An alternative approach to contrast-enhanced imaging: diffusion-weighted imaging and T-1-weighted imaging identifies and quantifies necrosis in Wilms tumour

摘要

ObjectivesVolume of necrosis in Wilms tumour is informative of chemotherapy response. Contrast-enhanced T-1-weighted MRI (T(1)w) provides a measure of necrosis using gadolinium. This study aimed to develop a non-invasive method of identifying non-enhancing (necrotic) tissue in Wilms tumour.MethodsIn this single centre, retrospective study, post-chemotherapy MRI data from 34 Wilms tumour patients were reviewed (March 2012-March 2017). Cases with multiple b value diffusion-weighted imaging (DWI) and T(1)w imaging pre- and post-gadolinium were included. Fractional T-1 enhancement maps were generated from the gadolinium T(1)w data. Multiple linear regression determined whether fitted parameters from a mono-exponential model (ADC) and bi-exponential model (IVIM - intravoxel incoherent motion) (D, D*, f) could predict fractional T-1 enhancement in Wilms tumours, using normalised pre-gadolinium T(1)w (T(1)w(norm)) signal as an additional predictor. Measured and predicted fractional enhancement values were compared using the Bland-Altman plot. An optimum threshold for separating necrotic and viable tissue using fractional T-1 enhancement was established using ROC.ResultsADC and D (diffusion coefficient) provided the strongest predictors of fractional T-1 enhancement in tumour tissue (p<0.001). Using the ADC-T(1)w(norm) model (adjusted R-2=0.4), little bias (mean difference =-0.093, 95% confidence interval = [-0.52, 0.34]) was shown between predicted and measured values of fractional enhancement and analysed via the Bland-Altman plot. The optimal threshold for differentiating viable and necrotic tissue was 33% fractional T-1 enhancement (based on measured values, AUC=0.93; sensitivity=85%; specificity=90%).ConclusionsCombining ADC and T(1)w imaging predicts enhancement in Wilms tumours and reliably identifies and measures necrotic tissue without gadolinium.Key Points center dot Alternative method to identify necrotic tissue in Wilms tumour without using contrast agents but rather using diffusion and T(1)weighted MRI.center dot A method is presented to visualise and quantify necrotic tissue in Wilms tumour without contrast.center dot The proposed method has the potential to reduce costs and burden to Wilms tumour patients who undergo longitudinal follow-up imaging as contrast agents are not used.