Purpose:

Scoliosis, a three-dimensional (3D) deformity of the spinal column, is generally characterized by a lateral deviation of the spine, accompanied by an axial rotation of the vertebrae¹. Radiography, computed tomography (CT), and magnetic resonance imaging (MRI) all have been used to play important roles in evaluating scoliosis and determining its underlying cause^2,3. In contrast to the other two imaging modalities, MRI is capable of offering excellent soft-tissue detail about the nature of the spinal canal, cord and nerve root but fails to provide direct visualization of cortical bone due to its low water content and short signal life times (T₂^* ~ 0.4 ms), yielding limited cortical bone signal. A novel MRI technique named zero-echo time (ZTE) has been recent developed⁴. It utilizes hard pulse excitation followed by immediately 3D radial sampling to achieve nominal TE of zero and consequently could provide efficient sampling short T₂^* signals in cortical bone. The aim of this study is to first establish a clinical feasible ZTE whole spine protocol and assess ZTE imaging performance to scoliosis.

Methods:

All MRI acquisitions were performed on a 1.5 T clinical scanner (Optima MR450w, GE Healthcare, Milwaukee, USA) using a large-size 16-channel flexible array coil as the signal detection and whole body coil for radio-frequency excitation. ZTE data were carried out in a prone position and acquired using a non-selective hard pulse excitation followed by 3D center-out radial sampling. The scanning parameters were as follows: TR=838 ms, flip angle=2 degree, receiver bandwidth= 31.2 kHz, field-of-view= 35 cm, isotropic resolution= 2.2 mm (interpolated to 1.36 × 1.36 × 1.1 mm), scan time= 2 min 20 s. Three-dimensional view of whole spine imaging was obtained on an Advantage Windows workstation using an advanced visualization platform (READY View (ver.4.6), GE Healthcare). The signal intensity of proton density-weighted ZTE images was inverted and rescaled to generate CT-like images proportional to tissue density.

Results and Discussions:

Whole spine ZTE MRI of a representative volunteer was shown in Fig. 1. Vertebral cortical bone was clearly visible at both views of ZTE images and there is no or minimal spine curvature to be visualized. Spinal curvature observed in the scoliosis patient by ZTE is similar with that in anteroposterior (AP) radiograph (Fig. 2). Whole spine ZTE imaging showed a coronal Cobb angle (T11-L3) of 25.8°, while the Cobb angle (T11-L3) measured at radiograph is 30.2°. As expected, the slight smaller Cobb angle was found at coronal ZTE image because MRI examination was performed in prone position, compared to AP radiograph in standing position. The ZTE performance in visualizing spinal cortical bone was consistence with both volunteer and scoliosis patient.

Conclusion:

The preliminary results obtained in this study suggest that the detection scoliosis and measurement of curvature using ZTE is possible, providing a potential alternative radiation-free diagnostic option that is especially relevant to scoliosis patients who need to undergo repeated examinations for evaluating the progress of spinal curvature. Further assessment of more scoliosis patients with various level of curvature is currently underway.

Acknowledgements

No acknowledgement found.