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Background: Pneumoperitoneum is defined by the presence of free air in the abdominal cavity; gastrointestinal perforation is an important cause of this pathological condition. In emergency situations, radiology is considered vital in the early detection and identification of the site and cause of the perforation, which is critical for proper surgical planning. Aim: The aim of our study was to evaluate a new diagnostic US tool, based on the US contrast-specific software generally used during contrast-enhanced US examination (CEUS), without the administration of sonographic contrast media, and to describe the specific imaging features in the detection of free intra-peritoneal air. Subjects and Methods: One hundred and fifty-seven consecutive and hemodynamically stable patients, who arrived in our E.D. with an acute abdomen between April 2018 and October 2019, underwent US and CT examination, performed by three radiologists (with 5, 5, and 25 years of experience). The US was performed first and divided into two steps, using B-mode US and both B-mode and contrast-specific software US, with no contrast media administration. All the patients underwent CT examination. Results: In 32 out of 157 patients, the surgery confirmed GI perforation. CT correctly detected 31 out of 32 patients; the contrast-specific software US identified 30 perforated patients. CT reached a sensitivity value of 97% and specificity value of 100%; contrast-specific software US demonstrated higher values than B-mode US in sensitivity (93% vs. 70%, respectively) and specificity (98% vs. 88%, respectively). Conclusion: the use of contrast-specific software in emergencies improves image quality, and reaches higher levels of sensitivity and specificity with no time delay compared to standard US examination, helping radiologists expedite diagnoses. [ABSTRACT FROM AUTHOR]