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Hidemasa Uematsu

Publications and source records attributed to Hidemasa Uematsu.

15 recordsLinked to original sources
PubMed2003

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

PURPOSE: 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. MATERIALS AND METHODS: The multi-phase spoiled gradient-echo pulse sequence using the double-echo magnetic resonance (MR) technique was modified. In the first half of the pulse sequence, the flip angle was varied systematically. Then, static T1 values were calculated using differences in MR signal intensities between different flip angles. In the latter half of this sequence, changes in absolute T1 were calculated using differences in signal intensities before and after injection of contrast agent. The double-echo MR data were used to minimize the T2* effect. Five cases of neurinoma and seven cases of meningioma were examined. Changes in T1 during the first pass of contrast agent were compared between neurinoma and meningioma. RESULTS: Changes in absolute T1 were clearly demonstrated on the parametric map. Although the changes in absolute T1 during the first pass of contrast agent did not allow differentiation between the two types of tumors, the mean gradient after the first pass was statistically higher for neurinoma than for meningioma (P < 0.05; meningioma, 0.011 +/- 0.012 second(-1)/second; neurinoma, 0.034 +/- 0.020 second(-1)/second). CONCLUSION: The present method appears to be useful for estimation of dynamic T1 changes in brain tumors in clinical settings.

Adult↗
PubMed2003

A direct comparison of signal behavior between 4.0 and 1.5 T: a phantom study.

INTRODUCTION: Higher magnetic fields (>or=3 T) afford higher spatial and/or temporal resolution in MR imaging with contrast agents, however, studies containing direct comparisons of signal intensity among different magnetic fields are substantially sparse. Our aim was to quantify the differences in terms of signal-to-noise ratios (SNRs) and contrast-to-noise ratios (CNRs) between higher and lower (<or=1.5 T) magnetic fields and to clarify the benefit of higher magnetic fields. METHODS: The same sets of phantom experiments were conducted at both 4 and 1.5 T on whole-body MR scanners with head coils. Phantoms included different concentrations of Gd chelate water solution. A standard contrast-enhanced MR angiographic sequence with the same imaging parameters was utilized to confirm changes in signal intensities. Furthermore, the results were compared with a computer simulation. RESULTS: Peak SNRs at 4 T increased at least 2.21 times higher compared with those at 1.5 T. Moreover, peak CNRs at 4 T increased at least 1.59 times higher compared with those at 1.5 T in the range of Gd concentration expected during clinical use. CONCLUSION: Higher magnetic fields benefit CNRs as well as SNRs. These advantages may lead to a high resolution imaging and reduction of scan time.

Computer Simulation↗
PubMed2003

Abdominal imaging at 4 T MR system: a preliminary result.

In this study, the potential for abdominal MR images at 4 T using a tailored coil was demonstrated using healthy volunteers. These images were compared with those obtained in the same subject at 1.5 T to discuss whether 4 T would be superior to 1.5 T in abdominal imaging. MR images at 4 T were characterized by high contrast and signal-to-noise ratios, more than 2.95 times higher than those at 1.5 T. In conclusion, abdominal MR imaging at 4 T was feasible. Furthermore, abdominal MR imaging at 4 T was superior to that at 1.5 T in qualitative and quantitative analyses.

Abdomen↗
PubMed2003

MR imaging at high magnetic fields.

Recently, more investigators have been applying higher magnetic field strengths (3-4 Tesla) in research and clinical settings. Higher magnetic field strength is expected to afford higher spatial resolution and/or a decrease in the length of total scan time due to its higher signal intensity. Besides MR signal intensity, however, there are several factors which are magnetic field dependent, thus the same set of imaging parameters at lower magnetic field strengths would provide differences in signal or contrast to noise ratios at 3 T or higher. Therefore, an outcome of the combined effect of all these factors should be considered to estimate the change in usefulness at different magnetic fields. The objective of this article is to illustrate the practical scientific applications, focusing on MR imaging, of higher magnetic field strength. First, we will discuss previous literature and our experiments to demonstrate several changes that lead to a number of practical applications in MR imaging, e.g. in relaxation times, effects of contrast agent, design of RF coils, maintaining a safety profile and in switching magnetic field strength. Second, we discuss what will be required to gain the maximum benefit of high magnetic field when the current magnetic field (< or = 1.5 T) is switched to 3 or 4 T. In addition, we discuss MR microscopy, which is one of the anticipated applications of high magnetic field strength to understand the quantitative estimation of the gain benefit and other considerations to help establish a practically available imaging protocol.

