Department of Radiology,
Lister Hospital,
Stevenage,
Herts SG1 4AB

Email: Dr. Amerasekera
Tel: 01438 781 028
Fax: 01438 781 176

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CT Scans

CT stands for Computerised Tomography It uses X-rays and a sophisticated computer to produce pictures of the inside of the head or body. The Service is available at Lister Hospital Stevenage. There no CT Scanner at Pinehill Hospital Hitchin.

What is a CT scan?

The CT scanner is operated by rotating an x-ray tube around your body while measuring the constantly changing absorption of the x-ray beam by different tissues in your body. The information is then fed into a computer which produces a reconstructed image of a thin cross section or "slice" of the body. Because the scanner is very sensitive, small differences in absorption of the beam by various body tissues are recorded sharper and clearer than even the best x-ray.

You may be startled by the size and shape of the scanner. Remember nothing touches you, so it will not hurt. You will be asked to lie on the table, usually on your back, and usually with your arms over your head. The moveable table will raise, lower and move in and out of the scanner. It is extremely important that you do not move during the entire procedure, which lasts from 15-30 minutes depending on the examination. The radiologist will study the final images and report the findings to your physician, who will in turn discuss the results with you.

Common CT Scans

• CT Scan of Head

  Looks at the skull bones for possible fracture; Brain for possible stroke, bleeding,tumours or abcess. Head CT: Your head will be placed in a holder with a strap across your forehead. Images will be taken. The examination will take from 15 - 30 minutes. No prior preparation is required. Sometimes intravenous contrast is required, which will be given in a vein in the arm or hand.

• CT Scan of Neck and Back

  This is done to look at the anatomy of spinal canal such as spinal stenosis ( tightness around the spine), possible fracture, or nerve impingment (nerve getting pressed by bony spurs or disc herniation).

• CT Scan of Chest

  To look at the lungs,heart, lymph nodes and the large vessels usually evaluating an abnormality first seen on a chest x-ray. Most chest CT scans are performed with an IV contrast and prior preparation is not necessary. You will be lying on your back with your arms above your head. The technologist may instruct you to hold your breath for each exposure. The examination should take from 20 minutes.

• CT Pulmonary Angiogram

  CT Pulmonary Angiogram CT pulmonary angiogram has evolved as the most sensitive test for the diagnosis of pulmonary embolic disease, the most common cause of unknown sudden death . Pulmonary embolus is caused by a blood clot which travels to the lung restricting blood flow to the heart. Symptoms may include dizziness, hypotension (loss of blood pressure) or difficulty breathing. CT pulmonary angiogram involves injection of a contrast material into a vein in the arm and CT imaging of veins to detect a suspected blood clot in the lungs.

• CT Scan of Abdomen and Pelvis

  Allows detailed look at the different organs in the upper and lower abdomen and pelvis. eg. Liver, Gall bladder, bile ducts, Pancreas, Kidneys, Spleen, Aorta , IVC and lymph nodes. Most CT scans of the abdomen and/or pelvis require preparation prior to the study. Usually you will be asked to skip the meal immediately prior to your exam. For an abdomen CT, you will be given a bottle of contrast material that outlines the intestines on the image and another bottle just prior to getting on the table for your exam. Most CT scans of the abdomen require an IV contrast injection in the hand or arm. You will be positioned on your back on the scan table with your arms over our head. You may be instructed by the technologist to hold your breath for each image taken. A scan of the abdomen and pelvis should take approximately 20 minutes.

