Measurement of tumor volume and activity is an increasingly important goal in tumor imaging for studying structural changes over time and correlating anatomic information with functional activity and pathology.
Size measurement of a tumor is a common way to assess the tumor response to a treatment. During a tumor monitoring trial, a baseline study and several follow-up studies are obtained. The response is classified as one of following categories: (i) complete response (CR); (ii) partial response (PR); (iii) progressive disease (PD); and (iv) stable disease (SD). The longest diameter has been used in evaluating the solid tumors in response evaluation criteria in solid tumor (RECIST) (21). In RECIST, CR is defined as disappearance of all target lesions; PR is defined as at least a 30% decrease in the sum of longest diameter of target lesions; PD is defined as at least a 20% increase in the sum of longest diameter of target lesions; and the remaining cases are defined as SD.
Functional images such as dynamic MR can be used to study the tumor physiological activities, which are useful in differential diagnosis, therapy planning, and therapy follow-up.
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