arXiv subjects

Ives R. Levesque

Publications and source records attributed to Ives R. Levesque.

4 recordsLinked to original sources

arXiv2026

Evaluation of reference region modelling techniques in quantitative dynamic contrast-enhanced magnetic resonance imaging of breast cancer

Purpose: To assess the validity of reference region model (RRM) techniques for quantitative perfusion analysis of low temporal resolution DCE-MRI of breast lesions. Methods: Tofts model (TM), extended Tofts model (ETM), RRM, and extended RRM (ERRM) were applied to a dataset of images from ten patients with confirmed breast cancer collected before and after one cycle of chemotherapy, with known pathologic treatment response. Quantitative maps of estimated perfusion parameters were produced using each model, and changes in median perfusion parameters before and after a cycle of chemotherapy were compared across models. Relative parameters from reference region models were made absolute using the reference region and input function tail (RRIFT) technique. Tumour region voxel count before and after treatment was also recorded. Results: RRMs produced similar absolute quantitative analysis compared to AIF-driven models (TM and ETM), with scaling dicerences in Ktrans parameter estimates and disagreement in vp parameter estimates between ETM and ERRM. RRMs and AIF-driven models were equally capable of separating complete responders based on change in median Ktrans parameter, while change in tumour voxel count was not predictive of treatment response. Both RRMs were also able to fully separate complete responders using relative Ktrans parameter estimates, with no AIF information. Conclusions: RRMs show similar performance as standard models in quantitative analysis of breast lesions, with reduced reliance on the AIF . Results imply that RRMs may be a suitable alternative at low temporal resolutions to provide reliable, patient-specific quantitative analysis.

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↗

arXiv2025

A flexible approach for fat-water separation with bipolar readouts and correction of gradient-induced phase and amplitude effects

Purpose: To develop a fat-water separation approach that corrects bipolar readout gradient induced effects, without additional scans, that is compatible with any fat-water separation method. Theory and Methods: The proposed approach combines joint fat-water separation of the odd and even echoes of a bipolar multi-echo gradient echo acquisition with an inverse problem to find least-squares estimates for phase and amplitude corrections to eliminate bipolar-induced effects. Optimization of sequence parameter selection through the calculation of the number of signal averages (NSA) with Cramér-Rao Bound theory (CRB) is presented. The application of the proposed approach is demonstrated with a graph cut optimization and further characterization of the accuracy was performed via Monte Carlo Simulations (MC). The proposed approach was tested in phantoms and in vivo. Proton density fat fraction maps (PDFF) were evaluated to quantify performance. Results: NSA calculations suggest short TE1 and ΔTE=1.5 ms as optimal alternatives for fat-water separation. MC simulations demonstrated accurate estimation of fat and water complex signals, ψ, and R_2^* with mean relative error within 1%. In phantoms and in vivo, the proposed approach effectively eliminated effects induced by bipolar readout gradients, improving the outcome of the fat-water separation. Conclusion: We proposed an approach to correct bipolar readout-induced effects that are detrimental for fat-water separation. This approach can extend the use of existing fat-water separation techniques designed for data acquired using unipolar readout gradients to data collected with bipolar readout gradients.

physics.med-ph↗