• Pancreatic Cancer Cancer of the pancreas is a disease in which cancer (malignant) cells are found in the tissues of the pancreas. The pancreas lies behind the stomach, inside a loop formed by part of the small intestine. The broader right end of the pancreas is called the head, the middle section is called the body, and the narrow left end is the tail. About 95% of pancreatic cancers begin in the exocrine pancreas producing digestive enzymes. The hormone-producing area of the pancreas is called the endocrine pancreas. Only about 5% of pancreatic cancers start here.Cancer of the pancreas is hard to diagnose because the organ is hidden behind other organs. The signs of pancreatic cancer are like many other illnesses, and there may be no signs in the first stages. You should see your doctor if you have any of the following: nausea, loss of appetite, weight loss without trying to lose weight, pain in the upper or middle of your abdomen, or yellowing of your skin (jaundice). If you have symptoms, your doctor will examine you and order tests to see if you have cancer and what your treatment should be. You may have an ultrasound, or a CT scan. Another special scan called magnetic resonance imaging (MRI), which uses magnetic waves to make a picture of the inside of your abdomen, may be done as well. A test called an ERCP (endoscopic retrograde cholangiopancreatography) may also be done. During this test, a flexible tube is put down the throat, through the stomach, and into the small intestine. Your doctor can see through the tube and inject dye into the drainage tube (duct) of the pancreas so that the area can be seen more clearly on an x-ray. During ERCP, your doctor may also put a fine needle into the pancreas to take out some cells. This is called a biopsy. The cells can then be looked at under a microscope to see if they contain cancer.You may need surgery to see if you have cancer of the pancreas. If this is the case, your doctor will cut into the abdomen and look at the pancreas and the tissues around it for cancer. If you have cancer and it looks like it has not spread to other tissues, your doctor may remove the cancer or relieve blockages caused by the tumor.
• CT Scan of Sinuses

  Indications for Sinus CT Imaging

1. Patient is considered a candidate for surgery Acute sinusitis with suspected intracranial or intraorbital extension
2. Patient with severe facial pain or headache when nasal endoscopy is not diagnostic
3. Patient fails to respond to standard therapy, including antibiotic treatment.
4. Prior to sinus endoscopy

• CT Scans of the arteries are called CT Angiography

• CT Scans are used to position needles accurately within the body for biopsy and other interventional procedures

• Virtual colonoscopy

  Is a new and still evolving technique which could one day prove to be more convenient and less expensive than traditional methods of colon cancer screening. A major advantage of virtual colonoscopy is its non-invasive nature and may increase the public's willingness to be screened for colon cancer. It is a kinder and a gentler bowel examination for the patient.Virtual colonoscopy involves spiral CT and computer technology. The procedure is quick and can be performed in less than a minute and carry little risk. It is used as a screening procedure as it is more attractive to patients than fibreoptic colonoscopy or barium enema. The cost of virtual colonoscopy would be lower than that of conventional bowel examinations. It can always reach the caecum and can also determine the degree of wall invasion when a neoplasm is found. Colorectal cancers almost always begin as abnormal growths, or polyps, springing from the lining of the large intestine or rectum. If the polyps are detected and removed before they become malignant (the chance of malignancy increases significantly as the polyp grows) the patient can escape this deadly cancer. Virtual colonoscopy is capable of identifying polyps and other small lesions.
• The patient's colon is cleansed using laxatives.
• The colon is inflated with gas.
• The abdomen and pelvis are scanned using spiral CT.
• CT images are manipulated by a computer to generate a virtual reality image of the colon. The result is a three-dimensional picture of the colon presented on a computer monitor. The whole length of the inside of the colon can be visualised in this way and the Radiologist will view the 3D images and formulate the report.

CT Scanning of children and infants

Generally, children and infants are given a light general anaesthetic or sedative. This is to ensure that they lie still during the test, which can take up to an hour. If your child requires an anaesthetic you will need to make sure he or she does not eat or drink anything for six hours before the test. You will also be given the opportunity to speak to an anaesthetist and will be required to sign a consent form. Children who have had sedation or an anaesthetic can usually go home one or two hours after the test, if all has gone well.

Spiral Computed Tomography

Spiral CT is an imaging modality which combines X-ray pictures which are processed by a computer to create topographic, or cross sectional images. These images can be combined to produce a 3 Dimensional Image. CT scanning is very sensitive to bone making it a good imaging choice for detecting fractures and visualizing particularly small bones such as facial bones. The CT's ability to take cross sectional images allows the visualization of many organs. Injections of an iodine contrast media are used to highlight a particular area of interest. Other advantage of Spiral CT is the extremely shortened scanning times, (over half the scanning time of conventional CT) minimize the time the patient must remain on the examination table and provide for quicker diagnosis.

Contrast Agents

Contrast agents are radio-opaque substances which are introduced into the body by mouth, per rectum or by injection. Some patients are allergic to these contrast agents. if you are allergic to any substances or have asthma or hay fever it is very important that you mention this to the Radiologist who will be performing the examination.

