Department of Medicine, University of California, San Diego, California.
J Appl Physiol (1985). 2022 Jun 1;132(6):1370-1378. doi: 10.1152/japplphysiol.00652.2021. Epub 2022 Apr 28.
Specific ventilation imaging (SVI) measures the spatial distribution of specific ventilation (SV) in the lung with MRI by using inhaled oxygen as a contrast agent. Because of the inherently low signal-to-noise ratio in the technique, multiple switches between inspiring air and O are utilized, and the high spatial resolution SV distribution is determined as an average over the entire imaging period (∼20 min). We hypothesized that a trade-off between spatial and temporal resolution could allow imaging at a higher temporal resolution, at the cost of a coarser, yet acceptable, spatial resolution. The appropriate window length and spatial resolution compromise were determined by generating synthetic data with signal- and contrast-to-noise characteristics reflective of that in previously published experimental data, with a known and unchanging distribution of SV, and showed that acceptable results could be obtained in an imaging period of ∼7 min (80 breaths), with a spatial resolution of ∼1 cm. Previously published data were then reanalyzed. The average heterogeneity of the temporally resolved maps of SV was not different from the previous overall analysis, however, the temporally resolved maps were less effective at detecting the amount of bronchoconstriction resulting from methacholine administration. The results further indicated that the initial response to inhaled methacholine and subsequent inhalation of albuterol were largely complete within ∼22 min and ∼9 min, respectively, although there was a tendency for an ongoing developing effect in both cases. These results suggest that it is feasible to use a shortened SVI protocol, with a modest sacrifice in spatial resolution, to measure temporally dynamic processes. Dynamic imaging providing maps of specific ventilation with a temporal resolution of ∼7 min with a spatial resolution of ∼1 cm using MRI was shown to be practical. The technique provides an ionizing radiation free means of temporally following the spatial pattern of specific ventilation. Reanalysis of previously published data showed that the effects of inhaled methacholine and albuterol were largely complete at ∼22 min and ∼9 min, respectively after administration.
特定通气成像 (SVI) 通过使用吸入的氧气作为对比剂，利用 MRI 测量肺部的特定通气 (SV) 的空间分布。由于该技术固有的信噪比低，因此会在吸气和 O 之间进行多次切换，并且整个成像期间（约 20 分钟）的高空间分辨率 SV 分布被确定为平均值。我们假设可以在更高的时间分辨率下进行成像，同时牺牲更粗糙但可接受的空间分辨率，从而在空间和时间分辨率之间进行权衡。通过使用反映先前发表的实验数据中的信号和对比噪声特性的合成数据来确定适当的窗口长度和空间分辨率折衷方案，这些数据具有已知且不变的 SV 分布，并表明可以在约 7 分钟（80 次呼吸）的成像时间内获得可接受的结果，空间分辨率约为 1 厘米。然后重新分析以前发表的数据。SV 的时间分辨图的平均异质性与以前的总体分析没有不同，但是，时间分辨图在检测乙酰甲胆碱给药引起的支气管收缩程度方面效果较差。结果进一步表明，吸入乙酰甲胆碱后的初始反应和随后吸入沙丁胺醇分别在约 22 分钟和约 9 分钟内基本完成，尽管在两种情况下都存在持续发展的趋势。这些结果表明，使用空间分辨率适度降低的缩短 SVI 协议来测量时间动态过程是可行的。使用 MRI 以约 7 分钟的时间分辨率和约 1 厘米的空间分辨率显示，特定通气的动态成像具有实用价值。该技术提供了一种无电离辐射的方法，可用于在时间上跟踪特定通气的空间模式。对以前发表的数据进行重新分析表明，吸入乙酰甲胆碱和沙丁胺醇的作用在给药后分别约 22 分钟和约 9 分钟基本完成。
