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Purpose In this study, we aimed to measure the apparent diffusion coefficients (ADCs) of major phosphorous metabolites in the human calf muscle at 7 T with a diffusion-weighted (DW)-STEAM sequence. Methods A DW-STEAM sequence with bipolar gradients was implemented at 7 T, and DW MR spectra were acquired in three orthogonal directions in the human calf muscle of six healthy volunteers (TE/TM/TR = 15 ms/750 ms/5 s) at three b-values (0, 800, and 1200 s/mm2). Frequency and phase alignments were applied prior to spectral averaging. Averaged DW MR spectra were analyzed with LCModel, and ADCs of 31P metabolites were estimated. Results Four metabolites (phosphocreatine (PCr), adenosine triphosphate (ATP), inorganic phosphate (Pi) and glycerol phosphorylcholine (GPC)) were quantified at all b-values with mean CRLBs below 10%. The ADC values of PCr, ATP, Pi, and GPC were (0.24 ± 0.02, 0.15 ± 0.04, 0.43 ± 0.14, 0.40 ± 0.09) × 10–3 mm2/s, respectively. Conclusion The ADCs of four 31P metabolites were successfully measured in the human calf muscle at 7 T, among which those of ATP, Pi and GPC were reported for the first time in humans. This study paves the way to investigate 31P metabolite diffusion properties in health and disease on the clinical MR scanner.

The Fluid And White matter Suppression (FLAWS) MRI sequence allows for the acquisition of multiple T1-weighted contrasts in a single sequence acquisition. However, its acquisition time is prohibitive for use in clinical practice when the k-space is linearly downsampled and reconstructed using the Generalized Autocalibrating Partially Parallel Acquisition (GRAPPA) technique. This study proposes a FLAWS sequence optimization tailored to allow for the acquisition of FLAWS images with a Cartesian phyllotaxis k-space undersampling and compressed sensing (CS) reconstruction at 3T. The CS FLAWS sequence parameters were determined using a method previously employed to optimize FLAWS imaging at 1.5T and 7T. In-vivo experiments show that the proposed CS FLAWS optimization allows to reduce the FLAWS sequence acquisition time from 8 mins to 6 mins without decreasing the FLAWS image quality. In addition, this study demonstrates for the first time that T1-weighted imaging with low B1 sensitivity and T1 mapping can be performed with the FLAWS sequence at 3T for both GRAPPA and CS reconstructions. The FLAWS T1 mapping was validated using in-silico, in-vitro and in-vivo experiments with comparison against the inversion recovery turbo spin echo and MP2RAGE T1 mappings. These new results suggest that the recent advances in FLAWS imaging allow to combine the MP2RAGE imaging benefits (T1-weigthed imaging with low B1 sensitivity and T1 mapping) and with the previous version of FLAWS imaging benefits (multi T1-weighted contrast imaging) in a single 6 mins sequence acquisition.Graphical abstract

Ce chapitre est consacré aux mesures de la diffusion des molécules d'eau in vivo par Imagerie par Résonance Magnétique (IRM). Il introduit la physique de la diffusion ; ensuite, des techniques de mesure de la diffusion seront décrites. Enfin, des applications cliniques de l'IRM de diffusion illustrent le texte.

International audience; OBJECTIVES: To access the performances of different algorithms for quantification of Intravoxel incoherent motion (IVIM) parameters D, f, [Formula: see text] in Vertebral Bone Marrow (VBM). MATERIALS AND METHODS: Five algorithms were studied: four deterministic algorithms (the One-Step and three segmented methods: Two-Step, Three-Step, and Fixed-[Formula: see text] algorithm) based on the least-squares (LSQ) method and a Bayesian probabilistic algorithm. Numerical simulations and quantification of IVIM parameters D, f, [Formula: see text] in vivo in vertebral bone marrow, were done on six healthy volunteers. The One-way repeated-measures analysis of variance (ANOVA) followed by Bonferroni’s multiple comparison test (p value = 0.05) was applied. RESULTS: In numerical simulations, the Bayesian algorithm provided the best estimation of D, f, [Formula: see text] compared to the deterministic algorithms. In vivo VBM-IVIM, the values of D and f estimated by the Bayesian algorithm were close to those of the One-Step method, in contrast to the three segmented methods. DISCUSSION: The comparison of the five algorithms indicates that the Bayesian algorithm provides the best estimation of VBM-IVIM parameters, in both numerical simulations and in vivo data.

International audience; BACKGROUND AND PURPOSE: The DKI-IVIM model that incorporates DKI (diffusional kurtosis imaging) into the IVIM (Intravoxel Incoherent Motion) concept was investigated to assess its utility for both enhanced diffusion characterization and perfusion measurements in ischemic stroke at 3 T. METHODS: Fifteen stroke patients (71 ± 11 years old) were enrolled and DKI-IVIM analysis was performed using 9 b-values from 0 to 1500 s/mm(2) chosen with the Cramer-Rao-Lower-Bound optimization approach. Pseudo-diffusion coefficient D*, perfusion fraction f, blood flow-related parameter fD*, the diffusion coefficient D and an additional parameter, the kurtosis, K were determined in the ischemic lesion and controlateral normal tissue based on a region of interest approach. The apparent diffusion coefficient (ADC) and arterial spin labelling (ASL) cerebral blood flow (CBF) parameters were also assessed and parametric maps were obtained for all parameters. RESULTS: Significant differences were observed for all diffusion parameters with a significant decrease for D (p

International audience; OBJECTIVE: This initial study aimed to investigate the feasibility of simultaneously measuring perfusion and diffusion including kurtosis features in acute ischemic stroke with the combined intravoxel incoherent motion and non-Gaussian diffusional kurtosis imaging (DKI-IVIM). MATERIAL AND METHODS: Five ischemic stroke patients underwent a 4-minute diffusion weighted imaging (DWI) protocol, using 8 b values chosen with the Cramer-Rao-Lower-Bound optimization approach, in addition to conventional DWI and arterial spin labeling sequences. Regions of interest in pathological and control regions were analyzed with DKI-IVIM, and parametric maps were reconstructed. RESULTS: The IVIM diffusion coefficient (D) decreased (P < 0.0001) in the infarcted areas, whereas higher kurtosis coefficient values were found (P = 0.0002). Regarding the perfusion, the individual IVIM perfusion fraction f decreased in 3 matching cases with the cerebral blood flow estimated through arterial spin labeling and the fD* decreased only in 2 patients of those. CONCLUSIONS: When compared with conventional stroke imaging protocol, DKI-IVIM 4-minute 2-in-1 acquisition can provide diffusion results comparable with conventional DWI with complementary kurtosis estimations but a limited robustness regarding perfusion estimations for clinical purpose.

