Reduction of motion, truncation and flow artifacts using BLADE sequences in cervical spine MR imaging

Abstract

Purpose

To assess the efficacy of the BLADE technique (MR imaging with ‘rotating blade-like k-space covering’) to significantly reduce motion, truncation, flow and other artifacts in cervical spine compared to the conventional technique.

Materials and methods

In eighty consecutive subjects, who had been routinely scanned for cervical spine examination, the following pairs of sequences were compared: a) T2 TSE SAG vs. T2 TSE SAG BLADE and b) T2 TIRM SAG vs. T2 TIRM SAG BLADE. A quantitative analysis was performed using the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) measures. A qualitative analysis was also performed by two radiologists, who graded seven image characteristics on a 5-point scale (0: non-visualization; 1: poor; 2: average; 3: good; 4: excellent). The observers also evaluated the presence of image artifacts (motion, truncation, flow, indentation).

Results

In quantitative analysis, the CNR values of the CSF/SC between TIRM SAG and TIRM SAG BLADE were found to present statistically significant differences (p < 0.001). Regarding motion and truncation artifacts, the T2 TSE BLADE SAG was superior compared to the T2 TSE SAG, and the T2 TIRM BLADE SAG was superior compared to the T2 TIRM SAG. Regarding flow artifacts, T2 TIRM BLADE SAG eliminated more artifacts than T2 TIRM SAG.

Conclusions

In cervical spine MRI, BLADE sequences appear to significantly reduce motion, truncation and flow artifacts and improve image quality. BLADE sequences are proposed to be used for uncooperative subjects. Nevertheless, more research needs to be done by testing additional specific pathologies.

Introduction

Magnetic resonance imaging has become an established tool for the assessment of the cervical spine. cervical spine MRI examinations are used to assess soft disc herniations, suspicion of disc hernia recurrence after operation, cervical spondylosis, osteophytes, joint arthrosis, spinal canal lesions (tumor, multiple sclerosis etc.), bone diseases and paravertebral spaces [1].

Pulsation and motion can lead to modulation of the MRI k-space data resulting in severe artifacts. The most common artifacts are: flow artifacts which are depicted as flow voids in MR images, pulsation artifacts which are coherent and localized ghosting, motion artifacts which are incoherent and distributed ghosting, truncation artifacts (they stem from swallowing and respiration during the acquisition of the sequence), which appear as intensity ripples following high contrast edges and a relatively new artifact is the indentation artifact, which composes signal voids not consistent with flow voids (see Fig. 6 in the study by Fellner et al. [2]). A number of techniques have been developed in an attempt to eliminate pulsation artifacts. The most widely used of these techniques include: ordered phase encoding [3], gradient moment nulling [4], [5], spatial pre-saturation [6] and multiple averaging [7]. MR imaging with ‘rotating blade-like k-space covering’ (BLADE) and ‘Periodically Rotated Overlapping Parallel Lines with Enhanced Reconstruction’ (PROPELLER) have been shown to effectively reduce motion and pulsatile flow artifacts [8], [9], [10], [11].

The term BLADE is the product name (used by Siemens Medical System, Erlagen, Germany) for a turbo spin echo (TSE) sequence that uses the PROPELLER k-space trajectory [12]. The BLADE method acquires a number of blades that are rotated around the center of the k-space (successive blades are acquired at different angles). Each blade consists of a number of lowest phase encoding lines of a conventional rectilinear k-space trajectory that are acquired after a single radiofrequency excitation. This technique can potentially eliminate pulsation in MR images when that pulsation is caused by the unwanted modulation of k-space data [12], [13], [14]. In cervical spine images, BLADE sequences have shown to be capable of eliminating motion, truncation and flow artifacts and improve the image quality [2], [13].

The most frequently used and useful sequences in cervical spine MRI are T2-weighted sagittal TSE and turbo inversion recovery (TIRM), which is mainly used to remove the fat signal. Therefore, the purpose of this study is to evaluate the efficiency of BLADE in combination with the TIRM sequence in reducing motion, pulsatile and flow artifacts and improve image quality in cervical spine MR images, due to the fact that TIRM sequences shows high sensitivity to demyelinating lesions [15], [16]. Additionally, this study aims at investigating the ability of these sequences (T2 TSE BLADE, T2 TIRM BLADE) to reduce impact of inherent artifacts such as indentation and wrap (or string) artifacts, which were presented by Finkenzeller et al. [17].

The originality of the present study is due to the fact that TIRM sequences have not been implemented in any MRI examination protocol for cervical spine. The present study is among the first to implement T2 TIRM SAG BLADE in MR imaging at a different however clinical case. Due to the very promising results that this sequence previously showed it was also implemented in cervical spine MRI as well.

In summary, the present work aims at providing a complete picture of the impact of the BLADE technique to the image quality by examining a series of artifacts both quantitatively as well as qualitatively. Its objective is to give more specific answers about what artifacts are eliminated, significantly reduced or just reduced and based on that what clinical cases will mostly benefit by the application of this technique and the respective change of the local protocols. In this study, it is the first time that TIRM sequences are examined quantitatively and qualitatively in cervical spine.