Contrast media viscosity and its potential effect on the diagnosis of vesicoureteral reflux in children.

OBJECTIVE: To confirm that contrast-enhanced voiding cystourosonography (ceVUS) diagnoses more vesicoureteral reflux (VUR) than voiding cystourethrography (VCUG) and assess whether this could be explained by contrast agent viscosity differences. MATERIALS AND METHODS: Children addressed for a VCUG for suspected or known VUR between April 2021 and June 2023 were prospectively included. CeVUS and VCUG were consecutively performed during the same procedure by two operators; for each pelviureteric unit (PUU), VUR presence was assessed and scored (I-V scale). At least 6 months later, three radiologists reassessed VUR grading on all ceVUS static images. The viscosity of the two contrast agents and of the urine were measured at 25 °C and 37 °C. Wilcoxon tests were used for comparisons and linear Cohen's Kappa coefficient for Interobserver and Intraobserver agreement. RESULTS: Eighty-nine children, representing 192 PUU, were included. VUR was detected in 54 PUUs by at least one technique, by both in 30/54, by ceVUS only in 21/54 (38.8%), and by VCUG only in 3/54 (5.5%). VUR grade was higher with ceVUS in 19/30 (63.3%, p < 0.0008) PUUs. The ceVUS agent viscosity at 25 °C/37 °C (1.13 cP/1.03 cP) was almost identical to urine viscosity (1.14 cP/1.02 cP) and it was respectively 8 and 6 times lower than VCUG contrast agent viscosity (9.44 cP/6.03 cP). The Cohen's kappa for ceVUS grading was between 0.75-0.97 (interobserver) and 0.93-0.98 (intraobserver). CONCLUSION: Our study confirms that ceVUS detects more VUR and grades them higher in comparison to VCUG in children. This could be explained by the lower viscosity of the US contrast agent. KEY POINTS: Question Why are there differences in detecting and grading VUR between ceVUS and VCUG? Finding VUR was detected by ceVUS or VCUG only in, respectively 38.8% and 5.5% of PUUs. VUR grade was higher with ceVUS in 63.3%. Clinical relevance The higher detection rate and grading of vesicoureteral reflux in children by ceVUS might be explained by the lower viscosity of its sonographic contrast agent. CeVUS might reproduce the urine movement in the urinary tract.

Combined prenatal US and post-mortem fetal MRI: can they replace conventional autopsy for fetal body abnormalities?

OBJECTIVES: The acceptance of conventional autopsy (CA), the gold standard method for investigating fetal death, often remains problematic. Post-mortem magnetic resonance imaging (PMMRI) is increasingly advocated, particularly for neurologic malformations. However, PMMRI performances to diagnose non-neurologic malformations remain unclear. We aim to clarify whether a full body CA remains needed after prenatal ultrasound (US) and PMMRI in assessing non-neurologic fetal malformations. METHODS: In this retrospective IRB-approved study, during a 6-year period, all fetuses who underwent PMMRI, prenatal US, and full body CA were included. Body abnormalities were identified in US, PMMRI, and CA reports. US and PMMRI images were all reviewed. All abnormalities were graded as major (2 points) or minor (1 point). Each technique (US, PMMRI, CA) was given a score by adding all grading points. In each fetus, results were compared for both separate and combined US and PMMRI to CA. Sensitivity and specificity were calculated for detecting major abnormalities. RESULTS: Fifty fetuses were included. The score of CA, US, and PMMRI was respectively 53, 37, and 46. Compared with US-PMMRI, CA added information in 2 cases (4%) with major abnormalities and 7 cases (14%) with minor abnormalities. PMMRI and US were concordant in 36/50 (72%) fetuses. Separate US/PMMRI sensitivities and specificities for detecting major body malformations respectively were 80%/80% and 100%/94%. Combined US-PMMRI had a sensitivity of 90% and a specificity of 94%. Two cardiac malformations (2/6) were only described by CA. CONCLUSIONS: After prenatal US and PMMRI, few additional fetal body malformations are discovered with CA. Nevertheless, fetal heart autopsy remains mandatory. CLINICAL RELEVANCE STATEMENT: A cardiac conventional autopsy complemented by prenatal ultrasound and post-mortem MRI allows to detect all major fetal body abnormalities. With this efficient and much less invasive approach, a higher acceptance rate of fetal autopsy can be expected. KEY POINTS: • Excepting cardiac malformations, most major fetal body malformations can reliably be identified by prenatal US combined with post-mortem MRI. • In the post-mortem diagnosis of fetal body malformations, a conventional autopsy limited to the fetal heart might replace a full body autopsy after a well-conducted prenatal US and post-mortem MRI.

