In resistive index calculation, which formula defines RI?

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Multiple Choice

In resistive index calculation, which formula defines RI?

Explanation:
Resistive index measures how pulsatile the blood flow is and reflects downstream resistance. It uses the peak systolic velocity (PSV) and the end-diastolic velocity (EDV) to quantify this pulsatility as a ratio. The correct formula takes the difference between PSV and EDV and divides by PSV, giving RI = (PSV − EDV) / PSV. This creates a value between 0 and 1, increasing as resistance rises (EDV drops relative to PSV). For example, with PSV 100 and EDV 20, RI = (100−20)/100 = 0.8, indicating higher resistance. Using PSV/EDV or EDV/PSV or simply PSV − EDV does not normalize the measure to PSV, fails to consistently reflect physiologic resistance, and can yield misleading values.

Resistive index measures how pulsatile the blood flow is and reflects downstream resistance. It uses the peak systolic velocity (PSV) and the end-diastolic velocity (EDV) to quantify this pulsatility as a ratio. The correct formula takes the difference between PSV and EDV and divides by PSV, giving RI = (PSV − EDV) / PSV. This creates a value between 0 and 1, increasing as resistance rises (EDV drops relative to PSV). For example, with PSV 100 and EDV 20, RI = (100−20)/100 = 0.8, indicating higher resistance. Using PSV/EDV or EDV/PSV or simply PSV − EDV does not normalize the measure to PSV, fails to consistently reflect physiologic resistance, and can yield misleading values.

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