Milan Prsa

Background: The performance of 5D imaging in CHD has been previously demonstrated using ferumoxytol rather than gadolinium. Purpose: To evaluate the performance of gadolinium enhanced 5D MRI relative to 2D and 3D MRI in CHD patients. Study Type: Retrospective. Subjects: 45 consecutive CHD patients referred for clinically indicated MRI who underwent 2D, 3D, and 5D MRI. Field Strength/Sequence: 2D bSSFP CINE, 3D bSSFP, and 5D FISS at 1.5 T. Assessment: Scan time (2D, 3D, and 5D), left and right ventricular (LV, RV) end diastolic and end systolic volumes (LVEDV, RVEDV, LVESV, and RVESV, respectively), ejection fraction (LVEF, RVEF) for 2D versus 5D, and image quality on a 4‐point Likert scale (3D vs. 5D). Statistical Tests: Paired comparisons were made using a paired t ‐test or Wilcoxon signed rank test. Agreement between measurements was evaluated with Bland–Altman analysis including the bias and 95% limits of agreement. Results: Scan time for 5D (6:18 [0]) was significantly shorter than 2D (7:16 [4:39]) and 3D (6:55 [1:30]) MRI. 5D measurements were strongly correlated with 2D measurements of LVEDV ( R ² = 0.94), LVESV ( R ² = 0.83), LVEF ( R ² = 0.51), ( R ² = 0.85), RVESV ( R ² = 0.80), and RVEF ( R ² = 0.66) but with significant biases. Sharpness of the coronary arteries were significantly higher for 3D (RCA: 36.8% ± 10.2%, LAD: 40.5% ± 10.5%) than 5D (RCA: 24.3% ± 7.5%, LAD: 31.7% ± 8.7%), but longer vessel segments were visible using 5D (LAD: 6.9 ± 2.5) than 3D (LAD: 5.3 ± 2.9 mm) acquisitions. The grades for 5D (R1: 3 [1], R2: 2.5 [0.5], R3: 3 [0.6]) were significantly higher than 3D (R1: 3 [1], R2: 2.5 [1], R3: 2 [1]). Data Conclusion: Gadolinium‐enhanced 5D MRI may provide an efficient and simplified acquisition for CHD patients, with multiple quantitative parameters from 5D being not significantly different from those from reference standard 2D and 3D MRI. Evidence Level: 4 Stage of Technical Efficacy: 1

Background: Tricuspid annular plane systolic excursion (TAPSE) and right ventricular (RV) fractional area change (FAC) are often used as surrogate measurements of RV systolic function. However, their reliability in children following cardiac surgery involving pericardiotomy remains unclear. The goal of this study was to evaluate whether TAPSE and FAC are valid surrogate markers of global RV systolic function in paediatric patients with and without prior pericardiotomy. Methods: We retrospectively analysed 120 paediatric patients who underwent ferumoxytol-enhanced, motion-resolved five-dimensional whole-heart cardiac MRI between 2020 and 2024. Patients were divided into two groups: those who had previous pericardiotomy (n=85) and those who had no previous surgery (n=35). TAPSE z-scores, RV FAC and RV ejection fraction (RVEF) were measured and compared between the two groups and correlation analyses were performed. Results: In the post-pericardiotomy group, TAPSE z-score was significantly decreased (−5.32±2) and did not correlate with RVEF (r=0.04), while RV FAC was preserved (41.3%) but correlated only weakly with RVEF (r=0.39). In patients without previous cardiac surgery, TAPSE z-score was within the normal range (0.17±1.48) but demonstrated a weak correlation with RVEF (r=0.28), while RV FAC was moderately correlated with RVEF (r=0.57). Differences in the correlation strengths between the two groups were not statistically significant. Conclusions: TAPSE and RV FAC showed limited reliability as surrogate markers of global RV systolic function in paediatric patients especially following surgery involving pericardiotomy. Only RVEF, measured by cardiac MRI, should be used to evaluate true RV systolic function after paediatric cardiac surgery.

