Published online Jul 21, 2019. doi: 10.3748/wjg.v25.i27.3619
Peer-review started: April 17, 2019
First decision: May 9, 2019
Revised: May 20, 2019
Accepted: June 8, 2019
Article in press: June 8, 2019
Published online: July 21, 2019
The diagnosis and monitoring of Crohn’s disease (CD) are important for the clinical therapy during its longstanding course. As avoiding the use of intravenous contrast agents, diffusion weighted (DW) imaging (DWI) is increasingly considered as a promising magnetic resonance (MR) enterography (MRE) technique to the qualitative and quantitative evaluation of CD in recent years, and is recommended as an optional MR sequence for CD. The quantitative DWI analysis may be more objective for CD assessment. However, the measurement reproducibility of quantitative DWI analysis in MRE has not been ascertained so far. Thus, the investigation of intra and interobserver agreements of quantitative DWI parameters could be valuable to facilitate the application of quantitative DW-MRE into the clinical routine.
DWI has shown a superb potential as a quantitative modality for CD evaluation. The characterization of reader agreement and variability with quantitative DWI parameters is imperative before such parameters are to be incorporated into clinical practice. Therefore, it is necessary to investigate the level of measurement reproducibility of quantitative DWI parameters.
This study aimed to explore intra and interobserver reproducibility of quantitative analysis for DW-MRE in CD, and then to assess the diagnosis efficiency of quantitative parameters for the evaluation of CD.
Forty-four subjects (21 diagnosed with CD and 23 normal control subjects) who underwent ileocolonoscopy and DW-MRE (b = 800 s/mm2) within one week were included. Two radiologists, blinded to clinical details as well as endoscopy results, measured the signal intensity (SI) of the terminal ileum and ipsilateral psoas muscle on DWI with b = 800 s/mm2. Separately and simultaneously, apparent diffusion coefficients (ADC) of the terminal ileum were recorded. Then, SI of ipsilateral psoas muscle on DWI with b = 800 s/mm2 was also measured by placing a larger oval ROI. Signal intensity ratio (SR) of the terminal ileum to ipsilateral psoas muscle was calculated according to the equation: SR = SIileum/SImuscle. After a washout period of 4 weeks, the same two radiologists repeated the above described measurements to assess intraobserver agreement. Between- and within-reader agreements were assessed using intraclass correlation coefficients (ICC), coefficients of variation (CoV), and 95% limits of agreement of Bland-Altman plots (BA-LA LoA). Diagnostic performances of ADC and SR for identifying inflamed terminal ileum from the normal were evaluated by receiver operating characteristic (ROC) curve analysis.
There were no significant differences in quantitative DWI parameters (ADC and SR) between the two sessions or between the two radiologists either in the CD or control group (paired t-test, P > 0.05). The intra and interobserver reproducibility of ADC (ICC: 0.952-0.984; CoV: 3.73%-6.28%; BA-LA LoA: ±11.27% to ±15.88%) and SR (ICC: 0.969-0.989; CoV: 3.51%-4.64%; BA-LA LoA: ±10.62% to ±15.45%) was excellent for CD. Agreement of ADC measurements was slightly less in control subjects (ICC: 0.641-0.736; CoV: 10.47%-11.43%; BA-LA LoA: ± 26.59% to ±30.83%). SR of the normal terminal ileum demonstrated high intra and interobserver reproducibility (ICC: 0.944-0.974; CoV: 3.73%-6.28%; BA-LA LoA: ± 18.58% to ± 24.43%). The areas under the ROC curve for SR (reader 1: 0.981; reader 2: 0.988) were slightly better than those of ADC (reader 1: 0.923; reader 2: 0.929), but these differences were not statistically significant (P-values: 0.117 for reader 1; 0.067 for reader 2). The cutoff values maximizing sensitivity and specificity for ADC and SR parameters were approximately 1.80 × 10-3 mm2/s and 2.00, respectively. In addition, SR was moderately and negatively correlated with ADC values in CD patients for both readers (reader 1: r = - 0.438, P = 0.047; reader 2: r = - 0.485, P = 0.026).
From this study, the intra and interobserver agreements of quantitative ADC and SR analysis from DW-MRE images were found to be good or excellent. Both the ADC and SR demonstrated high diagnostic yield for distinguishing inflamed terminal ileum in CD patients from the normal. Additionly, SR demonstrated moderately negative correlations with ADC in CD patients, and could also represent the diffusion condition of the terminal ileum. Therefore, ADC value or SR could serve as robust and efficient biomarkers to aid in the noninvasive evaluation of CD.
Quantitative ADC and SR values derived from DW-MRE achieved good to excellent intra and interobserver agreements with high diagnostic accuracy based on this initial study. The further exploration of these quantitative parameters in the differentiation of CD stages and medical therapy assessment during CD course is worthwhile in the future study.