Browsing by Author "Coronado, Ronal"

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    A Spatial Off-Resonance Correction in Spirals for Magnetic Resonance Fingerprinting
    (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2021) Coronado, Ronal; Cruz, Gastao; Castillo Passi, Carlos; Tejos, Cristian; Uribe, Sergio; Prieto, Claudia; Irarrazaval, Pablo
    In MR Fingerprinting (MRF), balanced Steady-State Free Precession (bSSFP) has advantages over unbalanced SSFP because it retains the spin history achieving a higher signal-to-noise ratio (SNR) and scan efficiency. However, bSSFP-MRF is not frequently used because it is sensitive to off-resonance, producing artifacts and blurring, and affecting the parametric map quality. Here we propose a novel Spatial Off-resonance Correction (SOC) approach for reducing these artifacts in bSSFP-MRF with spiral trajectories. SOC-MRF uses each pixel's Point Spread Function to create system matrices that encode both off-resonance and gridding effects. We iteratively compute the inverse of these matrices to reduce the artifacts. We evaluated the proposed method using brain simulations and actual MRF acquisitions of a standardized T1/T2 phantom and five healthy subjects. The results show that the off-resonance distortions in T1/T2 maps were considerably reduced using SOC-MRF. For T2, the Normalized Root Mean Square Error (NRMSE) was reduced from 17.3 to 8.3% (simulations) and from 35.1 to 14.9% (phantom). For T1, the NRMS was reduced from 14.7 to 7.7% (simulations) and from 17.7 to 6.7% (phantom). For in-vivo, the mean and standard deviation in different ROI in white and gray matter were significantly improved. For example, SOC-MRF estimated an average T2 for white matter of 77ms (the ground truth was 74ms) versus 50 ms of MRF. For the same example the standard deviation was reduced from 18 ms to 6ms. The corrections achieved with the proposed SOC-MRF may expand the potential applications of bSSFP-MRF, taking advantage of its better SNR property.
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    Accelerated DESPOT1 with variable parameters for 3D T1 brain mapping
    (2025) Coronado, Ronal; Varela-Mattatall, Gabriel; Sahonero-Álvarez, Guillermo; Botnar, René; Cecilia Besa; Irarrázaval, Pablo; Prieto, Claudia
    PURPOSE: Driven equilibrium single pulse observation of T1 (DESPOT1) is a reliable technique for clinical 3D T1 brain mapping. However, its fixed repetition time (TR) and bandwidth (BW) and its linear modeling to estimate T1 conveys to an inefficient imaging protocol. We propose a variable DESPOT1 (vDESPOT1) acquisition and modeling strategy to improve scan efficiency and to accelerate image acquisition. METHODS: vDESPOT1 uses SPGR acquisitions with optimized combinations of TRs, BWs, and FAs, coupled with dictionary-based reconstruction to achieve faster acquisition and more efficient T1 mapping. The proposed vDESPOT1 method was compared to DESPOT1 and inversion recovery spin echo (IR-SE) in phantom and in ten brain healthy subjects. RESULTS: Results demonstrate a reduction in scan time of approximately 40 %, allowing faster 3D brain T1 mapping while maintaining accuracy and T1NR in comparison to conventional DESPOT1. Also, the computational efficiency of a pre-computed dictionary of vDESPOT1 reduces the reconstruction time by ∼50× in comparison linear regression of conventional DESPOT1. Variable BW can enhance scan efficiency without significantly affecting the SNR for T1 when using vDESPOT1. CONCLUSION: These time improvements make vDESPOT1 particularly valuable for dynamic and high-field MRI applications, such as thermal therapy monitoring, pharmacokinetic analysis in DCE-MRI, and imaging in anatomies prone to motion, including the heart, liver, and lungs.
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    Fast and accessible T2 mapping using off-resonance corrected DESPOT2 with application to 3D prostate
    (2024) Coronado, Ronal; Castillo-Passi, Carlos; Besa, Cecilia; Irarrazaval, Pablo
    Purpose: Most T1 and T2 mapping take long acquisitions or needs specialized sequences not widely accessible on clinical scanners. An available solution is DESPOT1/T2 (Driven equilibrium single pulse observation of T1/T2). DESPOT1/T2 uses Spoiled gradient-echo (SPGR) and balanced Steady-State Free Precession (bSSFP) sequences, offering an accessible and reliable way for 3D accelerated T1/T2 mapping. However, bSSFP is prone to offresonance artifacts, limiting the application of DESPOT2 in regions with high susceptibility contrasts, like the prostate. Our proposal, DESPO+, employs the full bSSFP and SPGR models with a dictionary-based method to reconstruct 3D T1/T2 maps in the prostate region without off-resonance banding. Methods: DESPO+ modifies the bSSFP acquisition of the original variable flip angle DESPOT2. DESPO+ uses variable repetition and echo times, employing a dictionary-based method of the full bSSFP and SPGR models to reconstruct T1, T2, and Proton Density (PD) simultaneously. The proposed DESPO+ method underwent testing through simulations, T1/T2 phantoms, and on fourteen healthy subjects. Results: The results reveal a significant reduction in T2 map banding artifacts compared to the original DESPOT2 method. DESPO+ approach reduced T2 errors by up to seven times compared to DESPOT2 in simulations and phantom experiments. We also synthesized in-vivo T1-weighted/T2-weighted images from the acquired maps using a spin-echo model to verify the map's quality when lacking a reference. For in-vivo imaging, the synthesized images closely resemble those from the clinical MRI protocol, reducing scan time by around 50% compared to traditional spin-echo T1-weighted/T2-weighted acquisitions. Conclusion: DESPO+ provides an off-resonance insensitive and clinically available solution, enabling highresolution 3D T1/T2 mapping and synthesized T1-weighted/T2-weighted images for the entire prostate, all achieved within a short scan time of 3.6 min, similar to DESPOT1/T2.