Research article Received: 11 March 2014,
Revised: 17 October 2014,
Accepted: 25 October 2014,
Published online in Wiley Online Library: 13 November 2014
(wileyonlinelibrary.com) DOI: 10.1002/nbm.3235
MRI quantification of non-Gaussian water diffusion in normal human kidney: a diffusional kurtosis imaging study Yanqi Huanga,b, Xin Chena,b, Zhongping Zhangc, Lifen Yana, Dan Pana,b, Changhong Lianga and Zaiyi Liua* Our aim was to prospectively evaluate the feasibility of diffusional kurtosis imaging (DKI) in normal human kidney and to report preliminary DKI measurements. Institutional review board approval and informed consent were obtained. Forty-two healthy volunteers underwent diffusion-weighted imaging (DWI) scans with a 3-T MR scanner. b values of 0, 500 and 1000 s/mm2 were adopted. Maps of fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (D⊥), axial diffusivity (D||), mean kurtosis (MK), radial kurtosis (K⊥) and axial kurtosis (K||) were produced. Three representative axial slices in the upper pole, mid-zone and lower pole were selected in the left and right kidney. On each selected slice, three regions of interest were drawn on the renal cortex and another three on the medulla. Statistical comparison was performed with t-test and analysis of variance. Thirty-seven volunteers successfully completed the scans. No statistically significant differences were observed between the left and right kidney for all metrics (p values in the cortex: FA, 0.114; MD, 0.531; D⊥, 0.576; D||, 0.691; MK, 0.934; K⊥, 0.722; K||, 0.891; p values in the medulla: FA, 0.348; MD, 0.732; D⊥, 0.470; D||, 0.289; MK, 0.959; K⊥, 0.780; K||, 0.287). Kurtosis metrics (MK, K||, K⊥) obtained in the renal medulla were significantly (p 0.05), we used the average of these segments to represent the mean value of the renal cortex or medulla of each kidney. Then, a two-sample Student’s t-test for data of equal variances (checked with the Levene test) or the Welch–Satterthwaite approximate t-test for data of unequal variances was performed to calculate the difference in metrics between the cortex and medulla, as well as between the left and right kidney. All statistical analyses were executed using Statistical Package for the Social Sciences v.19.0 software (SPSS, version 19.0; IBM, Armonk, NY, USA). Differences were considered to be significant when p values were less than 0.05.
Statistical analysis
Population demographics
The intra-observer agreement of all metrics was evaluated using the intraclass correlation coefficient (ICC) (29). For every metric, the average values of all the 18 ROIs in the cortex and another 18 in the medulla in each case were used for the ICC calculation for the cortex and medulla, respectively. An ICC greater than 0.75 was considered to represent good agreement (30). As the values of all metrics followed a normal distribution (checked with the Shapiro–Wilk test for normality), the difference in the metrics among the three different anatomical locations (upper pole, mid-zone, lower pole) in each kidney was assessed by the one-way analysis of variance (ANOVA) test for data of equal variances (checked with the Levene test) or Brown–Forsythe test if the equal variance assumption had been violated. As we found no significant difference in diffusion or kurtosis metrics among the
Forty-two volunteers were enrolled in this study. Five subjects were excluded from the study because of intense motion artifacts (n =4) or incomplete acquisition of all sequences ascribed to a long acquisition time (n =1). Thirty-seven volunteers successfully completed the scans (23 men and 14 women; mean age ± standard deviation, 26.3 ± 5.53 years; age range, 20–32 years; mean age of men, 26.91 ± 6.24 years; age range of men, 23–51 years; mean age of women, 25.29 ± 4.14 years; age range of women, 22–39 years).
