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Norio Hayashi,
Tosiaki Miyati,
Takashi Minami,
Yumie Takeshita,
Yasuji Ryu,
Tsuyoshi Matsuda, Naoki Ohno,
Takashi Hamaguchi,
Kenichiro Kato,
Toshinari Takamura,
Osamu Matsui
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ABSTRACT: The focus of this study was on the investigation of the accuracy of the fat fraction of the liver by use of single-breath-holding magnetic resonance spectroscopy (MRS) with T (2) correction. Single-voxel proton MRS was performed with several TE values, and the fat fraction was determined with and without T (2) correction. MRS was also performed with use of the point-resolved spectroscopy sequence in single breath holding. The T (2) values of both water and fat were determined separately at the same time, and the effect of T (2) on the fat fraction was corrected. In addition, MRS-based fat fractions were compared with the degree of hepatic steatosis (HS) by liver biopsy in human subjects. With T (2) correction, the MRI-derived fat fractions were in good agreement with the fat fractions in all phantoms, but the fat fractions were overestimated without T (2) correction. R (2) values were in good agreement with the preset iron concentrations in the phantoms. The MRI-derived fat fraction was well correlated with the degree of HS. Iron deposited in the liver affects the signal strength when proton MRS is used for detection of the fat signal in the liver. However, the fat signal can be evaluated more accurately when the T (2) correction is applied. Breath-holding MRS minimizes the respiratory motion, and it can be more accurate in the quantification of the hepatic fat fraction.
Radiological Physics and Technology 12/2012;
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ABSTRACT: Diffusion-weighted imaging (DWI) has been used to characterize not only the brain, but also the breast by implementation of faster imaging techniques and higher magnetic field strengths. However, the optimum b value, which is an important scan parameter for DW images contrast on 3 T breast magnetic resonance imaging (MRI) has not been established. The purpose of this study was to investigate the influence of different b value combinations on the image contrast and apparent diffusion coefficient (ADC) in patients with known invasive carcinoma, ductal carcinoma in situ (DCIS), and normal mammary gland in breast DWI. The analysis procedure consisted of the following methods: 1) T(2) correction of DW images with echo-planar imaging (EPI) T(2)-weighted images; 2) contrast measurement between normal mammary gland and tumor tissues; 3) ADC measurement of normal mammary gland and tumor tissues. In many cases, the highest contrast between normal mammary gland and tumor tissues was obtained using a b value of 1500 s/mm(2). Our results indicated that when only one b value is used, the b value in which signal intensities of normal mammary gland decreases down to noise level, and the contrast between normal mammary gland and tumor tissues is recommended. ADC value decreased with increasing b value. Therefore, when determining the ADC threshold level, it is important to perform the evaluation using ADC values calculated from DW images with the same b value in clinical studies.
Nippon Hoshasen Gijutsu Gakkai zasshi 01/2012; 68(3):201-8.
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Naoki Ohno,
Tosiaki Miyati,
Mitsuhito Mase,
Tomoshi Osawa,
Hirohito Kan,
Harumasa Kasai,
Masaki Hara,
Yuta Shibamoto,
Norio Hayashi,
Toshifumi Gabata,
Osamu Matsui
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ABSTRACT: To determine whether temporal changes in apparent diffusion coefficient (ADC) over the cardiac cycle are different in patients with idiopathic normal-pressure hydrocephalus (INPH) as compared with patients with ex vacuo ventricular dilatation and healthy control subjects.
This prospective study was approved by the institutional review board and was performed only after informed consent was obtained from each patient. At 1.5 T, electrocardiographically triggered single-shot diffusion echo-planar magnetic resonance imaging (b = 0 and 1000 sec/mm(2)) was performed with sensitivity encoding and half-scan techniques to minimize bulk motion. ΔADC was defined as the difference between maximum and minimum ADC on a pixel-by-pixel basis over 20 phases of the cardiac cycle. Mean ADC during the diastolic phase and ΔADC in the frontal white matter were determined in patients with INPH (n = 13), patients with ex vacuo ventricular dilatation (n = 8), and healthy volunteers (n = 10). Kruskal-Wallis tests were used to determine significance between groups.
Mean ΔADC in the INPH group was significantly higher than that in the ex vacuo ventricular dilatation and control groups (P < .01 for both). There was no significant difference in ΔADC between the ex vacuo ventricular dilatation and control groups (P = .86). There was no significant difference in mean ADC during the diastolic phase among groups (P > .05 for all). There was no significant correlation between ΔADC and mean ADC during the diastolic phase in any group.
Determination of fluctuation of ADC over the cardiac cycle may render it possible to noninvasively obtain new and more detailed information than that provided by standard ADC measurement in suspected INPH, potentially facilitating the diagnosis of this disease.
