Coronal diffusion-weighted magnetic resonance imaging of the kidney: agreement with axial diffusion-weighted magnetic imaging in terms of apparent diffusion coefficient values

Abstract

Background: Coronal diffusion-weighted magnetic resonance imaging (DW-MRI) and apparent diffusion coefficient (ADC) values have gradually become applied (following conventional axial DW-MRI) in the renal analysis. To explore whether data obtained using coronal DW-MRI are comparable with those derived using axial DW-MRI, this preliminary study sought to assess the agreement in renal ADC values between coronal DW-MRI and axial DW-MRI.

Methods: Thirty-four healthy volunteers were enrolled in the study; written consents were obtained. All subjects underwent respiratory-triggered axial and coronal DW-MRI using a 1.5-MR system with b values of 0 and 800 s/mm 2 . The signal-to-noise ratios (SNRs) of the two DW-MRI sequences were measured and statistically compared using the paired t-test. The extent of agreement of ADC values of the upper pole, mid-pole, and lower pole of the kidney; the mean ADC values of the left kidney and right kidney; and the mean ADC values of the bilateral kidneys were evaluated via calculation of intraclass correlation coefficients (ICCs) or Bland-Altman method between the two DW-MRI sequences.

Results: The SNR of coronal DW-MR images was statistically inferior to that of axial DW-MR images (P < 0.001). The ICCs of the ADC values of each region of interest, and the mean ADC values of bilateral kidneys, between the two sequences, were greater than 0.5, and the mean ADCs of the bilateral kidneys demonstrated the highest ICC (0.869; 95% confidence interval: 0.739-0.935). In addition, 94.1% (32/34), 94.1% (32/34), and 97.1% (31/34) of the ADC bias was inside the limits of agreement in terms of the mean ADC values of the left kidneys, right kidneys, and bilateral kidneys when coronal and axial DWI-MRI were compared.

Conclusions: ADC values derived using coronal DW-MRI exhibited moderate-to-good agreement to those of axial DW-MRI, rendering the former an additional useful DW-MRI method, and causing the ADC values derived using the two types of DW-MRI to be comparable.

Figure 1

Axial Diffusion-weighted magnetic resonance images and apparent diffusion coefficient (ADC) maps of a healthy female volunteer. Three region of interests were placed in the upper pole (a, b), middle portion (c, d), and lower pole (e, f) of the bilateral kidneys, respectively. The mean ADC values of the left and right kidneys were 2.140 × 10⁻³ mm²/s and 2.170 × 10⁻³ mm²/s, respectively.

Figure 2

Coronal diffusion-weighted magnetic resonance image and apparent diffusion coefficient (ADC) map of the same volunteer in Figure 1. Three region of interests were placed in the upper pole, middle portion, and lower pole of the bilateral kidneys (a); respectively, and the mean ADC values of the left and right kidney were 2.167 × 10⁻³ mm²/s and 2.180 × 10⁻³ mm²/s, respectively (b).

Figure 3

Bland-Altman plots of differences in apparent diffusion coefficient (ADC) measurements between the mean ADC value of the left kidney on coronal diffusion-weighted magnetic resonance (DW-MR) imaging (Mean-L-Cor) and that on axial DW-MR (Mean-L-Ax) (y-axis) against the mean ADC value between the Mean-L-Cor and Mean-L-Ax (x-axis), with the mean absolute difference (bias) (continuous line) and the 95% confidence interval of the mean difference (limits of agreement) (dashed lines).

Figure 4

Bland-Altman plots of the difference in apparent diffusion coefficient (ADC) measurements between the mean ADC value of right kidney on coronal diffusion-weighted magnetic resonance (DW-MR) imaging (Mean-R-Cor) and that on axial DW-MR (Mean-R-Ax) (y-axis) against the mean ADC value between the Mean-R-Cor and Mean-R-Ax (x-axis), with the mean absolute difference (bias) (continuous line) and 95% confidence interval of the mean difference (limits of agreement) (dashed lines).

Figure 5

Bland-Altman plots of the difference in apparent diffusion coefficient (ADC) measurements between the mean ADC value of the bilateral kidneys on coronal diffusion-weighted magnetic resonance (DW-MR) imaging (Mean-B-Cor) and that on axial DW-MR (Mean-B-Ax) (y-axis) against the mean ADC value between the Mean-B-Cor and Mean-B-Ax (x-axis), with the mean absolute difference (bias) (continuous line) and 95% confidence interval of the mean difference (limits of agreement) (dashed lines).