Repeatability and reproducibility of ADC measurements: a prospective multicenter whole-body-MRI study.

OBJECTIVES: Multicenter oncology trials increasingly include MRI examinations with apparent diffusion coefficient (ADC) quantification for lesion characterization and follow-up. However, the repeatability and reproducibility (R&R) limits above which a true change in ADC can be considered relevant are poorly defined. This study assessed these limits in a standardized whole-body (WB)-MRI protocol. METHODS: A prospective, multicenter study was performed at three centers equipped with the same 3.0-T scanners to test a WB-MRI protocol including diffusion-weighted imaging (DWI). Eight healthy volunteers per center were enrolled to undergo test and retest examinations in the same center and a third examination in another center. ADC variability was assessed in multiple organs by two readers using two-way mixed ANOVA, Bland-Altman plots, coefficient of variation (CoV), and the upper limit of the 95% CI on repeatability (RC) and reproducibility (RDC) coefficients. RESULTS: CoV of ADC was not influenced by other factors (center, reader) than the organ. Based on the upper limit of the 95% CI on RC and RDC (from both readers), a change in ADC in an individual patient must be superior to 12% (cerebrum white matter), 16% (paraspinal muscle), 22% (renal cortex), 26% (central and peripheral zones of the prostate), 29% (renal medulla), 35% (liver), 45% (spleen), 50% (posterior iliac crest), 66% (L5 vertebra), 68% (femur), and 94% (acetabulum) to be significant. CONCLUSIONS: This study proposes R&R limits above which ADC changes can be considered as a reliable quantitative endpoint to assess disease or treatment-related changes in the tissue microstructure in the setting of multicenter WB-MRI trials. KEY POINTS: • The present study showed the range of R&R of ADC in WB-MRI that may be achieved in a multicenter framework when a standardized protocol is deployed. • R&R was not influenced by the site of acquisition of DW images. • Clinically significant changes in ADC measured in a multicenter WB-MRI protocol performed with the same type of MRI scanner must be superior to 12% (cerebrum white matter), 16% (paraspinal muscle), 22% (renal cortex), 26% (central zone and peripheral zone of prostate), 29% (renal medulla), 35% (liver), 45% (spleen), 50% (posterior iliac crest), 66% (L5 vertebra), 68% (femur), and 94% (acetabulum) to be detected with a 95% confidence level.

Multi-atlas segmentation of the skeleton from whole-body MRI-Impact of iterative background masking.

PURPOSE: To improve multi-atlas segmentation of the skeleton from whole-body MRI. In particular, we study the effect of employing the atlas segmentations to iteratively mask tissues outside of the region of interest to improve the atlas alignment and subsequent segmentation. METHODS: An improved atlas registration scheme is proposed. Starting from a suitable initial alignment, the alignment is refined by introducing additional stages of deformable registration during which the image sampling is limited to the dilated atlas segmentation label mask. The performance of the method was demonstrated using leave-one-out cross-validation using atlases of 10 whole-body 3D-T1 images of prostate cancer patients with bone metastases and healthy male volunteers, and compared to existing state of the art. Both registration accuracy and resulting segmentation quality, using four commonly used label fusion strategies, were evaluated. RESULTS: The proposed method showed significant improvement in registration and segmentation accuracy with respect to the state of the art for all validation criteria and label fusion strategies, resulting in a Dice coefficient of 0.887 (STEPS label fusion). The average Dice coefficient for the multi-atlas segmentation showed over 11% improvement with a decrease of false positive rate from 28.3% to 13.2%. For this application, repeated application of the background masking did not lead to significant improvement of the segmentation result. CONCLUSIONS: A registration strategy, relying on the use of atlas segmentations as mask during image registration was proposed and evaluated for multi-atlas segmentation of whole-body MRI. The approach significantly improved registration and final segmentation accuracy and may be applicable to other structures of interest.

