The Institute of Imaged-Guided Surgery (IHU Strasbourg) has two clinical MRIs, one with a 3T (Teslas) magnetic field used for diagnosis, the other with a magnetic field of 1,5T (Teslas) used for the interventional (Pre / per / postoperative).
Cholangiopancreatography by MRI (or bili-MRI) accounts for about 25% of MRI examinations at the IHU and is used for the diagnosis of pathologies affecting the bile ducts (lithiasis pathology, cholangitis, tumoral pathology of the bile ducts) and the pancreas (search for a causal pathology to pancreatitis (calculus), ductal pathology, ductal study in tumor pathology). It can be done in preoperative context (cholecystectomy) for research of an associated calculus in the bile ducts, or for an anatomical analysis of the bile ducts (possible anatomical variants ...).
The reference for the visualization of the biliary and pancreatic ducts is a very heavily weighted T2 3D SPACE sequence. A 3D volume is obtained in which they appear in white, and the projection of this volume makes it possible to visualize the entire tract. This sequence is relatively long and needs a breathing-synchronized acquisition. The time of acquisition is then very variable from one patient to another (4 to 8 minutes). This extended acquisition time in addition to the variability of rhythm and respiratory profile can lead to artefacts on the images (blur effect). These are the limits of the respiratory synchronization that triggers acquisition by referring to the position of the liver dome which is not perfectly reproducible from a breathing cycle to the other, potentially degrading the appearance of the bile ducts and the reliability of the diagnosis.
A solution that makes it possible to reduce and / or standardize the acquisition time as well as to limit artefacts is to use an accelerated sequence. Such a sequence is available in France recently in the form of WIP Siemens (Work In Progress: sequence in test phase at manufacturer to be marketed in the short or medium term on clinical machines). It incorporates a Compressed Sensing (CS) acquisition scheme allowing the acquisition of a 3D sequence similar to the usual sequence by drastically reducing the acquisition time, the sequence CS-SPACE. This sequence exists in two forms:
* An ultra-rapid sequence acquired in apnea
* An accelerated sequence but remaining synchronized with the breath. This sequence has been shown to provide comparable, if not better, results to those obtained with the usual sequence in terms of image quality and visualization of structures, but these results were only obtained at 3T and for a reduced cohort of patients.
A lot of work is done today in the field of MRI to reduce the time of sequence acquisition. Accelerated acquisition schemes like Compressed Sensing remain marginal but are set to become the norm in the long term. The use of the sequence CS-SPACE at the IHU therefore enters into this perspective of reducing examination times.
The study carried out here on a large number of patients, with two different magnetic fields, applied routinely for diagnosis or anticipation of surgery, could be used by the community of radiologists, hepatogastroenterologists and also digestive surgeons Hepatobiliary.
