CT Scans - Information for Patients

  • What is CT?
  • Why do I need a CT scan?
  • What happens in a CT exam?
  • How do I prepare?
  • Any risks or side effects?
  • CT Safety

What is a CT Scan?

 

A CT scan (CAT scan) is a non-invasive medical test that helps physicians diagnose and treat medical conditions. CT imaging combines special x-ray equipment with sophisticated computers to produce multiple pictures of the inside of the body. These cross-sectional images of the area being studied can then be reviewed in a multiplanar fashion on a computer workstation.

CT scans of internal organs (such as the liver, pancreas, lungs and kidney), bone, soft tissue and blood vessels provide greater clarity and reveal more details than routine x-ray exams.


Why do I need a CT Scan?

In the same way that an X-Ray would be used to detect a possible bone break, a CT is used as a very accurate method of disease detection throughout the body. Surgery can be deferred or treatments more accurately directed when your consultant has read the results of your CT scan.

CT scans are useful in a number of areas:

Analysing the size and location of tumours

Tumours in various parts of the body can be detected and measured by CT. Repeat CT scans are used to show change in size of the tumour after treatment and to rule out tumour recurrence after surgery. CT and MRI frequently complement each other and your doctor and your radiologist will refer you for the most appropriate test first depending on your clinical presentation.

Diagnosing brain disorders

CT can give very detailed images of the brain. CT is particularly sensitive for the detection of intracranial haemorrhage which may be spontaneous or as a result of a head injury. CT is used in the initial assessment of patients presenting with stroke. CT and MRI frequently complement each other and your doctor and your radiologist will refer you for the most appropriate test depending on your clinical presentation.

Evaluating the lungs for respiratory disorders

Chest X-rays are a useful tool in the assessment of respiratory disorders. High resolution CT (HRCT) is used to specifically characterise interstitial lung diseases which may not be apparent on conventional X-rays. CT is particularly well suited to detect other pulmonary conditions including lung cancer and pulmonary emboli.

Investigation of haematuria and renal calculi

Multidetector CT has a significantly higher sensitivity and specificity than IVU. It also takes less time to perform and is better at revealing alternative diagnosis as the cause of patient's symptoms. CT KUB and Urography are used to investigate suspected renal colic or unexplained haematuria where calculi, cysts and other renal masses can be assessed. Your GP or Urologist will decide if they feel that this test is indicated.

Assessing sinus disorders

CT provides rapid and accurate assessment of disorders of the paranasal sinuses and can demonstrate conditions which may not be apparent on conventional X-rays. Deviation of the nasal septum, the presence and location of mucosal thickening, retention cysts, inflammatory change, polyp disease and tumours may be depicted on CT. Your doctor or ENT specialist will decide if they feel CT of the paranasal sinuses is indicated.

Evaluating complex or subtle bony Injuries

Occult fractures which may not be evident on conventional X-rays may be shown in exquisite detail. Multiplanar 3D images of complex fractures can help your doctor or surgeon better understand your injury and plan the most appropriate treatment or surgery.

Assessing vascular disorders

CT is imaging modality of choice in the assessment of aneurysms and dissections of the thoracic and abdominal aorta. CT is useful in the assessment of the carotid, vertebral, renal and mesenteric arteries. CT may be used to assess the peripheral circulation. In elderly or diabetic patients the presence of calcified plaque may make assessment of the tibial and pedal vessels difficult and these patients may be better suited to having MR angiography.

Viewing the spine

CT can accurately depict injuries such as fractures of the spine. MRI is superior in looking at disc disease. CT can prove very helpful when used in a targeted fashion to confirm the presence of spondylolysis or to assess those patients with radicular pain for whom MRI is contraindicated.

What happens during the procedure?

The CT scanner itself is very quick, taking no more than 1- 2minutes to acquire all the images required.

The radiographer begins by positioning you on the CT table, usually lying flat on your back. Dilute contrast material may be used to help opacify your stomach and bowel. This is given as a drink taken up to 1 hour prior to your scan. Frequently contrast is injected through an intravenous line (IV) to help show up the blood vessels in the body and to help distinguish abnormalities which are hypervascular from normal or hypovascular lesions.
The table will move through the scanner to determine the correct starting position for the scans. Then, the table will move through the machine as the actual CT scanning is performed. You may be asked to hold your breath during the scanning. The radiographer will also keep an eye on you through an observation window during the scan and there is an intercom to let you talk to each other if necessary.

When the examination is completed, you will be asked to wait until the radiographer verifies that the images are adequate for accurate interpretation. The total time that you will be in the scan room is usually 15-20 minutes or less.

Who interprets the results?

A Radiologist (a Physician with specialist expertise in supervising and interpreting radiology examinations), will analyse the images and send a report to your GP or referring physician, who will discuss the results with you.

All Radiolgists working at Merlin Imaging are Consultants with University Teaching Hospital appointments and have full registration with the Medical Council being listed on the Register of Medical Specialists.

How do I prepare for a CT Exam?

You should wear comfortable, loose-fitting clothing to your exam. You may be given a gown to wear during the procedure. Metal objects including jewellery, dentures and hairpins may affect the CT images and should be left at home or removed prior to your exam. You may be asked not to eat or drink anything for several hours beforehand, especially if a contrast material will be used in your exam.

You should inform your physician of any medications you are taking and if you have any allergies.

Inform your doctor of any recent illnesses or other medical conditions, and if you have a history of heart disease, asthma, diabetes, kidney disease or thyroid problems.

Women should always inform their physician and the CT radiographer if there is any possibility that they are pregnant.


Are there any risks or side-effects?

A CT scanning is completely painless like a normal X-ray. A CT scan is also a very low-risk procedure. For information on the benefits and risks X-rays we hope you find the following leaflet useful :

X-Rays : How safe are they?

Download now

Your Doctor or Consultant has referred you for a CT scan as they consider that the benefits of a CT far out weight the small risk associated with this examination.

If you are :

  • over the age of 75
  • have diabetes
  • have kidney disease or a history of kidney surgery
  • have high blood pressure/ angina/ heart disease
  • have myeloma
  • take anti-inflammatory or pain medication
  • have liver disease
  • are taking Metformin (Glucophage)

Please notify your referring physician as it may be necessary to have perform a simple blood test prior to your CT scan.

For specific advice regarding Metformin (Glucophage) please do not hesitate to contact us.

Women should always inform their physician and x-ray or CT radiographer if there is any possibility that they are pregnant.

CT Safety

If the patient:

  • is over the age of 75
  • has diabetes
  • has kidney disease or a history of kidney surgery
  • has high blood pressure/ angina/ heart disease
  • has myeloma
  • takes anti-inflammatory or pain medication
  • has liver disease
  • is taking Metformin (Glucophage)

It may be necessary to perform a simple blood test prior to the scan. For specific advice regarding Metformin (Glucophage) please do not hesitate to contact us.

Women should always inform their physician and X-ray or CT technologist if there is any possibility that they are pregnant.

Allergies

Please notify us in advance if patients have a history of allergies to contrast.