Apparent Diffusion Coefficient In White Matter Research Articles

Apparent diffusion coefficient values of the white matter in magnetic resonance imaging of the neonatal brain may help predict outcome in congenital cytomegalovirus infection

BackgroundWhite matter change is a well-known abnormality in congenital cytomegalovirus (cCMV) infection, but grading remains challenging and clinical relevance unclear.ObjectiveTo investigate if quantitative measurement of white matter apparent diffusion coefficient (ADC) values in magnetic resonance imaging (MRI) of the neonatal brain can predict outcome in cCMV.Materials and methodsA retrospective, single-center observational study, including patients with cCMV who had a neonatal brain MRI with diffusion-weighted imaging, was performed between 2007 and 2020. Regions of interest were systematically placed in the white matter on the ADC maps. Two pediatric radiologists independently scored additional brain abnormalities. Outcome measures were neonatal hearing and cognitive and motor development. Statistical analysis included simple and penalized elastic net regression.ResultsNeonatal brain MRI was evaluated in 255 patients (median age 21 days, 25–75 percentiles: 14–28 days, 121 male). Gyral abnormalities were noted in nine patients (3.5%), ventriculomegaly in 24 (9.4%), and subependymal cysts in 58 (22.7%). General white matter ADC was significantly higher in patients with neonatal hearing loss and cognitive and motor impairment (P< 0.05). For neonatal hearing loss, simple logistic regression using only general white matter was the best prediction model, with a receiver operating characteristic area under the curve (AUC)=0.76. For cognitive impairment, interacting elastic net regression, including other brain abnormalities and frontoparietal white matter ADC, performed best, with AUC=0.89. For motor impairment, interacting elastic net regression, including other brain abnormalities and deep anterior frontal white matter performed best, with AUC=0.73.ConclusionNeonatal white matter ADC was significantly higher in patients with clinical impairments. Quantitative ADC measurement may be a useful tool for predicting clinical outcome in cCMV.Graphical

Feasibility study of super-resolution deep learning-based reconstruction using k-space data in brain diffusion-weighted images.

The purpose of this study is to evaluate the influence of super-resolution deep learning-based reconstruction (SR-DLR), which utilizes k-space data, on the quality of images and the quantitation of the apparent diffusion coefficient (ADC) for diffusion-weighted images (DWI) in brain magnetic resonance imaging (MRI). A retrospective analysis was performed on 34 patients who had undergone DWI using a 3T MRI system with SR-DLR reconstruction based on k-space data in August 2022. DWI was reconstructed with SR-DLR (Matrix = 684 × 684) and without SR-DLR (Matrix = 228 × 228). Measurements were made of the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) in white matter (WM) and grey matter (GM), and the full width at half maximum (FWHM) of the septum pellucidum. Two radiologists assessed image noise, contrast, artifacts, blur, and the overall quality of three image types using a four-point scale. Quantitative and qualitative scores between images with and without SR-DLR were compared using the Wilcoxon signed-rank test. Images with SR-DLR showed significantly higher SNRs and CNRs than those without SR-DLR (p < 0.001). No statistically significant variances were found in the apparent diffusion coefficients (ADCs) in WM and GM between images with and without SR-DLR (ADC in WM, p = 0.945; ADC in GM, p = 0.235). Moreover, the FWHM without SR-DLR was notably lower compared to that with SR-DLR (p < 0.001). SR-DLR has the potential to augment the quality of DWI in DL MRI scans without significantly impacting ADC quantitation.

Application value of 3D pCASL in early assessment of potential radiation encephalopathy in nasopharyngeal carcinoma patients undergoing radiotherapy.

