Evaluation of Whole Body DiffusionWeighted Imaging in the Staging and Treatment Response of Lymphoma Compared With Fluoride-Oxyglucose (FDG) PET/CT as a Reference Standard

Introduction: Positron emission tomography/computed tomography (PET/CT) is currently considered standard of practice for the management of lymphoma with sensitivity and specificity approaching 100%. However, it is expensive, time-consuming and requires exposure to ionizing radiation. Whole body-diffusion weighted imaging (WB-DWI), does not involve exposure to ionizing radiation, is more widely available and can be performed within an acceptable time frame. PET/CT will be used as a reference standard in the evaluation of the value of WB-DWI in the initial staging and treatment response in patients with lymphoma. Methods: Nine patients with newly diagnosed lymphoma and a pre-treatment PET/CT were prospectively recruited. Patients were analyzed with both imaging modalities before treatment initiation and at four-weeks post-completion of chemotherapy. The presence or absence of nodal and extra-nodal involvement was independently assessed by two radiologists blinded to the PET/CT findings. The PET/CT images were assessed by a single nuclear medicine physician. Results: Compared to PET/CT, the overall sensitivity, specificity and accuracy of WB-DWI in staging were 62%, 98% and 87% respectively and the overall specificity and accuracy for treatment response were both 99%. Majority of false negative findings were a result of small nodes which showed uptake on PET/CT but were either not identified or did not show restricted diffusion. Further false negative and positive findings were due to reduced spatial resolution and increased motion and susceptibility artefact on magnetic resonance imaging (MRI). Conclusion: WB-DWI may be a viable alternative to PET/CT in the treatment response of lymphoma. However, in terms of staging, PET/CT probably remains the imaging modality of choice.