Radiology 09/2011; 261(2):560-5. · 5.73 Impact Factor
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Takashi Hamaguchi,
Tosiaki Miyati, Naoki Ohno,
Masaya Hirano,
Norio Hayashi,
Toshifumi Gabata,
Osamu Matsui,
Tatsuhiko Matsushita,
Tomoyuki Yamamoto,
Yasuhiro Fujiwara,
Hirohiko Kimura,
Hiroyasu Takeda,
Yasuo Takehara
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ABSTRACT: Acoustic noise both in terms of its magnitude and frequency during magnetic resonance imaging (MRI) scan is influenced by imaging parameters and pulse sequences. It varies because of many different factors such as structure, materials, and magnetic field strength. The purpose of our study is to evaluate the characteristics of acoustic noise independent of MRI scan protocol by measuring a gradient-pulse-to-acoustic-noise transfer function (GPAN-TF) at various MRI scanners.
We measured sound pressure levels in the frequency domain in a 0.4-T, seven 1.5-T, and three 3.0-T clinical MRI systems when applying a simple narrower trapezoidal gradient pulse. We calculated a GPAN-TF [μPa/(mT/m)] in each gradient coil (ie, X, Y, and Z-axis) by the deconvolution process.
GPAN-TF at a high-frequency range (1000-10,000 Hz) was larger than that at low frequency for all MRI (P<0.01) scanners except for a low static field machine. For high frequency (>1000 Hz), the 3.0-T MRI scanner had a larger GPAN-TF than that of 0.4-T and 1.5-T (P < .01). MR scanner with a vacuum chamber reduced GPAN-TF at a lower frequency (P < .01), but this effect decreased at higher frequency.
GPAN-TF analysis makes it possible to obtain more detailed information on acoustic noise properties among MRI scanners.
Academic radiology 01/2011; 18(1):101-6. · 2.09 Impact Factor
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ABSTRACT: In the direction where the phased array coil used in parallel magnetic resonance imaging (MRI) is perpendicular to the arrangement, sensitivity falls significantly. Moreover, in a 3.0 tesla (3T) abdominal MRI, the quality of the image is reduced by changes in the relaxation time, reinforcement of the magnetic susceptibility effect, etc. In a 3T MRI, which has a high resonant frequency, the signal of the depths (central part) is reduced in the trunk part. SCIC, which is sensitivity correction processing, has inadequate correction processing, such as that edges are emphasized and the central part is corrected. Therefore, we used 3T with a Gaussian distribution. The uneven compensation processing for sensitivity of an abdomen MR image was considered. The correction processing consisted of the following methods. 1) The center of gravity of the domain of the human body in an abdomen MR image was calculated. 2) The correction coefficient map was created from the center of gravity using the Gaussian distribution. 3) The sensitivity correction image was created from the correction coefficient map and the original picture image. Using the Gaussian correction to process the image, the uniformity calculated using the NEMA method was improved significantly compared to the original image of a phantom. In a visual evaluation by radiologists, the uniformity was improved significantly using the Gaussian correction processing. Because of the homogeneous improvement of the abdomen image taken using 3T MRI, the Gaussian correction processing is considered to be a very useful technique.
Nippon Hoshasen Gijutsu Gakkai zasshi 01/2011; 67(6):627-33.
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Hirohito Kan,
Tosiaki Miyati,
Mitsuhito Mase,
Harumasa Kasai,
Masaki Hara,
Yuta Shibamoto,
Makoto Kawano, Naoki Ohno,
Akihiro Kitanaka,
Risa Yorimitsu,
Takashi Minami
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ABSTRACT: Apparent diffusion coefficients (ADCs) are sometimes overestimated when they are measured in the brain near the basal ganglia because water molecules in brain tissues fluctuate with blood volume loading in the cranium. We determined detailed ADC changes during the cardiac cycle to evaluate the appropriate cardiac phases for accurate measurement of ADC values. Using 1.5 T MRI, we performed ECG-triggered single-shot EPI to obtain ADC maps in each cardiac phase using techniques minimizing the bulk motion effect. The coefficient of variation (CV) of the ADC values during the cardiac cycle was over 50% near the basal ganglia. Moreover, the cardiac phase of the peak ADC value during the cardiac cycle was from 10 to 40% cardiac phases that follow systole. However, the CV of the ADC values of whole cardiac phases was higher than those with phases over 50% of the cardiac cycle near the basal ganglia because the effect of water fluctuation was almost eliminated. Therefore, accurate measurement of ADC values should be obtained from ADC maps of phases over 50% of the cardiac cycle.
Nippon Hoshasen Gijutsu Gakkai zasshi 01/2011; 67(6):661-5.
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Radiological Physics and Technology 07/2010; 3(2):185.