Assessment of cardiac-driven liver movements with filtered harmonic phase image representation, optical flow quantification, and motion amplification.

PURPOSE: To characterize cardiac-driven liver movements using a harmonic phase image representation (HARP) with an optical flow quantification and motion amplification method. The method was applied to define the cardiac trigger delay providing minimal signal losses in liver DWI images. METHODS: The 16-s breath-hold balanced-SSFP time resolved 20 images/s were acquired at 3T in coronal and sagittal orientations. A peripheral pulse unit signal was recorded. Cardiac-triggered DWI images were acquired after different peripheral pulse unit delays. A steerable pyramid decomposition with multiple orientations and spatial frequencies was applied. The liver motion field-map was derived from temporal variations of the HARP representation filtered around the cardiac frequency. Liver displacements were quantified with an optical flow method; moreover the right liver motion was amplified. RESULTS: The largest displacements were observed in the left liver (feet-head:3.70 ± 1.06 mm; anterior-posterior: 2.35 ± 0.51 mm). Displacements were statistically significantly weaker in the middle right liver (0.47 ± 0.11 mm; P = 0.0156). The average error was 0.013 ± 0.022 mm (coronal plane) and 0.021 ± 0.041 mm (sagittal plane). The velocity field demonstrated opposing movements of the right liver extremities during the cardiac cycle. DWI signal loss was minimized in regions and instants of smallest amplitude of both velocity and velocity gradient. CONCLUSION: Cardiac-driven liver movements were quantified with combined cardiac frequency-filtered HARP and optical flow methods. A motion phase opposition between right liver extremities was demonstrated. Displacement amplitude and velocity were larger in the left liver especially along the vertical direction. Motion amplification visually emphasized cardiac-driven right liver displacements. The optimal cardiac timing minimizing signal loss in liver DWI images was derived.

Total choline quantification measured by 1H MR spectroscopy as early predictor of response after neoadjuvant treatment for locally advanced breast cancer: The impact of immunohistochemical status.

BACKGROUND: Validation of new biomarkers is essential for the early evaluation of neoadjuvant treatments. PURPOSE: To determine whether measurements of total choline (tCho) by 1H spectroscopy could predict morphological or pathological complete response (pCR) of neoadjuvant treatment and whether breast cancer subgroups are related to prediction accuracy. STUDY TYPE: Prospective, nonrandomized, monocentric, diagnostic study. POPULATION: Sixty patients were initially included with 39 women participating in the final cohort. FIELD STRENGTH/SEQUENCE: A 1.5T scanner was used for acquisition and MRS was performed using the syngo GRACE sequence. ASSESSMENT: MRS and MRI examinations were performed at baseline (TP1), 24-72 hours after first chemotherapy (TP2), after the end of anthracycline treatment (TP3), and MRI only after the end of taxane treatment (TP4). Early (EMR) and late (LMR) morphological response were defined as %ΔDmax13 or %ΔDmax14, respectively. Responders were patients with %ΔDmax >30. Pathological complete response (pCR) patients achieved a residual cancer burden score of 0. STATISTICAL TESTS: T-test, receiver operating characteristic (ROC) curves, multiple regression, logistic regression, one-way analysis of variance (ANOVA) analysis were used for the analysis. RESULTS: At TP1 there was a significant difference between response groups for tCho1 concerning EMR prediction (P = 0.05) and pCR (P < 0.05) and for Kep 1 (P = 0.03) concerning LMR prediction. At TP2, no modification of tCho and other parameters could predict response. At TP3, ΔtCho, ΔDmax, and ΔVol could predict LMR (P < 0.05 for all parameters), pCR (P < 0.05 for all parameters), and ΔKtrans could predict only pCR (P = 0.04). Logistic regression at baseline showed the highest area under the curve (AUC) of 0.9 for prediction of pCR. The triple negative (TN) subgroup showed significantly higher tCho at baseline (P = 0.02) and higher ΔtCho levels at TP3 (P < 0.05). DATA CONCLUSION: Baseline measurements of tCho in combination with clinicopathological criteria could predict non-pCR with a high AUC. Furthermore, tCho quantification for prediction of pCR was more sensitive for TN tumors. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 4 J. Magn. Reson. Imaging 2018;48:982-993.

