Visualizing non-Gaussian diffusion: clinical application of q-space imaging and diffusional kurtosis imaging of the brain and spine.

Recently, non-Gaussian diffusion-weighted imaging (DWI) techniques, including q-space imaging (QSI) and diffusional kurtosis imaging (DKI), have emerged as advanced methods to evaluate tissue microstructure in vivo using water diffusion. QSI and DKI have shown promising results in clinical applications, such as in the evaluation of brain tumors (e.g., grading gliomas), degenerative diseases (e.g., specific diagnosis of Parkinson disease), demyelinating diseases (e.g., assessment of normal-appearing tissue of multiple sclerosis), and cerebrovascular diseases (e.g., assessment of the microstructural environment of fresh infarctions). Representative metrics in clinical use are the full width at half maximum, also known as the mean displacement of the probability density function curve, which is derived from QSI, and diffusional kurtosis, which is derived from DKI. These new metrics may provide information on tissue structure in addition to that provided by conventional Gaussian DWI investigations that use the apparent diffusion coefficient and fractional anisotropy, recognized indices for evaluating disease and normal development in the brain and spine. In some clinical situations, sensitivity for detecting pathological conditions is higher using QSI and DKI than conventional DWI and diffusion tensor imaging (DTI) because DWI and DTI calculations are based on the assumption that water molecules follow a Gaussian distribution, whereas hindrance of the distribution of water molecules by complex and restricted structures in actual neural tissues produces distributions that are far from Gaussian. We review the technical aspects and clinical applications of QSI and DKI, focusing on clinical use and in vivo studies and highlighting differences from conventional diffusional metrics.

Integrated lymphography using fluorescence imaging and magnetic resonance imaging in intact mice.

We assessed lymph drainage in living mice by an integrated imaging method using fluorescence imaging (FLI) and magnetic resonance imaging (MRI). Mice were subcutaneously injected with quantum dots and gadofluorine 8 into the right rear footpad. They were fixed on a transparent flat plate and underwent FLI and MRI successively. Small markers were attached to the mouse surface for spatial coregistration, and image fusion of FLIs and MRIs was performed. Two-dimensional fluorescence reflectance imaging was used for FLI. FLI and MRI provided generally consistent results and demonstrated lymphatic flow to the popliteal, sacral, and iliac lymph nodes in most mice and to the renal, inguinal, and lumbar-aortic lymph nodes in some mice. On the fusion images, the locations of the lymph nodes in the mouse trunk were in good agreement between FLI and MRI, indicating successful spatial registration even for the deep structures. The popliteal node tended to be visualized a little farther caudally in FLI than in MRI, presumably because the overlying tissues were thicker in the cranial portion. Integrated FLI/MRI lymphography with image fusion appears to be a useful tool for analysis of the murine lymphatic system.

Diffusion-tensor neuronal fiber tractography and manganese-enhanced MR imaging of primate visual pathway in the common marmoset: preliminary results.

PURPOSE: To investigate whether diffusion-tensor tractography (DTT) of neuronal fibers is useful for delineating the configuration of the neuronal fiber trajectories in the primate visual pathway, including the well-developed optic chiasm, in comparison with tract tracing at manganese-enhanced magnetic resonance (MR) imaging. MATERIALS AND METHODS: The handling methods used for all the animals in this study were approved by the institutional committee for animal experiments. Diffusion-tensor MR imaging was performed in four healthy common marmosets, and in two of these animals, manganese-enhanced MR imaging tract tracing was performed by using a 7.0-T MR imaging unit. The visual pathways were quantitatively investigated in terms of the manganese distribution observed on the manganese-enhanced MR images. The images obtained with DTT and manganese-enhanced MR imaging tract tracing were qualitatively compared, and the features of the visual pathway were verified through fusion of the reconstructed images obtained by using these two modalities. RESULTS: DTT provided information regarding the neuroanatomic features of the marmoset visual pathway and revealed the bilateral branching patterns of the typical primate retinogeniculate pathways, although several incorrectly tracked fibers were noted. The distribution of manganese on the manganese-enhanced MR images revealed bilateral innervation of the retinal projections and depicted the layered internal structure of the lateral geniculate nuclei bilaterally, depending on the ocularity of each layer. These morphologic findings were consistent with those of previous histopathologic studies. CONCLUSION: The findings of this preliminary study raise the possibility that DTT is useful for visualizing the neuronal fiber trajectories in primate visual pathways. SUPPLEMENTAL MATERIAL: http://radiology.rsnajnls.org/cgi/content/full/249/3/855/DC1.

Tract-specific analysis of the superior occipitofrontal fasciculus in schizophrenia.

Diffusion tensor imaging has been highlighted as a non-invasive tool to explore neural connectivity in vivo. Several studies have suggested disorganization of the neural network (circuitry) including the thalamo-prefrontal connection in schizophrenia. Recent research using post-mortem brains showed that the superior occipitofrontal fasciculus (SOFF) fibers extended to the thalamus. We postulated that the SOFF has some relationship with the anatomical structural components of the thalamo-prefrontal circuitry. We quantitatively assessed the diffusion abnormalities of the SOFF using diffusion tensor tractography (DTT) in schizophrenia. Nineteen male patients with schizophrenia and 20 age-matched normal controls were studied. DTT of the SOFF (DTT-SOFF) was visualized using free software (dTV II/VOLUME-ONE), and we performed tract-specific measurement of the fractional anisotropy (FA), then calculated the apparent diffusion coefficient (ADC) of the DTT-SOFF. Tractography and tract-specific analysis of the SOFF were successfully performed in all subjects. All tracts appeared to be connecting the prefrontal area to the thalamus. The mean FA value of patients with schizophrenia [0.376 (S.D. 0.030)] was significantly lower than that of controls [0.432 (S.D. 0.032)], and the ADC value of patients with schizophrenia [0.771 (x10(-3) mm(2)/s) (S.D. 0.041)] was significantly higher than that of controls [0.726 (x10(-3) mm(2)/s) (S.D. 0.027)]. Our results suggest that the so-called SOFF may be a structural component connecting the prefrontal area to the thalamus and that it is deteriorated in schizophrenia.