CT - Your questions answered

What is CT?

Most people are familiar with the term 'CT' or 'CAT' scan.  This stands for 'Computed Axial Tomography'.  The scanner which produces these scans looks like a giant upended ring doughnut.  The patient moves through the ring on a couch and at the same time the x-ray machine in the ring takes pictures from many different angles. 

The images obtained are then processed by a computer to give 2D cross-sectional views (tomograms) or 'slices' through the body.  The images can be further manipulated to give 3D views of the internal organs.

Many patients have an injection of dye or 'contrast' into a vein which enables internal structures to be outlined and seen in more detail, or are given a special drink which serves the same purpose. 

CT was developed in the late 1970s but the technology has evolved extremely quickly and CT is now the diagnostic imaging tool most widely used in complex cases.  Such is the demand that CT scanning is now available 24 hours a day every day of the year at both Cheltenham General and Gloucestershire Royal Hospital. 

What conditions is it used to diagnose? 

In addition to diagnosing traumatic injuries, cancer, and many other cranial, chest and abdominal conditions, the new scanner is also capable of: 

 

• In patients who have suffered a stroke, rapid and accurate identification is possible of areas of the brain who functionality can be restored if treated quicky. (This process invoves analysis of cerebral blood flow to determine whether to proceed to thrombolysis.)
• In patients with acute chest pain (who often come in to the hospital via A&E), coronary artery disease can be diagnosed with one scan, without the need for the many tests, some invasive, which would otherwise be necessary.  Other conditions such as dissection (split arteries) and pulmonary embolism (lung clot which can be fatal) can be excluded at the same time.  (Highly accurate carotid and coronary artery scanning means there is no need for invasive cardiac catheterisation.)
• CT of the bones produces highly accurate images of the joints and can be used in complex orthopaedic problems.
• Colonic cancer can be diagnosed using 3D imaging of the inside of the colon.
• Problems in bood circulation can be diagnosed using CT limb angiography to track blood flow through veins and arteries.

 

 

How many patients do you see each year?

Over 22,000 CT scans will be carried out in 2011 in Cheltenham and demand is rising steadily by 8-10% per year. 

Where are they referred from? 

• Patients are referred from all specialties within the hospitals in eastern Gloucestershire, with Oncology, General Medicine and General Surgery referring most patients. 
• The Emergency Department is increasingly using CT to decide whether to admit or discharge patients. 
• Complex scans are performed for Cardiology and for Vascular Surgery with the new scanner this service will expand. 

What conditions do they have and numbers? 

About 73% of patients undergoing CT scanning in Cheltenham have cancer-related problems.  These patients are referred not only from the on-site Gloucestershire Oncology Unit but also from Hereford, Worcestershire and Eastern Wales. Around 65 -70% of patients referred for CT scans have been diagnosed with, treated or followed up for cancer. 

Examples of the purpose of these scans include: 

• Many hundreds of patients are scanned each year as part of clinical trials. 
• Patients with prostate cancer have CT to look for secondary cancers in their bones, lymph node enlargement and to work out the best place to position brachytherapy seeds if they are going to have this treatment. 
• CT images are used to guide instrument placement during biopsies and procedures to drain the fluid which builds up around tumours. 
• CT is used to assess the pulmonary arteries, as cancer patients are more prone to clots than other patients, and also the coronary arteries in patients on drugs such as Herceptin, which are cardio-toxic (i.e. can adversely affect the heart).  

What's the problem with not having a new CT? 

1. We currently have two scanners in Cheltenham, one 4-slice scanner and one 32-slice.  We would like to replace the 4-slice scanner with a 320-slice scanner.  As you can imagine, the difference in detail between the images produced on the scanners is enormous.  The images obtained on our current scanner are not always clear enough to advance diagnosis and the machine is not capable of performing the new and more complex examinations recommended by NICE.  
2. Our machine takes longer to carry out scans than newer models.  This has several consequences: 

• The technique is unsuitable for patients in discomfort who are unable to lie still for long enough for satisfactory images to be produced. 
• On any scanner, breath-holding is required for clear images to be obtained.  Patients  will not need to hold their breath for as long on the new CT scanner so that breathless patients can be scanned. 
• Patients will not spend as long in the new scanner, which in turn means the radiation dose is reduced. 

What are the patient benefits of a new CT? 

A new CT scanner would enable us to provide a much better service to the huge number of patients undergoing CT scanning.  In particular: 

• Use of the new scanner would dramatically reduce the duration of scans and therefore the radiation dose to patients, e.g. scan time for a scan of the chest, abdomen and pelvis would be reduced from 26 seconds on a 32-slice scanner to 4 seconds; radiation dose from a CT of the heart would be reduced from 15 mSv to 1 mSv (this equates to the dose delivered by 100 chest x-rays, as opposed to that of 1500 chest x-rays on the old scanner). 
• More complex types of scan could be offered, e.g. detailed scanning of the whole heart, which can assess heart function and detect coronary artery disease without the need for more invasive procedures.  Each of these scans would take only 0.35 seconds.  This amazingly short scan time would enable patients with acute chest pain to be imaged, markedly speeding up diagnosis. 
• More patients could be scanned, and CT could be performed on patients for whom it is currently unsuitable.  

How many are there in the region/country? 

There are currently about 6 scanners of this type in the country. 

What research could it be used for? 

One of our radiologists, Dr Garrett McGann, is one of only four in the south west who has attained the BSCI Level 3 accreditation necessary to teach cardiac CT scanning.  If we had a new CT scanner installed on the CGH site, it would enable trainees on attachment to our department to gain valuable experience in this technique and provide them and other staff with many opportunities to develop research projects focussing on the use of cardiac CT. 

How will we measure the success of having a new CT? 

We should see a decrease in referrals for investigations which will no longer be necessary once CT investigation for acute chest pain becomes possible, e.g. cardiac catheterisation, MUGA scans. 

Is it a new way of working? 

The introduction of cardiac CT in the investigation of acute chest pain could revolutionise how this is managed. 

Who are the key people involved? 

• Radiographers, who carry out the scans 
• Radiologists, who
  • decide which type of scan is required for each patient, according to what condition is to be diagnosed/what question is to be answered
  • supervise complex scans
  • interpret the scans obtained and send reports back to referrers 
• Cardiologists 

Cheltenham General Hospital has a large radiology department, with 12 radiologists who are all involved in CT, each specialising in imaging of a different area of the body.  The lead radiologist is Dr Garrett McGann. 

The lead radiographer for CT in Cheltenham is Mr David Reed.  There are a further 12 radiographers in the CT team.