Robustness of a Combined Modified Dixon and PROPELLER Sequence with Two Interleaved Echoes in Clinical Head and Neck MRI

Abstract

Purpose: The combination of modified Dixon (mDixon) and periodically rotated overlapping parallel lines with enhanced reconstruction sequence with two interleaved echoes, which promotes uniform fat-suppression and motion insensitivity, has recently become available for commercial magnetic resonance imaging (MRI) scanners. To compare the robustness of this combination sequence with that of standard Cartesian mDixon sequence for fat-suppressed T₂-weighted imaging in clinical head and neck MRI.

Methods: Fifty patients with head and neck tumors were involved this study. All patients underwent MRI using both the combination and standard sequences. Two radiologists independently scored motion artifacts and water-fat separation error using a 4-point scale (1, unacceptable; 4, excellent). Furthermore, comprehensive comparative evaluation was performed using a 5-point scale (1, substantially inferior; 5, substantially superior). Data were statistically analyzed using the Wilcoxon signed-rank test.

Results: In the motion artifact assessment, ratings of 3 or 4 points were assigned to 45% (observer-1, 58.0%; observer-2, 32.0%) and 97% (100%; 94.0%) of images for the standard and combination sequences, respectively (P < 0.001). For the water-fat separation error assessment, ratings of 3 or 4 points were assigned to 100% (100%; 100%) and 85% (84.0%; 86.0%) of images, respectively (P < 0.001). In the comprehensive evaluation, of the 100 cases (observer-1, 50; observer-2, 50), 96 were rated at four or five points. In cases with slight or no motion artifacts and water-fat separation errors, the combination sequence was superior to the standard sequence in term of noise and sharpness, and equal in terms of contrast.

Conclusion: Although water-fat separation errors increased significantly in the combination sequence, most of these were acceptable. The significantly decreased motion artifacts in the combination sequence significantly improved image quality overall.

Keywords: Dixon; fat suppression; head and neck; magnetic resonance imaging; periodically rotated overlapping parallel lines with enhanced reconstruction.

Fig. 1

Comparison between T₂W_mD sequence and T₂W_mD_MV sequence. Upper panel: The pharynx in a 63-year-old male patient with oropharynx squamous cell carcinoma before treatment. Lower panel: The oral cavity in a 68-year-old male patient with oral tongue squamous cell carcinoma before treatment. The T₂W_mD sequence shows severe motion artifacts which cover signal changes [(a and c) dotted arrows]. The T₂W_mD_MV sequence shows no motion artifact; thus, the tumor signals are observed clearly [(b and d) arrow]. However, in the T₂W_mD_MV sequence, water–fat separation errors occurred in a portion of subcutaneous fat [(d), arrowhead]. T₂W, T₂-weighted image; mD, modified Dixon_XD; MV, MultiVane_XD.

Fig. 2

Unacceptable water–fat separation error in the T₂W_mD_MV sequence. Upper panel: An 88-year-old female patient with postoperative recurrence of buccal mucosa squamous cell carcinoma. Lower panel: A 47-year-old male patient with nasopharynx squamous cell carcinoma after radiation-chemotherapy. (a and d) Sagittal image from T₂W_mD sequence. (b and e) Transverse image at the level of the jaw from T₂W_mD sequence. (c and f) Transverse image at the level of the jaw from T₂W_mD_MV sequence. A severe water–fat separation error is observed on not only subcutaneous fat [(c and f) arrows], but also mandibular marrow [(c and f) arrowheads]. T₂W, T₂ weighted image; mD, modified Dixon_XD; MV, MultiVane_XD.

Fig. 3

Image quality assessment between T₂W_mD sequence and T₂W_mD_MV sequence in cases with slight or no motion artifact and water–fat separation error. (a) Noise assessment. (b) Sharpness assessment. (c) Contrast assessment. Each bar graph shows a comparison of 16 cases by the two respective observers. The five categories correspond to the T₂W_mD_MV sequence being substantially better or worse than (>>), better or worse than (>), or equal to (=) the T₂W_mD sequence. Grey and black colors represent the two radiologists’ comparisons, respectively. T₂W, T₂-weighted image; mD, modified Dixon_XD; MV, MultiVane_XD.

Fig. 4

Comprehensive comparative assessment between the T₂W_mD sequence and T₂W_mD_MV sequence. Bar graph shows a comparison of all cases by the two respective observers. The five categories correspond to the T₂W_mD_MV sequence being substantially better or worse than (>>), better or worse than (>), or equal to (=) the T₂W_mD sequence. Grey and black colors represent the two radiologists’ comparisons, respectively. T₂W, T₂-weighted image; mD, modified Dixon_XD; MV, MultiVane_XD.