Diffusion-weighted magnetic resonance imaging (DWI) provides functional information and can be used for the detection and characterization of pathologic processes, including malignant tumors. The recently introduced concept of "diffusion-weighted whole-body imaging with background body signal suppression" (DWIBS) now allows acquisition of volumetric diffusionweighted images of the entire body. This new concept has unique features different from conventional DWI and may play an important role in wholebody oncological imaging. This review describes and illustrates the basics of DWI, the features of DWIBS, and its potential applications in oncology.

Non-contrast-enhanced whole-heart coronary MRA at 1.5-T can noninvasively detect significant CAD with high sensitivity and moderate specificity. A negative predictive value of 88% indicates that whole-heart coronary MRA can rule out CAD.

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18 F-FDG PET is an established functional imaging modality for the evaluation of human disease. Diffusion-weighted MRI (DWI) is another rapidly evolving functional imaging modality that can be used to evaluate oncologic and nononcologic lesions throughout the body. The information provided by 18 F-FDG PET and DWI can be complementary, because the 2 methods are based on completely different biophysical underpinnings. This article will describe the basic principles, clinical applications, and limitations of DWI. In addition, the available evidence that correlates and compares 18 F-FDG PET and DWI will be reviewed. PET,usi ng the radiotracer 18 F-FDG, is an established functional imaging modality for a variety of oncologic and nononcologic (e.g., inflammatory and infectious) applications (1-3). The contribution of 18 F-FDG PET to medicine has been unmatched by any other functional imaging modality (4). At present, there is also growing interest in the application of diffusion-weighted MRI (DWI) in the body (5-7). DWI allows visualization and quantification of the mobility of water molecules and has many potential clinical applications. Importantly, although 18 F-FDG PET and DWI are both functional imaging modalities and provide a high lesion-to-background contrast, they are based on completely different biophysical and biochemical underpinnings. Therefore, the information provided by the 2 imaging modalities may be regarded as complementary. Given the developing applications of DWI, the increasing use of multimodality imaging (8), and the expected advent of fully integrated PET/MRI systems (9), knowledge of the characteristics, possibilities, and limitations of DWI technique is becoming increasingly important. This is true for both the imaging specialists and the clinicians who use these modalities. This article will review the basic principles, clinical applications, and limitations of DWI. Furthermore, the available evidence that correlates and compares 18 F-FDG PET with DWI will be reviewed.

Purpose:To examine the usefulness of diffusion-weighted MRI (DW-MRI) for the detection of both primary colorectal cancer and regional lymph node metastases, and compare its performance with 2-[fluorine-18]-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) in the same patients. Materials and Methods:We studied 25 patients with known colorectal cancer. All underwent both DW-MRI and FDG-PET studies. The images were retrospectively assessed by visual inspection and the imaging findings were compared with histopathological findings on surgical specimens. Results:Of the 27 primary colorectal lesions surgically excised in 25 patients, 23 (85.2%) were true-positive on both DW-MRI and FDG-PET. Two cancers were false-negative on DW-MRI but true-positive on FDG-PET, and two were false-negative on both DW-MRI and FDG-PET. With respect to the detectability of metastatic lymph nodes, DW-MRI and FDG-PET manifested a sensitivity of 80% (8/10) and 30.0% (3/10), a specificity of 76.9% (10/13) and 100% (13/13), and an accuracy of 78.3% (18/23) and 69.6% (16/23), respectively.Conclusion: DW-MRI is inferior to FDG-PET for the detection of primary lesions, but superior for the detection of lymph node metastases.