Animals↗
PubMed2003

Recent advances in magnetic resonance perfusion imaging of the lung.

Magnetic resonance imaging has been relatively underused for clinical application in the lung; however, developments in magnetic resonance perfusion imaging using contrast agents and spin labeling techniques have shown significant potential for clinical application in lung perfusion. This article reviews the recent publications on magnetic resonance pulmonary perfusion.

Contrast Media↗
PubMed2002

Magnetic resonance microimaging of intraaxonal water diffusion in live excised lamprey spinal cord.

Anisotropy of water diffusion in axon tracts, as determined by diffusion-weighted MRI, has been assumed to reflect the restriction of water diffusion across axon membranes. Reduction in this anisotropy has been interpreted as degeneration of axons. These interpretations are based primarily on a priori reasoning that has had little empirical validation. We used the experimental advantages of the sea lamprey spinal cord, which contains several very large axons, to determine whether intraaxonal diffusion is isotropic and whether anisotropy is attributable to restriction of water mobility by axon surface membranes. Through the application of magnetic resonance microimaging, we were able to measure the purely intraaxonal diffusion characteristics of the giant reticulospinal axons (20-40 microm in diameter). The intraaxonal apparent diffusion coefficients of water parallel (longitudinal ADC, l-ADC) and perpendicular (transverse ADC, t-ADC) to the long axis were 0.98 +/- 0.06 (10(-3) mm2 sec) and 0.97 +/- 0.11 (10(-3) mm2 sec), respectively. In white matter regions that included multiple axons, l-ADCs were almost identical regardless of axon density in the sampled axon tract. By comparison, t-ADCs were reduced and varied inversely with the number of axons (and thus axolemmas) in a fixed cross-sectional area. Thus, diffusion was found to be isotropic when measured entirely within a single axon and anisotropic when measured in regions that included multiple axons. These findings support the hypothesis that the cell membrane is the primary source of diffusion anisotropy in fiber tracts of the central nervous system.

Animals↗
PubMed2002

Peritumoral brain edema in intracranial meningiomas evaluated by dynamic perfusion-weighted MR imaging: a preliminary study.

Our objective was to semi-quantitatively evaluate the cerebral perfusion in the peritumoral brain edema of meningiomas using dynamic perfusion-weighted MR imaging. Six patients with intracranial meningiomas accompanied by peritumoral brain edema were prospectively examined by perfusion-weighted MR imaging. One patient was examined twice, once before and once 5 months after the surgical resection. The relative regional cerebral blood volume (rrCBV), the relative regional cerebral blood flow (rrCBF), and the relative regional mean transit time (rrMTT) were calculated for peritumoral brain edema and the contralateral white matter. These parameters were compared between peritumoral brain edema and the contralateral white matter. The time-concentration curve of the peritumoral brain edema was less prominent than that of the contralateral white matter, resulting in a significantly lower rrCBV (mean 46%) and rrCBF (mean 45%) in peritumoral brain edema than those of contralateral white matter. The serial perfusion-weighted MR imaging also demonstrated the recovery of these parameters after the removal of meningioma by means of surgical resection. Perfusion-weighted MR imaging can demonstrate significantly decreased rrCBV and rrCBF in peritumoral brain edema compared with those in normal white matter.

Aged↗
PubMed2002

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.

Adult↗
PubMed2002

MR-pathologic correlation of lung specimens.

The aim of this study was to assess the feasibility of a new MR-pathologic correlation method utilizing a high-resolution MR technique with a 3-inch surface coil and elimination of susceptibility by replacing air in the pulmonary alveoli of lung specimens with water. Inflated cadaver lung specimens of various lung disorders were imaged using a conventional spin echo (SE) sequence in a clinical 1.5 T MR scanner. The MR images were correlated with pathologic specimens. In six out of seven specimens, MR revealed detailed images corresponding to pathological changes. MR may provide a non-invasive and non-destructive method for examining lung specimens and for image-pathologic correlation.

Cadaver↗
PubMed2002

CT and MR in pulmonary embolism: A changing role for nuclear medicine in diagnostic strategy.

The goal of this article is to summarize current data on computed tomography (CT) and magnetic resonance (MR) in the diagnosis of acute pulmonary embolism (PE) in relation to the radionuclide ventilation perfusion scan. It is important for the nuclear medicine, CT, and MR communities to develop a shared approach to this disorder. Triage using chest radiographs appears to be a practical method for enhancing both nuclear medicine and CT/MR performance. The realization that there is no clinically available gold standard for the diagnosis of PE suggests that the imaging community should replace impractical and idealistic discussions with more realistic outcome-oriented approaches. A simplified one-step evaluation of the pulmonary arteries and the lower extremity veins for deep venous thrombus can provide a comprehensive examination for PE. CT is currently a more practical diagnostic tool, whereas MR offers a scientific probe for pulmonary physiology including the regional mapping of ventilation-perfusion relationships. Nuclear medicine, CT, and MR thus form an imaging triad for the diagnosis of acute PE.