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Norio Hayashi,
Tosiaki Miyati,
Wataru Koda,
Masayuki Suzuki,
Shigeru Sanada, Naoki Ohno,
Takashi Hamaguchi,
Yukihiro Matsuura,
Kazuhiro Kawahara,
Tomoyuki Yamamoto,
Osamu Matsui
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ABSTRACT: Gd-EOB-DTPA is a new liver specific MRI contrast media. In the hepatobiliary phase, contrast media is trapped in normal liver tissue, a normal liver shows high intensity, tumor/liver contrast becomes high, and diagnostic ability improves. In order to indicate the degree of uptake of the contrast media, the enhancement ratio (ER) is calculated. The ER is obtained by calculating (signal intensity (SI) after injection-SI before injection) / SI before injection. However, because there is no linearity between contrast media concentration and SI, ER is not correctly estimated by this method. We discuss a method of measuring ER based on SI and T(1) values using the phantom. We used a column phantom, with an internal diameter of 3 cm, that was filled with Gd-EOB-DTPA diluted solution. Moreover, measurement of the T(1) value by the IR method was also performed. The ER measuring method of this technique consists of the following three components: 1) Measurement of ER based on differences in 1/T(1) values using the variable flip angle (FA) method, 2) Measurement of differences in SI, and 3) Measurement of differences in 1/T(1) values using the IR method. ER values calculated by these three methods were compared. In measurement made using the variable FA method and the IR method, linearity was found between contrast media concentration and ER. On the other hand, linearity was not found between contrast media concentration and SI. For calculation of ER using Gd-EOB-DTPA, a more correct ER is obtained by measuring the T(1) value using the variable FA method.
Nippon Hoshasen Gijutsu Gakkai zasshi 05/2010; 66(5):502-8.
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Yu Ueda MS,
DMSc Tosiaki Miyati PhD,
Naoki Ohno MS,
Yuko Motono MS,
PhD Masaki Hara MD,
PhD Yuta Shibamoto MD,
Harumasa Kasai MS,
Hideaki Kawamitsu MS,
Kosuke Matsubara PhD,
Yu Ueda,
Tosiaki Miyati, Naoki Ohno,
Yuko Motono,
Masaki Hara,
Yuta Shibamoto,
Harumasa Kasai,
Hideaki Kawamitsu,
Kosuke Matsubara
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ABSTRACT: Purpose:To assess the state of cancellous tissue we analyzed the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) in vertebral bone marrow.Materials and Methods:With 1.5 T magnetic resonance imaging (MRI), single-shot diffusion echo planar imaging was used with b factors of 0 and 1000 s/mm2, diffusion-sensitizing gradient in six directions, sensitivity encoding technique, effective TE of 74 msec, and TR of 1800 msec. ADC and FA were determined in the lumbar vertebral body of 11 normal subjects (age 31 632–635 years), and then compared with the bone mineral density (BMD) obtained with dual-energy x-ray absorptiometry (DXA). Moreover, fat fraction (FF) of the bone marrow was measured with spectral presaturation with inversion recovery (SPIR) in the same subject.Results:A strong negative correlation was found between ADC and BMD for low or moderate FF in vertebral bone marrow. Moreover, a significant positive correlation was noted between ADC and FF in this region. There was a positive correlation between FA and BMD, and no correlation between FA and FF in the vertebral bone marrow.Conclusion:Diffusion analyses with ADC and FA make it possible to obtain more detailed information on the structure of cancellous tissue and bone metabolism. J. Magn. Reson. Imaging 2010;31:632–635. © 2010 Wiley-Liss, Inc.
Journal of Magnetic Resonance Imaging 02/2010; 31(3):632 - 635. · 2.70 Impact Factor
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ABSTRACT: We evaluated dynamic changes in water diffusion in the brain during the cardiac cycle by using cine diffusion MRI. On a 1.5-T MRI, ECG-triggered single-shot diffusion echo planar imaging was used with sensitivity encoding, halfscan, and rectangular field of view techniques for minimizing bulk motion effects such as brain pulsation, with a data-sampling window of 3 ms. The apparent diffusion coefficient (ADC) and fractional anisotropy (FA) in the white matter zone were determined in ten healthy volunteers and then compared with the intracranial volume change (ICVC) revealed by phase-contrast cine MRI during the cardiac cycle. In addition, a frequency analysis of these waveforms was performed. ADC and FA values changed significantly during the cardiac cycle, despite minimizing the effect of bulk motion, i.e., independent of bulk motion. The ADC was synchronized with the ICVC during the cardiac cycle. A significant positive correlation was noted among their amplitudes. Analysis of the dynamic change of water diffusion by use of cine diffusion MRI facilitates the assessment of intracranial conditions.
Radiological Physics and Technology 07/2009; 2(2):133-7.
