Figure 4

High-field MR imaging (9.4 T, flip angle 40°) of the PSBs and the ISL. Post-mortem analysis of a specimen of a Friesian horse with axial osteitis of the PSBs and desmitis of the ISL (left images) and a non-diseased Friesian horse (right images). Top: T1 weighted GRE dorsal sequences. Middle: T1 mapping. Bottom: proton density sequences. On the T1 weighted images, a clear increase in signal intensity could be seen in the compact bone at the proximo-axial area of the PSBs in the diseased horse (white line marked area). Compared to the non-diseased horse, signal intensity of the spongiosa (asterisks) was reduced, signal intensity of the compacta was increased in the T1 weighted GRE (open arrows) and proton density (black arrows) images leading to homogeneous signal intensity across the PSBs in the diseased animal. In the non-diseased horse, heterogeneous signal intensity was present in T1 weighted and proton density images with the spongiosa having more intense signaling (asterisks) and peripheral compacta having less intense signaling (open arrows). Compared to the non-diseased horse, on the T1 map of the diseased horse, especially the apical part and the peripheral compact bone showed an increase in T1 values (black and white arrows), the ISL ligament also showed an increase in T1 values (white line marked area). The non-diseased horse showed a homogeneous pattern of the PSBs with hardly any signal on the T1 map. Integration of the findings on all images could be interpreted as loss of compact bone at the proximo-axial margin of the PSBs, osteoporosis of the peripheral compact bone and spongious bone of the PSBs, and inflammation and fibrous (scar) tissue formation of the ISL in the diseased horse.