Fig 1.
Analysis workflow for optimization of brain IVIM model for number of b values up to 900 s/mm2, using 20 repeated scans in four healthy volunteers, with two optimization strategies of General Linear Modelling (GLM) of standard deviation measurements in 95 b value settings, and Cramér-Rao Lower Bound analysis using noise measurements in the same data.
Fig 2.
Coefficient of variation (SD/mean) as a function of b values and number of averages, in the gray matter (left) and the white matter (right) for four healthy volunteers in DWI trace images in b-values ranging from 0 to 900 s/mm2 and number of repetitions for signal averaging in 1 to 20. Gray matter variation begins to drop after b = 170 s/mm2 and with 4 repetitions, while white matter variation is generally less and with negligible differences between b-values and repetitions in range 9% to 10.5%, and lowest points around b = 80–140 s/mm2 and when using 4 to 13 averages.
Table 1.
Suggested optimized b value sets for brain IVIM.
Fig 3.
Standard deviations (SD) of IVIM parameter maps D* and f in brain grey and white matter over four healthy volunteers, using optimized b value distributions for optimized b value settings from analysis of direct SD measurements, and CRLB using noise estimates, for 3, 6, and 12 minutes scans.
Fig 4.
Example of IVIM D* parameter maps with acquisition schemes found best according to their standard deviation for gray and white matter.
b values (number of averages) (A) 3 min (0 (5), 200 (5), 900 (5) s/mm2), (B) 6 min (0 (10), 200 (10), 900 (10) s/mm2), (C) 12 min (0 (20), 200 (20), 900 (20) s/mm2), (D) 12 min (0 (8), 10 (8), 20 (8), 40 (8), 80 (8), 140 (8), 200 (8), 900 (8) s/mm2), (E) 6 min (0 (5), 20 (9), 40 (1), 80 (1), 110 (9), 140 (1), 170 (2), 500 (3), 600 (1) s/mm2), (F) 12 min (0 (7), 20 (4), 140 (19), 300 (9), 500 (19), 700 (1), 800 (4), 900 (1) s/mm2).
Fig 5.
Example of IVIM f parameter maps with acquisition schemes found best according to their standard deviation for gray and white matter.
b values (number of averages) (A) 3 min (0 (5), 200 (5), 900 (5) s/mm2), (B) 6 min (0 (10), 200 (10), 900 (10) s/mm2), (C) 12 min (0 (20), 200 (20), 900 (20) s/mm2), (D) 12 min (0 (8), 10 (8), 20 (8), 40 (8), 80 (8), 140 (8), 200 (8), 900 (8) s/mm2), (E) 6 min (0 (5), 20 (9), 40 (1), 80 (1), 110 (9), 140 (1), 170 (2), 500 (3), 600 (1) s/mm2), (F) 12 min (0 (7), 20 (4), 140 (19), 300 (9), 500 (19), 700 (1), 800 (4), 900 (1) s/mm2).