Diffusional kurtosis imaging analysis in patients with hypertension

Magnetic Resonance Imaging in Childhood Primary Hypertension: Potential in the Study of Cognitive Outcomes

Primary hypertension in youth and young adulthood is associated with decreased neurocognitive test performance both in midlife and during youth itself, leading to concern of subsequent cognitive decline and dementia in later life. The early vascular effects of hypertension in youth are likely involved in the pathogenesis of hypertensive target organ damage to the brain, but the potential impact of antihypertensive treatment from youth on subsequent cognitive health is not known. This review will highlight the need to answer the question of whether treatment of hypertension from early in life would slow cognitive decline in adulthood, and will then outline, for the nonneurologist, magnetic resonance imaging techniques potentially useful in the study of the pathogenesis of decreased cognition in hypertensive youth and for use as potential biomarkers for early antihypertensive treatment interventions.

Bicarbonate, blood pressure, and executive function in pediatric CKD-is there a link?

BACKGROUND

In adult chronic kidney disease (CKD), metabolic acidosis is associated with diminished cognition, notably executive function (EF). Data from the Chronic Kidney Disease in Children (CKiD) study demonstrate a risk for impairment of EF, a finding associated with heightened blood pressure variability (BPV). We sought to determine whether low serum bicarbonate is also associated with performance on tests of EF in pediatric CKD and to investigate potential interaction with BPV.

METHODS

CKiD participants with serum bicarbonate, blood pressure, and selected cognitive measurements available were evaluated. An EF summary score was derived from scores on the Delis-Kaplan Executive Function System, Conners' Continuous Performance Test, and Digit Span Backwards subtest from the Wechsler Intelligence Scale for Children-IV-Integrated. Parents completed the Behavioral Rating Inventory of Executive Function (BRIEF) to yield a Global Executive Composite (GEC) score. Linear mixed models with bicarbonate and hypertension as predictors and linear regression with bicarbonate and BPV were used to predict EF level.

RESULTS

Data were available for 865 children. Twenty-two percent had low bicarbonate (CO₂ ≤ 20 mmol/L) at baseline. On multivariate analysis, there was no relationship between bicarbonate, hypertension, and EF. There was no significant CO₂×hypertension interaction found. A significant interaction (p = 0.01) between high CO₂ (≥ 26 mmol/L) and BPV was detected in the model with GEC as the EF outcome, indicating that while higher BPV was associated with worse EF in the low and normal CO₂ groups, higher BPV was associated with better EF in the high CO₂ group.

CONCLUSIONS

Our analyses revealed an interaction between one measure of BPV and low bicarbonate on neurocognition in pediatric CKD, suggesting a potential role for control of both bicarbonate and blood pressure in preserving cognition in early CKD. Further research is needed to confirm and further define this association.

Strong and specific associations between cardiovascular risk factors and white matter micro- and macrostructure in healthy aging

Cardiovascular health declines with age, increasing the risk of hypertension and elevated heart rate in middle and old age. Here, we used multivariate techniques to investigate the associations between cardiovascular health (diastolic blood pressure, systolic blood pressure, and heart rate) and white matter macrostructure (lesion volume and number) and microstructure (as measured by diffusion-weighted imaging) in the cross-sectional, population-based Cam-CAN cohort (N = 667, aged 18–88). We found that cardiovascular health and age made approximately similar contributions to white matter health and explained up to 56% of variance therein. Lower diastolic blood pressure, higher systolic blood pressure, and higher heart rate were each strongly, and independently, associated with white matter abnormalities on all indices. Body mass and exercise were associated with white matter health, both directly and indirectly via cardiovascular health. These results highlight the importance of cardiovascular risk factors for white matter health across the adult lifespan and suggest that systolic blood pressure, diastolic blood pressure, and heart rate affect white matter health via separate mechanisms.

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Cardiovascular health is related to white matter lesion burden and diffusivity.

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Low diastolic pressure, high systolic pressure, and higher heart rate contribute independently.

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Cardiovascular health and age explain up to 56% of variance in white matter health.

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The uncinate fasciculus, inferior fronto-occipital fasciculus, and forceps minor show most sensitivity.

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Lower BMI and more exercise may have protective effects.

Diffusion kurtosis imaging in the differential diagnosis of parotid gland disease and parotid adenolymphoma: preliminary results

OBJECTIVES

To study the value of diffusion kurtosis imaging (DKI) in diagnosis of parotid gland disease (PGD) with different pathological patterns and parotid adenolymphoma (PAL).

METHODS

57 patients with different kinds of PGD were enrolled and underwent DKI and conventional diffusion-weighted imaging (DWI). All patients were categorized into different groups according to their pathological patterns. The result of calculating the value of DKI-derived parameters (K_mean, K_rad, K_ax, D_mean, D_rad, D_ax, and FA) and apparent diffusion coefficient (ADC) of DWI were used to study their diagnostic accuracy in PGD with different pathological patterns. The binary logistic regression method was used to confirm clinical valuable diffusion parameters (obtained with DKI and DWI models) for diagnosing PAL. Using MedCalc 13.0, receiver operating characteristic (ROC) analysis was conducted to evaluate the diagnostic value of confirmed parameters based on the logistic regression equation.

