Browsing by Author "Çelik, H."
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Item Open Access COVID-19 Detection from respiratory sounds with hierarchical spectrogram transformers(Institute of Electrical and Electronics Engineers , 2023-12-05) Aytekin, Ayçe İdil; Dalmaz, Onat; Gönç, Kaan; Ankishan, H.; Sarıtaş, Emine Ülkü; Bağcı, U.; Çelik, H.; Çukur, TolgaMonitoring of prevalent airborne diseases such as COVID-19 characteristically involves respiratory assessments. While auscultation is a mainstream method for preliminary screening of disease symptoms, its util ity is hampered by the need for dedicated hospital visits. Remote monitoring based on recordings of respi ratory sounds on portable devices is a promising alter native, which can assist in early assessment of COVID-19 that primarily affects the lower respiratory tract. In this study, we introduce a novel deep learning approach to distinguish patients with COVID-19 from healthy controls given audio recordings of cough or breathing sounds. The proposed approach leverages a novel hierarchical spectro gram transformer (HST) on spectrogram representations of respiratory sounds. HST embodies self-attention mech anisms over local windows in spectrograms, and window size is progressively grown over model stages to capture local to global context. HST is compared against state-of the-art conventional and deep-learning baselines. Demon strations on crowd-sourced multi-national datasets indicate that HST outperforms competing methods, achieving over 90% area under the receiver operating characteristic curve (AUC) in detecting COVID-19 cases.Item Open Access Evaluation of internal MRI coils using ultimate intrinsic SNR(John Wiley & Sons, 2004) Çelik, H.; Eryaman, Y.; Altıntaş, A.; Abdel-Hafez, I. A.; Atalar, ErginThe upper bounds of the signal-to-noise ratio (also known as the "ultimate intrinsic signal-to-noise ratio" (UISNR)) for internal and external coils were calculated. In the calculation, the body was modeled as a dielectric cylinder with a small coaxial cylindrical cavity in which internal coils could be placed. The calculated UISNR values can be used as reference solutions to evaluate the performance of internal MRI coils. As examples, we evaluated the performance of a loopless antenna and an endourethral coil design by comparing their ISNR with the UISNR.