A semiautomatic postprocessing of liver R2* measurement for assessment of liver iron overload

Deng, Jie; Rigsby, Cynthia K.; Schoeneman, Samantha E.; Boylan, Emma E.

doi:10.1016/j.mri.2012.02.002

Cited by 12 publications

(14 citation statements)

References 21 publications

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“…ΔTE and TE max were varied by removing images with certain TEs from the entire echo train. Mean (±SD) R2* values were measured by manual selection of an ROI covering the whole liver cross‐section and exclusion of blood vessels based on histogram analysis . For each patient, the same ROI mask was used to calculate mean liver R2* values for different signal models and acquisition parameters.…”

Section: Methodsmentioning

confidence: 99%

“…Mean (±SD) R2* values were measured by manual selection of an ROI covering the whole liver cross-section and exclusion of blood vessels based on histogram analysis. 18,19 For each patient, the same ROI mask was used to calculate mean liver R2* values for different signal models and acquisition parameters. For each fit, the mean R2* values calculated by changing different UTE-A acquisition parameters were compared with those obtained with the 3-average UTE-A reference sequence.…”

Section: In Vivo Studymentioning

confidence: 99%

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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

Magnetic Resonance Imaging

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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.

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Section: Methodsmentioning

confidence: 99%

Section: In Vivo Studymentioning

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

Magnetic Resonance Imaging

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“…The MRI R2 and R2* relaxation rates have gained worldwide acceptance in the diagnosis and monitoring the therapy of iron-overloaded thalassemia 4–7 . It has been reported that the relaxometry decay rates R2 and R2* (the reciprocal of T2 and T2* relaxation times) have a good correlation with the biopsy-proven LIC 6, 8–10 and can be converted to the LIC by established calibration curves 11, 12 .…”

Section: Introductionmentioning

confidence: 99%

“…A region-of-interest (ROI) is firstly delineated in the homogenous parenchyma area without vessels and then the averaged signal intensity of all pixels in the ROI at each echo image is fitted to generate the representative R2* for the LIC quantification 7, 13 . The ROI approach has an advantage of avoiding contributions from vascular and biliary structures and is thus accurate and popular.…”

Section: Introductionmentioning

confidence: 99%

Improved Liver R2* Mapping by Averaging Decay Curves

Zhang

Peng

Feng

et al. 2017

Sci Rep

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Liver R2* mapping is often degraded by the low signal-to-noise ratio (SNR) especially in the presence of severe iron. This study aims to improve liver R2* mapping at low SNRs by averaging decay curves before the process of curve-fitting. Independently filtering echo images by nonlocal means (NLM) demonstrated improved quality of R2* mapping, but may introduce new errors due to the nonlinear nature of the NLM filter, during which the averaging weights may vary with different image contents at multiple echo times. In addition, the image denoising effect of the NLM may decline when no sufficient similar patches are available. To overcome these drawbacks, we proposed to filter decay curves instead of images. In this novel scheme, decay curves were averaged in a local window, each with a weight assigned according to the curve-similarity measured by the distance between one of the neighboring curves and the targeted one. The proposed method was tested on simulated, phantom and patient data. The results demonstrate that the proposed method can provide more accurate R2* mapping compared with the NLM algorithm, and hence has the potential to improve diagnosis and therapy in patients with liver iron.

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“…On a pixel- by-pixel basis, the signal decay was fitted to a mono-exponential decay by use of a nonlinear least-squares fit method, which accounts for bias caused by Rician noise [34, 35]. To quantify mean liver R2* values, an ROI encompassing the whole liver in the acquired axial slice was manually drawn, and blood vessels were excluded by histogram analysis for each patient, as detailed elsewhere [36, 37]. Because the FOV used for multiecho UTE imaging is larger than that used for multiecho GRE imaging, the ROIs were drawn separately for multiecho GRE and multiecho UTE images.…”

Section: Methodsmentioning

confidence: 99%

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

Tipirneni-Sajja

Krafft

McCarville

et al. 2017

American Journal of Roentgenology

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OBJECTIVE The objective of this study is to evaluate radial free-breathing (FB) multiecho ultrashort TE (UTE) imaging as an alternative to Cartesian FB multiecho gradient-recalled echo (GRE) imaging for quantitative assessment of hepatic iron content (HIC) in sedated patients and subjects unable to perform breath-hold (BH) maneuvers. MATERIALS AND METHODS FB multiecho GRE imaging and FB multiecho UTE imaging were conducted for 46 test group patients with iron overload who could not complete BH maneuvers (38 patients were sedated, and eight were not sedated) and 16 control patients who could complete BH maneuvers. Control patients also underwent standard BH multiecho GRE imaging. Quantitative R2* maps were calculated, and mean liver R2* values and coefficients of variation (CVs) for different acquisitions and patient groups were compared using statistical analysis. RESULTS FB multiecho GRE images displayed motion artifacts and significantly lower R2* values, compared with standard BH multiecho GRE images and FB multiecho UTE images in the control cohort and FB multiecho UTE images in the test cohort. In contrast, FB multiecho UTE images produced artifact-free R2* maps, and mean R2* values were not significantly different from those measured by BH multiecho GRE imaging. Motion artifacts on FB multiecho GRE images resulted in an R2* CV that was approximately twofold higher than the R2* CV from BH multiecho GRE imaging and FB multiecho UTE imaging. The R2* CV was relatively constant over the range of R2* values for FB multiecho UTE, but it increased with increases in R2* for FB multiecho GRE imaging, reflecting that motion artifacts had a stronger impact on R2* estimation with increasing iron burden. CONCLUSION FB multiecho UTE imaging was less motion sensitive because of radial sampling, produced excellent image quality, and yielded accurate R2* estimates within the same acquisition time used for multiaveraged FB multiecho GRE imaging. Thus, FB multiecho UTE imaging is a viable alternative for accurate HIC assessment in sedated children and patients who cannot complete BH maneuvers.

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A semiautomatic postprocessing of liver R2* measurement for assessment of liver iron overload

Cited by 12 publications

References 21 publications

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

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

Improved Liver R2* Mapping by Averaging Decay Curves

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

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