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.
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.


PURPOSE
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).


MATERIAL AND 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).


CONCLUSION
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.
['Schmidt|Sabine|S|', 'Dunet|Vincent|V|', 'Koehli|Melanie|M|', 'Montemurro|Michael|M|', 'Meuli|Reto|R|', 'Prior|John O|JO|']
D003287:Contrast Media D038524:Diffusion Magnetic Resonance Imaging D005260:Female D019788:Fluorodeoxyglucose F18 D005500:Follow-Up Studies D005770:Gastrointestinal Neoplasms D046152:Gastrointestinal Stromal Tumors D006801:Humans D007089:Image Enhancement D007091:Image Processing, Computer-Assisted D021621:Imaging, Three-Dimensional D008113:Liver Neoplasms D008297:Male D008536:Meglumine D008875:Middle Aged D064847:Multimodal Imaging D015588:Observer Variation D009942:Organometallic Compounds D010865:Pilot Projects D011446:Prospective Studies D019275:Radiopharmaceuticals D015203:Reproducibility of Results D016896:Treatment Outcome
18F-FDG PET/CT apparent diffusion coefficient (ADC) Gastrointestinal stromal tumor (GIST) MR diffusion imaging standard uptake value (SUV)