Liver apparent diffusion coefficient repeatability with individually predetermined optimal cardiac timing and artifact elimination by signal filtering.

PURPOSE: To prospectively assess liver ADC (apparent diffusion coefficient) repeatability from cardiac-triggered diffusion-weighted images obtained with an individually predetermined optimal cardiac time window minimizing cardiac-related effects and to evaluate a signal filtering method aimed at artifact elimination. MATERIALS AND METHODS: After Institutional Review Board approval and written informed consent, eight healthy volunteers underwent four repetitions of respiratory-triggered diffusion-weighted sequences (3T, b: 0,150,500 s/mm(2) ) without (RTnoCT, 51 sec) and with individually optimized cardiac triggering (RTCT, 306 sec). The optimal cardiac delay was individually predetermined using a 5-second breath-hold sequence. Monoexponential liver ADC and left-to-right-liver ADC ratio were computed from region of interest (ROI) signal measurements (two independent readers). A filtering method, excluding signal intensities lower than the mean intensity at fixed b-value, provided ADC recalculation. Limits-of-agreement (LOAs) from 95% confidence intervals for differences across the four repetitions provided the variability range. RESULTS: For Reader 1 (Reader 2), left-to-right-liver ADC ratios were significantly higher in RTnoCT 1.51 (1.52) than in RTCT 1.12 (1.15), P = 0.012 (P = 0.017). Respectively for RTnoCT and RTCT: left liver LOAs were ±835 (±775), ± 315 (±369) 10(-6) mm(2) /s; right liver LOAs were ±392 (±445), ± 172 (±140) 10(-6) mm(2) /s: LOAs were larger in the left than in the right lobe (both P < 0.001). After filtering, left liver ADC LOAs narrowed to ±650 (±367) 10(-6) mm(2) /s, P = 0.17 (P < 0.001); ± 152 (±208) 10(-6) mm(2) /s (both P < 0.002) and left-to-right-liver ADC ratio decreased to 1.28 (1.20), P = 0.017 (P = 0.012); 1.09 (1.08), P = 0.106 (P = 0.105). CONCLUSION: Compared to noncardiac-triggered acquisitions, individually optimized cardiac-triggered acquisitions improved ADC repeatability in both liver lobes and reduced ADC differences between left and right liver. Left liver ADC repeatability was further improved after signal filtering.

Quantitative DCE-MRI for prediction of pathological complete response following neoadjuvant treatment for locally advanced breast cancer: the impact of breast cancer subtypes on the diagnostic accuracy.

OBJECTIVES: To assess whether DCE-MRI pharmacokinetic (PK) parameters obtained before and during chemotherapy can predict pathological complete response (pCR) differently for different breast cancer groups. METHODS: Eighty-four patients who received neoadjuvant chemotherapy for locally advanced breast cancer were retrospectively included. All patients underwent two DCE-MRI examinations, one before (EX1) and one during treatment (EX2). Tumours were classified into different breast cancer groups, namely triple negative (TNBC), HER2+ and ER+/HER2-, and compared with the whole population (WP). PK parameters Ktrans and Ve were extracted using a two-compartment Tofts model. RESULTS: At EX1, Ktrans predicted pCR for WP and TNBC. At EX2, maximum diameter (Dmax) predicted pCR for WP and ER+/HER2-. Both PK parameters predicted pCR in WP and TNBC and only Ktrans for the HER2+. pCR was predicted from relative difference (EX1 - EX2)/EX1 of Dmax and both PK parameters in the WP group and only for Ve in the TNBC group. No PK parameter could predict response for ER+/HER-. ROC comparison between WP and breast cancer groups showed higher but not statistically significant values for TNBC for the prediction of pCR CONCLUSIONS: Quantitative DCE-MRI can better predict pCR after neoadjuvant treatment for TNBC but not for the ER+/HER2- group. KEY POINTS: • DCE-MRI-derived pharmacokinetic parameters can predict response status of neoadjuvant chemotherapy treatment. • Ktrans can better predict pCR for the triple negative group. • No pharmacokinetic parameter could predict response for the ER+/HER2- group.

Pancreatic neuroendocrine tumors: correlation between histogram analysis of apparent diffusion coefficient maps and tumor grade.

