Immersion of Achilles tendon in phosphate‐buffered saline influences T1 and T2 relaxation times: An ex vivo study

• Published in: NMR in biomedicine 2020-06, Vol.33 (6), p.e4288-n/a
• Main Authors: Krämer, Martin, Kollert, Matthias R., Brisson, Nicholas M., Maggioni, Marta B., Duda, Georg N., Reichenbach, Jürgen R.
• Format: Article
• Language: English
• Subjects: Achilles tendon; Biological products; Buffer solutions; ex vivo; Hydration; Immersion; Magnetic resonance imaging; Mapping; Parameter robustness; phosphate‐buffered saline; Preservation; Relaxation time; relaxation time constants; Submerging; Tendons; tissue swelling; Tissues; ultrashort echo time
• ISSN: 0952-3480; 1099-1492
• DOI: 10.1002/nbm.4288

Robust mapping of relaxation parameters in ex vivo tissues is based on hydration and therefore requires control of the tissue treatment to ensure tissue integrity and consistent measurement conditions over long periods of time. One way to maintain the hydration of ex vivo tendon tissue is to immerse the samples in a buffer solution. To this end, various buffer solutions have been proposed; however, many appear to influence the tissue relaxation times, especially with prolonged exposure. In this work, ovine Achilles tendon tissue was used as a model to investigate the effect of immersion in phosphate‐buffered saline (PBS) and the effects on the T1 and T2* relaxation times. Ex vivo samples were measured at 0 (baseline), 30 and 67 hours after immersion in PBS. Ultrashort echo time (UTE) imaging was performed using variable flip angle and echo train‐shifted multi‐echo imaging for T1 and T2* estimation, respectively. Compared with baseline, both T1 and T2* relaxation time constants increased significantly after 30 hours of immersion. T2* continued to show a significant increase between 30 and 67 hours. Both T1 and T2* tended to approach saturation at 67 hours. These results exemplify the relevance of stringently controlled tissue preparation and preservation techniques, both before and during MRI experiments. It is demonstrated that an experimental step as fundamental as immersing tendon samples in phosphate‐buffered saline (PBS) for measurement or preservation can have a significant effect on both T1 and T2* within 30 hours. The strong effect of swelling of tendon tissue in PBS on the measured relaxation times underscores the importance of closely controlling the handling and hydration of samples not only before, but also during the MRI of ex vivo tissue experiments, to yield valid and reliable results.