Abstract
Purpose
To further enhance and assess the ability to characterize middle ear effusion (MEE) using non-invasive ultrasound technology.
Materials and Methods
This is a prospective unblinded comparison study. Fifty-six children between the ages of 6 months and 17 years scheduled to undergo bilateral myringotomy with pressure equalization tube placement were enrolled. With the child anesthetized, the probe was placed into the external ear canal after sterile water was inserted. Ultrasound recordings of middle ear contents were analyzed by computer algorithm. Middle ear fluid was collected during myringotomy and analyzed for bacterial culture and viscosity.
Results
Ultrasound waveforms yielded a computer algorithm interpretation of middle ear contents in 66% of ears tested. When a result was obtained, the sensitivity and specificity for successfully characterizing middle ear fluid content as either void of fluid, thick fluid (mucoid), or thin fluid (serous or purulent) were at least 94%. Mucoid effusions had higher measured viscosity values ( P = .002). Viscosity measures were compared to culture result, and those with low viscosity (thin consistency) had a higher likelihood of having a positive culture ( P = .048).
Conclusion
The device sensitivity and specificity for fluid detection were 94% or greater among interpretable waveforms (66% of those tested). Although this technology provides important information of the middle ear effusion presence and characteristic, further technological improvements are needed.
1
Introduction
Otitis media is an inflammatory process affecting the middle ear and mastoid spaces causing the development of a MEE. Persistence of middle ear fluid can result in hearing loss and recurrent otitis media with effusion (OME) . With these important clinical implications, accurate interpretation of middle ear contents proves to be an important determination. The presence of middle ear fluid is commonly assessed by pneumotoscopy and tympanometry. However, these methods have been shown to be limited in accuracy and are dependent on the practitioner’s experience, with correct interpretation in 76% and 83% or less of cases using pneumotoscopy and tympanometry, respectively . Therefore, additional technologies that may assist in determining the presence of MEE are warranted.
Ultrasound waves are high-frequency sound waves that are commonly and safely used to image soft tissues. Images are created by the amount of energy that is reflected back to the ultrasound transducer and are dependent on the acoustic impedances of the tissues that the waves traverse. The acoustic impedance of a tissue is in turn dependent on the amount of sound pressure to which it is exposed and its ability to transverse these vibrations. Therefore, tissues of different impedances will produce different characteristic ultrasound images. In theory, the ultrasonic properties of the middle ear space will be dependent on the presence and consistency of fluid. In this manner we aim to utilize ultrasound to characterize the fluid content of the middle ear as either no effusion, thin effusion, or thick effusion.
Ultrasound data may be displayed in multiple forms, where B-mode is the most commonly utilized method clinically. A-mode (amplitude modulation) is a simple method of displaying the amount of reflected energy as a vertical amplitude spike of Volts along a horizontal axis of time. A-mode ultrasound was utilized in this technology. To demonstrate, in the case that effusion is not present in the middle ear, ultrasonic energy reflects back to the probe from the tympanic membrane (TM) producing one recorded peak ( Fig. 1 ). The wave does not travel beyond the TM if there is no middle ear fluid to propagate it. On the other hand, if middle ear effusion is present, a fraction of ultrasound energy is reflected by the TM, while the remaining energy propagates through the middle ear fluid and reflects back to the probe from the bony structures of the inner ear to produce a second recorded peak. Configuration and amplitude of these peaks are dependent on the material’s acoustic impedance. Hence, the waveform may be used to interpret the presence and character of MEE as either thick (mucoid) or thin (serous or purulent).
Previous studies have demonstrated the use of ultrasonography to determine the presence of MEE . Most recently Discolo et al . from our institution used a single propagating wave A-mode ultrasound in a preliminary group of patients. The waveforms produced were interpreted by a single human interpreter. This method was difficult, clinically inefficient, and ill-suited for practical usage. To advance this technology to clinical use, three key design changes were made. In order to automate waveform interpretation, a computer algorithm was created to provide this assessment. Further, to increase accuracy, strength of the ultrasound probe was increased to 20 MHz. In the prior study, the probe required adjustment and aiming of the ultrasound wave to different areas of the TM in order to achieve an adequate waveform. To reduce this adjustment, 9 separate ultrasound emitting elements were placed into the current study’s designed probe and arranged in a 3 × 3 array on the convex surface of the probe tip. This unique design maximizes the likelihood that 1 of the 9 emitted ultrasound waves will be perpendicular to the reflective surface of the TM and reflect back to the probe for adequate interpretation . An appropriately aligned ultrasound wave will produce a characteristic wave form revealing the middle ear fluid content, as demonstrated in Fig. 2 .
With improved probe design to eliminate the need for human waveform interpretation, increased ultrasound strength, and added accuracy by addition of a unique 9 element ultrasound emitter, we aimed to assess the clinical capability of this novel device. Ideally, these improvements to the device allow its utility and feasibility as a clinically relevant tool to determine MEE presence and characteristics.
