**Abstract**

Focal increased radiopharmaceutical uptake in a lesion results in focal Hot Spots in the scans. This can occur in benign infective or inflammatory disorders and cancerous diseases as well. Comparison between malignant and benign lesions is important. The Hot spots can be classified into benign and malignant lesions by Spatial Scintimetry or Temporal Scintimetry. Spatial Scintimetry compares the uptake in the region of interest with the adjacent tissue or the unaffected contralateral site. The quantitative indices are lesion/non lesion ratio, lesion/background activity and lesion to Bone ratio etc. The Temporal Scintimetry relies on the changes in the counts or uptake in the Hotspot lesion with reference to the dual point time of acquisition. The Hotspot in the bone scan can be classified using the quantitative index of retention ratio by Dr. V. Siva and Israel. In PET studies the focal hot spots can be differentiated into benign and malignant lesion using the dual phase PETCT evaluation using the Rong's Retention ratio and Dr. V. Siva's modified RRI values.

**Keywords:** radiopharmaceutical uptake, scintimetric characterization, spatial scintimetry, temporal scintimetry, quantitative indices
