Collier Guilhem J, Schulte Rolf F, Rao Madhwesha, Norquay Graham, Ball James, Wild Jim M
POLARIS, Imaging Sciences, Department of Infection, Immunity & Cardiovascular Disease, University of Sheffield, Sheffield, UK.
INSIGNEO institute, University of Sheffield, Sheffield, UK.
Magn Reson Med. 2023 Jun;89(6):2217-2226. doi: 10.1002/mrm.29602. Epub 2023 Feb 6.
Imaging of the different resonances of hyperpolarized Xe in the brain and lungs was performed using a 3D sampling density-weighted MRSI technique in healthy volunteers.
Four volunteers underwent dissolved-phase hyperpolarized Xe imaging in the lung with the MRSI technique, which was designed to improve the point-spread function while preserving SNR (1799 phase-encoding steps, 14-s breath hold, 2.1-cm isotropic resolution). A frequency-tailored RF excitation pulse was implemented to reliably excite both the Xe gas and dissolved phase (tissue/blood signal) with 0.1° and 10° flip angles, respectively. Images of xenon gas in the lung airspaces and xenon dissolved in lung tissue/blood were used to generate quantitative signal ratio maps. The method was also optimized and used for imaging dissolved resonances of Xe in the brain in 2 additional volunteers.
High-quality regional spectra of hyperpolarized Xe were achieved in both the lung and the brain. Ratio maps of the different xenon resonances were obtained in the lung with sufficient SNR (> 10) at both 1.5 T and 3 T, making a triple Lorentzian fit possible and enabling the measurement of relaxation times and xenon frequency shifts on a voxel-wise basis. The imaging technique was successfully adapted for brain imaging, resulting in the first demonstration of 3D xenon brain images with a 2-cm isotropic resolution.
Density-weighted MRSI is an SNR and encoding-efficient way to image Xe resonances in the lung and the brain, providing a valuable tool to quantify regional spectroscopic information.
在健康志愿者中使用三维采样密度加权磁共振波谱成像（MRSI）技术对大脑和肺部中超极化氙的不同共振进行成像。
四名志愿者采用MRSI技术进行肺部溶解相超极化氙成像，该技术旨在改善点扩散函数同时保持信噪比（1799个相位编码步，屏气14秒，各向同性分辨率2.1厘米）。实施了频率定制的射频激发脉冲，分别以0.1°和10°的翻转角可靠地激发氙气和溶解相（组织/血液信号）。肺部气腔中氙气和溶解在肺组织/血液中的氙气的图像用于生成定量信号比图。该方法还进行了优化，并用于另外两名志愿者大脑中溶解态氙共振的成像。
在肺部和大脑中均获得了高质量的超极化氙区域光谱。在1.5 T和3 T场强下，肺部均获得了具有足够信噪比（>10）的不同氙共振的比图，使得三重洛伦兹拟合成为可能，并能够在体素水平上测量弛豫时间和氙频移。该成像技术成功地应用于脑成像，首次展示了各向同性分辨率为2厘米的三维氙脑图像。
密度加权MRSI是一种在肺部和大脑中对氙共振进行成像的高效信噪比和编码方法，为量化区域光谱信息提供了一种有价值的工具。
