Yoshiyuki Ishimori

Transient MR signal changes in the splenium of the corpus callosum in rotavirus encephalopathy: value of diffusion-weighted imaging.

The authors report serial brain MR findings from a 2-year-old girl with rotavirus encephalopathy. The lesion in the splenium of the corpus callosum showed restricted proton diffusion, suggesting local cytotoxic edema. Diffusion-weighted images demonstrated the lesion more conspicuously than other techniques, such as fluid-attenuated inversion-recovery and T1- and T2-weighted images. The findings were reversible on follow-up MRI obtained 4 days later. Diffusion-weighted MRI is a potentially useful method for detecting early changes of rotavirus encephalopathy, although the mechanism of the restricted diffusion is not clearly identified.

Thalamic abnormalities in patients with schizophrenia revealed by proton magnetic resonance spectroscopy

Recent investigations suggest that thalamic abnormalities may underlie symptom formation in schizophrenia. We previously demonstrated reduced concentrations of N-acetylaspartate (NAA) in tissue from the thalamus of schizophrenic patients using in vitro proton magnetic resonance spectroscopy (1H-MRS). In the present study, in vivo 1H-MR spectra of the left thalamus and frontal lobe were investigated in 20 patients with schizophrenia and 16 age-matched control subjects to replicate our previous postmortem findings and support the hypothesis of thalamic abnormality in schizophrenia. Schizophrenic patients showed significantly lower NAA/total creatine (Cr) and choline-containing compounds (Cho)/Cr ratios in the thalamus than control subjects, while no significant difference was found in the frontal lobe. There was no significant correlation in the schizophrenic patients between the NAA/Cr or Cho/Cr ratio and other clinical data including clinical symptoms or neuroleptic dosage. These findings may further support other studies suggesting decreased thalamic volume or neuronal number and/or thalamic dysfunction, and reduction in size of white matter tracts adjacent to the thalamus in schizophrenia, as well as our previous postmortem MRS study.

Differentiation of prostate cancer from benign prostate hypertrophy using dual-echo dynamic contrast MR imaging

OBJECTIVE To investigate the usefulness of dynamic contrast magnetic resonance (MR) imaging in the differentiation of prostate cancer (PC) from benign prostate hypertrophy (BPH). MATERIALS AND METHODS Eleven PC patients and 13 BPH patients were entered into the analysis. The mean gradient (MG) was calculated from the T2* term-eliminated time-signal intensity curve obtained from dynamic contrast MR data, and the MG of PC and that of BPH were compared. RESULTS The MG of PC was significantly higher than that of BPH. When the threshold value was set to 1.88% per s for discriminating PC from BPH, the sensitivity, specificity, and accuracy were 100, 85, and 92%, respectively. CONCLUSION The MG, which is derived from the T2* term-eliminated time-signal intensity curve, may be a useful index for differentiating PC from BPH.

Dynamic T1 estimation of brain tumors using double-echo dynamic MR imaging

To assess the clinical utility of a new method for real‐time estimation of T1 during the first pass of contrast agent by using this method to examine brain tumors.

Assessment of the vascularity of uterine leiomyomas using double-echo dynamic perfusion-weighted MRI with the first-pass pharmacokinetic model: correlation with histopathology.

Objectives:To retrospectively evaluate the feasibility of perfusion-weighted MRI (PWI) in uterine leiomyomas. Materials and Methods:Eighteen uterine leiomyomas in 15 patients were evaluated. PWI was performed using a double-echo T2*-weighted spoiled gradient-recalled acquisition sequence, and the first-pass pharmacokinetic model was applied to calculate relative blood volume (rBV). Histopathologic analysis was performed to measure vascular area (VA). Results:PWI was successful in 13 of 15 patients. On quantitative analysis, mean (±SD) rBV calculated from PWI was 0.17 ± 0.13 (range, 0.06–0.55), whereas mean VA was 3.3% ± 1.6% (range, 1.7–8.5%). A significant correlation was identified between rBV and VA (r = 0.87, P < 0.001). Conclusions:The rBV determined at PWI correlates with histologic vascular area in uterine leiomyomas.

Artifact Reduction of Susceptibility-Weighted Imaging Using a Short-Echo Phase Mask

Background: Susceptibility-weighted imaging (SWI) is utilized in magnetic resonance (MR) venography and other applications, but can include artifacts caused by the phase-masking process. Purpose: To demonstrate risks of filter processes used in making phase masks for SWI, and to propose a simple method for reducing artifacts. Material and Methods: Phase linearity related to echo time (TE) was evaluated for the original phase and high-pass-filtered phase using a CuSO4-doped water phantom. Effect of filter size of the Hanning window and background homogeneity were also evaluated in a phantom study. Use of a phase mask generated by data with differing magnitudes of TE was attempted in a human study. Shorter TE was used for making the phase mask, and the number of multiplications was increased. As short and long TEs were necessary simultaneously for phase mask and T2* contrast, a dual-echo technique was used. Results: Linearity of TE and phase value collapsed, and an unexpected negative phase appeared in the high-pass-filtered phase. Using a short-TE phase mask, phase-aliasing artifacts were reduced and visibility of deep veins was equivalent to that under conventional methods with an increased number of multiplications. Conclusion: Use of a short-echo phase mask in SWI is useful for reducing artifacts.

