The Bathymetry and Composition of Titan’s Lakes and Seas

International audienceDespite pre-launch predictions that hydrocarbon liquids would be transparent to Cassini's 13.8 GHz radar [1] and that the radar's altimetry mode might be used as a sounder to probe Titan's liquids [2], experiments using liquefied natural gas by Paillou et al. [3] suggested that penetration would be significantly shallower than the altimeter's 35 m range resolution. Nevertheless, Mastrogiuseppe et al. [4] successfully detected subsurface reflections in altimetry echoes acquired over Ligeia Mare in May 2013 (Figure 1). Coherent processing of these echoes revealed the bottom reflection and allowed construction of a bathyme-try profile as well as an estimation of the liquid loss tangent from the relative variation in subsurface power. Subsequent altimetry observations of Kraken and Punga Maria obtained in August 2014 and January 2015, respectively, also showed detectable subsurface echoes. After applying these new techniques, subsur-face echoes were also observed in altimetry data acquired over Ontario Lacus in 2008. In this proceeding, we will report on the latest results from the analyses of these altimetry passe

Changes in Apparent Diffusion Coefficient (ADC) in Serial Weekly MRI during Radiotherapy in Patients with Head and Neck Cancer: Results from the PREDICT-HN Study

Background: The PREDICT-HN study aimed to systematically assess the kinetics of imaging MR biomarkers during head and neck radiotherapy. Methods: Patients with intact squamous cell carcinoma of the head and neck were enrolled. Pre-, during, and post-treatment MRI were obtained. Serial GTV and ADC measurements were recorded. The correlation between each feature and the GTV was calculated using Spearman’s correlation coefficient. The linear mixed model was used to evaluate the change in GTV over time. Results: A total of 41 patients completed the study. The majority (76%) had oropharyngeal cancer. A total of 36 patients had intact primary tumours that can be assessed on MRI, and 31 patients had nodal disease with 46 nodes assessed. Median primary GTV (GTVp) size was 14.1cc. The rate of GTVp shrinkage was highest between pre-treatment and week 4. Patients with T3-T4 tumours had a 3.8-fold decrease in GTVp compared to T1-T2 tumours. The ADC values correlated with residual GTVp. The median nodal volume (GTVn) was 12.4cc. No clinical features were found to correlate with GTVn reduction. The overall change in ADC for GTVn from pre-treatment was significant for 35th–95th percentiles in weeks 1–4 (p < 0.001). Conclusion: A discrepancy in the trajectory of ADC between primary and nodal sites suggested that they exhibit different treatment responses and should be analysed separately in future studies