Most newly-diagnosed renal cancers are localized (i.e., stage I-II, 60–70%) and approximately 76% clear cell renal cell carcinomas (ccRCC) [1,2]. Imaging guided percutaneous thermal ablations (TAs) such as radiofrequency ablation, cryoablation and microwave ablation are now clearly mentioned as valid alternatives to surgery for patients with T1 renal cancers < 3 cm according to the latest guidelines from the American Urological Associations. The European Association of Urology, the European Society of Medical Oncology, the French Urological Association or the Cardiovascular and Interventional Radiological Society of Europe recommend these treatments as alternatives for patients not fit for surgery, and those with important comorbidities [3], [4], [5], [6]. Several studies and meta-analyses have reported lower rates of complications, preservation of the renal function, similar metastatic recurrence free and overall survivals, but with a slightly greater recurrence rate [7], [8], [9], [10], [11], [12], [13], [14], [15]. Regular follow-up of patients treated with TAs using cross-sectional imaging is mandatory to rapidly detect and treat incomplete TA with residual disease and/or local recurrence [16].

Typically, ablation zones without recurrence (also named ‘scars’) are characterized by a heterogenous signal, disappearance of contrast enhancement and progressive decrease in longest diameter (LD). On the opposite, an increase in size of the ablation zone, and appearance of a nodular or crescent-like lesion on contrast-enhanced (CE) imaging examination should raise suspicion for local recurrence [17], [18], [19], [20]. Consequently, follow-up MRI after renal TA routinely includes the use of intravenous administration of a gadolinium-based contrast agent (GBCA) and comparative evaluations until five years after treatment [17,21,22].

Yet, the benefit of the use of GBCA for the follow-up of patients with ccRCC treated using percutaneous TA has never been clearly addressed. Initially, most follow-up examinations were performed with CT, which demonstrates lower spontaneous tissue contrast compared to MRI, making mandatory the intravenous administration of iodinated contrast material, which is not free from side-effects [23]. On the opposite, MRI conveys good contrast resolution and high tissue characterization capabilites on non-CE sequences. Nevertheless, post-TA follow-up MRI protocols always include multi-parametric imaging, including non-CE and CE sequences [21]. Furthermore, since few years, several animal and human studies have demonstrated the presence of GBCA deposits in central and peripheral neurologic structures, skin, liver or kidney, especially with linear agents, of which the long-term effects remain under scrutiny [24], [25], [26], [27]. Furthermore, after excretion from the patient's body via the urinary tract, gadolinium is responsible for contamination that have now be proven in environmental samples [28]. Lastly, in some situations GBCA cannot be injected, in particular in patients with prior allergy to GBCA or in pregnant women [29].

Therefore, given this uncertainty about the impact of repetitive GBCA administration in addition to the environmental aspect and its technical implications in terms of patients’ preparation and examination duration, the purpose of this study was to assess and compare the diagnostic performances and inter-observer reproducibility of non-CE to those of CE MRIs after percutaneous TA for ccRCC.