Single-shot distortion-corrected water-fat separation using multi-echo blip-rewound EPI for diffusion-weighted imaging

Quantitative diffusion-weighted imaging (DWI) MRI is a promising technique for cancer characterization and treatment monitoring. Knowledge of the reproducibility of DWI metrics in breast tumors is necessary to apply DWI as a clinical biomarker. To evaluate the repeatability and reproducibility of breast tumor apparent diffusion coefficient (ADC) in a multi-institution clinical trial setting, using standardized DWI protocols and quality assurance (QA) procedures. Prospective. In all, 89 women from nine institutions undergoing neoadjuvant chemotherapy for invasive breast cancer. DWI was acquired before and after patient repositioning using a four b-value, single-shot echo-planar sequence at 1.5T or 3.0T. A QA procedure by trained operators assessed artifacts, fat suppression, and signal-to-noise ratio, and determine study analyzability. Mean tumor ADC was measured via manual segmentation of the multislice tumor region referencing DWI and contrast-enhanced images. Twenty cases were evaluated multiple times to assess intra- and interoperator variability. Segmentation similarity was assessed via the Sørenson-Dice similarity coefficient. Repeatability and reproducibility were evaluated using within-subject coefficient of variation (wCV), intraclass correlation coefficient (ICC), agreement index (AI), and repeatability coefficient (RC). Correlations were measured by Pearson's correlation coefficients. In all, 71 cases (80%) passed QA evaluation: 44 at 1.5T, 27 at 3.0T; 60 pretreatment, 11 after 3 weeks of taxane-based treatment. ADC repeatability was excellent: wCV = 4.8% (95% confidence interval [CI] 4.0, 5.7%), ICC = 0.97 (95% CI 0.95, 0.98), AI = 0.83 (95% CI 0.76, 0.87), and RC = 0.16 * 10-3 mm2 /sec (95% CI 0.13, 0.19). The results were similar across field strengths and timepoint subgroups. Reproducibility was excellent: interreader ICC = 0.92 (95% CI 0.80, 0.97) and intrareader ICC = 0.91 (95% CI 0.78, 0.96). Breast tumor ADC can be measured with excellent repeatability and reproducibility in a multi-institution setting using a standardized protocol and QA procedure. Improvements to DWI image quality could reduce loss of data in clinical trials. 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:1617-1628.

The 8th edition of the American Joint Committee on Cancer staging system included the depth of invasion (DOI) for the T classification of oral cancer. However, no standardized method has been established to clinically measure the DOI. This study aimed to investigate the accuracy of MRI-based DOI for oral tongue squamous cell carcinoma (OTSCC) in each MRI sequence. We enrolled 49 patients with histologically proven OTSCC, treated surgically between April 2017 and February 2021. We divided the DOI into three groups using 5 and 10 mm, the thresholds for determining the T stage, and retrospectively evaluated the agreement between MRI-based DOI and pathological DOI (pDOI) for each MRI sequence, axial T1-weighted imaging (T1WI), T2-weighted imaging with fat suppression (FS-T2WI), contrast-enhanced T1WI with fat suppression (CE-T1WI), diffusion-weighted imaging (DWI), and apparent diffusion coefficient (ADC) maps. We also divided the DOI into two groups using 3 mm, the threshold for considering elective neck dissection, and evaluated the overestimation rate of MRI-based DOI in lesions with pDOI ≤ 3 mm. With 5-mm and 10-mm divisions, the accuracy of the DOI assessment was highest on DWI (0.82, weighted kappa = 0.85). With a 3-mm division, the accuracy was also highest on DWI (0.87, kappa = 0.73). The overestimation rate of the MRI-based DOI in lesions with pDOI ≤ 3 mm was lowest on DWI (27.8%). DOI on DWI exhibits a comparatively higher rate of concordance with pDOI. DWI may be more useful than other MRI sequences in evaluating the DOI of OTSCC.

The objective of this article is to discuss the acquisition of high-quality MR images of the musculoskeletal system with uniform fat suppression using iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL). IDEAL is a three-point water-fat separation method that provides robust fat suppression even in the complex magnetic environments commonly encountered during clinical musculoskeletal imaging. The IDEAL technique provides uniform fat saturation even in complex magnetic environments and simultaneously produces in-phase and opposed-phase images that may be useful for characterization of osseous lesions. The IDEAL water-fat separation method is highly versatile and has been successfully combined with T1-weighted, T2-weighted, steady-state free precession, and spoiled gradient-recalled echo techniques to produce high-quality MR images in clinically acceptable scanning times.

