Evaluation of the FOCUS Diffusion's Added Clinical Value Compared to Conventional MRI

This diffusion sequence has shown its usefulness in pancreatic pathology in the detection and characterization of focal pancreatic lesions, particularly for neuroendocrine tumors, the evaluation of chronic and autoimmune pancreatitis or the early detection of malignant transformation of certain high-risk cystic lesions. The diffusion sequence usually performed is called "wide field" because it covers the entire abdomen. The radiologist can thus analyse the neighbouring organs and in particular the liver, which makes it essential when a pancreatic tumour is suspected because of the risk of liver metastases.

This wide-field sequence suffers from several limitations: difficulty in differentiating adenocarcinomas from chronic pseudo-mass pancreatitis due to the overlap of CDA values and difficulty in defining the boundaries of cephalic or corporal adenocarcinomas due to the hypersignal of upstream chronic obstructive pancreatitis (9)(10). Technically, it is subject to movement artifacts related to respiration, adjacent organs and in particular the duodenum, and to an average spatial resolution of the pancreas.

Over the last 10 years, a diffusion sequence called "FOCUS" has been developed allowing a reduction of the field of view in the direction of phase coding and therefore a "zoomed" image with higher resolution. This sequence has shown interest in neuroradiology and prostate cancer detection in reducing artifacts and achieving better spatial resolution than the usual "wide field" diffusion sequence. 3 minutes and 30 seconds more are required to complete this sequence.

The pancreas is a good candidate for FOCUS diffusion imaging because of its small size, susceptibility to movement artifacts and spatial orientation, allowing antero-posterior reduction of the field of view. Initial work has established the feasibility of this FOCUS diffusion in pancreatic imaging and shown an improvement in image quality (more accurate and less artefacts) in FOCUS diffusion compared to the usual "wide field".

Due to its potential in pancreatic imaging, the FOCUS diffusion sequence has been performed in current practice since 2014 in the imaging department of the Groupe Hospitalier Paris Saint-Joseph (GHPSJ) in addition to the "wide field" diffusion sequence. The protocol thus created is called "combined protocol" as opposed to "standard protocol" which does not contain the FOCUS broadcast sequence.

Kim H et al showed an improvement in the subjective clinical utility of readers in the diagnosis of benign or malignant pancreatic lesions. However, it should be noted that in this study the authors compared the two sequences by opposing them rather than comparing the usual wide-field sequence with the combination of the two sequences.

Inclusion criteria

• Male or female whose age ≥ 18 years old (Adult patient)
• Francophone patient
• Pancreatic MRI performed at the GHPSJ on 3 Tesla MRI between September 2014 (date of introduction of the FOCUS diffusion sequence) and April 2018
• Presence of at least one proven benign or malignant focal pancreatic lesion visible on at least one of the MRI sequences

Exclusion criteria

• Patient under guardianship or curatorship
• Patient deprived of liberty
• Patient objecting to the use of their data for this research
• Papillary and mucinous intra-channel tumour of pancreas (TIPMP) of secondary channels measuring less than 30mm.