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Abstract
ObjectivesVolume of necrosis in Wilms tumour is informative of chemotherapy response. Contrast-enhanced T1-weighted MRI (T1w) 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 T1w imaging pre- and post-gadolinium were included. Fractional T1 enhancement maps were generated from the gadolinium T1w 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 T1 enhancement in Wilms tumours, using normalised pre-gadolinium T1w (T1wnorm) 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 T1 enhancement was established using ROC.ResultsADC and D (diffusion coefficient) provided the strongest predictors of fractional T1 enhancement in tumour tissue (p < 0.001). Using the ADC-T1wnorm model (adjusted R2 = 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 T1 enhancement (based on measured values, AUC = 0.93; sensitivity = 85%; specificity = 90%).ConclusionsCombining ADC and T1w imaging predicts enhancement in Wilms tumours and reliably identifies and measures necrotic tissue without gadolinium.Key Points• Alternative method to identify necrotic tissue in Wilms tumour without using contrast agents but rather using diffusion and T1weighted MRI.• A method is presented to visualise and quantify necrotic tissue in Wilms tumour without contrast.• 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.
Highlights
Wilms tumour is the most common type of paediatric renal tumour, accounting for approximately 90% of all kidney tumours [1]
There was high similarity in the size of the necrotic regions of interest (ROIs) defined by the two readers, with an intraclass correlation coefficient (ICC) of 0.83
This study investigated whether necrosis could be identified without using gadolinium contrast-enhanced T1-weighted imaging (T1w) images in Wilms tumour
Summary
Wilms tumour is the most common type of paediatric renal tumour, accounting for approximately 90% of all kidney tumours [1]. Necrosis within Wilms tumour post-chemotherapy is informative of treatment response, when tumour size remains stable. It has been suggested that patients with 100% necrosis post-chemotherapy, when assessed via histological analysis, are associated with relapse-free survival at 5-year follow-up [3]. Quantifying the degree of necrosis in Wilms tumour tissue is beneficial. MRI can identify necrotic tissue via administration of gadolinium-based contrast agents and T1-weighted imaging (T1w), where absent or decreased enhancement may represent necrosis. Recent reports have described gadolinium retention in neural and body tissue regardless of renal function; currently, there are no known sequelae related to this [4]. Gadolinium is still frequently administered and has many additional uses, an alternative approach to identify and quantify necrosis would be beneficial
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