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Effects of B1+ Heterogeneity on Spin Echo-Based Liver Iron Estimates.
Doyle, Eamon K; Thornton, Samuel; Ghugre, Nilesh R; Coates, Thomas D; Nayak, Krishna S; Wood, John C.
Afiliación
  • Doyle EK; Department of Biomedical Engineering, University of Southern California, Los Angeles, California, USA.
  • Thornton S; Division of Cardiology and Radiology, Children's Hospital Los Angeles, Keck School of Medicine, University of Southern California, Los Angeles, California, USA.
  • Ghugre NR; Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, California, USA.
  • Coates TD; Schulich Heart Research Program, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada.
  • Nayak KS; Physical Sciences Platform, Sunnybrook Research Institute, Toronto, Ontario, Canada.
  • Wood JC; Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada.
J Magn Reson Imaging ; 55(5): 1419-1425, 2022 05.
Article en En | MEDLINE | ID: mdl-34555245
BACKGROUND: Liver iron concentration (LIC) measured by MRI has become the clinical reference standard for managing iron overload in chronically transfused patients. Transverse relaxivity (R2 or R2* ) measurements are converted to LIC units using empirically derived calibration curves. HYPOTHESIS: That flip angle (FA) error due to B1+ spatial heterogeneity causes significant LIC quantitation error. B1+ scale (b1 , [FAactual /FAspecified ]) variation is a major problem at 3 T which could reduce the accuracy of transverse relaxivity measurements. STUDY TYPE: Prospective. POPULATION: Forty-seven subjects with chronic transfusional iron overload undergoing clinically indicated LIC assessment. FIELD STRENGTH/SEQUENCE: 5 T/3 T dual-repetition time B1+ mapping sequence ASSESSMENT: We quantified the average/standard deviation b1 in the right and left lobes of the liver from B1+ maps acquired at 1.5 T and 3 T. The impact of b1 variation on spin echo LIC estimates was determined using a Monte Carlo model. STATISTICAL TESTS: Mean, median, and standard deviation in whole liver and right and left lobes; two-sided t-test between whole-liver b1 means. RESULTS: Average b1 within the liver was 99.3% ± 12.3% at 1.5 T versus 69.6% ± 14.6% at 3 T and was independent of iron burden (P < 0.05). Monte Carlo simulations demonstrated that b1 systematically increased R2 estimates at lower LIC (<~25 mg/g at 1.5 T, <~15 mg/g at 3 T) but flattened or even inverted the R2 -LIC relationship at higher LIC (≥~25 mg/g to 1.5 T, ≥~15 mg/g to 3 T); changes in the R2 -LIC relationship were symmetric with respect to over and under excitation and were similar at 1.5 T and 3 T (for the same R2 value). The R2* -LIC relationship was independent of b1 . CONCLUSION: Spin echo R2 measurement of LIC at 3 T is error-prone without correction for b1 errors. The impact of b1 error on current 1.5 T spin echo-based techniques for LIC quantification is large enough to introduce measurable intersubject variability but the in vivo effect size needs a dedicated validation study. TECHNICAL EFFICACY STAGE: 2.
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Texto completo: 1 Colección: 01-internacional Base de datos: MEDLINE Asunto principal: Sobrecarga de Hierro / Hierro Tipo de estudio: Observational_studies Límite: Humans Idioma: En Revista: J Magn Reson Imaging Asunto de la revista: DIAGNOSTICO POR IMAGEM Año: 2022 Tipo del documento: Article País de afiliación: Estados Unidos Pais de publicación: Estados Unidos
Texto completo
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Texto completo: 1 Colección: 01-internacional Base de datos: MEDLINE Asunto principal: Sobrecarga de Hierro / Hierro Tipo de estudio: Observational_studies Límite: Humans Idioma: En Revista: J Magn Reson Imaging Asunto de la revista: DIAGNOSTICO POR IMAGEM Año: 2022 Tipo del documento: Article País de afiliación: Estados Unidos Pais de publicación: Estados Unidos