Synopsis

Keywords: Blood vessels, Vessels

Morphological characteristics of lenticulostriate arteries (LSAs) have important clinical significance. TOF MRA and intracranial vessel wall imaging (VWI) are powerful noninvasive vascular imaging techniques routinely used in vascular visualization. However, due to the small caliber of LSAs, it is difficult for conventional 3T TOF MRA to achieve the visualization of LSAs. High-resolution magnetic resonance imaging based on compressed sensing (CS) technology is expected to solve this dilemma. DSA is the gold standard for vascular visualization. This study proposes an optimized high-resolution TOF MRA scanning scheme based on CS technology and shows its feasibility in LSA visualization by comparing with DSA.

Introduction

Hypertension and atheromatous disease have been proved to damage lenticulostriate arteries (LSAs) and cause morphological changes of LSAs [1, 2]. The LSA bright blood visualization with TOF MRA was initially realized at ultra-high-field 7T with superior spatial resolution and vessel to tissue contrast[3, 4]. However, the availability of 7T systems in clinical settings is very limited[5]. At clinical field strength, study have shown that 3T vessel wall imaging (VWI) is capable of depicting LSAs, with comparable image quality to that of 7T TOF-MRA[6]. Conventional 3T TOF MRA techniques is difficult to accurately visualize LSAs[5], because of its limited resolution within clinical acceptable scanning time. Compressed sensing (CS) technology enables accelerated MRI by nonlinear iterative reconstruction of sparsely under-sampled k-space data. CS has been used to accelerate TOF MRA for artery visulization. DSA is considered as the gold standard for intracranial large vascular visualization[7].Therefore, this study proposes an optimized high-resolution TOF MRA scanning scheme based on CS acceleration technology and shows the feasibility of 3T high-resolution TOF MRA and VWI sequences in LSA visualization compared with DSA.

Methods

Two patients who underwent DSA were examined on a 3T MR scanner (Siemens Healthcare, Erlangen, Germany). The protocol consisted of 3D high-resolution TOF MRA and 3D T1 SPACE sequences. Imaging Parameters are shown in Table 1. TOF MRA and SPACE images were reconstructed by volume rendering (VR), maximum intensity projection (MIP) or minimum intensity projection (MinIP). The number of LSA stems and branches was counted by two experienced radiologists. Stems were defined as the portion of the LSA that originated directly from the MCA or ACA and branches are defined as daughter vessels originating from parent LSA stems. The maximal length was measured on the longest LSA in reformatted coronal image, which was the curved length from MCA to the visible end.

Results

The results of this study demonstrate the potential of 3T high-resolution TOF MRA and T1 SPACE in LSA visualization. The maximal length of LSA, the number of LSA stems and branches were recorded. VR, MIP and MinIP images are used to visualize LSAs.
Patient 1
A 53 years old female with a history of left middle cerebral artery bifurcation aneurysm embolization one year ago. High-resolution TOF MRA and T1 SPACE at 3T presented LSAs on VR, coronal MIP or MinIP images (Fig.1). The number of LSA stems in left/right cerebral hemisphere on MRA and T1 SPACE is 3/1 and 3/2, respectively. The number of LSA branches in left/right cerebral hemisphere on MRA and T1 SPACE is 5/5 and 4/6, respectively (Fig.1A-D). The maximal length of LSA in left/right cerebral hemisphere on MRA and T1 SPACE is 48.4/58.0mm and 47.3/49.3mm, respectively (Fig.1G-H). The initial segment of LSAs travelled naturally with better visualization effect on TOF MRA than T1 SPACE, while the reverse is true for the distal segment. Due to the influence of complete visualization of small intracranial arteries, it is difficult for DSA to recognize LSAs in left cerebral hemisphere (Fig.1E-F).

Patient 2
A 59 years old female with a history of anterior communicating aneurysm embolization one year ago. The number of LSA stems in right/left cerebral hemisphere on MRA and T1 SPACE is 3/2 and 4/3, respectively. The number of LSA branches in right/left cerebral hemisphere on MRA and T1 SPACE is 5/4 and 6/5, respectively (Fig.2A-D). The maximal length of LSA in right/left cerebral hemisphere on MRA and T1 SPACE is 47.2/37.7mm and 45,1/43.3mm, respectively (Fig.2G-H). T1 SPACE have shown more LSAs with smaller caliber than TOF MRA, but the assessment is more difficult than MRA. The visualization effect of DSA to recognize LSAs is poor (Fig.2E-F).

Discussion

Morphological characteristics of LSAs have important clinical significance and prognostic value. Ultra-high field-strength MR (5 T and 7 T) have shown the capability to visualize LSAs, however, it is still not easy to be implemented in routine clinical examinations[5]. This study has demonstrated that high-resolution TOF MRA based on CS technology at 3T is capable of depicting LSAs within 9 minutes. High-resolution TOF MRA and T1 SPACE demonstrated greater potential in visualization of the initial segment of LSAs than DSA.
3T T1 SPACE is capable of depicting LSAs and assess LSAs impairments[1, 6]. However, LSA evaluation is time-consuming and instability, because of its tortuous travelling and morphologic variations[8]. These drawbacks will bring more challenges to clinical implementation. Quantitative assessment of LSAs is easier to implement on TOF MRA than T1 SPACE. Automated processing pipeline for quantifying LSA on TOF MRA has been proposed[5, 8]. The application of VR image, combined with MIP image, is more beneficial to evaluate the morphologic variations of LSAs，which is consistent with this study.

Conclusions

High-resolution TOF MRA based on CS technology is capable of depicting LSAs. 3T high-resolution TOF MRA and T1 SPACE sequences show better visualization effects than DSA and provide a potential alternative imaging method of LSAs.

Table1

Table 1 Imaging Parameters of TOF MRA andT1 SPACE

	CS TOF MRA	T1 SPACE
Scan time	7:47	8:58
Voxle size	iso 0.3mm	iso 0.3mm
FOV	170mm	172mm
Matrix	348x352	320x320
Acceleration factor	Cs=3.8	Grappa =2
TR	37.96ms	800ms
TE	6.15ms	20ms
Acquisition orientation	transversal	sagittal
Flip angle (degrees)	20	N/A

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