Accelerated free-breathing liver fat and R 2 * quantification using multi-echo stack-of-radial MRI with motion-resolved multidimensional regularized reconstruction: Initial retrospective evaluation.

PURPOSE: To improve image quality, mitigate quantification biases and variations for free-breathing liver proton density fat fraction (PDFF) and R 2 * $$ {\mathrm{R}}_2^{\ast } $$ quantification accelerated by radial k-space undersampling. METHODS: A free-breathing multi-echo stack-of-radial MRI method was developed with compressed sensing with multidimensional regularization. It was validated in motion phantoms with reference acquisitions without motion and in 11 subjects (6 patients with nonalcoholic fatty liver disease) with reference breath-hold Cartesian acquisitions. Images, PDFF, and R 2 * $$ {\mathrm{R}}_2^{\ast } $$ maps were reconstructed using different radial view k-space sampling factors and reconstruction settings. Results were compared with reference-standard results using Bland-Altman analysis. Using linear mixed-effects model fitting (p < 0.05 considered significant), mean and SD were evaluated for biases and variations of PDFF and R 2 * $$ {\mathrm{R}}_2^{\ast } $$ , respectively, and coefficient of variation on the first echo image was evaluated as a surrogate for image quality. RESULTS: Using the empirically determined optimal sampling factor of 0.25 in the accelerated in vivo protocols, mean differences and limits of agreement for the proposed method were [-0.5; -33.6, 32.7] s-1 for R 2 * $$ {\mathrm{R}}_2^{\ast } $$ and [-1.0%; -5.8%, 3.8%] for PDFF, close to those of a previous self-gating method using fully sampled radial views: [-0.1; -27.1, 27.0] s-1 for R 2 * $$ {\mathrm{R}}_2^{\ast } $$ and [-0.4%; -4.5%, 3.7%] for PDFF. The proposed method had significantly lower coefficient of variation than other methods (p < 0.001). Effective acquisition time of 64 s or 59 s was achieved, compared with 171 s or 153 s for two baseline protocols with different radial views corresponding to sampling factor of 1.0. CONCLUSION: This proposed method may allow accelerated free-breathing liver PDFF and R 2 * $$ {\mathrm{R}}_2^{\ast } $$ mapping with reduced biases and variations.

Application of the magnetic resonance 3D multiecho Dixon sequence for quantifying hepatic iron overload and steatosis in patients with thalassemia.

OBJECTIVE: To investigate the feasibility and diagnostic efficacy of a 3D multiecho Dixon (qDixon) research application for simultaneously quantifying the liver iron concentration (LIC) and steatosis in thalassemia patients. MATERIALS AND METHODS: This prospective study enrolled participants with thalassemia who underwent 3 T MRI of the liver for the evaluation of hepatic iron overload. The imaging protocol including qDixon and conventional T2* mapping based on 2D multiecho gradient echo (ME GRE) sequences respectively. Regions of interest (ROIs) were drawn in the liver on the qDixon maps to obtain R2* and proton density fat fraction (PDFF). The reference R2* value was measured and calculated on conventional T2* mapping using the CMRtools software. Correlation analysis, Linear regression analysis, and Bland-Altman analysis were performed. RESULTS: 84 patients were finally included in this study. The median R2*-ME-GRE was 366.97 (1/s), range [206.68 (1/s), 522.20 (1/s)]. 8 patients had normal hepatic iron deposition, 16 had Insignificant, 42 had mild, 18 had moderate. The median of R2*-qDixon was 376.88 (1/s) [219.33 (1/s), 491.75 (1/s)]. A strong correlation was found between the liver R2*-qDixon and the R2*-ME-GRE (r = 0.959, P < 0.001). The median value of PDFF was 1.76% (1.10%, 2.95%). 8 patients had mild fatty liver, and 1 had severe fatty liver. CONCLUSION: MR qDixon research sequence can rapidly and accurately quantify liver iron overload, that highly consistent with the measured via conventional GRE sequence, and it can also simultaneously detect hepatic steatosis, this has great potential for clinical evaluation of thalassemia patients.

Wavelet MRE: Imaging propagating broadband acoustic waves with wavelet-based motion-encoding gradients.

PURPOSE: To demonstrate a novel MR elastography (MRE) technique, termed here wavelet MRE. With this technique, broadband motion sensitivity is achievable. Moreover, the true tissue displacement can be reconstructed with a simple inverse transform. METHODS: A wavelet MRE sequence was developed with motion-encoding gradients based on Haar wavelets. From the phase images' displacement was estimated using an inverse transform. Simulations were performed using a frequency sweep and a transient as ground-truth motions. A PVC phantom was scanned using wavelet MRE and standard MRE with both transient (one and 10 cycles of 90-Hz motion) and steady-state dual-frequency motion (30 and 60 Hz) for comparison. The technique was tested in a human brain, and motion trajectories were estimated for each voxel. RESULTS: In simulation, the displacement information estimated from wavelet MRE closely matched the true motion. In the phantom test, the MRE phase data generated from the displacement information derived from wavelet MRE agreed well with standard MRE data. Testing of wavelet MRE to assess transient motion waveforms in the brain was successful, and the tissue motion observed was consistent with a previous study. CONCLUSION: The uniform and broadband frequency response of wavelet MRE makes it a promising method for imaging transient, multifrequency motion, or motion with unknown frequency content. One potential application is measuring the response of brain tissue undergoing low-amplitude, transient vibrations as a model for the study of traumatic brain injury.

