Many imaging techniques have been used effectively, including the following: High-resolution CT with or without CT-guided biopsy and PTH immunoassay from thyroid venous drainage Contrast-enhanced four-dimensional (4D) CT MRI High-resolution ultrasonography Digital subtraction angiography Thallium-201-technetium-99 scanning Technetium-99 sestamibi, a radionuclide agent for parathyroid imaging, is more sensitive and specific than older agents and may be useful for identifying solitary adenomas.