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Kei Yamada

Publications and source records attributed to Kei Yamada.

36 records · Page 2Linked to original sources
PubMed2004

White matter loss in the splenium of the corpus callosum in a case of posterior cortical atrophy: a diffusion tensor imaging study.

There have been several functional imaging studies using PET and SPECT to investigate posterior cortical atrophy (PCA). These studies have suggested dysfunction of corticocortical connections which is consistent with the occipitoparietal stream. However, there are no reports suggesting disturbance of the white matter that interconnects the temporal, parietal and occipital cortices. We measured fractional anisotropy (FA) in the genu and splenium of the corpus callosum and created color maps using diffusion tensor imaging (DTI), which is a relatively new MRI technique that allows visualization of the directionality of water diffusion, in a patient with PCA and compared these findings with those in 5 typical Alzheimer disease (AD) patients. The PCA patient was a 75-year-old man presenting with progressive complex visual disorder who satisfied the clinical diagnostic criteria for PCA. In 5 typical AD patients, the FA index in the splenium was higher than that in the genu; however, in the PCA patient, the FA index in the splenium was significantly lower than that in the genu. A DTI-based color map of the PCA patient showed reduction of anisotropy and fiber volume in the splenium. These findings suggest that the splenium of the corpus callosum secondarily degenerated due to neuronal degeneration of the temporal, parietal and occipital cortices and suggest that reduction of the FA in the splenium is one of the characteristics of PCA.

Aged↗
PubMed2004

Equivalent cross-relaxation rate imaging of breast cancer.

PURPOSE: To determine whether equivalent cross-relaxation rate (ECR) imaging is a feasible method for demonstrating breast cancer. MATERIALS AND METHODS: Fifteen breast cancer patients underwent both ECR imaging, with off-resonance saturation pulses at frequency offsets of 7 and 19 ppm (ECR-7 and ECR-19, respectively) from water resonance, and gadolinium (Gd)-enhanced dynamic magnetic resonance imaging (MRI) of the breast. The mean tumor size was 26.5 mm. The tumor outlines defined by their shape and margin on ECR-7 images were compared with the subtraction images produced by the dynamic study, and the distribution of hyperintensity areas and their shapes on ECR-19 images were assessed. All patients had surgery and pathological findings were compared to ECR images. RESULTS: The tumor outline of 13/15 (87%) tumors on ECR-7 images was nearly identical to that on subtraction images; ECR-19 images demonstrated the location and degree of fibrosis. The tumor outline of the other two tumors was less clear on ECR-7 images, and internal hyperintensity on ECR-19 images reflected intratumoral fibrotic foci. ECR-7 and -19 imaging findings allowed identification of four distinct tumor types that reflected the tumor growth patterns and their internal structures associated with fibrosis. CONCLUSION: ECR imaging is a feasible imaging technique for demonstrating breast cancer.

Adult↗
PubMed2004

Stroke patients' evolving symptoms assessed by tractography.

PURPOSE: To test the hypothesis that an interval evolution in the location of the depicted sensorimotor tract relative to the infarct (the "tract-infarct relationship") may be related to stroke victims' symptom progression. MATERIALS AND METHODS: Patients (N = 7) who underwent multiple diffusion-tensor imaging (DTI) studies during symptomatic progression were included in this study. DTI was performed using a single-shot echo-planar imaging (EPI) technique with a motion-probing gradient in six orientations, a b-value of 800 seconds/mm2, and six image averages. The total scan time was four minutes and 24 seconds. Fiber-tracking of the sensorimotor pathways was performed, and the locations of these tracts were retrospectively assessed in relation to the evolution of the symptoms. RESULTS: Five of the seven patients showed an interval enlargement of the infarct on diffusion-weighted (DW) images. In two of these cases the lesion enlarged to involve the sensorimotor tracts, while in three cases the lesion enlarged only so far to come into close proximity to the sensorimotor tract. In the remaining two cases there was no interval enlargement of the infarct, and therefore the tract-infarct relationship could not account for the evolution of the symptoms in these cases. CONCLUSION: A tract-infarct relationship can be observed with the use of a fiber-tracking technique, and the results may improve our understanding of the symptom progression seen in stroke victims.

