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Research ArticleBRAIN

Distribution Characteristics, Reproducibility, and Precision of Region of Interest–Based Hippocampal Diffusion Tensor Imaging Measures

M.J. Müller, M. Mazanek, C. Weibrich, P.R. Dellani, P. Stoeter and A. Fellgiebel
American Journal of Neuroradiology February 2006, 27 (2) 440-446;

Article Figures & Data

Figures

  • Fig 1.
    Fig 1.

    Placement of regions of interest. Regions of interest (5.4 × 7.2 × 3.0 mm) for the measurement of hippocampal FA (middle) and MD (bottom) values. The T2-weighted image (top, b = 0 s/mm2) was used as an anatomic reference.

  • Fig 2.
    Fig 2.

    Correlation of first and second assessments of hippocampal FA and MD values. Data points are average DTI parameter values of the selected region of interest (n = 20). FA, fractional anisotropy [×103]; MD, mean diffusivity [μm2/s].

  • Fig 3.
    Fig 3.

    Cumulative frequency distributions of pooled FA and MD values and comparison with Gaussian distributions. Figures represent the distribution of average DTI parameter values (MD, left; FA, right) for all the data (ie, data of left and right hippocampus) and of first and second assessment pooled for each subject (80 data points, n = 20). D’AP-test, D’Agostino-Pearson test for deviation from normality.

Tables

  • Table 1:

    DTI Parameters and distribution characteristics (n = 20)

    Mean ± SD (CI 95%)Median (Range)Skewness (P Value) Kurtosis (P Value)D’AP Test for Non-normality
    1st2nd1st2nd1st2nd1st2nd
    FA left247 ± 26(235–259)245 ± 27(232–257)249(195–298)251(176–287)−0.16 (.74)−0.44 (.50)−0.75 (.14)0.78 (.34)P = .76P = .21
    FA right228 ± 20(219–238)229 ± 20(219–238)225(189–262)227(201–262)0.12 (.81)−0.81 (.33)0.12 (.81)−1.36 (.17)P = .60P = .39
    FA mean238 ± 16(230–245)237 ± 19(228–246)239(201–266)237(195–268)−0.28 (.57) 0.15 (.69)−0.29 (.55)0.07 (.76)P = .79P = .80
    MD left782 ± 46(760–803)781 ± 35(765–798)793(717–857)790(729–835)0.02 (.97)−1.34 (.18)−0.08 (.86)−1.24 (.20)P = .41P = .43
    MD right769 ± 27(756–782)769 ± 24(758–780)779(709–805)770(732–817)−0.50 (.31)−0.74 (.36)0.48 (.33)−0.08 (.75)P = .39P = .59
    MD mean775 ± 30(761–790)775 ± 25(763–787)774(727–819)780(731–825)−0.17 (.72)−1.21 (.21)−0.04 (.93)−0.78 (.34)P = .42P = .63

    • Note.— FA indicates fractional anisotropy (×103); MD, mean diffusivity (μm2/s); CI 95%, 95% confidence interval of mean; D’AP test, D’Agostino-Pearson test for deviation of an empirical frequency distribution from normal distribution (P < .05 indicating significant deviation).

  • Table 2:

    Intraobserver reliability and precision of hippocampal FA and MD values (n = 20)

    Mean ± SDDiff ± SDt valuerrsICCSEMCI 95%CVR95 (%)
    FA left246 ± 262 ± 120.94.90.88.958.4±163.5%23 (9.4%)
    FA right229 ± 20−1 ± 9−0.38.91.89.956.0±122.7%17 (7.3%)
    FA mean237 ± 171 ± 80.51.91.88.955.3±102.2%15 (6.2%)
    MD left782 ± 40−1 ± 200.08.91.94.9413.8±271.8%38 (4.9%)
    MD right769 ± 250 ± 160.08.82.81.9010.9±211.4%30 (3.9%)
    MD mean775 ± 280 ± 140.10.88.85.939.9±191.3%27 (3.5%)

    • Note.— FA indicates fractional anisotropy (×103); MD, mean diffusivity (μm2/s); Mean, pooled mean (1st and 2nd assessment of one observer) ± pooled SD; Diff, difference of 1st–2nd assessment ± SD of difference; t value, corresponding to paired t test, all P values >0.20; r, Pearson correlation coefficient; rs, Spearman rank correlation coefficient; ICC, intraclass correlation coefficient; SEM, standard error of measurement based on within-subject variance; CI 95%, 95% confidence interval (±1.96 × SEM); CV = √(mean of within subject variance/mean squared); R95, repeatability according to Bland and Altman20; R95 = √2 × 1.96 × SEM; %, percentage of mean = R95/mean × 100.

  • Table 3:

    Interobserver reliability and precision of hippocampal FA and MD values (n = 20)

    1st Investigator Mean ± SD (Range)2nd Investigator Mean ± SD (Range)Diff ± SDt valuerrsICCSEMCI 95%CVR95 (%)
    FA left247 ± 26243 ± 285 ± 131.58.89.87.939.5±193.9%26 (10.8%)
    (235–259)(179–283)
    FA right228 ± 20230 ± 23−2 ± 14−0.63.78.86.8810.1±204.1%28 (12.2%)
    (219–238)(198–286)
    FA mean238 ± 16236 ± 201 ± 110.52.85.87.907.6±153.1%21 (8.9%)
    (230–245)(195–279)
    MD left782 ± 46776 ± 285 ± 28.85.81.82.8419.8±392.5%55 (7.0%)
    (760–803)(728–821)
    MD right769 ± 27766 ± 233 ± 18 (25)0.68.75.79.8512.9±251.7%36 (4.6%)
    (756–782)(721–816)
    MD mean775 ± 30)771 ± 23)4 ± 18 (27)1.02.81.90.8712.7±251.6%35 (.5%)
    (761–790(733–817

    • Note.— FA indicates fractional anisotropy (×103); MD, mean diffusivity (μm2/s); Diff, difference of 1st assessment of first investigator (cf. Table 1, 1st column) and assessment of 2nd investigator ± SD of difference; t value, corresponding to paired t test, all P values >.10; r, Pearson correlation coefficient; rs, Spearman rank correlation coefficient; ICC, intraclass correlation coefficient; SEM, standard error of measurement based on within-subject variance; CI 95%, 95% confidence interval (±1.96 × SEM); CV = √(mean of within subject variance/mean squared); R95, repeatability according to Bland and Altman20: R95WSV = √2 × 1.96 × SEM; %, percentage of mean = R95/mean × 100.

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Distribution Characteristics, Reproducibility, and Precision of Region of Interest–Based Hippocampal Diffusion Tensor Imaging Measures
M.J. Müller, M. Mazanek, C. Weibrich, P.R. Dellani, P. Stoeter, A. Fellgiebel
American Journal of Neuroradiology Feb 2006, 27 (2) 440-446;
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