A Novel Functional Imaging Method of the Eustachian Tube

Abstract

Objectives: (1) Image the Eustachian tube (ET) lumen by computed tomography (CT) scanning during ET function (ETF) testing, (2) characterize the differences in image quality for different scanning protocols, and (3) establish a novel research methodology for studying ET anatomy and physiology. Methods: In a cadaver head without craniofacial or otologic abnormalities, the tympanic membrane was perforated and ETF test was done using the forced response test (FRT) in a CT scanner. Opening (OP), steady (PS), and closing (CP) pressures were measured during forced air flow from the middle ear (ME) to the nasopharynx across the open ET. Temporal bone CT scans with continuous 0.625 mm thickness were done at a low and standard radiation doses before and during the steady flow (SF) phase of the FRT, after instilling iodinated contrast into the ME and ET, and after the FRT cleared the contrast from the ET. Image analysis was done using the CT scanner console software to view the ET and peritubal structures in standard views and after image reconstructions. Results: The average OP, PS, and CP values were 488 ± 249, 376 ± 101, and 211 ± 62 daPa. While a distinct ET lumen could not be demonstrated during the FRT done with air, CT with intra-luminal contrast clearly demonstrated the entire ET lumen. Post-contrast FRT demonstrated residual contrast outlining the lumen. Conclusions: Standard temporal bone CT doses provided a slightly better signal-to-noise than the low-dose CT for the air but not for the contrast. Combining ETF testing and CT imaging has potential research applications.