Diffusion-weighted imaging of pancreatic cancer

Abstract

Magnetic resonance imaging (MRI) is a reliable and accurate imaging method for the evaluation of patients with pancreatic ductal adenocarcinoma (PDAC). Diffusion-weighted imaging (DWI) is a relatively recent technological improvement that expanded MRI capabilities, having brought functional aspects into conventional morphologic MRI evaluation. DWI can depict the random diffusion of water molecules within tissues (the so-called Brownian motions). Modifications of water diffusion induced by different factors acting on the extracellular and intracellular spaces, as increased cell density, edema, fibrosis, or altered functionality of cell membranes, can be detected using this MR sequence. The intravoxel incoherent motion (IVIM) model is an advanced DWI technique that consent a separate quantitative evaluation of all the microscopic random motions that contribute to DWI, which are essentially represented by molecular diffusion and blood microcirculation (perfusion). Technological improvements have made possible the routine use of DWI during abdominal MRI study. Several authors have reported that the addition of DWI sequence can be of value for the evaluation of patients with PDAC, especially improving the staging; nevertheless, it is still unclear whether and how DWI could be helpful for identification, characterization, prognostic stratification and follow-up during treatment. The aim of this paper is to review up-to-date literature data regarding the applications of DWI and IVIM to PDACs.

Dwi-MR and Adc Value in Characterization of Different Pancreatic Masses"

“…Radiologic examinations play an important role in characterization of pancreatic lesions. The sensitivity, specificity, and the detection of extrapancreatic extension, are generally superior with MRI, comparing with other imaging modalities [9,10] .…”

Modifications of pancreatic diffusion MRI by tissue characteristics: what are we weighting for?

“…The ADC describes the attenuated signal intensity, SI, in the presence of diffusion gradients, normalized by the image intensity observed without applying the diffusion‐sensitizing gradients, S 0 . According to the Stejskal‐Tanner equation SI/ S 0 = e (− bD ), where D is the directional diffusion coefficient and b , the b ‐value, represents the gradient strength, according to b = γ G 2 δ (Δ − δ /3), with γ the gyromagnetic ratio, G the diffusion‐sensitizing gradient amplitude, δ the duration of this gradient and Δ the diffusion time given by the time elapsed between the two diffusion‐sensitizing gradients used [See Figure in this calculation, the effect of the imaging gradients on the b ‐value has been ignored].…”

“…Despite disagreements on the exact ADC values that characterize cancer most specifically, there is firm evidence that pancreatic carcinoma exhibits slower diffusivity in comparison with non‐affected healthy pancreas, paving the way for the growing use of ADC as a cancer bio‐marker (see Figure ) …”

“…Diffusion‐weighted imaging (DWI) is playing an increasing role as an adjunct tool for conventional MRI sequences, in the diagnostic workup of pancreatic disease . In addition to the anatomical and vascular‐related contrast achieved with conventional sequences, DWI adds non‐invasive “functional” information, providing an intrinsic contrast between tissues due to changes in the thermodynamically driven self‐diffusion of water molecules.…”

Surveillance for neoplasia in the pancreas

“…Another promising modality is diffusion weighted MRI. By analysis of the diffusion of water molecules, this technique provides additional information on cell size and density, presence of fibrosis, edema and intratumoral blood vessels [78]. A recent meta-analysis found a sensitivity and specificity of 91% and 86%, respectively, to differentiate benign and malignant pancreatic tumors [79].…”