In this study, we investigated the effect of structural differences in collagen fibers in relation to the spin-spin (T₂) relaxation time of surrounding water molecules. We propose a simple experimental model of the magic angle effect based on magnetically oriented collagen gels. Experiments were performed with a 4.7T magnetic resonance imaging (MRI) system with a quadrature radio frequency coil operated at 200 MHz for ¹H resonance. Collagen gels were polymerized from collagen solutions exposed to a 4.7T magnetic field for 120 min. The T₂ relaxation time was measured with the Carr-Purcell-Meiboom-Gill (CPMG) sequence. The apparent diffusion coefficient (ADC) was measured with the stimulated echo acquisition mode (STEAM) sequence with a motion-probing gradient (MPG). Orienting the collagen fibers at an angle of about 55 degrees to the main magnetic field caused an increase in the T₂ relaxation times of water molecules in the collagen gels. The ADC in the direction parallel to the fibers was larger than that in the direction perpendicular to the fibers. The increase in the T₂ relaxation time and ADC are attributed to a change in the magnetic interaction between the water molecules and collagen fibers.

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Detection of weak magnetic fields induced by neuronal electrical activities with magnetic resonance imaging (MRI) is a potentially effective method for functional imaging of the brain. In this study, we compared the theoretical and practical limits of sensitivity for detecting weak magnetic fields with a columnar phantom. The theoretical limit of sensitivity was estimated from signal and noise intensities in magnetic resonance images. The theoretical limit of sensitivity was approximately 10^-8T. The practical limit was 10 times the theoretical limit. The dependence of the theoretical limit of sensitivity on acquisition parameters, such as the repetition time (TR), echo time (TE), number of pixels, and spectral width, was quantitatively evaluated. The results indicated the existence of an optimal value in T_E/T₂^*.

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Purpose: To present an implementation of generalized cross validation (GCV) for automatically determining the regularization parameter—i.e., the threshold value in deconvolution analysis based on truncated singular value decomposition (TSVD) of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) data—and to investigate the usefulness of this approach in comparison with TSVD with a fixed threshold value (TSVD-F).
Methods: Using computer simulations, we generated a time-dependent concentration of the contrast agent in the volume of interest (VOI) from the arterial input function (AIF) modeled as a gamma-variate function under various cerebral blood flows (CBFs), cerebral blood volumes (CBVs), and signal-to-noise ratios (SNRs) for three different types of residue functions (exponential, triangular, and box-shaped). We also considered the effects of delay and dispersion in AIF. The TSVD with GCV (TSVD-G) and TSVD-F with a fixed threshold value of 0.2 were used to estimate CBF values from the simulated concentration-time curves in the VOI and AIF, and the estimated values were compared with the assumed values. Additionally, the optimal threshold value was determined from the threshold value in TSVD-F giving the mean CBF value closest to the assumed value and was compared with the threshold value determined with TSVD-G.
Results: With TSVD-G, the CBF estimation was substantially improved over a wide range of CBFs for all types of residue functions at the cost of more noise than was seen with TSVD-F. The dependency of the threshold value determined with TSVD-G on the CBF, CBV, and SNR was similar to that of the optimal threshold value, with some discrepancy being observed for the box-shaped residue function, although they did not always agree in terms of absolute value.
Conclusion: Given an improved SNR, TSVD-G is useful for quantification of CBF with deconvolution analysis of DCE-MRI data.

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Improvements to the inherently high specific-absorption rate (SAR) of high-speed imaging at 3T are necessary in order to render this method clinically feasible. Various efforts have been undertaken to improve the associated hardware and software. In this review, we focus on whole-brain isotropic 3D imaging with a turbo spin-echo sequence with variable flip-angle echo trains (3D-TSE-VFL) and present its technical and clinical features. This sequence can be used to acquire images of various contrasts including T₂-weighted, fat-suppressed T₂-weighted, fluid-attenuated inversion recovery (FLAIR), fat-suppressed FLAIR, and STIR (short tau inversion recovery). Various aspects of 3D-TSE-VFL are discussed, including CSF (cerebrospinal fluid) and metal artifacts, STIR contrast, small-part visualization other than brain, and the possibility of serial subtraction. Some images from clinical cases are presented.

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Breast MRI (magnetic resonance imaging) has emerged as a highly sensitive modality for imaging of breast tumors. Differences in MR enhancement characteristics between benign and malignant lesions are believed to reflect differences in vascularity, vessel permeability, and extracellular diffusion space. However, interpretation of breast MRI remains a challenging task. Precise MR-pathologic correlations may also lead to an improved understanding of the histological heterogeneity of breast cancers and definitions of diagnostic criteria.

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The method of determining the longitudinal relaxation time of hyperpolarized ¹²⁹Xe in the mouse brain has been established in vivo with the ventilation technique under controlled-flow conditions. The uptake and washout processes for nine mice were traced through observation of time-dependent changes in NMR (nuclear magnetic resonance) signal amplitudes and analyzed by means of a two-compartment model, thus providing the quantitative value of 14.1±1.6 s as the relaxation time.

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The purpose of this study was to design a keyhole pulse sequence for quantitative 2D dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) based on a spoiled gradient echo T₁-weighted acquisition. Saturation recovery was applied to achieve a linear correlation between signal intensity and contrast agent concentration in an arterial input function (AIF) while simultaneously removing time-of-flight effect. To remove ghosting artifacts arising from incomplete presaturation, EXORCYCLE phase cycling with averaging was applied to the pulse sequence. RF spoiling by radiofrequency switching with the synthesizer can be combined with EXORCYCLE phase cycling. Images affected by the large difference in signal intensity before and after contrast agent administration with the keyhole technique were improved by interleaving of peripheral lines of k-space with groups of central lines. Both peripheral and central lines were renewed during the dynamic scan. AIFs were obtained from the rat abdominal aorta with this keyhole sequence.

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T₂-weighted MR (magnetic resonance) images of a 19-year-old woman undergoing concurrent chemoradiotherapy for a nasopharyngeal carcinoma revealed a lesion marked by focal hyper signal intensity in the splenium of the corpus callosum. The lesion was not visible two weeks later. She suffered from malnutrition caused by appetite loss during chemotherapy. We concluded that the lesion revealed by the abnormal signal intensity in the splenium had been caused by malnutrition.

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