Assessment of pharmacologically induced changes in canine kidney function by multiparametric magnetic resonance imaging and contrast enhanced ultrasound.

Introduction: Dynamic contrast-enhanced (DCE) MRI and arterial spin labeling (ASL) MRI enable non-invasive measurement of renal blood flow (RBF), whereas blood oxygenation level-dependent (BOLD) MRI enables non-invasive measurement of the apparent relaxation rate (R2*), an indicator of oxygenation. This study was conducted to evaluate the potential role of these MRI modalities in assessing RBF and oxygenation in dogs. The correlation between contrast-enhanced ultrasound (CEUS) and the MRI modalities was examined and also the ability of the MRI modalities to detect pharmacologically induced changes. Methods: RBF, using CEUS, ASL- and DCE-MRI, as well as renal oxygenation, using BOLD-MRI of eight adult beagles were assessed at two time-points, 2­3 weeks apart. During each time point, the anesthetized dogs received either a control (0.9% sodium chloride) or a dopamine treatment. For each time point, measurements were carried out over 2 days. An MRI scan at 3 T was performed on day one, followed by CEUS on day two. Results: Using the model-free model with caudal placement of the arterial input function (AIF) region of interest (ROI) in the aorta, the DCE results showed a significant correlation with ASL measured RBF and detected significant changes in blood flow during dopamine infusion. Additionally, R2* negatively correlated with ASL measured RBF at the cortex and medulla, as well as with medullary wash-in rate (WiR) and peak intensity (PI). ASL measured RBF, in its turn, showed a positive correlation with cortical WiR, PI, area under the curve (AUC) and fall time (FT), and with medullary WiR and PI, but a negative correlation with medullary rise time (RT). During dopamine infusion, BOLD-MRI observed a significant decrease in R2* at the medulla and entire kidney, while ASL-MRI demonstrated a significant increase in RBF at the cortex, medulla and the entire kidney. Conclusion: ASL- and BOLD-MRI can measure pharmacologically induced changes in renal blood flow and renal oxygenation in dogs and might allow detection of changes that cannot be observed with CEUS. However, further research is needed to confirm the potential of ASL- and BOLD-MRI in dogs and to clarify which analysis method is most suitable for DCE-MRI in dogs.

Optimization of Fair Arterial Spin Labeling Magnetic Resonance Imaging (ASL-MRI) for Renal Perfusion Quantification in Dogs: Pilot Study.

Arterial spin labeling (ASL) MRI allows non-invasive quantification of renal blood flow (RBF) and shows great potential for renal assessment. To our knowledge, renal ASL-MRI has not previously been performed in dogs. The aim of this pilot study was to determine parameters essential for ALS-MRI-based quantification of RBF in dogs: T1, blood (longitudinal relaxation time), λ (blood tissue partition coefficient) and TI (inversion time). A Beagle was scanned at 3T with a multi-TI ASL sequence, with TIs ranging from 250 to 2500 ms, to determine the optimal TI value. The T1 of blood for dogs was determined by scanning a blood sample with a 2D IR TSE sequence. The water content of the dog's kidney was determined by analyzing kidney samples from four dogs with a moisture analyzer and was subsequently used to calculate λ. The optimal TI and the measured values for T1,blood, and λ were 2000 ms, 1463 ms and 0.91 mL/g, respectively. These optimized parameters for dogs resulted in lower RBF values than those obtained from inline generated RBF maps. In conclusion, this study determined preliminary parameters essential for ALS-MRI-based RBF quantification in dogs. Further research is needed to confirm these values, but it may help guide future research.

Toward a marker of upper motor neuron impairment in amyotrophic lateral sclerosis: A fully automatic investigation of the magnetic susceptibility in the precentral cortex.

PURPOSE: Diagnostic work-up in motor neuron disease (MND) needs a quantitative biomarker of upper motor neuron (UMN) impairment. We investigated the susceptibility properties of the precentral cortex in a cohort of patients affected by Amyotrophic lateral sclerosis (ALS) to obtain a useful biomarker of UMN impairment in a fully automatic paradigm. MATERIALS AND METHODS: We retrospectively collected imaging and clinical data of 42 ALS patients who had undergone brain 3 T MRI including tridimensional T1-weighted and spoiled gradient-echo multi-echo T2-weighted images. We further acquired images from 23 healthy control (HC) volunteers. The precentral cortex was automatically segmented and the cortical thickness calculated. Histogram metrics (mean, median, standard deviation, skewness, kurtosis) derived from the quantitative susceptibility map (QSM) were extracted from the automatically segmented precentral cortex. Multivariate regression analyses were performed to identify the variables predicting the disease status (ALS vs HC), the Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised (ALSFRS-R) and the UMN score. RESULTS: A decreased cortical thickness (B = 9.40; Wald's test = 7.43; p = 0.006) and increased susceptibility skewness (B = -3.08; Wald's test = 4.36; p = 0.037) independently predicted ALS in a logistic regression model (χ2(3, N = 65) = 22.07, p < 0.001. No predictors of ALSFRS-R were identified. An increased susceptibility skewness (ß = 0.55; t = 4.23; p < 0.001) and longer disease duration (ß = 0.35; t = 2.67; p = 0.011) independently predicted a higher UMN score in a linear regression model (R2 = 0.32; p < 0.001). CONCLUSION: The susceptibility skewness might be an unbiased quantitative biomarker of UMN impairment in ALS patients.