Medical imagery

The medical imagery is the process by which a Médecin can examine the interior of the body of a patient without operating it. The medical imagery can be used with fine private clinics for the establishment of a diagnosis or for the treatment of Pathologie S but also within the framework of work of Scientific research studied the Physiologie living beings.

History of the medical imagery

Importance that revêt the medical imagery is due initially to the fact that an image is a concentrate of information much more effective than a text or than a verbal explanation.

The principle of the medical imagery

The goal of the medical imagery is to create a Représentation Visuel the understandable one of a Information in medical matter. These problems lie overall within the scope of the Image Scientifique and Technique: the objective is indeed to be able to represent under a relatively simple format a great quantity of information resulting from a multitude of measurements acquired according to a well defined mode.

The image obtained can be treated by means of computer to obtain for example:

a three-dimensional rebuilding of a body or a fabric;
a film showing the evolution or the movements of a body during time;
a quantitative imagery which represents the values measured for certain biological parameters in a given volume;
a multimode representation readjusting several data within the same document (contour of the heart and mobility of the walls for example).

In a broader direction, the field of the medical imagery includes all the techniques making it possible to store and handle this information. Thus, there exists a Norme for management Informatique of the data resulting from the medical imagery: the standard DICOM.

Various techniques of medical imagery

According to the techniques used, the examinations of medical imagery make it possible to obtain information on the anatomy of the Organe S (their size, their volume, their localization, the form of a possible lesion, etc) or on their operation (their Physiologie, them Métabolisme, etc). In the first case one speaks about imagery structural and in the second of functional imagery .

Among the structural methods of imagery most usually employed in medicine, one can quote on the one hand the tomographic methods based either on the X-rays (conventional Radiologie, Tomodensitomètre or CT-scan, Angiographie,…) maybe on the Magnetic resonance (IRM) and, in addition, the methods echographic (which use the Ultra-son S).

The functional methods of imagery also are very varied. They gather the techniques of Nuclear medicine (Mtoe, TEMP) based on the emission of Gamma rays by tracers Radioactif S which, after injection, concentrate in the areas of intense metabolic activity, the electrophysiological techniques which measure the modifications of the electrochemical state of fabrics (in particular in bond with the activity Nerveuse) or measurements thermographic.

These various types of techniques are often employed in a complementary way sometimes even within the same system of imagery which allows multimode acquisitions then, simultaneous or not.

Magnetic fields

Imagery by magnetic resonance (IRM), using the effect of an intense magnetic field on the Spin of the Proton S. It is a process tomographic, making it possible to obtain " cuts virtuelles" of the body following three plans of space (cut Sagittal E, cut Coronal E and cut Axial E). According to the parameters chosen, the IRM makes it possible to obtain images very contrasted of some fabrics according to their histological properties . It is thus a tool particularly used in cerebral imagery. Examinations IRM are considered to date without risk on the organization. However, any ferromagnetic object, sensitive to the magnetic field (Piercing, Pacemaker, some Prosthesis S, etc), is dangerous.
the Magnétoencéphalographie ( MEG ) is a measurement technique of weak the induced magnetic fields by the electric activity of the Neuron S of the Cerveau. Contrary to the IRM, it does not rest on the preliminary magnetization of fabrics. Consequently, the magnetic presence of object does not pose any risk.
the Magnétocardiographie is a technique very similar to the preceding one which consists in measuring the magnetic fields induced by the electric activity of the cells of the cardiac muscle on the level of the Torse. It only is used very little.

Radioactivity

The techniques of nuclear Scintigraphie rest on the use of a radioactive tracer which emits detectable radiations by the measuring devices. These Molécule S Radiopharmaceutique S is selected to be fixed preferentially on certain cells according to the type of desired diagnosis. A data processing of the data then makes it possible to reconstitute the space origin of these radiations and to deduce the areas from the body where the tracer concentrated. The image obtained is generally a projection but one can obtain a cut or a rebuilding 3D of the distribution of the tracer.

Tomography of monophotonic emission (TEMP or SPECT): it uses the emission of Photon S gamma by a molecule labelled by a radioactive Isotope injected in the organization.
Tomography with emission of positon (Mtoe or FART): it generally uses sugar (an analog of the Glucose) marked by a body Radioactif emitting Positon S (e.g., Fluor 18), and then makes it possible to see the cells at fort Métabolisme (ex: cancer cells, infection…).

The Mtoe in general makes it possible to obtain images of better quality that the TEMP. However, the number and the availability of radiopharmaceutic usable in TEMP as well as the moderate cost of the Gamma-camera S compensate for this defect.

The X-rays

The use of x-rays is of everyday usage. These radiations, as the gamma rays are ionizing and thus dangerous. In particular, the irradiation of a cell in phase of Mitose can cause a change DNA and which can cause the appearance of a Cancer in the long run. However, thanks to measurements of Protection against radiation, the inherent risk with examinations X is limited as much as possible.

Various types of examinations use x-rays:

Radiography, using X-rays and sometimes the injection of product of contrast. The images obtained are projections of the bodies and various systems according to a plan. Generally, radiography is used for the osseous system because it is about the most visible system on a radiography of the body.
Scanner X, Tomographie using x-rays. the images obtained is cuts millimetre-length (or infra-millimetre-length) being able to be studied in all the plans of space, as well as three-dimensional images.
Scanner DEXA measuring the osseous density (or osteodensitometry).

Ultrasounds

Echography, using Ultrason S. the image obtained is a studied cut of the body. It can be coupled by an examination Doppler analyzing the speed of blood in the vessels or the cardiac cavities .

See too

Distorts color
Endoscopie
Cœlioscopie
Manipulateur in medical electroradiology

External bonds

Cardiovascular and Interventional Radiological Society off Europe

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