Comparison of Dynamic Contrast-Enhanced 3T MR and 64-Row Multidetector CT Angiography for the Localization of Spinal Dural Arteriovenous Fistulas

Study Population

Our study was approved by our institutional review board. Prior informed consent for imaging examinations was obtained from all patients or their relatives. Between October 2008 and December 2012, 23 patients were referred for spinal 64-CTA and DCE-MRA at 3T and for the evaluation of possible SDAVF suspected on the basis of combined spinal MR imaging and clinical findings. Our inclusion criteria were a diagnosis of SDAVF on the basis of spinal DSA scans and verified at surgery after spinal 3T DCE-MRA and 64-CTA examinations. Exclusion criteria were renal dysfunction (estimated glomerular filtration rate <30 mL/min per 1.73 m²) and allergy to iodinated and gadolinium-based contrast materials. On the basis of these criteria, we enrolled 12 consecutive patients (11 men and 1 woman ranging in age from 46–83 years; mean age, 65 years). All patients presented with congestive myelopathy and a diffuse, continuous hyperintense cord lesion in various cord regions (Table 1), and all underwent spinal CTA, MRA, and intra-arterial DSA. The interval between CTA, MRA, and DSA studies ranged from 3–20 days (mean, 10 days).

DSA Technique

Diagnostic intra-arterial DSA through a femoral arterial approach was performed in a biplane angiography suite (Allura Xper FD; Philips Healthcare, Best, the Netherlands) by a trained neuroradiologist and/or a neurosurgeon. The angiographic technique included the selective manual injection of 3–5 mL of a 300-mg/mL iodinated nonionic contrast agent into the intended arteries and anteroposterior imaging at a rate of 3 frames/s. Images were obtained with a 2048 × 2048 matrix; the FOV was 42 cm.

When DCE-MRA and CTA findings suggested the location of the fistula, we first delivered a selective manual injection at the anticipated level. If the fistula was identified, the contralateral segmental artery and the segmental arteries ranging from 2 levels above to 2 levels below the fistula were studied to ensure complete evaluation of the fistula and the adjacent vasculature. If the fistula site was not identified, additional injections were delivered into segmental arteries from the supreme intercostal artery to the median sacral arteries, the bilateral internal iliac arteries, and the bilateral vertebral, subclavian, costocervical, thyrocervical, and external carotid arteries.

To obtain 3D images of the vessels injected from the feeder and of the bony structures, we acquired 3D rotational angiographs by use of the same angiography system. The parameters were 4.1-second rotation; rotation angle, 240° with 2° increments, resulting in 120 projections; rotation speed, 55°/s, acquisition matrix, 1024 × 1024; frame rate, 30 frames/s. The volume and the injection rate of the nonionic iodinated contrast agent were 15 mL and 1.5 mL/s respectively. We then reconstructed and analyzed the filling run-volume by use of a dedicated commercially available workstation (Philips Healthcare). The 3D images were reconstructed in a 512 × 512 × 512 matrix with an isotropic voxel size.

CT Data Acquisition

All CT studies were performed on a 64-detector CT system (Brilliance-64, Philips Healthcare) with a 0.5-second gantry rotation speed, an x-ray tube voltage of 120 kV, and an x-ray tube current of 412 mA. The collimation was 64 × 0.625 mm, the beam pitch was 0.515, and the table speed was 20.6 mm per rotation. A double-head power injector (Dual Shot-Type GX; Nemoto Kyorindo, Tokyo, Japan) was used to administer a bolus of 350 mgI/mL contrast medium (135 mL of iomeprol, Iomeron; Bracco, Milan, Italy) at 5.0 mL/s through a 20-gauge IV catheter in an antecubital vein; the contrast agent was followed by a 40-mL bolus of saline solution at the same rate.

Synchronization between the flow of contrast material and CT acquisition was achieved by use of a computer-assisted bolus tracking system. The CT attenuation value was monitored by a radiology technologist. The anatomic level for monitoring was set in the descending aorta at the T10 level on the scout CT image. The trigger threshold was set at 250 HU for the aortic ROI. CT data acquisition was started 10 seconds after triggering. Data were acquired during a single breath-hold in the head-to-foot direction. The CT scan was from the level of the foramen magnum to the groin.

