Jin Ho Cho

Alteration of functional connectivity in tinnitus brain revealed by resting-state fMRI?: A pilot study

Abstract Objective: We report a case study on possible alterations in resting-state functional connectivity between the auditory network and non-auditory brain regions in tinnitus patients. Design: Independent component analyses were performed to evaluate coherent spontaneous activity in distributed brain networks. The resting-state functional connectivity scores between the right and left auditory networks were measured. Direct comparison of resting-state connectivity between tinnitus patients and controls was made using a two-sample t-test. Study sample: Four patients (three male, one female; mean age 45 ± 3.92 years) with chronic tinnitus lateralized to the left ear, and six age-matched controls (four male, two female; mean age 45 ± 2.76 years) participated in this case study. Results: The average resting-state functional connectivity (FC) score between the left and right auditory cortical regions was significantly lower in tinnitus patients than in controls (P < 0.05). Direct comparison between patients and controls showed that increased functional connectivity caused by tinnitus occurred predominantly in the left amygdala and in the dorsomedial prefrontal cortex. Conclusions: Our pilot study suggested that resting state functional magnetic resonance imaging (fMRI) could be useful to investigate possible alterations in resting-state neuronal activity between the auditory and non-auditory networks in tinnitus patients.

Functional activity mapping of rat auditory pathway after intratympanic manganese administration.

In the present study, we report a new method of manganese enhanced magnetic resonance imaging (MEMRI) using intratympanic (IT) manganese administration. We explore Mn²⁺ uptake from the middle ear cavity into the cochlea through mechanically gated ion channels of the hair cell and also functional auditory tract tracing without the use of excessive auditory stimuli for a long time period outside the scanner. After manganese administration in animals with normal hearing and unilateral deafness, T1-weighted MR images were obtained for up to 48 h with a 3.0 T MR imager. In normal rats, the mean signal-to-noise ratio (SNR) at each region of interest on the auditory pathway was significantly higher in the IT injection group than in the intraperitoneal (IP) injection group (P<0.05). Furthermore, the cochlea showed Mn²⁺ signal enhancement only in the IT injection group. In unilateral deafness rats, the IT injection of Mn²⁺ into the deaf-side middle ear cavity demonstrated signal enhancement in the cochlea but not in other auditory structures without axonal transport of Mn²⁺ along the auditory pathway. On the other hand, the IT injection of Mn²⁺ into the normal-side middle ear cavity demonstrated that the mean SNRs at the cochlea, cochlear nucleus, superior olivary complex, lateral lemniscus and inferior colliculus were significantly higher in the ipsilateral auditory pathway than in the contralateral pathway (P<0.05). For the IP injection group, the mean SNRs at each auditory structure, except the cochlea, increased bilaterally. In conclusion, the present work demonstrated the potential advantages of a new IT MEMRI over conventional systemic injection strategies in that (i) the functional auditory tract tracing initiated by the hair cell function is possible and (ii) the axonal transport of Mn²⁺ ions by trans-synaptic activity is possible without auditory stimulation for a long time period outside MR scanner.

Implantable microphone with acoustic tube for fully implantable hearing devices

Fully Implantable hearing devices consist of a microphone that is implanted under the human skin. However after the implantation, the gain characteristics of the microphone are attenuated at the high frequencies because of the sound filtering effect of the skin and tissue. To solve this problems, we proposed an implantable microphone with an acoustic tube, which generates a resonance effect between the diaphragm and the acoustic transducer inside a case. By performing several experiments in water, it has been confirmed that the frequency response of the implantable microphone at high frequencies can be improved by use of the acoustic tube.

Intratympanic manganese administration revealed sound intensity and frequency dependent functional activity in rat auditory pathway

The cochlear plays a vital role in the sense and sensitivity of hearing; however, there is currently a lack of knowledge regarding the relationships between mechanical transduction of sound at different intensities and frequencies in the cochlear and the neurochemical processes that lead to neuronal responses in the central auditory system. In the current study, we introduced manganese-enhanced MRI (MEMRI), a convenient in vivo imaging method, for investigation of how sound, at different intensities and frequencies, is propagated from the cochlear to the central auditory system. Using MEMRI with intratympanic administration, we demonstrated differential manganese signal enhancements according to sound intensity and frequencies in the ascending auditory pathway of the rat after administration of intratympanic MnCl2.Compared to signal enhancement without explicit sound stimuli, auditory structures in the ascending auditory pathway showed stronger signal enhancement in rats who received sound stimuli of 10 and 40 kHz. In addition, signal enhancement with a stimulation frequency of 40 kHz was stronger than that with 10 kHz. Therefore, the results of this study seem to suggest that, in order to achieve an effective response to high sound intensity or frequency, more firing of auditory neurons, or firing of many auditory neurons together for the pooled neural activity is needed.

