4 flow acquisitions based on the 2D cine phase contrast sequence (present on all MRI systems) will be performed.

This sequence requires a cardiac synchronization by a plethysmograph put on the patient's finger.

32 cardiac phases are reconstructed per acquisition. The processing of the flow MRIs and the analysis of the flow curves of the LCS and blood during the cardiac cycle will be performed using the Amiens software.

Parameters measured via flow MRI are:

- Cerebral vascular flow, intracranial LCS dynamic volume, extracranial LCS dynamic volume

The test will be performed will include:

• Inserting a needle into the lumbar space, Ommaya reservoir or valve pre-chamber, as appropriate
• Connect the needle to the pressure transducer via saline filled manometer lines connected via a 3-way valve. The other end of the 3-way connection will be connected to a saline
• Recording of the opening pressure for 10 minutes
• The infusion test is terminated either when the pressure stabilizes again on a new plateau, or when the average pressure exceeds 40 mmHg, or in case of adverse effects or symptoms such as headache, nausea/vomiting or visual disturbances.
• At the end of the test, a depletion of 30 to 50 mL of CSF will be performed.
• The pressure recording during the test is then used to calculate the parameters of the mechanical properties of the CSF circulation and reported to the neurosurgeon ordering the test.

The MRICP parameter will combine the CSF pressure and CSF flows. MRICP parameter results of the interaction of intracranial pressures and fluids in order allowing to obtain information on the cerebral biomechanics.

Accumulation of CSF from the brain to another body cavity is neccessary to be determined.