Purpose To develop and evaluate magnetic resonance (MR) neurography of the brachial plexus with robust fat and blood suppression for increased conspicuity of nerves at 3.0 T in clinically feasible acquisition times. Materials and Methods This prospective study was HIPAA compliant, with institutional review board approval and written informed consent. A low-refocusing-flip-angle three-dimensional (3D) turbo spin-echo (TSE) sequence was modified to acquire both in-phase and out-of-phase echoes, required for chemical shift (Dixon) reconstruction, in the same repetition by using partial echoes combined with modified homodyne reconstruction with phase preservation. This multiecho TSE modified Dixon (mDixon) sequence was optimized by using simulations and phantom studies and in three healthy volunteers. The sequence was tested in five healthy volunteers and was evaluated in 10 patients who had been referred for brachial plexopathy at 3.0 T. The images were evaluated against the current standard of care, images acquired with a 3D TSE short inversion time inversion recovery (STIR) sequence, qualitatively by using the Wilcoxon signed-rank test and quantitatively by using the Friedman two-way analysis of variance, with P < .05 considered to indicate a statistically significant difference. Results Multiecho TSE-mDixon involving partial-echo and homodyne reconstruction with phase preservation achieved uniform fat suppression in half the imaging time compared with multiacquisition TSE-mDixon. Compared with 3D TSE STIR, fat suppression, venous suppression, and nerve visualization were significantly improved (P < .05), while arterial suppression was better but not significantly so (P = .06), with increased apparent signal-to-noise ratio in the dorsal nerve root ganglion and C6 nerve (P < .001) with the multiecho TSE-mDixon sequence. Conclusion The multiecho 3D TSE-mDixon sequence provides robust fat and blood suppression, resulting in increased conspicuity of the nerves, in clinically feasible imaging times and can be used for MR neurography of the brachial plexus at 3.0 T. © RSNA, 2016 Online supplemental material is available for this article.

PurposeTo develop a new water–fat separation and B0 estimation algorithm to effectively suppress the multiple resonances of fat signal in EPI. This is especially relevant for DWI where fat is often a confounding factor.MethodsWater–fat separation based on chemical‐shift encoding enables robust fat suppression in routine MRI. However, for EPI the different chemical‐shift displacements of the multiple fat resonances along the phase‐encoding direction can be problematic for conventional separation algorithms. This work proposes a suitable model approximation for EPI under B0 and fat off‐resonance effects, providing a feasible multi‐peak water–fat separation algorithm. Simulations were performed to validate the algorithm. In vivo validation was performed in 6 volunteers, acquiring spin‐echo EPI images in the leg (B0 homogeneous) and head‐neck (B0 inhomogeneous) regions, using a TE‐shifted interleaved EPI sequence with/without diffusion sensitization. The results are numerically and statistically compared with voxel‐independent water–fat separation and fat saturation techniques to demonstrate the performance of the proposed algorithm.ResultsThe reference separation algorithm without the proposed spatial shift correction caused water–fat ambiguities in simulations and in vivo experiments. Some spectrally selective fat saturation approaches also failed to suppress fat in regions with severe B0 inhomogeneities. The proposed algorithm was able to achieve improved fat suppression for DWI data and ADC maps in the head–neck and leg regions.ConclusionThe proposed algorithm shows improved suppression of the multi‐peak fat components in multi‐shot interleaved EPI applications compared to the conventional fat saturation approaches and separation algorithms.

Diffusion-weighted echo-planar imaging of the head and neck using 3-T MRI: Investigation into the usefulness of liquid perfluorocarbon pads and choice of optimal fat suppression method

Background: Several studies have shown that the majority of patients with simple appendicitis can be treated effectively and safely with antibiotics, avoiding unnecessary operation. Objectives: The objective of this study was to assess the role of diffusion-weighted imaging (DWI) in the follow-up of conservative treatment of simple appendicitis. Patients and Methods: Twenty-eight patients (mean age, 35 ± 14.6; age range, 18 - 72; M/F: 16/12) with simple appendicitis were enrolled in this prospective study. After the primary diagnosis by computed tomography (CT) at presentation, they underwent an initial DWI scan, and intravenous antibiotic therapy was started for all patients by the decision of the attending surgeon. A total of three control DWI scans were planned during the follow-up period for each patient. CT and DWI images were evaluated by two radiologists in consensus. B values 0, 500 and 1000 s/mm2 were used, and DWI images were analyzed both qualitatively and quantitatively. During follow-up, changes in the diameter of appendices and laboratory parameters were correlated with apparent diffusion coefficient (ADC) values. Results: We found statistically significant correlation between ADC values, maximum appendix diameter and laboratory parameters. During follow-up period four surgical procedures were performed for reccurent appendicitis. Conclusion: DWI may be used with a significant success for follow-up evaluation of patients with simple appendicitis. As a monitoring imaging method, DWI may also aid in determining the recurrences of appendicitis.

