2024/11/07 by Lutz, Max, Aigner, Christoph Stefan, Flassbeck, Sebastian +7
#600 Technik #7 Tesla #B1+ mapping #MRF #Medizin #angewandte Wissenschaften::610 Medizin und Gesundheit::610 Medizin und Gesundheit #body MRI #ultrahigh field MRI
paper · doi:10.14279/depositonce-21675
Purpose This study aims to map the transmit magnetic field (B1+B1+) 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). Methods A FLASH‐based MRF sequence (B1‐MRF) with high B1+B1+ 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). Results The MRF signal curve was highly sensitive to B1+B1+, while T1 sensitivity was comparatively low. The phantom experiment showed good agreement of B1+B1+ to PEX for a T1 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/m2). However, in larger BMI subjects (≥25.5 kg/m2), inconsistencies were observed in low B1+B1+ regions for satTFL and RPE‐AFI, while B1‐MRF still provided consistent results in these regions. Conclusion B1‐MRF provides accurate and precise B1+B1+ 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 B1+B1+ estimates, potentially advancing the frontiers of ultra‐high field (UHF) body imaging at 7T and beyond.