Medical imaging refers to the techniques and processes used to create images of the human body (or parts thereof) for clinical purposes. Thanks to modern mathematics and computer technology, medical imaging has developed very fast. Many methods have been found to detect tumours, here is a short summary of the most important screening methods. MAMMOGRAPHY In mammography X-rays of the breast are taken to look for small tumours. The results can be seen in the screening mammogram. Mammography is used to detect breast tissue changes in women who have no signs or symptoms of breast cancer. Mammograms make it possible to detect tumours that cannot be felt. Mammograms can also find microcalcifications (tiny deposits of calcium in the breast) that sometimes indicate the presence of breast cancer. If something unusual or suspicious is seen, the woman will have to undergo further tests. Women age 40 and older should have mammograms every 1 to 2 years. THERMOGRAPHY Digital Infrared Imaging DII Thermography works on the principle that the development of cancer is linked to an increase of metabolic activity. This increase in metabolic activity combined with an increased vascular circulation in both pre-cancerous tissue and the area surrounding a developing breast cancer causes a higher temperature in cancerous tissues than you find in normal, healthy breast tissue. So, if tissue in one breast is found to be warmer than the tissue of the other breast, this could be an early indication of cancer. Claudia Aumann, Susanne Neumann 2009 1/6
The temperature of the tissue is detected by a medical camera which is highly sensitive to infrared radiation and analyses temperature variations in body tissues. The data collected are then used to construct a heat map of the body a thermogram. ULTRASOUND SCANNING - Sonography The human ear can detect sounds up to a frequency of about 20 000 Hz. Sounds above the range of human hearing are called ultrasound. An ultrasound scan is a painless and harmless test that uses sound waves to create images of organs and structures inside your body. Ultrasound travels freely through fluid and soft tissues but is reflected back, when it hits a denser surface. So, as ultrasound 'hits' different structures in the body of different density, it sends back echoes of varying strength. The echoes are detected by the probe and are sent to the ultrasound machine. They are displayed as a picture on the monitor. For example, the ultrasound will travel freely through blood in a heart chamber, but when it hits a solid valve, a lot of the ultrasound echoes back. The US test helps to determine if an abnormal lump in one of the abdominal organs is a solid tumour or fluid-filled cyst. Organs of the abdomen would be the liver, gallbladder, pancreas, lymph nodes, ovaries, testes, kidneys and bladder. Ultrasound Scanning has the advantage of not exposing patients to X-rays and being cheaper than other methods, such as CT, MRI and PET. Claudia Aumann, Susanne Neumann 2009 2/6
CT-SCANS - CAT-Scans CT/ CAT stands for Computer assisted tomography. CT imaging combines X-rays with computers to produce multiple images of the inside of the body. CT-images provide detailed, cross-sectional views of all types of tissue and can be examined on a computer monitor or printed out. In a CT Scan X-rays are sent through the body from different angles. The X- rays are absorbed by different structures of the body in different amounts, so the computer can build a 3-dimensional picture in which a tumour can be picked out. With CT scanning, numerous X-ray beams and a set of electronic x-ray detectors rotate around you, measuring the amount of radiation being absorbed throughout your body. At the same time, the examination table is moving through the scanner, so that the x- ray beam follows a spiral path. A special computer program processes this large volume of data to create two-dimensional cross-sectional images of your body. When the images are reassembled by computer software, the result is a very detailed multidimensional view of the body's interior. CT imaging is often the preferred method for diagnosing many different cancers, including lung, liver and pancreatic cancer, since the image allows a physician to confirm the presence of a tumour and measure its size, precise location and the extent of the tumour's involvement with other nearby tissue. A reason for keeping the number of CT scans down is the potential harm done by these strong X-rays, which themselves increase the risk of cancer. Claudia Aumann, Susanne Neumann 2009 3/6
