Gastrointestinal stromal tumors (GIST) are the most common malignant subepithelial lesions (SELs) found in the gastrointestinal tract. The diagnosis and differentiation of these lesions from other subepithelial hypoechogenic tumors (i.e.as leiomyoma), is important as this may have an impact in the prognosis and treatment of either.

Due to GIST's notable features (vascularity and deep location), endoscopic ultrasound (EUS) is the first-line diagnostic approach. Based on this, three models (color-doppler EUS, power-doppler EUS, and e-FLOW EUS), are useful for real-time vascularity detection; however, these modalities are not helpful for fine and slow flow vessel detection. For overcoming this limitation, contrast-enhanced EUS (CE-EUS) is proposed as a first-line approach. Nevertheless, the use of contrast may be harmful, thus limited to some patients. To avoid contrast-related adverse events, a novel diagnostic method known as detective flow imaging endoscopic ultrasonography (DFI-EUS) has emerged. This technique detects fine vessels and slow flow without contrast. Despite the advantages of the latter, few studies have compared it with other diagnostic approaches in the evaluation and differentiation of SELs.

Hence, the investigators aim to evaluate the utility of DFI-EUS in the diagnosis of SELs (GIST and leiomyoma) by comparing it with CE-EUS.

Subepithelial lesions (SELs) are a frequent finding on routine endoscopy (0.2%-3%), The importance of its diagnosis and management is based on its high risk of malignant transformation. According to literature, gastrointestinal stromal tumors (GIST) are the most common malignant SELs of the gastrointestinal tract. GIST appear as subepithelial lesions often covered by normal mucosa. For prognosis and treatment purposes, GIST should be differentiated from other benign submucosal hypoechogenic lesions such as leiomyoma, slow growing tumors, located preponderantly in the esophagus. The differential diagnosis between GISTs and leiomyoma is challenging because both can rise from the same second and forth muscular layers (muscularis mucosae and muscularis propria) and important because of the malignant potential of the former and consequently different management approach.

GISTs' diagnosis is approached by a combination of clinical signs and symptoms, laboratory tests and imaging techniques. Endoscopic techniques, such as esophagogastroduodenoscopy (EGD), is not useful to delineate the depth of invasion or subepithelial appearance of the lesions; also, conventional tissue acquisition through this modality is difficult when the tumor is not ulcerated. Due to this, EUS is considered critical for an accurate diagnosis, being the first-line diagnostic approach.

To date, color- doppler EUS, power doppler EUS, and e-FLOW EUS are EUS technologies that may be useful for observing vascularity in real time, but not for proper visualization of fine vessels and slow flow. On the other hand, contrast-enhanced EUS (CE-EUS) increases the detectability of vessels with high sensitivity yet holding the risk and limitations inherent to contrast administration.

To overcome diagnostic limitations, a new diagnostic method known as detective flow imaging endoscopic ultrasonography (DFI-EUS) has emerged. DFI-EUS detects fine vessels and low-velocity blood flow without the use of contrast agents. Despite its promising benefits, few studies have evaluated its advantages for the diagnosis and differentiation of GISTs. Only two studies have compared this technology against e-FLOW EUS, but in pancreatic tissue.

In the present study the investigators aim to evaluate the utility of DFI-EUS in the diagnosis of SELs (GIST and leiomyoma) by comparing it with CE-EUS.

Inclusion Criteria:

• Patients referred to our center with an indication of EUS for the evaluation of SELs
• Patients who authorized for DFI or CE-EUS.
• Written informed consent

Exclusion Criteria:

• Patients with contraindication for contrast agent administration.
• Any clinical condition which makes EUS-DFI or CE-EUS inviable
• Pregnancy