Lactate observation in vivo by spectral editing in real time

Fast tissue segmentation based on a 4D feature map in characterization of intracranial lesions

The aim of this work was to develop a fast and accurate method for tissue segmentation in magnetic resonance imaging (MRI) based on a four-dimensional (4D) feature map and compare it with that derived from a 3D feature map. High-resolution MRI was performed in 5 normal individuals, in 12 patients with brain multiple sclerosis (MS), and 9 patients with malignant brain tumors. Three inputs (proton-density, T2-weighted fast spin-echo, and T1-weighted spin-echo MR images) were routinely utilized. As a fourth input, either magnetization transfer MRT was used or T1-weighted post-contrast MRI (in patients only). A modified k-nearest neighbor segmentation algorithm was optimized for maximum computation speed and high-quality segmentation. In that regard, we a) discarded the redundant seed points; b) discarded the points within 0.5 standard deviation from the cluster center that were non-overlapping with other tissue; and c) removed outlying seed points outside 5 times the standard deviation from the cluster center of each tissue class. After segmentation, a stack of color-coded segmented images was created. Our new technique utilizing all four MRI inputs provided better segmentation than that based on three inputs (P < 0.001 for MS and P < 0.001 for tumors). The tissues were smoother due to the reduction of statistical noise, and the delineation of the tissues became sharper. Details that were previously blurred or invisible now became apparent. In normal persons a detailed depiction of deep gray matter nuclei was obtained. In malignant tumors, up to five abnormal tissue types were identified: 1) solid tumor core, 2) cyst, 3) edema in white matter 4) edema in gray matter, and 5) necrosis. Delineation of MS plaque in different stages of demyelination became much sharper. In conclusion, the proposed methodology warrants further development and clinical evaluation.

Detection of homonuclear decoupled in vivo proton NMR spectra using constant time chemical shift encoding: CT-PRESS

A new pulse sequence, termed CT-PRESS, is presented, which allows the detection of in vivo 1H NMR spectra with effective homonuclear decoupling. A PRESS sequence with a short echo-time TE, used for spatial localization, is supplemented by an additional 180 degrees pulse. The temporal position of this 180 degree pulse is shifted within a series of experiments, while the time interval between signal excitation and detection is kept constant. CT-PRESS is a two-dimensional (2D) spectroscopic experiment as far as data acquisition and processing are concerned, although only diagonal signals are generated in the 2D spectrum. However, since the principle of constant time chemical shift encoding is used in the t1 domain, effective homonuclear decoupling is obtained by projecting the 2D spectrum onto the corresponding f1 axis. Thus, good spectral resolution and high signal-to-noise ratio are obtained. The main advantage, as compared to localized 2D J-resolved MRS, is that optimized experiments can be performed for coupled resonances of interest by choosing the sequence parameters dependent on the type of multiplets, the J-coupling constants and T2. Major fields of application will be parametric studies on coupled resonances, (e.g., T1, diffusion behavior or magnetization transfer) and/or the detection of spatial and temporal changes of metabolites with coupled spin systes.