Nuclear medicine - SpeedyLook encyclopedia

The nuclear medicine is the whole of the medical applications of the radiotraceurs, or not sealed radioactive sources.

Use

The various scopes of application are:

the functional imagery in vivo which consists of the administration of a radioactive tracer to the patient allowing his external detection. They are the scintiscannings (emission of gamma rays) or the Mtoe (Tomographies of emission of positons).
the biological diagnosis in vitro: it is radioimmunology
the metabolic radiotherapy: that gathers the therapeutic applications using the administration of a radioactive product whose course in the matter is sufficiently weak to deposit its energy directly in contact with target fabric and to destroy it. example: the radiotherapy of thyroid cancers by iodine 131.

Although historically, its first contributions were done especially in the field of the Oncologie, the nuclear medicine make it possible today to practically study all the systems of the human body and find by this fact of the applications in all the medical specialities, including the Neurologie, the Cardiologie, the Oncologie, the Endocrinologie, the Néphrologie, the Gastro-entérologie, the Pneumologie, the Infectiologie, the various surgical disciplines , etc

The nuclear medicine is distinguished from the majority of the other techniques of medical imagery in what one rather obtains from the physiological images than anatomical. Molecules whose biological behavior is known are introduced into the body of the patient in the way appropriate to the test in progress: injected, swallowed, inhaled etc Their behavior is then studied by the means of the Imagerie by emission. The images obtained can static beings but, contrary in the majority of the methods of imageries by transmission, it is often possible to obtain dynamic images. One will thus be able, for example, to study:

the blood perfusion of the bodies (vascular flood);
the metabolism hépatobiliaire and biliary dynamics vésiculaire;
functions of filtration and renal elimination, including the search for obstruction to renal draining, by the means, if need be, of a test of provocation to the diurétique one;
functions of filling and draining of the urinary bladder, including the search for backward flow vésico urétéral;
test of thyroid organification of iodine, by the means of a test of purification to perchlorate;
test of cerebral perfusion, by the means of the cartography of collecting and tissue draining of Xenon-133;
etc

Certain techniques allow a dynamic rebuilding (movement) by superposition of images taken different times (Cœur). The nuclear medicine lends itself to the quantification.

Some radioisotopes used in nuclear medicine

Tc^99m

The Technétium 99 Métastable is the most useful Radio-isotope in nuclear Medical imagery. Its physical characteristics are almost ideal for this end:

the Demi-vie 6 hours is enough long to make it possible to follow the physiological processes of interest, but enough short to limit the useless irradiation
the energy of the photon gamma, 142 keV, is ideal since enough energy to cross living tissue, but enough weak to be able to be detected conveniently: it can be intercepted effectively by a sodium iodide crystal of which the typical thickness will be about 10 to 15 mm
the abundance of photon gamma is large, approximately 98% of the Désintégration S. Few nonpenetrating particles are emitted, thus supporting a weaker deposition of energy in living tissue

The Technétium is usually obtained in the form of pertechnétate sodic: NaTcO₄. It can be used in this form for its ic properties Anion. In this form, indeed, its biological behavior will mimera that of the Anion S Cl or I. Thus, one will be able for example to make research of the diverticula of Meckel or to color the Thyroid gland.

However, its principal use will be made like marker biologically active Molécule S. By binding a Atom of Tc^99m:

with various phosphates or phosphonates, one will be able to color the metabolism Os seux
with unquestionable chelating such DTPA, one will color the renal function. Same DTPA, in the form of Aérosol will be inhaled to chart the pulmonary Ventilation
with albumin macro-aggregates which will make it possible to color the pulmonary Perfusion
with the Diimino-acetic acid or its derivatives, one will color the hépato-biliary function
with various Colloïde S, habituellememt of Soufre, to chart the distribution of the hepatic cells of Kupffer
to the red globules of the patient, to seek digestive Hémangiome S or bleedings
with some lipophilic Molécule S the such MIBI or Teboroxime, to chart the blood Perfusion regional; useful in particular for the evaluation of myocardic ischaemia or the search for certain tumors

Tl²⁰¹

This atom has chemical properties similar to those of potassium. Absorbed by the cells via pump NAK Atpase, it will be distributed according to the regional blood perfusion. Used a long time, in particular to evaluate the myocardic blood perfusion, it tends to being forsaken with the profit of the technéciés markers lipophilic.

Indeed, its physical properties are less than ideal: the energy of its photons gamma is weak. The images obtained are thus prone to the degradation caused by the attenuation and the diffusion. Moreover, the amount which it is possible to manage is limited because of the relatively important abundance of nonpenetrating radiations, for which it is advisable to limit the exposure of the patients.

I¹²³

Isotope of iodine used to study the thyroid metabolism. Its radiation rich person in photons gamma and its half-life 13 hours make of it an agent well adapted to the imagery.

I¹³¹

Another isotope of iodine, its radiations rich in particles beta and its 8 days relatively long half-life make of it an agent more favourable with the treatment than the imagery. One will use it for the ablation of hyperactive thyroid nodules, for the treatment of certain forms of hyperthyroïdie, for example the disease of Serious-Basedow or the disease Plummer, or for the search and the ablation for metastases of well differentiated thyroid carcinomes.

Ga⁶⁷

MIME metabolism of iron. Useful to color the function of osseous marrow and for the search for certain infections, of lymphomas and certain tumors.

In^111m

The DTPA marked with the Indium can be injected in space under-arachnoïdien, by lumbar Ponction, in order to color the production, the migration and the reabsorption of the céphalo-rachidian Liquide.

Use

Some radioisotopes used in nuclear medicine

Tc99m

Tl201

I123

I131

Ga67