Segmental quantification of hepatic lipid content based on volumetric MRI data in patients with suspected iron overload.

PURPOSE: To investigate the segmental distribution of hepatic fat fraction, determined with MRI (MR proton density fat fraction, short MR-PDFF) in patients suspected of having liver iron overload. METHODS: The liver of 44 patients examined with MRI using a 3D multi-echo gradient-echo sequence was segmented semiautomatically and subdivided into nine segments (segment 4 divided in 4a and 4b). Segmental fat content was determined on MR-PDFF maps. Whole-liver steatosis grades were compared to those found in individual segments. Segmental MR-PDFF differences were tested for statistical significance. RESULTS: The most common diseases were thalassemia, various forms of anemia, and hereditary hemochromatosis. No patients suffered from fat metabolism disease. Iron overload was present in 37/44 (84 %) patients. For the whole liver, 22 patients showed a steatosis grade of 0, 21 patients were graded S1, and one patient had a steatosis grade of 2. The grade of steatosis was underestimated in 5 of 21 patients (24 %) in segment 8 and in 8 of 21 patients (38 %) in segment 7. Highly significant segmental MR-PDFF differences were detected with p < 0.00 001, e. g., comparing segment 2 to 5. Segments 1 to 3 had the highest fat content, segments 7 and 8 had the lowest. CONCLUSION: Our results suggest that the storage of fat in the liver is inhomogeneous, so that segment-wise differing fat concentrations were found. Fat distribution in patients with suspected hepatic iron overload was similar to living liver donors. However, it showed significant differences compared with the values published for NAFLD patients, which were less pronounced in the group with high average hepatic MR-PDFF values than in the group with normal lipid content. In patients suspected of having iron overload, segment 8, which is mainly targeted for biopsy, and segment 7 may underestimate steatosis grade. KEY POINTS: · A volumetric analysis of 3D MRI data of patients with suspected hepatic iron overload yielded a markedly elevated MR proton density fat fraction (MR-PDFF) in hepatic segments 1 to 3.. · This hepatic fat distribution, observed for the whole patient cohort, is similar to healthy living liver donors.. · The subgroup of patients with a high average MR-PDFF ≥ 6.5 % shows this effect with lower segmental deviations.. · In patients without fat metabolic disorders, the steatosis grade may be underestimated when taking biopsies in segment 8 or 7..

Self-supervised MRI denoising: leveraging Stein's unbiased risk estimator and spatially resolved noise maps.

Thermal noise caused by the imaged object is an intrinsic limitation in magnetic resonance imaging (MRI), resulting in an impaired clinical value of the acquisitions. Recently, deep learning (DL)-based denoising methods achieved promising results by extracting complex feature representations from large data sets. Most approaches are trained in a supervised manner by directly mapping noisy to noise-free ground-truth data and, therefore, require extensive paired data sets, which can be expensive or infeasible to obtain for medical imaging applications. In this work, a DL-based denoising approach is investigated which operates on complex-valued reconstructed magnetic resonance (MR) images without noise-free target data. An extension of Stein's unbiased risk estimator (SURE) and spatially resolved noise maps quantifying the noise level with pixel accuracy were employed during the training process. Competitive denoising performance was achieved compared to supervised training with mean squared error (MSE) despite optimizing the model without noise-free target images. The proposed DL-based method can be applied for MR image enhancement without requiring noise-free target data for training. Integrating the noise maps as an additional input channel further enables the regulation of the desired level of denoising to adjust to the preference of the radiologist.

Preliminary Study of Confounder-Corrected Fat Fraction and R2* Mapping of Bone Marrow in Children With Acute Leukemia.