Purpose: To develop a framework (ACROBATIC) for correcting motion in 3D radial fetal MRI. Methods: Data were simulated ( N = 200) and acquired in utero ( N = 11, gestational age: 32 ± 2 weeks). Motion due to maternal respiration was estimated by extracting a self‐gating signal and applying focused navigation. Bulk motion was estimated by splitting the acquisition into sequential bins, reconstructing 3D volumes and applying rigid image registration. These combined motion estimates were used to correct k‐space. Self‐gating signals were compared to ground truth in simulations and an external sensor in utero. The cumulative position error (CPE) measured the accuracy of motion estimations relative to ground truth in simulations and relative sharpness measured the corresponding impact on image quality for both simulations and in utero data. An expert reviewer performed a blinded ranking of in utero images including uncorrected and corrected data. Results: Self‐gating signals correlated strongly with ground truth for simulations ( R = 0.97 ± 0.01) and a external sensor for in utero data ( R = 0.75 ± 0.23). CPE decreased significantly using ACROBATIC (uncorrected: 13.33[12.73–14.05], corrected: 2.20[1.80–2.61]). Relative image sharpness increased with ACROBATIC for both simulated (4.51[2.89–5.79]) and in utero data (1.12[0.77–1.44]) consistent with expert ranking where ACROBATIC images were given the best rank in the majority of cases. Conclusion: ACROBATIC enables motion correction in 3D radial fetal MRI. Correction of displacement due to maternal respiration and bulk motion results in improved image quality in simulations and in utero. Comparison to 2D frameworks are now warranted to establish the added diagnostic value of this approach.

Purpose: To compare two blind source separation (BSS) techniques to principal component analysis and the electrocardiogram for the identification of cardiac triggers in self‐gated free‐running 5D whole‐heart MRI. To ascertain the precision and robustness of the techniques, they were compared in three different noise and contrast regimes.Methods: The repeated superior–inferior (SI) projections of a 3D radial trajectory were used to extract the physiological signals in three cardiac MRI cohorts: (1) 9 healthy volunteers without contrast agent injection at 1.5T, (2) 30 ferumoxytol‐injected congenital heart disease patients at 1.5T, and (3) 12 gadobutrol‐injected patients with suspected coronary artery disease at 3T. Self‐gated cardiac triggers were extracted with the three algorithms (principal component analysis [PCA], second‐order blind identification [SOBI], and independent component analysis [ICA]) and the difference with the electrocardiogram triggers was calculated. PCA and SOBI triggers were retained for image reconstruction. The image sharpness was ascertained on whole‐heart 5D images obtained with PCA and SOBI and compared among the three cohorts.Results: SOBI resulted in smaller trigger differences in Cohorts 1 and 3 compared to PCA (p < 0.01) and in all cohorts compared to ICA (p < 0.04). In Cohorts 1 and 3, the sharpness increased significantly in the reconstructed images when using SOBI instead of PCA (p < 0.03), but not in Cohort 2 (p = 0.4).Conclusion: We have shown that SOBI results in more precisely extracted self‐gated triggers than PCA and ICA. The validation across three diverse cohorts demonstrates the robustness of the method against acquisition variability.

A similarity-driven multi-dimensional binning algorithm (SIMBA) reconstruction of free-running cardiac magnetic resonance imaging data was previously proposed. While very efficient and fast, the original SIMBA focused only on the reconstruction of a single motion-consistent cluster, discarding the remaining data acquired. However, the redundant data clustered by similarity may be exploited to further improve image quality. In this work, we propose a novel compressed sensing (CS) reconstruction that performs an effective regularization over the clustering dimension, thanks to the integration of inter-cluster motion compensation (XD-MC-SIMBA). This reconstruction was applied to free-running ferumoxytol-enhanced datasets from 24 patients with congenital heart disease, and compared to the original SIMBA, the same XD-MC-SIMBA reconstruction but without motion compensation (XD-SIMBA), and a 5D motion-resolved CS reconstruction using the free-running framework (FRF). The resulting images were compared in terms of lung-liver and blood-myocardium sharpness, blood-myocardium contrast ratio, and visible length and sharpness of the coronary arteries. Moreover, an automated image quality score (IQS) was assigned using a pretrained deep neural network. The lung-liver sharpness and blood-myocardium sharpness were significantly higher in XD-MC-SIMBA and FRF. Consistent with these findings, the IQS analysis revealed that image quality for XD-MC-SIMBA was improved in 18 of 24 cases, compared to SIMBA. We successfully tested the hypothesis that multiple motion-consistent SIMBA clusters can be exploited to improve the quality of ferumoxytol-enhanced cardiac MRI when inter-cluster motion-compensation is integrated as part of a CS reconstruction.