The study explores the application value of three-dimensional arterial spin labeling magnetic resonance imaging (3D pCASL) in early assessment of radiation encephalopathy (REP) in patients with nasopharyngeal carcinoma (NPC). A retrospective analysis of 39 cases of NPC was performed. Routine enhanced MRI scan and 3D pCASL imaging were used to examine the apparent diffusion coefficient (ADC) and brain blood flow (CBF) before and after treatment with intensity-modulated radiotherapy (IMRT). Dosimetric analysis of irradiation was performed. Receiver operating characteristic curve (ROC) was used to analyze diagnostic performance of two imaging methods. There was no statistically significant difference between the two methods for the measurement of temporal white matter ADC, but statistically significant difference was found in CBF. 3D pCASL imaging showed more sensitivity, specificity and higher accuracy than conventional MRI enhanced scan in showing REP. The maximum dose of the temporal lobe was at the enhanced area. The present study demonstrates that 3D pCASL scan at month 3 can reflect blood flow perfusion differences in NPC patients after IMRT and can accurately assess the possibility of REP at early stage. Enhanced areas have a higher probability of REP than the surrounding areas. There is few magnetic resonance angiography studies used to evaluate arterial circulation on its application on potential REP after radiotherapy for NPC. In our study, we evaluate the application value of 3D pCASL in the early assessment of potential REP in patients with NPC after radiotherapy. The study was to provide an improved understanding of the early specific characteristics on MRI imaging and evolution of potential radiation encephalopathy using 3D pCASL technique, which can quantitatively evaluate the changes of blood flow in tissues at early stage and help to diagnose and treat potential radiation encephalopathy as early as possible.

Benign ve malign orbital lezyonların ayrımında difüzyon ağırlıklı MRG ve konvansiyonel MRG’nin tanısal değeri

Purpose: The aim of this study was to assess the role of diffusion-weighted imaging (DWI) and conventional magnetic resonance imaging (MRI) in the differentiation of benign and malignant orbital lesions. &#x0D; Materials and Methods: 43 patients (27 women and 16 men; mean age: 26.3±28.5) with orbital lesions were assessed with conventional MRI and DWI. The apparent diffusion coefficient (ADC) of the lesions was measured, and maximum ADC (ADCmax), mean ADC (ADCmean), minimum ADC (ADCmin), the ratio of ADCmean to cerebral white matter ADC (ADCmeanratio), and the ratio of ADCmin to cerebral white matter ADC (ADCminratio) were calculated. T1-weighted and T2-weighted imaging features and contrast enhancement patterns were determined. The diagnostic performances of ADC variables and conventional MRI features for the differentiation of benign and malignant orbital lesions were assessed.&#x0D; Results: ADCmean, ADCmin, ADCmeanratio, and ADCminratio of the malignant lesions were significantly lower than those of the benign ones . ADCmeanratio had the highest diagnostic performance with a sensitivity and specificity of 87.5% and 70.4% at a threshold of 1.27. Selecting a cut-off ADCmean of 0.97 × 10-3 mm2/s for differentiating benign and malignant lesions revealed 75% sensitivity and 74% specificity. Conventional MRI features were not associated with the malignant diagnosis).&#x0D; Conclusion: ADC values obtained from DWI contribute to the differentiation of benign and malignant orbital lesions.

Evaluation of Fetuses with Intrauterine Hydrocephaly with Diffusion-Weighted Imaging

Objective: Hydrocephaly is an important factor for neurological development. Microstructural changes of cerebral tissue are detected in diffusion-weighted imaging (DWI), and abnormal brain development can be detected early. In this study, it was aimed to evaluate fetuses with hydrocephaly by magnetic resonance imaging (MRI). Method: In our study, nineteen fetuses with hydrocephaly and twenty-two fetuses without any pathology were analyzed retrospectively. Apparent diffusion coefficient (ADC) of fetal brain frontal, parietal, temporal white matter, cerebellar hemisphere and pons was measured. Case and control groups were compared statistically. Results: When the individuals in the study and control groups were compared in terms of trimester, no significant difference was found (p>0.05). When the frontal, parietal and temporal white matter ADC values of the fetuses in both groups were compared, the difference between the groups was significant (p<0.05). Individuals in the study group also had lower ADC values. When the pons and cerebellum ADC values of the fetuses were compared, no significant difference was found between the groups (p>0.05). Conclusions: Hydrocephaly is one of the most common congenital anomalies. Increased cerebrospinal fluid (CSF) pressure causes parenchymal compression, thus reducing perfusion and ischemia. As a result of ischemia, lactate concentration increases and fluid transfers into the cell. Then, diffusion restriction and a decrease in ADC values occur. Measurement of cerebral ADC values gives information about the neurological development of fetuses with hydrocephaly and can provide early recognition of problems that may occur in the postnatal period.

