About

The Laboratory of Mathematics in Imaging (LMI) is focused on the application of mathematical theory, analysis, modeling, and signal processing to medical imaging. Research projects within the group cover both novel theoretical contributions and translational clinical efforts. The research team combine strengths in computer science and mathematics with radiology, neuroscience, and novel MRI sequence developmentLearn more

Recent Publications

Space-time variant weighted regularization in compressed sensing cardiac cine MRI

Godino-Moya A, Royuela-Del-Val J, Usman M, Menchón-Lara R-M, Martín-Fernández M, Prieto C, Alberola-López C. Space-time variant weighted regularization in compressed sensing cardiac cine MRI. Magn Reson Imaging. 2019;58 :44-55.Abstract
PURPOSE: To analyze the impact on image quality and motion fidelity of a motion-weighted space-time variant regularization term in compressed sensing cardiac cine MRI. METHODS: k-t SPARSE-SENSE with temporal total variation (tTV) is used as the base reconstruction algorithm. Motion in the dynamic image is estimated by means of a robust registration technique for non-rigid motion. The resulting deformation fields are used to leverage the regularization term. The results are compared with standard k-t SPARSE-SENSE with tTV regularization as well as with an improved version of this algorithm that makes use of tTV and temporal Fast Fourier Transform regularization in x-f domain. RESULTS: The proposed method with space-time variant regularization provides higher motion fidelity and image quality than the two previously reported methods. Difference images between undersampled reconstruction and fully sampled reference images show less systematic errors with the proposed approach. CONCLUSIONS: Usage of a space-time variant regularization offers reconstructions with better image quality than the state of the art approaches used for comparison.
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Comparison of basis functions and q-space sampling schemes for robust compressed sensing reconstruction accelerating diffusion spectrum imaging

Tobisch A, Schultz T, Stirnberg R, Varela-Mattatall G, Knutsson H, Irarrázaval P, Stöcker T. Comparison of basis functions and q-space sampling schemes for robust compressed sensing reconstruction accelerating diffusion spectrum imaging. NMR Biomed. 2019;32 (3) :e4055.Abstract
Time constraints placed on magnetic resonance imaging often restrict the application of advanced diffusion MRI (dMRI) protocols in clinical practice and in high throughput research studies. Therefore, acquisition strategies for accelerated dMRI have been investigated to allow for the collection of versatile and high quality imaging data, even if stringent scan time limits are imposed. Diffusion spectrum imaging (DSI), an advanced acquisition strategy that allows for a high resolution of intra-voxel microstructure, can be sufficiently accelerated by means of compressed sensing (CS) theory. CS theory describes a framework for the efficient collection of fewer samples of a data set than conventionally required followed by robust reconstruction to recover the full data set from sparse measurements. For an accurate recovery of DSI data, a suitable acquisition scheme for sparse q-space sampling and the sensing and sparsifying bases for CS reconstruction need to be selected. In this work we explore three different types of q-space undersampling schemes and two frameworks for CS reconstruction based on either Fourier or SHORE basis functions. After CS recovery, diffusion and microstructural parameters and orientational information are estimated from the reconstructed data by means of state-of-the-art processing techniques for dMRI analysis. By means of simulation, diffusion phantom and in vivo DSI data, an isotropic distribution of q-space samples was found to be optimal for sparse DSI. The CS reconstruction results indicate superior performance of Fourier-based CS-DSI compared to the SHORE-based approach. Based on these findings we outline an experimental design for accelerated DSI and robust CS reconstruction of the sparse measurements that is suitable for the application within time-limited studies.
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Diffusion tensor distribution imaging

Topgaard D. Diffusion tensor distribution imaging. NMR Biomed. 2019 :e4066.Abstract
Conventional diffusion MRI yields voxel-averaged parameters that suffer from ambiguities for heterogeneous anisotropic materials such as brain tissue. Using principles from solid-state NMR spectroscopy, we have previously introduced the shape of the diffusion encoding tensor as a separate acquisition dimension that disentangles isotropic and anisotropic contributions to the observed diffusivities, thereby allowing for unconstrained data inversion into diffusion tensor distributions with "size," "shape," and orientation dimensions. Here we combine our recent non-parametric data inversion algorithm and data acquisition protocol with an imaging pulse sequence to demonstrate spatial mapping of diffusion tensor distributions using a previously developed composite phantom with multiple isotropic and anisotropic components. We propose a compact format for visualizing two-dimensional arrays of the distributions, new scalar parameters quantifying intra-voxel heterogeneity, and a binning procedure giving maps of all relevant parameters for each of the components resolved in the multidimensional distribution space.
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HBV infection suppresses the expression of inflammatory macrophage miR‑210

