Department of Diagnostic Physics, Oslo University Hospital, Oslo, Norway.
Department of Physics, University of Oslo, Oslo, Norway.
Phys Med Biol. 2020 Nov 17;65(22):225020. doi: 10.1088/1361-6560/abb71a.
Dynamic susceptibility contrast (DSC) imaging is a widely used technique for assessment of cerebral blood volume (CBV). With combined gradient-echo and spin-echo DSC techniques, measures of the underlying vessel size and vessel architecture can be obtained from the vessel size index (VSI) and vortex area, respectively. However, how noise, and specifically the contrast-to-noise ratio (CNR), affect the estimations of these parameters has largely been overlooked. In order to address this issue, we have performed simulations to generate DSC signals with varying levels of CNR, defined by the peak of relaxation rate curve divided by the standard deviation of the baseline. Moreover, DSC data from 59 brain cancer patients were acquired at two different 3 T-scanners (N = 29 and N = 30, respectively), where CNR and relative parameter maps were obtained. Our simulations showed that the measured parameters were affected by CNR in different ways, where low CNR led to overestimations of CBV and underestimations of VSI and vortex area. In addition, a higher noise-sensitivity was found in vortex area than in CBV and VSI. Results from clinical data were consistent with simulations, and indicated that CNR < 4 gives highly unreliable measurements. Moreover, we have shown that the distribution of values in the tumour regions could change considerably when voxels with CNR below a given cut off are excluded when generating the relative parameter maps. The widespread use of CBV and attractive potential of VSI and vortex area, makes the noise-sensitivity of these parameters found in our study relevant for further use and development of the DSC imaging technique. Our results suggest that the CNR has considerable impact on the measured parameters, with the potential to affect the clinical interpretation of DSC-MRI, and should therefore be taken into account in the clinical decision-making process.
动态对比磁共振成像（DSC）是一种广泛应用于评估脑血容量（CBV）的技术。通过联合梯度回波和自旋回波 DSC 技术，可以分别从血管大小指数（VSI）和涡流区域获得有关基础血管大小和血管结构的测量值。然而，噪声（特别是对比噪声比，CNR）如何影响这些参数的估计在很大程度上被忽视了。为了解决这个问题，我们进行了模拟，生成了具有不同 CNR 的 DSC 信号，由弛豫率曲线的峰值除以基线的标准偏差来定义。此外，我们在两台不同的 3T 扫描仪（分别为 29 例和 30 例，N=29 和 N=30）上获取了 59 例脑癌患者的 DSC 数据，获得了 CNR 和相对参数图。我们的模拟结果表明，所测量的参数受到 CNR 的不同影响，其中低 CNR 导致 CBV 的高估和 VSI 和涡流区域的低估。此外，涡流区域的噪声灵敏度高于 CBV 和 VSI。临床数据的结果与模拟结果一致，并表明 CNR<4 会导致高度不可靠的测量。此外，我们还表明，当在生成相对参数图时排除 CNR 低于给定截止值的体素时，肿瘤区域中的值分布可能会发生很大变化。CBV 的广泛应用以及 VSI 和涡流区域的诱人潜力，使得我们在研究中发现的这些参数的噪声灵敏度与 DSC 成像技术的进一步使用和发展相关。我们的结果表明，CNR 对测量参数有相当大的影响，有可能影响 DSC-MRI 的临床解释，因此在临床决策过程中应予以考虑。
