Quantitative T2 maps during and 90 min after end of indentation of 6 BN and 6 SD rats with occluded or not occluded saphenous artery. 

Context in source publication

Context 1

... model: 11-week-old SD rats (♀, 214-272 g, n=6) and BN rats (♀, 152-180 g, n=6) were used. The right leg of the rat was shaved and placed in a plastic profile filled with alginate mold for fixation, while keeping the TA muscle accessible for indentation. Indentation was performed with a previously described MR compatible indentation setup. 1 Indentation of the TA muscle, for a period of 2 hours, took place inside the MR scanner. In vivo MRI: A Bruker 7.0T small animal MRI scanner was used with a 2 cm diameter receive surface coil, placed on top of the TA muscle inside the indentation device, in combination with a 86 mm excitation volume coil. Skeletal muscle injury and blood flow were assessed with T2 mapping (Spin-Echo, 20 slices, FOV = 2.5 x 2.5 cm 2 , MTX = 256 x 256, TE = 6.95 -180.7 ms, 26 echoes, TR = 4 s, fat suppression), and Time-Of-Flight (TOF) angiography (FLASH, 120 slices, FOV = 4 x 4 cm 2 , MTX = 256 x 256, TE = 3.8 ms, TR = 12 ms) protocols. All measurements were performed pre, during and up to 2 h after indentation. During the MRI scans and indentation isoflurane (1-2%) was used as anesthetic and temgesic 0.05 mg/kg as analgesia. Data analysis: Quantitative T2 maps were obtained by fitting the MR signal pixel wise. Pixels with R 2 < 0.9 were excluded. Region of interest based T2 analysis on the whole TA muscle was performed. The TOF angiograms were processed by visualizing maximum intensity projections (MIP) in OsiriX (Pixmeo) and visual inspection of occlusion of the saphenous artery. Fig. 1 shows angiography MIPs pre, during and after indentation, during deformation the indentor is clearly visible through its filling with 1g/L CuSO4 solution. In some cases, the saphenous artery, responsible for the main blood supply to the lower leg, was occluded (bottom middle) during indentation. In other cases, it was not (top middle). Multiple small vessels became visible during indentation in the occluded cases, which indicates a compensatory mechanism in collateral vessels to account for loss of blood supply. In the cases where the saphenous artery was not collapsed during indentation a small increase in the number of visible small vessels was observed which indicates a larger demand of blood to the muscle in response to the deformation. Within a few minutes after load release multiple small vessels became apparent for both the occluded and non-occluded cases and all vessels were better visible. This is likely caused by an increase in blood flow and indicative for a hyperemic effect. This hyperemic effect was observed up to 90 min after end of indentation, which was the time point of last scan, and was more pronounced in the occluded cases. In Fig. 2 quantitative T2 maps of a slice in the center of deformation during and 90 min after end of indentation of the TA muscle are shown for both BN and SD rats. T2 values are grouped in occluded and not occluded saphenous artery subjects. In both groups increased T2 values were found, indicative for the formation of edema and skeletal muscle damage. The percentage of elevated T2 pixels (T2 ≥ T2 mean prior to indentation + 3 x Std dev) in the TA was significant larger in those rats for which the saphenous artery was collapsed during indentation (paired t-test, p<0.001, 23.7 ± 12.8 % and 74.3 ± 10.7 %, for not occluded and occluded, respectively). The T2 enhancement was patchy with a structure that resembled the peri-and endomysium organization of skeletal muscle. In addition, edema between muscle and skin was observed for most of the occluded cases. No difference in response on skeletal muscle deformation between the BN and SD rat type was observed. The reason that the saphenous artery for some subjects was occluded and for some not, is most probably related to the strength and position of the indentation, which differed between animals due to small anatomical differences. Fig. 3 shows the ROI T2 analysis of the whole TA muscle pre, during and 90 min after end of indentation for SD and BN rats. T2 values were again grouped for the occlusion and not occlusion cases. Both rat strains showed a similar T2 enhancement and T2 was more elevated in case of occlusion of the saphenous artery 90 min after end of indentation, indicative of more skeletal muscle damage in the latter case. Conclusion This study showed that skeletal muscle damage due to application of a sustained mechanical load is aggravated in cases where the loading leads to collapse of a major supplying blood vessel. In a rat model, the combination of skeletal muscle deformation and occlusion of a main supplying vessel, led to high T2 values in the muscle indicative of edema and muscle damage. T2 enhancement due to skeletal muscle damage appeared highly structured and matched the peri-and endomysium organization of skeletal ...