Objective

Diffusion-weighted, hyperpolarized ¹²⁹Xe MRI is useful for the characterization of microstructural changes in the lung. A stretched exponential model was proposed for morphometric extraction of the mean chord length (L_m) from diffusion-weighted data. The stretched exponential model enables accelerated mapping of L_m in a single-breathhold using compressed sensing. Our purpose was to compare L_m maps obtained from stretched-exponential model analysis of accelerated versus unaccelerated diffusion-weighted ¹²⁹Xe MRI data obtained from healthy/injured rat lungs.

Material and methods

L_m maps were generated using a stretched-exponential model analysis of previously acquired fully sampled diffusion-weighted ¹²⁹Xe rat data (b values = 0 … 110 s/cm²) and compared to L_m maps generated from retrospectively undersampled data simulating acceleration factors of 7/10. The data included four control rats and five rats receiving whole-lung irradiation to mimic radiation-induced lung injury. Mean L_m obtained from the accelerated/unaccelerated maps were compared to histological mean linear intercept.

Results

Accelerated L_m estimates were similar to unaccelerated L_m estimates in all rats, and similar to those previously reported (< 12% different). L_m was significantly reduced (p < 0.001) in the irradiated rat cohort (90 ± 20 µm/90 ± 20 µm) compared to the control rats (110 ± 20 µm/100 ± 15 µm) and agreed well with histological mean linear intercept.

Discussion

Accelerated mapping of L_m using a stretched-exponential model analysis is feasible, accurate and agrees with histological mean linear intercept. Acceleration reduces scan time, thus should be considered for the characterization of lung microstructural changes in humans where breath-hold duration is short.

中文翻译：

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拉伸指数模型在大鼠肺加速扩散加权 129Xe MRI 形态测量分析中的应用。

客观的

弥散加权超极化¹²⁹ Xe MRI 可用于表征肺的微观结构变化。提出了一种拉伸指数模型，用于从扩散加权数据中提取平均弦长 ( L _m ) 的形态计量学。拉伸指数模型能够使用压缩感知在单次呼吸中加速映射L _m。我们的目的是比较从健康/受伤大鼠肺获得的加速与非加速扩散加权¹²⁹ Xe MRI 数据的拉伸指数模型分析中获得的L _m图。

材料与方法

L _m地图使用拉伸指数模型分析先前获得的完全采样的扩散加权¹²⁹ Xe 大鼠数据（b值 = 0 … 110 s/cm ²）生成，并与从模拟加速因子的回顾性欠采样数据生成的L _m地图进行比较7/10。数据包括四只对照大鼠和五只接受全肺照射以模拟辐射诱导的肺损伤的大鼠。从加速/非加速图获得的平均L _m与组织学平均线性截距进行了比较。

结果

加速大号_米估计类似于加速的大号_米所有大鼠估计，并且类似于先前报道的（<12％不同）的那些。 与对照大鼠 (110 ± 20 µm/100 ± 15 µm) 相比，辐照大鼠队列 (90 ± 20 µm/90 ± 20 µm) 中的L _m显着降低 ( p < 0.001)，并且与组织学平均线性截距一致.

讨论

使用拉伸指数模型分析加速映射L _m是可行的、准确的，并且与组织学平均线性截距一致。加速减少了扫描时间，因此在屏气持续时间较短的情况下，应考虑表征人类肺微观结构变化。