and Conjugates, Pz 247, DyLight 750 and 800 Fluors, Cy 5.5 and 7 Fluors, Alexa Fluor 680 and 750 Dyes, IRDye 680 and 800CW Fluors. Quantum dots, with their photostability and bright emissions, have generated a great deal of interest; however, their size precludes efficient clearance from the circulatory and renal systems while exhibiting long-term toxicity.. Several studies have demonstrated the use of infrared dye-labeled probes in optical imaging. In a comparison of gamma scintigraphy and NIR imaging, a cyclopentapeptide dual-labeled with and an NIR fluorophore was used to image αvβ3-integrin positive melanoma xenografts. Near-infrared labeled RGD targeting αvβ3-integrin has been used in numerous studies to target a variety of cancers. An NIR fluorophore has been conjugated to epidermal growth factor (EGF) for imaging of tumor progression. An NIR fluorophore was compared to Cy5.5, suggesting that longer-wavelength dyes may produce more effective targeting agents for optical imaging. Pamidronate has been labeled with an NIR fluorophore and used as a bone imaging agent to detect osteoblastic activity in a living animal. An NIR fluorophore-labeled GPI, a potent inhibitor of PSMA (prostate specific membrane antigen). Use of human serum albumin labeled with an NIR fluorophore as a tracking agent for mapping of sentinel lymph nodes. 2-Deoxy-D-glucose labeled with an NIR fluorophore. It is important to note that addition of an NIR probe to any vector can alter the vector's biocompatibility and biodistribution. Therefore, it can not be unequivocally assumed that the conjugated vector will behave similarly to the native form. Single photon emission computed tomography The development of computed tomography in the 1970s allowed mapping of the distribution of the radioisotopes in the organ or tissue, and led to the technique now called single photon emission computed tomography (SPECT). The imaging agent used in SPECT emits gamma rays, as opposed to the positron emitters (such as ) used in PET. There are a range of radiotracers (such as , , , ) that can be used, depending on the specific application. Xenon () gas is one such radiotracer. It has been shown to be valuable for diagnostic inhalation studies for the evaluation of pulmonary function; for imaging the lungs; and may also be used to assess rCBF. Detection of this gas occurs via a gamma camera—which is a scintillation detector consisting of a collimator, a NaI crystal, and a set of photomultiplier tubes. By rotating the gamma camera around the patient, a