Objectives <p>A standardized grading system for venous post-thrombotic syndrome (PTS) in cross-sectional imaging is lacking. This study aimed to develop and validate GRAVITS (GRavity of Venous Insufficiency in post-Thrombotic Syndrome scoring), a novel MRI-Venography/CT-Venography-based scoring system for venous obstruction, using a Delphi consensus.</p> Materials and methods <p>The Delphi consensus involved a survey distributed to 22 experts from the French Society of Cardiovascular Imaging. Data was reviewed and discussed in a consensus meeting, where a structured voting process established the GRAVITS system. A retrospective cohort of 40 PTS patients from three centers was analyzed. Twelve venous imaging specialists evaluated venous sequelae in axial MRV/CTV slices using GRAVITS. Inter-observer reproducibility was measured using Krippendorff’s alpha (<i>α</i>) and tested across vein types, imaging types, and vein pathological reference status. Intra-observer reproducibility was measured using weighted Kappa (<i>κ</i>_w). Correlations between GRAVITS scores and clinical scores (Villalta, CIVIQ-20) were assessed using Spearman tests.</p> Results <p>GRAVITS, defined as an ordinal score with four levels (“A: normal vein” to “D: totally occluded vein”), was evaluated in 851 venous segments (40 patients, median age 43.4, 55% women). Inter-observer reproducibility was substantial (<i>α</i> = 0.607), with the highest reproducibility for the external iliac vein (<i>α</i> = 0.693) and the lowest for the popliteal veins (<i>α</i> = 0.364). TrueFISP and BFFE had the highest reproducibility (<i>α</i> = 0.679), while direct CTV was lower (<i>αK</i> = 0.548). <i>κ</i>_w for two radiologists was calculated using a random sample of 168 venous segments, yielding values of 0.777 and 0.882 (both <i>p</i> &lt; 0.0001). Average GRAVITS scores were significantly correlated with CIVIQ-20 (rho = 0.515, <i>p</i> = 0.0042).</p> Conclusion <p>GRAVITS demonstrated substantial reproducibility and significant correlation with CIVIQ-20, supporting its potential as a reliable tool for grading venous sequelae in PTS. Further validation is warranted to refine its clinical utility.</p> Key Points <p><Emphasis Type="BoldItalic">Question</Emphasis> <i>GRAVITS (GRavity of Venous Insufficiency in post-Thrombotic Syndrome scoring) is a novel MRI/CT-based scoring system developed via Delphi consensus to standardize the assessment of venous obstruction in post-thrombotic syndrome (PTS) patients.</i></p> <p><Emphasis Type="BoldItalic">Findings</Emphasis> <i>The GRAVITS score demonstrated high inter-observer reproducibility, particularly in assessing the external iliac vein, with the best results obtained using MRI TrueFISP and BFFE sequences.</i></p> <p><Emphasis Type="BoldItalic">Clinical relevance</Emphasis> <i>GRAVITS provides a standardized, reproducible scoring system for grading venous obstruction in post-thrombotic syndrome using MRI and CT venography. Its correlation with quality-of-life scores highlights its potential clinical utility in assessing patient impairment and guiding management decisions.</i></p> Graphical Abstract <p></p>