What is (PET-)?

(PET-) is an advanced technique that combines positron emission tomography (PET) and computed tomography (CT). PET is used to inject tracers containing radioisotopes to capture metabolic activity in the body, which is then combined with anatomical images provided by CT to form high-resolution synthetic images. The uniqueness of this technique is that it not only shows the shape of the organ, but also reflects its functional state, providing doctors with a more comprehensive diagnostic basis.

The basic principle of PET-CT is based on the physical phenomenon of positron emission. When a radioactive tracer enters the human body, it releases positrons, which disappear when the positrons meet the surrounding electrons, creating two γ lines in opposite directions. By detecting these γ lines, PET scanners can accurately determine the distribution of tracers in the body. CT, on the other hand, provides detailed anatomical images that, when combined, allow doctors to observe metabolic abnormalities and specific anatomical locations simultaneously.正電子電腦掃描

Compared to traditional methods such as hysterosalpingography, PET-CT offers significant advantages. First, metabolic abnormalities can be detected in the early stages of the disease, often manifesting themselves earlier than structural changes. Secondly, it allows for information about both function and structure in a single examination, reducing the inconvenience for patients who need to undergo multiple examinations. Additionally, the application value of PET-CT in fields such as oncology, cardiology, and neurology is widely recognized.

Main Applications of PET-CT

In clinical applications, the most important application of PET-CT is in cancer diagnosis and staging. According to data from the Hong Kong Cancer Registry, PET-CT can diagnose malignant tumors such as lung cancer and lymphoma with an accuracy of more than 90%. In addition to detecting the primary tumor, it can also detect distant metastases, allowing doctors to develop more accurate treatment plans. In addition, PET-CT can be used to compare metabolic changes before and after treatment to assess treatment effects and determine whether the tumor responds to treatment.

In the evaluation of heart disease, PET-CT can diagnose myocardial infarction and assess myocardial activity. For patients considering angioplasty or bypass surgery, this test can determine which areas of the heart muscle are still viable and guide surgical decisions. In diagnosing brain diseases, PET-CT can help in the early diagnosis of Alzheimer's disease, Parkinson's disease, and epilepsy, especially when conventional imaging tests have not detected significant structural abnormalities.

It is worth noting that PET-CT has a wide range of applications, covering almost all systems throughout the body, unlike specialized tests such as hysterosalpingography. However, each test has its indications, and the doctor selects the most suitable method based on the specific situation of the patient.

Detailed explanation of the flow of PET-CT examination

Thorough preparation is required before the PET-CT examination. Patients should usually start fasting 4-6 hours before the test, but they can drink clean water. People with diabetes may need to adjust their insulin dosage, and those taking certain medications (such as steroids) should inform their doctor beforehand. Most healthcare institutions in Hong Kong provide detailed pre-screening guidelines, including dietary restrictions, medication discontinuation, and other precautions.

On the day of the test, the medical staff injects the patient with a radioactive tracer, most commonly fluorodeoxyglucose (FDG). This tracer, like glucose, is taken in large quantities by metabolically active cells such as cancer cells. After the injection, you need to wait about 60 minutes for the tracer to be fully distributed in the body. During this period, the patient should be quiet and not talk or move to reduce the tracer's non-specific muscle uptake.

The scanning process usually lasts 20-30 minutes, and the patient lies flat on the examination table and remains still. The machine moves slowly through the patient's body without causing discomfort. Compared to hysterosalpingography, PET-CT does not require catheter insertion or contrast injection (except for tracers), and the process is relatively simple. After the examination, the doctor recommends drinking enough water to speed up the discharge of the tracer and avoid close contact with pregnant women and infants for 24 hours.

Risks and side effects of PET-CT

The main risk of PET-CT is due to radiation exposure. The radiation dose for PET-CT examination is about 7 to 10 millisieverts, which is equivalent to 2 to 3 years of natural background radiation. The Hong Kong Association of Radiologists says this dose is moderate for medical imaging, lower than abdominal CT but higher than chest X-ray. While radiation can increase the risk of cancer, its diagnostic value often far outweighs the potential risk of medical conditions requiring this test.

Radiotracers can cause allergic reactions, but the incidence is very low, around 0.01%. Mild symptoms include rash and itching, and in severe cases, difficulty breathing may occur. Healthcare institutions in Hong Kong are equipped with first aid equipment and medications to deal with allergic reactions. Compared to iodine contrast agents used in hysterosalpingography, PET-CT tracers have a lower risk of allergies.

It is important to note that pregnant women are generally not suitable candidates for PET-CT examinations, as radiation can affect fetal development. Breastfeeding women should pause breastfeeding for 12-24 hours. These limitations are similar to other tests, where the doctor assesses the risk-benefit ratio based on the patient's specific situation.

PET-CT Cost and Insurance

In Hong Kong, the cost of PET-CT scans varies widely, mainly depending on the hospital level, the examination site, and the type of tracer used. Private hospitals typically charge between HK$15,000 and HK$25,000, while public hospitals may offer subsidies to eligible patients. According to the Hong Kong Federation of Insurers, most premium medical insurance plans cover PET-CT examinations, but they usually require prior approval and proof of medical necessity.

Factors affecting the cost of PET-CT include the level of old and new hospital equipment, whether special tracers are used (e.g., PSMA for prostate cancer), and whether additional image reconstruction techniques are needed. PET-CT is more expensive compared to specialized tests like hysterosalpingography, but many patients and doctors find it worth the money considering it provides comprehensive information.

It is important to note that the public healthcare system in Hong Kong has strict restrictions on PET-CT benefits, typically only for staging or treatment evaluation for specific cancers. Patients should understand their insurance coverage and out-of-pocket costs beforehand if they have financial considerations. As technology advances, the coverage of PET-CT continues to expand, and more indications may be covered by insurance in the future.影像診斷

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