International audience; Objective - MRI is a reliable and accurate technique to characterize rheumatoid arthritis. The aim of this study was to provide voxel-by-voxel 3D maps of the proton density fat fraction (PDFF), the T of water (T), the T of fat (T), the T* of water (T*), the T* of fat (T*) in the wrist bone marrow. Materials and methods - The experiments were conducted on 14 healthy volunteers (mean age: 24 ± 4). The data were acquired at 1.5 T using two optimized four-echo 3D 1.2 × 1.2 × 1.2 mm-isotropic spoiled gradient sequences. A repeatability study was carried out. The measurements were done using a homemade parametric viewer software. Results - The inter-volunteer results were, on average: PDFF = 86 ± 3%, T = 441 ± 113 ms, T = 245 ± 19 ms, T* = 6 ± 1 ms and T* = 16 ± 3 ms. The coefficients of variation were for fat based biomarkers CV

Purpose - To demonstrate that fluid and white matter suppression (FLAWS) imaging can be used for high-resolution T mapping with low transmitted bias field ( ) sensitivity at 7T. Methods - The FLAWS sequence was optimized for 0.8-mm isotropic resolution imaging. The theoretical accuracy and precision of the FLAWS T mapping was compared with the one of the magnetization-prepared two rapid gradient echoes (MP2RAGE) sequence optimized for low sensitivity. FLAWS images were acquired at 7T on six healthy volunteers (21 to 48 years old; two women). MP2RAGE and saturation-prepared with two rapid gradient echoes (SA2RAGE) datasets were also acquired to obtain T mapping references and maps. The contrast-to-noise ratio (CNR) between brain tissues was measured in the FLAWS-hco and MP2RAGE-uni images. The Pearson correlation was measured between the MP2RAGE and FLAWS T maps. The effect of on FLAWS T mapping was assessed using the Pearson correlation. Results - The FLAWS-hco images were characterized by a higher brain tissue CNR ( , , ) than the MP2RAGE-uni images ( , , ). The theoretical accuracy and precision of the FLAWS T mapping ( ) were in agreement with those provided by the MP2RAGE T mapping ( ). A good agreement was found between in vivo T values measured with the MP2RAGE and FLAWS sequences (r = 0.91). A weak correlation was found between the FLAWS T map and the map within cortical gray matter and white matter segmentations ( ; ). Conclusion - The results from this study suggest that FLAWS is a good candidate for high-resolution T -weighted imaging and T mapping at the field strength of 7T.

Objective Cortical lesions are common in multiple sclerosis (MS), but their visualization is challenging on conventional magnetic resonance imaging. The uniform image derived from magnetization prepared 2 rapid acquisition gradient echoes (MP2RAGE(uni)) detects cortical lesions with a similar rate as the criterion standard sequence, double inversion recovery. Fluid and white matter suppression (FLAWS) provides multiple reconstructed contrasts acquired during a single acquisition. These contrasts include FLAWS minimum image (FLAWS(min)), which provides an exquisite sensitivity to the gray matter signal and therefore may facilitate cortical lesion identification, as well as high contrast FLAWS (FLAWS(hco)), which gives a contrast that is similar to one of MP2RAGE(uni). In this study, we compared the manual detection rate of cortical lesions on MP2RAGE(uni), FLAWS(min), and FLAWS(hco) in MS patients. Furthermore, we assessed whether the combined detection rate on FLAWS(min) and FLAWS(hco) was superior to MP2RAGE(uni) for cortical lesions identification. Last, we compared quantitative T1 maps (qT1) provided by both MP2RAGE and FLAWS in MS lesions. Materials and Methods We included 30 relapsing-remitting MS patients who underwent MP2RAGE and FLAWS magnetic resonance imaging with isotropic spatial resolution of 1 mm at 3 T. Cortical lesions were manually segmented by consensus of 3 trained raters and classified as intracortical or leukocortical lesions on (1) MP2RAGE uniform/flat images, (2) FLAWS(min), and (3) FLAWS(hco). In addition, segmented lesions on FLAWS(min) and FLAWS(hco) were merged to produce a union lesion map (FLAWS(min + hco)). Number and volume of all cortical, intracortical, and leukocortical lesions were compared among MP2RAGE(uni), FLAWS(min), and FLAWS(hco) using Friedman test and between MP2RAGE(uni) and FLAWS(min + hco) using Wilcoxon signed rank test. The FLAWS T1 maps were then compared with the reference MP2RAGE T1 maps using relative differences in percentage. In an exploratory analysis, individual cortical lesion counts of the 3 raters were compared, and interrater variability was quantified using Fleiss K. Results In total, 633 segmentations were made on the 3 contrasts, corresponding to 355 cortical lesions. The median number and volume of single cortical, intracortical, and leukocortical lesions were comparable among MP2RAGE(uni), FLAWS(min), and FLAWS(hco). In patients with cortical lesions (22/30), median cumulative lesion volume was larger on FLAWS(min) (587 mu L; IQR, 1405 mu L) than on MP2RAGE(uni) (490 mu L; IQR, 990 mu L; P = 0.04), whereas there was no difference between FLAWS(min) and FLAWS(hco), or FLAWS(hco) and MP2RAGE(uni). FLAWS(min + hco) showed significantly greater numbers of cortical (median, 4.5; IQR, 15) and leukocortical (median, 3.5; IQR, 12) lesions than MP2RAGE(uni) (median, 3; IQR, 10; median, 2.5; IQR, 7; both P < 0.001). Interrater agreement was moderate on MP2RAGE(uni) (K = 0.582) and FLAWS(hco) (K = 0.584), but substantial on FLAWS(min) (K = 0.614). qT1 in lesions was similar between MP2RAGE and FLAWS. Conclusions Cortical lesions identification in FLAWS(min) and FLAWS(hco) was comparable to MP2RAGE(uni)., The combination of FLAWS(min) and FLAWS(hco) allowed to identify a higher number of cortical lesions than MP2RAGE(uni), whereas qT1 maps did not differ between the 2 acquisition schemes.

