Magnetic resonance imaging biomarkers for pulsed focused ultrasound treatment of pancreatic ductal adenocarcinoma

Table 1 14T magnetic resonance imaging parameter acquisition methods

Method	Sequence type	TR/TE (ms)	Comments
T1	RARE	5500, 3000, 1500, 1000, 385.8/9.66	NA = 1; FOV = 30 mm × 30 mm; rare factor = 2, matrix size = 256 × 128 (reconstructed phase encoding steps = 128; acquisition phase encoding steps = 96); yielding spatial resolution of 0.117 × 0.234 mm/pixel. Approximately 9 min acquisition time.
T2	MSME, fat suppressed	4000/twelve echoes equally spaced from 6.28 to 75.4	NA = 1; FOV = 30 mm × 30 mm; matrix size = 256 × 128 (reconstructed phase encoding steps = 128; acquisition phase encoding steps = 91); spatial resolution of 0.117 × 0.234 mm/pixel. 10 contiguous slices were acquired with respiration gating to cover the entire abdomen. Approximately 6 min acquisition time.
ADC	EPI	2500/17.7	Echo train length = 16; Pulse duration = 3.0 ms; Diffusion time = 7.46 ms; NA = 1; FOV = 30 × 30 mm2; matrix size = 128 × 128; spatial resolution of 0.234 × 0.234 mm/pixel; 8 b values (7, 47, 81, 126, 180, 234, 340, 549) s/mm2. 10 contiguous slices were acquired to cover the entire abdomen. Approximately 2 min 40 s acquisition time.
CEST	(1) RARE	(1) 2200 / 7	(1) Center frequency estimate: Continuous-wave block saturation pulse with B1 = 3 μT and duration = 1 s; 25 frequency offsets from -360 Hz to 360 Hz with an interval of 0.5 ppm (WASSR approach). FOV = 30 mm x 30 mm; Matrix size = 128 x 128; Flip angle = 180o; NA = 1. A single, 1 mm slice delineating the tumor was acquired.
	(2) RARE	(2) 5000 / 7	(2) Frequency shift saturation: 14 frequency offsets at ± 0.5, ± 1.0. ± 1.5, ± 2.0, ± 2.5, ± 3.0, ± 3.5 ppm were acquired through the same single slice using respiration gating with an off-resonance radiofrequency pulse applied for 1 s at a power of 3 μT. Matrix = 128 × 128 (reconstructed phase encoding steps = 128; acquisition phase encoding steps = 96); FOV = 30 mm × 30 mm; rare factor = 8.
	(3) RARE	(3) 5000 / 7	(3) Control image: A control image was acquired through the same slice using the same settings as #2, except with saturation offset at 300 ppm. Approximately 30 min total acquisition time.
MTR	GRE	625 / 2	Flip angle = 30°; off-resonance frequency 7000 Hz; saturation pulse block pulse shape = 50 ms width and 10 µT amplitude; FOV = 30 mm × 30 mm; matrix size = 256 × 256; spatial resolution of 0.117 x 0.117 mm/pixel. 10 contiguous images were acquired to cover the entire abdomen. Approximately 3 min acquisition time.

ADC: Apparent diffusion coefficient; CEST: Chemical exchange saturation transfer; MTR: Magnetization transfer ratio.