The Role of Adjustable Scout Lines in Advanced Cervical Spinal Imaging.

STUDY DESIGN/SETTING:: Retrospective cohort at a Level 1 trauma center. OBJECTIVE:: To compare the anterior-posterior diameter of the cervical central canal using imaging software with both fixed and user-adjustable scout line axial images. SUMMARYOF BACKGROUND DATA:: The majority of imaging software programs generate oblique axial images through the lordotic and kyphotic regions of the spine due to a fixed reference line. These oblique axial images are not representative of true canal diameter and often provide inaccurate representation of neural compression. METHODS:: Thirty-three consecutive head trauma patients without evidence of pathology in the cervical spine from September 2011 were chosen for the study. The anterior-posterior diameter of the cervical (levels C2-T1) central canal was measured on axial slices using the default non-adjustable ("fixed") reference line on the picture archiving and communication viewer by three observers and then re-measured using an adjustable scout line on the midline sagittal that most bisected the endplates in a parallel fashion. The two measurements from the three independent observers were then compared directly for differences in the AP canal diameter at each level. RESULTS:: The average difference between the measurements of the central canal using the fixed scout line versus the adjustable scout line ranged from -1.34±1.59 mm at the C2-C3 level to 1.78±2.32 mm at the C7-T1 level. Standard axial images of the cervical spine underestimated the canal space in the upper cervical spine and overestimated the space in the lower cervical spine. The measurement values using the fixed scout line versus the adjustable scout line did not correlate as indicated by low to moderate Pearson r and ICC values. CONCLUSIONS:: There are clear differences between axial slices generated with adjusted and fixed scout lines particularly at disc levels that are not orthogonal to the screen edges.