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Osamu Takizawa

Publications and source records attributed to Osamu Takizawa.

12 recordsLinked to original sources
PubMed2005

Observation of contrast enhancement in the cochlear fluid space of healthy subjects using a 3D-FLAIR sequence at 3 Tesla.

In animals, the enhancement of perilymph in the cochlea has been reported using 1.25 mmol/kg of Gd-DTPA, allowing the separate visualisation of perilymph and endolymph for the diagnosis of Meniere's disease. The purpose of this study was three-fold: (1) to determine the optimal timing for detecting cochlear fluid enhancement using 3D-FLAIR (fluid-attenuated inversion recovery) after intravenous administration of 0.1 mmol/kg of Gd-DTPA in healthy human subjects; (2) to examine the reliability of enhancement in multiple healthy subjects; and (3) to investigate whether endolymph and perilymph space can be visually discriminated. In two healthy subjects, 3D-FLAIR images were obtained before, immediately after and 2 h, 4 h and 6 h after the injection. Three more healthy subjects were scanned before and 4 h after the injection. In all four ears of the initial two subjects, cochlear fluid was found to be most intensely enhanced 4 h after the injection. In all of the additional three subjects, the cochlear fluid signal had increased after 4 h from injection. However, visual differentiation of endolymph and perilymph fluid could not be achieved. Using 3D-FLAIR and Gd-DTPA, cochlear fluid enhancement can be observed in healthy human ears, even with a single dose of contrast-medium injection.

Cochlea↗
PubMed2005

Differentiation of noncancerous tissue and cancer lesions by apparent diffusion coefficient values in transition and peripheral zones of the prostate.

PURPOSE: To compare the apparent diffusion coefficient (ADC) values of prostate cancer in both the peripheral zone (PZ) and the transition zone (TZ) with those of benign tissue in the same zone using echo-planar diffusion weighted imaging with a parallel imaging technique. MATERIALS AND METHODS: A total of 29 consecutive male patients (mean age 61.3 years, age range 53-88 years) with suspected prostate cancer were referred for MR imaging. All patients underwent transrectal ultrasound (TRUS)-guided biopsy of the prostate after MR imaging at 1.5 T, including ADC. For each patient, seven to 10 specimens were obtained from the prostate, and regions of interest (ROIs) were drawn on the ADC map by referring to the urologist's illustration of TRUS-guided biopsy sites. ADC values of cancerous tissue in both the PZ and TZ were compared to those of noncancerous tissue in the same zone. RESULTS: Out of 29 patients, 23 had cancer tissue. In the 23 patients with cancer, the mean ADC value of all cancer ROIs and that of all noncancer ROIs, respectively, were 1.11 +/- 0.41 x 10(-3) and 1.68 +/- 0.40 x 10(-3) mm(2)/second (values are mean +/- SD) (P < 0.01). The mean ADC value of TZ cancer ROIs and that of TZ noncancer ROIs, respectively, were 1.13 +/- 0.42 x 10(-3) and 1.58 +/- 0.37 x 10(-3) mm(2)/second (P < 0.01). CONCLUSIONS: ADC measurement with a parallel imaging technique showed that ADC values of prostate cancer in both the PZ and TZ were significantly lower than those of benign tissue in the PZ and TZ, respectively.

Adenocarcinoma↗
PubMed2005

Diffusion-weighted images of the liver: comparison of tumor detection before and after contrast enhancement with superparamagnetic iron oxide.

PURPOSE: To study the recognition of malignant lesions of the liver on diffusion-weighted images (DWI) can be improved by the administration of superparamagnetic iron oxide (SPIO). MATERIALS AND METHODS: Pre- and post-SPIO mediated DWI of the liver was compared in six patients with suspected malignant liver lesions at 1.5 Tesla using a parallel imaging technique. RESULTS: Post-SPIO DWI showed improved contrast-to-noise ratio between malignant lesions and liver. Furthermore, the spleen signal was decreased on post-SPIO DWI, thus avoiding the overlap of the spleen and left lobe of the liver on maximum intensity projections (MIP). CONCLUSION: Recognition of malignant lesions of the liver was improved by SPIO on DWI. On MIP images of DWI, SPIO helped to decrease the overlap of spleen signal on the liver in some projection angles.

Adult↗
PubMed2004

Apparent diffusion coefficient in cervical cancer of the uterus: comparison with the normal uterine cervix.

