Fast approximation to pixelwise relaxivity maps: Validation in iron overloaded subjects

• Published in: Magnetic resonance imaging Vol. 31; no. 7; pp. 1074 - 1080
• Main Authors: Meloni, Antonella, Zmyewski, Heather, Rienhoff, Hugh Young, Jones, Amber, Pepe, Alessia, Lombardi, Massimo, Wood, John C.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Inc 01.09.2013
• Subjects: Adolescent; Adult; Algorithms; Fast R2 mapping; Female; Humans; Image Processing, Computer-Assisted - methods; Iron - chemistry; Iron Overload - diagnosis; Iron Overload - pathology; Iron overload assessment; Liver; Liver - metabolism; Liver - pathology; Magnetic Resonance Imaging - methods; Male; Observer Variation; Radiology; Reproducibility of Results; Young Adult; Fast R2 mapping; Liver; Iron overload assessment
• ISSN: 0730-725X; 1873-5894; 1873-5894
• DOI: 10.1016/j.mri.2013.05.005

Liver iron quantification by MRI has become routine. Pixelwise (PW) fitting to the iron-mediated signal decay has some advantages but is slower and more vulnerable to noise than region-based techniques. We present a fast, pseudo-pixelwise mapping (PPWM) algorithm. The PPWM algorithm divides the entire liver into non-contiguous groups of pixels sorted by rapid relative relaxivity estimates. Pixels within each group of like-relaxivity were binned and fit using a Levenberg–Marquadt algorithm. The developed algorithm worked about 30 times faster than the traditional PW approach and generated R2* maps qualitatively and quantitatively similar. No systematic difference was observed in median R2* values with a coefficient of variability (CoV) of 2.4%. Intra-observer and inter-observer errors were also under 2.5%. Small systematic differences were observed in the right tail of the R2* distribution resulting in slightly lower mean R2* values (CoV of 4.2%) and moderately lower SD of R2* values for the PPWM algorithm. Moreover, the PPWM provided the best accuracy, giving a lower error of R2* estimates. The PPWM yielded comparable reproducibility and higher accuracy than the TPWM. The method is suitable for relaxivity maps in other organs and applications.