UCL Centre for Translational Cardiovascular Imaging, University College London, London, UK.
Institute of Nuclear Medicine, University College Hospital, London, UK.
Magn Reson Med. 2024 Jan;91(1):325-336. doi: 10.1002/mrm.29841. Epub 2023 Oct 5.
Sodium MRI can be used to quantify tissue sodium concentration (TSC) in vivo; however, UTE sequences are required to capture the rapidly decaying signal. 2D MRI enables high in-plane resolution but typically has long TEs. Half-sinc excitation may enable UTE; however, twice as many readouts are necessary. Scan time can be minimized by reducing the number of signal averages (NSAs), but at a cost to SNR. We propose using compressed sensing (CS) to accelerate 2D half-sinc acquisitions while maintaining SNR and TSC.
Ex vivo and in vivo TSC were compared between 2D spiral sequences with full-sinc (TE = 0.73 ms, scan time ≈ 5 min) and half-sinc excitation (TE = 0.23 ms, scan time ≈ 10 min), with 150 NSAs. Ex vivo, these were compared to a reference 3D sequence (TE = 0.22 ms, scan time ≈ 24 min). To investigate shortening 2D scan times, half-sinc data was retrospectively reconstructed with fewer NSAs, comparing a nonuniform fast Fourier transform to CS. Resultant TSC and image quality were compared to reference 150 NSAs nonuniform fast Fourier transform images.
TSC was significantly higher from half-sinc than from full-sinc acquisitions, ex vivo and in vivo. Ex vivo, half-sinc data more closely matched the reference 3D sequence, indicating improved accuracy. In silico modeling confirmed this was due to shorter TEs minimizing bias caused by relaxation differences between phantoms and tissue. CS was successfully applied to in vivo, half-sinc data, maintaining TSC and image quality (estimated SNR, edge sharpness, and qualitative metrics) with ≥50 NSAs.
2D sodium MRI with half-sinc excitation and CS was validated, enabling TSC quantification with 2.25 × 2.25 mm resolution and scan times of ≤5 mins.
钠 MRI 可用于活体组织中钠浓度（TSC）的定量；然而，需要使用 UTE 序列来捕获快速衰减的信号。2D MRI 能够实现高的平面分辨率，但通常具有较长的 TE。半 sinc 激励可实现 UTE；然而，需要两倍多的读取。通过减少信号平均次数（NSA）可以最小化扫描时间，但代价是 SNR。我们提出使用压缩感知（CS）来加速 2D 半 sinc 采集，同时保持 SNR 和 TSC。
比较了使用全 sinc（TE=0.73ms，扫描时间≈5min）和半 sinc 激励（TE=0.23ms，扫描时间≈10min）的 2D 螺旋序列与 150 NSA 之间的离体和体内 TSC。离体情况下，将这些序列与参考 3D 序列（TE=0.22ms，扫描时间≈24min）进行了比较。为了缩短 2D 扫描时间，使用较少的 NSA 对半 sinc 数据进行了回顾性重建，比较了非均匀快速傅里叶变换和 CS。将重建结果的 TSC 和图像质量与参考的 150 NSA 非均匀快速傅里叶变换图像进行了比较。
离体和体内，半 sinc 采集的 TSC 明显高于全 sinc 采集。离体情况下，半 sinc 数据更接近参考 3D 序列，表明准确性更高。计算机模拟证实，这是由于较短的 TE 最小化了由于体模和组织之间的弛豫差异引起的偏倚。CS 成功应用于体内半 sinc 数据，保持 TSC 和图像质量（估计 SNR、边缘锐度和定性指标），NSA≥50。
验证了使用半 sinc 激励和 CS 的 2D 钠 MRI，实现了分辨率为 2.25×2.25mm 和扫描时间≤5min 的 TSC 定量。