RESULTS

Both DKI parameters and conventional ADC showed statistical significance in diagnosing PGD with different pathological patterns (p < .01). By using the DKI model, kurtosis coefficients showed higher diagnostic capability than diffusion coefficients ([K_mean+K_rad + K_ax] vs [D_mean +D_rad + D_ax]: 22 vs 15, p < .01) did in the differential diagnosis among different PGD groups. In the diagnosis of PAL among all PGD patterns, the ROC analysis demonstrated that the area under curve (AUC) FA +K_ax [0.881 ± 0.057 (0.824 to 0.938)] is higher than that when using FA [0.629 ± 0.095 (0.534 to 0.724)] and K_ax [0.800 ± 0.070 (0.730 to 0.870)] alone (p < .05), with sensitivity, specificity, accuracy, and both positive and negative predictive values of 71.43, 95.78, 91.77, 76.92, and 94.44%, respectively.

CONCLUSIONS

DKI showed higher diagnostic capacity in the differential diagnosis of PGD with different pathological patterns. Combined parameters of DKI can differentiate PAL from other PGD pathological patterns with a high degree of accuracy. This technique shows great potential for DKI in the differential diagnosis of PGD within a certain pathological category.

The Relationship between Neurite Density Measured with Confocal Microscopy in a Cleared Mouse Brain and Metrics Obtained from Diffusion Tensor and Diffusion Kurtosis Imaging

Purpose:

Diffusional kurtosis imaging (DKI) enables sensitive measurement of tissue microstructure by quantifying the non-Gaussian diffusion of water. Although DKI is widely applied in many situations, histological correlation with DKI analysis is lacking. The purpose of this study was to determine the relationship between DKI metrics and neurite density measured using confocal microscopy of a cleared mouse brain.

Methods:

One thy-1 yellow fluorescent protein 16 mouse was deeply anesthetized and perfusion fixation was performed. The brain was carefully dissected out and whole-brain MRI was performed using a 7T animal MRI system. DKI and diffusion tensor imaging (DTI) data were obtained. After the MRI scan, brain sections were prepared and then cleared using aminoalcohols (CUBIC). Confocal microscopy was performed using a two-photon confocal microscope with a laser. Forty-eight ROIs were set on the caudate putamen, seven ROIs on the anterior commissure, and seven ROIs on the ventral hippocampal commissure on the confocal microscopic image and a corresponding MR image. In each ROI, histological neurite density and the metrics of DKI and DTI were calculated. The correlations between diffusion metrics and neurite density were analyzed using Pearson correlation coefficient analysis.

Results:

Mean kurtosis (MK) (P = 5.2 × 10⁻⁹, r = 0.73) and radial kurtosis (P = 2.3 × 10⁻⁹, r = 0.74) strongly correlated with neurite density in the caudate putamen. The correlation between fractional anisotropy (FA) and neurite density was moderate (P = 0.0030, r = 0.42). In the anterior commissure and the ventral hippocampal commissure, neurite density and FA are very strongly correlated (P = 1.3 × 10⁻⁵, r = 0.90). MK in these areas were very high value and showed no significant correlation (P = 0.48).

Conclusion:

DKI accurately reflected neurite density in the area with crossing fibers, potentially allowing evaluation of complex microstructures.

Non-Gaussian diffusion alterations on diffusion kurtosis imaging in patients with early Alzheimer's disease

OBJECTIVE

To evaluate non-Gaussian diffusion changes of the whole-brain and its correlation with cognitive performance in patients with early Alzheimer's disease (AD), using diffusion kurtosis imaging (DKI).

METHODS

Twenty-six patients with early AD and twenty-six normal controls underwent diffusion imaging. Seven parametric maps were calculated from multiple b-value diffusion data, including mean kurtosis (MK), axial kurtosis (AK), radial kurtosis (RK), fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AxD) and radial diffusivity (RD). Voxel-based analyses were performed to evaluate the group difference between the AD patients and normal controls. Then correlation between the diffusion parameters (MK, FA and MD) and cognitive performance were analyzed in AD patients.

RESULTS

For AD patients, increased MD, AxD and RD were found in white matter (WM), including the genu of corpus callosum, bilateral cingulate bundle, bilateral temporal and frontal WM, and were also found in gray matter (GM), including the bilateral temporal GM, parahippocampal gyrus, hippocampus, cingulate gyrus, thalamus, and amygdala. These regions were partially overlapped with those showing decreased FA, MK, AK and RK. However, only kurtosis indices could detect the significant differences in the lentiform nucleus between AD patients and health control. DKI indices in AD patients significantly correlated with the clinical scores in genu of CC, cingulate bundle, temporal and frontal lobe, while the voxel number showing significant correlation with MK was more than that with FA and MD.

CONCLUSIONS

Early AD patients already have microstructural changes in both WM and GM. DKI can provide supplementary information in reflecting these changes and may be sensitive in diagnosing early AD.

Physics, Techniques and Review of Neuroradiological Applications of Diffusion Kurtosis Imaging (DKI)

In recent years many papers about diagnostic applications of diffusion tensor imaging (DTI) have been published. This is because DTI allows to evaluate in vivo and in a non-invasive way the process of diffusion of water molecules in biological tissues. However, the simplified description of the diffusion process assumed in DTI does not permit to completely map the complex underlying cellular components and structures, which hinder and restrict the diffusion of water molecules. These limitations can be partially overcome by means of diffusion kurtosis imaging (DKI). The aim of this paper is the description of the theory of DKI, a new topic of growing interest in radiology. DKI is a higher order diffusion model that is a straightforward extension of the DTI model. Here, we analyze the physics underlying this method, we report our MRI acquisition protocol with the preprocessing pipeline used and the DKI parametric maps obtained on a 1.5 T scanner, and we review the most relevant clinical applications of this technique in various neurological diseases.