RESULTS
Intra-observer agreement of metrics in the kidney There was no statistically significant difference between the first and second measurements for each metric, with p values ranging from 0.254 to 0.755. The intra-observer ICCs of all metrics calculated on the basis of the reader’s two measurements were good, ranging from 0.764 to 0.979. Therefore, all outcomes were based on the first measurements of the reader. Image quality assessment SNRs were 34.67 for b =0 s/mm2, 14.34 for b =500 s/mm2 and 9.52 for b =1000 s/mm2 images of the representative case (Fig. 2). Diffusion and kurtosis metrics of the kidney
Figure 1. Representative locations of regions of interest (ROIs) for the cortex and medulla at the mid-zone of the right kidney on the 2 b =0 mm /s image. The same ROIs were then copied to maps of all metrics.
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Representative diffusivity and kurtosis maps of the kidney from one volunteer are shown in Figures 3 and 4. Representative figures illustrating the b-value dependence along six selected directions are shown in Figure. 5. We found no significant differences in diffusion metrics (p =0.118–0.938) or kurtosis metrics (p =0.153–0.860) among the upper pole, mid-zone and lower pole of the kidneys. Therefore,
2
Figure 2. Representative b =0 mm /s (a), b =500 mm /s (b) and b =1000 mm /s (c) images.
wileyonlinelibrary.com/journal/nbm
Copyright © 2014 John Wiley & Sons, Ltd.
NMR Biomed. 2015; 28: 154–161
DIFFUSIONAL KURTOSIS IMAGING IN HUMAN KIDNEY
Figure 3. Representative diffusivity maps. Diffusivity maps of the fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (D⊥) and axial diffusivity (D||) are given in (a)–(d), respectively.
Figure 4. Representative kurtosis maps. Kurtosis maps of the mean kurtosis (MK), radial kurtosis (K⊥) and axial kurtosis (K||) are given in (a)–(c), respectively.
2
Figure 5. Representative figures illustrating the b-value dependence along six selected directions: (a) b0 image; (b) b =500 mm /s images along six 2 directions; (c) b =1000 mm /s images along six directions.
we used the average of these segments to represent the mean value of the renal cortex or medulla of each kidney.
Diffusion metrics
NMR Biomed. 2015; 28: 154–161
Kurtosis metrics As illustrated in Table 2, kurtosis values (MK, K⊥, K||) in the renal medulla were significantly (p
Revised: 17 October 2014,
Accepted: 25 October 2014,
Published online in Wiley Online Library: 13 November 2014
(wileyonlinelibrary.com) DOI: 10.1002/nbm.3235
MRI quantification of non-Gaussian water diffusion in normal human kidney: a diffusional kurtosis imaging study Yanqi Huanga,b, Xin Chena,b, Zhongping Zhangc, Lifen Yana, Dan Pana,b, Changhong Lianga and Zaiyi Liua* Our aim was to prospectively evaluate the feasibility of diffusional kurtosis imaging (DKI) in normal human kidney and to report preliminary DKI measurements. Institutional review board approval and informed consent were obtained. Forty-two healthy volunteers underwent diffusion-weighted imaging (DWI) scans with a 3-T MR scanner. b values of 0, 500 and 1000 s/mm2 were adopted. Maps of fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (D⊥), axial diffusivity (D||), mean kurtosis (MK), radial kurtosis (K⊥) and axial kurtosis (K||) were produced. Three representative axial slices in the upper pole, mid-zone and lower pole were selected in the left and right kidney. On each selected slice, three regions of interest were drawn on the renal cortex and another three on the medulla. Statistical comparison was performed with t-test and analysis of variance. Thirty-seven volunteers successfully completed the scans. No statistically significant differences were observed between the left and right kidney for all metrics (p values in the cortex: FA, 0.114; MD, 0.531; D⊥, 0.576; D||, 0.691; MK, 0.934; K⊥, 0.722; K||, 0.891; p values in the medulla: FA, 0.348; MD, 0.732; D⊥, 0.470; D||, 0.289; MK, 0.959; K⊥, 0.780; K||, 0.287). Kurtosis metrics (MK, K||, K⊥) obtained in the renal medulla were significantly (p 0.05), we used the average of these segments to represent the mean value of the renal cortex or medulla of each kidney. Then, a two-sample Student’s t-test for data of equal variances (checked with the Levene test) or the Welch–Satterthwaite approximate t-test for data of unequal variances was performed to calculate the difference in metrics between the cortex and medulla, as well as between the left and right kidney. All statistical analyses were executed using Statistical Package for the Social Sciences v.19.0 software (SPSS, version 19.0; IBM, Armonk, NY, USA). Differences were considered to be significant when p values were less than 0.05.
