Lutz Max, Aigner Christoph Stefan, Flassbeck Sebastian, Krueger Felix, Gatefait Constance G F, Kolbitsch Christoph, Silemek Berk, Seifert Frank, Schaeffter Tobias, Schmitter Sebastian
Physikalisch-Technische Bundesanstalt, Braunschweig and Berlin, Germany.
Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University Grossman School of Medicine, New York, New York, USA.
Magn Reson Med. 2024 Dec;92(6):2473-2490. doi: 10.1002/mrm.30242. Epub 2024 Aug 12.
This study aims to map the transmit magnetic field ( ) in the human body at 7T using MR fingerprinting (MRF), with a focus on achieving high accuracy and precision across a large dynamic range, particularly at low flip angles (FAs).
A FLASH-based MRF sequence (B1-MRF) with high sensitivity was developed. Phantom and in vivo abdominal imaging were performed at 7T, and the results were compared with established reference methods, including a slow but precise preparation-based method (PEX), saturated TurboFLASH (satTFL), actual flip angle imaging (AFI) and Bloch-Siegert shift (BSS).
The MRF signal curve was highly sensitive to , while T sensitivity was comparatively low. The phantom experiment showed good agreement of to PEX for a T range of 204-1691 ms evaluated at FAs from 0° to 70°. Compared to the references, a dynamic range increase larger than a factor of two was determined experimentally. In vivo liver scans showed a strong correlation between B1-MRF, satTFL, and RPE-AFI in a low body mass index (BMI) subject (18.1 kg/m). However, in larger BMI subjects (≥25.5 kg/m), inconsistencies were observed in low regions for satTFL and RPE-AFI, while B1-MRF still provided consistent results in these regions.
B1-MRF provides accurate and precise maps over a wide range of FAs, surpassing the capabilities of existing methods in the FA range < 60°. Its enhanced sensitivity at low FAs is advantageous for various applications requiring precise estimates, potentially advancing the frontiers of ultra-high field (UHF) body imaging at 7T and beyond.
本研究旨在利用磁共振指纹识别（MRF）技术在7T磁场下绘制人体的发射磁场（ ），重点是在大动态范围内实现高精度和高精准度，尤其是在低翻转角（FA）情况下。
开发了一种具有高灵敏度的基于快速低角度激发（FLASH）的MRF序列（B1-MRF）。在7T磁场下进行了体模和腹部活体成像，并将结果与已确立的参考方法进行比较，包括一种缓慢但精确的基于准备的方法（PEX）、饱和快速低角度激发（satTFL）、实际翻转角成像（AFI）和布洛赫-西格特位移（BSS）。
MRF信号曲线对 高度敏感，而对T的敏感度相对较低。体模实验表明，在0°至70°的FA下评估的204 - 1691 ms的T范围内， 与PEX具有良好的一致性。与参考方法相比，通过实验确定动态范围增加了两倍以上。在低体重指数（BMI）受试者（18.1 kg/m²）的活体肝脏扫描中，B1-MRF、satTFL和RPE-AFI之间显示出很强的相关性。然而，在BMI较大的受试者（≥25.5 kg/m²）中，在低 区域观察到satTFL和RPE-AFI存在不一致性，而B1-MRF在这些区域仍能提供一致的结果。
B1-MRF在广泛的FA范围内提供准确和精确的 图谱，在FA范围<60°时超越了现有方法的能力。其在低FA下增强的灵敏度有利于各种需要精确 估计的应用，可能推动7T及更高场强的超高场（UHF）人体成像的前沿发展。
