Intra-Individual, Inter-Vendor Comparison of Diffusion-Weighted MR Imaging of Upper Abdominal Organs at 3.0 Tesla with an Emphasis on the Value of Normalization with the Spleen

Abstract

Objective: To compare the apparent diffusion coefficient (ADC) values of upper abdominal organs with 2 different 3.0 tesla MR systems and to investigate the usefulness of normalization using the spleen.

Materials and methods: Forty-one patients were enrolled in this prospective study, of which, 35 patients (M:F, 27:8; mean age ± standard deviation, 62.3 ± 12.3 years) were finally analyzed. In addition to the routine liver MR protocol, single-shot spin-echo echo-planar diffusion-weighted imaging using b values of 0, 50, 400, and 800 s/mm(2) in 2 different MR systems was performed. ADC values of the liver, spleen, pancreas, kidney and liver lesion (if present) were measured and analyzed. ADC values of the spleen were used for normalization. The Pearson correlation, Spearman correlation, paired sample t test, Wilcoxon signed rank test and Bland-Altman method were used for statistical analysis.

Results: For all anatomical regions and liver lesions, both non-normalized and normalized ADC values from 2 different MR systems showed significant correlations (r = 0.5196-0.8488). Non-normalized ADC values of both MR systems differed significantly in all anatomical regions and liver lesions (p < 0.001). However, the normalized ADC of all anatomical regions and liver lesions did not differ significantly (p = 0.065-0.661), with significantly lower coefficient of variance than that of non-normalized ADC (p < 0.009).

Conclusion: Normalization of the abdominal ADC values using the spleen as a reference organ reduces differences between different MR systems, and could facilitate consistent use of ADC as an imaging biomarker for multi-center or longitudinal studies.

Keywords: 3.0 T; Apparent diffusion coefficient; Diffusion-weighted imaging; Inter-vendor differences.

Fig. 1. Axial single-shot echo-planar diffusion-weighted (DW) MR images for b values of 0 s/mm² (A, C) and apparent diffusion coefficient (ADC) maps (B, D) in 54-year-old man with hepatitis B cirrhosis.

A and B are DW MR images acquired from Achieva while C and D are acquired from Verio. Region of interests for ADC measurements of right liver lobe, left liver lobe and spleen are shown as red circles. ADC values from Achieva and Verio of right liver, left liver and spleen were 1.079, 1.130, 0.774 and 1.238, 1.395, 0.886 × 10^-3 mm²/s, respectively. Normalized ADC of Achieva and Verio of right liver and left liver were 1.395, 1.459 and 1.398, 1.575, respectively.

Fig. 2. Bland-Altman plot of normalized apparent diffusion coefficient (ADC) in 5 anatomical regions (A, right liver lobe; B, left liver lobe; C, pancreas; D, right kidney; E, left kidney) and liver lesion (F).

95% limits of agreement in percentage of mean of normalized ADC was -30.2–22.9% for 5 anatomical regions and -22.2–23.5% for liver lesions.