Original ArticleImprove the image quality of orbital 3 T diffusion-weighted magnetic resonance imaging with readout-segmented echo-planar imaging☆
Introduction
Diffusion-weighted imaging (DWI) which can evaluate microscopic water motion within tissue in vivo, promises increased diagnostic accuracy for the orbital abscess, the characterization of retinoblastoma in pediatric patients, the differentiation between benign and malignant orbital tumors [1], [2], [3], [4], [5]. Mainly due to its resistance to patient motion and scanning speed, single-shot echo-planar imaging (ss-EPI) is the sequence used mostly in current clinical DWI related studies. However, ss-EPI DWI is prone to susceptibility artifacts which manifests as geometric distortion, signal-intensity drop-out, and overall T2⁎-induced image blurring. These detrimental effects are more severe at high field strengths and particular pronounced in regions with poor magnetic field homogeneity [6], [7]. Thus, orbital DWI is particular challenging because it is adjacent to nasal sinus, bone and skin. Nearly 6% of the study population were excluded due to the inadequate image quality of DWI in one previous study [4].
One approach to overcome these disadvantages is the introduction of parallel imaging. However, ss-EPI DWI in combination with parallel imaging can only reduce distortion to a certain content. Because distortion is proportional to the matrix size in EPI, distortion and blurring artifacts can become increasingly prohibitive at higher resolutions [8]. Another approach to reduce distortion is the use of interleaved (or multishot) EPI DWI. Despite the absence of geometric distortion artifacts, the long scanning time and the ghosting artifacts in the presence of motion limit its clinical practice [9].
Recently, DWI based on read-out segmented EPI (rs-EPI), in which k-space is divided into several segments along the direction of the readout, has attracted increasing attention [6], [7], [8], [9], [10], [11], [12], [13], [14]. It permits the useage of shortened echo spacing in each segment, and can reduce geometric distortion and susceptibility artifacts by accelerating the k-space traversal along the direction of the readout. This technique has be proven to be useful to reduce geometric distortions, image blurring and ghosting artifacts in various organs at 3 T magnetic resonance (MR) imaging, including pediatric and adult brain, breast, kidney and neck region [6], [7], [8], [9], [10], [11], [12], [13], [14]. However, few studies have applied the rs-EPI in the orbital DWI till now.
Therefore, the purpose of our study is to evaluate the clinical usefulness of rs-EPI in the orbital DWI, and to compare its image quality with that of ss-EPI DWI at 3 T MR imaging unit in healthy adults.
Section snippets
Patients
The institutional review board of our hospital approved our study protocol, and the requirement for written informed consents was waived due to the retrospective nature of analysis. Siemens Healthcare (Erlangen, Germany) provided the DW imaging sequence based on rs-EPI. We included the volunteers based on the following inclusion criterions: 1) 18 years or older; 2) no history of orbital disease; 3) no systematic disease that would influence the orbital morphology. Finally, forty-two consecutive
Qualitative comparison of image quality
Good to excellent inter- and intra-reader agreements were obtained in the qualitative assessments. Detailed Kappa values for qualitative assessment were showed in Table 3.
The average number of the normal anatomical structure that could be clearly distinguished were 2.52 ± 0.08 for ss-EPI and 3.19 ± 0.67 for rs-EPI. For fat suppression, the qualitative score were 2.86 ± 0.35 for ss-EPI and 2.90 ± 0.30 for rs-EPI. For ghosting artifact, they were 1.62 ± 0.66 for ss-EPI and 2.67 ± 0.48 for rs-EPI. For overall
Discussion
Our study demonstrated that the image quality of orbital DWI could be significantly improved by using the rs-EPI protocol. During the qualitative image assessment, rs-EPI was found to be superior to ss-EPI in normal anatomical structure distinction, ghosting artifact and better overall image quality, while no difference on fat suppression, which was consistent with previous studies [6], [7]. During the quantitative image assessment, the rs-EPI was superior to ss-EPI in geometric distortion,
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