Background

In recent years (1986 to the present), several "nonionic" or "low osmolar" agents have been introduced and widely marketed in the U.S. and UK. These include iohexol (Omnipaque, Winthrop), iopamidol (Isovue, Squibb) and ioversol (Optiray, Mallinckrodt). An additional agent, ioxaglate (Hexabrix, Mallinckrodt) is best described as an ionic, but low osmolar contrast agent. We will subsequently refer to this group of agents interchangeably as either nonionic or low osmolar, unless specified otherwise. The cardiovascular effects of the newer low osmolar agents have been thoroughly investigated during premarketing surveillance and subsequent clinical use (7-14). These data suggest that the low osmolar agents are better tolerated than the high osmolar agents and are possibly safer in hemodynamically compromised patients, but that the low osmolar agents are much more expensive.

The low osmolar agents cost approximately 10 times more than conventional ionic agents. Despite the high cost, use of these agents is increasing. In our practice we do not use ionic agents intravenously . Controversy exists over whether the possible safety benefits of low osmolar agents outweigh their substantial increase in costs.

Administration of high osmolar contrast agents produces a systemic arterial vasodilation. This phenomenon results in characteristic flushing or sensation of warmth experienced by the patient. These effects are dose dependent. This sensation is clearly reduced by low osmolar agents.

Renal Toxicity

Administration of iodinated contrast medium may produce acute renal insufficiency. This is frequently manifested as an alteration in the laboratory measures of renal function, but less commonly requires treatment with dialysis or results in permanent injury. A number of risk factors have been identified in predicting this complication including diabetes mellitus, multiple myeloma and volume depletion.

Allergic Manifestations

Anaphylactoid reactions occur in 1% to 2% of patients undergoing procedures utilizing iodinated contrast media. The incidence of severe reactions is approximately 0.1%.

Morbidity and Mortality

Fatal reactions to contrast media are very uncommon. Several very large scale radiologic studies have compared complications (including mortality) in patients who receive contrast agents, usually intravenously, for procedures such as pyelography or computed tomography. However, these large studies were not randomized and the choice of contrast agent was determined by the radiologist. The low incidence of contrast agent related mortality in general radiography (I in 40,000) has precluded definitive conclusions from the published studies regarding the relative mortality risk of the available agents.

Preparing For Your Scan

If you suffer from any allergies, asthma or hayfever please inform the Radiologist. If you have had a reaction to any injections please let us know. Those on tablets (Metformin) for their diabetes ask the Radiologist whether it is safe to proceed with the examination. We take great care to avoid reactions to contrast although reactions are rare. You are most welcome to speak to the Radiologist or the Radiographer if there are any queries. Phone: Lister 01438 781028 or Pinehill 01462-422822 If you are taking treatment for kidney or heart problems please let the Radiologist know and discuss this with your own Physician

• At home

  Just relax, go about your normal routine and continue to take any prescribed medicine Please follow the enclosed instructions, which are specific to your scan.

• At the Department of Radiology

  Report to the Department of Radiology, 10 minutes prior to the appointment time.

• Will I have to undress?

  For examinations of the chest, abdomen, pelvis or spine you will be asked to undress and put on a hospital gown and dressing gown. You are welcome to bring your own dressing gown if you prefer.

• Will I have an injection?

  Sometimes it is necessary to give you an injection to show up specific parts of the body The pictures obtained after the injection may give vital extra information You may be asked to drink something to help show up the stomach and the rest of the bowel.

• Will it be painful?

  You will feel nothing from the scan itself You will be asked to keep very still and, in some cases, to hold your breath, as moving can blur the pictures There is an automatic voice inside the Scanner which will instruct you to hold your breath at the appropriate time.

• How long will it take?

  This procedure will take up to 45 minutes. It does not hurt and you should experience no after effects. Please allow 2 hours for your stay in the Department, as occasionally emergency cases arise, causing unavoidable delay to booked appointments.

• Who does the scan?

  The person who carries out the scan is called a Radiographer. He or she will explain how to position yourself and make sure you are as comfortable as possible. It is important that you stay still the whole time the pictures are being taken.

• After the scan

  Please don’t ask the Radiographer for the results. Your pictures will be interpreted by a Consultant Radiologist who will send a report directly to your Doctor. That is why you have to wait a few days for the results.

• Known benefits

• Detailed images mean greater accuracy in detecting disease
• Early detection means early treatment
• CT Scans are painless

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Copyright © 2000 - Dr. Douglas Amerasekera