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.

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In constant time (CT) point-resolved spectroscopy (PRESS), echo centers shift with the fast decay of short T₂* on two-dimensional (2D) time domain (TD) data under inhomogeneous B₀ field like in vivo conditions. Though ¹H decoupling along the F₁ direction is a feature of this method, the tilted and broadened peak pattern on the F₁-F₂ plane after reconstruction causes the peaks to overlap.
To enhance resolution to achieve highly resolved 2D CT-PRESS spectra in the human brain, we propose a 2-part window function that comprises an enhancement part for shifting echoes with fast decay and a conventional part, such as Lorentzian, Gaussian, or sine-bell function.
We obtained 2D spectra from human brains at 4.7T. The 3 diagonal peaks of C4H of glutamate (Glu C4H) at 2.35 ppm, C2H of γ-amino butyric acid (GABA C2H) at 2.28 ppm, and C4H of glutamine (Gln C4H) at 2.44 ppm-overlapped on the spectra processed with the conventional window but clearly resolved on the spectra using the proposed enhancement window. The signal-to-noise ratio per unit measurement time of Glu C4H on a CT-PRESS spectrum of the human brain was 1.7 times higher than that on a spectrum obtained by CT-correlation spectroscopic (COSY).
In conclusion, 2D CT-PRESS spectra processed with the proposed window function to enhance resolution can resolve peaks of coupled ¹H spins with higher accuracy and sensitivity.

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Purpose: We present and demonstrate a new compressed sensing (CS) method to improve the image quality obtained in magnetic resonance CS. The sparsifying function, which transforms the image function to sparsified domain, is very important since it controls the quality of reconstructed image. We investigate the utility of a multi-step directional transform for improving the quality of reconstructed images in CS reconstruction.
Methods: As a sparsifying function, we used the Fresnel domain band split transformation (FREBAS), a method to decompose images with highly directional representation and optional scaling of the decomposition. Our image reconstruction algorithm involved linear and nonlinear operations, such as projection onto a convex set and hard thresholding in the transform domain.
Results: Several numerical experiments demonstrated the acquisition of images of better quality using multi-step successive thresholding and different scaling parameters in the FREBAS domain rather than single-step FREBAS thresholding. Reconstruction experiments showed much more detail of the imaging subject with fewer artifacts in CS images based on the FREBAS transform compared to CS based on the wavelet transform.
Conclusion: The proposed method using multi-step FREBAS as the sparsifying transformation function is suitable for CS magnetic resonance imaging.

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Purpose: The maximum limit of MR scanner noise and necessity of ear protection is defined in the IEC standard (IEC60601-2-33) of MR safety. With improvements in MR scanner performance, pulse sequences generating higher scanning noise have been used clinically. In this study, we investigated the factors significantly related to potential acoustic trauma cases (PATC) after MR examinations. To consider the future direction for MR safety and prevention of acoustic trauma, issues related to noise generation by MR scanners and acoustic trauma were systematically reviewed.
Methods: A statistical analysis was performed using the data set from a survey (n=974) conducted in 2010 by the JSMRM safety committee. Hierarchical clustering analysis was used to extract the characteristics of the responders. With this classification as a reference, tests of independence and a residual analysis were employed to evaluate the factors related to PATC.
Results: No significant relationship was observed between the ear protection policy and the incidence or the reported outcome of PATC. While the two main clusters out of the six clusters extracted were associated with who reported the PATC and the confirmation process of the acoustic noise level of MR scanners, no cluster was associated with the frequency of PATC. An absence of PATC was significantly less reported (p=0.03) and more PATC was reported (p=0.04) by facilities with 3T MR systems.
Discussion: Although the total frequency was 4 cases, it should be noted that persistent hearing disturbances are a possible consequence of MR examinations. Neither the condition of the subjects nor the ear protection method was significantly related to the probability of PATC, suggesting the difficulty of predicting the potential risk of acoustic trauma. It is recommended to more systematically follow up PATC cases and clarify the risk factors.

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Purpose: Accurate longitudinal relaxation time (T₁) of arterial blood is important in evaluating blood flow in tissue by arterial spin labeling magnetic resonance (MR) imaging. Few studies have reported the T₁ of human arterial blood in vivo, especially using 3-tesla MR imaging. T₁ values of human venous blood in vivo have been reported, but they differ from those measured in vitro. We aimed to evaluate the accurate T₁ of human arterial blood in vivo.
Methods: We measured T₁ values of blood in 10 healthy volunteers in vivo using an inversion-recovery fast gradient-echo sequence and 3-tesla MR imaging unit. We also measured hematocrit (Hct) values of venous blood samples. After nonselective application of the inversion pulse using a body coil, we obtained MR imaging signals of arterial blood in the abdominal aorta. Similarly, we measured the signals of venous blood in the internal jugular vein. Inversion times varied between 200 and 5000 ms for imaging of the abdominal aorta and 200 and 2500 ms for imaging of the jugular vein. We also acquired signals without the inversion pulse. We estimated T₁ values from the data by nonlinear least squares fitting of a 3-parameter model.
Results: The T₁ value (mean±standard deviation) of arterial blood was 1779±80 ms and of venous blood, 1694±77 ms. The average Hct value was 0.47. The R₁ (=1/T₁) of arterial blood was related to the Hct value as: R₁=(0.59±0.16)Hct+(0.29±0.07) (mean±standard error) s⁻¹. For the venous blood, R₁=(0.70±0.11)Hct+(0.27±0.05) s⁻¹.
Conclusion: We observed a T₁ of human arterial blood in vivo of 1779±80 ms at a mean hematocrit value of 0.47 as determined by 3T MR imaging; an even longer T₁ value is expected with a hematocrit value less than 0.47.

