CT Scan: How It Works and What To Expect

What is a CT scan?

A CT scan, or computed tomography scan, is a type of imaging test that combines regular X-rays with a computer algorithm. It works by rotating its X-ray scanner around the area of interest to produce cross-sectional images called "slices."

These slices can then be analysed individually or processed by a computer to create 3D images of your bones, blood vessels and organs. This technology overcomes the limitations of conventional X-rays, which are only capable of producing flat, 2-dimensional images.

How CT scans work

As explained above, a CT scan is basically a narrow beam of X-ray rotated 360° around a ring-shaped structure called a gantry. Each time the x-ray source completes one full rotation, its motorised bed will be gradually moved towards the gantry to capture another slice of the body as necessary.

A CT scan can produce images thanks to detectors on the opposite sides of the X-ray source that will catch the radiation passing through your body. As different tissues absorb X-rays at different rates, clear and detailed images of the body can be produced.

For example, calcium in bones absorbs the most X-rays, which is why bones appear white on CT scan images. However, other soft tissues like fat and organs absorb less radiation, making them appear grey. Organs such as lungs filled with air will appear black, as air absorbs the least amount of radiation.

When would I need a CT scan?

A CT scan can be performed when your healthcare provider determines that detailed images of specific body parts or organs are necessary to diagnose your condition or monitor treatment progress. This imaging technique can be used to assess a variety of medical conditions, including:

Traumatic injuries

• A CT scan can be used to identify fractures and internal bleeding in organs, muscles, or ligaments following a traumatic injury.

Joint and spinal conditions

• Computed tomography can assess conditions such as arthritis (joint degeneration) and various spinal conditions, such as herniated discs.

Cancer detection and monitoring

• This medical imaging technique can be used to locate, measure, and evaluate the spread of cancerous tumours in various parts of the body, such as the lungs, liver, pancreas, or brain.

• It can also be used to monitor how these cancerous cells are responding to treatments like chemotherapy.

Infections

• A CT scan can help to pinpoint infections in various parts of the body, such as abscesses (pus-filled pockets due to infection) or osteomyelitis (infection in a bone).

Vascular conditions

• To diagnose a vascular condition, a variation of CT scan known as CT angiography is used. A contrast dye, which can be given orally or through an IV, is used in this imaging method to make an x-ray picture of blood vessels and blood flow more clear.

• A CT angiography can detect various types of vascular conditions, such as aneurysms (swelling or bulging blood vessels), blood clots, and coronary artery disease (heart artery blockages or narrowing).

Gastrointestinal conditions

• A computed tomography scan can show problems with the intestines that block the flow of food from the mouth to the rectum. These problems include appendicitis (inflammation of the appendix), kidney stones, gallstones, ulcers, and more.

Brain and nervous system conditions

• A CT scan can be used to diagnose various neurological and brain conditions, including stroke, hydrocephalus (fluid buildup in the brain), traumatic brain injury, and brain abscesses (infections in the brain).

Kidney and urinary conditions

• Various kidney and urinary conditions, such as cystic kidney disease, urinary tract obstructions, and bladder cancer, can be assessed through this radiation therapy.

Respiratory and lung diseases

• CT scans are used to diagnose respiratory and lung diseases such as pneumonia, pulmonary fibrosis (a lung disease that scarred the lung tissue), pulmonary embolism (blood clots in the lungs), and tuberculosis (TB).

Congenital abnormalities

• This medical imaging can help identify birth abnormalities such as spina bifida (spinal cord abnormality) and other birth abnormalities in organs, blood vessels, or bones.

Other conditions

• A CT imaging can also be used to assess chronic pain or other unexplained symptoms that require further investigation.

If you would like more information about this imaging test, request a consultation with Thomson Medical. Our specialists can provide you with further explanation about CT scans, including the advantages and disadvantages you should be aware of.