Reduced field-of-view (rFOV) diffusion-weighted imaging (DWI) using 2D echo-planar radiofrequency (2DRF) excitation has been widely and successfully applied in clinical settings. The purpose of this work is to further improve its clinical utility by overcoming slice coverage limitations without any scan time penalty while providing robust fat suppression. During multislice imaging with 2DRF pulses, periodic sidelobes in the slice direction cause partial saturation, limiting the slice coverage. In this work, a tilting of the excitation plane is proposed to push the sidelobes out of the imaging section while preserving robust fat suppression. The 2DRF pulse is designed using Shinnar-Le Roux algorithm on a rotated excitation k-space. The performance of the method is validated via simulations, phantom experiments, and high in-plane resolution in vivo DWI of the spinal cord. Results show that rFOV DWI using the tilted 2DRF pulse provides increased signal-to-noise ratio, extended coverage, and robust fat suppression, without any scan time penalty. Using a tilted 2DRF excitation, a high-resolution rFOV DWI method with robust fat suppression and unrestricted slice coverage is presented. This method will be beneficial in clinical applications needing large slice coverage, for example, axial imaging of the spine, prostate, or breast. Magn Reson Med 76:1668-1676, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

Slice interleaving, a limited phase encode (PE) field of view (FOV), and effective fat suppression are vital for efficient cardiac diffusion tensor imaging (cDTI) with minimal artifacts. This study aimed to optimize reduced FOV and fat suppression methods for interleaved multislice cDTI to improve signal-to-noise ratio (SNR) and minimize artifacts. Two-slice motion compensated spin echo datasets from 20 healthy volunteers were acquired. Four reduced PE FOV sequences were evaluated: 2DRF pulse; applying either or pulses in PE direction; and the proposed flip-back sequence with a nonselective pulse after readout to restore inverted magnetization. Four fat suppression techniques were implemented: no fat suppression (standard); fat saturation; binomial water excitation and spectral attenuated inversion recovery (SPAIR). The proposed flip-back sequence with SPAIR achieved the highest median SNR, and its SNR values are significantly higher ( ) than 2DRF with SPAIR as current state-of-the-art. SPAIR and water excitation demonstrated comparable performance when combined with the flip-back sequence, and both yielded superior image quality than with no suppression or fat saturation. SPAIR showed robust fat suppression across most subjects, whilst water excitation exhibited advantages in some subjects with a high body mass index. The proposed flip-back sequence with SPAIR enables efficient interleaved multislice imaging with reduced PE FOV and effective fat suppression, facilitating clinical translation of in vivo cDTI.

Over the past few years, diffusion-weighted imaging (DWI) has become an increasingly important diagnostic tool in the diagnosis of liver lesions. The objective of the present study was to evaluate the diagnostic benefit of high b-value computed diffusion-weighted imaging (c-DWI) compared with standard DWI in patients with hepatocellular carcinoma (HCC) and whether there is an association with microvascular invasion (MVI). In total, 37 patients with histopathologically confirmed HCC were retrospectively ana-lyzed. DWI was acquired with b-values of 50, 400, and 800 or 1000 s/mm² on a 1.5 T magnetic resonance imaging (MRI) scanner. The c-DWI was calculated using a monoexponential model with high b-values of 1000, 2000, 3000, 4000, and 5000 s/mm². All high b-value c-DWI images were compared to the standard DWI in terms of volume, detectability of hepatic lesions, and image quality. Regarding lesion volume and image quality there were no statistically significant differences between standard and c-DWI. HCC lesions measured on DWI images were statistically significantly larger compared to c-DWI images starting from a b value of 2000 s/mm2 (DWI vs. c-DWI b 2000 s/mm2: 2 cm3 [1-12] cm3 vs. 1 cm3 [0-17] cm3, p < 0.05). Moreover, there was deterioration of image quality starting at b = 2000 s/mm2. There were no significant differences in terms of lesion signal intensity in DWI and c-DWI images. There were no differences for the DWI parameters according to MVI status. C-DWI images with high b-values up to b = 1000 s/mm2 demonstrate comparable detectability of HCC compared to standard DWI. The investigated DWI parameters were not associated with MVI status. Further research is needed to evaluate the potential benefit of high b-value c-DWI.