Adult↗
PubMed2003

Fiber-tracking method reveals sensorimotor pathway involvement in stroke patients.

BACKGROUND AND PURPOSE: We tested the feasibility of a new MRI technique that provides visualization of the sensorimotor tracts in vivo in a group of stroke victims. SUMMARY OF REPORT: Fourteen patients with small infarctions involving the white matter of the supratentorial brain were evaluated. Sensorimotor tracts on the lesional and contralesional sides were successfully depicted in all cases. The position of the sensorimotor tracts relative to the infarct was in good agreement with clinical symptoms. The overall sensitivity and specificity for sensorimotor tract involvement were 100% and 77%, respectively. CONCLUSIONS: Our proposed fiber-tracking method was shown to be a clinically feasible technique that correlates well with clinical symptoms.

Aged↗
PubMed2003

Implications of SENSE MR in routine clinical practice.

Sensitivity encoding (SENSE) uses multiple MRI receive coil elements to encode spatial information in addition to traditional gradient encoding. Requiring less gradient encodings translates into shorter scan times, which is extremely beneficial in many clinical applications. SENSE is available to routine diagnostic imaging for the past 2 years. This paper highlights the use of SENSE with scan time reduction factors up to 6 in contrast-enhanced MRA, routine abdominal imaging, mammography, cardiac and neuro imaging. It is shown that SENSE has opened new horizons in both routine and advanced MR imaging.

Contrast Media↗
PubMed2003

Optimization of TI values in inversion-recovery MR sequences for the depiction of fine structures within gray and white matter: separation of globus pallidus interna and externa.

RATIONALE AND OBJECTIVES: The authors' purpose was to search the inversion time (TI) values that enable the best differentiation of fine structures in gray matter (gray-gray differentiation). MATERIALS AND METHODS: Seven healthy adult volunteers with no history of neurologic disease or head trauma were recruited and gave their informed consent. The subjects consisted of two men and five women ranging in age from 25 to 38 years, with a mean age of 28 years +/- 5. The subjects were imaged with a turbo spin-echo inversion-recovery sequence. This sequence was performed in the axial plane at the level of the basal ganglia with the following parameters: repetition time, 3,200 msec; echo time, 15 msec; three signals acquired; echo train, seven; section thickness, 3 mm; matrix size, 256 x 256; and field of view, 180 mm. The tested values were TI = 100, 200, 300, 400, and 500 msec. Region-of interest measurements were performed at the following anatomic structures and represent gray-gray and white-white differentiations, respectively: globus pallidus externa versus globus pallidus interna, and optic radiation versus surrounding white matter. RESULTS: The maximum contrast index value occurred at TI = 400 msec for globus pallidus externa versus globus pallidus interna (P < .05) With the contrast-to-noise ratio, no significant difference in gray-gray differentiation was observed among the various TIs. The minimum signal-to-noise ratio of the gray matter occurred at TI = 400 msec (P < .05). A subjective evaluation revealed an overall superiority of gray-matter differentiation with TI = 400 msec. CONCLUSION: A TI of 400 msec was the most suitable for this purpose.

Adult↗
PubMed2003

Brain fiber tracking with clinically feasible diffusion-tensor MR imaging: initial experience.

Two technical challenges must be overcome before brain fiber tracking with diffusion-tensor magnetic resonance (MR) imaging can be applied to clinical practice: Imaging time must be shortened, and image distortion must be minimized. Single-shot echo-planar MR imaging with parallel imaging technique enabled both objectives to be accomplished. Twenty-three consecutive patients with brain tumors underwent MR imaging with a 1.5-T whole-body MR system. Fiber tracts on the lesion side in the brain had varying degrees of displacement or disruption as a result of the tumor. Tract disruption resulted from direct tumor involvement, compression on the tract, and vasogenic edema surrounding the tumor. This diffusion-tensor MR imaging method with the parallel imaging technique allows clinically feasible brain fiber tracking.

