Are we expecting too much from the diffusion-weighted MRI?

Abstract

Diffusion-weighted magnetic resonance imaging (DW-MRI) is a method where the signal required to produce a MRI image is determined by the "mobility of water". Diffusivity measurements have multiple components related to tissue cellularity and organization, integrity of the cell membranes, extracellular space tortuosity and perfusion (1).Until recent years, main limitation for the use of DWI in the body area wa the artefacts originating from the physiologic movements which decrease the diagnostic yield of the method. With advanced technology, elimination of disturbing artifacts can be possible to a degree… Diffusion-weighted imaging signal intensity and the values of apparent diffusion coefficient (ADC) are of particular interest, because these parameters can sometimes show changes in bowel wall, when no abnormalities are typically seen on conventional MR images. Therefore, this method is rapidly becoming an adjunct to a conventional body MRI study, especially in the early detection of cancer. The ADC map provides quantitative information on diffusion. It is a measure of the freedom of water diffusion and is useful in tissue characterization. Malign lesions are characterized by a high signal on DWI and a low signal on ADC. Measured values from ADC map are believed to be low because of a shift (diffusion) of water within malign tissue, from the extracellular to the intracellular compartment, is relatively restricted. Thus, one of the important advantages of the DWI is that it can manifest the nature of the lesion without the need for intravenous contrast material injection. This is particularly beneficial in patients with reduced renal function (1).In the current issue of Turkish Journal of Gastroenterology, Solak and colleagues (2) have investigated the value of DW-MRI in the differentiation of benign and malignant diffuse bowel wall thickening. They discussed the diagnostic importance and potential use of ADC measurements. For quantitative analysis in DW-MRI, a radiologist has measured the thickened colonic wall ADC values in the three regions of interest (ROI) by using dedicated software at the workstation. A circular ROI with a diameter of at least 4 mm2 has been placed to three different portions of the thickened wall to obtain average ADC values of the lesion. The authors concluded that benign bowel pathologies leading to wall thickening had significantly higher ADC values than those of malignant ones. In ROC curve analysis, the cut-off value of ADC to differentiate benign from malignant wall thickening was found as 1.21mm 2 /s with a sensitivity of 100%, a specificity of 87,3%, and an accuracy of 89,3%. With visual assessment of the DWIs and the measurements of ADC values, malignant lesions were differentiated from benign ones with sensitivity of 100%, specificity of 89,2%, and an accuracy of 90,4%.Before considering whether this bald conclusion does justice to the possible contribution of DWI to the noninvasive differentiation of benign and malign bowel lesions, it is worth considering that, even in the abs...