Abstract TP97: White Matter And Deep Grey Matter Structural Variations In Childhood Moyamoya Disease

Background: Moyamoya disease is a progressive steno-occlusive arteriopathy that increases stroke risk. Clinically, cognitive decline is known to occur over time, even in the absence of stroke. MRI measures of cerebrovascular reactivity (CVR) provide an in vivo assessment of cerebrovascular reserve and stroke risk. Typically, in normal-appearing white matter (WM) lower (quantified as negative) CVR is associated with increased apparent diffusion coefficient (ADC). However, the association between negative CVR and ADC in children is not well understood. Objectives: To determine (i) whether negative CVR is associated with changes in ADC in normal-appearing WM of children with Moyamoya, ii) whether there is an association between CVR and ADC with structural damage to the brain (by measuring the volume of subcortical structures). Methods: Retrospective analysis of a consecutive cohort of nine children with Moyamoya (male = 4, median age = 12.1) with no history of stroke, and seven age and sex-matched controls. ADC values and fractional negativity (fneg), calculated from CVR parametric maps as the fraction of negative CVR voxels within a region of interest (ROI), were extracted from WM and subcortical GM ROIs. Volumes from the subcortical GM regions were extracted and normalized for head size. Analyses of differences was calculated per hemisphere (n=18, bilateral disease n = 4, unilateral n=5) and categorized as affected and unaffected and compared to controls. Results: Mean (m) ADC in WM of affected hemispheres (m=807.05, p&lt;0.01) and unaffected (m=814.68, p&lt;0.05) hemispheres were significantly larger compared to controls (m=761.04). A positive relationship was found between fneg and ADC in affected (r=0.37, p=0.24) and unaffected (r=0.26, p=0.62) hemispheres, but with no statistical significance. Increased ADC in the caudate was associated with smaller volume in the affected hemisphere of patients (r =-0.83, p=0.02). Conclusions: ADC in normal appearing WM in children with Moyamoya is elevated, and is associated with volume of the caudate in this cohort demonstrating the association between abnormal CVR, perfusion and structural damage in children with Moyamoya and no stroke.

Empirical validation of gradient field models for an accurate ADC measured on clinical 3T MR systems in body oncologic applications.

To empirically corroborate vendor-provided gradient nonlinearity (GNL) characteristics and demonstrate efficient GNL bias correction for human brain apparent diffusion coefficient (ADC) across 3T MR systems and spatial locations. Spatial distortion vector fields (DVF) were mapped in 3D using a surface fiducial array phantom for individual gradient channels on three 3T MR platforms from different vendors. Measured DVF were converted into empirical 3D GNL tensors and compared with their theoretical counterparts derived from vendor-provided spherical harmonic (SPH) coefficients. To illustrate spatial impact of GNL on ADC, diffusion weighted imaging using three orthogonal gradient directions was performed on a volunteer brain positioned at isocenter (as a reference) and offset superiorly by 10-17cm (>10% predicted GNL bias). The SPH tensor-based GNL correction was applied to individual DWI gradient directions, and derived ADC was compared with low-bias reference for human brain white matter (WM) ROIs. Empiric and predicted GNL errors were comparable for all three studied 3T MR systems, with <1.0% differences in the median and width of spatial histograms for individual GNL tensor elements. Median (±width) of ADC (10-3mm2/s) histograms measured at isocenter in WM reference ROIs from three MR systems were: 0.73±0.11, 0.71±0.14, 0.74±0.17, and at off-isocenters (before versus after GNL correction) were respectively 0.63±0.14 versus 0.72±0.11, 0.53±0.16 versus 0.74±0.18, and 0.65±0.16 versus 0.76±0.18. The phantom-based spatial distortion measurements validated vendor-provided gradient fields, and accurate WM ADC was recovered regardless of spatial locations and clinical MR platforms using system-specific tensor-based GNL correction for routine DWI.