Adolescent↗
PubMed2002

Imaging findings in intracranial aspergillosis.

RATIONALE AND OBJECTIVES: The authors' purpose was to elucidate the various computed tomographic (CT) and magnetic resonance (MR) imaging findings in intracranial aspergillosis. MATERIALS AND METHODS: Retrospective analysis of cranial imaging findings was performed in eight proved cases of central nervous system aspergillosis. The patients ranged in age from 17 to 75 years. Four patients were immunocompromised, and four were immunocompetent. CT was performed in all eight patients, and MR imaging in five. RESULTS: Six patients (75%) had multiple lesions seen on the imaging studies, with a total of 27 focal brain lesions demonstrated. The lesions were most commonly seen in the cerebral hemispheres (n = 21), with lesser involvement of the basal ganglia (n = 2) and the posterior fossa (n = 4). Seven lesions were hemorrhagic on CT and/or MR images. There was a correlation between lesion size and hemorrhage, with hemorrhage more likely in larger lesions (>15 mm). At pathologic examination, foci of hemorrhage were noted within both infarcts and abscesses. Enhancement was noted in five lesions, four of which were confirmed abscesses. Contrast enhancement of the lesions was vague and week in immunocompromised patients but solid and strong in immunocompetent patients. There were 18 lesions without hemorrhage or enhancement; they were either infarcts or abscesses at pathologic examination. Some of these small nonhemorrhagic nonenhancing brain lesions in the subcortical white matter mimicked lacunar infarcts. CONCLUSION: Typical imaging findings of intracranial aspergillosis include multifocal lesions involving the cerebral hemispheres, with hemorrhage in approximately 25% of lesions. Lesional contrast enhancement tends to be stronger in immunocompetent hosts.

Adolescent↗
PubMed2002

Effect of intravenous gadolinium-DTPA on diffusion-weighted images: evaluation of normal brain and infarcts.

BACKGROUND AND PURPOSE: Diffusion-weighted imaging (DWI) is usually done before administration of intravenous contrast agents. Repetition of DWI is occasionally necessary after administration, but the effects of contrast material on DWI and apparent diffusion coefficient (ADC) values have not yet been fully examined. The present study assesses whether administration of gadolinium-based contrast material significantly affects DWI and ADC values. METHODS: We examined DWI data from 39 patients (mean age, 67.9 years; range, 34 to 87 years) who were evaluated with a stroke protocol at our institute. All patients were scanned at the acute or subacute stages of infarct from 3 hours to 5 days after symptom onset. We obtained DWI images using single-shot echo-planar imaging with a b value of 1000 s/mm2. Patients were injected with 0.1 mmol gadopentetate dimeglumine per 1 kg body weight. We examined the signal-to-noise ratio of the normal brain and the infarct and evaluated the contrast-to-noise ratio of each lesion. In addition, we compared the ADC values calculated from the DWI images before and after administration of contrast. The statistical significance of differences between precontrast and postcontrast administration was determined by use of a paired t test. RESULTS: The signal-to-noise and contrast-to-noise ratios of the DW images were not significantly different before and after administration of contrast agent. The ADC values were slightly lower after administration of contrast agent for both normal brain (P=0.0011) and infarcts (P=0.038). The estimated differences in the ADC values were approximately 1.3% and 3.5% for normal brain and infarcts, respectively. CONCLUSIONS: The lack of a significant difference between the signal-to-noise and contrast-to-noise ratios of DW images before and after administration of contrast agent indicates the feasibility of postcontrast DWI.

Adult↗
PubMed2002

Magnetic resonance perfusion-weighted imaging of acute cerebral infarction: effect of the calculation methods and underlying vasculopathy.

