From the Department of Radiology, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden (J.J., I.M.B.-B., M.L., H.H., S.E.M.); Department of Medical Radiation Sciences, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden (K.L.); Department of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, Region Västra Götaland, Gothenburg, Sweden (J.J., K.L.); Department of Radiology, Sahlgrenska University Hospital, Region Västra Götaland, Gothenburg, Sweden (I.M.B.-B., M.L., H.H.); and Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA (S.E.M.).
Invest Radiol. 2024 Oct 1;59(10):727-736. doi: 10.1097/RLI.0000000000001081. Epub 2024 Apr 9.
Increasing gradient performance on modern magnetic resonance imaging scanners has profoundly reduced the attainable diffusion and echo times for clinically available pulsed-gradient spin echo (PGSE) sequences. This study investigated how this may impact the measured apparent diffusion coefficient (ADC), which is considered an important diagnostic marker for differentiation between normal and abnormal brain tissue and for therapeutic follow-up.
Diffusion time and echo time dependence of the ADC were evaluated on a high-performance 3 T magnetic resonance imaging scanner. Diffusion PGSE brain scans were performed in 10 healthy volunteers and in 10 brain tumor patients using diffusion times of 16, 40, and 70 ms, echo times of 60, 75, and 104 ms at 3 b-values (0, 100, and 1000 s/mm 2 ), and a maximum gradient amplitude of 68 mT/m. A low gradient performance system was also emulated by reducing the diffusion encoding gradient amplitude to 19 mT/m. In healthy subjects, the ADC was measured in 6 deep gray matter regions and in 6 white matter regions. In patients, the ADC was measured in the solid part of the tumor.
With increasing diffusion time, a small but significant ADC increase of up to 2.5% was observed for 6 aggregate deep gray matter structures. With increasing echo time or reduced gradient performance, a small but significant ADC decrease of up to 2.6% was observed for 6 aggregate white matter structures. In tumors, diffusion time-related ADC changes were inconsistent without clear trend. For tumors with diffusivity above 1.0 μm 2 /ms, with prolonged echo time, there was a pronounced ADC increase of up to 12%. Meanwhile, for tumors with diffusivity at or below 1.0 μm 2 /ms, no change or a reduction was observed. Similar results were observed for gradient performance reduction, with an increase of up to 21%. The coefficient of variation determined in repeat experiments was 2.4%.
For PGSE and the explored parameter range, normal tissue ADC changes seem negligible. Meanwhile, observed tumor ADC changes can be relevant if ADC is used as a quantitative biomarker and not merely assessed by visual inspection. This highlights the importance of reporting all pertinent timing parameters in ADC studies and of considering these effects when building scan protocols for use in multicenter investigations.
现代磁共振成像扫描仪梯度性能的提高，极大地缩短了临床可用的脉冲梯度自旋回波（PGSE）序列可达到的扩散和回波时间。本研究旨在探讨这可能如何影响测量的表观扩散系数（ADC），ADC 被认为是区分正常和异常脑组织以及治疗随访的重要诊断标志物。
在高性能 3T 磁共振成像扫描仪上评估 ADC 的扩散时间和回波时间依赖性。使用扩散时间为 16、40 和 70ms，回波时间为 60、75 和 104ms，在 3 个 b 值（0、100 和 1000s/mm2）下，在 10 名健康志愿者和 10 名脑肿瘤患者中进行扩散 PGSE 脑部扫描，最大梯度幅度为 68mT/m。还通过将扩散编码梯度幅度降低至 19mT/m 来模拟低梯度性能系统。在健康受试者中，在 6 个深部灰质区域和 6 个白质区域测量 ADC。在患者中，在肿瘤的实体部分测量 ADC。
随着扩散时间的增加，观察到 6 个聚合深部灰质结构的 ADC 有小但显著的增加，最大可达 2.5%。随着回波时间的增加或梯度性能的降低，观察到 6 个聚合白质结构的 ADC 有小但显著的降低，最大可达 2.6%。在肿瘤中，扩散时间相关的 ADC 变化没有明显趋势，不一致。对于弥散率高于 1.0μm2/ms 的肿瘤，随着回波时间的延长，ADC 有明显的增加，最大可达 12%。同时，对于弥散率等于或低于 1.0μm2/ms 的肿瘤，观察到无变化或减少。梯度性能降低也观察到类似的结果，增加最大可达 21%。在重复实验中确定的变异系数为 2.4%。
对于 PGSE 和所探索的参数范围，正常组织的 ADC 变化似乎可以忽略不计。同时，如果 ADC 被用作定量生物标志物，而不仅仅是通过视觉检查进行评估，则观察到的肿瘤 ADC 变化可能具有相关性。这突出表明在 ADC 研究中报告所有相关的时间参数以及在构建用于多中心研究的扫描协议时考虑这些影响的重要性。
