Computed Tomography (CT) combines the use of X-Ray and computing software to create detailed pictures of the body to look for any injuries, growth or abnormalities.
A Computed Tomography (CT) scan is a procedure performed using an X-ray scanner to produce detailed cross-sectional imaging of the body, including bones, muscles, organs and blood vessels. The CT machine resembles a large “doughnut” with a scan table going through the middle. Patients are required to lie down on the scan table which will move in and out of the machine during the scan as CT images are acquired.
Although ionising radiation is used during a CT examination, the benefit of an accurate diagnosis derived from the CT examination usually outweighs the radiation risk.
CT scans can be performed with or without contrast media. A radiological dye, also known as contrast media, may be used to highlight the blood vessels and organs during the scan to aid in detection of abnormalities. The contrast media can be administered orally (by mouth), rectally (by enema) or intravenously (by blood vessel).
A CT examination can vary between 5 to 20 minutes and is performed by a trained Diagnostic Radiographer. During the scan, the machine may produce faint sounds due to the rotation of X-ray tubes within. The CT examination does not cause any pain. However, you may experience some discomfort from having to lie still or during the administration of contrast media (if any).
As with most radiological procedures, there may be preparations that will be required to be done by you. Below are some preparations needed to ensure a successful and smooth CT scan appointment.
Please inform your doctor if you have a history of asthma. You may require some preparatory medication if your scan requires the use of contrast media.
Please inform your doctor if you have done imaging tests previously with contrast media and had developed allergic reactions subsequently (e.g. rashes, swelling around the eyes). You may require some preparatory medication prior to the scan. An alternative diagnostic test may also be suggested.
If you have problems with your kidney function or currently on dialysis, please inform your doctor before scheduling the examination. You may be asked to do a creatinine serum blood test to check for your kidney function before the day of your CT scan appointment. The blood test, if done on the same day as the CT examination, will be sent to the laboratory for processing and can take up to 2 hours from your scheduled appointment time.
Metformin is encouraged to be withheld for 48 hours after the administration of intravenous contrast media unless otherwise indicated. Do check with your doctor or the attending Radiographer when in doubt.
If you are pregnant or think you may be pregnant, please inform your doctor before scheduling the examination. For females of child bearing age (12 to 55 years old inclusive), you will be asked for the first day of your last menstrual period (LMP) and if there is any possibility of pregnancy prior to the scan.
If you have done a CT scan recently or scheduled to do a CT scan with another clinician, please inform your doctor before scheduling the examination.
As you will be going through the middle of a "doughnut", please inform your doctor before scheduling the examination if you are claustrophobic or easily anxious.
If your scan is ordered without contrast, you can eat and drink prior to your examination.
If your scan is ordered with contrast, do not eat anything 3 hours prior to your scan. Sips of plain water is allowed. You may also take your prescribed medications unless otherwise instructed.
You are advised to wear loose clothing without accessories (e.g. buttons, zippers, hooks, piercings, and jewellery). You may be asked to change into a hospital gown depending on the type of scan. A locker will be provided to secure your personal belongings.
CT scans are done mostly with patient lying supine. If you have difficulties lying on your back, please inform your doctor before scheduling the examination.
CT Scans with Contrast Media An intravenous (IV) cannula (a thin tube intended for collection of sample/delivery of fluid) will be inserted on your peripheral hand or arm prior to the scan to allow administration of IV contrast media.
For oral contrast, you will be asked to drink the contrast media at interval timings before the scan. You may need to wait up to 2 hours from your scheduled appointment time for a better visualisation of your bowels during your scan.
You will be asked for any history of asthma, diabetes, contrast allergies or multiple drug allergies prior to the scan. If you have not taken the prescribed preparatory medicine before the scan as required, we may need to reschedule the scan appointment.
Scan Procedure You will be asked to lie down on the scan table which will be raised to move into the CT machine. During the scan, the radiographer will be in the control room where the scanner controls are located. You will be in constant sight, and you can communicate with the radiographer through the telecommunication system inside the CT machine if you have any concerns or feel discomfort.
It is important for you to remain still during the scan to ensure that the CT image quality is optimal for accurate diagnosis. You may be asked to hold your breath or swallowing depending on the type of scan.
When contrast media is injected intravenously, you may feel some effects for example, a warm flush though your body, metallic taste in the mouth, headache, nausea or the sensation to urinate. These effects usually last for a short period of time.
Our radiologists will review and report your scan images. A small number of patients may be recalled back by the radiologists after the scan for additional imaging to ensure accuracy of the CT report. The scan results will be sent electronically to your referring clinician who will discuss it with you on your next appointment.
CT Scans with Contrast Media For patients who have undergone the CT examination with contrast media, you will be monitored for any signs or symptoms of an allergic reaction after your scan. If you develop any symptoms like shortness of breath, body redness, itchiness or swelling, please inform any medical staff. If you develop any symptoms at home, head down to the nearest Emergency Department and inform them that you have went for a CT scan with contrast media earlier in the day.
The IV cannula used for intravenous injection of contrast media will be removed after the scan. You are advised to drink plenty of fluids to facilitate the excretion of contrast media from your body. You can resume your usual diet and activities unless differently instructed.
For patients who are on diabetic medication (Metformin), you may be asked to stop your use of medication for 48 hours after the scan.
For nursing mothers, you are advised to wait for 24 hours after the scan before resuming breast feeding. You may wish to plan ahead and ensure sufficient storage of breast milk in anticipation of this. Breast milk from both breasts express during the 24 hours after the scan may be discarded.