Different cancer imaging agents target tumors based on their growth patterns and metabolic demands. Patients receive radiopharmaceuticals before imaging procedures, and substances are eliminated through urine or feces. Scientists have developed compounds that fluoresce only within living cells, allowing for targeted illumination of specific tumors. Oncologists use various imaging agents to detect and monitor tumor growth, including 18F FDG and 18NaF for soft tissue and bone tumors, and FMISO for tumors with low oxygen levels.
The fluorescent dye commonly used in cancer imaging procedures to highlight abnormal growths is known as an imaging agent. Different cancer imaging agents are designed to target tumors based on the unusual growth patterns and metabolic demands of the malignant mass. Some agents not only differentiate between healthy and cancerous cells, but also between different types of cancer. Using an imaging agent, oncologists can make diagnoses, monitor treatment regimens, and assess the extent of metastases.
Patients often receive a radiopharmaceutical before undergoing computed tomography (CT), magnetic resonance imaging (MRI), or positron emission tomography (PET) procedures. Radiology technicians administer the agent orally, intravenously, or by enema. Depending on the body part or structure being imaged, patients might also receive an imaging agent through an artery or within a specific body cavity. Substances are typically eliminated by the kidneys in the urine or in the evacuation of fecal waste. Patients usually receive post-procedure instructions suggesting increasing fluid intake to speed up the elimination process.
Early imaging agents not only targeted and highlighted tumors, but passed from the mass after cell damage or death occurred. The imaging agent continued to fluoresce, illuminating a trail to other areas. Scientists have devised several compounds that fluoresce only when they are in a living cell and stop when they leave dead or dying cells. One of these later formulations includes boron-dipyrromethene, often called BODIPY, which fluoresces only within living cells. Scientists further modified the substance by binding certain molecules that targeted specific tumors, allowing BODIPY to illuminate breast tumors with the protein HER-2 (human epidermal growth factor receptor2).
Oncologists often use the imaging agent known as 18F-fluorodeoxyglucose (18F FDG) for the detection of malignant mass. Cancer cells grow and reproduce at an accelerated rate compared to normal tissue, which means they have a higher rate of nutritional consumption. Compound 18F FDG contains a sugar molecule that cancer cells rapidly absorb to meet nutritional needs. The fluorescent compound, however, does not effectively illuminate the growth of malignant cells in bone tissue. Instead, sodium-18 fluoride (18NaF) is used to produce illumination in bone tissue, and oncologists often combine this agent with 18F FDG to visualize the presence of tumors in soft tissue and bone.
Fluorescent compounds can also be used to monitor tumor growth by analyzing the development of vascular structures in and around the malignant tissue. Using vascular endothelial growth factor (VEGF), a protein common to all malignant tissue, doctors follow the development of blood vessels created by the tumor. Radiologists might also use certain compounds to identify tumors and determine treatment. The imaging agent 18F-fluoromisonidazole (FMISO), detects tissue that has low oxygen levels. These tumors generally have a poor response to chemotherapy or radiation.
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