BACKGROUND: The bone marrow (BM) evaluation of acute leukemia (AL) mainly depends on invasive BM puncture biopsy. Noninvasive and accurate MR examination technology has potential clinical application value in the BM evaluation of AL patients. Multi-gradient-echo (MGRE) has been found useful to evaluate changes in BM fat and iron content, but has not yet been applied in AL. PURPOSE: To explore the diagnostic capability of BM infiltration of quantitative BM fat fraction (FF) and R2* values obtained from a 3D MGRE sequence in children with primary AL. STUDY TYPE: Prospective. POPULATION/SUBJECTS: Sixty-two pediatric patients with untreated AL and 68 healthy volunteers. AL patients were divided into acute lymphoblastic leukemia (ALL) (n = 39) and acute myeloid leukemia (AML) (n = 23) groups. FIELD STRENGTH/SEQUENCE: 3T, 3D chemical-shift-encoded multi-gradient-echo, T1WI, T2WI, T2_STIR. ASSESSMENT: BM FF and R2* values were assessed by manually drawing regions of interest at the L3, L4, ilium, and 1 cm below the bilateral trochanter of the femur (upper femur). STATISTICAL TESTS: Independent sample t-tests, variance analysis, Spearman correlation. RESULTS: BM FF and R2* at L3, L4, ilium, and upper femur, FFtotal and R2*total were significantly lower in the AL than control group. BM FF did not significantly differ between ALL and AML groups (PL3 = 0.060, PL4 = 0.086, Pilium = 0.179, Pupper femur = 0.149, and Ptotle = 0.097, respectively). The R2* was significantly lower in ALL group than AML group for L3, L4, and R2*total . BM FF was moderately positively correlated with R2* in ALL group, and strongly positively correlated in AML group. Area under the receiver operating characteristic curves showed that BM FF had higher AUC in AL, ALL, and AML (all AUC = 1.000) than R2* (0.976, 0.996, and 0.941, respectively). DATA CONCLUSION: MGRE-MRI mapping can be applied to measure BM FF and R2* values, and help evaluate BM infiltration and iron storage in children with AL. EVIDENCE LEVEL: 1 Technical Efficacy: 2.

Chemical Shift MRI Monitoring of Chemoembolization Delivery for Hepatocellular Carcinoma: Multicenter Feasibility of Initial Clinical Translation.

Purpose To demonstrate the feasibility of using chemical shift fat-water MRI methods to visualize and measure intrahepatic delivery of ethiodized oil to liver tumors following conventional transarterial chemoembolization (cTACE). Materials and Methods Twenty-eight participants (mean age, 66 years ± 8 [SD]; 22 men) with hepatocellular carcinoma (HCC) treated with cTACE were evaluated with follow-up chemical shift MRI in this Health Insurance Portability and Accountability Act-compliant prospective, institutional review board-approved study. Uptake of ethiodized oil was evaluated at 1-month follow-up chemical shift MRI. Measurements of tumor size (MRI and CT), attenuation and enhancement (CT), fat content percentage, and tumor:normal ratio (MRI) were compared by lesion for responders versus nonresponders, as assessed with modified Response Evaluation Criteria in Solid Tumors and European Association for the Study of the Liver (EASL) criteria. Adverse events and overall survival by the Kaplan-Meier method were secondary end points. Results Focal tumor ethiodized oil retention was 46% (12 of 26 tumors) at 24 hours and 47% (18 of 38 tumors) at 1 month after cTACE. Tumor volume at CT did not differ between EASL-defined responders and nonresponders (P = .06). Tumor ethiodized oil volume measured with chemical shift MRI was statistically significantly higher for EASL-defined nonresponders (P = .02). Doxorubicin dosing (P = .53), presence of focal fat (P = .83), and a combined end point of focal fat and low doxorubicin dosing (P = .97) did not stratify overall survival after cTACE. Conclusion Chemical shift MRI allowed for assessment of tumor delivery of ethiodized oil out to 1 month after cTACE in participants with HCC and demonstrated tumor ethiodized oil volume as a potential tool for stratification of tumor response by EASL criteria. Keywords: MRI, Chemical Shift Imaging, CT, Hepatic Chemoembolization, Ethiodized Oil Clinicaltrials.gov registration no.: NCT02173119 Supplemental material is available for this article. © RSNA, 2023.

A Faster Prostate MRI: Comparing a Novel Denoised, Single-Average T2 Sequence to the Conventional Multiaverage T2 Sequence Regarding Lesion Detection and PI-RADS Score Assessment.