Purpose To improve the image quality of 3D radial free-running MRI data of the heart through a deliberate and stepwise extension of the XD-GRASP reconstruction. Methods Ferumoxytol-enhanced cardiac free-running 3D-radial data were reconstructed using an XD-GRASP reconstruction improved by 4 new developments: motion-compensated temporal-Total-Variation (MC-tTV) regularization for 3D images, a new coil-sensitivity, a new k-space density compensation and a revisited conjugate-gradient-descent (with exact line search) for solving the least-square sub-problem of ADMM. The resulting images were compared quantitatively and qualitatively to reconstructions lacking some of the newly implemented measures. Also, the measurement of ejection-fraction by a threshold-based method on the new reconstruction was compared to a reference standard. Results The new reconstruction significantly increased the sharpness of the right coronary artery (4% to 6%, p < 0.05) and the left anterior descending coronary artery (4% to 5% p < 0.05). It also increased blood-myocardium interface sharpness (between 20% and 25%, p < 0.05) and decreases spatial-Total-Variation in the blood-pool (13%, p < 0.05). The qualitative evaluation suggests better anatomical depiction of small structures using the new reconstruction. As compared to a reference standard method, ejection fraction could also be correctly evaluated. Conclusion Compressed sensing image reconstruction for 3D-radial free-running cardiac acquisition was successfully improved by including MC-tTV regularization, a new density compensation, a new coil-sensitivity and a revisited conjugate-gradient-descent with exact line search. Quantitative and qualitative quality metrics demonstrated significant improvement in image quality when using the new reconstruction, while extracted dynamic information compared favorably with the gold standard.

Editorial: Management of the hypoplastic left heart syndrome: from fetus to adult

Purpose: To validate a respiratory motion correction method called focused navigation (fNAV) for free‐running radial whole‐heart 4D flow MRI.Methods: Using fNAV, respiratory signals derived from radial readouts are converted into three orthogonal displacements, which are then used to correct respiratory motion in 4D flow datasets. Hundred 4D flow acquisitions were simulated with non‐rigid respiratory motion and used for validation. The difference between generated and fNAV displacement coefficients was calculated. Vessel area and flow measurements from 4D flow reconstructions with (fNAV) and without (uncorrected) motion correction were compared to the motion‐free ground‐truth. In 25 patients, the same measurements were compared between fNAV 4D flow, 2D flow, navigator‐gated Cartesian 4D flow, and uncorrected 4D flow datasets.Results: For simulated data, the average difference between generated and fNAV displacement coefficients was 0.04 0.32 mm and 0.31 0.35 mm in the x and y directions, respectively. In the z direction, this difference was region‐dependent (0.02 0.51 mm up to 5.85 3.41 mm). For all measurements (vessel area, net volume, and peak flow), the average difference from ground truth was higher for uncorrected 4D flow datasets (0.32 0.11 cm², 11.1 3.5 mL, and 22.3 6.0 mL/s) than for fNAV 4D flow datasets (0.10 0.03 cm², 2.6 0.7 mL, and 5.1 .9 mL/s, p < 0.05). In vivo, average vessel area measurements were 4.92 2.95 cm², 5.06 2.64 cm², 4.87 2.57 cm², 4.87 2.69 cm², for 2D flow and fNAV, navigator‐gated and uncorrected 4D flow datasets, respectively. In the ascending aorta, all 4D flow datasets except for the fNAV reconstruction had significantly different vessel area measurements from 2D flow. Overall, 2D flow datasets demonstrated the strongest correlation to fNAV 4D flow for both net volume (r² = 0.92) and peak flow (r² = 0.94), followed by navigator‐gated 4D flow (r² = 0.83 and r² = 0.86, respectively), and uncorrected 4D flow (r² = 0.69 and r² = 0.86, respectively).Conclusion: fNAV corrected respiratory motion in vitro and in vivo, resulting in fNAV 4D flow measurements that are comparable to those derived from 2D flow and navigator‐gated Cartesian 4D flow datasets, with improvements over those from uncorrected 4D flow.