Simultaneous field and R2 mapping to quantify liver iron content using autoregressive moving average modeling

Purpose:

To investigate the use of a complex multigradient echo (mGRE) acquisition and an autoregressive moving average (ARMA) model for simultaneous susceptibility and R measurements for the assessment of liver iron content (LIC) in patients with iron overload.

Materials and Methods:

Fifty magnetic resonance imaging (MRI) exams with magnitude and phase mGRE images were processed using the ARMA model, which provides fat‐separated field maps, R maps, and T₁‐W imaging. The LIC was calculated by measuring the susceptibility between the liver and the right transverse abdominal muscle from the field maps. The relationship between LIC derived from susceptibility measurements and LIC from R measurements was determined using linear least‐squares regression analysis.

Results:

LIC measured from R is highly correlated to the LIC with the susceptibility method (mg/g dry = 8.99 ± 0.15 × [mg Fe/mL of wet liver] ?2.38 ± 0.29, R² = 0.94). The field inhomogeneity in the liver is correlated with R (R² = 0.85).

Conclusion:

By using the ARMA model on complex mGRE images, both susceptibility and R‐based LIC measurements can be made simultaneously. The susceptibility measurement can be used to help verify R measurements in the assessment of iron overload. J. Magn. Reson. Imaging 2012;35:1125‐1132. © 2011 Wiley Periodicals, Inc.

     

QUIPSS II with window-sliding saturation sequence (Q2WISE)

A series of periodic saturation pulses used to minimize the error caused by varying transit delays in assessing perfusion using quantitative imaging of perfusion using a single subtraction II with thin-slice TI(1) periodic saturation (Q2TIPS) increases the specific absorption rate. Quantitative imaging of perfusion using a single subtraction II with window-sliding saturation sequence (Q2WISE) has been developed, in which numerous thin saturation pulses are replaced by two thin pulses and one thick saturation pulse arranged in a window-sliding manner within the labeling region to maintain a sharp slice profile while reducing specific absorption rate. Q2WISE essentially is a hybrid between Q2TIPS and quantitative imaging of perfusion using a single subtraction II for use in specific absorption rate intensive applications. Q2WISE was implemented on a 3 T MRI scanner to measure perfusion rates in the brain and kidneys of eight healthy volunteers and results were compared with those from Q2TIPS. Mean perfusion values of both methods for the brain (75 ± 17 [Q2WISE] and 74 ± 13 mL/100 g/min [Q2TIPS]) and kidney (308 ± 48 [Q2WISE] and 299 ± 43 mL/100 g/min [Q2TIPS]) were in very good agreement.