In our previous work, we addressed one part of that challenge by showing that CT-based surveillance could be made substantially safer through major radiation dose reduction. We found that the key tumor features that matter most in AS—particularly tumor size—could be assessed reproducibly even at markedly reduced dose levels, and that deep-learning-based denoising could push dose reduction even further.1 That study pointed toward a practical future in which safer CT surveillance can be implemented on a broad scale, even on older CT systems.
In the present study, we extend that concept further and broaden the imaging armamentarium for AS of SRMs beyond low-dose CT alone. Specifically, we evaluated whether an abbreviated non-contrast MRI protocol, focused on axial T2-weighted imaging, could provide a comparable assessment to contrast-enhanced CT in the follow-up of known solid SRMs.2
This question was inspired both by our own clinical experience and by the broader literature on abbreviated MRI. In 2019, Canellas and colleagues highlighted the promise of abbreviated MRI protocols for abdominal imaging as a way to reduce scan time, complexity, costs, and patient burden while preserving clinically relevant information.3 Notably, they also suggested exploring whether abbreviated non-contrast MRI, primarily based on an axial T2-weighted sequence, could have a role in renal mass surveillance. Yet while abbreviated MRI has been explored extensively in other domains, including prostate and pancreatic imaging, its potential role in renal mass surveillance has remained scarcely investigated. This is a notable gap, particularly in a patient population that may require repeated imaging over many years.
To address this, we performed a multi-observer study comparing contrast-enhanced CT and abbreviated non-contrast MRI in patients with solid SRMs undergoing AS. Using a web-based observer-performance research platform, we included radiologist readers from five institutions, allowing us to evaluate reproducibility in a setting that better reflects real-world imaging practice than a conventional small single-center reader study.
The key findings were notable. Tumor size measurements were highly comparable across modalities, with a non-significant mean difference of just 0.4 mm between contrast-enhanced CT and abbreviated non-contrast MRI. Interobserver agreement for size assessment was also very similar, at approximately ±3 mm for both modalities, a level of variability that appears small relative to the degree of interval growth that would typically prompt clinical concern during active surveillance. Assessment of tumor nearness, a component of the clinically well-established RENAL nephrometry score, was likewise comparable. Taken together, these findings suggest that abbreviated non-contrast MRI can provide much of the same practical information as contrast-enhanced CT for the central imaging tasks of active surveillance.
This is clinically relevant because the radiation burden of AS matters. Even when each individual CT scan is modest in dose, repeated surveillance over the years may result in substantial cumulative radiation exposure, especially in younger patients. Repeated iodinated contrast administration may also be undesirable in some settings. A surveillance strategy that selectively incorporates abbreviated non-contrast MRI may therefore be attractive, as it may reduce both radiation exposure and contrast burden while preserving the reproducibility of the measurements that guide clinical decision-making. From the patient’s perspective, an abbreviated non-contrast MRI protocol may also be less burdensome with respect to how the examination is conducted, as it avoids intravenous access and contrast injection and does not require the more extensive workflow of a full diagnostic MRI examination, which could in turn support adherence to long-term surveillance.
Our findings also build on the limited prior literature in this area. Mawi et al. previously suggested that unenhanced MRI may be adequate for surveillance of cT1a solid renal masses.4 Taken together, that earlier work and our present findings support the growing view that T2-weighted non-contrast MRI may be a viable surveillance option for selected patients with known SRMs. The added value of our study lies in its broader multi-observer, multi-institution design, which supports broader applicability.
More broadly, we believe these results support a more individualized imaging strategy for active surveillance of small renal masses. At a time when both the optimal frequency of surveillance and the interval between scans remain matters of debate, the imaging modality itself may also be more flexible than traditionally assumed. Some patients may still be followed with CT, potentially at a substantially lower dose than before, whereas others may be particularly well suited to abbreviated non-contrast MRI. In selected cases, an MRI obtained for another clinical indication may substitute for a dedicated active surveillance CT. The broader message is that surveillance imaging need not be one-size-fits-all, but should instead be tailored to preserve diagnostic robustness while minimizing long-term burden to patients.
Important questions remain for future research. Beyond sporadic SRMs, abbreviated non-contrast MRI may merit study in hereditary renal cell carcinoma syndromes. In this setting, surveillance is primarily a detection task rather than the size assessment that defines AS of known SRMs, and reducing lifelong radiation exposure is especially relevant.5
In summary, our earlier work showed that CT surveillance of SRMs can be made substantially safer through dose reduction. The present study extends that concept further by suggesting that surveillance imaging may, in selected settings, reduce reliance on contrast-enhanced CT. Abbreviated non-contrast MRI appears to offer comparable assessment of tumor size while avoiding both radiation and intravenous contrast. As active surveillance becomes more widely used and extends over longer periods, broadening the available imaging options may help make surveillance not only effective but also more sustainable for patients.
Written by:
- Jens Borgbjerg, MD, PhD, Department of Radiology, Akershus University Hospital, Norway
- Bendik Breen, MD, Department of Radiology, Akershus University Hospital, Norway
- Jens Brøndum, Frøkjær, MD, PhD, Department of Radiology, Aalborg University Hospital, Denmark
- Ole Graumann, MD, PhD, Department of Radiology, Aarhus University Hospital, Denmark
- Anne Negård, MD, PhD, Department of Radiology, Akershus University Hospital, Norway
- Stig Müller, MD, PhD, Department of Urology, Akershus University Hospital, Norway
- Borgbjerg J, Breen BS, Kristiansen CH, Larsen NE, Medrud L, Mikalone R, et al. Agreement between Routine-Dose and Lower-Dose CT with and without Deep Learning-based Denoising for Active Surveillance of Solid Small Renal Masses: A Multiobserver Study. Radiol Imaging Cancer. 2025;7: e240250.
- Breen B, Alghofaily K, Christensen HS, Frøkjær JB, Graumann O, Kleivane M, et al. Agreement of axial T2-MRI versus Contrast-Enhanced CT for solid renal mass active surveillance. Abdom Radiol (NY). 2026. doi:10.1007/s00261-026-05376-6
- Canellas R, Rosenkrantz AB, Taouli B, Sala E, Saini S, Pedrosa I, et al. Abbreviated MRI Protocols for the Abdomen. Radiographics. 2019;39: 744–758.
- Mawi H, Narine R, Schieda N. Adequacy of Unenhanced MRI for Surveillance of Small (Clinical T1a) Solid Renal Masses. AJR Am J Roentgenol. 2021;216: 960–966.
- Miranda M, Ferreira C, Fernandes M, Lopes F, Ye A, Sousa AB, et al. Hereditary renal cell carcinoma surveillance protocols: a review of the literature and proposed recommendations. Fam Cancer. 2026;25: 10.