Radial Ultrashort TE Imaging Removes the Need for Breath-Holding in Hepatic Iron Overload Quantification by R2* MRI

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confidence: 77%

“…Non‐Cartesian trajectories, such as 3D stack‐of‐radial trajectories, have inherent robustness to motion, potentially allowing for FB

{normalR}_{2}^{*}

mapping throughout the entire placenta . There have been a few studies performing

{normalR}_{2}^{*}

mapping using stack‐of‐radial trajectories in the liver . Improved image quality using an FB stack‐of‐radial technique was previously observed for hepatic

{normalR}_{2}^{*}

mapping compared to conventional BH Cartesian techniques in a population who could not perform a BH .…”

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confidence: 99%

“…There have been a few studies performing

{normalR}_{2}^{*}

mapping using stack‐of‐radial trajectories in the liver . Improved image quality using an FB stack‐of‐radial technique was previously observed for hepatic

{normalR}_{2}^{*}

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confidence: 99%

See 1 more Smart Citation

3D mapping of the placenta during early gestation using free‐breathing multiecho stack‐of‐radial MRI at 3T

Armstrong

Liu

Martin

et al. 2018

“…Another important advantage of UTE imaging is that it can be performed under free breathing, as it is intrinsically less sensitive to motion because of radial sampling . A recent study validated that free‐breathing UTE outperforms free‐breathing GRE in sedated and breath‐hold noncompliant patients, which makes it a viable alternative to breath‐hold GRE for accurate R2* quantification even under conditions of nonmassive iron overload . Hence, UTE imaging can extend the measurable R2*‐based HIC range and eliminate the need for breath‐holding when assessing hepatic iron overload by R2*‐MRI.…”

Section: Discussionmentioning

confidence: 99%

“…breathing GRE in sedated and breath-hold noncompliant patients, which makes it a viable alternative to breath-hold GRE for accurate R2* quantification even under conditions of nonmassive iron overload. 21 Hence, UTE imaging can extend the measurable R2*-based HIC range and eliminate the need for breath-holding when assessing hepatic iron overload by R2*-MRI. This will increase the clinical suitability of UTE acquisition for assessing iron overload in pediatric populations and patients who are unable to hold their breath.…”

Section: Discussionmentioning

confidence: 99%

Ultrashort echo time imaging for quantification of hepatic iron overload: Comparison of acquisition and fitting methods via simulations, phantoms, and in vivo data

Tipirneni-Sajja

Loeffler

Krafft

et al. 2018

Self Cite

Background Current R2*‐MRI techniques for measuring hepatic iron content (HIC) use various acquisition types and fitting models. Purpose To evaluate the accuracy and precision of R2*‐HIC acquisition and fitting methods. Study Type Signal simulations, phantom study, and prospective in vivo cohort. Population In all, 132 patients (58/74 male/female, mean age 17.7 years). Field Strength/Sequence 2D‐multiecho gradient‐echo (GRE) and ultrashort echo time (UTE) acquisitions at 1.5T. Assessment Synthetic MR signals were created to mimic published GRE and UTE methods, using different R2* values (25–2000 s−1) and signal‐to‐noise ratios (SNR). Phantoms with varying iron concentrations were scanned at 1.5T. In vivo data were analyzed from 132 patients acquired at 1.5T. R2* was estimated by fitting using three signal models. Accuracy and precision of R2* measurements for UTE acquisition parameters (SNR, echo spacing [ΔTE], maximum echo time [TEmax]) and fitting methods were compared for simulated, phantom, and in vivo datasets. Statistical Tests R2* accuracy was determined from the relative error and by linear regression analysis. Precision was evaluated using coefficient of variation (CoV) analysis. Results In simulations, all models had high R2* accuracy (error <5%) and precision (CoV <10%) for all SNRs, shorter ΔTE (≤0.5 msec), and longer TEmax (≥10.1 msec); except the constant offset model overestimated R2* at the lowest SNR. In phantoms and in vivo, all models produced similar R2* values for different SNRs and shorter ΔTEs (slopes: 0.99–1.06, R2 > 0.99, P < 0.001). In all experiments, R2* results degraded for high R2* values with longer ΔTE (≥1 msec). In vivo, shorter and longer TEmax gave similar R2* results (slopes: 1.02–1.06, R2 > 0.99, P < 0.001) for the noise subtraction model for 25≤R2*≤2000 s−1. However, both quadratic and constant offset models, using shorter TEmax (≤4.7 msec) overestimated R2* and yielded high CoVs up to ∼170% for low R2* (<250 s−1). Data Conclusion UTE with TEmax ≥ 10.1 msec and ΔTE ≤ 0.5 msec yields accurate R2* estimates over the entire clinical HIC range. Monoexponential fitting with noise subtraction is the most robust signal model to changes in UTE parameters and achieves the highest R2* accuracy and precision. Level of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:1475–1488.

Hepatic Iron Quantification Using a Free‐Breathing 3D Radial Gradient Echo Technique and Validation With a 2D Biopsy‐Calibrated R₂^* Relaxometry Method

Rohani

Morin

Zhong

et al. 2021

Self Cite

Background: Hepatic iron content (HIC) is an important parameter for the management of iron overload. Non-invasive HIC assessment is often performed using biopsy-calibrated two-dimensional breath-hold Cartesian gradient echo (2D BH GRE) R 2 * -MRI. However, breath-holding is not possible in most pediatric patients or those with respiratory problems, and three-dimensional free-breathing radial GRE (3D FB rGRE) has emerged as a viable alternative. Purpose: To evaluate the performance of a 3D FB rGRE and validate its R 2 * and fat fraction (FF) quantification with 3D breath-hold Cartesian GRE (3D BH cGRE) and biopsy-calibrated 2D BH GRE across a wide range of HICs. Study Type: Retrospective. Subjects: Twenty-nine patients with hepatic iron overload (22 females, median age: 15 [5-25] years). Field Strength/Sequence: Three-dimensional radial and 2D and 3D Cartesian multi-echo GRE at 1.5 T. Assessment: R 2 * and FF maps were computed for 3D GREs using a multi-spectral fat model and 2D GRE R 2 * maps were calculated using a mono-exponential model. Mean R 2 * and FF values were calculated via whole-liver contouring and T 2 *thresholding by three operators. Statistical Tests: Inter-and intra-observer reproducibility was assessed using Bland-Altman and intraclass correlation coefficient (ICC). Linear regression and Bland-Altman analysis were performed to compare R 2 * and FF values among the three acquisitions. One-way repeated-measures ANOVA and Wilcoxon signed-rank tests, respectively, were used to test for significant differences between R 2 * and FF values obtained with different acquisitions. Statistical significance was assumed at P < 0.05. Results: The mean biases and ICC for inter-and intra-observer reproducibility were close to 0% and >0.99, respectively for both R 2 * and FF. The 3D FB rGRE R 2 * and FF values were not significantly different (P > 0.44) and highly correlated (R 2 ≥ 0.98) with breath-hold Cartesian GREs, with mean biases ≤ AE2.5% and slopes 0.90-1.12. In non-breath-holding patients, Cartesian GREs showed motion artifacts, whereas 3D FB rGRE exhibited only minimal streaking artifacts. Data Conclusion: Free-breathing 3D radial GRE is a viable alternative in non-breath-hold patients for accurate HIC estimation.