arXiv subjects

Jorge Campos Pazmiño

Publications and source records attributed to Jorge Campos Pazmiño.

3 recordsLinked to original sources

arXiv2026

Advancing oxygen-enhanced MRI acquisition and modelling through dynamic $ΔR_{1}$ and $ΔR_2^*$ sensing

Purpose: To develop a multiparametric mapping framework for quantifying fat- and water-specific longitudinal and effective transverse relaxation rates, as well as changes in these parameters induced by a gas challenge. Theory and Methods: The proposed framework, termed SR-Fat DESPOT (single-reference fat-water separated driven equilibrium single-pulse observation of $T_1$), combines a two-component signal model with a single-reference variable flip angle (SR-VFA) approach. The signal model explicitly incorporates gas challenge-induced changes in relaxation rates. The single-reference acquisition strategy reduces data acquisition requirements while preserving sensitivity to both baseline parameters and dynamic changes. Sequence parameters were optimized using Cramer-Rao lower bound theory. SR-Fat DESPOT was evaluated using a modified open-surce abdominal numerical phantom and in two in vivo experiments: a single participant test-retest experiment and a pilot study with six participants. Results: In the abdominal numerical phantom, SR-Fat DESPOT was accurate for quantification of baseline relaxation rates with a normalized median absolute error (nMedAE) <3% for signal-to-noise ratio (SNR) >30 when comparing ground truth and estimates. SR-Fat DESPOT was also able to accurately recover median changes in relaxation rates, with differences within 0.001 $s^-1$ when compared to ground truth. In vivo, SR-Fat DESPOT measured changes in relaxation rates for spleen, kidneys, liver, and muscle under 100% O2 breathing, consistent with reports in literature. Changes detected in the spleen and kidneys were statistically significant across participants. Conclusion: SR-Fat DESPOT can quantify changes in relaxation rates induced by a gas challenge while reducing data requirements compared to more conventional approaches used in MR-oximetry literature.

physics.med-ph↗

arXiv2026

Mapping fat-water separated R1, R2*, and proton density fat fraction with the multi-echo MP2RAGE sequence

Purpose: To develop a technique for joint measurement of fat and water-specific longitudinal relaxation rates (R1f and R1w), effective transverse relaxation rate (R2*), and proton density fat fraction (PDFF) combining the Multi-Echo Magnetization Prepared Two Rapid Acquisition of Gradient Echoes (ME-MP2RAGE) sequence and fat-water separation. Theory and Methods: R1f and R1w were calculated with fat-specific and water-specific MP2RAGE signals. R2* and PDFF maps were obtained from fat-water separation applied to the second RAGE block. Sequence parameters optimization was performed via Cramér-Rao lower bounds theory, and we designed four protocols with different combinations of number of echoes and readout gradient schemes (I: 3 echoes unipolar, II: 6 echoes unipolar, III: 6 echoes bipolar, and IV: 10 echoes bipolar). We tested and validated these protocols with numerical simulations, phantom and in vivo experiments. In phantoms, we compared ME-MP2RAGE measurements with inversion recovery spin-echo (IR-SE) global R1 and 3D Fast Low Angle Shot (3D FLASH) R2* and PDFF. In vivo, we scanned the lower leg and neck of a healthy volunteer. Results: Numerical simulations showed accurate quantification of relaxation rates with mean relative bias < 3% and PDFF with mean bias < 0.003 using protocol ME-MP2RAGE IV (10 echoes bipolar). Phantom experiments showed excellent agreement with IR-SE and 3D FLASH measurements. In vivo, measurements in the lower leg and neck were consistent with literature values. Conclusion: We proposed an accurate method for simultaneous quantification of R1f, R1w, R2*, and PDFF from a single acquisition with the ME-MP2RAGE sequence.

physics.med-ph↗

arXiv2025

Phase-sensitive modelling improves Fat DESPOT multiparametric relaxation mapping in fat-water mixtures

Purpose: To improve on the original form of Fat DESPOT, a multiparametric mapping technique that returns the fat- and water-specific estimates of $R_1$ ($R_{1f}$, $R_{1w}$), $R_2^*$ , and proton density fat fraction (PDFF) by upgrading the fat-water separation method used for selection of initial parameter guesses, and by introducing explicit model sensitivity to the phase of the water and fat signals. Methods: We compared the 3-point Dixon and Graph Cut (GC) approaches to initial guesses for Fat DESPOT in phantom experiments at 3 T in a variable fat fraction gel phantom. Also in phantom, we then compared the original Fat DESPOT approach to a magnitude approach modelling the phases of fat and water separately (Fat DESPOT$_{mϕ}$), and an approach that models the complex data (Fat DESPOT$_c$). The best-performing approach was then used in the lower leg of a healthy human participant. Results: In phantoms, Fat DESPOT using the 3-point Dixon and GC performed similarly in parametric estimates and precision, though the Dixon approach deviated from the overall trend in the 50% nominal fat fraction ROI. Furthermore, Fat DESPOT$_c$ showed the best agreement with reference PDFF (average error 1.5 +/- 1.2%) and the lowest combined standard deviation across ROIs, for PDFF, $R_{1f}$, and $R_{1w}$ (σ = 0.13%, 0.19 s$^{-1}$, 0.0082 s$^{-1}$). Conclusion: With a higher precision of $R_{1f}$ and $R_{1w}$ , accuracy of PDFF, and more echo time versatility than other compared approaches, this work demonstrates the advantages of the GC approach for initial guesses paired with complex fitting for Fat DESPOT multiparametric imaging.

physics.med-ph↗