Koroid Pleksus Ksantogranülomu: Bilgisayarlı Tomografi ve Manyetik Rezonans Görüntüleme Bulguları

INTRODUCTION: Seventy-five adult patients with retrospectively detected incidental choroid plexus xanthogranulomas (CPX) were evaluated with non-contrast brain computed tomography (CT) and contrast-enhanced brain magnetic resonance imaging (MRI) images. In this study, we aim to determine the imaging properties of CPX with CT and MRI, to evaluate the difference between white matter and CPX with diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC), and ensure its potential use in the follow-up and treatment of CPX patients. METHODS: In this study, lesions between 5-25 mm were evaluated. CPX and white matter ADC measurements were performed on CT and MRI images in all lesions. An independent sample t-test was used for statistics. Cases with a history of cranial operation and any malignancy were excluded due to the possibility of metastasis. RESULTS: Bilateral CPX was detected in 41 and unilateral CPX in 34 patients. On CT, bilateral CPX calcifications were observed in 21 and unilateral calcifications in 44 patients. Calcification was not observed in brain CT in 10 patients. ADC (apparent diffusion coefficients) measurement was made from the widest and non-calcific parts of all lesions. ADC measurements were between 1.33-1.69x10-3/mm2/s and the mean value was 1.48x10-3/mm2/s. In all cases, the ADC value was lower relative to the white matter. ADC value was found to be higher and closer to the white matter ADC values than cases with a homogenous appearance in CPX patients with heterogeneous internal structure. DISCUSSION AND CONCLUSION: ADC value is useful in the diagnosis of CPX. In conclusion, the follow-up of the ADC value is useful in the diagnosis and follow-up of CPX.

Multishot diffusion‐prepared magnitude‐stabilized balanced steady‐state free precession sequence for distortion‐free diffusion imaging

To develop and evaluate a multishot diffusion-prepared (DP) magnitude-stabilized balanced steady-state free precession (bSSFP) diffusion imaging sequence with improved geometric fidelity. A signal spoiler (magnitude stabilizer; MS) was implemented in a DP-bSSFP diffusion sequence. Effects of magnitude stabilizers with respect to phase errors were simulated using Bloch simulation. Phantom study was conducted to compare the apparent diffusion coefficient (ADC) accuracy and geometric reliability, quantified using target registration error (TRE), with diffusion-weighted single-shot echo-planar imaging (DW-ssEPI). Six volunteers were recruited. DW-ssEPI, DP-bSSFP with and without ECG triggering, and DP-MS-bSSFP with and without ECG triggering were acquired 10 times with b = 500 s/mm2 in a single-shot manner to evaluate magnitude variability. Diffusion trace images and diffusion tensor images were acquired using a 4-shot DP-MS-bSSFP. Simulation showed that the DP-MS-bSSFP approach is insensitive to phase errors. The DP-MS-bSSFP approach had satisfactory ADC accuracy on the phantom with <5% difference with DW-ssEPI. The mean/max TRE for DW-ssEPI was 2.31/4.29 mm and was 0.51/1.20 mm for DP-MS-bSSFP. In the repeated single-shot study, DP-bSSFP without ECG triggering had severe signal void artifacts and exhibited a nonrepeatable pattern, which can be partially mitigated by ECG triggering. Adding the MS provided stable signal magnitude across all repetitions. High-quality ADC maps and color-coded fractional anisotropy maps were generated using the 4-shot DP-MS-bSSFP. The mean/max TRE was 2.89/10.80 mm for DW-ssEPI and 0.59/1.69 mm for DP-MS-bSSFP. Good agreements of white matter ADC, cerebrospinal fluid ADC, and white matter fractional anisotropy value were observed between DP-MS-bSSFP and DW-ssEPI. The proposed DP-MS-bSSFP approach provided high-quality diffusion-weighted and diffusion-tensor images with minimal geometric distortion.

Improving apparent diffusion coefficient accuracy on a compact 3T MRI scanner using gradient nonlinearity correction.

