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DISPOSITIF SUPRACONDICTEUR À INTERFÉRENCE QUANTIQUE (DSIQ)

Le SQUID est une modalité d'imagerie utilisant un champ magnétique très faible avec des détecteurs très sensibles mesurant l'interférence du fer avec ce champ magnétique. Une mesure est effectuée en plaçant le patient dans un champ magnétique connu et constant, puis en mesurant le changement du flux magnétique par rapport au changement d'un milieu aqueux de référence. Le détecteur nécessite un environnement refroidi, puisqu'il doit être supraconducteur pour fonctionner [47]. Même si le SQUID est encore considéré comme étant encore au stade de l'investigation, on a mis en évidence des corrélations linéaires entre les mesures faites avec le SQUID et les niveaux de fer mesurés sur des biopsies hépatiques [48–50].

Technique de mesure du fer avec le SQUID

Fischer [47]. © 1998 Wiley-VCH Verlag GmbH & Co KGaA, reproduit après autorisation.

Relation linéaire entre SQUID et biopsie du foie

Fischer [51]. © 1992 Elsevier Inc, reproduit après autorisation.

Même si le SQUID mesure directement la susceptibilité magnétique de la ferritine et de l'hémosidérine, à l'heure actuelle ses résolutions spatiale et temporelle ne sont pas suffisantes pour évaluer le fer du myocarde. L'utilisation du SQUID est actuellement limitée puisqu'il n'y a uniquement que 4 installations dans le monde ayant un appareil SQUID disponible pour la mesure des niveaux en fer. De plus, durant le développement clinique du deferasirox, il a été montré que les LIC obtenues en SQUID sous-estimaient d'un un facteur de 0.46 les valeurs LIC obtenues en biopsie [52].

Un des 4 établissements possédant un SQUID dans le monde

ÉCHOCARDIOGRAPHIE, VENTRICULOGRAPHIE RADIOISOTOPIQUE

L'évaluation exacte de la FEVG peut être effectuée de manière non invasive par une échocardiographie de repos ou d'effort [53, 54], ou par une ventriculographie radioisotopique [55, 56]. Ces techniques peuvent être utiles pour diagnostiquer au stade précoce des atteintes cardiaques liées au fer, puisqu'on a montré qu'une dysfonction diastolique a une valeur pronostique dans le développement des affections cardiaques symptomatiques liées au fer [10, 57].

L'échocardiographie est la technique la plus utilisée à des fins de diagnostic et de pronostic de la fonction ventriculaire gauche [58]. Cependant une limite importante de cet examen est que les anomalies échocardiographiques peuvent se développer relativement tard dans l'évolution de la cardiomyopathie. De plus, cette technique repose sur l'habileté de l'opérateur et nécessite de faire des suppositions sur la géométrie ventriculaire, augmentant ainsi la variabilité inter-observateur. Par conséquent, les mesures de la fraction d'éjection au repos par angiographie radioisotopique et IRM sont plus fiables que celles de l'échocardiographie, et offrent un plus grand intérêt pour reconnaître une dysfonction systolique pré-clinique [59].

Résumé des principales méthodes disponibles permettant d'évaluer la concentration en fer dans le corps .

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Références

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Learn about the benefits of chelation therapy in treating transfusional iron overload.