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. 2024 Nov 22;19:635. doi: 10.1186/s13019-024-03135-6

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© The Author(s) 2024

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Fig. 3 — Fast Fourier transform (FFT) analysis of intraoperative transit-time flow measurement (TTFM) waveform [15]. As a parameter representing gradual decrease in power of the harmonics of the fundamental frequency, the FFT ratio is calculated as F₀/H₁, where F₀ is a power of the fundamental frequency and H₁ is a power of the first harmonic