title: Diffusion-weighted MR imaging of the rectum: clinical applications.
abstract: Dramatic advances in image quality over the past few years have made diffusion-weighted magnetic resonance imaging (DW-MRI) a promising tool for rectal lesion evaluation. DW-MRI derives its image contrast from differences in the motion of water molecules between tissues. Such imaging can be performed quickly without the need for the administration of exogenous contrast medium. The technique yields qualitative and quantitative information that reflects changes at a cellular level and provides information about tumor cellularity and the integrity of cell membranes. The sensitivity to diffusion is obtained by applying two bipolar diffusion-sensitizing gradients to a standard T2-weighted spin echo sequence. The diffusion-sensitivity can be varied by adjusting the "b-factor", which represents the gradient duration, gradient amplitude and the time interval between the two gradients. The higher the b-value, the greater the signal attenuation from moving water protons. In this review, technical considerations relatively to image acquisition and to quantification methods applied to rectal DW-MRI are discussed. The current clinical applications of DW-MRI, either in the field of inflammatory or neoplastic rectal disease are reviewed. Also, limitations, mainly in terms of persistent lack of standardization or evaluation of tumoral response, and future directions of rectal DW-MRI are discussed. The potential utility of DW-MRI for the evaluation of rectal tumor response is on its way to being admitted but future well-designed and multicenter studies, as well as standardization of DW-MRI, are still required before a consensus can be reached upon how and when to use DW-MRI.
authors.affiliation: Department of Radiology, Hôpital Robert Debré, Avenue du Général Koenig, 51092 Reims Cedex, France. Electronic address: nguyen.tl.francis@gmail.com.
authors.forename: Truong Luong Francis
authors.initials: TL
authors.lastname: Nguyen
authors.affiliation: Department of Radiology, Hôpital Lariboisière, 2 rue Ambroise Paré, 75010 Paris, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Soyer
authors.affiliation: Department of Histopathology and Cytology, Hôpital Robert Debré, Avenue du Général Koenig, 51092 Reims Cedex, France.
authors.forename: Paul
authors.initials: P
authors.lastname: Fornès
authors.affiliation: Department of Radiology, Hôpital Hôtel Dieu, 1 place du Parvis de Notre Dame, 75181 Paris Cedex 4, France.
authors.forename: Pascal
authors.initials: P
authors.lastname: Rousset
authors.affiliation: Department of Abdominal Surgery, Hôpital Robert Debré, Avenue du Général Koenig, 51092 Reims Cedex, France.
authors.forename: Reza
authors.initials: R
authors.lastname: Kianmanesh
authors.affiliation: Department of Radiology, Hôpital Robert Debré, Avenue du Général Koenig, 51092 Reims Cedex, France.
authors.forename: Christine
authors.initials: C
authors.lastname: Hoeffel
mesh_terms: D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006801:Humans; D012002:Rectal Diseases / Q000175:diagnosis*; D012007:Rectum / Q000473:pathology*
keywords: Apparent diffusion coefficient; Diffusion-weighted imaging; Inflammation; Lesion detection; Rectum; Tumor staging