Ultrasound positive predictive values by BI-RADS categories 3-5 for solid masses: An independent reader study.

OBJECTIVE: We assessed multiple readers' positive predictive values (PPVs) for ACR BI-RADS 3, 4a, 4b, 4c and 5 masses on ultrasound (US) pre- and post-proposed guidelines. METHODS: This retrospective, IRB-approved study included four American and four non-American readers who assigned BI-RADS categories for US images of 374 biopsy-proved masses. Readers were offered guidelines and re-classified the masses. We assessed readers' abilities to achieve ACR benchmarks BI-RADS categories pre- and post-guidelines. RESULTS: PPVs increased with BI-RADS category. The PPVs pre- and post-guidelines were 6.0% and 4.4% for category 3, 27.3% and 30.5% for category 4a, 49.9% and 51.5% for category 4b, 69.0% and 67.4% for category 4c, and 79.3% and 80.1% for category 5. Readers achieved the PPV benchmark for category 4c, but not for categories 3, 4a, 4b and 5, with no significant improvement after guidelines. Regular BI-RADS 4 subcategory users missed benchmarks by less than non-regular users. CONCLUSION: Pre- and post-guidelines, readers' PPVs increased with BI-RADS categories, ACR PPV benchmarks were achieved in category 4c, missed in other categories, especially in the critical 4a subcategory, where the PPV was too high. BI-RADS 4 subcategory users performed better than non-users. KEY POINTS: • Readers failed to achieve benchmarks for BI-RADS 4 subcategories, especially 4a. • USA and Brazilian readers performed similarly in ACR BI-RADS 4 subcategorization. • Proposed guidelines did not improve overall, USA or Brazilian reader performance. • Regularly BI-RADS 4 subcategory users performed better than did non-users. • US features distinguished between benign and malignant, not BI-RADS 4 subcategories.

South American precipitation dipole forced by interhemispheric temperature gradient.

Tropical South American hydroclimate sustains the world's highest biodiversity and hundreds of millions of people. Whitin this region, Amazonia and northeastern Brazil have attracted much attention due to their high biological and social vulnerabilities to climate change (i.e. considered climate change hotspots). Still, their future response to climate change remains uncertain. On precession timescale, it has been suggested that periods of decreased western Amazonian precipitation were accompanied by increased northeastern Brazilian precipitation and vice-versa, setting an east-west tropical South American precipitation dipole. However, the very existence of this precession-driven precipitation dipole remains unsettled given the scarcity of long and appropriate northeastern Brazilian records. Here we show that the precession-driven South American precipitation dipole has persisted over the last 113 ka as revealed by a northern northeastern Brazilian precipitation record obtained from quartz thermoluminescence sensitivity measured in marine sediment cores. Precession-induced austral summer insolation changes drove the precipitation dipole through the interhemispheric temperature gradient control over the regional Walker circulation and the Intertropical Convergence Zone seasonal migration range. Since modern global warming affects the interhemispheric temperature gradient, our study provides insights about possible future tropical South American hydroclimate responses.

Meridional changes in the South Atlantic Subtropical Gyre during Heinrich Stadials.

Subtropical ocean gyres play a key role in modulating the global climate system redistributing energy between low and high latitudes. A poleward displacement of the subtropical gyres has been observed over the last decades, but the lack of long-term monitoring data hinders an in-depth understanding of their dynamics. Paleoceanographic records offer the opportunity to identify meridional changes in the subtropical gyres and investigate their consequences to the climate system. Here we use the abundance of planktonic foraminiferal species Globorotalia truncatulinodes from a sediment core collected at the northernmost boundary of the South Atlantic Subtropical Gyre (SASG) together with a previously published record of the same species from the southernmost boundary of the SASG to reconstruct meridional fluctuations of the SASG over last ca. 70 kyr. Our findings indicate southward displacements of the SASG during Heinrich Stadials (HS) 6-4 and HS1, and a contraction of the SASG during HS3 and HS2. During HS6-4 and HS1, the SASG southward displacements likely boosted the transfer of heat to the Southern Ocean, ultimately strengthening deep-water upwelling and CO2 release to the atmosphere. We hypothesize that the ongoing SASG poleward displacement may further increase oceanic CO2 release.