PURPOSE: To explore the role of histogram analysis of apparent diffusion coefficient (ADC) MRI maps based on entire tumor volume data in determining pancreatic neuroendocrine tumor (PNT) grade. METHODS AND MATERIALS: Retrospective evaluation of 22 patients with PNTs included low-grade (G1; n = 15), intermediate-grade (G2; n = 4), and high-grade (G3; n = 3) tumors. Regions of interest containing the lesion were drawn on every section of the ADC map containing the tumor and summated to obtain histograms for entire tumor volume. Calculated histographic parameters included mean ADC (mADC), 5th percentile ADC, 10th percentile ADC, 25th percentile ADC, 50th percentile ADC, 75th percentile ADC (ADC75), 90th percentile ADC (ADC90) and 95th percentile ADC (ADC95), skewness and kurtosis. Histogram parameters were correlated with tumor grade by repeated measures analysis of variance with Tukey-Kramer post hoc comparisons. RESULTS: The mADC, ADC75, ADC90, and ADC95 were significantly higher in G1 tumors (1283 ± 267; 1404 ± 300; 1495 ± 318; 1562 ± 347 × 10(-6) mm(2)/s) compared to G2 (892 ± 390; 952 ± 381; 1036 ± 384; 1072 ± 374 × 10(-6) mm(2)/s) and to G3 tumors (733 ± 225; 864 ± 284; 1008 ± 288; 1152 ± 192 × 10(-6) mm(2)/s) (p value <0.05). Skewness and kurtosis were significantly different between G1 (0.041 ± 0.466; 2.802 ± 0.679) and G3 (1.01 ± 1.140; 5.963 ± 4.008) tumors (p value <0.05). Tumor volume (mL) was significantly higher on G3 (55 ± 15.7) compared to G1 (1.9 ± 2.7) and G2 (4.5 ± 3.6) tumors (p value <0.05). In this small sample size, we did not detect statistically significant parameters between G2 (n = 4) and G3 (n = 3) tumors. CONCLUSIONS: Histographic analysis of ADC maps on the basis of the entire tumor volume can be useful in differentiating histologic grades of PNTs.

Detection and characterization of unruptured intracranial aneurysms: Comparison of 3T MRA and DSA.

PURPOSE: To compare magnetic resonance angiography (MRA) at 3 Tesla (3T) and digital subtraction angiography (DSA) for the detection and characterization of unruptured intracranial aneurysms (UIA). MATERIALS AND METHODS: This study has been approved by our local ethical committee. From February to August 2010, 40 consecutive patients with UIA contemporarily underwent MRA at 3T including time-of-flight (TOF-MRA) and contrast enhanced (CE-MRA) techniques and DSA. MR images were independently reviewed by 3 radiologists and DSA images were reviewed by 2 radiologists together. Interobserver and intertechnique agreements were assessed for aneurysm detection and characterization including maximal diameter, neck width and the presence of a bleb or a branch arising from the sac. RESULTS: DS angiography revealed 56 aneurysms. Mean sensitivity and positive predictive value of MRA were 91.4% and 93.4% respectively. For UIA < 3 mm and those ≥ 3 mm, MRA had a mean sensitivity of 74.1% and 100% respectively. Intertechnique and interobserver agreements were substantial for the measurement of UIA maximal diameter (mean κ, 0.607 and 0.601 respectively) and were moderate and fair for neck width measurement respectively (mean κ, 0.456 and 0.285 respectively). For bleb detection, intertechnique and interobserver agreements were fair and slight respectively (mean κ, 0.312 and 0.116 respectively) whereas both were slight for detection of branches arising from the sac (mean κ, 0.151 and 0.070 respectively). CONCLUSION: MR angiography at 3T has a high sensitivity for the detection of UIA. However, it remains significantly inferior to DSA for morphological characterization of UIA.

Normal hepatic parenchyma visibility and ADC quantification on diffusion-weighted MRI at 3 T: influence of age, gender, and iron content.