What to expect during a CT scan

To take a CT scan, you'll need to visit a hospital or imaging centre equipped with this medical device. The scan can be conducted either on an outpatient basis or as part of your hospital treatment.

A CT scan is quick and painless. The whole process won't take longer than 15 minutes to complete. The CT scan procedure may vary depending on your condition and your doctor's practice, but in general, here is how this imaging test is performed:

Before the CT scan

Before the CT scan begins, there are a few preparation steps that you need to take, including:

Filling the paperwork

• During the day of the procedure, it's recommended that you come early so that you’ll have time to complete any required paperwork or health history forms.

Allergy medication

• If your CT scan requires the use of contrast dye, your healthcare provider will assess whether you need to take allergy medications such as steroids and antihistamines. This is because iodine may cause some patients to have an allergic reaction, such as a rash.

Fasting

• You'll need to fast for at least 4 to 6 hours before the CT imaging to avoid any nausea post-procedure, especially if contrast dye is used. Even for CT scans without contrast dye, you should not eat anything for 2.5 hours beforehand.

• Even so, you'll still be able to drink water, strained fruit juices, tea, or even black coffee up to 2 hours before the scan begins.

Changing into a gown

• Before the procedure, you may be asked to change into a hospital gown and remove any jewellery, dental dentures, watches, or other metal objects that can affect the scan results.

Contrast dye administration

• Some types of CT imaging, such as CT angiography, require the use of contrast dye to highlight certain areas, like blood vessels or organs. This dye can be administered orally as a drink, through an intravenous (IV) injection, or in some situations, given rectally.

Notify the healthcare provider about your condition

• If you are taking medications for conditions like diabetes or are on blood thinners, it's recommended to consult your doctor before the procedure begins.

• Inform your doctor if you're pregnant or suspect you might be before the imaging tests. This is because a CT scan involves radiation, which could potentially pose a risk to your pregnancy or conception.

• Notify your healthcare provider if you have any body piercing on your chest and/or abdomen. 


• If your child requires a CT scan, parents may want to ascertain whether the healthcare provider has modified the machine settings specifically for children.

During the scan

After the preparation stage above, the procedures then will commence.

• During the scan, you'll lie on a motorised bed that gradually moves through the gantry. As the x-ray scanner rotates around you, you may hear clicking sounds, which are completely normal.

• You'll also be asked to remain still during the scan to capture clear x-ray images. Additionally, you may also be asked to hold your breath for a few seconds when the scan is focused on the chest or abdomen to minimise blurry images.

• If your procedure uses a contrast dye, you might experience a warm sensation, a metallic taste in your mouth, or a brief headache. Don't worry, this is a normal side effect and will be gone in a while.

• During this procedure, the CT scan operator (technologist) will be in another room to operate the scanner and observe the procedure. If any issues arise during the procedure, you can communicate with them through an intercom.

After the CT scan

• Once the scan is over, the technician will help you to get up from the bed. You can return to your normal activities right away, unless instructed otherwise by your doctor.

• If you received contrast dye, you’ll be recommended to drink plenty of water afterward to help flush it out of your body.

• A radiologist, a physician who specialises in interpreting CT scans and various radiologic examinations, will review the images from your CT scan. This report will usually be sent back to your healthcare provider within 24 to 48 hours.

• After your healthcare provider has evaluated the report, they will discuss the results with you at a follow-up appointment, usually within a few days after the CT scan.

If you require a CT scan, request an appointment with Thomson Medical. Our diagnostic radiologists are ready to help you determine if this is the right imaging test for your medical condition.

Cost of CT scan in Singapore

The cost of a CT scan in Singapore can vary depending on what type of scan is performed, ranging from approximately SGD 400 for a lung CT scan to around SGD 2000 for a CT coronary angiography (which are used to examine the coronary arteries of the heart).

To help cover the cost of a CT scan, you may use up to SGD 300 annually from your MediSave account. This annual amount increases to SGD 600 for cancer patients.

