Accuracy of Postcontrast 3D Turbo Spin-Echo MR Sequence for the Detection of Enhanced Inflammatory Lesions in Patients with Multiple Sclerosis

Image Acquisition

All patients were examined on a 3T MR imaging scanner (Achieva; Philips Healthcare) by using a 32-channel array head coil. The routine MR imaging protocol included 2D axial MR images (pre- and postcontrast T1 SE, diffusion-weighted T2 TSE, and FLAIR) and 3D double inversion recovery (DIR) MR images. In addition, the postcontrast 3D TSE T1-weighted sequence (3D BrainView) was performed in all patients. The 3D TSE sequence is characterized by a long TSE impulsion train and a combination of advanced features, among which are variable refocusing angles. A specific refocalization scheme is also applied to preserve T1 contrast and minimize the blurring effect. Intravenous gadobutrol (Gadovist 1.0; Bayer-Schering Pharma, Berlin, Germany) was administered at a concentration of 0.1 mmol/kg. The 2D axial SE and 3D TSE T1-weighted postcontrast MR images were obtained 10 minutes after the gadolinium administration for all patients. The order in which these 2 postcontrast sequences were performed was randomized. 3D TSE source images were reformatted into 4-mm-thick axial sections to match the section thickness and the acquisition plane of the 2D SE T1-weighted images.

The parameters for each MR image are summarized in the Table.

Image Analysis

The reference standard for the diagnosis of enhanced MS lesions was defined by 2 neuroradiologists (X.L. and J.-P.P.) with >25 years' experience. They reviewed together all the MR imaging datasets by using clinical data and all the MR images available. An enhanced MS lesion was defined as a focal enhancement on postcontrast images, with a size superior to 2 mm, involving gray or white matter and associated with a parenchymal hyperintensity on FLAIR or DIR images. Focal enhancement without DIR- or FLAIR-associated hyperintensities was not considered a real MS lesion. First, the readers were asked to assess enhanced MS lesions for each patient. Second, the readers were asked to notice high-signal-intensity artifacts related to vascular pulsation within the postcontrast 2D SE and 3D TSE images according to the following scale: 0, no artifacts; 1, artifacts that did not impair image analysis; 2, artifacts that impaired image analysis.

For the evaluation of the 3D TSE sequence, 2 neuroradiologists (E.R. and A.-L.B.) with 7 and 6 years' experience, respectively, analyzed, independently and separately, all postcontrast T1-weighted images on a PACS workstation. First, the readers assessed 3 sets of images in a randomized order: 1) 2D axial SE images, 2) 4-mm-thick axial reformations from 3D TSE sequences, and 3) multiplanar analysis from 3D TSE sequences with thin sections and MIP reformations in arbitrary planes. They were blinded to clinical data and to other MR images and were asked to notice the number and location of the enhanced inflammatory lesions for each patient. An enhanced lesion was retained when a focal enhancement involving the gray or white matter was detected. Second, a consensus reading was performed between the 2 blinded readers to resolve their disagreements.

One radiologist (X.L.) measured the contrast rate (CR) of the largest enhanced MS lesions (ie, measuring at least 1 cm) by using both the axial 2D T1 SE images (4-mm-thick) and the 4-mm-thick axial reformatted views from the 3D TSE sequence. For each patient, regions of interest were drawn within the enhanced MS lesions and their background (ie, adjacent white matter), allowing the measurement of signal intensities (SI). Using the PACS workstation, we drew the same ROIs on the 2D images and axial reformatted views. As previously reported,^8,9 the contrast rate was calculated between the MS lesion and its background according to the following formula: CR = [(SI Lesion − SI Background)/SI Background] × 100.

Statistical Analysis

All statistical analyses were performed by using R Statistical Software (Version 3.0.0; http://www.r-project.org/).

Interobserver agreement was calculated by using the Cohen κ test. κ values were interpreted as follows: κ = 0 indicates poor agreement; κ = 0.01–0.20, minor agreement; κ = 0.21–0.40, fair agreement; κ = 0.41–0.60, moderate agreement; κ = 0.61–0.80, good agreement; and κ = 0.81–1, excellent agreement.

To compare 2D SE and 3D TSE sequences, we evaluated both the overall number of enhanced MS lesions detected and the number of patients diagnosed with at least 1 enhanced MS lesion. The overall number of enhanced MS lesions detected by using 2D axial SE images, 4-mm-thick axial reformations from 3D TSE sequences, and multiplanar analysis of the 3D TSE sequences was compared with the reference standard by using the Cohen κ test. For the diagnosis of patients with at least 1 enhanced MS lesion, standard diagnostic accuracy parameters (sensitivity and specificity) of 2D axial SE images, 4-mm-thick axial reformations from the 3D TSE sequences, and multiplanar analysis of the 3D TSE sequences were calculated according to the reference standard.

Comparisons of κ values were performed to determine whether the agreements were significantly different for each parameter evaluated.

We also compared the MS lesion contrast rate and the artifacts grading between 2D SE and 3D TSE sequences by using a nonparametric statistical test (Wilcoxon test). P values < .05 were considered statistically significant.