Gradient nonlinearity (GNL) leads to biased apparent diffusion coefficients (ADCs) in diffusion-weighted imaging. A gradient nonlinearity correction (GNLC) method has been developed for whole body systems, but is yet to be tested for the new compact 3T (C3T) scanner, which exhibits more complex GNL due to its asymmetrical design. To assess the improvement of ADC quantification with GNLC for the C3T scanner. Phantom measurements and retrospective analysis of patient data. A diffusion quality control phantom with vials containing 0-30% polyvinylpyrrolidone in water was used. For in vivo data, 12 patient exams were analyzed (median age, 33). Imaging was performed on the C3T and two commercial 3T scanners. A clinical DWI (repetition time [TR] = 10,000 msec, echo time [TE] = minimum, b = 1000 s/mm2 ) sequence was used for phantom imaging and 10 patient cases and a clinical DTI (TR = 6000-10,000 msec, TE = minimum, b = 1000 s/mm2 ) sequence was used for two patient cases. The 0% vial was measured along three orthogonal axes, and at two different temperatures. The ADC for each concentration was compared between the C3T and two whole-body scanners. Cerebrospinal fluid and white matter ADCs were quantified for each patient and compared to values in literature. Paired t-test and two-way analysis of variance (ANOVA). For all PVP concentrations, the corrected ADC was within 2.5% of the reference ADC. On average, the ADC of cerebrospinal fluid and white matter post-GNLC were within 1% and 6%, respectively, of values reported in the literature and were significantly different from the uncorrected data (P < 0.05). This study demonstrated that GNL effects were more severe for the C3T due to the asymmetric gradient design, but our implementation of a GNLC compensated for these effects, resulting in ADC values that are in good agreement with values from the literature. 4 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;48:1498-1507.

Importance of Fractional b Value for Calculating Apparent Diffusion Coefficient in DWI.

The purpose of this study is to examine how the fractional b value affects the calculation of apparent diffusion coefficient (ADC) using DWI. The fractional b value is the point of intersection between the fast and slow components of biexponential decay in DWI. Human brains were imaged using multiple b values on echo-planar DWI. The ADCs of white matter, gray matter, and thalamus were calculated using the combination of b values by two-point and multipoint methods, and the characteristics of each ADC value were compared. When the two selected points for calculation were smaller than the fractional b value (b = 1700 s/mm2), the ADC value was 0.0007-0.0008 mm2/s, but when the two points used for calculation were greater than the fractional b value, the ADC value was 0.0003-0.0004 mm2/s. When a range of b values was included in the fast and slow components by use of the multipoint method, the ADC value showed a statistically significant increase as the number of multiple b values increased. The ADC value fluctuated when the b values used for calculation were higher than the fractional b value. Therefore, it is important to determine the fractional b value of the target tissue.

Effects of Posthemorrhagic Ventricular Dilatation in the Preterm Infant on Brain Volumes and White Matter Diffusion Variables at Term-Equivalent Age

To evaluate the differential impact of germinal matrix-intraventricular hemorrhage (GMH-IVH) and posthemorrhagic ventricular dilatation (PHVD) on brain and cerebrospinal fluid (CSF) volumes and diffusion variables in preterm born infants at term-equivalent age (TEA). Nineteen infants (gestational age <31weeks) with GMH-IVH grade II-III according to Papile etal and subsequent PHVD requiring intervention were matched against 19 controls with GMH-IVH grade II but no PHVD and 19 controls without GMH-IVH. Outcome variables on magnetic resonance imaging (MRI) including diffusion weighted imaging at TEA were volumes of white matter, cortical gray matter, deep gray matter, brainstem, cerebellum, ventricles, extracerebral CSF, total brain tissue, and intracranial volume (ICV), as well as white matter and cerebellar apparent diffusion coefficients (ADCs). Effects of GMH-IVH and PHVD on TEA-MRI measurements were evaluated using multivariable regression analysis. Brain and CSF volumes were adjusted for ICV to account for differences in bodyweight at TEA-MRI and ICV between cases and controls. PHVD was independently associated with volumes of deep gray matter (β [95% CI]: -1.4cc [-2.3; -.5]), cerebellum (-2.7cc [-3.8; -1.6]), ventricles (+12.7cc [7.9; 17.4]), and extracerebral CSF (-11.2cc [-19.2; -3.3]), and with ADC values in occipital, parieto-occipital, and parietal white matter (β: +.066-.119×10(-3)mm(2)/s) on TEA-MRI (P<.05). No associations were found between GMH-IVH grade II-III and brain and CSF volumes or ADC values at TEA. PHVD was negatively related to deep gray matter and cerebellar volumes and positively to white matter ADC values on TEA-MRI, despite early intervention for PHVD in the majority of the infants. These relationships were not observed for GMH-IVH.