But you need to keep in mind that this MediSave scheme is only applicable to outpatient CT scans and is not applicable to standard X-rays or other types of scans, as these are covered by a different MediSave scheme.

The information provided above is intended for general reference only. For detailed fee information and payment options, please consult with your healthcare provider directly. Request an appointment with our specialists at Thomson Medical today for a detailed cost breakdown and personalised care plan.

CT scan side effects

CT scans are generally safe, but as this medical imaging uses radiation (X-rays) and sometimes uses contrast dye, there may be some side effects. Here are some of the side effects you may experience after undergoing a CT scan, such as:

Reaction to contrast dye

If your CT scan requires a contrast dye (either orally or through an IV), there’s a small risk of an allergic reaction caused by iodine contained in it. Here are some reactions that may happen, such as:

• Nausea or vomiting.

• A metallic taste in the mouth (particularly when oral contrast is used).

• A warm or flushed feeling, which is common when the contrast is administered via an IV.

• Mild skin rash or itch.

• Difficulty breathing.

• Swelling of the face, lips, or throat.

• Feeling fatigued for a short time.

Kidney problems

For patients with pre-existing kidney conditions, the use of contrast dye can potentially impair kidney function. This occurs due to the dye's direct toxicity to kidney cells, which can cause cellular damage and lead to a condition called contrast-induced nephropathy (CIN). 

To minimise this risk, it is important to notify your healthcare provider about any kidney issues prior to undergoing the procedure.

Radiation exposure

A CT scan utilises X-rays that emit radiation that can damage cells (ionising radiation). Even though a radiation dose from a single scan is low, cumulative radiation exposures from multiple scans over time can slightly increase the risk of cancer.

Discomfort or anxiety

Since the CT scanner (gantry) is shaped like a doughnut, you may feel anxious while lying on its motorised bed. If you experience any discomfort during the procedure, do not hesitate to communicate your concerns to the technologist.

You may also feel some discomfort from lying still for some time, but don't worry, as the CT scan procedure doesn't take long, this discomfort will usually go away on its own.

FAQ

What is a CT scan used to detect?

CT scans are used to detect a wide variety of conditions by providing detailed cross-sectional (slice) images of the body. These images can then be processed by computer algorithms to create a 3D rendering of the area of interest. Here are some common conditions that CT scans can test for, including:

• Traumatic injuries

• Joint and spinal conditions

• Cancer detection and monitoring

• Infections

• Vascular conditions

• Gastrointestinal conditions

• Brain and nervous system conditions

• Kidney and urinary conditions

• Respiratory and lung diseases

• Congenital abnormalities

What are the side effects of a CT scan?

Although a CT scan is a safe imaging technique, it does emit radiation and utilises contrast dye to make blood vessels and blood flow easily seen in the X-ray.

Because of this, there are some potential side effects you may experience after undergoing this procedure, including:

• Allergic reaction (such as nausea, mild skin rash, shortness of breath, and fatigue).

• Kidney issues.

• Discomfort or anxiety.

• Slightly increased risk of cancer if you need to do the CT scan multiple times.

What is the difference between a CT scan and an MRI?

Both MRIs and CT scans are medical imaging techniques that are capable of creating detailed images of the internal body to help diagnose a range of various medical conditions. Here are the differences between a CT scan and an MRI scan:

How long does a CT scan take?

A CT scan usually lasts between 10 to 15 minutes, but it can vary based on the specific area of the body being examined and whether a contrast dye is administered. After the procedure, you can return to your normal activities, unless instructed otherwise by your healthcare provider.

What cancers can a CT scan detect?

A CT scan can help your healthcare provider to assess a wide range of cancers, such as:

• Lung cancer

• Liver cancer

• Colorectal cancer

• Pancreatic cancer

• Kidney cancer

• Brain tumors

• Ovarian cancer

The information provided is intended for general guidance only and should not be considered medical advice. For personalised recommendations based on your medical condition, request an appointment with Thomson Medical.