Various embodiments of a device for in-vivo measurements radiopharmaceuticals used for diagnosis and monitoring of radiotherapy are presented. In some embodiments, the present disclosure relates to a device having a cannula that may include a measurement chamber, a radiation detector and a delivery lumen, wherein the device may be used to both deliver material to the patient (e.g., radiotracers used in radiopharmaceuticals) and measure levels and concentrations of radioactive material in, for example, the patient's blood both during and after administration of the radioactive material. In some embodiments, particles emitted by the radioactive material interact with a scintillation material, resulting in the release of light that may be transmitted, via the scintillation material and/or fiber optic material, to an optical detectors or processor for processing. In some embodiments, particle absorbing materials may be used to limit measurements to materials within the measurement chamber or other area of interest.