Study design
This prospective trial was implemented in the pediatric neurology department of our tertiary care center between January 2014 and December 2014. The approval of the local Institutional Review Board (2014/208) was obtained prior to the study. Parents gave written informed consent, and the study strictly adhered to the principles announced in the Helsinki Declaration.
A total of 137 participants were included in the study. To reduce the movement artifact in children, 50 mg/kg chloral hydrate was administered orally to induce sleep (n = 39). A sedative was not used in participants who cooperated (n = 98). MRI indications are headache (n = 19), epilepsy (n = 15), high fever (n = 14), dizziness (n = 13), gait disturbance (n = 13), visual disturbance (n = 12), hearing loss (n = 11), severe nausea and vomiting (n = 11), neuromotor retardation (n = 10), loss of strength in extremities (n = 10), and convulsion (n = 9), respectively. Participants did not have any systemic diseases or cranial pathologies nor were they on any medications. All MRI examinations of the day, the same hour, were made in the morning. PC-MR images were of diagnostic quality in all cases, and no cases were excluded from this study. In the neonatal age group, MRI cases in which brain pathology was detected and continuous drug users were excluded from the study.
HC was measured by passing the tape just above the participant’s eyebrows and round to the occipital pole at the back of the head [11].
Magnetic resonance imaging
All participants routinely underwent T2-weighted and fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI) on the axial plan and PC-MRI. Quantitative evaluation of CSF flow was made with 1.5 Tesla MRI (Magnetom Avanto, Siemens Healthcare, Erlangen, Germany). Images were obtained on the axial plane using standard head coil for 2D Q FLOW phase contrast MR angiography technique.
Duration of PC-MRI was approximately 5 min for every participant. Former images were obtained on midline in sagittal, coronal, and axial T1 views. Subsequently, average modulus (rephase), the magnitude of the complex difference (magnitude), and directional phase difference (phase) images were obtained on a semi-axial plane perpendicular to the cerebral aqueduct in the sagittal axis. Details of axial MRI images were as follows: TR: 31.25 ms, TE: 8.06 msn, slice thickness: 5.5 mm, NSA: 1, FOV: 16 × 10 cm, matrix: 128 × 256, and deviation angle: 10 degrees. Cardiac phase cuts were taken that varied between 14 and 30 according to the heart rate. Cardiac triggering was made prospectively with finger plethysmography. Velocity encoding (Venc) of PC-MRI was set at 20 cm/s. The craniocaudal flow was defined as “positive,” and the caudocranial direction was defined as “negative.”
Analysis of magnetic resonance images
ARGUS is an image analysis program that evaluates ventricular volume, blood, and CSF flows quantitatively in cine mode. This program measures average forward and reverse flows and average and maximum flow velocities in major and minor vessels and in aqueducts with a regular flow. As seen in Figs. 1 and 2, images obtained via FLASH through in-plane and in-plane sequences were transferred to an ARGUS image analysis program (ARGUS, Siemens Medical Solutions, Erlangen, Germany) on a Leonardo Workstation (Magnetom Avanto, Siemens Medical Solutions, Erlangen, Germany). Phase, rephase, and magnitude images were obtained in semi-axial and sagittal planes (Figs. 3 and 4). Initially, CSF flow was visually evaluated in all participants. For phase and magnitude images, flow with a high signal intensity was observed in a cerebral aqueduct in phase and magnitude views, whereas caudal flow had low signal intensity. Because contrast is more prominent for the CSF flow in aqueduct in phase and magnitude images, regions of interest (ROIs) were placed in a circular shape for each section (Fig. 5). On semi-axial images that occupy the whole aqueduct, velocity (cm/s) and flow (ml/s) values and a velocity–flow curve were obtained (Figs. 1 and 2), and average CSF flow was calculated.
Participants that required anesthesia underwent PC-MRI under sedo-analgesia, whereas no additional preparations were carried out for participants that did not require anesthesia. Instructions were given to avoid deep inspiration or expiration during imaging.
Eddy flows resulted in distortion of gradient profile and adversely affected the accuracy of encoded images. To minimize the impact of eddy flows, ROIs should be maintained as small as possible [12]. In aqueducts with a small diameter, the likelihood of error increases due to noise and poor contrast.
Statistical analysis
Analysis of our data was made with Statistical Package for Social Sciences program (SPSS Inc., Chicago, IL, USA), version 17.0. Absolute values were considered for rates. The peak velocity, mean velocity cranial volume, caudal volume, net volume passing through aqueductus cerebri in a cardiac cycle, peak velocity parameters and average aqueductus cerebri area were compared according to age, gender, HC, and BMI groups. Quantitative variables were expressed as mean ± standard deviation or median-interquartile range. The normal distribution of quantitative variables was evaluated using the Shapiro–Wilk test. Kruskal–Wallis test was used to determine whether there was a significant difference between the mean scores of two dependent groups of one or more dependent variables. The variance analysis was used to test hypotheses about whether the difference between two or more group averages is meaningful. The Mann–Whitney U test was applied to test whether the values obtained for two independent groups differed significantly from each other. The median values of the groups were compared. Spearman rank correlation test was used to evaluate the strength and direction of the linear relationship between two continuous variables. The level of statistical significance was set at p < 0.05.