The helical data were reconstructed in the axial plane with a 0.5-mm section thickness at 0.3-mm intervals before storage and transfer to a workstation (M900QUADRA; Amin, Tokyo, Japan). The multiplanar reformation images, including oblique coronal images with craniocaudal angulations and curved planar reformation images, were reconstructed at a voxel size of 0.4 × 0.4 × 0.7 mm to confer the greatest possible likelihood that the spinal vessels were included in the scan. Volume-rendering (VR) CTA images were also reconstructed for image interpretation.

MR Data Acquisition

All MR studies were performed on a 3T MR imaging system (Magnetom Trio, Siemens, Erlangen, Germany) equipped with a phased-array spine coil. The patients were imaged in the supine position with a 20-gauge intravenous catheter inserted into the antecubital vein. Conventional MR imaging was with sagittal and axial T1- and T2-weighted sequences.

A test bolus was delivered to determine the arrival time of the contrast agent in the arteries feeding the spine. The intravenous injection of 0.2 mL gadopentetate dimeglumine (Magnevist; Bayer HealthCare Pharmaceuticals, Wayne, New Jersey) per kilogram of body weight, delivered at a flow rate of 3 mL/s, was followed by a 30-mL saline flush administered with an automated power injector. On the basis of test bolus results, we injected the contrast agent and started dynamic 3-phase DCE-MRA with a 3D FLASH sequence in the coronal plane. To facilitate subtraction DCE-MRA, 1 precontrast phase, composed of the exact same pulse sequence parameters as the DCE-MRA sequence, was acquired. The imaging data were acquired during breath-holding. The FOV of contrast-enhanced MRA was positioned to cover the entire T2 hyperintense cord and dilated vessels. If previous contrast-enhanced MR images were available, they were also used for determining the positioning of the FOV. The acquisition parameters for the contrast-enhanced MRA sequence were TR/TE, 3.1 ms/1.1 ms; flip angle, 15°; image matrix, 280 × 390; FOV, 400 mm; slab thickness, 78 mm; generalized autocalibrating partially parallel acquisition, 2. The reconstructed voxel size and temporal resolution were 1.4 × 1.2 × 1.5 mm and 17 seconds, respectively. Subtracted maximum-intensity projection, partial MIP, and VR DCE-MRA images in arterial and venous phases and their MPR images were reconstructed for image interpretation.

Image Evaluation

Two independent readers (Y.K. and Y.O., with 23 and 14 years of experience in neuroangiography, respectively) qualitatively evaluated the entire series of DSA images on a PACS workstation. Disagreements were resolved by consensus. Two other readers (T.H. and Y.I., with 21 and 8 years of experience in diagnostic neuro-MR imaging, respectively), blinded to the clinical, CTA, and DSA results, independently evaluated the DCE-MRA data on a PACS workstation. In each case, the subtracted source, MPR, MIP, partial MIP, and VR DCE-MRA images and conventional MR imaging data were displayed with all regions visible. Two other readers (D.U. and S.O., with 16 and 8 years of experience in CTA, respectively), blinded to the clinical, DCE-MRA, and DSA results, independently evaluated the CTA data on a PACS workstation. In each case, the source, MPR, and VR CTA images were displayed with all regions visible. Our software allowed the enlargement of regions of special interest in any given spatial orientation.

Each reviewer for DSA, DCE-MRA, and CTA recorded the shunt level of the SDAVF on the basis of continuity between the feeding artery and abnormal spinal vessels. When the 2 reviewers disagreed, final determinations were based on consensus readings.

After the blinded study, the observers consensually reviewed the reasons of incorrect interpretation for the fistula location with the DSA findings. The observers also determined whether CTA provided additional information to DCE-MRA with regard to the fistula location of SDAVF.

Statistical Analysis

The level of interobserver agreement (between readers 1 and 2 for DSA, DCE-MRA, and CTA) and of intermodality agreement (between consensus readings of DCE-MRA/CTA and DSA images) with respect to the location of the SDAVF was 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) with a 95% CI. The laterality of the fistula site was not put into the statistical analyses. We also recorded the exact number and percentage of times when the results from both readers and both modalities were in exact agreement. MedCalc for Windows (MedCalc Software, Mariakerke, Belgium) was used for all analyses.