TABLE 1.

Protocols for MRI of the myelin bilayer

Protocol	FOV [mm]	Δr [mm]	BW [kHz]	TE [μs]	RF pulse	TR [ms]	NSA	Scan time [m:s]	HYFI‐A	HYFI‐T2 [μs]
SPI	50	1.56	7.5–470	2067–33	2 μs hard	3	4	03:34	N/A	N/A
HYFI	50	0.39	425	12	2 μs hard	1	32	27:41	0.17	50

Note: The first protocol uses an SPI ³¹ sequence with spherical k‐space support to acquire a multi‐TE image series. The second protocol uses a HYFI ³² sequence to acquire a high‐resolution ultrashort‐T₂ reference image. Pulse power was adjusted for maximum steady‐state signal, calibrated in a D₂O sample to specifically optimize non‐aqueous signals. The flip angles of approximately a few degrees were adjusted for the two protocols according to their different TRs to yield equivalent contrast. The scan time stated for the SPI protocol is per image, and the full multi‐TE series consisted of 14 images.

Abbreviations: BW, image bandwidth; HYFI‐A, HYFI amplitude coefficient; HYFI‐T₂, HYFI target T₂; NSA, number of signal averages; Δr, nominal 3D isotropic resolution.