Fig. 2.

MRI of the orbits in the coronal plane displaying a healthy control on the left column (panels A, C, E, G, I) and a patient with chronic progressive external ophthalmoplegia (CPEO) on the right column (panels B, D, F, H, J). Coronal T1-weighted (panels A and B) and corresponding short-tau inversion recovery (STIR, panels C and D) sequences demonstrate T1-weighted hyperintense and STIR-suppressed foci intrinsic to the extra-ocular muscles (EOMs). If the diameter of the focus was approximately equal in all dimensions in the coronal plane it was termed a 'dot’, whilst if unequal it was termed a 'streak’. An example of a ‘dot’ is demonstrated in the right inferior rectus muscle on paired panels A and C, and examples of ‘streaks’ are shown in both lateral recti on paired panels B and D respectively (arrows). Panels E and F demonstrate an example of the regions of interest (ROI) used to calculate the surface area of each of the EOMs within the right orbit in a control volunteer and CPEO patient respectively: superior-rectus levator complex (SR); superior oblique (SO); medial rectus (MR); lateral rectus (LR); and inferior rectus (IR). Central ROI were placed within the same muscles for the T2-relaxometry measurements in order to avoid contamination by the surrounding fat, as demonstrated in panels G and H within the right orbits of a control volunteer and CPEO patient respectively. Panels I and J demonstrate false colour T2-relaxometry maps