Improved liver R2* mapping by pixel-wise curve fitting with adaptive neighborhood regularization.
PURPOSE
To improve liver R2* mapping by incorporating adaptive neighborhood regularization into pixel-wise curve fitting.


METHODS
Magnetic resonance imaging R2* mapping remains challenging because of the serial images with low signal-to-noise ratio. In this study, we proposed to exploit the neighboring pixels as regularization terms and adaptively determine the regularization parameters according to the interpixel signal similarity. The proposed algorithm, called the pixel-wise curve fitting with adaptive neighborhood regularization (PCANR), was compared with the conventional nonlinear least squares (NLS) and nonlocal means filter-based NLS algorithms on simulated, phantom, and in vivo data.


RESULTS
Visually, the PCANR algorithm generates R2* maps with significantly reduced noise and well-preserved tiny structures. Quantitatively, the PCANR algorithm produces R2* maps with lower root mean square errors at varying R2* values and signal-to-noise-ratio levels compared with the NLS and nonlocal means filter-based NLS algorithms. For the high R2* values under low signal-to-noise-ratio levels, the PCANR algorithm outperforms the NLS and nonlocal means filter-based NLS algorithms in the accuracy and precision, in terms of mean and standard deviation of R2* measurements in selected region of interests, respectively.


CONCLUSIONS
The PCANR algorithm can reduce the effect of noise on liver R2* mapping, and the improved measurement precision will benefit the assessment of hepatic iron in clinical practice. Magn Reson Med 80:792-801, 2018. © 2018 International Society for Magnetic Resonance in Medicine.
['Wang|Changqing|C|', 'Zhang|Xinyuan|X|', 'Liu|Xiaoyun|X|', 'He|Taigang|T|', 'Chen|Wufan|W|', 'Feng|Qianjin|Q|', 'Feng|Yanqiu|Y|']
D000293:Adolescent D000328:Adult D000465:Algorithms D003198:Computer Simulation D005260:Female D006801:Humans D007091:Image Processing, Computer-Assisted D007501:Iron D019190:Iron Overload D008099:Liver D008279:Magnetic Resonance Imaging D008297:Male D019047:Phantoms, Imaging D055815:Young Adult
R2* mapping adaptive neighborhood regularization MR relaxometry hepatic iron concentration noncentral chi noise