Reproducibility, Interrater Agreement, and Age-Related Changes of Fractional Anisotropy Measures at 3T in Healthy Subjects: Effect of the Applied b-Value

S. Bisdas; D.E. Bohning; N. Bešenski; J.S. Nicholas; Z. Rumboldt

doi:10.3174/ajnr.A1044

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Fig 1.
Normal subject. FA map shows highly directional white matter tracts (corticospinal tracts) in the region of brain stem. The ROIs (50 mm²) for the estimation of the FA values are placed exclusively within the central portion of the visualized white matter tracts.

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Table 1:

Descriptive statistics of FA values (×10³) (SD), as well as results of the performed t test (P) in the examined anatomic structures on the basis of 2 b-values (mm²/s) and both scanning sessions.

Anatomic Structure	b-Value	Session 1	Session 2
Right internal capsule anterior limb	1000	691 (71)	672 (54)
	700	702 (63)	718 (60)
Right internal capsule genu	1000	702 (51)^*	737 (48)
P = .02	700	745 (67)^*	760 (51)
Right internal capsule posterior limb	1000	745 (33)	732 (45)
	700	761 (54)	751 (37)
Corpus callosum genu	1000	782 (71)	816 (64)
	700	769 (74)	782 (70)
Corpus callosum splenium	1000	823 (71)	836 (69)
	700	829 (53)	851 (47)
Left internal capsule anterior limb	1000	617 (81)^*	682 (65)
Left internal capsule genu	1000	729 (53)	746 (65)
	700	741 (44)	752 (57)
Left internal capsule posterior limb	1000	766 (51)	745 (55)
	700	781 (53)	767 (65)
Right corticospinal tract	1000	646 (67)^†	570 (54)^†
P = .048	700	661 (54)	631 (60)
Left corticospinal tract	1000	672 (73)	649 (61)
	700	662 (91)	672 (72)
Right thalamus	1000	349 (36)^†	316 (24)^†
P = .024	700	358 (41)	340 (39)

Note:—The values are based on the readings of the first rater.
* Statistically significant changes in the obtained FA between the 2 b-values are shown.
† Statistically significant changes in the obtained FA between the 2 scanning sessions are shown.

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Table 2:

Intraclass correlation coefficients for interrater agreement between 2 observers for the examined FA values in various anatomic locations

Anatomic Location	b-Values	Intraclass Correlation Coefficients (95% Confidence Intervals), mm²/s
Right internal capsule anterior limb	1000	0.70 (0.49–0.85)
	700	0.71 (0.61–0.92)
Left internal capsule anterior limb	1000	0.58 (0.31–0.72)
	700	0.37 (0.20–0.56)
Right internal capsule posterior limb	1000	0.40 (0.28–0.60)
	700	0.31 (0.10–0.52)
Left internal capsule posterior limb	1000	0.46 (0.20–0.67)
	700	0.53 (0.33–0.87)
Right internal capsule genu	1000	0.58 (0.31–0.77)
	700	0.39 (0.20–0.62)
Left internal capsule genu	1000	0.38 (0.17–0.49)
	700	0.28 (0.13–0.47)
Corpus callosum genu	1000	0.73 (0.47–0.89)
	700	0.60 (0.47–0.79)
Corpus callosum splenium	1000	0.82 (0.61–0.90)
	700	0.88 (0.59–0.96)
Right corticospinal tract	1000	0.35 (0.18–0.58)
	700	0.38 (0.16–0.53)
Left corticospinal tract	1000	0.34 (0.29–0.62)
	700	0.47 (0.29–0.75)
Right thalamus	1000	0.64 (0.56–0.79)
	700	0.65 (0.51–0.89)

Note:—The coefficients are calculated for 2 b-values.

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Table 3:

Mean difference (SD) and 95% limits of agreement of the FA values (×10³) for the ROI analysis between the 2 sessions, as well as measurement error and repeatability for the serial FA measurements in healthy subjects

Anatomic Structure	b-Value	Mean Difference (SD)	95% Limits of Agreement	Within-Subject SD	Within-Subject Coefficient of Variation, %	Repeatability Coefficient	Significant Change for a Single Subject, %
Right internal capsule anterior limb	1000	−18.4 (95.71)	−206 to 169.2	17	1.3	13	19
	700	−27 (88.03)	−145 to 199.5	40	6	11	16
Right internal capsule genu	1000	74.7 (99.31)	−119.9 to 269.4	16	1.2	11	16
	700	−5.7 (130.17)	−260.9 to 249.4	26	3	9	10
Right internal capsule posterior limb	1000	16.9 (35.48)	−52.6 to 86.5	13	0.6	7	7
	700	9.5 (28.99)	−47.3 to 66.3	14	2	5	5
Corpus callosum genu	1000	−22.2 (41.42)	−103.4 to 59.0	12	0.4	4	4
	700	12.9 (49.71)	−84.5 to 110.3	22	3	6	7
Corpus callosum splenium	1000	10.6 (43.98)	−103.4 to 59.0	20	2	7	6
	700	−22.7 (37.51)	−92.9 to 50.9	21	2	6	7
Left internal capsule anterior limb	1000	−4.1 (59.45)	−199.0 to 190.8	51	6	12	18
	700	−20.7 (43.58)	−106.2 to 64.0	40	6	13	17
Left internal capsule genu	1000	−8.5 (66.63)	−139.2 to 122.0	33	4	8	11
	700	−3.4 (80.07)	−160.4 to 153.5	46	5	11	15
Left internal capsule posterior limb	1000	23.0 (52.81)	−80.5 to 126.5	31	3	7	19
	700	28.3 (28.3)	−41.0 to 97.5	22	2	6	7
Right corticospinal tract	1000	74.7 (99.31)	−119.9 to 269.4	60	8	16	24
	700	−6.7 (130.17)	−260.9 to 249.4	62	10	17	27
Left corticospinal tract	1000	54.9 (99.27)	−139.7 to 249.5	51	7	15	20
	700	−11.5 (131.9)	−139.7 to 247.1	63	9	18	26
Right thalamus	1000	36.5 (29.32)	−20.9 to 94.0	22	6	16	17
	700	10.9 (56.26)	−95.4 to 117.3	26	8	7	21