Purpose. Metastatic complications are responsible for 90% of cancer-associated mortality. Magnetic resonance imaging (MRI) can be used to observe the brain’s microstructure and potentially correlate changes with metastasis occurrence. Diffusion weighted imaging (DWI) is an MRI technique that utilizes the kinetics of water molecules within the body. The aim of this study is to use DWI to characterize diffusion changes within brain metastases in cancer patients pre- and post-stereotactic radiosurgery (SRS). Methods. We retrospectively analyzed 113 metastases from 13 patients who underwent SRS for brain metastasis recurrence. Longitudinal apparent diffusion coefficient (ADC) maps were registered to Gd-T1 images and CT, and clinical metastasis ROIs from all SRS treatments were retrospectively transferred onto these ADC maps for analysis. Metastases were characterized based on pre-SRS diffusion pattern, primary cancer site, and post-SRS outcome. ADC values were calculated pre- and post-SRS. Results.ADC values were significantly elevated (980.2נ10⁻⁶ mm² s⁻¹ and 1040.3נ10⁻⁶ mm² s⁻¹ pre- and post-SRS, respectively) when compared to healthy brain tissue (826.8נ10⁻⁶ mm² s⁻¹) for all metastases. Three identified pre-SRS patterns were significantly different before SRS and within 6 months post-SRS. No significant differences were observed between different primaries pre-SRS. Post-SRS, Lung metastases ADC decreased by 86.2נ10⁻⁶ mm² s⁻¹, breast metastases increased by 116.7נ10⁻⁶ mm² s⁻¹, and genitourinary metastases showed no significant ADC change. SRS outcomes showed ADC variability pre-treatment but no significant differences pre- and post-SRS, except at 6–9 months post-SRS where progressing metastases were elevated when compared to other response groups. Conclusion. This study provided a unique opportunity to characterize diffusion changes in brain metastases before their manifestation on standard Gd-T1 images and post-SRS. Identified patterns may improve early detection of brain metastases as well as predict their response to treatment.

目的。转移性并发症占癌症相关死亡率的 90%。磁共振成像 (MRI) 可用于观察大脑的微观结构，并可能将变化与转移发生相关联。扩散加权成像 (DWI) 是一种利用体内水分子动力学的 MRI 技术。本研究的目的是使用 DWI 来表征癌症患者术前和术后立体定向放射外科 (SRS) 脑转移灶内的扩散变化。方法。我们回顾性分析了 13 例因脑转移复发而接受 SRS 的患者的 113 例转移灶。纵向表观扩散系数 (ADC) 图被配准到 Gd-T1 图像和 CT，所有 SRS 治疗的临床转移 ROI 被回顾性地转移到这些 ADC 图上进行分析。根据 SRS 前扩散模式、原发癌部位和 SRS 后结果对转移进行表征。在 SRS 之前和之后计算 ADC 值。结果。与健康脑组织相比， ADC 值显着升高（SRS 前后分别为 980.2 和 10 ^-6 mm ² s ^-1和 1040.3 ^-6 mm ² s ^-1）（826.8 和 10^-6 mm ² s ^-1 ) 适用于所有转移灶。三种确定的 SRS 前模式在 SRS 之前和 SRS 后 6 个月内显着不同。在 SRS 之前的不同初选之间没有观察到显着差异。SRS 后，肺转移瘤 ADC 下降 86.2נ10 ^-6 mm ² s ^-1，乳腺转移瘤增加 116.7נ10 ^-6 mm ² s ^-1，泌尿生殖转移瘤 ADC 无明显变化。SRS 结果显示治疗前 ADC 变异性，但在 SRS 前后没有显着差异，除了在 SRS 后 6-9 个月，与其他反应组相比，进展性转移升高。结论. 这项研究提供了一个独特的机会来描述脑转移灶在标准 Gd-T1 图像和 SRS 后表现之前的扩散变化。确定的模式可以改善脑转移的早期检测并预测它们对治疗的反应。