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What is computed tomography (CT)?

A CT scan is an advanced diagnostic imaging procedure that uses a combination of X-rays and computer technology to construct images of the inside of the body including bones, muscles, fat, organs, and blood vessels. The images can be in two-dimensional or even three-dimensional form, depending on the technology and computer software. These detailed images allow doctors to detect any abnormalities or changes inside the patient’s body.


CT scans have been used in a wide variety of areas, notably for disease detection including cancer, cardiovascular disease, stroke, inflammation, calculi, and bone fractures. A CT scan may be performed depending on the patient’s condition.

Are there side effects with CT scans?

CT scans emit a limited dose of radiation with no noticeable side effects. However, patients may develop a reaction to the contrast media that is often used in CT scans. They may experience mild itching, swelling or rashes during and after the injection of contrast media. These are normal reactions which typically subside in about 3 to 5 minutes. The risks of CT scans are mainly related to the complications of the contrast media, which include:


  1. Mild side effects include itching, hives, nausea, vomiting, rashes, arm pain, sneezing, coughing
  2. Relatively severe side effects may include difficulty breathing, a fast heartbeat, chest pain, cramps, kidney failure, low blood pressure or coma
  3. Death is extremely rare with less than one death per 40,000 patients
  4. Few patients might show side effects retrospectively, including arm pain, itching, skin rash, salivary gland swelling, or pain


If you have had a reaction to any contrast media in the past and/or any other kidney problems, please advise your doctor or radiologist before undergoing a CT scan. If you are taking prescribed antidiabetic drugs that contains METFORMIN, you are advised to discontinue use of this medication the day before the scan. Before you discontinue the use of the medication, you must consult your GP.


The impact of radiation emitted from a CT scan during pregnancy remain largely unclear. Female patients should check with their doctor before scheduling the examination if they are pregnant or think they may be pregnant.

Ultra-low dose CT scanner - GE Revolution GSI

With the advanced iterative reconstruction technology, ASiR, the GE Revolution Gemstone Spectral Imaging (GSI) CT scanner at our centre allows a CT scan to be performed at ultra-low radiation – up to 50% dose reduction, but not at the expense of diagnostic image quality.


The innovative spectral imaging technology, the Gemstone DetectorTM, takes CT beyond classical anatomical assessment to quantitative tissue characterization and advanced functional imaging, achieving greater diagnostic accuracy. In terms of cancer diagnosis, the technology has greatly improved the clinicians’ ability to pinpoint the nature of cancer, differentiate between benign and malignant tumours, and detect small tumours that may hide in lymph nodes. Furthermore, the GE Revolution GSI incorporates a breakthrough in design, the revolutionary SnapShot Freeze technology is designed to reduce blurred artefacts due to motion in coronary vessels that cannot be addressed by gantry speed alone, providing best-in-class cardiac CT in greater efficiency and accuracy.

Are there any diagnostic methods that can replace MRI?

MRI is not the only imaging technique available for cancer scanning. There are various imaging procedures with different benefits and uses. Patients should consult their doctor and pick the scanning method that fits their actual diagnostic needs.


Benefits:Generate detailed images of internal body structures

Cancer Treatment:Breast cancer screening and diagnosis, including 3D mammography.

Level of Radiation:Minimal level of radiation


Benefits:Detect the real-time changes in organs but with a decreased sensitivity for tissues like bones and a lower imaging resolution.

Cancer Treatment:Cancer scanning such as prostate ultrasound and bladder ultrasound.

Level of Radiation:No ionizing radiation

Computer Tomography (CT)

Benefits:Capture the details of internal structures from many angles and produce two-dimensional and three-dimensional images.

Cancer Treatment:Applied to various cancer diagnoses.

Level of Radiation:A higher level of radiation that X-Ray but there is a low-dose CT scan
For more information

Positron Emission Tomography/Computed Tomography(PET-CT)

Benefits:Generate three-dimensional colored images with accuracy further improved by CT and data.

Cancer Treatment:Applied to early-stage cancer detection, malignant tumor detection, cancer staging, tumor localization, treatment monitoring.

Level of Radiation:The latest AsiR low-radiation technology can reduce 50% of radiation doses than conventional PET-CT scan.
For more information

Magnetic Resonance Imaging(MRI)

Benefits:Produce detailed images of the soft-tissue masses and nerves.

Cancer Treatment:Detect the location and changes of the tumor.

Level of Radiation:No ionizing rediation

Other Frequently Asked Questions

  • How long does a CT scan normally take?

    CT scans take about 10 to 15 minutes; cardiovascular tests take about 20 to 40 minutes.


    During a CT scan, the patient lies on a bed that slowly moves through the gantry while the x-rays rotate around the patient. A CT computer uses sophisticated mathematical techniques to analyse and construct images of the patient’s body and organs. The doctor may inject a contrast media to improve the accuracy of the images if needed. Children may need to be sedated to ensure a successful scan.

  • Can I eat before a CT scan?

    Patients are generally advised not to eat anything 4 to 6 hours prior to the test if their studies are ordered with contrast. They are advised to drink clear liquids and stay away from drinks that contain sugar. After the CT scan is completed, patients may resume normal diet. Alternatively, if the CT scan is to be performed without contrast, patients can eat, drink and take their prescribed medications prior to their exam.

  • What do I need to prepare before taking a CT scan?

    Please remove any metal objects such as dentures, belts, jewellery or glasses that might interfere with image results.

  • Who is likely to develop a reaction to CT scan?

    You are advised to inform your personal doctor about your allergies in the past. Before you get a CT scan test, your doctor should be aware of your current prescribed medications, and any history of food allergies, asthma, hives, eczema or allergic rhinitis (hay fever).