Humans↗
PubMed2002

Measurement of the vascularity and vascular leakage of gliomas by double-echo dynamic magnetic resonance imaging: a preliminary study.

RATIONALE AND OBJECTIVE: To evaluate the vascularity and vascular leakage of well-enhanced gliomas by double-echo dynamic magnetic resonance (MR) imaging. MATERIALS AND METHODS: Eight patients with glioblastoma multiforme (GBM) and two patients with juvenile pilocytic astrocytoma (JPA) were studied. Double-echo dynamic MR imaging was utilized to separate the T2* shortening effect and the T1 shortening effect. The former was represented by the vascularity index, and the latter was represented by the leakage index. These indexes were compared with histopathologic data. RESULTS: The mean vascularity index of the GBM was higher than that of the JPA (mean +/- SD, 3.48 +/- 1.57 [GBM] versus 0.51 +/- 0.29 [JPA]), and the mean leakage index of the JPA was higher than that of the GBM (1.35 +/- 0.87 [JPA] versus 0.27 +/- 0.15 [GBM]). Abundant vascularity was noted in the tight interstitial space in the pathologic specimen of GBM. Conversely, sparse vasculature was observed in the wide interstitial space in the pathologic specimen of JPA. CONCLUSION: This method may enable better characterization of grade in well-enhanced glioma by providing the information on the vascularity and leakage indexes.

Adult↗
PubMed2002

Large coalescent parenchymal nodules in pulmonary sarcoidosis: "sarcoid galaxy" sign.

OBJECTIVE: The purpose of this study was to evaluate the large parenchymal nodules in pulmonary sarcoidosis and to describe a new CT sign termed the "sarcoid galaxy." CONCLUSION: The CT appearance of pulmonary sarcoidosis suggests that the large nodules arise from a coalescence of small nodules. The large nodules are surrounded by many tiny satellite nodules. These findings were considered to simulate the appearance of a galaxy. This observation was supported by radiologic-pathologic correlation. The sarcoid galaxy sign may be a useful adjunct in the diagnosis of pulmonary sarcoidosis.

Adult↗
PubMedDate not supplied

Susceptibility-induced changes in signal intensity from spin-echo versus gradient-echo sequences.

This manuscript describes a study of the evaluation of T2 and T2* changes in a hypervascular tumor model (hemodialyzer phantom) under conditions simulating dynamic perfusion study. The measured 1/T2* was strongly dependent on the compartmentalization of contrast material within the model, whereas the observed 1/T2 was not. Gradient-echo magnetic resonance (MR) imaging may be more suitable than a spin-echo MR imaging for the evaluation of tumor vascularity.

Contrast Media↗
PubMedDate not supplied

H(2) (15)0 positron emission tomography validation of semiquantitative prostate blood flow determined by double-echo dynamic MRI: a preliminary study.

PURPOSE: Information regarding prostate blood flow as determined by positron emission tomography (PET) with H 0 may provide useful information about tumor diagnosis; however, PET requires a cyclotron for the production of an extremely short half-life (2 minutes) tracer. Therefore, the aim of this study was to propose a complementary index for blood flow as determined by MRI to validate the results and compare them with PET, especially for prostate tissue. METHODS: Six consecutive patients with prostate disease were studied. The two semiquantitative indices for tumor blood flow were calculated from the time-concentration curve measured from double-echo MR images. The theory of nondiffusible tracers by means of indicator dilution theory was applied to MR data. The relative regional blood flow (rrBF) was calculated as the ratio of the relative regional blood volume to relative regional mean transit time. Another proposed index was the maximum height of the time-concentration curve. PET studies were also performed, and absolute blood flow values were calculated for each subject. These indices calculated from different modalities were then compared. RESULTS: A significant correlation was found between the rrBF and the absolute blood flow as determined by PET (r = 0.69, p < 0.005). A significant correlation was also found between the maximum height of the time-concentration curve and the absolute blood flow (r = 0.85, p < 0.0001). CONCLUSIONS: The semiquantitative tumor blood flow indices measured with MRI have a good correlation with the corresponding measurements by PET; therefore, these indices may provide useful information about tumor diagnosis in clinical settings.

Aged↗