1. Principle of action of positron emission emission scanning contrast agent

PET scans are advanced medical imaging techniques widely used in cancer diagnosis, brain disease assessment, and cardiac function testing. At its core, PET tracers are used, which emit positrons in the body and react with surrounding electrons to produce high-energy γ lines. These rays of light are captured by a PET scanner and reconstructed by a computer to form a high-resolution 3D image.

1.1 How to generate positrons

Positrons are antimatter of electrons, usually produced by radioisotope decay. In PET scans, commonly used radioisotopes include fluorine-18 (¹⁸F), carbon-11 (¹¹C), and oxygen-15 (¹⁵O). These isotopes are artificially synthesized via cyclotrons and combine with specific biomolecules to form a developer. For example, fluorine-18 binds to deoxyglucose to form FDG (fluorinated deoxyglucose), which is currently the most commonly used positron emission scanning contrast agent.

1.2 Combining Developer and Target Tissue

The design principle of the developers is to simulate metabolites in the human body. For example, in the case of FDG, it is structurally similar to glucose and can be taken up by cells to participate in metabolic processes. Because cancer cells have a much higher metabolic rate than normal cells, FDG accumulates in large quantities at the tumor site and forms hot spots on the image. This specific combination makes PET scans highly sensitive in early diagnosis of cancer.

1.3 Improve image clarity

To improve image clarity, PET scans are used in conjunction with CT (computed tomography) or MRI (magnetic resonance imaging), often forming PET-CT or PET-MRI. This multimodal imaging technique not only shows metabolic abnormalities but also pinpoints the anatomical location of lesions. According to the Hong Kong Hospital Authority, PET-CT has an accuracy of over 90% in diagnosing lung cancer, which is much higher than traditional imaging tests.

2. Common Types of PET Scanning Contrast Agents

There are many types of PET scanning contrast agents, each targeting different diseases and physiological processes. Choosing the right developer is one of the key factors in the success of a PET scan.

2.1 FDG (Fluorodeoxyglucose): The Most Commonly Used Contrast Agent Used in Cancer Diagnosis

FDG is currently the most widely used PET scan contrast agent, accounting for more than 80% of the world's PET scans. It is primarily used to assess glucose metabolic rate and aids in diagnosing cancer, neurological and inflammatory diseases. According to a study by the Chinese University of Hong Kong, FDG-PET has an accuracy of over 85% in staging lymphoma, which is much higher than traditional CT scans.

2.2 Other contrast agents: for certain diseases (e.g., brain, heart)

In addition to FDG, there are many contrast agents that specifically target specific organs or diseases.pet ct scan

• Brain contrast agent: for example, ¹¹C-labeled PIB (Pittsburgh compound B) for amyloid plaque detection in Alzheimer's disease.
• Cardiac contrast agent: For example, ¹³N-ammonia (¹³N-ammonia) used to assess myocardial blood flow perfusion.
• Prostate cancer contrast agent: ⁶⁸Ga-PSMA, which specifically targets prostate-specific membrane antigen (PSMA), etc.

3. Contrast Injection Method and Dosage

The injection method and dosage of positron emission scanning contrast agent should be strictly controlled to ensure the safety and accuracy of the test.

3.1 Route of injection: intravenous injection

The contrast agent usually enters the human body by intravenous injection, and the injection site is mainly selected for the antecubital vein. The injection process requires a professional nuclear medicine technician to ensure that the contrast agent is evenly distributed. After injection, the patient should rest quietly for 45-60 minutes so that the contrast agent is completely dispersed in the target tissue.

3.2 Dosage Calculation: Based on Weight, Age and Other Factors

The dosage of contrast agent should be personalized according to the patient's weight, age, and testing purposes. In general, the adult dose range for FDG is 5-10 mCi (185-370 MBq). In children or patients with renal failure, the dose should be reduced accordingly. Healthcare institutions in Hong Kong typically refer to the guidelines of the International Commission on Radiological Protection (ICRP) to determine the optimal dose.

4. Precautions after contrast injection

After undergoing PET emission scan contrast agent injections, patients should pay attention to the following points to ensure a smooth examination and mitigate potential risks:

4.1 Possible side effects: mild allergic reaction, nausea

PET scans are well tolerated in most patients, but some patients may experience mild side effects such as pain, warmth, and nausea at the injection site. Severe allergic reactions are very rare and occur in less than 0.1%. According to the Hong Kong Health Bureau, about 5,000 PET scans are performed every year, of which less than 5 serious side effects have been reported.

4.2 Drink plenty of water to promote developer drainage

After the examination, the patient should drink enough fluids (at least 500-1000 ml recommended) to speed up the excretion of contrast agent from the urine. Typically, most radioactive materials are discharged within 24 hours. During this period, prolonged close contact with pregnant women and children should be avoided to reduce unnecessary radiation exposure.

5. Treatment and prevention of contrast media allergies

Although the incidence of positron emission scanning contrast allergy is low, healthcare organizations need to be prepared for prevention and emergencies.

5.1 Notification of Allergy History Before Testing

Patients should inform their healthcare provider in detail of their allergy history, especially to iodine contrast agents or other radioactive materials, prior to the examination. For high-risk patients, allergy testing or pre-administration of anti-allergic drugs may be considered prior to testing.

5.2 Prepare First Aid Medication

All healthcare facilities that perform PET scans should be equipped with complete first aid equipment and medications, such as epinephrine, antihistamines, and corticosteroids. Hong Kong's nuclear medicine department typically conducts regular allergy emergency drills to ensure that medical staff can respond quickly to emergencies.

6. Development trends of new positron emission emission scanning developers

With the rapid development of molecular imaging, new positron emission scanning contrast agents continue to emerge, opening up new avenues for precision medicine.

In recent years, developers, targeting specific molecular targets, have become a hot topic of research. For example, ⁶⁸Ga-DOTATATE is used to diagnose neuroendocrine tumors, and ¹⁸F-fluorbetapill is used for the early diagnosis of Alzheimer's disease. A research team from the Hong Kong University of Science and Technology is developing a new contrast agent that can specifically label liver cancer cells and will enter clinical trials within the next three years.pet scan chinese

Furthermore, the application of artificial intelligence (AI) technology has also revolutionized PET scanning. Deep learning algorithms can significantly reduce the amount of contrast agent (more than 50% reduction) without affecting image quality, which is especially important for children and patients who require multiple tests.

In conclusion, positron emission scanning contrast agents are at the core of PET scanning technology, and with technological advancements, their types and applications will continue to expand, providing a more powerful tool for disease diagnosis and therapeutic monitoring. For Chinese patients, knowing this knowledge can help them strengthen their cooperation in testing and obtain accurate diagnostic results.

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