A relation between apparent diffusion coefficient (ADC) values and tumor cellular density has been reported. The purpose of this study was to measure the ADC values of cervical cancers in the uterus and compare them with those of normal cervical tissues, and to test whether ADC could differentiate between normal and malignant cervical tissues in the uterus. Twelve consecutive female patients with cervical cancer of the uterus and ten female patients with other pelvic abnormalities were included in this study. ADC was measured at 1.5 T with b-factors of 0, 300 and 600 s/mm2 using single-shot echo-planar diffusion-weighted imaging and a parallel imaging technique. The mean ADC value of cervical cancer lesions was 1.09+/-0.20 x 10(-3) mm2/s, and that of normal cervix tissue was 1.79+/-0.24 x 10(-3) mm2/s (P<0.0001). In nine patients treated by chemotherapy and/or radiation therapy, the mean ADC value of the cervical cancer lesion increased significantly after therapy (P<0.001). The present study showed, with a small number of patients, that ADC measurement has a potential ability to differentiate between normal and cancerous tissue in the uterine cervix. Further study is necessary to determine the accuracy of ADC measurement in monitoring the treatment response.

Adult↗
PubMed2004

Comparison of flow artifacts between 2D-FLAIR and 3D-FLAIR sequences at 3 T.

It has been reported that 3D-FLAIR can reduce the flow artifact resulting from cerebrospinal fluid (CSF) at 1.5 T compared to 2D-FLAIR. Flow-related artifacts tend to be worse at 3 T than at 1.5 T. The purpose of this study was to compare the CSF flow artifacts of 2D-FLAIR and 3D-FLAIR sequences at 3 T in eight healthy volunteers. The grade of CSF-related artifacts were scored through observing the perimedullary cistern, cerebellopontine angle cisterns, fourth ventricule, prepontine cistern, suprasellar cistern, ambient cisterns, sylvian fissures, third ventricle and lateral ventricles. Grading was performed on either axial or sagittal images. The CSF in-flow artifact scores were significantly higher on axial 2D-FLAIR than on axial 3D-FLAIR MPR images in all areas except the bilateral sylvian fissures, and higher on sagittal 2D-FLAIR than on sagittal 3D-FLAIR MPR images in perimedullary, bilateral CP angle and suprasellar cisterns. The CSF-related flow artifacts were significantly reduced by 3D-FLAIR, while structures in the cistern were depicted more clearly, even at 3 T. Further study is necessary to compare the clinical efficacy between 2D-FLAIR and 3D-FLAIR in depicting subtle abnormalities.

Adult↗
PubMed2004

Whole-brain vascular reactivity measured by fMRI using hyperventilation and breath-holding tasks: efficacy of 3D prospective acquisition correction (3D-PACE) for head motion.

Functional MR imaging (fMRI) study using hyperventilation and breath-holding task has been reported to be one of the non-invasive methods to examine whole-brain vascular reactivity. The purpose of this study was to evaluate the efficacy of a method for 3D prospective detection and correction of head motion (3D-PACE) in a study of whole-brain vascular reactivity using hyperventilation and breath-holding tasks. Eight healthy volunteers were scanned using an fMRI protocol of hyperventilation and breath-holding task blocks at 3 T in separate runs with and without 3D-PACE. In two subjects, two more runs with and without 3D-PACE were repeated. The mean total number of activated voxels +/- standard deviation was 26,405.3+/-1,822.2 in the run with 3D-PACE and 17,329.9+/-2,766.3 in the run without 3D-PACE ( P<0.05), although there is some intersubject variation regarding the effect of 3D-PACE. In the two subjects whose performed two more runs, the number of activated voxels were smaller in the run without 3D-PACE than even in the run with 3D-PACE performed later. We conclude that 3D-PACE is beneficial for fMRI studies of whole-brain vascular reactivity induced by hyperventilation and breath-holding.

Adult↗
PubMed2004

High-speed imaging at 3 Tesla: a technical and clinical review with an emphasis on whole-brain 3D imaging.

Improvements to the inherently high specific-absorption rate (SAR) of high-speed imaging at 3T are necessary in order to render this method clinically feasible. Various efforts have been undertaken to improve the associated hardware and software. In this review, we focus on whole-brain isotropic 3D imaging with a turbo spin-echo sequence with variable flip-angle echo trains (3D-TSE-VFL) and present its technical and clinical features. This sequence can be used to acquire images of various contrasts including T2-weighted, fat-suppressed T2-weighted, fluid-attenuated inversion recovery (FLAIR), fat-suppressed FLAIR, and STIR (short tau inversion recovery). Various aspects of 3D-TSE-VFL are discussed, including CSF (cerebrospinal fluid) and metal artifacts, STIR contrast, small-part visualization other than brain, and the possibility of serial subtraction. Some images from clinical cases are presented.

