CT scanners look like a large doughnut (called the gantry) with a narrow, motorized bed. The motorized X-ray source rotates around the patient such that multiple projections of X-rays pass through the patient and are picked up by an electronic detector array. Each full rotation creates an image of a “slice” of the object, and the motorized bed moves into the gantry incrementally until the desired number of image slices is obtained. The image slices can be stacked together by computer to visualize the 3D internal structure of the object.
CT scan can produce detailed 3D images of internal organs, blood vessels and bones. As compared to plain film X-rays, which may show overlapping body structures on the image, CT scan eliminates the superimposition of images outside the area of interest and has greater resolution for a more detailed examination.
CT scan can:
CT scan can be performed on all body parts and is particularly useful to diagnose diseases or injuries involving many body parts (e.g. after a car crash) or to image complex body structures whose details are only visible on 3D images.
A CT scan without contrast generally requires no prior preparation.
If deemed necessary by the doctor, a contrast agent may be given to patients by injection, ingestion or enema to show soft tissues more clearly on the image, e.g. barium is used to highlight the digestive system and iodine is used to highlight blood vessels.
Also, you should:
CT scan uses X-ray that is radioactive and may increase the risk of birth defects. It is very important to inform your doctor or radiologist if you know or you suspect you are pregnant.
You will need to lie on the motorized bed that slides into and out of the gantry (the “doughnut”). Velcro straps or other devices may be used to keep you in position. During a head scan, a special cradle may be placed to hold your head still.
The CT scanner, unlike the MRI one, does not surround your entire body at once, so you should not feel claustrophobic. Once the part being examined gets in the correct position, the X-ray tube and the detectors of the scanner rotate around you, making a loud buzzing and whirring noise.
During the CT procedure, you must lie very still to avoid blurring the image. Sometimes, you may be instructed to hold your breath. Young children may be given sedatives to keep them calm and still.
CT scan should not have any aftereffects. However, if you have taken a contrast agent, you may need to wait in the hospital for up to an hour to make sure you feel well.
Your CT scan result usually will not be available immediately as the data need to be processed by the computer and analyzed by the radiologist. Your doctor/ radiologist will discuss the result with you when it is ready and proceed with the next steps if treatment is necessary.
It is a common concern that exposure to radiation such as that of an X-ray will lead to cell mutations and cancers. The amount of radiation you are exposed to during a CT scan depends on how much (and which parts) of your body are scanned. As a CT scan takes many X-ray images from different angles, the radiation dosage is generally higher than a plain film X-ray. While the dosage of a plain film pelvic X-ray scan is equal to the amount of natural background radiation in 4 months, that of a pelvic CT is equal to 4.5 years, with the risk of causing cancer being around 1 in 2,000, according to the UK NHS. Due to its higher amount of radiation, a CT scan usually will not be recommended for screening, but only when a condition is highly suspected and needs confirmation or monitoring by CT.
If the abdomen or pelvis is not being scanned, the CT scan is unlikely to expose your fetus to radiation.
An abdominal/ pelvis CT scan exposing your fetus to direct X-ray beams may cause harm if the amount of radiation exposure is high. Extreme high-dose radiation exposure within the first two weeks following conception may cause a miscarriage. 2 to 8 weeks after conception, high-dose radiation may heighten the risk of fetal growth restriction or birth abnormalities. Between weeks 8 and 16, exposure may increase the likelihood of developing a learning or intellectual disability.
The doctors will use the lowest possible amount of radiation in a CT scan so that the risk of the above harm is low. But it is a must to tell your doctor/ radiologist before having a CT scan if you are or may be pregnant. Your doctor may advise you to postpone the CT examination, calculate the fetal radiation dose carefully to minimize the dosage or consider other non-radioactive examinations (such as MRI).
CT examinations are classified as private services in the public healthcare system, with prices ranging from HK$740 to $5,480, depending on the body parts involved. Keep in mind that waiting times in the public sector can be extremely long (up to 3 years) due to the high demand.
In the private sector, you may visit any of the 13 private hospitals in Hong Kong, private clinics or imaging centers for a CT scan. Based on our research, the cost can range from HK$1,350 to over $19,000 per examination, depending on the body parts involved. Please contact your service provider for the exact pricing and appointments.
When prescribed by a medical doctor and used to make a diagnosis for treatment, CT scan fees are reimbursed in Hong Kong. However, most Hong Kong local plans have an annual cap and depending on the actual fees, you may have to pay any outstanding balance out of pocket. High-end medical plans, meanwhile, are more likely to pay CT scanning charges in full with no sublimits. Read your health insurance table of benefits for these categories: Diagnostic scans and tests, Brain and Body scans, Diagnostics, or Advanced Medical Imaging. Contact an Alea advisor at [email protected] if you have any health insurance questions.
A CT scan may take 10-30 minutes, depending on which parts of your body are being scanned.
CT scan is generally painless, fast and easy. You may feel some discomfort though when you need to stay still for several minutes while the scanner may be making loud noise.
Generally yes, except when the metal part (the nose piece) of the mask overlaps with the area of examination, it may interfere with the images.
This article was independently written by Healthy Matters. It is informative only and not intended to be a substitute for professional medical advice, diagnosis or treatment. It should not be relied upon for specific medical advice.
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