OBJECTIVES: To investigate how normal liver parenchyma visibility on 3 T diffusion-weighted images (DWI) and apparent diffusion coefficient (ADC) quantification are influenced by age, gender, and iron content. METHODS: Between February 2011 and April 2013, 86 patients (52 women) with normal livers who underwent respiratory-triggered abdominal 3 T DWI (b = 0, 150, 600, 1,000 s/mm(2)) were retrospectively included. Normal liver and spleen parenchyma visibility was scored independently by two readers. Correlations between visibility scores or ADC with age, gender, T2*, or recent serum ferritin (SF) were investigated. RESULTS: Liver visibility scores in b = 1,000 s/mm(2) images correlated with the age (Spearman R = -0.56 in women, -0.45 in men), T2* (R = 0.75) and SF (R = -0.64) and were significantly higher in women (P < 0.01). SF and T2* were within normal values (T2*: 13 - 31 ms, SF: 14 - 230 µg/L). Liver ADC correlated with visibility scores (R = 0.69) and T2* (R = 0.64) and was age- and gender-dependent. ADC ROI standard deviation negatively correlated with visibility scores (R = -0.65) and T2* (R = -0.62). The spleen visibility did not depend on age or gender. CONCLUSIONS: Normal liver parenchyma visibility in DWI is age- and gender-dependent, according to the iron content. Visibility scores and iron content significantly affect ADC quantification in the normal liver. KEY POINTS: Normal DWI liver visibility is gender-dependent and superior in women. In women, normal DWI liver visibility is superior before age 50 years. Normal DWI liver visibility negatively correlates with normal range iron content markers. Liver ADC quantification depends on liver iron content even within normal range. Normal liver T2* is age- and gender-dependent.

BOLD response to deviant face detection informed by P300 event-related potential parameters: a simultaneous ERP-fMRI study.

INTRODUCTION: Faces are multi-dimensional stimuli conveying parallel information about identity and emotion. Although event-related potential (ERP) studies have disclosed a P300 component in oddball responses to both deviant identity and emotional target faces, it is hypothesized that partially different neural processes should subtend emotion vs. identity within the core network of face processing. In the present study, we used simultaneous ERP-fMRI recordings and ERP-informed analysis of functional magnetic resonance imaging (fMRI) data to evidence the specific neural networks underlying P300 generation in response to different deviant emotional vs. identity faces. METHOD: 18 participants were scanned during a visual oddball task in which they had to detect 3 types of deviant faces representing a change in emotion-fear or happiness-or in identity, within a series of frequent neutral ones. Amplitude and latency parameters of the P300 component, recorded for each type of deviant faces, were used to constrain fMRI analyses. RESULTS: Analysis of fMRI data informed by single-trial parameters of the P300 component disclosed specific activation patterns for fearful, happy and identity deviant faces. For fearful faces, P300 amplitudes were associated with BOLD changes in the left fusiform gyrus whereas latencies were linked to left superior orbito-frontal and right fusiform activations. P300 amplitude modulations for happy deviant faces involved the left posterior cingulate gyrus and right parahippocampal regions whereas P300 latencies related to the right insula and left caudate regions. Finally, identity deviant faces were associated with widespread activities involving cortical and subcortical regions when P300 amplitudes were considered, and P300 latencies were associated with activity in right hippocampal/parahippocampal regions. DISCUSSION: Our results suggest the existence of differential cerebral functional processes involved in the responses to deviant face stimuli, depending on the quality of the deviance (fear vs. happiness vs. identity).

Language development at 2 years is correlated to brain microstructure in the left superior temporal gyrus at term equivalent age: a diffusion tensor imaging study.

This study aims at testing the hypothesis that neurodevelopmental abilities at age 2 years are related with local brain microstructure of preterm infants at term equivalent age. Forty-one preterm infants underwent brain MRI with diffusion tensor imaging sequences to measure mean diffusivity (MD), fractional anisotropy (FA), longitudinal and transverse diffusivity (λ// and λ[perpendicular]) at term equivalent age. Neurodevelopment was assessed at 2 years corrected age using the Bayley III scale. A voxel-based analysis approach, statistical parametric mapping (SPM8), was used to correlate changes of the Bayley III scores with the regional distribution of MD, FA, λ// and λ[perpendicular]. We found that language abilities are negatively correlated to MD, λ// and λ[perpendicular] in the left superior temporal gyrus in preterm infants. These findings suggest that higher MD, λ// and λ[perpendicular] values at term-equivalent age in the left superior temporal gyrus are associated with poorer language scores in later childhood. Consequently, it highlights the key role of the left superior temporal gyrus for the development of language abilities in children. Further studies are needed to assess on an individual basis and on the long term the prognostic value of brain DTI at term equivalent age for the development of language.