BACKGROUND AND PURPOSE: Various calculation methods are available to estimate the transit-time on MR perfusion-weighted imaging (PWI). Each method may affect the results of PWI. Steno-occlusive disease in the parent vessels is another factor that may affect the results of the PWI. The purpose of this study was to elucidate the effect of the calculation methods and underlying vasculopathy on PWI. METHODS: From a pool of 113 patients who had undergone PWI during the study period, a total of 12 patients with nonlacunar ischemic strokes who were scanned within 24 hours after onset of symptom were selected for the study. The patient population consisted of 6 patients who had extracranial internal carotid artery stenosis (>70%) and 6 individuals without stenosis. Seven different postprocessing methods were evaluated: first moment, ratio of area to peak, time to peak (TTP), relative TTP, arrival time, full-width at half-maximum, and deconvolution methods. Follow-up MR or CT images were used to determine the areas that evolved into infarcts, which served as the gold standard. Sensitivity and specificity of each transit time technique were calculated. RESULTS: Calculation methods with high sensitivity were the first moment (sensitivity, 74%), TTP (sensitivity, 77%), and deconvolution methods (sensitivity, 81% to 94%). Between the 2 groups with and without internal carotid artery stenosis, the specificity of most of the techniques was lower in the internal carotid artery stenosis group. The first moment and deconvolution methods maintained relatively high specificity even in the stenosis group. CONCLUSIONS: The calculation technique and presence of underlying vasculopathy have a direct impact on the results of PWI. The methods with high sensitivity even in the presence of steno-occlusive disease were the first moment and deconvolution methods with arterial input function derived from the peri-infarct arteries; the deconvolution method was the superior choice because of higher lesion conspicuity.

Acute Disease↗
PubMed2002

Proton chemical shift imaging in pick complex.

BACKGROUND AND PURPOSE: Pick complex (PC) is the name given to a group of diseases comprising Pick disease and its variations, all of which have a large degree of pathologic and clinical overlap. Because of this overlap, the observation of neuropathologic changes in vivo is difficult, although these changes play important roles in the criteria used for classification. The purpose of this study was to evaluate changes in brain metabolism in PC with proton chemical shift imaging ((1)H-CSI). METHODS: Nine patients with PC (three each with frontotemporal dementia, corticobasal degeneration [CBD], and primary progressive aphasia [PPA]) and five healthy subjects underwent (1)H-CSI. Volumes of interest were selected at the level of the basal ganglia by using a spin-echo sequence (TR/TE, 2000/13). Peak areas and ratios of N-acetylaspartate (NAA), creatine (Cr), and choline (Cho) were calculated in voxels in the basal ganglia and perisylvian regions. RESULTS: Reduced NAA/Cho ratios were observed in the right basal ganglia of the patients with PC. In patients with CBD or PPA, low NAA/Cr values were detected in the right perisylvian region. CONCLUSION: In PC, (1)H-CSI decreased NAA values in a wide area. Significantly reduced NAA levels in the right hemisphere in patients with PC suggests a neurodegenerative change and may reflect cases in which the right hemisphere is dominantly affected, compared with the left hemisphere. (1)H-CSI provided information that could not be obtained with other imaging techniques. Thus, (1)H-CSI may provide useful information for understanding the pathologic process underlying PC.

Adult↗
PubMedDate not supplied

High-resolution imaging of the spine using multidetector-row computed tomography: differentiation between benign and malignant vertebral compression fractures.

OBJECTIVE: The purpose of this study was to investigate the ability of high-resolution computed tomography (CT) images to distinguish between benign and malignant vertebral compression fractures. METHODS: Computed tomography images of 45 benign compression fractures in 40 patients and 33 malignant compression fractures in 33 patients were evaluated. A 16-slice multidetector-row CT scanner was used for data acquisition, and axial images with a slice thickness of 1 mm and sagittal and coronal multiplanar reconstruction images with a slice thickness of 0.7 to 1 mm were used for interpretation. RESULTS: The following findings were significantly more frequent in malignant fractures: destruction of the anterolateral and/or posterior cortex of the vertebral body, destruction of the cancellous bone of the vertebral body, destruction of the end plate, destruction of the pedicle, a paraspinal soft tissue mass, and an epidural mass. The extremely reliable signs of malignancy were destruction of the anterolateral and/or posterior cortex of vertebral body (100% accuracy) and destruction of the cancellous bone of the vertebral body (97.4% accuracy). CONCLUSION: High-resolution CT can provide many useful signs for differentiating between benign and malignant vertebral compression fractures, and its diagnostic ability is sufficient for clinical use.