International audience; Brain morphometry performed with magnetic resonance (MR) imaging is affected by partial volume (PV) effects when single voxels contain the signal from two different tissues. This paper proposes a generalization of the MP2 RAGE sequence PV estimation model which accounts for transmitted magnetic field (B1 {+}) inhomogeneities at 7T. Our simulation experiments demonstrated that the PV estimation error of the proposed model is significantly lower than the error obtained with the same model neglecting B1 {+} inhomogeneities (p

1AbstractMagnetic Resonance Imaging (MRI) motion artefacts frequently complicate structural and diffusion MRI analyses. While diffusion imaging is easily ‘scrubbed’ of motion affected volumes, the same is not true for structural images. Structural images are critical to most diffusion-imaging pipelines thus their corruption can lead to disproportionate data loss. To enable diffusion-image processing when structural images have been corrupted, we propose a means by which synthetic structural images can be generated from diffusion MRI. This technique combines multi-tissue constrained spherical deconvolution, which is central to many existing diffusion analyses, with the Bloch equations which allow simulation of MRI intensities given scanner parameters and magnetic resonance (MR) tissue properties. We applied this technique to 32 scans, including those acquired on different scanners, with different protocols and with pathology present. The resulting synthetic T1w and T2w images were visually convincing and exhibited similar tissue contrast to acquired structural images. These were also of sufficient quality to drive a Freesurfer-based tractographic analysis. In this analysis, probabilistic tractography connecting the thalamus to the primary sensorimotor cortex was delineated with Freesurfer, using either real or synthetic structural images. Tractography for real and synthetic conditions was largely identical in terms of both voxels encountered (Dice 0.88 – 0.95) and mean fractional anisotropy (intrasubject absolute difference 0.00 – 0.02). We provide executables for the proposed technique in the hope that these may aid the community in analysing datasets where structural image corruption is common, such as studies of children or cognitively impaired persons.HighlightsWe propose a simple means of synthesizing T1w and T2w images from diffusion dataThe proposed method worked well for a variety of acquisitionsSynthetic images showed tissue contrast akin to acquired imagesSynthetic images were high enough quality to be used for Freesurfer seeded diffusion tractographyThis method enables analysis of datasets where motion has corrupted acquired structural MRIs

International audience; IntraVoxel Incoherent Motion (IVIM) Diffusion-Weighted Magnetic Resonance Imaging (DW-MRI) is of great interest for evaluating tissue diffusion and perfusion and producing parametric maps in clinical applications for liver pathologies. However, the presence of macroscopic blood vessels (not capillaries) in a given Region of Interest (ROI) results in a confounding effect that bias the quantification of tissue perfusion. Therefore, it is necessary to identify those voxels affected by blood vessels. In this paper, an efficient algorithm for an automatic identification of blood vessels in a given ROI is proposed. It relies on the sparsity of the spatial distribution of blood vessels. This sparsity prior can be easily incorporated using the all-voxel IVIM-MRI model introduced in this paper. In addition to the identification of blood vessels, the proposed algorithm provides a quantification of blood vessels, tissue diffusion and tissue perfusion of all voxels in a given ROI, in one single step. Besides, two strategies are proposed in this paper to deal with the nonnegativity of the model parameters. The efficiency of the proposed algorithm compared to the Non-Negative Least Square (NNLS)-based method, recently introduced to deal with the confounding blood vessel effect in the IVIM-MRI model, is confirmed using both realistic and real DW-MR images.

Background A limited number of studies have used the intravoxel incoherent motion (IVIM) approach on bone marrow. In none of the previous studies were the effects of fat suppression on the IVIM parameters investigated. Purpose To measure the water diffusion coefficient and the perfusion fraction in vertebral bone marrow using IVIM with multishot, readout-segmented (RESOLVE) echo-planar imaging and to assess the effects of different fat suppression techniques on the measurement of the IVIM parameters. Study type Prospective. Population/subjects Six healthy volunteers (24.2 ± 4.3 years). Field strength/sequence 1.5T, RESOLVE. Assessment Four experiments were performed: 1) RESOLVE imaging without fat suppression, 2) with fat saturation (FS), 3) with spectral attenuated inversion recovery (SPAIR), and 4) with short-tau inversion recovery (STIR). The water diffusion coefficient D, pseudo-diffusion coefficient D*, and the perfusion fraction f were assessed in the vertebral bodies of the lumbar vertebrae. Statistical tests One-way repeated-measures analysis of variance (ANOVA) followed by Bonferroni's multiple comparison test. Results The RESOLVE IVIM protocol allowed for measurement of D, D*, and f in all volunteers. The signal of lipid protons affected the quantification of the IVIM diffusion coefficient: D = 0.24 ± 0.10 (×10-3 mm2 /s), no FS; D = 0.43 ± 0.07 (×10-3 mm2 /s), FS; D = 0.42 ± 0.07 (×10-3 mm2 /s), SPAIR; D = 0.35 ± 0.10 (×10-3 mm2 /s), STIR; and IVIM perfusion fraction f = 7.5 ± 1.9% no FS, f = 14.5 ± 5.4%, FS; f = 12.5 ± 2.6%, SPAIR; f = 18.1 ± 6.1%, STIR. No significant effect (P = 0.36) was found on the quantification of D*. Data conclusion An IVIM-MRI protocol using the RESOLVE sequence was implemented for measurements of vertebral bone marrow diffusion and the perfusion. The comparison between the protocols with and without fat suppression indicates that the lipid signal results in an underestimation of both D and f. Level of evidence Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2019;49:768-776.