Relationship between gestational age and apparent diffusion coefficient values in different regions of fetal brain from middle to late trimester

To analyze the relationship between gestational age and apparent diffusion coefficient (ADC) values in different regions of fetal brain from middle to late trimester. DW images performed in 70 singleton non-sedated fetuses with questionably abnormal results on sonography and normal fetal MR imaging results were retrospectively reviewed. The median gestational age was 32.4 weeks (range, 24-38).With the formula of ADC = ln (S600/S0)/(B0-B600), the mean ADC values were obtained for fetal parietal white matter (WM), frontal WM, temporal WM, occipital WM, pons, cerebellum, basal ganglia and thalamus. The relationship of mean ADC values in different regions with gestational age was analyzed with linear regression. The mean ADC values were 1.77 ± 0.32 mm(2)/s (SD) in fetal parietal white matter (WM), 1.71 ± 0.32 mm(2)/s in occipital WM, 1.31 ± 0.18 mm(2)/s in thalamus, 1.34 ± 0.15 mm(2)/s in basal ganglia. And the mean ADC values in cerebellum, pons, frontal WM and temporal WM were 1.17 ± 0.16, 1.41 ± 0.18, 1.87 ± 0.18 and 1.74 ± 0.19 mm(2)/s respectively. A significant negative correlation between ADC values and gestational age was found for parietal WM, occipital WM, pons, cerebellum, basal ganglia and thalamus (P < 0.05). Frontal WM ADC (P > 0.05) and temporal WM ADC (P = 0.05) did not significantly change with gestational age whereas only a downward trend was present. The correlation coefficient (r) and coefficient of regression (b) were 0.420 and -0.045 in parietal WM; 0.470 and -0.052 in occipital WM; 0.370 and -0.027 in cerebellum; 0.027 and -0.020 in pons; 0.320 and -0.027 in thalamus; 0.300 and -0.021 in basal ganglia. The mean ADC values peaked in frontal WM and lowest in pons. The mean ADC values in white matter were higher than those in deep gray nuclei, cerebellum and pons.With the development of fetal brain,ADC values declined the fastest in cerebellum and occipital WM, followed by basal ganglia and thalamus. Regional differences in non-sedated fetal brain ADC values and their evolutions with gestational age are likely to reflect variations in brain maturation.

Stroke Assessment With Diffusional Kurtosis Imaging

Despite being the gold standard technique for stroke assessment, conventional diffusion MRI provides only partial information about tissue microstructure. Diffusional kurtosis imaging is an advanced diffusion MRI method that yields, in addition to conventional diffusion information, the diffusional kurtosis, which may help improve characterization of tissue microstructure. In particular, this additional information permits the description of white matter (WM) in terms of WM-specific diffusion metrics. The goal of this study is to elucidate possible biophysical mechanisms underlying ischemia using these new WM metrics. We performed a retrospective review of clinical and diffusional kurtosis imaging data of 44 patients with acute/subacute ischemic stroke. Patients with a history of brain neoplasm or intracranial hemorrhages were excluded from this study. Region of interest analysis was performed to measure percent change of diffusion metrics in ischemic WM lesions compared with the contralateral hemisphere. Kurtosis maps exhibit distinct ischemic lesion heterogeneity that is not apparent on apparent diffusion coefficient maps. Kurtosis metrics also have significantly higher absolute percent change than complementary conventional diffusion metrics. Our WM metrics reveal an increase in axonal density and a larger decrease in the intra-axonal (Da) compared with extra-axonal diffusion microenvironment of the ischemic WM lesion. The well-known decrease in the apparent diffusion coefficient of WM after ischemia is found to be mainly driven by a significant drop in the intra-axonal diffusion microenvironment. Our results suggest that ischemia preferentially alters intra-axonal environment, consistent with a proposed mechanism of focal enlargement of axons known as axonal swelling or beading.

Mapping white matter diffusion and cerebrovascular reactivity in carotid occlusive disease

To characterize the relationship between cerebrovascular reactivity (CVR) and white matter (WM) diffusion in patients with internal carotid artery (ICA) occlusive disease. In this exploratory observational study, 41 patients with severe stenosis or occlusion of the extracranial ICA and 12 healthy control subjects underwent CVR mapping using the fMRI response to hypercapnia. Conventional anatomic and diffusion-weighted MRI sequences were used to calculate maps of the apparent diffusion coefficient (ADC) and to exclude areas of previous ischemic injury. In all subjects, ADC was compared between WM with positive and negative CVR. In 27 patients with unilateral ICA involvement, ADC and CVR were compared between ipsilateral and contralateral WM while covarying for relevant clinical risk factors. In patients with bilateral disease and in the ipsilateral hemisphere of patients with unilateral disease, negative CVR was associated with increased WM ADC (p < 0.01 and p < 0.005, respectively). In patients with unilateral disease, the ipsilateral CVR deficit was correlated with the degree of hemispheric WM ADC elevation (p < 0.005). ADC elevation remained significant after correction for potential confounding risk factors. CVR impairment is associated with ADC elevation in normal-appearing WM of patients with severe stenosis or occlusion of the extracranial ICA. This finding is consistent with the presence of early, low-grade ischemic injury.

