History of Brooke Hospital London - Hospital health - History of Brooke Hospital - History of Brooke Hospital London

How can vets look inside the body of an animal?

Without lifting a knife, doctors looking at the body today can see the tiniest cracks in bones, tell whether a tumour is malignant or benign, even identify certain chemicals in the brain. This is all possible with cameras and computer screens. This new perspective on the inside of the body started with the discovery of X-rays. They were discovered on November 8, 1895, quite by chance, by the German physicist Wilhelm R�ntgen. He called them X-rays because he neither knew what they were nor understood their properties. Scientists now know they are electromagnetic waves, like light and radio waves, but with a shorter wavelength.

X-rays can pass through objects or substances with a low density, but are stopped by heavier or denser materials. So whereas skin and muscle allow the rays to pass through them, solid bone reflects them. Within a few months of Rontgen's discovery, X-rays were being used to take photographs to aid medical diagnosis of bone fractures, tumours and dental cavities.

Photographic negatives are produced by directing X-rays through the body and onto a negative plate. The rays appear as areas of white on the negative. Any diseases or structural faults in the bone can be seen. Radiologists, who are specialists in reading X-ray photographs, can even spot non-bone disorders, such as fluid in the lungs, by looking for various shadows on the film, which are a sign of disease.

Because conventional X-ray photographs depict the body in two dimensions only, they cannot reveal the shape or depth of a diseased area. In 1973 a new method of observing the body was introduced, which produced a three-dimensional image of the body's organs. It is known as a CT, or CAT, scan, which stands for Computerised Axial Tomography.

The CT system shows cross-sections, or `slices' of the body, on a screen. By using a series of these images, a three-dimensional picture of the body, or a part of the body, can be built up.

When a CT scan is taken, the patient is laid on a table surrounded by a doughnut-shaped metal ring which rotates around the patient's body. The scanner has X-ray tubes around one side, and detectors opposite them. As the scanner moves round, the X-ray tubes shoot thin beams of rays through the patient's body. Small amounts of the rays are absorbed by the body's tissues. When the beams pass out of the other side of the body, they strike the detectors, which convert them to electronic signals. A computer analyses the amount of radiation that has been absorbed.

The computer's analysis is coded into colours which indicate the relative density of tissue - the denser the tissue, the more radiation it will have absorbed. This coloured image, called a tomogram, is projected onto a screen for analysis.

The CT takes one 'slice' through the brain in five seconds. A similar machine, called a Dynamic Spatial Reconstructor, which portrays an organ on a video screen, can produce 75,000 cross-sections in the same time. It allows scientists to observe an organ moving and responding to stimuli and see if it is working normally.

Another kind of scanning device, which produces similar images of horizontal slices through the body, is called a PET scan (Positron Emission Tomography). This method involves injecting a radioactive chemical into a patient. The chemical is absorbed by some organs of the body, and emits positive electrons (positrons) which collide with negative electrons in the organs' cells. The collision causes gamma rays to be released, which are recorded by a computer.

Some diseased parts of organs do not absorb the chemical and this shows up on the image produced by the computer, allowing medical scientists to diagnose the sites of diseases such as cancer. The PET scanning system can also be used to detect the accumulation of certain chemicals in the brain which are a sign of mental illnesses such as schizophrenia, manic depression and epilepsy.

An even more advanced way of taking a picture of what is happening inside the body is called Nuclear Magnetic Resonance Imaging (NMR). This involves large magnets which beam energy through the body causing hydrogen atoms in the body to resonate. This gives out energy in the form of tiny electrical signals. A computer attached to the scanner detects these signals, which vary in different parts of the body and according to whether an organ is healthy or not. The variation enables a picture to be produced on a screen. Because NMR does not involve radiation it can often be used where X-rays would be dangerous.

Ultrascan, or ultrasound, which may be used to monitor development of the foetus in pregnant women, uses high-frequency sound waves beyond the audible level. The sound is reflected from different depths within the body - and a computer converts the signals into pictures. In this way such factors as growth and deformity can be checked.

There are still some conditions, such as stomach ulcers, which scanners of different types do not reveal adequately. However, doctors can look directly into the body through an endoscope.

An endoscope is a flexible tube which is inserted into the body. Two glass-fibre tubes which transmit light waves are inserted into the endoscope, allowing the doctor to see directly inside the patient. One fibre is used to shoot a beam of light down the tube, the other is fixed to a camera, or an eyepiece. The light bends, so that the doctor can see around twists and curves.

Endoscopes have even been used to photograph the development of a foetus inside its mother's womb. They are also used in the frontiers of surgery where, instead of the knife, surgeons operate by laser.

Other types of monitoring the body include: Doppler scans using sound waves to seek out blood clots; echocardiography, which checks heart disease and efficiency; and electrocardiography (ECG), in which electrodes on the skin create a graph that can show up signs of heart trouble.

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