Diffusion-weighted imaging (DWI) has shown high sensitivity in the diagnosis of acute arterial strokes. The pathophysiology of cerebral venous thrombosis with associated venous stroke appears to differ from that of arterial strokes. The purpose of this study was to describe DWI findings in venous strokes. The authors reviewed 3 adults with superior sagittal sinus thrombosis who underwent DWI and magnetic resonance imaging within 24 hours of symptom onset. DWI was obtained at 1.5 T using the multishot echo planar technique (TR = 8000, TE = 97, field of view = 30 x 19 cm, slice thickness = 6.0 mm, interslice gap = 0.5 mm, matrix 128 x 128, NEX = 1). The diffusion gradients were applied in 3 orthogonal directions with 3 increasing b values (0-1000 s/mm2) to create average (trace) DWI images. Apparent diffusion coefficient (ADC) values were calculated on a pixel-by-pixel basis and displayed as ADC maps. DWI showed hyperintensities in patients 1 and 2 and hypointensity in patient 3 in corresponding to parenchymal lesions on conventional images. As compared to the homologous uninvolved location in the contralateral hemisphere, ADC values were decreased (0.53 x 10(-3) mm2/s [patient 1] and 0.68 x 10(-3) mm2/s [patient 2]) and increased (1.1 x 10(-3) mm2/s [patient 3]). The ADC ratio of the lesion in the involved to uninvolved side was 88% (patient 1), 81% (patient 2), and 120% (patient 3). Acute cerebral venous strokes may contain cytotoxic edema and/or vasogenic edema on DWI scans. DWI may be helpful in diagnosing cerebral venous thrombosis in cases with cryptic presentations.

Progressive multifocal leukoencephalopathy (PML) is a severe demyelinating disease of the central nervous system due to JC polyoma virus infection of oligodendrocytes. PML develops in patients with impaired T-cell function as occurs in HIV, malignancy or immunosuppressive drugs users. Until now no imaging methods have been reported to correlate with clinical status. Diffusion-weighted imaging (DWI) is a robust MRI tool in investigating white matter architecture and diseases. The aim of our work was to assess diffusion abnormalities in focal white matter lesions in patients with PML and to correlate the lesion load measured with conventional MRI and DWI to clinical variables. We evaluated eight patients with a biopsy or laboratory-supported diagnosis of PML. All patients underwent MRI including conventional sequences (fluid attenuated inversion recovery-FLAIR) and DWI. Mean diffusivity (MD) maps were used to quantify diffusion on white matter lesions. Global lesion load was calculated by manually tracing lesions on FLAIR images, while total, central core and peripheral lesion loads were calculated by manually tracing lesions on DWI images. Lesion load obtained with the conventional or DWI-based methods were correlated with clinical variables such as disease duration, disease severity and survival. White matter focal lesions are characterized by a central core with low signal on DWI images and high MD (1.853 x 10(-3) mm2/s), surrounded by a rim of high signal intensity on DWI and lower MD (1.1 x 10(-3) mm2/s). The MD value of normal-appearing white matter is higher although not statistically significant (0.783 x 10(-3) mm2/s) with respect to control subjects (0.750 x 10(-3) mm2/s). Inter-rater correlations of global lesion load between FLAIR (3.96%) and DWI (3.43%) was excellent (ICC=0.87). Global lesion load on FLAIR and DWI correlates with disease duration and severity (respectively, p=0.037, p=0.0272 with Karnofsky scale and p=0.0338 with EDSS on FLAIR images; p=0.043, p=0.0296 with Karnofsky scale and p=0.0365 with EDSS on DW images). Central core lesion load on DWI correlates with disease duration and severity (respectively p=0.043, p=0.0103 with Karnofsky scale and p=0.0112 with EDSS), while peripheral lesion load does not correlate with any clinical variable. The global lesion load in PML correlates with disease duration and severity. DWI images, which can distinguish within lesions a central core from a peripheral rim, reveal that a larger central core component correlates to a worsened clinical status and longer disease duration. On the other hand the peripheral rim lesion load visualized on DWI images does not correlate with clinical variables and does not achieve obtaining further prognostic information with respect to conventional imaging.