International audience; To apply the Virtual Phantom (ViP) method for generating reference signals, to the chemical shift imaging (CSI) technique. The ViP method, previously used for generating reference images in magnetic resonance imaging (MRI), was here extended to generate reference peaks in the MR spectra acquired with a 2D-CSI sequence. Theoretical analysis was carried out to design the ViP signal. ViP-2D-CSI experiments were performed on a 4.7 Tesla MR scanner. Data analysis was carried out with the jMRUI software to fit the ViP peaks to determine their amplitude and frequency. Based on the theoretical analysis, it was found that the ViP peak could be generated by transmitting the ViP signal only in one repetition time of the 2D-CSI sequence. The amplitude and frequency of the ViP peak could be precisely adjusted and fine-tuned. The ViP peak was uniform over all CSI voxels, both in amplitude and in frequency. Furthermore, a good stability of the ViP reference amplitude and frequency was observed. The ViP method provides a means to generate a reference MR peak in 2D-CSI experiments. This could be of interest for signal quantification in CSI experiments.

Background T2 -weighted imaging (T2 -WI) information has been used in a qualitative manner in the assessment of prostate cancer. Quantitative derivatives (T2 relaxation time) can be generated from T2 -WI. These outputs may be useful in helping to discriminate clinically significant prostate cancer from background signal. Purpose/hypothesis To investigate changes in quantitative T2 parameters in lesions and noncancerous tissue of men on active surveillance for prostate cancer taking dutasteride 0.5 mg or placebo daily for 6 months. Study type Retrospective. Population/subjects Forty men randomized to 6 months of daily dutasteride (n = 20) or placebo (n = 20). Field strength/sequence Multiparametric 3T MRI at baseline and 6 months. This included a multiecho MR sequence for quantification of the T2 relaxation times, in three regions of interest (index lesion, noncancerous peripheral [PZ] and transitional [TZ] zones). A synthetic signal contrast (T2 Q contrast) between lesion and noncancerous tissue was assessed using quantitative T2 values. Signal contrast was calculated using the T2 -weighted sequence (T2 W contrast). Assessment Two radiologists reviewed the scans in consensus according to Prostate Imaging Reporting and Data System (PI-RADS v. 2) guidelines. Statistical tests Wilcoxon and Mann-Whitney U-tests, Spearman's correlation. Results When compared to noncancerous tissue, shorter T2 values were observed within lesions at baseline (83.5 and 80.5 msec) and 6 months (81.5 and 81.9 msec) in the placebo and dutasteride arm, respectively. No significant differences for T2 W contrast at baseline and after 6 months were observed, both in the placebo (0.40 [0.29-0.49] vs. 0.43 [0.25-0.49]; P = 0.881) and dutasteride arm (0.35 [0.24-0.47] vs. 0.37 [0.22-0.44]; P = 0.668). There was a significant, positive correlation between the T2 Q contrast and the T2 W contrast values (r = 0.786; P Data conclusion The exposure to antiandrogen therapy did not significantly influence the T2 contrast or the T2 relaxation values in men on active surveillance for prostate cancer. Level of evidence 4 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:1646-1653.

Purpose In context of head-and-neck radiotherapy, this study aims to compare MR image quality according to diagnostic (DIAG) and radiotherapy (RT) setups; and to optimise an MRI-protocol (including 3D T1 and T2-weighted sequences) for dose-planning (based on pseudo-CT generation). Materials and methods To compare DIAG and RT setups, signal-to-noise-ratio (SNR) and percentage-image-uniformity (PIU) were computed on T1 images of phantoms and volunteers. Influence of the sample conductivity on SNR was quantified using homemade phantoms. To obtain reliable T1 and T2 images for RT-planning, an experimental design was performed on volunteers by using SNR, contrast-to-noise-ratio (CNR) and mean-opinion-score (MOS). Further, pseudo-CTs were generated from 8 patients T2 images with a state-of-art deep-learning method. These pseudo-CTs were evaluated by mean-absolute-error (MAE) and mean-error (ME). Results SNR was higher for DIAG-setup compared to RT-setup (SNR-ratio = 1.3). A clear influence of the conductivity on SNR was observed. PIU was higher for DIAG-setup (38.8%) compared to RT-setup (33.5%). Regarding the protocol optimisation, SNR, CNR, and MOS were 20.6, 6.16, and 3.91 for the optimal T1 sequence. For the optimal T2 sequence, SNR, CNR and MOS were 25.6, 44.46 and 4.0. In the whole head-and-neck area, the mean MAE and ME of the pseudo-CTs were 82.8 and -3.9 HU. Conclusion We quantified the image quality decrease induces by using an RT-setup for head-and-neck radiotherapy. To compensate this decrease, an MRI protocol was optimised by using an experimental design. This protocol of 15 minutes provides accurate images which could be used for MRI-dose-planning in clinical practice.

International audience; Object - The MRI tissue characterization of vertebral bone marrow includes the measurement of proton density fat fraction (PDFF), T and T* relaxation times of the water and fat components (T, T, T*, T*), IVIM diffusion D, perfusion fraction f and pseudo-diffusion coefficient D*. However, the measurement of these vertebral bone marrow biomarkers (VBMBs) is affected with several confounding factors. In the current study, we investigated these confounding factors including the regional variation taking the example of variation between the anterior and posterior area in lumbar vertebrae, B inhomogeneity and the effect of fat suppression on f. Materials and methods - A fat suppressed diffusion-weighted sequence and two 3D gradient multi-echo sequences were used for the measurements of the seven VBMBs. A turbo flash B map sequence was used to estimate B inhomogeneities and thus, to correct flip angle for T quantification. We introduced a correction to perfusion fraction f measured with fat suppression, namely f. Results - A significant difference in the values of PDFF, f and f, T, T* and D was observed between the anterior and posterior region. Although, little variations of flip angle were observed in this anterior-posterior direction in one vertebra but larger variations were observed in head-feet direction from L1 to L5 vertebrae. Discussion - The regional difference in PDFF, f and T* can be ascribed to differences in the trabecular bone density and vascular network within vertebrae. The regional variation of VBMBs shows that care should be taken in reproducing the same region-of-interest location along a longitudinal study. The same attention should be taken while measuring f in fatty environment, and measuring T. Furthermore, the MRI-protocol presented here allows for measurements of seven VBMBs in less than 6 min and is of interest for longitudinal studies of bone marrow diseases.

