Department of Biomedical Engineering, University of Alberta, Edmonton, Alberta, Canada.
Division of Neurology, University of Alberta, Edmonton, Alberta, Canada.
NMR Biomed. 2024 Aug;37(8):e5139. doi: 10.1002/nbm.5139. Epub 2024 Mar 11.
T1-weighted magnetization-prepared rapid gradient-echo (MPRAGE) is commonly included in brain studies for structural imaging using magnitude images; however, its phase images can provide an opportunity to assess microbleed burden using quantitative susceptibility mapping (QSM). This potential application for MPRAGE-based QSM was evaluated using in vivo and simulated measurements. Possible factors affecting image quality were also explored. Detection sensitivity was evaluated against standard multiecho gradient echo (MEGE) QSM using 3-T in vivo data of 15 subjects with a combined total of 108 confirmed microbleeds. The two methods were compared based on the microbleed size and susceptibility measurements. In addition, simulations explored the detection sensitivity of MPRAGE-QSM at different representative magnetic field strengths and echo times using microbleeds of different size, susceptibility, and location. Results showed that in vivo microbleeds appeared to be smaller (× 0.54) and of higher mean susceptibility (× 1.9) on MPRAGE-QSM than on MEGE-QSM, but total susceptibility estimates were in closer agreement (slope: 0.97, r: 0.94), and detection sensitivity was comparable. In simulations, QSM at 1.5 T had a low contrast-to-noise ratio that obscured the detection of many microbleeds. Signal-to-noise ratio (SNR) levels at 3 T and above resulted in better contrast and increased detection. The detection rates for microbleeds of minimum one-voxel diameter and 0.4-ppm susceptibility were 0.55, 0.80, and 0.88 at SNR levels of 1.5, 3, and 7 T, respectively. Size and total susceptibility estimates were more consistent than mean susceptibility estimates, which showed size-dependent underestimation. MPRAGE-QSM provides an opportunity to detect and quantify the size and susceptibility of microbleeds of at least one-voxel diameter at B of 3 T or higher with no additional time cost, when standard T*-weighted images are not available or have inadequate spatial resolution. The total susceptibility measure is more robust against sequence variations and might allow combining data from different protocols.
T1 加权磁化准备快速梯度回波（MPRAGE）是脑结构成像中常用的方法，用于采集幅度图像；然而，其相位图像可通过定量磁化率映射（QSM）来评估微出血负担。本研究使用体内和模拟测量来评估 MPRAGE 基 QSM 的这种潜在应用，并探讨了可能影响图像质量的因素。使用 15 名受试者的 3-T 体内数据，对微出血总数为 108 个的检测灵敏度进行了评估，该数据基于多回波梯度回波（MEGE）QSM。两种方法均基于微出血的大小和磁化率测量值进行比较。此外，还使用不同大小、磁化率和位置的微出血对不同代表性磁场强度和回波时间的 MPRAGE-QSM 检测灵敏度进行了模拟探索。结果表明，与 MEGE-QSM 相比，体内 MPRAGE-QSM 上的微出血似乎更小（×0.54），平均磁化率更高（×1.9），但总磁化率估计值更接近（斜率：0.97，r：0.94），检测灵敏度相当。在模拟中，1.5 T 时的 QSM 对比度噪声比低，导致许多微出血的检测受到干扰。3 T 及以上的信噪比（SNR）水平可提高对比度，增加检测。在 SNR 水平分别为 1.5、3 和 7 T 时，直径最小为一个体素、磁化率为 0.4-ppm 的微出血的检测率分别为 0.55、0.80 和 0.88。大小和总磁化率估计值比平均磁化率估计值更一致，后者显示出与大小相关的低估。当标准 T*加权图像不可用或空间分辨率不足时，MPRAGE-QSM 可在 3 T 或更高场强下提供检测和量化至少一个体素直径微出血大小和磁化率的机会，且无额外时间成本。总磁化率测量值对序列变化更稳健，并且可能允许合并来自不同协议的数据。
