Fast generation of T2* maps in the entire range of clinical interest: application to thalassemia major patients

T2n maps obtainedbytheprocessingofmultiechoMRsequencescanbeusefulinseveralclinical applications. T2n map generationproceduresshouldjoinaprocessingtimecompatiblewithon-line image analysiswithagoodprecisionintheentire T2n rangeofclinicalinterest.Fastgenerationof T2n maps canbeachievedbytheestimationofthe T2n valuesbytheweightedlinear fitting ofthelogarithm of thesignal(WLSL)method.Thisapproachfailsifthesignaldecaydivergesfromapureexponential decay,ashappensatlow T2n valueswheretherapiddecayinthesignalintensityleadstoaplateauinthe later echotimes(TE). Theproposedmethodimplementstheautomatictruncationofthesignaldecay curves tobe fitted inordertocompensateforthesignalcollapseatlow T2n values,allowingthe extensionoftheWLSLmethodthroughtheentireclinicalrangeof T2n values. Validation wasperformedonsyntheticimagesandon60thalassemiamajorpatientswithdifferent levels ofmyocardialironoverload.Phantomexperimentsshowedthata5% fitting errorthreshold representedthebestcompromisebetween T2n valuemeasurementprecisionandprocessingtime.A good agreementwasfoundbetween T2n map pixel-wisemeasurementsandROI-basedmeasurements performed byexpertreaders(CoV¼1.84%inglobalheart T2n, CoV¼5.8% insegmentalanalysis).In conclusion, thedevelopedprocedurewaseffectiveingeneratingcorrect T2n maps fortheentire T2n clinical range.