R/P Overview

Question 1

Chemisorption

Answer 1

Surface binding of R/P to a solid structure.

Ex: NM bone scan

Question 2

Compartmental Localization

Answer 2

Placement of a radiotracer in a fluid space and imaging of that fluid space.

Ex: In111 DTPA for Cisternograms, Xe133 for pulmonary ventilation.

Question 3

Active Transport

Answer 3

Involves a carrier mediated, metabolic, or energy dependent pathway in the body to move a R/P across a cell membrane and into the cell.

Ex: I131 NaI for thyroid imaging. DMSA

Question 4

Simple/exchange diffusion

Answer 4

A mechanism whereby a radiotracer diffuses across cell membranes and then binds/attaches to a cell component.

Ex: F18 NaF for bone imaging.

Question 5

Capillary blockade

Answer 5

Intentional microembolizatiln of a capillary bed with particles.

Ex: Tc99m MAA for pulmonary perfusion imaging.

Question 6

Phagocytosis

Answer 6

Physical entrapment of colloidal particles by Kupffer cells in the RE System.

Ex: Tc99m sulfur colloid for liver/spleen imaging.

Question 7

WBC Chemotaxis

Answer 7

Process of harvesting WBCs from venous circulation, isolating the WBCs (primarily Neutrophils), tagging them with In111 or Tc99m HMPAO, wait 24 hrs to allow WBC migration to sites of acute infection.

Question 8

Receptor-binding

Answer 8

Binding of R/P to high-affinity receptor sites.

Ex: In111 octreotide for localization of neuroendocrine and other tumors based on binding of a somatostatin analog to receptor sites in tumors.

Question 9

Antigen/antibody reaction

Answer 9

Uptake at tumor site due to specific binding of radiolabeled antibody to surface antigens on tumors.

Ex: In111 Onconscint for localization of recurrent ovarian or colorectal carcinoma.

Question 10

Cell Sequestration

Answer 10

Take advantage of an organ’s usual function…. eg. Spleen’s job is to remove damaged RBCs from circulation.

Injection of damaged RBCs to produces spleen scan with no visualization of the liver using heat damaged autologous Tc99m RBCs.

Question 11

Metabolic Trapping

Answer 11

Cellular metabolism permits trapping of FDG similarity to glucose, but it is not metabolized and is “trapped” in a metabolic pathway allowing us to image tumors which use high amounts of glucose.

Ex: F18 FDG: Cells normally trap sugar to use in cell metabolism.

Question 12

Metabolic Trapping

Answer 12

Cellular metabolism permits trapping of FDG similarity to glucose, but it is not metabolized and is “trapped” in a metabolic pathway allowing us to image tumors which use high amounts of glucose.

Ex: F18 FDG: Cells normally trap sugar to use in cell metabolism.