extracranial arterial vessel wall for the patient obtained with the proposed coil system are shown in Fig. 3(a) with isotropic spatial resolution of 0.6mm3. The plaques at M1 segment of the mid cerebral artery and carotid bifurcations are demonstrated in Fig. 3(b) and (c). The vessel wall of intracranial and extracranial artery and surrounding tissues visualization can be clearly depicted in this case. This manifests that the proposed “24+8” channel coil system is capable of intracranial and extracranial arterial vessel wall imaging in human examinations.

Discussion/Conclusion

In this study, a “24+8” channel coil system is developed by combining a 24-channel head coil with dedicated 8-channel carotid coil for MR imaging of intracranial and extracranial arteries wall. Compared to the “12+4+8” configuration, the proposed “24+8” channel coil system is superior in terms of SNR in head part and nearly the same in neck part. The high resolution images with 0.6 mm3 are obtained with the proposed “24+8” channel coil system from a patient in vivo. For the “24+8” channel coil system, the SNR is not sufficient in upper torso. Some optimizations of the “24+8” channel coil system are needed in the future study to image the arterial vessel wall in upper torso.

Acknowledgements

This work is supported in part by national grants No. 51307171, 61571433, 61401450 and 81470077, provincial grants No. 2014A030313691, 2015B020214006 and 2014A030310200, city grant No. JCYJ20140610152828673, and internal grant No. 201314.

References

[1] Fisher M, et al., Stroke, 2005;36(2):253-257. [2] Tartari S, et al., AJR, 2011;196(5):1164-1171. [3] X. Hu, et al., ISMRM 2015, p. 4386. [4] X. Hu, et al., ISMRM 2014, p. 2543. [5] B. Keil et al., JMR 2013, 229, 75-89.

Figures

Fig. 1. The proposed “24+8” channel coil system in phantom study (A1) and in-vivo study (A2).

Fig. 2. The SNR map of proposed “24+8” channel coil system (A1 and A3) and “12+4+8” configuration(A2 and A4) in sagittal and coronal plane. The A1 and A2 correspond to sagittal plane. The A3 and A4 correspond to coronal plane. The SNR profile in sagittal plane (A5) and coronal plane (A6) through a line 40mm away from boundary for proposed “24+8” channel coil system and “12+4+8” configuration.

Fig. 3. (a) The curve reconstruction results of left and right intracranial and extracranial arterial vessel wall for a patient. obtained with 32-channel coil system. (b) The plaque in intracranial arterial vessel wall. (c) The plaque in extracranial arterial vessel wall.



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