Statistical analysis
Population demographics
The intra-observer agreement of all metrics was evaluated using the intraclass correlation coefficient (ICC) (29). For every metric, the average values of all the 18 ROIs in the cortex and another 18 in the medulla in each case were used for the ICC calculation for the cortex and medulla, respectively. An ICC greater than 0.75 was considered to represent good agreement (30). As the values of all metrics followed a normal distribution (checked with the Shapiro–Wilk test for normality), the difference in the metrics among the three different anatomical locations (upper pole, mid-zone, lower pole) in each kidney was assessed by the one-way analysis of variance (ANOVA) test for data of equal variances (checked with the Levene test) or Brown–Forsythe test if the equal variance assumption had been violated. As we found no significant difference in diffusion or kurtosis metrics among the
Forty-two volunteers were enrolled in this study. Five subjects were excluded from the study because of intense motion artifacts (n =4) or incomplete acquisition of all sequences ascribed to a long acquisition time (n =1). Thirty-seven volunteers successfully completed the scans (23 men and 14 women; mean age ± standard deviation, 26.3 ± 5.53 years; age range, 20–32 years; mean age of men, 26.91 ± 6.24 years; age range of men, 23–51 years; mean age of women, 25.29 ± 4.14 years; age range of women, 22–39 years).
RESULTS
Intra-observer agreement of metrics in the kidney There was no statistically significant difference between the first and second measurements for each metric, with p values ranging from 0.254 to 0.755. The intra-observer ICCs of all metrics calculated on the basis of the reader’s two measurements were good, ranging from 0.764 to 0.979. Therefore, all outcomes were based on the first measurements of the reader. Image quality assessment SNRs were 34.67 for b =0 s/mm2, 14.34 for b =500 s/mm2 and 9.52 for b =1000 s/mm2 images of the representative case (Fig. 2). Diffusion and kurtosis metrics of the kidney
Figure 1. Representative locations of regions of interest (ROIs) for the cortex and medulla at the mid-zone of the right kidney on the 2 b =0 mm /s image. The same ROIs were then copied to maps of all metrics.
156
2
2
Representative diffusivity and kurtosis maps of the kidney from one volunteer are shown in Figures 3 and 4. Representative figures illustrating the b-value dependence along six selected directions are shown in Figure. 5. We found no significant differences in diffusion metrics (p =0.118–0.938) or kurtosis metrics (p =0.153–0.860) among the upper pole, mid-zone and lower pole of the kidneys. Therefore,
2
Figure 2. Representative b =0 mm /s (a), b =500 mm /s (b) and b =1000 mm /s (c) images.
wileyonlinelibrary.com/journal/nbm
Copyright © 2014 John Wiley & Sons, Ltd.
NMR Biomed. 2015; 28: 154–161
DIFFUSIONAL KURTOSIS IMAGING IN HUMAN KIDNEY
Figure 3. Representative diffusivity maps. Diffusivity maps of the fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (D⊥) and axial diffusivity (D||) are given in (a)–(d), respectively.
Figure 4. Representative kurtosis maps. Kurtosis maps of the mean kurtosis (MK), radial kurtosis (K⊥) and axial kurtosis (K||) are given in (a)–(c), respectively.
2
Figure 5. Representative figures illustrating the b-value dependence along six selected directions: (a) b0 image; (b) b =500 mm /s images along six 2 directions; (c) b =1000 mm /s images along six directions.
we used the average of these segments to represent the mean value of the renal cortex or medulla of each kidney.
Diffusion metrics
NMR Biomed. 2015; 28: 154–161
Kurtosis metrics As illustrated in Table 2, kurtosis values (MK, K⊥, K||) in the renal medulla were significantly (p