International audience; Introduction The fluid and white matter suppression sequence (FLAWS) provides two T1-weighted co-registered datasets a white matter (WM) suppressed contrast (FLAWS1) and a cerebrospinal fluid (CSF) suppressed contrast (FLAWS2). FLAWS has the potential to improve the contrast of the subcortical brain regions that are important for Deep Brain Stimulation surgery planning. However, to date FLAWS has not been optimized for 1.5 T. In this study, the FLAWS sequence was optimized for use at 1.5 T. In addition, the contrast-enhancement properties of FLAWS image combinations were investigated using two voxel-wise FLAWS combined images the division (FLAWS-div) and the high contrast (FLAWS-hc) image. Methods FLAWS sequence parameters were optimized for 1.5 T imaging using an approach based on the use of a profit function under constraints for brain tissue signal and contrast maximization. MR experiments were performed on eleven healthy volunteers (age 18–30). Contrast (CN) and contrast to noise ratio (CNR) between brain tissues were measured in each volunteer. Furthermore, a qualitative assessment was performed to ensure that the separation between the internal globus pallidus (GPi) and the external globus pallidus (GPe) is identifiable in FLAWS1. Results The optimized set of sequence parameters for FLAWS at 1.5 T provided contrasts similar to those obtained in a previous study at 3 T. The separation between the GPi and the GPe was clearly identified in FLAWS1. The CN of FLAWS-hc was higher than that of FLAWS1 and FLAWS2, but was not different from the CN of FLAWS-div. The CNR of FLAWS-hc was higher than that of FLAWS-div. Conclusion Both qualitative and quantitative assessments validated the optimization of the FLAWS sequence at 1.5 T. Quantitative assessments also showed that FLAWS-hc provides an enhanced contrast compared to FLAWS1 and FLAWS2, with a higher CNR than FLAWS-div. © 2019

International audience; A novel magnetic resonance imaging (MRI) sequence called fluid and white matter suppression (FLAWS) was recently proposed for brain imaging at 3T. This sequence provides two co-registered 3D-MRI datasets of T1-weighted images. The voxel-wise division of these two datasets yields contrast-enhanced images that have been used in preoperative Deep Brain Stimulation (DBS) planning. In the current study, we propose a new way of combining the two 3D-MRI FLAWS datasets to increase the contrast-to-noise ratio of the resulting images. Furthermore, since many centers performing DBS are equipped with 1. 5T MRI systems, we also optimized the FLAWS sequence parameters for the data acquisition at the field strength of 1. 5T.

International audience; Background: A limited number of studies have used the intravoxel incoherent motion (IVIM) approach on bone marrow. In none of the previous studies were the effects of fat suppression on the IVIM parameters investigated.Purpose: To measure the water diffusion coefficient and the perfusion fraction in vertebral bone marrow using IVIM with multishot, readout‐segmented (RESOLVE) echo‐planar imaging and to assess the effects of different fat suppression techniques on the measurement of the IVIM parameters.Study Type: Prospective.Population/Subjects: Six healthy volunteers (24.2 ± 4.3 years).Field Strength/Sequence: 1.5T, RESOLVE.Assessment: Four experiments were performed: 1) RESOLVE imaging without fat suppression, 2) with fat saturation (FS), 3) with spectral attenuated inversion recovery (SPAIR), and 4) with short‐tau inversion recovery (STIR). The water diffusion coefficient D, pseudo‐diffusion coefficient D*, and the perfusion fraction f were assessed in the vertebral bodies of the lumbar vertebrae.Statistical Tests: One‐way repeated‐measures analysis of variance (ANOVA) followed by Bonferroni's multiple comparison test.Results: The RESOLVE IVIM protocol allowed for measurement of D, D*, and f in all volunteers. The signal of lipid protons affected the quantification of the IVIM diffusion coefficient: D = 0.24 ± 0.10 (×10−3 mm2/s), no FS; D = 0.43 ± 0.07 (×10−3 mm2/s), FS; D = 0.42 ± 0.07 (×10−3 mm2/s), SPAIR; D = 0.35 ± 0.10 (×10−3 mm2/s), STIR; and IVIM perfusion fraction f = 7.5 ± 1.9% no FS, f = 14.5 ± 5.4%, FS; f = 12.5 ± 2.6%, SPAIR; f = 18.1 ± 6.1%, STIR. No significant effect (P = 0.36) was found on the quantification of D*.Data Conclusion: An IVIM‐MRI protocol using the RESOLVE sequence was implemented for measurements of vertebral bone marrow diffusion and the perfusion. The comparison between the protocols with and without fat suppression indicates that the lipid signal results in an underestimation of both D and f.

Object Virtual Phantom Magnetic Resonance Imaging (ViP MRI) is a method to generate reference signals on MR images, using external radiofrequency (RF) signals. The aim of this study was to assess the feasibility of ViP MRI to generate complex-data images of phantoms mimicking water–fat systems. Materials and methods Various numerical phantoms with a given fat fraction, T2* and field map were designed. The k-space of numerical phantoms was converted into RF signals to generate virtual phantoms. MRI experiments were performed at 4.7 T using a multi-gradient-echo sequence on virtual and physical phantoms. The data acquisition of virtual and physical phantoms was simultaneous. Decomposition of the water and fat signals was performed using a complex-based water–fat separation algorithm. Results Overall, a good agreement was observed between the fat fraction, T2* and phase map values of the virtual and numerical phantoms. In particular, fat fractions of 10.5 ± 0.1 (vs 10% of the numerical phantom), 20.3 ± 0.1 (vs 20%) and 30.4 ± 0.1 (vs 30%) were obtained in virtual phantoms. Conclusion The ViP MRI method allows for generating imaging phantoms that i) mimic water–fat systems and ii) can be analyzed with water–fat separation algorithms based on complex data.