MRI-SCANS Magnetic resonance imaging is a diagnostic test that uses electromagnetic radio waves to produce two- or three-dimensional computer images of internal body structures such as organs, muscles, bones, and nerves. A MRI scan involves the patient lying completely still inside a large, cylindershaped magnet. The nuclei of the tissues align with this strong magnetic field. Radio waves at just the right frequency for the protons to absorb them are then sent through the body. This affects the body's atoms, forcing the nuclei into a different position. The protons then snap back to alignment, producing a detectable rotating magnetic field as they do so. Our body consists mainly of water, and water contains hydrogen atoms. For this reason, the nucleus of the hydrogen atom is often used to create an MRI scan. Tissue with few hydrogen atoms (such as bones) turns out dark, while tissue with many hydrogen atoms (such as fatty tissue) looks much brighter. The magnetic fields in different parts of the body are measured and a computer uses the data collected to build images. As a MRI scan is able to provide clear pictures of parts of the body that are surrounded by bone tissue, so the technique is useful when examining the brain and spinal cord. MRI is particularly good for some types of brain tumours, primary bone tumours, soft tissue sarcomas, and for tumours affecting the spinal cord. Compared to CT scan, MRI does not involve ionising radiation and produces more detailed images of soft tissue and organs and differentiates between similar tissues more effectively. MRI is completely painless, but the scanner is very noisy, producing a loud clanging inside the cylinder and which goes on throughout the scan. Claudia Aumann, Susanne Neumann 2009 4/6
Many patients feel very uncomfortable being closed in and not being allowed to move while undergoing MRI scanning. Some people might even get claustrophobic during the test. Patients who are afraid this might happen should talk to the doctor beforehand about giving them some medication to help them relax. There are no known dangers or side effects connected to an MRI scan. Because of a small theoretical risk to the foetus in the first 12 weeks of pregnancy, MRI scans are not performed on pregnant women during this time. PET-SCANS PET stands for positron emission tomography. Radiologists use radioactive material called radiotracers, which are either injected into your bloodstream, swallowed or inhaled as a gas. They stay in your body for a few hours only. The most common radiotracer is F18 fluoro-2-deoxyglucose (FDG 18), which is a radioactive version of glucose. Cells take in the radioactive glucose and try to use it for cell respiration to get energy, as they usually do during cell respiration with normal glucose. Cancerous cells grow at a much faster rate than healthy cells, so they need more glucose for their metabolism. The more metabolically active cells are, the higher their intake of FDG 18. Eventually the radiotracer accumulates in an organ. As the radioisotope undergoes positron emission decay (also known as positive beta decay), it emits a positron. After travelling up to a few millimetres the positron encounters and is annihilated by an electron, producing a pair of gamma photons moving in opposite directions. These photons can be detected by the machine: but those which do not arrive in pairs (i.e., within a few nanoseconds) are ignored. The PET scanner detects this and builds up a picture of the body showing different rates of metabolic activity. Areas of high glucose intake are dramatically displayed in the PET scan image. An area with unexpectedly high activity can indicate that a tumour is growing there. Claudia Aumann, Susanne Neumann 2009 5/6
The radiotracer FDG 18 indicates: 1. cancers because they use larger amounts of glucose than normal tissue. 2. changes in tissues that use glucose as their main source of energy for example, the brain. PET scans can diagnose and stage many types of cancer, but not all types. There is strong evidence that PET scanning works well for staging, e.g. Non-small cell lung cancer, Non Hodgkin's lymphoma and Hodgkin's lymphoma. Staging describes the extent or severity of a cancer based on the extent of the primary tumour and the extent of spread in the body. PET and PET/CT scans are performed to: detect cancer determine whether a cancer has spread in the body assess the effectiveness of a treatment plan, such as cancer therapy determine if a cancer has returned after treatment evaluate brain abnormalities, such as tumours, memory disorders and seizures and other central nervous system disorders to map normal human brain and heart function There are no side effects of this type of scan. Nevertheless PET scan patients should not have close contact with pregnant women, babies and young children for about 6 hours after their scan. This is because during this period there is radiation in their body. Claudia Aumann, Susanne Neumann 2009 6/6