Improving Visualization of Superficial Temporal Artery Using Segmented TOF MR Angiography at 7T
Zihao Zhang1,2, Ning Wei1,2, Xiaofeng Deng3, Dehe Weng4, Jing An4, Yan Zhuo1, Xiaohong Joe Zhou5, and Rong Xue1,6

1State Key Laboratory of Brain and Cognitive Science, Beijing MR Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China, People's Republic of, 2Graduate School, University of Chinese Academy of Sciences, Beijing, China, People's Republic of, 3Department of Neurosurgery, Beijing Tiantan Hospital, Capital Medical University, Beijing, China, People's Republic of, 4Siemens Shenzhen Magnetic Resonance Ltd., Shenzhen, China, People's Republic of, 5Center for MR Research and Department of Radiology, University of Illinois at Chicago, Chicago, IL, United States, 6Beijing Institute for Brain Disorders, Beijing, China, People's Republic of


Time-of-Flight MR Angiography (TOF-MRA) can benefit from better contrast and higher spatial resolution using ultra-high field 7T MRI. In a segmented TOF technique at 7T, the Specific Absorption Rate (SAR) of saturation pulses was reduced to enable the suppression of venous blood signal. In this study, the TOF technique was successfully used to discriminate between the superficial temporal artery (STA) and vein (STV), and depict blood flow in tiny vessels, facilitating future applications in pre-operative assessment for STA-MCA bypass surgery.


TOF-MRA benefits substantially from increasing the static B0 field strength from 3T to 7T, because of improved SNR and longer T1 relaxation.1 However, venous saturation (VS) band is typically omitted at 7T to satisfy the SAR limitation. Segmented TOF2 is an efficient approach to suppress venous signal with sparse saturation pulses. With this technique, the flow signal from small arteries can be imaged at 7T without contamination from veins.

The purpose of this study is to apply segmented TOF with VS to imaging STA while suppressing STV at 7T, and compare the results with 3T to demonstrate the advantage for depicting small branches of vessels.


17 volunteers aged 18–27 without cerebral vascular diseases were recruited. Each participant underwent MRI and whole-brain imaging of segmented TOF with VS and conventional TOF without VS at 7T (Siemens Healthcare, Erlangen, Germany) by using a prototype sequence as well as conventional TOF with VS at Prisma 3T (Siemens Healthcare, Erlangen, Germany). A Nova 32-channel phased-array head coil was used at 7T, and a Siemens 64-channel phased-array head/neck coil at 3T. Extracranial ROIs were manually identified on all images. Maximum Intensity Projection (MIP) was applied to extracranial TOF images on left and right sides, respectively. The number of visible vessels in frontal and parietal branches of STA at 7T and 3T were compared using a paired t-test.

In segmented TOF at 7T with VS, the number of segments was set to 5 to satisfy the SAR limitation. Common parameters in segmented TOF and conventional TOF at 7T were pre-optimized as: TR=20ms, FA=18°, TE=5.1ms, voxel=0.34x0.34x0.45mm3, GRAPPA=3, and the time of acquisition (TA)=10:28min. The protocol of conventional TOF at 3T was optimized to achieve the maximal SNR and resolution: TR=21ms, FA=18°, TE=3.5ms, voxel= 0.50x0.50x0.50mm3, GRAPPA=2, and TA=10:22min.


Fig. 1 showed a typical set of unilateral MIP images of extracranial vessels. The overlap of STA and STV signal was found unilaterally (on left or right side) in 6 subjects (35%), and bilaterally in 4 subjects (24%).

In Fig. 1, more tiny branches were visible in 7T images than in 3T images (denoted by yellow arrows). The averaged numbers of vessels in STA were illustrated in Fig. 2. The numbers of vessels in 7T images were significantly higher in parietal branches on both left (p<0.01) and right (p<0.001) sides.


In this study, the overlap of STA and STV was observed in 59% of the subjects. This indicated the necessity of VS for 7T TOF-MRA when STA is concerned in STA-MCA bypass surgery. Similar to the intracranial TOF-MRA2, segmented TOF at 7T MRI has an advantage on imaging flow signal of tiny extracranial vessels.

The superiority of 7T did not reach statistical significance in frontal branches on either side. The reason for that might be the limited coverage on the frontal side of the coil in 7T MRI. On the other hand, there were considerable individual differences of blood flow and visible vessels between subjects (as shown in Fig. 1). With an increased sample size, this may reach a statistical significance.

The depiction of STA and its branches is important for pre-operative planning of STA-MCA bypass surgery. Presently, the gold standard for STA imaging is digital subtraction angiography (DSA), which is an invasive technique and requires local anesthesia. 3T MRA is noninvasive, but it may not provide adequate information on STA, limiting its use. Segmented TOF at 7T MRI is a promising technique as it depicts STA and its branches much more clearly compared to 3T MRA. Segmented TOF at 7T MRI can be a strong competitor to DSA for patients with planned STA-MCA bypass surgery.


We demonstrated for the first time that segmented TOF with venous saturation is a valuable technique on imaging tiny branches of STA without the interference of STV at 7T. This sequence is expected to be valuable for pre-operative planning of STA-MCA bypass surgery.


The work is supported in part by Chinese MOST grant (2012CB825500), CAS grants (XDB02010001 and XDB02050001).


1. Morze C von, Xu D, Purcell DD, Hess CP, Mukherjee P, Saloner D, Kelley DAC, Vigneron DB. Intracranial time-of-flight MR angiography at 7T with comparison to 3T. J. Magn. Reson. Imaging 2007;26:900–904.

2. Zhang Z, Deng X, Weng D, An J, Zuo Z, Wang B, Wei N, Zhao J, Xue R. Segmented TOF at 7T MRI: Technique and clinical applications. Magn. Reson. Imaging 2015;33:1043–1050.


Fig. 1. The MIP images on left and right sides of 2 subjects. The yellow arrows indicate tiny vessels that are invisible at 3T MRI. The images on the right show the interference of STV when no VS was applied at 7T MRI.

Fig. 2. The number of visible vessels in the frontal and parietal branches of STA, on the left and right sides, respectively. The error bars show the standard errors.

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