The most common and reliable method is thyroid fine needle aspiration biopsy, which is usually guided by ultrasound images, a fine needle is used to aspirate some cells and a pathologist analyses the morphology and differentiation of the aspirated cells to confirm whether the nodule is benign or malignant. PET-CT is another effective test that can be used to determine whether a nodule is malignant or not by measuring the activity of the cells on the image, but the disadvantage of this test is that it is more expensive and therefore not widely available.