Dept. of Radiology, Geisel School of Medicine, Dartmouth College, Hanover, NH, USA.
Thayer School of Engineering, Dartmouth College, Hanover, NH, USA.
Mol Imaging Biol. 2024 Jun;26(3):391-402. doi: 10.1007/s11307-023-01887-6. Epub 2024 Jan 4.
Within this special issue, many eminent investigators report on measurements of oxygen (O) levels in tissues. Given the complexities of spatial and temporal heterogeneities of O in tissues and its many sources, this commentary draws attention to what such measurements do and do not actually assess regarding O levels in tissues. Given this limitation, it also discusses how these results can be used most effectively. To provide a convenient mechanism to discuss these issues more fully, this analysis focuses on measurements using EPR oximetry, but these considerations apply to all other techniques. The nature of the delivery of O to tissues and the mechanisms by which O is consumed necessarily result in very different levels of O within the volume of each voxel of a measurement. Better spatial resolution cannot fully resolve the problem because the variations include O gradients within each cell. Improved resolution of the time-dependent variation in O is also very challenging because O levels within tissues can have fluctuations of O levels in the range of milliseconds, while most methods require longer times to acquire the data from each voxel. Based on these issues, we argue that the values obtained inevitably are complex aggregates of averages of O levels across space and time in the tissue. These complexities arise from the complex physiology of tissues and are compounded by the limitations of the technique and its ability to acquire data. However, one often can obtain very meaningful and useful results if these complexities and limitations are taken into account. We illustrate this, using results obtained with in vivo EPR oximetry, especially utilizing its capacity to make repeated measurements to follow changes in O levels that occur with interventions and/or over time.
在本期特刊中，许多杰出的研究人员报告了组织中氧 (O) 水平的测量结果。鉴于组织中 O 的空间和时间异质性及其众多来源的复杂性，本评论提请注意这些测量实际上评估了组织中 O 水平的哪些方面。鉴于这一局限性，它还讨论了如何最有效地利用这些结果。为了提供一个方便的机制来更充分地讨论这些问题，本分析重点关注使用 EPR 血氧仪进行的测量，但这些考虑因素适用于所有其他技术。O 向组织的输送性质和 O 消耗的机制必然导致每个测量体素体积内的 O 水平非常不同。更好的空间分辨率并不能完全解决问题，因为这些变化包括每个细胞内的 O 梯度。O 水平随时间变化的分辨率的提高也非常具有挑战性，因为组织内的 O 水平波动范围可以达到毫秒级，而大多数方法需要更长的时间从每个体素获取数据。基于这些问题，我们认为所获得的值不可避免地是组织中 O 水平在空间和时间上的平均值的复杂组合。这些复杂性源于组织的复杂生理学，并且由于技术的限制及其获取数据的能力而变得更加复杂。然而，如果考虑到这些复杂性和局限性，通常可以获得非常有意义和有用的结果。我们将使用体内 EPR 血氧仪获得的结果来说明这一点，特别是利用其进行重复测量以跟踪干预和/或随时间发生的 O 水平变化的能力。