Magnetic resonance quantification of water and metabolites in the brain of cirrhotics following induced hyperammonaemia

Hepatic encephalopathy (HE) is now thought to be caused by cerebral oedema although the precise pathogenesis is uncertain. We hypothesised that if ammonia is a key factor, induced hyperammonaemia would lead to transient changes in brain water distribution and metabolite concentration, detectable by diffusion tensor imaging (DTI) and magnetic resonance spectroscopy (MRS). Thirteen cirrhotic patients being evaluated for liver transplantation were challenged with 54 g of equal parts of threonine, serine, and glycine. Conventional magnetic resonance imaging was performed to exclude structural lesions and localise regions of interest. DTI was used to generate white matter apparent diffusion coefficient (ADC) maps and proton MRS to measure brain metabolite concentrations before and after the challenge. The challenge caused a mean (±SD) rise in blood ammonia of 58 (±41) μmol/L, which was accompanied by a significant 9% increase in ADC (p=0.004). Increased ADC significantly correlated with blood ammonia (r=0.58, p=0.04). The change in ammonia levels also correlated with the increase in glutamine levels (r=0.78, p=0.002). Myo-inositol concentration decreased significantly by 0.7 (±0.7)mMol/L between scans and this correlated with the mean difference in ADC (r=0.59, p<0.04). These results show that ammonia can directly drive changes in brain water distribution as a mechanism for cerebral oedema development. Since cerebral astrocytes contain glutamine synthetase, our MRS data suggest intracerebral formation of glutamine from ammonia. The rapid decrease in myo-inositol indicates that this organic osmolyte plays a protective role in HE by release from astrocytes in order to maintain cell volume.

Diffusion-Weighted Imaging Predicts Cognition in Pediatric Brain Injury

Apparent diffusion coefficient maps from diffusion-weighted imaging predict gross neurologic outcome in adults with traumatic brain injury. Few studies in children have been reported, and none have used apparent diffusion coefficient maps to predict long-term (>1 year) neurocognitive outcomes. In this study, pooled regional and total brain diffusion coefficients were used to predict long-term outcomes in 17 pediatric brain injury patients. Apparent diffusion coefficient values were grouped into peripheral and deep gray and white matter, posterior fossa, and total brain. Regions of interest excluded areas that appeared abnormal on T(2)-weighted images. Apparent diffusion coefficient values from peripheral regions were inversely correlated with cognitive functioning. No significant correlations were apparent between the cognitive scores and apparent diffusion coefficient values for deep tissue or the posterior fossa. Regression analyses suggested that combined peripheral gray and white matter apparent diffusion coefficients explained 42% of the variance in the combined neurocognitive index. Peripheral gray diffusion coefficients alone explained an additional 20% of variance after accounting for clinical variables. These results suggest that obtaining apparent diffusion coefficient values, specifically from peripheral brain regions, may predict long-term outcome after pediatric brain injury. Discrepancies in the literature on this topic, as well as possible explanations, including sampling and clinical considerations, are discussed.

T2 at MR Imaging Is an Objective Quantitative Measure of Cerebral White Matter Signal Intensity Abnormality in Preterm Infants at Term-equivalent Age

