Comparison of FDG-18 Uptake and ADC Values in Thyroid Cancer

PET/MRI is a relatively recent diagnostic tool for the evaluation of oncologic disease. It combines the excellent soft tissue contrast of MRI with the physiologic data regarding glucose metabolism of PET. It has been described that ADC values may be useful in oncologic imaging, with development of central necrosis within a malignancy corresponding with increased ADC values. It has long been known that decreased FDG-avidity on PET imaging within a malignancy correlates with favorable response to treatment. With the increasing use of PET/MRI in oncologic imaging, changes in both ADC and FDG-avidity in malignancy can be evaluated with the same exam. ADC values and FDG-avidity in patients with thyroid cancer were evaluated to determine if a correlation between these two measurements existed. 11 patients with histopathologically proven papillary thyroid cancer that underwent PET/MRI imaging were evaluated. Of these, 3 patients had biopsy-proven disease with technically adequate ADC maps. A negative correlation between ADC values and FDG-avidity with soft tissue metastasis was observed, but not seen with bone metastasis.