Changes in longitudinal relaxation time (T1) and proton density (PD) are sensitive indicators of microstructural alterations associated with various central nervous system diseases as well as brain maturation and aging. In this work, we introduce a new approach for rapid and accurate high-resolution (HR) or ultra HR (UHR) mapping of T1 and apparent PD (APD) of the brain with correction of radiofrequency field, B1, inhomogeneities. The four-angle method (FAM) uses four spoiled-gradient recalled-echo (SPGR) images acquired at different flip angles (FA) and short repetition times (TRs). The first two SPGR images are acquired at low-spatial resolution and used to accurately map the active B1+ field with the recently introduced steady-state double angle method (SS-DAM). The estimated B1+ map is used in conjunction with the two other SPGR images, acquired at HR or UHR, to map T1 and APD. The method is evaluated with numerical, phantom, and in-vivo imaging measurements. Furthermore, we investigated imaging acceleration methods to further shorten the acquisition time. Our results indicate that FAM provides an accurate method for simultaneous HR or UHR mapping of T1 and APD in human brain in clinical high-field MRI. Derived parameter maps without B1+correction suffer from large inaccuracies, but this issue is well-corrected through use of the SS-DAM. Furthermore, the use of SPGR imaging with short TR and phased-array coil acquisition permits substantial imaging acceleration and enables robust HR or UHR T1 and APD mapping in a clinically acceptable time frame, with whole brain coverage obtained in less than 2 min or 5 min, respectively. The method exhibits high reproducibility and benefits from the use of the conventional SPGR sequence, available in all preclinical and clinical MRI machines, and very simple modeling to address a critical outstanding issue in neuroimaging.

中文翻译：

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四角法用于大脑纵向弛豫时间和表观质子密度的实用超高分辨率磁共振成像。

纵向弛豫时间（T1）和质子密度（PD）的变化是与各种中枢神经系统疾病以及脑成熟和衰老相关的微结构改变的敏感指标。在这项工作中，我们介绍了一种新方法，可对T1和大脑的表观PD（APD）进行快速，准确的高分辨率（HR）或超HR（UHR）映射，并校正射频场，B1和不均匀性。四角度方法（FAM）使用以不同的翻转角度（FA）和较短的重复时间（TRs）采集的四个损坏梯度的回波（SPGR）图像。前两个SPGR图像是在低空间分辨率下获取的，并用于通过最近引入的稳态双角度方法（SS-DAM）准确映射活动的B1 +场。估算的B1 +图与其他两个SPGR图像结合使用，在HR或UHR获得，以绘制T1和APD。该方法通过数字，幻像和体内成像测量进行评估。此外，我们研究了成像加速方法，以进一步缩短采集时间。我们的结果表明，FAM为临床高场MRI中人脑中T1和APD的同时HR或UHR映射提供了一种准确的方法。没有进行B1 +校正的派生参数图存在较大的误差，但是通过使用SS-DAM，可以很好地解决此问题。此外，具有短TR和相控阵线圈采集功能的SPGR成像的使用可实现显着的成像加速，并在临床上可接受的时间范围内实现强大的HR或UHR T1和APD映射，并在不到2分钟或5分钟的时间内获得全脑覆盖， 分别。