Fast approximation to pixelwise relaxivity maps: validation in iron overloaded subjects.

Area of Science:

• Medical imaging
• Magnetic Resonance Imaging (MRI)
• Quantitative analysis

Background:

• Liver iron quantification via MRI is a standard clinical procedure.
• Traditional pixelwise (PW) fitting is accurate but slow and sensitive to noise.
• Region-based methods offer speed but may lack precision.

Purpose of the Study:

• To introduce a novel, rapid pseudo-pixelwise mapping (PPWM) algorithm for liver iron quantification.
• To compare the speed, accuracy, and reproducibility of PPWM against traditional PW methods.

Main Methods:

• The PPWM algorithm groups pixels with similar relaxivity, then fits these groups using a Levenberg-Marquardt algorithm.
• Liver segmentation into non-contiguous pixel groups based on relative relaxivity estimates.
• Application of the Levenberg-Marquardt algorithm for fitting binned pixel data.

Main Results:

• PPWM demonstrated a 30-fold increase in speed compared to traditional PW fitting.
• Generated R2* maps showed qualitative and quantitative similarity to PW results.
• PPWM achieved comparable reproducibility (median R2* CoV 2.4%) with improved accuracy and lower R2* estimation errors.

Conclusions:

• The PPWM algorithm provides a faster, highly accurate, and reproducible method for liver iron quantification.
• PPWM's efficiency and accuracy make it suitable for relaxivity mapping in other organs and applications.