Poster Design & Printing by Genigraphics ® - 800.790.4001 A Novel Functional Imaging Method of the Eustachian Tube Cuneyt M. Alper 1,2 , Tanya J. Rath 3,4 , J. Douglas Swarts 2 , Miriam S. Teixeira 2 , William J. Doyle 2 1) Division of Pediatric Otolaryngology, Children's Hospital of Pittsburgh of UPMC, 2) Department of Otolaryngology, University of Pittsburgh School of Medicine 3) Department of Radiology, University of Pittsburgh School of Medicine, 4) Division of Neuroradiology, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania INTRODUCTION DISCUSSION RESULTS A. 1.25 mm in soft tissue algorithm, soft tissue window (Window 145, Level - 55). The paratubal fat (black arrows) is seen similar in density to subcutaneous fat (white arrow) displayed as dark grey. No definite air density could be visually seen in the eustachian tube when using air (white asterisk) in the nasopharynx as a reference. B. Displayed in thinner 0.625 mm bone algorithm with a lower level (Window 432, Level -200), small foci of air (black arrows) were suspected in the eustachian tube using air (white asterisk) in the nasopharynx as a reference. C. When the window was narrowed and dichotomized (Window 1, Level -200) to show only air displayed as black, versus all other densities displayed as white, only 2 small foci of possible air(black arrow) could be seen, suggesting that air passing through the eustachian tube during the forced response test is not clearly detected by CT due to inadequate special resolution and partial volume averaging with adjacent paratubal fat. Figure 2. Figure 2 A, B. Axial 0.625 mm low dose eustachian tube CT (kVp 100 mA 200 ; Window 974/Level 271) after instilling water soluble iodinated contrast in to the middle ear cavity and eustachian tube. A. Iodinated contrast which is displayed as white is easily seen within the eustachian tube (white arrows) and in the nasopharynx (black asterisk) B. An oblique reformat along the long axis of the eustachian tube following the instillation of water soluble contrast into the eustachian tube. The entirety of the cartilaginous portion of the eustachian tube (black arrows) is easily visualized with dense contrast from the bony eustachian tube to the nasopharynx. Contrast is seen pooling in the nasopharynx (black asterisk) ABSTRACT Outcome Objectives: 1) Image the Eustachian tube (ET) lumen by 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 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. Multiplanar reformats of the ET were created using post-processing software. 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 at any radiation dose, CT with intra-luminal contrast clearly demonstrated the entire ET lumen. Post-contrast FRT demonstrated residual contrast outlining the lumen. Conclusion: Standard temporal bone CT dose provided a slightly better signal-to-noise than low dose CT but neither provided adequate spatial resolution to demonstrate an air filled ET during FRT. ET lumen was easily visualized with iodinated water soluble contrast at all radiation doses. Combining ETF testing and CT imaging has potential research applications. This is the first report of combining a reliable ET function test (FRT) with CT scan for visualizing the ET lumen. While ET lumen is closed at rest (unless patulous), and current standard imaging techniques fail to capture the tube during this short opening time. FRT maintains a steady opening through the lumen while constantly running air with a pump. However, even though the lumen is kept open, the CT scan was unable to demonstrate a distinct air column. Instilling water soluble contrast facilitated the visualization of the ET lumen , however, running FRT after contrast still showed contrast but no air column. Running FRT pump at high speed or using standard temporal bone and high dose CT scan protocols did not change the outcome. In conclusion, there was no difference in the ability to detect air with any of the techniques though the radiologists found the standard T bone CT and high dose to be visually more pleasing with less noise. Scanning of a cadaveric head was performed helically on a 64-channel multidetector CT scanner (GE LightSpeed VCT; GE Healthcare, Milwaukee, WI). Forced Response Test (FRT) was performed by running air with a pump from the external ear canal, through middle ear and the ET into the nasopharynx. FRT standard speed was 23 cc/min., and high speed was 60 cc/min. This was repeated after injection of water soluble iodinated contrast (IC) through the middle ear. The sequence of CT protocols performed were as follows with example images provided in Figure 1: 1. A (localizer) -Low dose (100kVp, 180mA, pitch 0.969) 2. B (helical) -Low dose (100kVp, 200mA, pitch 0.531) with standard speed FRT 3. B CT technique with IC 4. B CT technique with IC and standard speed FRT 5. Standard dose Temporal bone CT (120kVp, 195 mA) with standard speed FRT 6. B CT technique with IC and high speed FRT 7. High dose CT (120fVp 320 MA) with IC and high speed FRT Axial 0. 