Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA.
Montreal Neurological Institute and Hospital, the Neuro, McGill University, Montréal, Quebec, Canada.
NMR Biomed. 2024 Dec;37(12):e5228. doi: 10.1002/nbm.5228. Epub 2024 Aug 21.
Quantitative maps of rotating frame relaxation (RFR) time constants are sensitive and useful magnetic resonance imaging tools with which to evaluate tissue integrity in vivo. However, to date, only moderate image resolutions of 1.6 x 1.6 x 3.6 mm have been used for whole-brain coverage RFR mapping in humans at 3 T. For more precise morphometrical examinations, higher spatial resolutions are desirable. Towards achieving the long-term goal of increasing the spatial resolution of RFR mapping without increasing scan times, we explore the use of the recently introduced Transform domain NOise Reduction with DIstribution Corrected principal component analysis (T-NORDIC) algorithm for thermal noise reduction. RFR acquisitions at 3 T were obtained from eight healthy participants (seven males and one female) aged 52 ± 20 years, including adiabatic T1ρ, T2ρ, and nonadiabatic Relaxation Along a Fictitious Field (RAFF) in the rotating frame of rank n = 4 (RAFF4) with both 1.6 x 1.6 x 3.6 mm and 1.25 x 1.25 x 2 mm image resolutions. We compared RFR values and their confidence intervals (CIs) obtained from fitting the denoised versus nondenoised images, at both voxel and regional levels separately for each resolution and RFR metric. The comparison of metrics obtained from denoised versus nondenoised images was performed with a two-sample paired t-test and statistical significance was set at p less than 0.05 after Bonferroni correction for multiple comparisons. The use of T-NORDIC on the RFR images prior to the fitting procedure decreases the uncertainty of parameter estimation (lower CIs) at both spatial resolutions. The effect was particularly prominent at high-spatial resolution for RAFF4. Moreover, T-NORDIC did not degrade map quality, and it had minimal impact on the RFR values. Denoising RFR images with T-NORDIC improves parameter estimation while preserving the image quality and accuracy of all RFR maps, ultimately enabling high-resolution RFR mapping in scan times that are suitable for clinical settings.
定量旋转框架弛豫（RFR）时间常数图是敏感且有用的磁共振成像工具，可用于评估体内组织的完整性。然而，迄今为止，在 3T 下对全脑覆盖 RFR 映射仅使用了 1.6x1.6x3.6mm 的中等图像分辨率。为了进行更精确的形态学检查，需要更高的空间分辨率。为了在不增加扫描时间的情况下实现长期提高 RFR 映射空间分辨率的目标，我们探索了使用最近引入的变换域降噪与分布校正主成分分析（T-NORDIC）算法来减少热噪声。在 3T 下，从 8 名年龄为 52±20 岁的健康参与者中获得 RFR 采集数据，包括绝热 T1ρ、T2ρ 和非绝热旋转框架中虚构场的 Relaxation Along a Fictitious Field（RAFF）的 rank n=4（RAFF4），图像分辨率分别为 1.6x1.6x3.6mm 和 1.25x1.25x2mm。我们比较了在两种分辨率和 RFR 指标下，分别对每个分辨率和 RFR 指标的体素和区域水平拟合去噪和非去噪图像时获得的 RFR 值及其置信区间（CI）。通过双样本配对 t 检验比较去噪和非去噪图像获得的指标，并在经过 Bonferroni 校正多重比较后，将统计显著性设置为 p<0.05。在拟合过程之前，将 T-NORDIC 应用于 RFR 图像可降低参数估计的不确定性（较低的 CI），在两种空间分辨率下均如此。在高空间分辨率下，RAFF4 的效果尤其明显。此外，T-NORDIC 不会降低图谱质量，并且对 RFR 值的影响最小。用 T-NORDIC 对 RFR 图像进行去噪可以改善参数估计，同时保持所有 RFR 图谱的图像质量和准确性，最终使在适合临床的扫描时间内实现高分辨率 RFR 映射成为可能。