Primary objective: Cerebral oedema is a common complication of traumatic brain injury (TBI). The use of Fluid-Attenuated Inversion Recovery (FLAIR) imaging in combination with Diffusion Weighted Imaging (DWI) has the potential to distinguish between cytotoxic and vasogenic oedema. This study hypothesized a significant relationship between cytotoxic lesion volume and outcome.Research design: This observational study reports on a convenience sample where MRI was obtained for clinical purposes.Methods and procedures: Clinical post-TBI FLAIR and DWI images were analysed. For this study, lesions were defined as primarily cytotoxic oedema if the ratio of FLAIR to DWI lesion volume was comparable, defined as a ratio <2. If the ratio of FLAIR to DWI lesion volume was ≥2, oedema was considered predominantly of vasogenic origin.Main outcomes and results: The sample consisted primarily of males with TBIs whose injury severity ranged from complicated mild to severe. Analysis revealed that both oedema types are common after TBI and both are associated with functional deficits 6 months after injury.Conclusions: Acute MRI may be useful to assess pathology at the tissue after traumatic brain injury. Clinical trials targeting cytotoxic and vasogenic mechanisms of oedema formation may benefit from using DWI and FLAIR MRI as a means to differentiate the predominant oedema type after TBI.

Silicone breast prostheses prove technically challenging when performing diffusion-weighted MR imaging in the breasts. We describe a combined fat and chemical suppression scheme to achieve dual suppression of fat and silicone, thereby improving the quality of diffusion-weighted images in women with breast implants. MR imaging was performed at 3.0 and 1.5 T in women with silicone breast implants using short-tau inversion recovery (STIR) fat-suppressed echo-planar (EPI) diffusion-weighted MR imaging (DWI) on its own and combined with the slice-select gradient-reversal (SSGR) technique. Imaging was performed using dedicated breast imaging coils. Complete suppression of the fat and silicone signal was possible at 3.0 T using EPI DWI with STIR and SSGR, evaluated with dedicated breast coils. However, a residual silicone signal was still perceptible at 1.5 T using this combined approach. Nevertheless, a further reduction in silicone signal at 1.5 T could be achieved by employing thinner slice partitions and the addition of the chemical-selective fat-suppression (CHESS) technique. DWI using combined STIR and SSGR chemical suppression techniques is feasible to eliminate or reduce silicone signal from prosthetic breast implants. Breast magnetic resonance imaging (MRI) is frequently needed following breast implants. Unsuppressed signal from silicone creates artefacts on diffusion-weighted MR sequences. Dual fat/chemical suppression can eliminate signal from fat and silicone. STIR with slice selective gradient reversal can suppress fat and silicone signal.

Multiple myeloma (MM) is a blood cancer caused by the unlimited proliferation of intramedullary plasma cells. The presence of focal lesions (FLs) is presumed to be a more relevant factor for patient outcomes and risk distribution than diffuse bone marrow signal abnormalities. Signal changes in these FLs also have a good correlation with prognosis. As the cell density increased, a lower apparent diffusion coefficient (ADC) value was found with the diffusion-weighted imaging (DWI) sequence. Therefore, whole-body magnetic resonance imaging (MRI) with DWI sequences is sensitive to cell density and viability and may be vital for disease detection and therapy response assessments. However, the correlation between the DWI signal and the degree of bone destruction and the proportion of bone marrow plasma cells (BMPC) was still unclear in patients with MM. Water-fat separation MRI is used mainly for evaluating liver and bone marrow fat quantification, and fat quantification in other diseases. Meanwhile, it is also possible to assess the extent of bone marrow invasion in medullary lesions. This study aimed to investigate the correlation between ADC values from whole-body DWI and water/fat MRI signals from T1-weighted water-fat separation in evaluating bone marrow infiltration in patients with MM. The study included 35 patients with MM who underwent whole-body DWI and T1-weighted water-fat separation Dixon examinations before therapy. The ADC values, normalized fat signal intensity (nMfat), normalized water molecular signal intensity (nMwater), and normalized fat fraction (nFF) of the thoracolumbar spine was measured in FLs and the normal-appearing bone marrow (NABM). The differences in values were compared using the independent-samples t-test. The correlation between ADC values and water-fat MRI signals was estimated using the Pearson or Spearman correlation test. The correlation between the MRI above parameters and proportions of BMPC was also explored. Statistically significant differences were found between the mean ADC values in FLs and NABM (0.72 vs. 0.33 mm2/s, P<0.0001). Significantly elevated nMwater values and decreased nMfat and nFF values were observed in FLs; no correlations were found in NABM (P>0.05). The ADC value highly correlated with nMfat and nFF values and moderately with the nMwater value in FLs (r=-0.899, -0.834, 0.642, respectively, P<0.0001). Correlations were also observed between the proportion of BMPC and MRI parameters in MM (r=0.984, 0.716, -0.938, and -0.905, respectively, P<0.05). The ADC value combined with water-fat separation parameters could be used for evaluating thoracolumbar bone marrow infiltration in MM. All parameters correlated with the proportion of BMPC, which helped assess the early response in MM therapy.