Han S H, Cho J H, Jung H S, Suh J Y, Kim J K, Kim Y R, Cho G, Cho H
Ulsan National Institute of Science and Technology, Ulsan, South Korea.
Korea Basic Science Institute, Ochang, South Korea.
Neuroimage. 2015 May 15;112:382-389. doi: 10.1016/j.neuroimage.2015.03.042. Epub 2015 Mar 24.
Intravascular superparamagnetic iron oxide nanoparticles (SPION)-enhanced MR transverse relaxation rates (∆R2(⁎) and ∆R2) are widely used to investigate in vivo vascular parameters, such as the cerebral blood volume (CBV), microvascular volume (MVV), and mean vessel size index (mVSI, ∆R2(⁎)/∆R2). Although highly efficient, regional comparison of vascular parameters acquired using gradient-echo based ∆R2(⁎) is hampered by its high sensitivity to magnetic field perturbations arising from air-tissue interfaces and large vessels. To minimize such demerits, we took advantage of the dual contrast property of SPION and both theoretically and experimentally verified the direct benefit of replacing gradient-echo based ∆R2(⁎) measurement with ultra-short echo time (UTE)-based ∆R1 contrast to generate the robust CBV and mVSI maps. The UTE acquisition minimized the local measurement errors from susceptibility perturbations and enabled dose-independent CBV measurement using the vessel/tissue ∆R1 ratio, while independent spin-echo acquisition enabled simultaneous ∆R2 measurement and mVSI calculation of the cortex, cerebellum, and olfactory bulb, which are animal brain regions typified by significant susceptibility-associated measurement errors.
血管内超顺磁性氧化铁纳米颗粒（SPION）增强的磁共振横向弛豫率（∆R2(⁎)和∆R2）被广泛用于研究体内血管参数，如脑血容量（CBV）、微血管体积（MVV）和平均血管大小指数（mVSI，∆R2(⁎)/∆R2）。尽管效率很高，但基于梯度回波的∆R2(⁎)所获取的血管参数的区域比较受到其对气-组织界面和大血管产生的磁场扰动高度敏感的阻碍。为了尽量减少此类缺点，我们利用了SPION的双重对比特性，并在理论和实验上验证了用基于超短回波时间（UTE）的∆R1对比取代基于梯度回波的∆R2(⁎)测量以生成可靠的CBV和mVSI图的直接益处。UTE采集将由磁化率扰动引起的局部测量误差降至最低，并使用血管/组织∆R1比值实现了与剂量无关的CBV测量，而独立的自旋回波采集则实现了对皮质、小脑和嗅球的∆R2测量和mVSI计算，这些都是动物脑区，其典型特征是存在与磁化率相关的显著测量误差。