2
Methods
The institutional review board of the Cleveland Clinic, Cleveland, Ohio, approved this study which took place between October 2004 and July 2006. During this time, children between ages 6 months to 17 years with diagnosis of OME who were scheduled to undergo bilateral myringotomy with pressure equalization tube placement were invited to enroll. Children undergoing additional procedures on the same operative day, such as adenoidectomy or tonsillectomy, were included in enrollment. Ears with presence of a previously placed ear tube were excluded. Children were consecutively invited to enroll in the study and were not excluded on the basis of syndrome or other co-morbidities. The results of the ultrasonic probe analysis did not change the planned surgical procedure(s). Full parental informed consent and minor assent, when appropriate, was obtained for all subjects.
Children were anesthetized either by mask anesthetic or general anesthesia with endotracheal tube. All ears were then examined under microscopic visualization, and debris was appropriately removed from the external auditory canal (EAC). If testing was to be performed, 0.5 to 1.0 mL of sterile water at room temperature was placed into the EAC using a dropper. The ultrasound probe was placed into the EAC at about 0.5 to 1 cm from the TM. Minor adjustments of probe positioning were made in order to provide an adequate ultrasound signal. The ultrasound signal was displayed on a monitor screen. After appropriate signal acquisition, the water was suctioned from the EAC. The planned ear tube placement was performed on that side. If middle ear fluid was encountered, collection was attempted with a suction trap. If sufficient amounts of fluid were collected, it was sent for routine culture and analyzed for viscosity measurements. Viscosity measures were performed with a cone-and-plate viscometer (Brookfield Engineering, Middleboro, Massachusetts). The experimental procedure was repeated on the contralateral side. Duration of ultrasound probe assessment was on average less than one minute per ear, and the total delay in operation was less than five minutes for all cases. The patients were re-evaluated post-operatively in clinic or by phone call.
The scans obtained were stored on a secured hard drive in digital format and then analyzed by a laboratory-based computer system. Fourier analysis and a computer algorithm (designed by Biomec, Inc., Cleveland, Ohio and now licensed to ElectroSonics Medical, Inc, Cleveland, Ohio) were used to interpret the ultrasonic wave produced. The experimental setup further consisted of a custom nine-channel pulser/receiver (Biomec, now licensed to ElectroSonics Medical, Inc.) and digital acquisition system (Acquisition Logistic, Worthington, Ohio). These components were assembled on personal computer boards. The ultrasound probe was custom designed (Biomec, now licensed and under development by ElectroSonics Medical, Inc.) and is shown in Fig. 3 . In vitro testing has been performed and previously described .
Continuous measures distributions are described using means, standard deviations, and percentiles of interest. Sensitivity and specificity measures along with 95% confidence intervals for the ultrasonic probe were calculated. Comparisons of viscosity by other study conditions were performed using nonparametric Wilcoxon rank sum tests, due to group imbalance and potential non-normality of the viscosity distribution. P -values less than .05 were considered statistically significant.
2
Methods
The institutional review board of the Cleveland Clinic, Cleveland, Ohio, approved this study which took place between October 2004 and July 2006. During this time, children between ages 6 months to 17 years with diagnosis of OME who were scheduled to undergo bilateral myringotomy with pressure equalization tube placement were invited to enroll. Children undergoing additional procedures on the same operative day, such as adenoidectomy or tonsillectomy, were included in enrollment. Ears with presence of a previously placed ear tube were excluded. Children were consecutively invited to enroll in the study and were not excluded on the basis of syndrome or other co-morbidities. The results of the ultrasonic probe analysis did not change the planned surgical procedure(s). Full parental informed consent and minor assent, when appropriate, was obtained for all subjects.
Children were anesthetized either by mask anesthetic or general anesthesia with endotracheal tube. All ears were then examined under microscopic visualization, and debris was appropriately removed from the external auditory canal (EAC). If testing was to be performed, 0.5 to 1.0 mL of sterile water at room temperature was placed into the EAC using a dropper. The ultrasound probe was placed into the EAC at about 0.5 to 1 cm from the TM. Minor adjustments of probe positioning were made in order to provide an adequate ultrasound signal. The ultrasound signal was displayed on a monitor screen. After appropriate signal acquisition, the water was suctioned from the EAC. The planned ear tube placement was performed on that side. If middle ear fluid was encountered, collection was attempted with a suction trap. If sufficient amounts of fluid were collected, it was sent for routine culture and analyzed for viscosity measurements. Viscosity measures were performed with a cone-and-plate viscometer (Brookfield Engineering, Middleboro, Massachusetts). The experimental procedure was repeated on the contralateral side. Duration of ultrasound probe assessment was on average less than one minute per ear, and the total delay in operation was less than five minutes for all cases. The patients were re-evaluated post-operatively in clinic or by phone call.
The scans obtained were stored on a secured hard drive in digital format and then analyzed by a laboratory-based computer system. Fourier analysis and a computer algorithm (designed by Biomec, Inc., Cleveland, Ohio and now licensed to ElectroSonics Medical, Inc, Cleveland, Ohio) were used to interpret the ultrasonic wave produced. The experimental setup further consisted of a custom nine-channel pulser/receiver (Biomec, now licensed to ElectroSonics Medical, Inc.) and digital acquisition system (Acquisition Logistic, Worthington, Ohio). These components were assembled on personal computer boards. The ultrasound probe was custom designed (Biomec, now licensed and under development by ElectroSonics Medical, Inc.) and is shown in Fig. 3 . In vitro testing has been performed and previously described .