Adult↗
PubMed2003

Optimization of diffusion-tensor MR imaging data acquisition parameters for brain fiber tracking using parallel imaging at 3 T.

The purpose of this study was to optimize the parameters of diffusion-tensor magnetic resonance imaging (DT MRI) for brain fiber tracking using a slice thickness of 2 mm, a resolution advantage allowed by the high signal-to-noise ratio at 3 T, combined with an 8-channel phased-array head coil. The b-factor, number of motion probing gradient (MPG) directions, and number of averages were varied, and the results of brain fiber tracking for the pyramidal tract and trigeminal nerve were compared qualitatively and quantitatively. The DT MRI data sufficient for brain fiber tracking in healthy subjects can be obtained in <2 min with a 2-mm slice thickness, 700-s/mm2 b-factor, 6 MPG directions, and no averaging (number of averages=1).

Adult↗
PubMed2003

Measurement of in vivo local shear modulus using MR elastography multiple-phase patchwork offsets.

Magnetic resonance elastography (MRE) is a method that can visualize the propagating and standing shear waves in an object being measured. The quantitative value of a shear modulus can be calculated by estimating the local shear wavelength. Low-frequency mechanical motion must be used for soft, tissue-like objects because a propagating shear wave rapidly attenuates at a higher frequency. Moreover, a propagating shear wave is distorted by reflections from the boundaries of objects. However, the distortions are minimal around the wave front of the propagating shear wave. Therefore, we can avoid the effect of reflection on a region of interest (ROI) by adjusting the duration of mechanical vibrations. Thus, the ROI is often shorter than the propagating shear wavelength. In the MRE sequence, a motion-sensitizing gradient (MSG) is synchronized with mechanical cyclic motion. MRE images with multiple initial phase offsets can be generated with increasing delays between the MSG and mechanical vibrations. This paper proposes a method for measuring the local shear wavelength using MRE multiple initial phase patchwork offsets that can be used when the size of the object being measured is shorter than the local wavelength. To confirm the reliability of the proposed method, computer simulations, a simulated tissue study and in vitro and in vivo studies were performed.

Algorithms↗
PubMed2002

Cystic ovarian lesions in SSFP diffusion imaging.

PURPOSE: MR assessments of ovarian cystic lesions are usually based on morphological features, signal intensities and enhancement with contrast media. This study was performed to evaluate the usefulness of the steady-state free precession (SSFP) diffusion imaging of cystic ovarian lesions for analyzing cystic contents. MATERIALS AND METHODS: Sixty-one ovarian cystic lesions in 37 patients were examined. The diffusion-related coefficient (DRC) and the ratio of the relative apparent diffusion coefficient of the lesion to that of subcutaneous fat tissue (rADC(L)/rADC(F)) were calculated from SSFP diffusion images. RESULTS: The DRCs and the rADC(L)/rADC(F) ratios in endometrial cysts and in the fatty parts of dermoid cysts were significantly lower than in other cystic tumors. CONCLUSION: SSFP diffusion imaging can be included in clinical practice to analyze ovarian cystic lesions within a short scan time; the DRC and the rADC(L)/rADC(F) ratio are useful for evaluating cystic contents.

Adolescent↗
PubMed2002

Proton two-dimensional chemical shift imaging for evaluation of prostate cancer: external surface coil vs. endorectal surface coil.

PURPOSE: To compare the diagnostic ability of proton magnetic resonance spectroscopy (MRS) using an external surface coil with that using an endorectal surface coil in patients with prostate cancer. MATERIALS AND METHODS: MR imaging (MRI) and two-dimensional chemical shift imaging (2D CSI) were performed in 5 healthy volunteers and in 35 patients with prostate cancer. The receiver coil was the anterior lower part of a phased-array coil or an endorectal surface coil. RESULTS: Receiver-operating characteristic analysis for diagnosing prostate cancer showed no significant difference (P = 0.784) between the area under the curve of phased-array coil CSI and that of endorectal surface coil CSI. CONCLUSION: The phased-array coil CSI could provide comparable detection accuracy to endorectal surface coil CSI. In patients with rectal diseases or patients who could not tolerate the discomfort with insertion of an endorectal surface coil, we recommend the phased-array coil CSI.

Adult↗