18F-Choline (FCH) uptake parameters are strong indicators of aggressive disease in prostate cancer. Functional parameters derived by magnetic resonance imaging (MRI) are also correlated to aggressive disease. The aim of this work was to evaluate the relationship between metabolic parameters derived by FCH PET/CT and functional parameters derived by MRI. Fourteen patients with proven prostate cancer who underwent FCH PET/CT and multiparametric MRI were enrolled. FCH PET/CT consisted in a dual phase: early pelvic list-mode acquisition and late whole-body acquisition. FCH PET/CT and multiparametric MRI examinations were registered and tumoral volume-of-interest were drawn on the largest lesion visualized on the apparent diffusion coefficient (ADC) map and projected onto the different multiparametric MR images and FCH PET/CT images. Concerning the FCH uptake, kinetic parameters were extracted with the best model selected using the Akaike information criterion between the one- and two-tissue compartment models with an imaging-derived plasma input function. Other FCH uptake parameters (early SUVmean and late SUVmean) were extracted. Concerning functional parameters derived by MRI scan, cell density (ADC from diffusion weighting imaging) and vessel permeability (Ktrans and Ve using the Tofts pharmakinetic model from dynamic contrast-enhanced imaging) parameters were extracted. Spearman’s correlation coefficients were calculated to compare parameters. The one-tissue compartment model for kinetic analysis of PET images was selected. Concerning correlation analysis between PET parameters, K1 was highly correlated with early SUVmean (r = 0.83, p

Diffusion and perfusion evaluation is important for liver pathologies. Intravoxel incoherent motion (IVIM) diffusion weighted magnetic resonance imaging (DW-MRI) is a good method to quantify the apparent diffusion coefficient (ADC) and perfusion fraction $(PF)$. However the existence of large blood vessels in the liver leads to a confounding effect on the conventional bi-exponential IVIM model. Actually, such confounding effect can be considered as a third contribution of the image signal. In this study, an all-in-one approach for blood vessels localization and tissue diffusion/perfusion estimation based on an all-voxel tri-exponential IVIM model in human liver is proposed. The proposed approach assumes sparse distribution of blood vessels in the considered region of interest. Besides, it deals with the non-negativity of the model parameters by resorting to a change of variables into square. Model parameters are estimated alternatively in an iterative way following the spirit of the ADMM algorithm. The good behavior of the proposed approach is assessed using both realistic and real diffusion-weighted magnetic resonance imaging in the liver.

Fourteen patients with proven prostate cancer who underwent FCH PET/CT and multiparametric MRI were enrolled. FCH PET/CT consisted in a dual phase: early pelvic list-mode acquisition and late whole-body acquisition. FCH PET/CT and multiparametric MRI examinations were registered and tumoral volume-of-interest were drawn on the largest lesion visualized on the apparent diffusion coefficient (ADC) map and projected onto the different multiparametric MR images and FCH PET/CT images. Concerning the FCH uptake, kinetic parameters were extracted with the best model selected using the Akaike information criterion between the one- and two-tissue compartment models with an imaging-derived plasma input function. Other FCH uptake parameters (early SUVmean and late SUVmean) were extracted. Concerning functional parameters derived by MRI scan, cell density (ADC from diffusion weighting imaging) and vessel permeability (KThe one-tissue compartment model for kinetic analysis of PET images was selected. Concerning correlation analysis between PET parameters, KNo significant correlation was found between FCH PET/CT and multiparametric MRI metrics except FCH influx which is moderately linked to the vessel permeability in prostate cancer.

Object: To determine whether glycine can be measured at 7 T in human brain with 1H magnetic resonance spectroscopy (MRS). Materials and methods: The glycine singlet is overlapped by the larger signal of myo-inositol. Density matrix simulations were performed to determine the TE at which the myo-inositol signal was reduced the most, following a single spin-echo excitation. 1H MRS was performed on an actively shielded 7 T scanner, in five healthy volunteers. Results: At the TE of 30ms, the myo-inositol signal intensity was substantially reduced. Quantification using LCModel yielded a glycine-to-creatine ratio of 0.14 ±0.01, with a Cramér-Rao lower bound (CRLB) of 7 ± 1%. Furthermore, quantification of metabolites other than glycine was possible as well, with a CRLB mostly below 10%. Conclusion: It is possible to detect glycine at 7 T in human brain, at the short TE of 30ms with a single spin-echo excitation scheme

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Purpose - To assess the feasibility of measuring the fat fraction, T1 and T2 * relaxation times of water and fat signals in vertebral bone marrow using breath-hold magnetic resonance imaging (MRI) gradient echo images of the spine. Materials and methods - MRI experiments were performed at 1.5T on eight healthy volunteers (35.1 ± 15.7 years, five men and three women) using two sagittal four-echo 3D gradient echo volumetric interpolated breath-hold examination (VIBE Dixon) sequences acquired at two different flip angles (5° and 15°). The water/fat decomposition was performed in the vertebral bodies of L1 to L5 by fitting the signal to a function that depends on the echo time and the flip angle to calculate the fat fraction (FF) and T1 and T2 * relaxation times of water and fat signals. Repeatability was assessed by scanning one volunteer six times. Results - The mean fat fraction over L1 to L5 was 33 ± 8%. The mean T1 and T2 * of water and fat signals were respectively T1w = 701 ± 151 msec, T2 *w = 13.7 ± 2.9 msec, T1f = 334 ± 113 msec, and T2 *f = 11.4 ± 2.7 msec. When considering each vertebra separately, the fat fraction increased from L1 to L5 and the T1w decreased from L1 to L5. The mean coefficients of variation obtained from the repeatability study were 8% (FF), 11% (T1w ), 17% (T1f ), 8% (T2 *w ), and 27% (T2 *f ). Conclusion - The method introduced in the current study allows for the measurement of the fat fraction and water and fat relaxation times, with a total acquisition time of less than 40 seconds. J. Magn. Reson. Imaging 2016;44:549-555.

