Medicine and Radiology - Research Publications
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ItemA continuum of T-2(*) components: Flexible fast fraction mapping in sodium MRI(WILEY, 2019-06-01)PURPOSE: Parameter mapping in sodium MRI data is challenging due to inherently low SNR and spatial resolution, prompting the need to employ robust models and estimation techniques. This work aims to develop a continuum model of sodium T2* -decay to overcome the limitations of the commonly employed bi-exponential models. Estimates of mean T2* -decay and fast component fraction in tissue are emergent from the inferred continuum model. METHODS: A closed-form continuum model was derived assuming a gamma distribution of T2* components. Sodium MRI was performed on four healthy human subjects and a phantom consisting of closely packed vials filled with an aqueous solution of varying sodium and agarose concentrations. The continuum model was applied to the phantom and in vivo human multi-echo 7T data. Parameter maps by voxelwise model-fitting were obtained. RESULTS: The continuum model demonstrated comparable estimation performance to the bi-exponential model. The parameter maps provided improved contrast between tissue structures. The fast component fraction, an indicator of the heterogeneity of localised sodium motion regimes in tissue, was zero in CSF and high in WM structures. CONCLUSIONS: The continuum distribution model provides high quality, high contrast parameter maps, and informative voxelwise estimates of the relative weighting between fast and slow decay components.
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ItemZero-gradient-excitation ramped hybrid encoding (zG(RF)-RHE) sodium MRI(WILEY, 2019-02-01)PURPOSE: Fast bi-exponential transverse signal decay compounds sodium image quality. This work aims at enhancing image characteristics using a special case of ramped hybrid encoding (RHE). Zero-gradient-excitation (zGRF )-RHE provides (1) gradient-free excitation for high flip angle, artifact-free excitation profiles and (2) gradient ramping during dead-time for the optimization of encoding time (tenc ) to reduce T2* signal decay influence during acquisition. METHODS: Radial zGRF -RHE and standard radial UTE were investigated over a range of receiver bandwidths in simulations, phantom and in vivo brain experiments. Central k-space in zGRF -RHE was acquired through single point measurements at the minimum achievable TE. T2* blurring artifacts and image SNR and CNR were assessed. RESULTS: zGRF -RHE enabled 90° flip angle artifact-free excitation, whereas gradient pre-ramping provided greater tenc efficiency for any readout bandwidths. Experiments confirmed simulation results, revealing sharper edge characteristics particularly at short readout durations (TRO ). Significant SNR improvements of up to 4.8% were observed for longer TRO . CONCLUSION: zGRF -RHE allows for artifact-free high flip angle excitation with time-efficient encoding improving on image characteristics. This hybrid encoding concept with gradient pre-ramping is trajectory independent and can be introduced in any center-out UTE trajectory design.
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ItemSocial Isolation Alters Social and Mating Behavior in the R451C Neuroligin Mouse Model of Autism(HINDAWI LTD, 2017-01-01)Autism spectrum disorder (ASD) is a neurodevelopmental disorder typified by impaired social communication and restrictive and repetitive behaviors. Mice serve as an ideal candidate organism for studying the neural mechanisms that subserve these symptoms. The Neuroligin-3 (NL3) mouse, expressing a R451C mutation discovered in two Swedish brothers with ASD, exhibits impaired social interactions and heightened aggressive behavior towards male mice. Social interactions with female mice have not been characterized and in the present study were assessed in male NL3R451C and WT mice. Mice were housed in social and isolation conditions to test for isolation-induced increases in social interaction. Tests were repeated to investigate potential differences in interaction in naïve and experienced mice. We identified heightened interest in mating and atypical aggressive behavior in NL3R451C mice. NL3R451C mice exhibited normal social interaction with WT females, indicating that abnormal aggressive behavior towards females is not due to altered motivation to engage. Social isolation rearing heightened interest in social behavior in all mice. Isolation housing selectively modulated the response to female pheromones in NL3R451C mice. This study is the first to show altered mating behavior in the NL3R451C mouse and has provided new insights into the aggressive phenotype in this model.