BACKGROUND: The T2 w sequence is a standard component of a prostate MRI examination; however, it is time-consuming, requiring multiple signal averages to achieve acceptable image quality. PURPOSE/HYPOTHESIS: To determine whether a denoised, single-average T2 sequence (T2 -R) is noninferior to the standard multiaverage T2 sequence (T2 -S) in terms of lesion detection and PI-RADS score assessment. STUDY TYPE: Retrospective. POPULATION: A total of 45 males (age range 60-75 years) who underwent clinically indicated prostate MRI examinations, 21 of whom had pathologically proven prostate cancer. FIELD STRENGTH/SEQUENCE: A 3 T; T2 w FSE, DWI with ADC maps, and dynamic contrast-enhanced images with color-coded perfusion maps. T2 -R images were created from the raw data utilizing a single "average" with iterative denoising. ASSESSMENT: Nine readers randomly assessed complete exams including T2 -R and T2 -S images in separate sessions. PI-RADS version 2.1 was used. All readers then compared the T2 -R and T2 -S images side by side to evaluate subjective preference. An additional detailed image quality assessment was performed by three senior level readers. STATISTICAL TESTS: Generalized linear mixed effects models for differences in lesion detection, image quality features, and overall preference between T2 -R and T2 -S sequences. Intraclass correlation coefficients (ICC) were used to assess reader agreement for all comparisons. A significance threshold of P = 0.05 was used for all statistical tests. RESULTS: There was no significant difference between sequences regarding identification of lesions with PI-RADS ≥3 (P = 0.10) or PI-RADS score (P = 0.77). Reader agreement was excellent for lesion identification (ICC = 0.84). There was no significant overall preference between the two sequences regarding image quality (P = 0.07, 95% CI: [-0.23, 0.01]). Reader agreement was good regarding sequence preference (ICC = 0.62). DATA CONCLUSION: Use of single-average, denoised T2 -weighted images was noninferior in prostate lesion detection or PI-RADS scoring when compared to standard multiaverage T2 -weighted images. EVIDENCE LEVEL: 3. TECHNICAL EFFICACY: Stage 3.

Application of deep learning-based super-resolution to T1-weighted postcontrast gradient echo imaging of the chest.

OBJECTIVES: A deep learning-based super-resolution for postcontrast volume-interpolated breath-hold examination (VIBE) of the chest was investigated in this study. Aim was to improve image quality, noise, artifacts and diagnostic confidence without change of acquisition parameters. MATERIALS AND METHODS: Fifty patients who received VIBE postcontrast imaging of the chest at 1.5 T were included in this retrospective study. After acquisition of the standard VIBE (VIBES), a novel deep learning-based algorithm and a denoising algorithm were applied, resulting in enhanced images (VIBEDL). Two radiologists qualitatively evaluated both datasets independently, rating sharpness of soft tissue, vessels, bronchial structures, lymph nodes, artifacts, cardiac motion artifacts, noise levels and overall diagnostic confidence, using a Likert scale ranging from 1 to 4. In the presence of lung lesions, the largest lesion was rated regarding sharpness and diagnostic confidence using the same Likert scale as mentioned above. Additionally, the largest diameter of the lesion was measured. RESULTS: The sharpness of soft tissue, vessels, bronchial structures and lymph nodes as well as the diagnostic confidence, the extent of artifacts, the extent of cardiac motion artifacts and noise levels were rated superior in VIBEDL (all P < 0.001). There was no significant difference in the diameter or the localization of the largest lung lesion in VIBEDL compared to VIBES. Lesion sharpness as well as detectability was rated significantly better by both readers with VIBEDL (both P < 0.001). CONCLUSION: The application of a novel deep learning-based super-resolution approach in T1-weighted VIBE postcontrast imaging resulted in an improvement in image quality, noise levels and diagnostic confidence as well as in a shortened acquisition time.

Water-Fat Separated T1 Mapping in the Liver and Correlation to Hepatic Fat Fraction.

(1) Background: T1 mapping in magnetic resonance imaging (MRI) of the liver has been proposed to estimate liver function or to detect the stage of liver disease, among others. Thus far, the impact of intrahepatic fat on T1 quantification has only been sparsely discussed. Therefore, the aim of this study was to evaluate the potential of water-fat separated T1 mapping of the liver. (2) Methods: A total of 386 patients underwent MRI of the liver at 3 T. In addition to routine imaging techniques, a 3D variable flip angle (VFA) gradient echo technique combined with a two-point Dixon method was acquired to calculate T1 maps from an in-phase (T1_in) and water-only (T1_W) signal. The results were correlated with proton density fat fraction using multi-echo 3D gradient echo imaging (PDFF) and multi-echo single voxel spectroscopy (PDFF_MRS). Using T1_in and T1_W, a novel parameter FF_T1 was defined and compared with PDFF and PDFF_MRS. Furthermore, the value of retrospectively calculated T1_W (T1_W_calc) based on T1_in and PDFF was assessed. Wilcoxon test, Pearson correlation coefficient and Bland-Altman analysis were applied as statistical tools. (3) Results: T1_in was significantly shorter than T1_W and the difference of both T1 values was correlated with PDFF (R = 0.890). FF_T1 was significantly correlated with PDFF (R = 0.930) and PDFF_MRS (R = 0.922) and yielded only minor bias compared to both established PDFF methods (0.78 and 0.21). T1_W and T1_W_calc were also significantly correlated (R = 0.986). (4) Conclusion: T1_W acquired with a water-fat separated VFA technique allows to minimize the influence of fat on liver T1. Alternatively, T1_W can be estimated retrospectively from T1_in and PDFF, if a Dixon technique is not available for T1 mapping.

Volumetric Evaluation of 3D Multi-Gradient-Echo MRI Data to Assess Whole Liver Iron Distribution by Segmental R2* Analysis: First Experience.

