title: Diffusion-weighted magnetic resonance imaging in metastatic gastrointestinal stromal tumor (GIST): a pilot study on the assessment of treatment response in comparison with 18F-FDG PET/CT.
abstract: BACKGROUND
  Diffusion-weighted magnetic resonance imaging (MRI) is increasingly being used for assessing the treatment succes in oncology, but the real clinical value needs to evaluated by comparison with other, already established, metabolic imaging techniques.
  
  
  OBJECTIVE
  To prospectively evaluate the clinical potential of diffusion-weighted MRI with apparent diffusion coefficient (ADC) mapping for gastrointestinal stromal tumor (GIST) response to targeted therapy compared with 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT).
  
  
  METHODS
  Eight patients (mean age, 56 ± 11 years) known to have metastatic GIST underwent 18F-FDG PET/CT and MRI (T1Gd, DWI [b = 50,300,600], ADC mapping) simultaneously, before and after change in targeted therapy. MR and PET/CT examinations were first analyzed blindly. Second, PET/CT images were co-registered with T1Gd-MR images for lesion detection. Only 18F-FDG avid lesions were considered. Maximum standardized uptake value (SUVmax) and the corresponding minimum ADCmin were measured for the six largest lesions per patient, if any, on baseline and follow-up examinations. The relationship between changes in SUVmax and ADCmin was analyzed (Spearman's correlation).
  
  
  RESULTS
  Twenty-four metastases (12 hepatic, 12 extra-hepatic) were compared on PET/CT and MR images. SUVmax decreased from 7.7 ± 8.1 g/mL to 5.5 ± 5.4 g/mL (P = 0.20), while ADCmin increased from 1.2 ± 0.3 × 10(-3)mm(2)/s to 1.5 ± 0.3 × 10(-3)mm(2)/s (P = 0.0002). There was a significant association between changes in SUVmax and ADCmin (rho = - 0.62, P = 0.0014), but not between changes in lesions size (P = 0.40).
  
  
  CONCLUSIONS
  Changes in ADCmin correlated with the response of 18F-FDG avid GIST to targeted therapy. Thus, diffusion-weighted MRI may represent a radiation-free alternative for follow-up treatment for metastatic GIST patients.
authors.affiliation: Department of Radiology.
authors.forename: Sabine
authors.initials: S
authors.lastname: Schmidt
authors.forename: Vincent
authors.initials: V
authors.lastname: Dunet
authors.forename: Melanie
authors.initials: M
authors.lastname: Koehli
authors.forename: Michael
authors.initials: M
authors.lastname: Montemurro
authors.forename: Reto
authors.initials: R
authors.lastname: Meuli
authors.forename: John O
authors.initials: JO
authors.lastname: Prior
mesh_terms: D003287:Contrast Media; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D019788:Fluorodeoxyglucose F18; D005500:Follow-Up Studies; D005770:Gastrointestinal Neoplasms / Q000175:diagnosis* / Q000473:pathology / Q000556:secondary; D046152:Gastrointestinal Stromal Tumors / Q000175:diagnosis* / Q000473:pathology; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D008113:Liver Neoplasms / Q000175:diagnosis* / Q000556:secondary; D008297:Male; D008536:Meglumine; D008875:Middle Aged; D064847:Multimodal Imaging / Q000379:methods*; D015588:Observer Variation; D009942:Organometallic Compounds; D010865:Pilot Projects; D011446:Prospective Studies; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D016896:Treatment Outcome
chemical_list: D003287:Contrast Media; D009942:Organometallic Compounds; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D008536:Meglumine; C072417:gadoterate meglumine
keywords: 18F-FDG PET/CT; Gastrointestinal stromal tumor (GIST); MR diffusion imaging; apparent diffusion coefficient (ADC); standard uptake value (SUV)