Original contributionDiffusion tensor imaging focusing on lower cervical spinal cord using 2D reduced FOV interleaved multislice single-shot diffusion-weighted echo-planar imaging: comparison with conventional single-shot diffusion-weighted echo-planar imaging
Introduction
Diffusion tensor imaging (DTI) provides not only structural integrity information, but also directional information by measuring water molecule diffusion within tissues. Obtained metrics from DTI are fractional anisotropy (FA), the values of apparent diffusion coefficient (ADC), and eigenvalues, which provide information on the scalar properties of the diffuse translation for extracellular water molecules [1], [2], [3], [4]. Previous studies have shown that these metrics reflect the microstructure of the spinal cord and provides visualization of fiber tractography, enabling tracking of the white matter pathways in the brain and spinal cord. Moreover, the application of DTI at the cervical spinal cord allows characterization of microstructural changes including demyelinating disease, infarction, myelopathy, traumatic injury, and spinal cord tumor [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15].
However, in practice, the usefulness of DTI at the cervical spinal cord (CSC) has been impeded by 1) the small dimension of the CSC, 2) partial volume artifacts from surrounding cerebral spinal fluid (CSF) and lipid, 3) motion artifacts from breathing, swallowing, and CSF pulsation, and 4) large bony structures that cause abrupt changes in magnetic susceptibility [16], [17], [18], [19]. For DTI of the CSC, standard single-shot diffusion-weighted echo-planar imaging (ss-DWEPI) is widely used in clinical cervical MR imaging. However, this protocol has a long readout time and low bandwidth in the phase encode direction, and is therefore prone to distortions and motion artifacts. In previous studies, these limitations were emphasized in the lower CSC [11], [20], [21].
Degenerative changes of the cervical spine including spondylosis and disc herniation are known to affect the lower segment because of the relative burden of weight and extensive range of motion [22]. However, several previous studies have emphasized the limitations of cervical DTI of the lower segment. This is mainly because of its location close to the lungs and heart, and negative effects associated with the construction of the surface coil [11], [20], [21]. Over the past decades, there have been several efforts using various EPI-based methods to overcome these limitations, including line scan imaging [23], [24], navigated fast spin-echo [3], propeller-based imaging [25], [26], [27], parallel EPI [28], [29], [30], ZOOM-EPI [31], multichannel coil [32], and more recently, reduced effective field of view (FOV) in the phase encoding direction, an approach that is currently in the limelight. Reducing the FOV in the phase encode (PE) direction enables a drastic shortening of the readout time and also increases the (pseudo)bandwidth in the phase-encoding direction. In addition, geometric distortion in ss-DWEPI is proportional to the FOV in the phase-encoding direction; therefore, susceptibility-related artifacts and pixel misregistration can be reduced in ss-DWEPI [16], [18], [19].
An equally important method is the interleaved multisection inner volume (IMIV) technique, which provides double inversion/refocusing radio-frequency pulses at 2D ss-DWEPI. This allows for acquisition of the entire cervical spinal cord with 1 interleaved image in the sagittal plane [7]. A few reports on the application of IMIV techniques at the CSC have been published [7], [33], [34], [35], but there are no direct comparisons with conventional protocols focusing on the lower CSC.
Therefore, the purpose of this study was to evaluate the performance of DTI in the cervical spinal cord by comparing 2D ss-IMIV-DWEPI (iDTI) and conventional 2D ss-DWEPI (cDTI) in a clinical population, focusing on the lower cervical spinal cord.
Section snippets
Study population
This retrospective study was approved by the institutional review board for human research. A total of 34 consecutive patients underwent cervical spinal MRI between July 2013 and September 2013. Any patients with unstable vital signs, history of interbody fixation, syringomyelia, or spinal cord tumor were excluded. As a result, 9 of the 31 patients were excluded; 5 patients had a clinical history of interbody fixation and 4 showed increased signal of the CSC due to compressive myelopathy and
Quantitative analysis
The mean values of DTI metrics in whole, upper, and lower CSC using cDTI versus iDTI were as follows: (a) FA value of whole CSC, 0.563 versus 0.679 (p < 0.001); (b) ADC value (× 10− 3 mm2s− 1) of whole spine, 1026.2 versus 631.1 (p < 0.001); (c) FA value of upper CSC, 0.554 versus 0.717 (p = 0.009); (d) ADC value of upper CSC, 1051.2 versus 589.1 (p < 0.001); (e) FA value of lower CSC, 0.574 versus 0.628 (p < 0.001); (f) ADC value of lower CSC, 993 versus 687 (p < 0.001).
Qualitative evaluation
The iDTI imaging was strongly
Discussion
The present study demonstrates the high performance of 2D ss-IMIV-DWEPI with reduced FOV for cervical spinal DTI. Although an increasing number of studies have demonstrated the feasibility of cervical spinal cord DTI [5], [6], [7], [8], [9], [10], [11], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], cervical spinal cord DTI was difficult to implement in clinical practice until fairly recently, compared with brain DTI, because of the scan time for DTI acquisition,
Acknowledgement
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (2012R1A2A1A01011328).
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