International audience; Purpose: The purpose of this study was to implement Virtual Phantom Magnetic Resonance Imaging (ViP MRI), a technique that allows for generating reference signals in MR images using radiofrequency (RF) signals, on a clinical MR system and to test newly designed virtual phantoms.Methods: MRI experiments were conducted on a 1.5 T MRI scanner. Electromagnetic modelling of the ViP system was done using the principle of reciprocity. The ViP RF signals were generated using a compact waveform generator (dimensions of 26 cm × 18 cm × 16 cm), connected to a homebuilt 25 mm-diameter RF coil. The ViP RF signals were transmitted to the MRI scanner bore, simultaneously with the acquisition of the signal from the object of interest. Different types of MRI data acquisition (2D and 3D gradient-echo) as well as different phantoms, including the Shepp–Logan phantom, were tested. Furthermore, a uniquely designed virtual phantom — in the shape of a grid — was generated; this newly proposed phantom allows for the investigations of the vendor distortion correction field.Results: High quality MR images of virtual phantoms were obtained. An excellent agreement was found between the experimental data and the inverse cube law, which was the expected functional dependence obtained from the electromagnetic modelling of the ViP system. Short-term time stability measurements yielded a coefficient of variation in the signal intensity over time equal to 0.23% and 0.13% for virtual and physical phantom, respectively. MR images of the virtual grid-shaped phantom were reconstructed with the vendor distortion correction; this allowed for a direct visualization of the vendor distortion correction field. Furthermore, as expected from the electromagnetic modelling of the ViP system, a very compact coil (diameter ~ cm) and very small currents (intensity ~ mA) were sufficient to generate a signal comparable to that of physical phantoms in MRI experiments.Conclusions: The ViP MRI technique was successfully implemented on a clinical MR system. One of the major advantages of ViP MRI over previous approaches is that the generation and transmission of RF signals can be achieved with a self-contained apparatus. As such, the ViP MRI technique is transposable to different platforms (preclinical and clinical) of different vendors. It is also shown here that ViP MRI could be used to generate signals whose characteristics cannot be reproduced by physical objects. This could be exploited to assess MRI system properties, such as the vendor distortion correction field.

International audience; Objectives The aim of this study was to demonstrate the feasibility to assess cerebral hypoperfusion with a hyperventilation (HV) challenge protocol using intravoxel incoherent motion (IVIM) magnetic resonance imaging. Materials and Methods Magnetic resonance imaging experiments were performed on 10 healthy volunteers at 1.5 T, with a diffusion IVIM magnetic resonance imaging protocol using a set of b-values optimized by Cramer-Rao Lower Bound analysis. Hypoperfusion was induced by an HV maneuver. Measurements were performed in normoventilation and HV conditions. Biexponential curve fitting was used to obtain the perfusion fraction (f), pseudodiffusion coefficient (D*), and the product fD* in gray matter (GM) regions of interest (ROIs). Regional cerebral blood flow in the same ROIs was also assessed with arterial spin labeling. Results The HV challenge led to a diminution of IVIM perfusion-related parameters, with a decrease of f and fD* in the cerebellum (P = 0.03 for f; P = 0.01 for fD*), thalamus GM (P = 0.09 for f; P = 0.01 for fD*), and lenticular nuclei (P = 0.03 for f; P = 0.02 for fD*). Mean GM cerebral blood flow (in mL/100 g tissue/min) measured with arterial spin labeling averaged over all ROIs also decreased (normoventilation: 42.7 4.1 vs HV: 33.2 +/- 2.2, P = 0.004) during the HV challenge. Conclusions The optimized IVIM protocol proposed in the current study allows for measurements of cerebral hypoperfusion that might be of great interest for pathologies diagnosis such as ischemic stroke.

Tissue perfusion measurements by IntraVoxel Incoherent Motion (IVIM) Diffusion-Weighted Magnetic Resonance Imaging (DW-MRI) are of great interest for investigating liver pathologies. However, perfusion estimation in the liver is more challenging than in other organs due to the presence of several blood vessels (not capillaries) whose visual identification, in the considered Region-Of-Interest (ROI), is not evident. These blood vessels are the source of a confounding perfusion parameter, which can be modelled as a third exponential decay in the IVIM-MRI model. Thus, a new algorithm to estimate the tissue perfusion parameters including those confounding ones related to the potential presence of blood vessels is presented in this paper. Based on the sparsity of the spatial distribution of the blood vessels in the considered ROI, the parameter estimation of the tri-exponential IVIM model is performed in an iterative way following the spirit of the alternating direction method of multipliers where the Gauss-Newton method is employed to deal with the model nonlinearity. To the best of our knowledge, this is the first time a all-voxel tri-exponential IVIM-MRI model is considered in the IVIM-MRI framework. The efficiency of the proposed algorithm was validated on realistic DW-MR images. The estimated parametric maps of the water diffusion coefficient and tissue perfusion of the IVIM model were in good agreement with ground-truth values. A good performances of this algorithm was also observed on clinical MRI data in the liver.

TTo investigate changes in quantitative TRetrospective.Forty men randomized to 6 months of daily dutasteride (n = 20) or placebo (n = 20).Multiparametric 3T MRI at baseline and 6 months. This included a multiecho MR sequence for quantification of the TTwo radiologists reviewed the scans in consensus according to Prostate Imaging Reporting and Data System (PI-RADS v. 2) guidelines.Wilcoxon and Mann-Whitney U-tests, Spearman's correlation.When compared to noncancerous tissue, shorter TThe exposure to antiandrogen therapy did not significantly influence the T4 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:1646-1653.