Functional mapping of the auditory tract in rodent tinnitus model using manganese-enhanced magnetic resonance imaging

Animal models of salicylate-induced tinnitus have demonstrated that salicylate modulates neuronal activity in several brain structures leading to neuronal hyperactivity in auditory and non-auditory brain areas. In addition, these animal tinnitus models indicate that tinnitus can be a perceptual consequence of altered spontaneous neural activity along the auditory pathway. Peripheral and/or central effects of salicylate can account for neuronal activity changes in salicylate-induced tinnitus. Because of this ambiguity, an in vivo imaging study would be able to address the peripheral and/or central involvement of salicylate-induced tinnitus. Therefore, in the present study, we developed a novel manganese-enhanced magnetic resonance imaging (MEMRI) method to map the in vivo functional auditory tract in a salicylate-induced tinnitus animal model by administrating manganese through the round window. We found that acute salicylate-induced tinnitus resulted in higher manganese uptake in the cochlea and in the central auditory structures. Furthermore, serial MRI scans demonstrated that the manganese signal increased in an anterograde fashion from the cochlea to the cochlear nucleus. Therefore, our in vivo MEMRI data suggest that acute salicylate-induced tinnitus is associated with higher spontaneous neural activity both in peripheral and central auditory pathways.

Liver extraction in the abdominal CT image by watershed segmentation algorithm

In this paper, we proposed a liver extracting procedure for computer aided liver diagnosis system. An extraction of liver region is difficult due to interferences of other organs in the abdominal CT image. For this reason, liver region is extracted in ROI. ROI is selected by using the window for measuring the distribution of liver region’s Hounsfield Unit in abdominal CT image. The distribution is measured by using an existential probability of liver’s value in the window. If the probability of any window exceeded 50%, it would be assigned to ROI. Actually, liver region is not clearly discerned from the adjacent organs as muscle, spleen, and pancreas in abdominal CT image. Liver region is extracted by the watershed segmentation algorithm which is effective in this situation. This segmentation algorithm is very sensitive to the slight variance of contrast. So it generally produces over-segmentation regions. For optimal segmentation these regions are required to merge into the significant regions. Finally, a liver region is selected and extracted by prior information based on anatomic information.

In vivo evaluation of mastication noise reduction for dual channel implantable microphone.

Input for fully implantable hearing devices (FIHDs) is provided by an implantable microphone under the skin of the temporal bone. However, the implanted microphone can be affected when the FIHDs user chews. In this paper, a dual implantable microphone was designed that can filter out the noise from mastication. For the in vivo experiment, a fabricated microphone was implanted in a rabbit. Pure-tone sounds of 1 kHz through a standard speaker were applied to the rabbit, which was given food simultaneously. To evaluate noise reduction, the measured signals were processed using a MATLAB program based adaptive filter. To verify the proposed method, the correlation coefficients and signal to-noise ratio before and after signal processing were calculated. By comparing the results, signal-to-noise ratio and correlation coefficients are enhanced by 6.07dB and 0.529 respectively.

Measurement of stapes vibration in Human temporal bones by round window stimulation using a 3-coil transducer

Round window placement of a 3-coil transducer offers a new approach for coupling an implantable hearing aid to the inner ear. The transducer exhibits high performance at low-frequencies. One remarkable feature of the 3-coil transducer is that it minimizes leakage flux. Thus, the transducer, which consists of two permanent magnets and three coils, can enhance vibrational displacement. In human temporal bones, stapes vibration was observed by laser Doppler vibrometer in response to round window stimulation using the 3-coil transducer. Coupling between the 3-coil transducer and the round window was connected by a wire-rod. The stimulation created stapes velocity when the round window stimulated. Performance evaluation was conducted by measuring stapes velocity. To verify the performance of the 3-coil transducer, stapes velocity for round window and tympanic membrane stimulation were compared, respectively. Stapes velocity by round window stimulation using the 3-coil transducer was approximately 14 dB higher than that achieved by tympanic membrane stimulation. The study shows that 3-coil transducer is suitable for implantable hearing aids.

Necessity of human middle ear characteristics at design of piezoelectric type round window vibrator

A new implantable hearing device, which vibrates round window (RW) of human cochlea, has been widely developed in the world. This device has been remarkable owing to compensate conductive hearing loss of hearing impaired people which was damaged their ossicles. Recently, piezoelectric actuator has been applied to RW drive type hearing devices because of flat and excellent vibrational characteristics at audible frequency range. However, in case of the RW vibration, patients cannot hear natural sound because the auditory pathway dont include middle ear. And human middle ear has resonant characteristics. Thus, piezoelectric vibrators need the resonance corresponding to the middle ear characteristics for hearing natural sound.

The Design of Temporal Bone Type Implantable Microphone for Reduction of the Vibrational Noise due to Masticatory Movement

Abstract A microphone for fully implantable hearing device was generally implanted under the skin of the temporal bone. So, the implantedmicrophone’s characteristics can be affected by the accompanying noise due to masticatory movement. In this paper, the implantablemicrophone with 2-channels structure was designed for reduction of the generated noise signal by masticatory movement. And anexperimental model for generation of the noise by masticatory movement was developed with considering the characteristics of humantemporal bone and skin. Using the model, the speech signal by a speaker and the artificial noise by a vibrator were suppliedsimultaneously into the experimental model, the electrical signals were measured at the proposed microphone. The collected signals wereprocessed using a general adaptive filter with least mean square(LMS) algorithm. To confirm performance of the proposed methods, thecorrelation coefficient and the signal to noise ratio(SNR) before and after the signal processing were calculated. Finally, the results werecompared each other.