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Patients: Prospective study was conducted on 140 patients presented by ventriculomegaly or dilated CSF spaces.
The patients were categorized into 7 groups according to the primary site of obstruction,
type of the lesion or malformation.
Conventional MRI imaging with 3D –CISS were included routinely as part of the examination followed by dynamic phase contrast sequence (magnitude and phase contrast cine images) that was tailored according to the suspected site of obstruction or malformation.
Time-SLIP sequence was used in selected cases,
mainly to enforce visualization of communication between examined ventricles or CSF spaces.
MR Imaging Technique:
• Conventional study including axial TSE T1,
axial FLAIR and axial,
sagittal,
and coronal TSE T2.
• 3D-constructive interference in the steady state applied in the sagittal plane to cover the entire ventricular region and the fourth ventricular exits.
It is a high resolution heavy T2 gradient-echo sequence providing a combination of high signal intensity levels and extremely high spatial resolution (compared to conventional images).
This allows identification of fine anatomic details of CSF pathways.
Patients with communicating hydrocephalus secondary to inflammation or haemorrhage have an obstructive component that may benefit from endoscopic division of these membranes.
This technique could demonstrate the membranes within the prepontine and basal cisterns as well as its location,
number,
and extent.
[4]
Disadvantage: poor tissue distinction within the brain parenchyma.
However,
this technique is aimed at tissue/fluid distinction for which it is highly sensitive and specific.
• Cine- Phase contrast (PC) CSF flow imaging technique: (Figure 1)
Cardiac gated (using pulse oximeter) flow sensitive sequence depending upon the application of two phase encoding pulses in opposite sensitization directions.
When subtracting the acquired two data sets,
the signal contribution from stationary nuclei is eliminated and only flowing nuclei are visible.
For qualitative and quantitative assessment of CSF flow,
two PC sequences in two planes were acquired:
• Midline high-resolution sagittal.
• According to the anatomic region,
the axial-oblique,
coronal oblique,
or sagittal-oblique cine PC was obtained with the same parameters except for the velocity encoding (VENC),
which is set to the through plane taking into account the expected velocity of flow in every case in order to avoid aliasing artifact.
It should always be chosen to exceed the expected maximum velocity within the selected region of interest (ROI).
N.B Velocity encoding (Venc) is given in centimeters per second.
It determines the highest and lowest detectable velocity encoded by a PC sequence.
Two sets of images for each plane are then evaluated:
1- Magnitude image ( magnitude of difference signal)
§ The background is totally suppressed (dark color).
§ Flow appears as bright signal (regardless of its direction).
2- Phase image ( phase of difference signal)
§ The background is mid-grey.
§ Flow has different signal according to its direction (forward diastolic flow is bright,
while backward systolic flow is dark).
Time-spatial labeling inversion pulse (time-SLIP) imaging technique:[3] (Figure 2)
An application of spin-labeling methods to CSF flow.
Spin-labeling methods were introduced in the late 1980s,
it has been used for vascular imaging by selectively saturating the spins of the blood in vessels to a given region.
A similar but unique approach can be used to visualize the bulk and turbulent flow of CSF in the CNS over several cardiac cycles using CSF as an internal tracer.
A series of single-shot images with incremental inversion recovery delay times are acquired using a 2D Fast Advanced Spin Echo (FASE) sequences.
A nonselective inversion recovery was applied to null the background signals and a labeling-selective pulse was then applied to observe the movement of labeled "tagged" CSF.
Tagged CSF will appear bright in contrast to dark "untagged" CSF and background.
Time-SLIP technique enables the labeling of a variable volume of CSF in any orientation and in any place in the central nervous system.
Time-SLIP CSF imaging is purely qualitative; it allows visualization of the linear and turbulent movement of CSF,
communication between two CSF spaces and flow through the aqueduct or surgically created stoma.[5]