**1. Radiopharmaceuticals**

Radiopharmaceuticals are radioactive drugs that can be used either for diagnostic or therapeutic purposes in nuclear medicine applications. In nuclear medicine, 95% of radiopharmaceuticals are used in diagnosis and 5% of them in therapeutic usage [1, 2]. The pharmaceutical component directs radioactivity to the target site of the body (disease regions, organs). A radionuclide emits detectable signals from outside the organism for visualization or delivers therapeutic levels of radiation dose to target sites. Radiopharmaceuticals are bound to accumulate in certain organs or tissues according to the physical, chemical and biological properties of the pharmaceutical part [1]. They are not chemically distinguishable from nonradioactive analogues and participate in biochemical events in the organism [2]. Organ functions can be visualized by the radiation emitted by radionuclides in their structure. A pathological change that can lead/leading to abnormal function can be diagnosed at the molecular level without going to the morphological level. So, diseases can be treated quickly after imaging [1].

With the widespread use of radiopharmaceuticals, the need for specialized pharmacists as known radiopharmacists has increased. Radiopharmaceuticals should be prepared by radiopharmacists and administered by clinicians to the patient. The doses of radiopharmaceuticals are defined either millicurie or microcurie. The pharmaceutical form of the radiopharmaceuticals may be solutions, kit, capsules and aerosols. The amount of active substance in the radiopharmaceutical is at a low dose that does not have a pharmacological effect. The shelf life of a radiopharmaceutical depends on half-life of radionuclide. Quality control of radiopharmaceuticals should be done before administration to patients.

A radiopharmaceutical optimal performance should have some characteristics. While the radiopharmaceuticals used for diagnosis emit gamma ray, the radiopharmaceuticals used for treatment emit beta ray. Alpha and beta radiation, which have particle radiation, are not desirable for diagnosis due to high linear energy transfers (LET). Because this energy is completely absorbed in the body, some particles that can escape to the body and cannot reach the crystal in the imaging system [3].

The ideal radionuclide energy for imaging should be around 100–300 kilo electron volts (keV). The quality of image falls when it is above or below these energy values. In radiopharmaceuticals used for treatment, the energy should be higher than above 1 MeV.

Ideally, the effective half-life of a radiopharmaceutical should be greater than about 1.5 times the imaging time. This pro vides a good image between the maximum dose and the minimum dose that can be injected into the patient, so that the counting statistics and image quality are optimal. On the other hand, the effective half-life of radiopharmaceuticals used in treatment is indicated by hours and days.

The localization of radiopharmaceuticals should be high in the desired organs or tissues. Low dose for both, patient and personnel, is necessary of ideal radiopharmaceutical. When the radioactivity ratio in the target/non-target area is low and the radiation dose increases in non-target areas, treatment or diagnosis efficiency of radiopharmaceuticals decreases. They must be non-toxic, sterile and pyrogen-free for patient compliance. Finally, radiopharmaceuticals must maintain their chemical stability during usage, should be cheap and easy to find, easy to prepare and appropriate quality controls [4].
