Ultrahigh-frequency Ultrasonography (UHFUS) in Detection of Small Pulmonary Ground Glass Opacity (GGO)

Lung cancer (LC) is a leading cause of mortality worldwide. According to the International Agency for Research (IARC) on Cancer, LC was projected to contribute to 2.3 million new cancer cases and 1.8 million deaths worldwide in 2020. With widespread use of chest computed tomography (CT), LC is increasingly detected at an early stage, in which 63%-95% lesions present as ground glass opacity (GGO). GGO refers to a non-specific radiological appearance, referring to a focal, hazy shadow with increased attenuation that does not obscure the contours of bronchi or blood vessels on CT. It can be benign lesions, preinvasive, or invasive adenocarcinoma. Surgery is the main treatment for suspected malignant GGOs. Whether excised targeted GGOs thoroughly affects patients' prognosis crucially, especially for patients with multiple GGOs. Generally, the most frequent intraoperative location approach of pulmonary nodules is palpation, which distinguished by the texture between normal lung tissue and nodules. However, different from solid nodules, the texture of GGO nodules is similar to lung parenchyma that increases the difficulty of palpation localization. Thus, detection of GGOs and in lung tissue poses a common challenge, particularly in the presence of pure GGO (tumor without an solid component) and small GGO nodules (≤1cm). In the current clinical practice, even with preoperative localization (CT-guided percutaneous and intraoperative electromagnetic navigation bronchoscopy), it remains challenging to confirm complete resection of all small, pure GGOs. Therefore, there is an urgent need for a new method that can accurately evaluate nodules in excised lung tissue. Since Roberto used thoracoscopic ultrasound (TUS) to examine pulmonary nodules in 1999, subsequently, several studies have validated the safety and efficacy for using US in identifying pulmonary nodules intraoperatively. However, past research all focused on solid nodules or large nodules (maximum diameter more than 2cm) using 5-12MHz US transducer. Few studies have studied the detection rate of small GGO nodules. Previous studies have found 12MHz of US probe could show pulmonary nodules better than 5MHz and 7.5MHz. Ultrahigh frequency ultrasound (UHFUS) refers to higher frequency (≥20MHz) ultrasound waves with higher resolution even less than 50μm. It is capable to display nodules less than 3mm distinctively in the extremely superficial tissue, which may satisfy intraoperative GGO imaging requirement. Therefore, the objects of this study are to assess the feasibility of localizing GGOs in excised lung tissue by UHFUS and further summarize its UHFUS features.