PURPOSE: MR transverse relaxation rate R2* has been shown to be useful for monitoring liver iron overload. A sequence enabling acquisition of the whole liver in a single breath hold is now available, thus allowing volumetric hepatic R2* distribution studies. We evaluated the feasibility of computer-assisted whole liver segmentation of 3 D multi-gradient-echo MRI data, and compared whole liver R2* determination to analyzing only a single slice. Also, segmental R2* differences were studied. MATERIALS AND METHODS: The liver of 44 patients, investigated by multi-gradient echo MRI at 1.5 T, was segmented and divided into nine segments. Segmental R2* values were examined for all patients together and with respect to two criteria: average R2* values, and reason for iron overload. Correlation of single-slice and volumetric data was tested with Spearman's rank test, segmental and group differences were evaluated by analysis of variance. RESULTS: Whole-liver R2* values correlated excellent to single slice data (p < 0.001). The lowest R2* occurred in segment 1 (S1), differences of S1 with regard to other segments were significant in five cases and highly significant in two cases. Patients with high average R2* showed significant differences between S1 and segments 2, 6, and 7. Disease-related differences with respect to S1 were significant in segments 3 to 5 and 7. CONCLUSION: Our results suggest inhomogeneous hepatic iron distribution. Low R2* in S1 may be explained by its special vascularization. KEY POINTS: · Hepatic R2* distribution is not as homogeneous as previously thought.. · Liver segments might have a functional relevance.. · Segmental and total liver R2* values coincide best in segment 8.. CITATION FORMAT: · Wunderlich AP, Cario H, Kannengießer S et al. Volumetric Evaluation of 3D Multi-Gradient-Echo MRI Data to Assess Whole Liver Iron Distribution by Segmental R2* Analysis: First Experience. Fortschr Röntgenstr 2023; 195: 224 - 233.

Combined Deep Learning-based Super-Resolution and Partial Fourier Reconstruction for Gradient Echo Sequences in Abdominal MRI at 3 Tesla: Shortening Breath-Hold Time and Improving Image Sharpness and Lesion Conspicuity.

RATIONALE AND OBJECTIVES: To investigate the impact of a prototypical deep learning-based super-resolution reconstruction algorithm tailored to partial Fourier acquisitions on acquisition time and image quality for abdominal T1-weighted volume-interpolated breath-hold examination (VIBESR) at 3 Tesla. The standard T1-weighted images were used as the reference standard (VIBESD). MATERIALS AND METHODS: Patients with diverse abdominal pathologies, who underwent a clinically indicated contrast-enhanced abdominal VIBE magnetic resonance imaging at 3T between March and June 2021 were retrospectively included. Following the acquisition of the standard VIBESD sequences, additional images for the non-contrast, dynamic contrast-enhanced and post-contrast T1-weighted VIBE acquisition were retrospectively reconstructed using the same raw data and employing a prototypical deep learning-based super-resolution reconstruction algorithm. The algorithm was designed to enhance edge sharpness by avoiding conventional k-space filtering and to perform a partial Fourier reconstruction in the slice phase-encoding direction for a predefined asymmetric sampling ratio. In the retrospective reconstruction, the asymmetric sampling was realized by omitting acquired samples at the end of the acquisition and therefore corresponding to a shorter acquisition. Four radiologists independently analyzed the image datasets (VIBESR and VIBESD) in a blinded manner. Outcome measures were: sharpness of abdominal organs, sharpness of vessels, image contrast, noise, hepatic lesion conspicuity and size, overall image quality and diagnostic confidence. These parameters were statistically compared and interrater reliability was computed using Fleiss' Kappa and intraclass correlation coefficient (ICC). Finally, the rate of detection of hepatic lesions was documented and was statistically compared using the paired Wilcoxon test. RESULTS: A total of 32 patients aged 59 ± 16 years (23 men (72%), 9 women (28%)) were included. For VIBESR, breath-hold time was significantly reduced by approximately 13.6% (VIBESR 11.9 ± 1.2 seconds vs. VIBESD: 13.9 ± 1.4 seconds, p < 0.001). All readers rated sharpness of abdominal organs, sharpness of vessels to be superior in images with VIBESR (p values ranged between p = 0.005 and p < 0.001). Despite reduction of acquisition time, image contrast, noise, overall image quality and diagnostic confidence were not compromised, as there was no evidence of a difference between VIBESR and VIBESD (p > 0.05). The inter-reader agreement was substantial with a Fleiss' Kappa of >0.7 in all contrast phases. A total of 13 hepatic lesions were analyzed. The four readers observed a superior lesion conspicuity in VIBESR than in VIBESD (p values ranged between p = 0.046 and p < 0.001). In terms of lesion size, there was no significant difference between VIBESD and VIBESR for all readers. Finally, there was an excellent inter-reader agreement regarding lesion size (ICC > 0.9). For all readers, no statistically significant difference was observed regarding detection of hepatic lesions between VIBESD and VIBESR. CONCLUSION: The deep learning-based super-resolution reconstruction with partial Fourier in the slice phase-encoding direction enabled a reduction of breath-hold time and improved image sharpness and lesion conspicuity in T1-weighted gradient echo sequences in abdominal magnetic resonance imaging at 3 Tesla. Faster acquisition time without compromising image quality or diagnostic confidence was possible by using this deep learning-based reconstruction technique.

