Diffusion-weighted whole-body MR screening
Introduction
Whole-body MR imaging (WBMRI) has been developed in recent years using different methods, either with a moving table platform in combination with the body-coil, or a special designed rolling table platform with multiple phase-array coils [1], [2]. The clinical impact of WBMRI for bone marrow involvement, tumor staging and screening has been reported in previous reports [3], [4], [5]. Furthermore, improvements in software and hardware can now evaluate the whole body on MR imaging with a short time period. A WBMRI protocol should include also a T1-weighted and a short tau inversion recovery (STIR) imaging, which have proven highly efficient for the assessment of bone and soft tissue structures [2], [6].
In the last decade, diffusion-weighted (DW) imaging has revealed great potential in cancer and bone marrow imaging of the body [7], [8], [9]. Recent advances in MR gradient technology allow the acquisition of DW images with a high b-factor, even in the body, thanks to the advent of fast imaging sequences like echo planar imaging (EPI) and parallel imaging techniques [10], [11]. A whole-body DW imaging is a recently application, performing multiple stations and a composite image of the entire body. The true utility of the DW imaging of the whole body has only recently shown the preliminary clinical results [12]. The potential and clinical values of this emerging technique are reviewed in this article.
Section snippets
Principles of DW imaging
We summarize the basic concepts of this technique, as an extent discussion of the physics of DW is beyond the purpose of this article, which the reader may refer to related articles [7], [9].
DW sequences provide microscopic information to supplement the static and macroscopic information provided by conventional sequences. DW sequences reflect the random movement of water molecules of the body, which includes both intracellular and extracellular movement, as well as transcellular and
DW imaging technique of the whole body
The examination protocol for DW imaging technique of the whole body relies on the MR equipment and the field strength to be used. Other authors with different MR equipment are using a short T1 inversion recovery (STIR)-EPI sequence, with or without parallel acquisition [11], [12]. Our protocol is performed with a 1.5-T MR system (Signa Excite HD; GE Medical Systems, Milwaukee, WI, USA) equipped with a high-performance gradient system with amplitude of 33 mT/m and slew rate of 130 mT/(m ms). The
Postprocessing and analysis
The DW images have to be processed on the workstation. The 3D data sets from the different axial series are combined, reformatted and viewed along any axis as maximum intensity projections as a unique series. The multiplanar reformatted images can be displayed as a whole-body image in the coronal plane (Fig. 1). An inverse grey-white scale intensity scale is applied to the data sets for visual interpretation, which seem more familiar to clinicians, as they have some resemblance to the usual
Clinical experience of diffusion-weighted whole-body MR imaging
Initial studies describing DWWB MR imaging have focused on the detection of osseous metastases in patients with primary malignancies that had the potential to metastasize to the skeletal system [11]. The technique has also been described as a potential mean to rapidly evaluate the therapeutic response in human bone marrow [10]. Other recently preliminary results of DWWB MR imaging have demonstrated the additional value of this sequence, comparable to skeletal scintigraphy to detect bone
Conclusions
Whole-body MR imaging with the addition of a DW sequences of the entire body could be an effective method to evaluate patients with suspected malignant or benign diffuse disease. WB-MR imaging using DW sequences is more sensitive than scintigraphy, supplying additional information on non-bone-related lesions. The technique described could provide a potential improvement in the image evaluation on whole-body MR imaging strategy. Whole-body diffusion imaging technique might help the clinicians to
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