Positron Emission Tomography-Computed Tomography (PET-CT Scan)

A PET scan is an advanced imaging examination that offers detailed information on a particular body organ or specific function of the body. It is commonly used to evaluate and diagnose cancer, neurological disorders of the brain, and cardiovascular disease.

During the PET scan, a radiologist will inject a radioactive tracer into the patient’s body and images of the patient’s body are recorded with a PET scanner. A specialised camera can detect the radiation emitted by the radioactive tracer, and a multidimensional image of the examined area will be generated by the computer.

PET Scan 掃描是「Positron Emission Tomography」（「正電子斷層掃描」），是屬於核子醫學的技術，和 CT Scan 和 MRI Scan 兩種最大的不同是，正電子掃描屬於功能性的檢查（CT 和 MRI 是結構性檢查）。病人需要注射帶有放射性的藥物（一般來說是葡萄糖），如身體有癌細胞、炎症、感染等等，其活躍性會被顯示出來。如果以攝影來做比喻的話，PET Scan 就像一個紅外線相機，而 CT 就是一部高清數碼相機。現在很多癌症病人進行的 PET-CT scan 就是結合了 PET 的功能性及 CT 的結構性檢查，所以正電子斷層掃描非常全面。建議每個病人應該和專家討論，並結合臨床病徵，以便確定最佳的診斷方法。

PET 掃描主要用作檢測和監控包括癌症、腦部神經障礙和心血管疾病等病症，比其他影像技術（例如電腦斷層掃描和磁力共振成像掃描）更早檢測出癌症，亦可確定癌症是否正在擴散至其他身體部位，以及擴散至何處。

PET 掃描可顯示大腦哪個部位導致腦癇發作，有助制定腦癇症的緩解手術。這檢查也同時用作評估阿茲海默症和柏金遜症，產生的影像可精確地指出未正常運作的大腦區域。及早發現神經系統失調可讓病人接受更有效的舒緩。

1. Patients should not have undergone any barium x-ray examination 10 days prior to the PET-CT scan.
2. A 6-hour fasting is required prior to the scan. Consumption of alcohol and beverages is prohibited (except water). Avoid medication with high sugar content (e.g. cough syrup, glucose). Avoid chewing gum or candy.
3. A bland and easy-to-digest diet is recommended 1 day prior to the scan.
4. Patients are advised to drink enough water, at least 6 to 8 cups of water 1 day prior to the scan.
5. Avoid intense muscular activities such as strenuous exercise and heavy lifting.
6. Pregnant and lactating women, people with unstable emotions, people with acutely persistent muscle cramps, and diabetic patients with poor blood sugar control should not be screened.

The radiopharmaceutical (also known as a tracer) is injected into the patient's body prior to the scan. The radiotracers usually accumulate in diseased tissues more than in healthy tissues. The images of the body are then acquired by a gamma camera in the PET scanner. The camera detects the positrons emitted from the tracers in the body, and a multi-dimensional image of the examined body part will eventually be generated by the computer. The patient has to lie still after the injection for about 1 hour to wait for the drug to be absorbed, followed by a full body scan (about 30 minutes). The patient will take another 1-1.5 hours of rest as the radiotracer becomes less radioactive over time. The risk of having side effects is low.

PET scans are rarely recommended for pregnant and breastfeeding women.

Children are more susceptible to radiation than adults and are not suitable for PET scanning.