Deep learning-based super-resolution gradient echo imaging of the pancreas: Improvement of image quality and reduction of acquisition time.

PURPOSE: The purpose of this study was to evaluate the impact of a deep learning-based super-resolution technique on T1-weighted gradient-echo acquisitions (volumetric interpolated breath-hold examination; VIBE) on the assessment of pancreatic MRI at 1.5 T compared to standard VIBE imaging (VIBESTD). MATERIALS AND METHODS: This retrospective single-center study was conducted between April 2021 and October 2021. Fifty patients with a total of 50 detectable pancreatic lesion entities were included in this study. There were 27 men and 23 women, with a mean age of 69 ± 13 (standard deviation [SD]) years (age range: 33-89 years). VIBESTD (precontrast, dynamic, postcontrast) was retrospectively processed with a deep learning-based super-resolution algorithm including a more aggressive partial Fourier setting leading to a simulated acquisition time reduction (VIBESR). Image analysis was performed by two radiologists regarding lesion detectability, noise levels, sharpness and contrast of pancreatic edges, as well as regarding diagnostic confidence using a 5-point Likert-scale with 5 being the best. RESULTS: VIBESR was rated better than VIBESTD by both readers regarding lesion detectability (5 [IQR: 5, 5] vs. 5 [IQR: 4, 5], for reader 1; 5 [IQR: 5, 5] vs. 4 [IQR: 4, 5]) for reader 2; both P <0.001), noise levels (5 [IQR: 5, 5] vs. 5 [IQR: 4, 5] for reader 1; 5 [IQR: 5, 5] vs. 4 [IQR: 4, 5] for reader 2; both P <0.001), sharpness and contrast of pancreatic edges (5 [IQR: 5, 5] vs. 5 [IQR: 4, 5] for reader 1; 5 [IQR: 5, 5] vs. 4 [IQR: 4, 5] for reader 2; both P <0.001), as well as regarding diagnostic confidence (5 [IQR: 5, 5] vs. 5 [IQR: 4, 5] for reader 1; 5 [IQR: 5, 5] vs. 4 [IQR: 4, 5] for reader 2; both P <0.001). There were no significant differences between lesion sizes as measured by the two readers on VIBESR and VIBESTD images (P > 0.05). The mean acquisition time for VIBESTD (15 ± 1 [SD] s; range: 11-16 s) was longer than that for VIBESR (13 ± 1 [SD] s; range: 11-14 s) (P < 0.001). CONCLUSION: Our results indicate that the newly developed deep learning-based super-resolution algorithm adapted to partial Fourier acquisitions has a positive influence not only on shortening the examination time but also on improvement of image quality in pancreatic MRI.

Comparison of spin-echo echo-planar imaging magnetic resonance elastography with gradient-recalled echo magnetic resonance elastography and their correlation with transient elastography.

PURPOSE This study aimed to assess the agreement between liver stiffness (LS) values obtained by the gradient-recalled echo (GRE) magnetic resonance elastography (MRE) and spin-echo echo-planar imaging (SE-EPI) MRE with those of transient elastography (TE), respectively. METHODS We retrospectively included 48 participants who underwent liver MRE with both GRE and SE-EPI sequences in the same session and also TE within 1 year. We obtained LS values for MRE by drawing free-hand region of interest, and TE was performed using a FibroScan device. We assessed the relationship between the mean LS values obtained by each MRE sequence and TE using the correlation coefficients and Bland-Altman plots, respectively. We also compared LS values and technical failure rates of measured values from MRE between SE-EPI and GRE sequences using the paired t-test and McNemar's test. The MRE failure was defined as the absence of pixel value with a confidence index above 95%. RESULTS The LS values from SE-EPI and GRE sequences strongly correlated with those from TE (GRE; r = 0.73, P < .001 vs. SE-EPI; r = 0.79, P < .001). In addition, the LS values from the 2 MRE sequences showed excellent relationship (intraclass correlation coefficient, 0.94 [0.89-0.97], P < .001). The LS values from SE-EPI and GRE MRE were not significantly different (4.14 kPa vs. 3.88 kPa, P = .19). Furthermore, the technical success rate of SE-EPI MRE was superior to that of GRE (100% vs. 83.8%, P = .031). CONCLUSION The measured LS values obtained using TE correlated strongly with those obtained using GRE and SE-EPI MRE techniques, even though SE-EPI-MRE resulted a higher technical success rate than GRE-MRE. Therefore, we believe that TE, GRE, and SE-EPI MR elastography techniques may complement each other according to the appropriate individual situation.