625 mm bone and 1.25 mm soft tissue reconstructions were performed for all scans. An edge enhancing reconstruction kernel was used (Bone Plus; GE Healthcare, Milwaukee, WI). All reformats were performed by a CAQ certified neuroradiologist (T.J.R) using dedicated post-processing software (Vitrea® Core; Vital Images, Minnetonka, MN). Axial oblique and coronal oblique 1 mm thick reconstructions with 1 mm increment parallel and perpendicular to the long axis of the ET were obtained. We would like to acknowledge Barton F. Branstetter IV, MD, Professor of Radiology, University of Pittsburgh, for his review of images and input with respect to this project. The Eustachian tube (ET) is a natural tube that connects the middle ear (ME) to the back of the nose (nasopharynx). The posterior 1/3 of the ET is a bony extension of the ME with a patent lumen while the anterior 2/3 is a membrano-cartilaginous structure that opens into the nasopharynx. The physiologic functions attributed to the ET are middle ear pressure regulation, clearance of secretions and protection from reflux of nasal secretions. The ET is usually closed due to the natural pressure of the surrounding tissue and is opened intermittently by the active contraction of the tensor veli palatini (mTVP) and levator veli palatini (mLVP) muscles, allowing equilibrium between the ambient and middle ear pressures. Inefficient ET openings are associated with the progressive development of ME under pressure and set the basis for several middle ear diseases such as acute and chronic otitis media, otitis media with effusion (OME), retraction pockets, cholesteatoma, barotrauma and hearing loss. The ET is located at the base of the skull and its complexity and difficult access resulted in frustrated attempts of imaging studies previously. Another challenge comes from the fact that the ET has a virtual lumen that only opens for a few hundred milliseconds during middle-ear and ambient pressure equalization (0.2 – 0.4 sec on average). An example of ET imaging is nasopharyngoscopy, a routine outpatient procedure in which a flexible or rigid endoscope is introduced through the nostrils allowing examination of the nasal cavity and the back of the nose. It requires expensive equipment, the use of topical anesthesia and decongestants, is uncomfortable and cannot be tolerated by many patients, especially young children. Although it is very useful for assessment of peritubal diseases and nasal and pharyngeal infectious or inflammatory processes, it only allows the visualization of the opening of the tube and sometimes a few millimeters of the lumen. Magnetic Resonance Imaging (MRI) and Computerized Tomography (CT) are imaging techniques largely used by the medical community to study biological tissues from all regions of the body. The development of high resolution three- dimensional (3-D) reconstruction software has broadened their use to explore the anatomy of small structures such as the ET. Initially, MRI seemed ideal as it does not involve ionizing radiation exposure, but unfortunately it is limited by very long scan time, significant imaging artifacts and large asymmetric voxel sizes. When those variables are applied to small areas, the 3-D reconstructions yield a poorly defined image. On the other hand, recent publications have shown that the faster helical CT scans can provide clear reconstructions of the lumen and surrounding tissues along all ET segments. Although promising, this is only possible in patients with a patulous ET, a situation in which the tube remains abnormally open. This limits the usefulness of the technique to only a subset of patients, as the great majority of ET problems come from failure to dilate the cartilaginous segment due to strictures or poor muscular efficiency. A study was conducted in order to develop a novel functional imaging model for visualization of the ET. METHODS AND MATERIALS 1. Alper, CM; Swarts, JD; Singla, A; Banks, J; Doyle, WJ. Relationship between the electromyographic activity of the paratubal muscles and eustachian tube opening assessed by sonotubometry and videoendoscopy. 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Alper, M.D. Professor of Otolaryngology Director, Pediatric Otolaryngology Fellowship Program Children’s Hospital of Pittsburgh of UPMC Department of Otolaryngology University of Pittsburgh School of Medicine Email: [email protected] Phone: 412-692-8577 Website: http://www.chp.edu/CHP/ent CONTACT University of Pittsburgh Supported in Part by: National Institute of Health P-50 Grant DC007667 R21 Grant DC013167 Figure 1. Figure 1 A, B & C. Axial CT, low dose eustachian tube all obtained during the same forced response test displayed in different techniques. A B A C B