Currently, various 3D MR sequences such as 3D FSE, GRE, and steady-state sequences have been developed and used to obtain MR images of submillimeter thicknesses in the spine. However, the question,“which 3D sequence has better image contrasts of the tissues in spinal MRI?”, has come up. Therefore, we examined optimal imaging parameters of variable refocus flip angle 3D FSE (Cube) and 3D Fiesta-c sequences for T2-weighted images in cervical spine MRI and compared the two different 3D sequences for better image contrasts of the tissues on T2-weighted images in cervical spine MRI.

All images were obtained with 3T MRI (Discovery 750w; GE Healthcare) using a GEM head and neck coil. Transverse T2-weighted images of the cervical spine using Cube and Fiesta-c sequences were obtained and compared them for better image contrasts of the tissues.

1) Quantitative assessment

A total of three healthy subjects were included. Cube T2-weighted images of three different TEs and Fiesta-c T2-weighted images of the cervical spine were obtained in transverse plane. The imaging parameters of Cube sequence were as follows; TR/TE:1060/60, 90,120msec, slice thickness: 0.6mm, FOV:18cm, voxel size: 0.35×0.6mm, scantime: 3min36sec. The imaging parameters of Fiesta-c sequence were as follows; TR/TE: 6.6/2.1msec, slice thickness: 0.6mm, FOV: 18cm, voxel size: 0.35×0.6mm, FA: 55°, scan time: 3min45sec. Circular ROIs were set at the spinal cord, cerebrospinal fluid, vertebral body, subcutaneous fat, paraspinal muscle, intervertebral disc, yellow ligamentum flavum, and air (background) on T2-weighted images using Cube sequence of three different TEs and Fiesta-c sequence. Signal-to-noise ratios (SNRs) and contrast-to-noise ratios (CNRs) were calculated by the following equation; SNR_a=(signal_a)/(SD_a),CNR_a-b=(signal_a-signal_b)/(signal_air)(π/2)^1/2. signal: signal intensity, SD: standard deviation.

2) Qualitative assessment

A total of three healthy subjects and three patients were included. Cube and Fiesta-c T2-weighted images of the cervical spine were obtained in transverse plane. Regarding Cube T2-weighted images, TE was set at 90msec from the results of quantitative assessments as above. From the 3D data sets of Cube and Fiesta-c sequences, oblique sagittal images perpendicular to the nerve root foramen and coronal images were reconstructed. Image contrasts of the spinal cord versus cerebrospinal fluid, vertebral body, subcutaneous fat, paraspinal muscle, intervertebral disc, yellow ligamentum flavum, and carotid and vertebral arteries were scored according the 3 grading system (3: excellent, 2: good, and 1: poor) by one radiologist.

1) Quantitative assessment

In Cube T2-weighted images, SNR of the cerebrospinal fluid was increased with TEs, SNRs of the paraspinal muscle and yellow ligamentum flavumwere unchanged with TEs, and SNRs of the remaining tissues were decreased with TEs. Therefore, TE of 90msec was thought to be appropriate for Cube T2-weighted images. In Fiesta-c T2-weighted images, SNRs of the tissues was similar to those in Cube T2-weighted images. Regarding CNRs, higher CNR of the cerebrospinal fluid versus spinal cord was found on Fiesta-c T2-weighted images compared to Cube T2-weighted images, whereas higher CNRs of the spinal cord versus other tissues were found on Cube T2-weighted images in comparison with Fiesta-c T2-weighted images.

2) Qualitative assessment

Image contrasts of the spinal cord versus cerebrospinal fluid, vertebral body, and subcutaneous fat were similar between on Cube and Fiesta-c T2-weighted images. However, higher image contrast of the spinal cord versus carotid and vertebral arteries was found on Fiesta-c T2-weighted images compared to Cube T2-weighted images, whereas higher image contrasts of the spinal cord versus paraspinal muscle, intervertebral disc, and yellow ligamentum flavum were found on Cube T2-weighted images compared to Fiesta-c T2-weighted images.

SNRs of the various tissues were similar between on T2-weighted images using Cube and Fiesta-c sequences. In addition, CNRs of the spinal cord versus other tissues except the cerebrospinal fluid were better on Cube T2-weighted images than those on Fiesta-c T2-weighted images. Regarding image contrast of the tissues, Cube T2-weighted images showed better image contrasts of the spinal cord versus other tissues except cerebrospinal fluid, vertebral body, and subcutaneous fat compared to those on Fiesta-c T2-weighted images. In Fiesta-c T2-weighted images, however, blurring was more prominent than that in Cube T2-weighted images. Therefore, Cube T2-weighted images are considered to be better to evaluate abnormalities of the cervical spine compared to Fiesta-c T2-weighted images.3D FSE Cube T2-weighted images had better image contrasts of the spinal cord versus other tissues except cerebrospinal fluid, vertebral body, and subcutaneous fat in the cervical spine compared to those on 3D Fiesta-c T2-weighted images. Therefore, 3D FSE Cube sequence is believed to be more appropriate for T2-weighted images in cervical spine MRI compared to 3D Fiesta-c sequence.