Accelerated Three-dimensional T2-Weighted Turbo-Spin-Echo Sequences with Inner-Volume Excitation and Iterative Denoising in the Setting of Pelvis MRI at 1.5T: Impact on Image Quality and Lesion Detection.

RATIONALE AND OBJECTIVES: To investigate image quality and rate of lesion detection in a novel three-dimensional T2-weighted turbo-spin-echo sequence with inner-volume excitation (zoomed imaging) and iterative denoising processing in pelvic MRI at 1.5T. Two-dimensional T2-weighted turbo-spin-echo sequences were used as the clinical reference standard (2D-T2-TSE). MATERIALS AND METHODS: This is a prospective study of patients with various pelvic pathologies. Each patient underwent standard 2D-T2-TSE in three planes with two-fold acceleration as well as a single three-dimensional T2-TSE in the sagittal plane with four-fold acceleration known as Sampling-Perfection-with-Application-optimized-Contrast-using-different-flip-angle-Evolutions (3D-T2-SPACE). The 3D-T2-SPACE images were reconstructed in three orthogonal planes at a slice thickness of 2 mm (vs. 2D-T2-TSE at 4 mm). Two radiologists conducted a qualitative image analysis on standard 2D-T2-TSE and multiplanar reconstructed 3D-T2-SPACE images. These parameters were compared and inter-reader agreement was computed. Furthermore, each reader documented the observed lesions of various pelvic organs. The rate of lesion detection was compared between readers and sequences. Inter-reader and inter-sequence agreement were computed. RESULTS: Forty patients (25 females) were included. Mean patient age was 58 ± 13 years. 3D-T2-SPACE enabled an approximate 22% reduction of acquisition time and 50% of reconstructed slice thickness. 3D-T2-SPACE showed fewer artifacts than 2D-T2-TSE (p < 0.001). However, 2D-T2-TSE was rated to have significantly higher signal intensity than 3D-T2-SPACE (p < 0.001). There were no significant differences between the two sequences regarding all other parameters. Inter-reader agreement regarding image quality parameters was substantial (Kappa = 0.772). For all analyzed pelvic anatomic structures, inter-reader and inter-sequence agreement for lesion detection was excellent (Kappa > 0.80). CONCLUSION: 3D-T2-SPACE with the inner-volume excitation and iterative denoising is clinically feasible at 1.5 T, enabling faster imaging, thinner slices, and significant reduction of artifacts. Despite that signal intensity was inferior in the SPACE images, overall image quality, diagnostic confidence and lesion detection were not compromised. This prospective study sets the stage for further clinical implementation and future investigations tailored to specific indications in pelvis MRI.

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

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) R2* -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 R2* 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: R2* and FF maps were computed for 3D GREs using a multi-spectral fat model and 2D GRE R2* maps were calculated using a mono-exponential model. Mean R2* and FF values were calculated via whole-liver contouring and T2* -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 R2* 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 R2* 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 R2* and FF. The 3D FB rGRE R2* and FF values were not significantly different (P > 0.44) and highly correlated (R2 ≥ 0.98) with breath-hold Cartesian GREs, with mean biases ≤ ±2.5% 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. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY: Stage 2.

Free-breathing MR elastography of the lungs: An in vivo study.

PURPOSE: Lung stiffness alters with many diseases; therefore, several MR elastography (MRE) studies were performed earlier to investigate the stiffness of the right lung during breathhold at residual volume and total lung capacity. The aims of this study were 1) to estimate shear stiffness of the lungs using MRE under free breathing and demonstrate the measurements' repeatability and reproducibility, and 2) to compare lung stiffness under free breathing to breathhold and as a function of age and gender. METHODS: Twenty-five healthy volunteers were scanned on a 1.5 Tesla MRI scanner. Spin-echo dual-density spiral and a spin-echo EPI MRE sequences were used to measure shear stiffness of the lungs during free breathing and breathhold at midpoint of tidal volume, respectively. Concordance correlation coefficient and Bland-Altman analyses were performed to determine the repeatability and reproducibility of the spin-echo dual-density spiral-derived shear stiffness. Repeated measures analyses of variances were used to investigate differences in shear stiffness between spin-echo dual-density spiral and spin-echo EPI, right and left lungs, males and females, and different age groups. RESULTS: Free-breathing MRE sequence was highly repeatable and reproducible (concordance correlation coefficient > 0.86 for both lungs). Lung stiffness was significantly lower in breathhold than in free breathing (P < .001), which can be attributed to potential stress relaxation of lung parenchyma or breathhold inconsistencies. However, there was no significant difference between different age groups (P = .08). The left lung showed slightly higher stiffness values than the right lung (P = .14). There is no significant difference in lung stiffness between genders. CONCLUSION: This study demonstrated the feasibility of free-breathing lung MRE with excellent repeatability and reproducibility. Stiffness changes with age and during the respiratory cycle. However, gender does not influence lungs stiffness.

