UPDATE - Issue 17 - April 2004
A quick scan of the patient scanning scene
Scanning has become a vital element in the diagnosis of tumours. Accurate location of cancerous cells enables treatment to be optimally focused with minimum side effects. We visited the Paul Strickland Scanner Centre at Mount Vernon Hospital Middlesex to learn more.
The Centre was opened in 1985. It has its fourth generation of CT (computer tomography) scanners, two MRI (Magnetic Resonance Imaging) scanners and a recently purchased PET (Positron Emission Tomography) system, one of only six in the country. The centre now carries out more than 10,000 scans each year.
Siemens Sensation 16
Magnetic Resonance Imager
Although all scanners look rather similar, the physical principles involved are quite different. CT scanning uses X-rays and is good at looking at bone. MRI makes use of what happens when the body cells are placed within an oscillating magnetic field. Much of its value lies in its ability to take images of soft tissue. PET scanning locates the positioning of radio-isotopes which the patient has taken earlier. It is commonly used to study glucose uptake and, hence, the metabolic rate of body tissues.
CT Scanning
While the patient passes through a CT scanner, an x-ray source and 16 detectors, mounted inside the body of the machine, rotate around the patient twice each second. The rotation of the detectors and forward movement of the patient enable the collection of a large number of images from different angles through the area being scanned. The computer analyses the output as a volume and then produces a series of cross-sectional images, often representing very thin slices.
CT scanning now provides a viable alternative for patients needing various oscopies because the sophisticated image collection and computer reconstruction enables doctors to fly through patients' internal organs without inserting a camera or probe.
MRI Scanning
A Magnetic Resonance Imaging (MRI) system uses a magnetic field to align molecules in the patient's body. The scanner transmits radio frequency waves into the patient which alters the molecular alignment. When the radio waves are turned off, the molecules return to alignment and send a signal back, which is picked up by aerials and converted into images. The switching on and off of the signal happens many times per second. The images produced are a series of slices as thin as 2mm and aligned in which ever plane displays the area best. Scans generally produce images in at least two planes.
There is a range of coils (the aerials of the system) with which to carry out high quality imaging and investigation of all parts of the body. In addition, a substantial range of dynamic studies can be carried out. The system provides good clarity to show blood flow in the brain, neck, aorta and kidneys and can indicate blockages or kidney stones.
Prostate cancer
MRI scanning is often used for accurate diagnosis of prostate cancer. The scanning process can see tumours in the gland itself, in lymph nodes and elsewhere in the body when metastatic disease is involved. It is an important tool in planning treatment be it surgery or radiotherapy. Dr Padhani at the Paul Strickland Scanner Centre has published papers recently on dynamic contrast enhanced MRI as a tool for planning intensity modulated radiotherapy for patients with prostate cancer. This maximises the chance of tumour eradication and reduces the risk of normal tissue damage.
Image of prostate gland showing tumour
on the left hand side
(Picture: Dr Anwar Padhani)
Why a charity?
One would expect that such a crucial part of the National Health infrastructure would be financed by the Department of Health. Not so. The capital cost of the equipment is paid for out of charitable donations. Hospital Trusts that send patients to the Centre pay for their scans on a per patient basis. Over a period of time, therefore, the Centre should obtain money to recoup the costs of their original purchases. However, they have to offer the latest equipment and technology and so are faced with finding from their supporters the costs of ever higher performance machines as they become available.
For more information visit: www.paulstrickland-scannercentre.org.uk.