Acoustic radiation force impulse (ARFI) imaging of the gastrointestinal tract

Currently, the evaluation of lesions in the gastrointestinal (GI) tract using ultrasound suffers from poor contrast between healthy and diseased tissue. Acoustic radiation force impulse (ARFI) imaging provides information about the mechanical properties of tissue using brief, high-intensity, focused ultrasound to generate radiation force, and conventional, ultrasonic correlation-based methods to track tissue displacement. Using conventional linear arrays, ARFI imaging has shown improved contrast over B-mode images when applied to solid masses in the breast and liver. The purpose of this work is to (1) demonstrate that ARFI imaging can be performed with an endocavity probe, and (2) demonstrate that ARFI imaging can provide improvements over conventional B-mode imaging of GI lesions. An EC94, 6.2 MHz, endocavity probe was modified to perform ARFI imaging in tissue-mimicking phantoms using a Siemens SONOLINE Antares/spl trade/ scanner. ARFI imaging was performed on fresh, surgically excised, GI lesions using a 75L40, 7.2 MHz. linear array on a modified Siemens SONOLINE Elegra/spl trade/ scanner. The endocavity probe created ARFI images to a depth of over 2 cm in tissue-mimicking phantoms, with maximum displacements of 5 /spl mu/m. The endocavity probe did not heat appreciably during ARFI imaging, demonstrating that the probe's small size will not limit in vivo ARFI imaging. ARFI images of an adenocarcinoma of the gastroesophageal (GE) junction status post chemotherapy and radiation treatment, demonstrate better contrast between healthy and fibrotic/malignant tissue than standard B-mode images. ARFI images of healthy gastric, esophageal, and colonic tissue specimens differentiate normal anatomic tissue planes (i.e., mucosal, muscularis, and adventitial layers), as confirmed by histologic evaluation. ARFI imaging of an ex vivo colon cancer portrays interesting contrast and structure not present in B-mode images. These findings support the clinical feasibility of endoscopic ARFI imaging to guide diagnosis and staging of disease processes in the GI tract.