Magnetic Resonance Elastography for Assessing Fibrosis in Patients with Crohn's Disease: A Pilot Study.

BACKGROUND: Patients with Crohn's disease can develop intestinal strictures, containing various degrees of inflammation and fibrosis. Differentiation of the main component of a stricturing lesion is the key for defining the therapeutic management. AIMS: We assessed for the first time the accuracy of magnetic resonance elastography in detecting intestinal fibrosis and predicting clinical course in patients with Crohn's disease. METHODS: This was a prospective study of adult patients with Crohn's disease and magnetic resonance imaging examination, including magnetic resonance elastography, between April 2019 and February 2020. The association between the bowel stiffness value and the degree of fibrosis was evaluated. The relationship between the stiffness value and the occurrence of clinical events was also investigated. RESULTS: A total of 69 patients were included. The stiffness value measured by magnetic resonance elastography was correlated with the degree of fibrosis (p < 0.001). A bowel stiffness ≥ 3.57 kPa predicted the occurrence of clinical events with an area under the curve of 0.82 (95% CI 0.71-0.93). Bowel stiffness ≥ 3.57 kPa was associated with an increased risk of clinical events (p < 0.0001). CONCLUSION: In Crohn's disease, magnetic resonance elastography is a reliable tool for detecting intestinal fibrosis and predicting a worse disease outcome.

Iterative denoising accelerated 3D SPACE FLAIR sequence for brain MR imaging at 3T.

PURPOSE: The purpose of this study was to prospectively evaluate image quality of three-dimensional fluid attenuated inversion recovery (3D-FLAIR) sequence acquired with a high acceleration factor and reconstructed with iterative denoising (ID) for brain magnetic resonance imaging (MRI) at 3-T. MATERIAL AND METHODS: Patients with brain tumor who underwent brain MRI were consecutively included. Two 3D-FLAIR sequences were successively performed for each patient. A first conventional FLAIR acquisition (conv-FLAIR) was performed with an acceleration factor of 6. The second acquisition was performed with an increased acceleration factor of 9. Two series one without ID (acc-FLAIR) and one with ID (acc-FLAIR-ID) were reconstructed. Two neuroradiologists independently assessed image quality, deep brain nuclei visualization and white matter/gray matter (WM/GM) differentiation on a 4-point scale. RESULTS: Thirty patients with brain tumor were consecutively included in this study. There were 16 women and 14 men with a mean age of 54 ± 17 (SD) years (range: 22-78 years). Scanning time of Acc-FLAIR-ID and Acc-FLAIR (4 min 40 sec) was 37% shorter than that of conv-FLAIR (2 min 50 sec) (P < 0.01). Improved image quality score was significantly different for both conv-FLAIR and acc-FLAIR-ID compared to acc-FLAIR (P < 0.01 for both). WM/GM differentiation score of conv-FLAIR was not significantly different compared to acc-FLAIR-ID (P = 0.10). Improved WM/GM differentiation score was different for both sequences compared to acc-FLAIR (P = 0.017 and P < 0.001). Deep brain nuclei visualization score was not different between conv-FLAIR and acc-FLAIR-ID (P = 0.71). However, the improved deep brain nuclei visualization score was significantly different for both sequences compared to acc-FLAIR (P < 0.001 for both). CONCLUSION: Scanning time of 3D-FLAIR sequence using a high acceleration factor reconstructed with ID algorithm can be reduced by 37% while preserving image quality for brain MRI.

T2-weighted Imaging of the Breast at 1.5T Using Simultaneous Multi-slice Acceleration.

AIM: To evaluate the image quality and time saving using simultaneous multi-slice (SMS)-accelerated T2-weighted turbo spin echo (TSE) sequences compared to standard T2 TSE sequences in breast magnetic resonance imaging (MRI). PATIENTS AND METHODS: Thirty patients were examined with an SMS-accelerated T2 TSE sequence and a standard T2 TSE sequence as part of a breast MRI protocol at 1.5T. Image quality, signal homogeneity and tissue delineation were evaluated. For quantitative assessment, the signal-to-noise ratio (SNR) was measured from representative SNR maps. RESULTS: There were no significant differences regarding tissue delineation and signal homogeneity. Image quality was rated equal at the chest wall and the breasts but decreased in the axilla on SMS-T2 TSE (p=0.01) with a simultaneous decrease of SNR (p=0.03). This did not significantly impact the overall image quality (p=0.2). The acquisition time for SMS-T2 TSE was 48% shorter compared to standard T2 TSE. CONCLUSION: SMS-acceleration for T2-weighted imaging of the breast at 1.5T substantially reduces acquisition time while maintaining comparable quantitative and qualitative image quality. This may pave the way for protocol abbreviation especially in a high-throughput clinical workspace.