Cerebral arterial asymmetries in the neonate

Materials Ultrasound measurements. Transcranial Doppler ultrasonography is a non-invasive, reliable, inexpensive technique for examining neonatal parenchyma, vascular structures, and arterial hemodynamics. Transcranial cerebrovascular imaging will be performed using the portable General Electric EPIQ 9 ultrasound unit stored in the neonatal unit of the Royal Women’s Hospital, Melbourne. Imaging software. Post-processing of the ultrasound data will be conducted using SYNAPSE (PACS) 64-bit imaging software. Revised Edinburgh Handedness Inventory. Parental handedness will be assessed with a revised version of the Edinburgh Handedness Inventory. Procedure Transcranial Doppler Ultrasound Assessment. Ultrasound assessment will take place at a postnatal age of 1 to 7 days. Standard medical procedure will be followed during the analysis which will be performed by the principal investigator. All infants will undergo 10 minutes of supine rest on a clean cot (sourced from the neonatal unit) in the ultrasound room. This room is sound proofed and will ensure that the testing environment will be without auditory or visual distractions. Parents will accompany their infant into the ultrasound room and will be instructed to have fed the infant prior to the scanning session. Parents will be situated at the head of the cot, behind the principal investigator so as not to distract the infant. Infant behavioural state will be recorded. If an infant becomes distressed, an attempt will be made to soothe the infant using methods that the parent would normally use. Prior to the hemodynamic analysis, an initial two-dimensional B mode Grey-Scale Imaging screening will be performed through the anterior fontanelle in the sagittal plane for lenticulostriate artery identification. The lenticulostriate arteries will then be screened for the presence of any pathology. An C3-10, 6 MHz curvilinear probe with an insonation angle close to 0° will be used. Further settings will include a small sample volume of 1 mm with a low velocity wall filter of 4cm-s to reduce noise. Two lenticulostriate arties in each cerebral hemisphere will be chosen for further scanning based on the clarity of the image and orientation of the vessel (i.e. the two arteries on each side that are most oriented in the vertical plane). Once the arteries are identified, B-Flow Imaging will be activated and the probe will be moved so at to optimise the visualisation of one of the selected vessels. This mode uses non-Doppler technology to display true hemodynamics and enables direct visualization of the vessel without the limitations of Doppler. These images are clear and unaffected by gain. Dual-view Imaging will then be initiated to replicate the image into two identical left and right images. The left image will be activated and flow measurements will be performed on the longitudinal sections of the selected artery, prior to its first bifurcation, with Pulsed Wave Doppler Mode. Peak systolic velocity (PSV), end-diastolic velocity (EDV), and heart rate measures will be obtained from homogeneous blood flow wave patterns over five consecutive cardiac cycles. Three diameter measures will be taken in the exact location of the artery in the corresponding right B-Flow image. The procedure will then be repeated for the second unilateral and two contralateral lenticulostriate arteries in a randomized order. Using a transtemporal approach, the transducer will be placed on the left temporal bone, below the zygomatic arch, to locate the proximal portion of the middle cerebral artery (horizontal segment that lies between the circle of Willis and branches of the lenticulostriate arteries). An initial two-dimensional B mode Grey-Scale Imaging screening will be performed through the temporal window for the identification and screening of the left middle cerebral artery. Using the same probe, ultrasound settings, and imaging protocol, B-Flow and Pulsed Wave Doppler will be utilised in dual-view imaging to record arterial diameter and peak systolic velocity (PSV), end-diastolic velocity (EDV), and heart rate measures of the proximal portion of the middle cerebral artery. The distal portion of the middle cerebral artery (distal to the origins of the lenticulostriate arteries) approximately 10 mm from the middle cerebral artery bifurcation/trifurcation will be located and haemodynamic and diameter measures will be repeated on the left and right side in a randomized order. At this distance the vessel will have a uniform diameter and will require minimal angle correction. In any necessary instance, an angle of correction will be performed if the angle of incidence is greater than 15° to ensure the transducer remains parallel to the vector of blood flow and accurate measures are obtained. Proximal haemodynamic measures reflect the general haemodynamic status of the basal ganglia, posterior limb of the internal capsule and insular and lateral surfaces of the cortex. Distal measures reflect neocortical flow. Differences between proximal and distal measures will be calculated offline to determine subcortical flow. All images will be stored on optical disc for off-line analysis using SYNAPSE (PACS) 64-bit imaging software and will be averaged across the waveforms for each infant. Infant Head Posture Assessment. The naturalistic observation of infant head posture will occur after the transcranial Doppler ultrasound analysis. This ensures that haemodynamic analyses are conducted blind to participant laterality. While lying in the cot, the infant’s head will be held gently in a midline position and maintained in this position until no lateralised pressure is experienced against the examiner’s hands. The head will then be released. Once the infant’s head posture deviates from the midline, a five minute period of observation will begin. During this period, the head posture together with the infant’s ongoing behavioural state will be recorded on a check sheet in consecutive 30 second intervals. This five minute observation period will be filmed with a GoPro Hero4 recording device (out of the line of sight of the infant) so as to eliminate any subjective bias in scoring. Reliability of head posture scores will be assessed with a third party during data analysis. Each data collection session, including the arterial scan, neonatal head posture assessment, and assessment of parental handedness, will take 30 to 45 minutes.