To compare quantitative T2 relaxometry of cerebral white matter (WM) with qualitative assessment of conventional T2-weighted magnetic resonance (MR) images, to assess the relationship between cerebral WM T2 and region-specific apparent diffusion coefficient (ADC), and to examine WM T2 regional variation in preterm infants at term. The local ethical committee granted ethical permission for this study; informed parental consent was obtained for each infant. Sixty-two preterm infants born at less than 32 weeks gestation and nine control infants were examined at 1.5 T; T2-weighted fast spin-echo MR images, T2 relaxometry data, and diffusion-weighted MR images were acquired. Conventional T2-weighted MR images were assessed by a pediatric neuroradiologist for diffuse excessive high signal intensity (DEHSI) in WM. Regions of interest were positioned in frontal WM, central WM, and posterior WM at the level of the centrum semiovale. In preterm infants at term, T2 was longer in all WM regions than in control infants; in infants with DEHSI, T2 was longer than in infants without DEHSI and control infants, with posterior WM T2 being longer than central or frontal WM T2. In control infants, T2 was similar in all WM regions. Frontal and posterior WM ADCs were higher in preterm infants at term than in control infants. Cerebral WM T2 is an objective quantitative measurement that can easily and rapidly be obtained during clinical MR imaging in preterm infants at term.

Normative Apparent Diffusion Coefficient Values in the Developing Fetal Brain

Previous studies of diffusion-weighted imaging (DWI) in fetuses are limited. Because of the need for normative data for comparison with young fetuses and preterm neonates with suspected brain abnormalities, we studied apparent diffusion coefficient (ADC) values in a population of singleton, nonsedated, healthy fetuses. DWI was performed in 28 singleton nonsedated fetuses with normal or questionably abnormal results on sonography and normal fetal MR imaging results; 10 fetuses also had a second fetal MR imaging, which included DWI. ADC values in the periatrial white matter (WM), frontal WM, thalamus, basal ganglia, cerebellum, and pons were plotted against gestational age and analyzed with linear regression. We compared mean ADC in different regions using the Tukey Honestly Significant Difference test. We also compared rates of decline in ADC with increasing gestational age across different areas by using the t test with multiple comparisons correction. Neurodevelopmental outcome was assessed. Median gestational age was 24.28 weeks (range, 21-33.43 weeks). Results of all fetal MR imaging examinations were normal, including 1 fetus with a normal variant of a cavum velum interpositum. ADC values were highest in the frontal and periatrial WM and lowest in the thalamus and pons. ADC declined with increasing gestational age in periatrial WM (P = .0003), thalamus (P < .0001), basal ganglia (P = .0035), cerebellum (P < .0001), and pons (P = .024). Frontal WM ADC did not significantly change with gestational age. ADC declined fastest in the cerebellum, followed by the thalamus. Regional differences in nonsedated fetal ADC values and their evolution with gestational age likely reflect differences in brain maturation and are similar to published data in premature neonates.

Cognitive function correlates with frontal white matter apparent diffusion coefficients in patients with leukoaraiosis

Diffusion weighted imaging (DWI) displays a high sensitivity to white matter changes, even in areas where no lesions are visible. Correlation with vascular risk factors and cognitive dysfunction seems to be feasible using this technique. We aimed to test relations between age, blood pressure and cognitive function,with lesion load and average Apparent Diffusion Coefficient (ADC) values in lesioned (LWM) and in normal appearing white matter (NAWM), in patients with age related white matter lesions (ARWML). Subjects were 29 patients (mean age 72.6 +/- 5.2 years) with different severity of ARWML on MRI and no (or mild) disability assessed by the Instrumental Activities of Daily Living Scale. Imaging lesion load was quantified in bilateral frontal, temporal, parieto-occipital, basal ganglia and infratentorial regions, using a simple visual rating scale; ADC was measured bilaterally in Regions of Interest in parieto-occipital and frontal NAWM, and in frontal periventricular LWM. Neuropsychological examination consisted of Raven Colored Progressive Matrices, Rey's Complex Figure, Digit Canceling. Symbol digit Substitution, Inverse Digit Repetition and Verbal Fluency tests. Visual scales scores and ADC were significantly higher in frontal and parieto-occipital regions. Both were significantly correlated to age and blood pressure, in frontal (visual scale scores and ADC) and parieto-occipital regions (ADC). Attention skills were negatively correlated to ADC in LWM and NAWM in frontal regions and with frontal region visual scale scores. Our findings suggest that severity of white matter ischemic changes is correlated with worse cognitive function, as well as advanced age and higher blood pressure.A higher vulnerability of frontal white matter to vascular disease seems to play an important role in executive dysfunction, mainly determined by impairment of attentional skills.DWI results suggest this could be true even for NAWM.