Aged↗
PubMedDate not supplied

Do white matter changes have clinical significance in Alzheimer's disease?

BACKGROUND: Although white matter changes visible with MRI are generally considered to result from ischemia, it has become clear that these changes also appear in patients with Alzheimer's disease (AD). However, their significance in AD is unknown. OBJECTIVE: We evaluated the clinical significance of white matter changes in AD. METHODS: Ninety-six AD patients (79.4 +/- 5.92 years old) and 48 age-matched control subjects (80.0 +/- 7.03 years old) participated in the study. Three neuroradiologists assessed the degree of periventricular hyperintensities (PVH) and deep white matter hyperintensities (DWMH) using a modified Fazekas' rating scale. We examined whether there was a difference in the severity and the histogram pattern of the white matter changes, or in vascular factors (hypertension, diabetes mellitus, and ischemic heart disease) between the two groups. We also analyzed the association between the severity of the white matter changes and the degree of dementia (MMSE score and disease duration). RESULTS: There were no differences in the vascular factors between AD and control subjects. The degree of PVH in AD was severe compared with that in the control subjects. In histograms of the number of subjects with each degree of PVH severity, the distribution of AD patients had peaks at both the low and intermediate degrees of PVH, while most of the controls had a low degree of PVH. There was no difference in the degree or the histogram pattern of DWMH between the two groups. The severity of white matter changes was not associated with severity of dementia in AD. CONCLUSIONS: Although PVH might have several causative factors, and may have some clinical significance, the change itself does not contribute to the progression of AD.

Aged↗
PubMedDate not supplied

Iron-induced susceptibility effect at the globus pallidus causes underestimation of flow and volume on dynamic susceptibility contrast-enhanced MR perfusion images.

BACKGROUND AND PURPOSE: Age-related iron accumulation in extrapyramidal nuclei causes T2 shortening, which may result in decreased signal intensity in these areas on MR images. Because the dynamic susceptibility contrast-enhanced technique uses heavily T2*- or T2-weighted images, the iron-induced susceptibility may have direct impact on perfusion imaging. The purpose of this study was to assess the effect of iron-induced susceptibility on the calculated perfusion parameters. The difference of this effect between gradient-echo and spin-echo sequences was also assessed. METHODS: Dynamic susceptibility contrast-enhanced MR perfusion imaging data of 12 patients were used for this study. Perfusion images were obtained using a single shot spin-echo echo-planar imaging sequence in seven patients and a gradient-echo echo-planar imaging sequence in five patients. Region of interest measurements of relative cerebral blood flow, relative cerebral blood volume, and mean transit time were obtained at various parts of the gray matter, including the globus pallidus, putamen, caudate nucleus, thalamus, and cerebral cortex of temporal, frontal, and occipital lobes. The baseline signal intensity on the source images and the magnitude of signal change (DeltaR2* or DeltaR2) were also assessed. RESULTS: The globus pallidus had statistically significantly lower values of relative cerebral blood flow, relative cerebral blood volume, baseline signal intensity, and magnitude of signal change compared with other parts of the gray matter for both gradient-echo and spin-echo sequences (P <.05). Underestimations of these values were more prominent for the gradient-echo than for the spin-echo sequence. Little variance in the measured mean transit time was noted. CONCLUSION: Iron-induced susceptibility effect may lead to underestimation of relative cerebral blood flow and relative cerebral blood volume in the basal ganglia.

Aged↗