High-Resolution PET/CT Assesses Brain Stem Function

Positron emission tomography/computed tomography (PET/CT) imaging of the inferior colliculus (IC) can help evaluate cochlear implant sustainability in patients with hearing impairment, claims a new study.

Researchers at the University of Freiburg Medical Center (IMS; Germany) conducted a study in 13 patients with asymmetric hearing loss, who underwent ¹⁸F-FDG PET/CT imaging. The scans were reviewed by two experienced readers who examined regional glucose metabolism in the IC and the primary auditory cortex (PAC), which is known to undergo metabolic changes following external acoustical input and transformation to neuronal signals from the cochlea hair cells to the auditory nerve fibers.

The readers rated glucose metabolism as none, mild, moderate, or strong asymmetry to the left or to the right for IC and PAC separately, and determined the effect of the duration of hearing impairment. The results showed that regional glucose metabolism of both the IC and PAC was significantly reduced on the contralateral side of the poorer-hearing ear, as compared to the ipsilateral side. Longer duration of hearing impairment was also associated with a higher metabolism on the contralateral PAC. Duration of hearing impairment did not predict regional glucose metabolism for the ipsilateral PAC or either side of the IC. The study was published in the March 2020 issue of The Journal of Nuclear Medicine.

“Previous studies suggest that the association between longer duration of hearing impairment and higher glucose metabolism indicates cortical reorganization. In bilateral deaf patients this has been shown to lessen the benefits of cochlear implants,” said lead author Iva Speck, MD. “Prediction of a successful cochlear implant outcome might benefit from improved imaging with fully digital PET/CT systems, as large parts of the auditory system, including small brain nuclei such as the IC, can be assessed for preoperative patient characterization.”

In a normal ear, sound vibrations in the air lead to resonant vibrations of the basilar membrane inside the cochlea. The movement of hair cells, located all along the basilar membrane, creates an electrical disturbance that can be picked up by the surrounding nerve cells, allowing the brain to interpret the nerve activity and determine what sound frequency is being heard. The cochlear implant bypasses the hair cells and stimulates the cochlear nerves directly using electrical impulses. This allows the brain to interpret the frequency of sound as it would if the hair cells of the basilar membrane were functioning properly.

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University of Freiburg Medical Center