3T High-Spatial-Resolution Contrast-Enhanced MR Angiography of the Intracranial Venous System with Parallel Imaging

SUMMARY: The diagnostic image quality of contrast-enhanced (CE) 3D MR venography (MRV) was prospectively compared with that of 2D time-of-flight (TOF) MRV and contrast-enhanced 3D magnetization-prepared rapid acquisition of gradient echo (MPRAGE) sequences for the visualization of the intracranial venous system at 3T in 22 patients. CE MRV provides high-quality images and was shown to be superior to TOF MRV and MPRAGE sequences in visualizing the normal intracranial venous system.


MR Examinations
We performed all MR imaging studies using a 3T system (Trio; Siemens Medical Systems, Erlangen, Germany) with an 8-element head coil. After routine MR imaging, we performed the following protocol: TOF MRV, nonenhanced MPRAGE sequence, bolus-detection sequence, and nonenhanced CE MRV acquisition. Also, after a single injection of contrast medium, a contrast-enhanced CE MRV acquisition and a contrast-enhanced MPRAGE sequence were performed. The imaging parameters are listed in Table 1. As contrast agent, gadopentetate dimeglumine (Magnevist; Bayer Schering Pharma, Berlin, Germany) at a dose of 0.1 mmoL/kg was injected intravenously at a rate of 3 mL/s with use of an injector.

Image Analysis
The source images, subtraction images, 2D multiplanar reconstructed (MPR) images as well as 3D maximum intensity projection (MIP) angiograms were interpreted prospectively by 2 experienced neuroradiologists. The image quality of 34 predefined venous structures was graded as follows: intense and continuous ϭ 3, faint and continuous ϭ 2, noncontinuous ϭ 1, and invisible ϭ 0. The grades assigned were the result of a consensus among the observers. In addition, the number of bridging veins seen on coronal images (Fig 1) was compared.

Statistical Analysis
We analyzed the differences in the number of bridging veins using the Wilcoxon matched-pairs signed-rank test. The nonparametric sign test was used to analyze differences in the image quality of the cerebral veins and dural sinuses. A commercially available statistical software package (SPSS 14.0; SPSS, Chicago, Ill) was used.

Results
We found significantly higher image quality scores on the CE MRV compared with the TOF MRV or MPRAGE sequences and on the MPRAGE sequences compared with the TOF MRV ( Table 2 and 3). The number of detected bridging veins was significantly higher with the CE MRV compared with the TOF MRV or MPRAGE sequences (Table 3). In all of the 22 patients, MR imaging results did not show signs of cerebral venous thrombosis. Well-known disadvantages of TOF MRV are signal intensity loss because of in-plane saturation effect as well as the slow and turbulent flow. In our study, the transverse and sigmoid sinuses were visualized best by CE MRV. As with Ayanzen et al, 8 we observed flow gaps in the transverse sinuses with TOF MRV in several patients (Fig 2). In isolated cortical vein thrombosis, the diagnosis can be extremely difficult. In our study, the superficial veins were visualized best by CE MRV (Fig 3). At 1.5T, Liang et al 7 showed MPRAGE sequences to be superior to TOF MRV. In our study, disadvantages of the MPRAGE sequences were a signal intensity loss at the upper and lower end of the head coil in every patient and dural contrast enhancement, as some venous structures could not easily be distinguished from dural enhancement (Fig 1).
Our study had the following limitations: There was low statistical impact because of a small number of patients. Furthermore, cerebral venous thrombosis could not be detected in any of the participants; thus, the drawing of conclusions from these data about the performance of CE MRV and MPRAGE sequences in the detection of venous thrombosis remains difficult. Technical disadvantages, such as a relatively long TE on TOF MRV sequences, anisotropic voxels, and low acceleration factors at parallel imaging were limitations to this study. Furthermore, the performance of contrast-enhanced CE MR acquisition before contrast-enhanced MPRAGE sequence in all patients was considered a possible disadvantage.