Li F, Bian H, Wang W, Ning L, Xu M, Sun S, Ren W, Qin C, Qi J. HBV infection suppresses the expression of inflammatory macrophage miR‑210. Mol Med Rep. 2019;19 (3) :1833-1839.Abstract
It has been previously reported that hepatitis B e‑antigen (HBeAg) induces microRNA (miR)‑155 expression and promotes liver injury by increasing inflammatory cytokine production in macrophages. Moreover, it was previously demonstrated that miR‑210 alleviates lipopolysaccharide‑stimulated proinflammatory cytokine production in macrophages. In addition, accumulating evidence suggests that miR‑210 is able to suppress hepatitis B virus (HBV) replication in HepG2.2.15 cells. However, it remains unclear whether miR‑210, similar to miR‑155, affects the progress of hepatitis B by regulating macrophage function. Reverse transcription‑quantitative polymerase chain reaction analysis was used to detect miR‑210 levels in serum and cells. HBV‑associated antigens stimulated different types of macrophages and facilitated the observation of the effects of these antigens on miR‑210 expression in macrophages. Co‑culture of peripheral blood monocytes from healthy controls and the serum of patients with chronic hepatitis B (CHB) was conducted to evaluate the effect of HBV‑associated elements in the serum on the expression of the macrophage miR‑210 in vivo. It was observed that miR‑210 expression levels were decreased in the peripheral blood monocytes (PBMs) and serum of patients with CHB and negatively associated with serum alanine aminotransferase and aspartate aminotransferase, but not other clinical parameters including hepatitis B surface antigen (HBsAg), HBeAg, anti‑HBe antibody (HBeAb) and hepatitis B core antibody (HBcAb) and HBV‑DNA. Notably, it was demonstrated that miR‑210 expression was not affected by treatment with HBV‑associated antigens in different types of macrophages. Notably, the serum of patients with CHB was able to markedly downregulate the miR‑210 expression of PBMs in healthy controls. These findings suggested that, unlike the induction of miR‑155 by HBeAg, there may be certain other elements, apart from HBV‑associated antigens, regulating miR‑210 levels in the serum and PBMs of patients with CHB that affect macrophage activation.
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The influence of respiration on brainstem and cardiovagal response to auricular vagus nerve stimulation: A multimodal ultrahigh-field (7T) fMRI study

Sclocco R, Garcia RG, Kettner NW, Isenburg K, Fisher HP, Hubbard CS, Ay I, Polimeni JR, Goldstein J, Makris N, et al. The influence of respiration on brainstem and cardiovagal response to auricular vagus nerve stimulation: A multimodal ultrahigh-field (7T) fMRI study. Brain Stimul. 2019.Abstract
BACKGROUND: Brainstem-focused mechanisms supporting transcutaneous auricular VNS (taVNS) effects are not well understood, particularly in humans. We employed ultrahigh field (7T) fMRI and evaluated the influence of respiratory phase for optimal targeting, applying our respiratory-gated auricular vagal afferent nerve stimulation (RAVANS) technique. HYPOTHESIS: We proposed that targeting of nucleus tractus solitarii (NTS) and cardiovagal modulation in response to taVNS stimuli would be enhanced when stimulation is delivered during a more receptive state, i.e. exhalation. METHODS: Brainstem fMRI response to auricular taVNS (cymba conchae) was assessed for stimulation delivered during exhalation (eRAVANS) or inhalation (iRAVANS), while exhalation-gated stimulation over the greater auricular nerve (GANctrl, i.e. earlobe) was included as control. Furthermore, we evaluated cardiovagal response to stimulation by calculating instantaneous HF-HRV from cardiac data recorded during fMRI. RESULTS: Our findings demonstrated that eRAVANS evoked fMRI signal increase in ipsilateral pontomedullary junction in a cluster including purported NTS. Brainstem response to GANctrl localized a partially-overlapping cluster, more ventrolateral, consistent with spinal trigeminal nucleus. A region-of-interest analysis also found eRAVANS activation in monoaminergic source nuclei including locus coeruleus (LC, noradrenergic) and both dorsal and median raphe (serotonergic) nuclei. Response to eRAVANS was significantly greater than iRAVANS for all nuclei, and greater than GANctrl in LC and raphe nuclei. Furthermore, eRAVANS, but not iRAVANS, enhanced cardiovagal modulation, confirming enhanced eRAVANS response on both central and peripheral neurophysiological levels. CONCLUSION: 7T fMRI localized brainstem response to taVNS, linked such response with autonomic outflow, and demonstrated that taVNS applied during exhalation enhanced NTS targeting.
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