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One issue in externally triggered cine-magnetic resonance imaging (EC-MRI) for the dynamic observation of speech organs is motion artifact in the phase-encoding direction caused by unstable repetitions of speech during data acquisition. We propose a technique to reduce such artifact by rearranging the k-space data used to reconstruct MR images based on the analysis of recorded speech sounds.
We recorded the subject's speech sounds during EC-MRI and used post hoc acoustical processing to reduce scanning noise and detect the onset of each utterance based on analysis of the recorded sounds. We selected each line of k-space from several data acquisition sessions and rearranged them to reconstruct a new series of dynamic MR images according to the analyzed time of utterance onset. Comparative evaluation showed significant reduction in motion artifact signal in the dynamic MR images reconstructed by the proposed method. The quality of the reconstructed images was sufficient to observe the dynamic aspects of speech production mechanisms.

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Purpose: To demonstrate the reduction in vascular bed volume (VBV) of uterine fibroids after administration of gonadotropin-releasing hormone analogue (GnRHa) using magnetic resonance (MR) imaging including dynamic double-echo R₂* imaging (DDE-R₂*I) and to assess the value of DDE-R₂*I as a predictor of such reduction.
Methods: Twenty-one women with uterine intramural fibroids underwent MR imaging including DDE-R₂*I before GnRHa treatment. DDE-R₂*I was acquired using a single-section, double-echo, fast spoiled gradient recalled acquisition in the steady state (SPGR) sequence. We calculated the area under the curve (AUC) of the signal intensity on R₂*I within a 3×3-cm² region of interest that served to represent the VBV. We repeated MR imaging after 2 administrations of GnRHa and repeated image analyses. We statistically analyzed correlations between (A) pre-treatment AUC (AUC(pre)) and AUC reduction and (B) AUC(pre) and volume reduction.
Results: The interval between the 2 MR studies ranged from 56 to 119 days (mean: 80.4 days). The average volume of the fibroids before GnRHa treatment was 647.8 mL compared with 463.4 mL after the therapy (decreased by an average of 28.5%; P<0.0001). Meanwhile, measured AUC was reduced by 55.3% (483.4 vs. 206.5; P<0.0001). AUC(pre) correlated with volume reduction (r=0.68), but not AUC reduction.
Conclusions: We confirmed reduction in the VBV of fibroids using DDE-R₂*I. The measurement of AUC(pre) on DDE-R₂*I aids prediction of fibroid volume reduction but correlates poorly with the percentage of AUC reduction.

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Purpose: We evaluated the use of magnetic resonance (MR) elastography (MRE) for staging liver fibrosis in patients with chronic hepatitis C and compared the ability of MRE and serum fibrosis markers for discriminating each stage of fibrosis.
Methods: We evaluated 114 patients with chronic hepatitis C in whom the pathological fibrosis stage was determined (fibrosis stage 0 [F0], 3; F1, 15; F2, 28; F3, 25; and F4, 43). All patients underwent MRE using a 1.5-tesla MR system and pneumatic driver system. We measured stiffness values (kPa) of the liver in a circular region of interest placed on elastograms. We determined the optimal cutoff value and diagnostic ability for discriminating each stage of fibrosis using receiver operating characteristic (ROC) curve analysis and compared the discriminative ability of MRE with that of serum fibrosis markers.
Results: The mean stiffness values of the liver increased with stage of fibrosis: F0, 2.10±0.10 kPa; F1, 2.42±0.29 kPa; F2, 3.16±0.32 kPa; F3, 4.21±0.78 kPa; and F4, 6.20±1.08 kPa. The mean area under the ROC curve (Az) values for discriminating liver fibrosis stages were: ≥F1, 0.984 (95% confidence interval,
0.933–0.996); ≥F2, 0.986 (0.956–0.996); ≥F3, 0.973 (0.935–0.989); and ≥F4, 0.976 (0.945–0.990). The Az values for discriminating fibrosis stages were significantly higher for MRE than serum fibrosis markers.
Conclusion: MRE is a reliable technique for staging liver fibrosis and discriminating liver fibrosis stages in patients with chronic hepatitis C.

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We present a case of a 57-year-old woman who underwent gamma-knife radiosurgery (GKRS) for pontine metastasis. Magnetic resonance (MR) imaging 2.8 months after GKRS showed T₂ hyperintensity and hypertrophy of the left inferior olivary nucleus (ION) without gadolinium enhancement and smaller pontine metastasis. We diagnosed the signal change in the left ION as hypertrophic olivary degeneration (HOD) resulting from damage to the left central tegmental tract. We believe this is the first report to describe HOD after GKRS for pontine metastasis.

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To visualize endolymph, perilymph, and bone separately in a single image after intravenous injection of single-dose gadodiamide, we generated a HYDROPS2 image (subtraction of MR cisternography from heavily T₂-weighted 3-dimensional fluid-attenuated inversion recovery image) in 12 patients with suspected Ménière's disease. The contrast-to-noise ratio of endo- and perilymph did not differ significantly between the HYDROPS2 and previously reported HYDROPS (hybrid of reversed image of positive endolymph signal and native image of positive perilymph Signal) images, and scan time was 40% shorter for the HYDROPS2 than HYDROPS.

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