Optimization of the MRI protocol for imaging the sacral plexus and its branching nerves

The pediatric urologist is often confronted with children suffering from
dysfunctioning of the bladder. When this dysfunctioning of the bladder is
neurogenic, this is often caused by congenital anomalies as spina bifida,
sacral agenesis or other congenital anomalies of the spinal cord or sacrum. The
innervation of the bladder in these children is disturbed, and causes problems
with the storage of urine or emptying of the bladder. Long-term bladder
dysfunctioning can lead to severe deterioration of the bladder and upper
urinary tract function. The hypothesis of this study is that there exist
variations of the sacral plexus that lead to the complicated incontinence in
children with spinal or sacral congenital anomalies. More insight in the
disturbed innervation of the bladder in these children is necessary for better
understanding and a better treatment of these congenital anomalies. This can
result in improved quality of life of these children.

MRI of the sacral plexus and its branching nerves, that are responsible for
innervation of the bladder, is a challenge. This is because of the close
anatomical relationship of the nerves and surrounding tissues, like muscles and
veins, which have similar relaxation times as the nerves. With
diffusion-weighted imaging these problems can be overcome and the peripheral
nerves can be visualized over long trajectories. First results are promising,
but optimization of the parameter settings is necessary. By applying DWI
acquisitions in multiple directions, the random movement of water molecules can
be measured. In nerves this movement of water molecules is directed along the
fibers, which makes fiber tracking possible. This so called diffusion tensor
imaging (DTI) is also an appropriate sequence for visualizing the nerves of the
sacral plexus. However, the spatial resolution of DWI and DTI is low. Recently,
3D isotropic sequences are developed, with a voxelsize down to 0.5 mm3 at 3.0 T
and an acceptable acquisition time. A multi-echo data image combination (MEDIC)
sequence will be used. This gradient-echo (GE) sequence uses muliple echoes for
multiple aqcuisitions. This leads to a high signal to noise ratio in the same
acquisition time. Also 3D turbo spin echo (TSE) with variable flip angles is
such a new 3D sequence. TSE is used a lot in daily clinical routine, but TSE at
higher field strengths is limited to the specific absorption rate (SAR). By
first bringing the protons in a pseudo steady state, high signal intensities
can be acquired with the variable flip angles for the whole k-space filling.
High signal intensities are obtained, while the SAR can be reduced with 70%.

For optimization of the MRI sequences we choose to set up a subject study in
healthy adult volunteers, before we want to depict the sacral plexus of the
children with it.

The aim of this research is to study the MRI-sequence with the best parameter
settings for the most optimal image quality to visualize the sacral plexus and
its branching nerves. Diffusion-weighted imaging, diffusion tensor imaging,
3D-GE-MEDIC and TSE with variable flip angles will be compared.

This will be a unicenter, cross-sectional study (timeschedule: 3 months). 10
volunteers will undergo a MRI-scan in a 3.0 T MRI-scanner. Diffusion-weighted
images, diffusion tensor images, 3D-GE-MEDIC images and 3D TSE with variable
flip angles images will be made. The MRI-images will be analysed.

Every volunteer will undergo 1 MRI-scan. The MRI-scan will last approximately
55 minutes, with the volunteer lying still. The MRI-scan is completely
non-invasive, no contrast agent is necessary and it is without any
side-effects.