Multi-Line Balanced SSFP for Rapid Functional Imaging at Ultra High-Field

a) Overlay of MP2RAGE and bSSFP data. Top: Gray matter outlines obtained from MP2RAGE segmentation on top of bSSFP images. Bottom: bSSFP activation maps on top of MP2RAGE images. As can be seen, the distortion-free bSSFP data allow for accurate registration. b) shows a bSSFP image, a T2*-weighted image, as well as an overlay of a bSSFP activation map (0.6 mm isotropic resolution, same z-score scaling as in a)) on top of the T2*-weighted image. The strong intravascular signal from a draining vein (marked by a white arrow) is clearly visible. — a) Overlay of MP2RAGE and bSSFP data. Top: Gray matter outlines obtained from MP2RAGE segmentation on top of bSSFP images. Bottom: bSSFP activation maps on top of MP2RAGE images. As can be seen, the distortion-free bSSFP data allow for accurate registration. b) shows a bSSFP image, a T₂^*-weighted image, as well as an overlay of a bSSFP activation map (0.6 mm isotropic resolution, same z-score scaling as in a)) on top of the T₂^*-weighted image. The strong intravascular signal from a draining vein (marked by a white arrow) is clearly visible.

a) Overlay of MP2RAGE and bSSFP data. Top: Gray matter outlines obtained from MP2RAGE segmentation on top of bSSFP images. Bottom: bSSFP activation maps on top of MP2RAGE images. As can be seen, the distortion-free bSSFP data allow for accurate registration. b) shows a bSSFP image, a T₂^*-weighted image, as well as an overlay of a bSSFP activation map (0.6 mm isotropic resolution, same z-score scaling as in a)) on top of the T₂^*-weighted image. The strong intravascular signal from a draining vein (marked by a white arrow) is clearly visible.

Balanced steady-state free precession (bSSFP) is a BOLD-sensitive acquisition method that is highly sensitive to small vessels in the range of 5 to 20 µm. Thus, it shows a high potential to represent oxygenation changes within the microvasculature in contrast to gradient echoes with their huge and unspecific sensitivity to larger draining veins. A major drawback of bSSFP is its significantly reduced imaging speed compared to EPI. In this work we present a multi-line bSSFP for functional BOLD imaging that approaches the speed of EPI, and that shows an increased BOLD sensitivity compared to single-line bSSFP. Depending on the length of the echo train, we were able to acquire 16 slices with a 0.9 mm isotropic resolution in a volume TR of 1.21 to 1.66 s, compared to 3.14 s for a single-line acquisition. We analyze the acquisition efficiency, temporal and thermal signal to noise, as well as the observed BOLD signal changes upon a visual task on a 9.4 T system. With increasing TR and echo train length, the BOLD-related signal change as well as thermal and temporal noise was improved. Activation patterns and signal changes were stable and reproducible across subjects.

Ehses P, Scheffler K.:

Multiline balanced SSFP for rapid functional imaging at ultrahigh field.

Magn Reson Med. 2018 Feb;79(2):994-1000. Epub 2017 May 25. PMID: 28547846

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