Introduction: Chronic obstructive pulmonary disease (COPD) is associated with metabolic abnormalities in muscles of the lower limbs, but it is not known whether these abnormalities are generalized or limited to specific muscle groups, nor is there an easy way of predicting their presence. Methods: Metabolism in the quadriceps and biceps of 14 COPD patients and controls was assessed during sustained contraction using 31-phosphorus magnetic resonance spectroscopy (31P MRS). T1 MRI was used to measure quadriceps intermuscular adipose tissue (IMAT). Results: COPD patients had prolonged quadriceps phosphocreatine time (patients: 38.8 ± 12.7 s; controls: 25.2 ± 10.6 s; P = 0.006) and a lower pH (patents: 6.88 ± 0.1; controls: 6.99 ± 0.06; P = 0.002). Biceps measures were not significantly different. IMAT was associated with a nadir pH

Object To assess the feasibility of measuring diffusion and perfusion fraction in vertebral bone marrow using the intravoxel incoherent motion (IVIM) approach and to compare two fitting methods, i.e., the non-negative least squares (NNLS) algorithm and the more commonly used Levenberg–Marquardt (LM) non-linear least squares algorithm, for the analysis of IVIM data. Materials and Methods MRI experiments were performed on fifteen healthy volunteers, with a diffusion-weighted echo-planar imaging (EPI) sequence at five different b -values (0, 50, 100, 200, 600 s/mm 2 ), in combination with an STIR module to suppress the lipid signal. Diffusion signal decays in the first lumbar vertebra (L1) were fitted to a bi-exponential function using the LM algorithm and further analyzed with the NNLS algorithm to calculate the values of the apparent diffusion coefficient (ADC), pseudo-diffusion coefficient ( D *) and perfusion fraction. Results The NNLS analysis revealed two diffusion components only in seven out of fifteen volunteers, with ADC = 0.60 ± 0.09 (10 − 3 mm 2 /s), D * = 28 ± 9 (10 − 3 mm 2 /s) and perfusion fraction = 14% ± 6%. The values obtained by the LM bi-exponential fit were: ADC = 0.45 ± 0.27 (10 − 3 mm 2 /s), D * = 63 ± 145 (10 − 3 mm 2 /s) and perfusion fraction = 27% ± 17%. Furthermore, the LM algorithm yielded values of perfusion fraction in cases where the decay was not bi-exponential, as assessed by NNLS analysis. Conclusion The IVIM approach allows for measuring diffusion and perfusion fraction in vertebral bone marrow; its reliability can be improved by using the NNLS, which identifies the diffusion decays that display a bi-exponential behavior.

Object To design and build a single phantom, encompassing various elementary tubes, that mimics the 1H magnetic resonance (MR) spectra of liver, prostate, muscle and brain. Materials and Methods High-resolution NMR tubes were filled with water and the metabolite of interest, at a concentration of 50 mM, or with dairy cream or oil. The tubes (5 mm outer diameter) were placed into a plastic support, the ensemble was positioned in the center of a cuboid container filled with water. Simulations of the magnetic field inhomogeneity arising from the susceptibility variations in the current phantom were also performed. MR localized spectroscopy was performed on a 1.5 T clinical scanner. Results MR spectra of voxels positioned in four different locations of the phantom closely mimicked the resonance peaks of liver, prostate, muscle and brain in vivo MR spectra. In particular, for the muscle spectrum, the intramyocellular lipid (IMCL) and extramyocellular lipid (EMCL) resonances were obtained using dairy cream and oil, respectively. Simulations of the magnetic field inhomogeneity in the phantom showed that in the case of an NMR tube length five times greater than the thickness of the volume of interest, it is not necessary to fill the container with water. However, to ensure a good reception level and shim settings, the NMR tubes were immersed in water. Conclusions A single phantom of new design, that is easily built and highly reconfigurable, is here presented, to mimic the in vivo MR spectra of liver, prostate, muscle, brain and other models as needed.

International audience; OBJECT: The ability to generate reference signals is of great benefit for quantitation of the magnetic resonance (MR) signal. The aim of the present study was to implement a dedicated experimental set-up to generate MR images of virtual phantoms. MATERIALS AND METHODS: Virtual phantoms of a given shape and signal intensity were designed and the k-space representation was generated. A waveform generator converted the k-space lines into a radiofrequency (RF) signal that was transmitted to the MR scanner bore by a dedicated RF coil. The k-space lines of the virtual phantom were played line-by-line in synchronization with the magnetic resonance imaging data acquisition. RESULTS: Virtual phantoms of complex patterns were reproduced well in MR images without the presence of artifacts. Time-series measurements showed a coefficient of variation below 1 % for the signal intensity of the virtual phantoms. An excellent linearity (coefficient of determination r (2) = 0.997 as assessed by linear regression) was observed in the signal intensity of virtual phantoms. CONCLUSION: Virtual phantoms represent an attractive alternative to physical phantoms for providing a reference signal. MR images of virtual phantoms were here generated using a stand-alone, independent unit that can be employed with MR scanners from different vendors.

International audience; Purpose - Bone marrow is found either as red bone marrow, which mainly contains haematopoietic cells, or yellow bone marrow, which mainly contains adipocytes. In adults, red bone marrow is principally located in the axial skeleton. A recent study has introduced a method to simultaneously estimate the fat fraction (FF), the T1 and T2* relaxation times of water (T1w, T2*w) and fat (T1f and T2*f) in the vertebral bone marrow. The aim of the current study was to measure FF, T1w, T1f, T2*w and T2*f in five sites of bone marrow, and to assess the presence of regional variations. Methods - MRI experiments were performed at 1.5T on five healthy volunteers (31.6±15.6years) using a prototype chemical-shift-encoded 3D multi-gradient-echo sequence (VIBE) acquired with two flip angles. Acquisitions were performed in the shoulders, lumbar spine and pelvis, with acquisition times of