Orbital Doppler ultrasonography (ODUS)

Patients in whom brain death was suspected and the diagnostic procedure was initiated underwent ODUS .ODUS were performed during the apnoea test and the first neurological examination. At the second neurological examination at 12 hours, ODUS were repeated.

During measurement, Doppler settings were adjusted to detect low flow and the smallest available Doppler gate was used for all ODUS examinations. The imaging probe position for ODUS was used transversely and axially, and mean values were recorded. ODUS 10-18 MHz linear probe was used.

Orbital artery Doppler ultrasound (ODUS) ODUS measurements: T1; when brain death testing started; T2; 12 hours after the first measurement, T3; before CT angiography, T4; after CT angiography Peak systolic velocity (PSV) cm/s , end-diastolic velocity (EDV) cm/s measurement results. The absence of diastolic flow, reverse diastolic flow (oscillatory flow), and resistive index >1 were considered brain death.

The resistive index (RI) is a calculated flow parameter in ultrasound, derived from the maximum, minimum, and mean Doppler frequency shifts during a defined cardiac cycle. Along with the pulsatility index (PI), it is typically used to assess the resistance in a pulsatile vascular system.resistive index >1 were considered brain death.

RI measurements: T1; when brain death testing started; T2; 12 hours after the first measurement, T3; before CT angiography, T4; after CT angiography .

RI = (PSV - EDV) / PSV

PSV = peak systolic velocity and EDV = end-diastolic velocity.

Transcranial Doppler ultrasound (TDUS) ultrasonography involves the use of a low-frequency (≤2 MHz) transducer, placed on the scalp, to insonate the basal cerebral arteries through relatively thin bone windows and to measure the cerebral blood flow velocity (CBFV) normal flow: mean = 55cm/sec. mild: > 120cm/sec. moderate: > 160cm/sec. s