Comprehensive functional mapping scheme for non-invasive primary sensorimotor cortex mapping.

We introduce a novel multimodal scheme for primary sensorimotor hand area (SM1ha) mapping integrating multiple functional indicators from functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG). Ten right-handed healthy subjects (19-33 years; 5 females, 5 males) and four patients (24-64 years; 2 females, 2 males) suffering from space-occupying brain lesion close to the central sulcus were studied. Functional indicators of the SM1ha were obtained from block-design fMRI motor protocol, and six MEG protocols: somatosensory evoked fields to electrical median-nerve stimulation, mu-rhythm suppression (~10 and ~20 Hz), corticomuscular coherence, and corticokinematic coherence with and without finger contacts. To assess the spatial spread of the functional indicators, their coordinates were subjected to principal component analysis to produce a centered ellipsoid with axis along principal components. Five to seven functional indicators were obtained for each participant. In all participants, the ellipsoid co-localized with the anatomical SM1ha. In healthy subjects, 50-100% of functional indicators were located within 10 mm from the center of the ellipsoid. In patients, 17-100% of functional indicators were located within 10 mm from the center of the ellipsoid. In conclusion, the multimodal scheme proposed led to a functional mapping of SM1ha that co-localized with anatomical SM1ha in all participants. The spread of the SM1ha functional indicators in some patients with brain lesions highlights the potential benefit of the proposed multimodal approach to assess the reliability of the non-invasive SM1ha mapping.

Comparison of intra- and inter-patient intensity standardization methods for multi-parametric whole-body MRI.

Objective.To test and compare different intensity standardization approaches for whole-body multi-parametric MR images, aiming to compensate voxel intensity differences between scans. These differences, common for magnetic resonance imaging, pose problems in image quantification, assessment of changes between a baseline and follow-up scan, and hinder performance of image processing and machine learning algorithms.Approach.In this work, we present a comparison on the accuracy of intensity standardization approaches with increasing complexity, for intra- and inter-patient multi-parametric whole-body MRI. Several approaches were used: z-scoring of the intensities, piecewise linear mapping and deformable mapping of intensity distributions into established reference intensity space. For each method, the impact on standardization algorithm on the use of single image or average population distribution reference; as well as, whole image and region of interest were additionally investigated. All methods were validated on a data set of 18 whole-body anatomical and diffusion-weighted MR scans consisting of baseline and follow-up examinations acquired from advanced prostate cancer patients and healthy volunteers.Main results.The piecewise linear intensity standardisation approach provided the best compromise between standardization accuracy and method stability, with average deviations in intensity profile of 0.011-0.027 and mean absolute difference of 0.29-0.37 standard score (intra-patient) and 0.014-0.056 (inter-patient), depending on the type of used MR modality.Significance.Linear piecewise approaches showed the overall best performance across multiple validation metrics, mostly because of its robustness. The inter-patient standardization proved to perform better when using population average reference image; in contrary to intra-patient approach, where the best results were achieved by standardizing towards a reference image taken as the baseline scan.

Nonlinear microstructural changes in the right superior temporal sulcus and lateral occipitotemporal gyrus between 35 and 43 weeks in the preterm brain.

Using diffusion tensor imaging (DTI), we explored microstructural brain maturation in a population of 65 preterm neonates who underwent magnetic resonance imaging between 35 and 43 weeks of corrected gestational age. A voxel-based analysis approach, statistical parametric mapping (SPM8), was used to evidence the nonlinear changes with the corrected gestational age in the regional distribution of mean diffusivity (MD), fractional anisotropy (FA), longitudinal and transverse diffusivities (λ//and λ⊥). We found that FA changes nonlinearly with age around the right superior temporal sulcus and in the right lateral occipitotemporal gyrus, with FA decrease between 34 and 39 weeks followed by FA increase from 40 weeks to 43 weeks. Considering the key role of these brain areas in verbal and non-verbal communicative behaviors, the effect of these microstructural changes in terms of early social network functional maturation needs to be assessed by joint functional and anatomical studies.