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2090. Is Unenhanced MRI Adequate for Surveillance of Small (Clinical T1a) Solid Renal Masses?
Authors * Denotes Presenting Author
  1. Hatem Mawi *; The Ottawa Hospital
  2. Rishi Narine; The Ottawa Hospital
  3. Nicola Schieda; The Ottawa Hospital
Objective:
To determine if GBCAs are necessary for MRI surveillance of cT1a solid renal masses.

Materials and Methods:
With IRB approval, we consecutively identified 36 patients who underwent =2 (median 4 [range 2-10]) contrast-enhanced (CE)-MRI for surveillance of 39 cT1a solid renal masses between 2009-2019 (median time between scans 2 [1-7] years). Two radiologists (R1/R2) independently measured the size of each mass in two sessions on baseline and follow-up exams using: 1) T1-weighted nephrographic phase CE-MRI and 2) unenhanced single-shot T2-weighted (T2W) in mixed-order with a 4-week washout period. Absolute measurements and linear-growth (? size between exams) for each mass were compared using Pearson correlation. Bland-Altman analysis determined inter-observer agreement.

Results:
Mean size of renal masses measured on CE-MRI and T2W were: 18±5 (range 9 to 37) and 18±5 (range 9 to 37) R1 and 19±7 (range 10 to 39) and 19±6 (range 10 to 39) R2 with near perfect correlation in measurements (Beta= 0.9897 R1 and 0.9317 R2, p<0.0001). Inter-observer agreement in measurements comparing R1 and R2 on CE-MRI and T2W and intra-observer agreement for measurements on CE-MRI and T2W were excellent. Mean growth rate of renal masses measured on CE-MRI and T2W were: 2±2 (range -5 to 8) and 2±3 (range -3 to 8) R1 and 3±5 (range -1 to 18) and 3±6 (range -1 to 24) R2 with high correlation in measurements (Beta=0.8313 R1 and 0.848 R2, p=-<0.0001, 0.0020). Inter-observer agreement in measurements was excellent comparing R1 and R2 on CE-MRI and T2W.

Conclusion:
In this study, size measurements on T2W had near-perfect correlation to measurements using CE-MRI in cT1a solid renal masses with high agreement between and within observers. This indicates that after an initial GBCA-enhanced baseline MRI, contrast is not necessary for follow-up size measurements of size in cT1a solid renal masses undergoing surveillance.