Fat quantification by use of phase change in dual-echo magnetic resonance imaging

The demand for measurement of visceral fat in medical checkups is increasing because of attention to central obesity. Computed tomography is widely used for this purpose, but carries risks associated with radiation exposure. Fast imaging with a dual-echo technique acquiring water and fat signals both in-phase and out-of-phase using magnetic resonance imaging is desirable, but not all scanners are capable of this technique. We tried to quantify fat content by using a dual-echo gradient echo pulse sequence with an arbitrary echo time (TE) set. We calculated the phase change during the TE interval and extracted the region of fat by threshold processing. Variations in the precision of counting fat pixels caused by differences between TE1 and TE2 were measured in phantom experiments. We then evaluated the validity of this method by examination of a volunteer. The phantom study showed a large error when the TE interval was a multiple of the in-phase time for fat and water, and the error increased according to the prolongation of the TE. In the human study, phase wrapping readily occurred in the phase-change image. However, the region of fat was easily extracted with high-pass filtering. The fat signal can also be extracted by use of scanners that cannot be set simultaneously to in-phase and out-of-phase TE.

Simultaneous acquisition of high-contrast and quantitative liver T1 images using 3D phase-sensitive inversion recovery: a feasibility study:

Background Tumor-to-liver contrast is low in images of chronically diseased livers because gadolinium-based hepatocyte-specific contrast agents (Gd-EOB-DTPA) accumulate less to hepatocytes. Purpose To determine whether phase-sensitive inversion recovery (PSIR) could improve the T1 contrasts of Gd-based contrast agents and liver parenchyma and simultaneously provide accurate T1 values for abdominal organs. Material and Methods The image contrasts of phantoms with different Gd concentrations that were obtained using PSIR were compared to conventional turbo field echo (TFE) results. T1 value was estimated using PSIR by performing iterations to investigate the two IR magnetization evolutions. The estimated T1 values were validated using IR-spin echo (IR-SE) and Look-Locker (L-L) sequences. In an in vivo study, the liver-to-spleen and liver-to-muscle contrasts of the PSIR and TFE images of seven volunteers were compared, as were the T1 values of liver parenchyma, spleen, and muscle obtained using PSIR and L-L sequences. Results The PSIR images showed T1 contrasts higher than those in the TFE results. The PSIR and IR-SE T1 values were linearly correlated. Additionally, the R1 estimated using PSIR were correlated with those measured using IR-SE and L-L. In the in vivo study, the liver-to-spleen and liver-to-muscle contrasts of PSIR were significantly higher than those obtained using TFE. T1 values of abdominal organs obtained using PSIR and L-L were clearly correlated. Conclusion PSIR may be capable of improving liver image T1 contrasts when Gd-based contrast agents are employed and simultaneously yielding accurate T1 values of abdominal organs.

Feasibility of MR perfusion-weighted imaging by use of a time-spatial labeling inversion pulse.

Perfusion-weighted imaging (PWI) by use of arterial spin labeling (ASL) has been introduced to the clinical setting. However, it is not widely available because it requires specialized pulse sequences. Imaging using a time-spatial labeling inversion pulse (time-SLIP), which is a magnetic resonance angiography (MRA) technique that is based on ASL, can be used in various situations. In this study, we examined the feasibility of time-SLIP PWI. Two types of time-SLIP sequences were evaluated: (1) a single inversion recovery (IR) pulse sequence, which is the same as that used in conventional time-SLIP MRA except for the timing of data acquisition, and (2) a dual IR pulse sequence, where a second, non-selective, IR pulse was added during the inflow time to suppress background signals. Subtraction processing is performed between the “on” and “off” settings of the first IR pulse (time-SLIP tag) to obtain PWI. The average signal intensity was measured in a uniform phantom as the residual of the background, and in five healthy subjects as the perfusion signal. The average signal-to-noise ratio (SNR) was also measured in the five subjects. All imaging was performed with a 1.5-T MR scanner. Images using the dual IR method showed lower background signals and higher perfusion signals compared with images using the single IR method. However, the SNR was lower in images with the dual IR method. These results demonstrate that a time-SLIP, which is an MRA method, can be used for obtaining cerebral PWI simply by adjusting the imaging parameters.

Wide slab is useful for routine quality control of MRI slice thickness

Although slice thickness accuracy is important for the performance of magnetic resonance imaging systems, long scan times are required to perform reliable measurements. Inclined slabs and wedges are conventionally used as test devices to obtain slice profiles. In this study, a novel dedicated device with a widened slab was created, and its efficacy was compared with that of a conventional wedge. The signal-to-noise ratio (SNR) of the profile and the coefficient of variation (CV) of the measured slice thickness were measured. Wide slab usage showed sufficient SNR by averaging multiple profile lines, even with single acquisition. Therefore, it is possible to substantially shorten the measurement time. When ≥ 20 lines were averaged, CV was < 1%. Furthermore, a 200-mm slab width enabled evaluation of the positional dependence of slice thickness in a single imaging. Thus, quality control of MRI slice thickness can be easily implemented with this device.