Evaluation of Dural Arteriovenous Fistulas with 4D Contrast-Enhanced MR Angiography at 3T

Study Population

Our study was approved by our institutional review board, and informed consent for imaging examinations was obtained from all patients or their relatives. Our study included 18 patients (11 women and 7 men ranging from 35 to 82 years of age; mean age, 64.8 years) with intracranial DAVFs who underwent 4D-CE-MRA between March 2007 and August 2008. Of these, 17 were initially diagnosed and 1 manifested a residual DAVF after embolization. All patients underwent intra-arterial DSA; the interval between DSA and MRA ranged from 3 to 22 days (mean, 9 days).

DSA showed that of the 18 DAVFs, 8 were located at the transverse-sigmoid sinus (TS); 8, at the cavernous sinus (CS); and 2, at the sinus adjacent to the foramen magnum (FM) (the hypoglossal canal). The primary presenting symptoms were headache in 10 patients, double vision in 5, seizures in 2, and tinnitus in 1 patient.

DSA Technique

After catheterization of the internal and external carotid and the vertebral arteries via a femoral artery approach, diagnostic biplanar intra-arterial DSA (Allura Xper FD; Philips Medical Systems, Best, the Netherlands) was performed by a trained neuroradiologist and a neurosurgeon. Images were obtained with a 1024 × 1024 matrix and an FOV of 17 cm. Temporal resolution of the images was 3 frames per second. For each projection, a 6- to 10-mL bolus of undiluted iodinated contrast material with an iodine concentration of 300 mg/mL (isopamidol, Iopamiron 300; Bayer-Schering, Berlin, Germany) was manually injected.

MR Imaging

4D-CE-MRA was performed on a 3T MR imaging system (Achieva; Philips Medical Systems) by using a commercially available 8-channel head coil. The MR imaging unit was equipped with a gradient system that allowed a maximal achievable gradient amplitude of 40 mT/m, a rise time of 0.2 ms, and a slew rate of 200 T/m/s.

The patients were positioned with a 20-gauge intravenous catheter inserted into the antecubital vein. The intravenous injection of 0.2-mL gadopentetate dimeglumine (Magnevist; Bayer-Schering) per kilogram of body weight (flow rate, 3 mL/s) was followed by a 30-mL saline flush delivered with an automated power injector. 4D-CE-MRA was started after the injection of the contrast agent. The acquisition parameters for 4D-CE-MRA were the following: TR/TE, 2.9 ms/1.4 ms; flip angle, 20°; image matrix, 256 × 256; FOV, 256 mm covering the entire head.

A combination of keyhole acquisition with a segmented central k-space ordering (CENTRA) technique was used to improve temporal resolution at CE-MRA at a constant spatial resolution.^17,18 We acquired 120 thin sagittal partitions of 2 mm with a 1-mm overlap between sections by using a sensitivity encoding (SENSE) factor of 2 in the section-selection direction and of 4 in the phase-encoding direction and a keyhole diameter of 15%; this yielded a voxel size of 1.0 × 1.0 × 1.5 mm (1.5 mm³) with zero-filling. In total, 24 dynamic volumes were acquired with an average keyhole imaging duration of 1.9 s/volume, followed by dynamic reference imaging with a duration of 3.9 seconds. The total acquisition time for the 4D-CE-MRA sequence was 50 seconds. Time-resolved MRA yielded a total acceleration factor of 88.8 (6.66 [15% keyhole] × 8 [SENSE]) / 0.6 [half-scan factor]) compared with standard CE-MRA without such techniques. Image processing included mask subtraction to suppress the background signal intensity of stationary tissue. Images were displayed with a reconstructed isotropic image matrix of 1 × 1 × 1 mm. In addition, routine MR imaging included pre- and postcontrast T1-weighted spin-echo and T2-weighted fast spin-echo sequences.

Image Analysis

Independent readers (T.H. or Y.O. with 20 and 10 years of experience in neuroangiography, respectively) qualitatively evaluated the entire series of DSA images on a PACS workstation. They reviewed evaluations that did not agree to reach a consensus. Two other readers (T.O. and M.K. with 21 and 18 years of experience in neuroradiologic MR imaging, respectively) independently evaluated the 4D-CE-MRA data at a PACS workstation; they were blinded to the clinical and DSA results. The 3D data were displayed with all regions visible. The software allowed the enlargement of regions of special interest in any given spatial orientation.

4D-CE-MRA and conventional DSA data were assessed for the fistula site, the main arterial feeders, and the venous drainage of the underlying DAVF. Main arterial feeders were defined as branches deriving from the internal maxillary and/or middle meningeal artery (IMA-MMA), the ascending pharyngeal artery (APA), the occipital artery (OA), the internal carotid artery, or other arteries. DAVFs were classified with respect to the fistula site as fistulas at the CS, the TS, the sinuses adjacent to the FM, and other sites. According to the classification of Borden et al,² DAVF drainage was recorded as type 1, drainage directly into the dural venous sinus; type 2, drainage into the dural venous sinus with cortical venous reflux; and type 3, drainage directly into subarachnoid veins (cortical venous reflux only). The 2 readers re-evaluated assessments that did not agree until a consensus was reached.

Statistical Analysis

The levels of interobserver agreement (between readers 1 and 2 for DSA and 4D-CE-MRA) and intermodality agreement (between consensus readings of 4D-CE-MRA and DSA images) with respect to the main arterial feeders, fistula site, and venous drainage were determined by calculating the κ coefficient (κ < 0.20 = poor, κ = 0.21–0.40, fair; κ = 0.41–0.60, moderate; κ = 0.61–0.80, good; κ = 0.81–0.90, very good; and κ > 0.90, excellent agreement). In addition, we recorded the exact number and percentage of times when results from the 2 readers and the 2 modalities were in exact agreement, including exact and 95% confidence intervals (CIs). A statistical package, MedCalc for Windows (MedCalc Software, Mariakerke, Belgium), was used for all analyses.