New MRI techniques for staging malignant lymphoma

Malignant lymphomas are a heterogenous group of malignancies, belonging to the ten most frequent types of cancers worldwide. Once a malignant lymphoma has been diagnosed, it is important to assess disease extent (staging), because this has prognostic and therapeutic implications. Computed tomography (CT) and 18F-fluoro-2-deoxyglucose positron emission tomography (FDG-PET)/CT are commonly used imaging methods for the staging of malignant lymphoma. An important disadvantage of CT and FDG-PET/CT, however, is the use of ionizing radiation, which may lead to the development of cancers in later life. Although this risk is relatively low, it cannot be ignored, especially in children. Magnetic resonance (MR) imaging does not have this disadvantage, and may be an alternative to CT and perhaps FDG-PET/CT for the evaluation of lymphoma. The aim of this thesis was to introduce and assess the value of whole-body magnetic resonance (MR) imaging, including diffusion-weighted imaging (DWI), for the staging of patients with newly diagnosed malignant lymphoma. Of interest, DWI is an advanced MR technique that may improve the detection and functional evaluation of lymphomatous tissue. In this thesis, new concepts were introduced to perform whole-body MR imaging studies, including whole-body DWI. It was shown that noninvasive measurement of diffusivity in lymph nodes by means of DWI is challenging in terms of observer agreement, but it could potentially aid in the discrimination between normal and lymphomatous lymph nodes. Unfortunately, whole-body MR imaging with DWI was found insufficiently reliable to replace bone marrow biopsy (BMB) for the assessment of the bone marrow for lymphomatous involvement. Nevertheless, it may increase the diagnostic yield of BMB alone, although this hypothesis requires further investigation. Head-to-head comparisons of whole-body MR imaging/DWI to CT and whole-body MR imaging/DWI to FDG-PET/CT in patients with newly diagnosed malignant lymphoma showed that these techniques are mostly in agreement with regard to Ann Arbor staging. However, disagreements in staging between the different imaging methods occurred; future studies are required to determine the rates at which whole-body MR imaging/DWI provides correct up- or downstaging in these cases. In addition, although DWI correctly changed Ann Arbor stage in several cases, further research is warranted to determine its additional diagnostic value. Finally, it was shown that future MR imaging studies may be limited to the head/neck and trunk, because in a series of 100 patients, whole-body MR imaging did not detect any clinically relevant lesions (i.e. lesions that change Ann Arbor stage) outside the head/neck and trunk. In conclusion, whole-body MR imaging, including DWI, is a feasible technique for staging newly diagnosed malignant lymphoma, and may be readily applied in those populations in which CT radiation is a major issue and in patients at risk for (severe) adverse reactions to CT contrast agents. However, further technical developments and prospective large-scale studies on staging performance are required before whole-body MR imaging will become a widespread accepted alternative to CT and FDG-PET/CT