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Masaaki Hori

Publications and source records attributed to Masaaki Hori.

13 recordsLinked to original sources
PubMed2006

Line scan diffusion tensor MRI at low magnetic field strength: feasibility study of cervical spondylotic myelopathy in an early clinical stage.

PURPOSE: To implement line scan diffusion tensor MR imaging (LSDTI) on a 0.2 Tesla MR imager, and investigate the findings in the spinal cord of patients with cervical spondylotic myelopathy in an early clinical stage. MATERIALS AND METHODS: Fourteen patients with clinical symptoms of cervical myelopathy underwent LSDTI. The signal-to-noise ratio (SNR) in the spinal cord and cerebrospinal fluid (CSF) was evaluated. The apparent diffusion coefficient (ADC) and fractional anisotropy (FA) were measured. We classified the ROIs into two groups: 1) unaffected (no clinical symptoms and no abnormality on conventional images) and 2) affected (some clinical symptoms but no abnormal signal on conventional images). Three-dimensional (3D) fiber-tracking was also studied. RESULTS: The isotropic ADC values (10(-3)mm2/sec) were 1.28 +/- 0.11 in group 1 and 1.59 +/- 0.23 in group 2. The FAs were 0.55 +/- 0.07 in group 1, and 0.47 +/- 0.11 in group 2. The ADC value in group 2 increased (P < .001, Mann-Whitney U-test) and the FA in group 2 decreased (P = 0.24) on average, compared to those in group 1. 3D fiber-tracking was successful in 64% (9/14) of the cases. CONCLUSION: LSDT images at low field strength may be a sensitive method for elucidating the structural characteristics of spinal cord pathology in vivo. However, clinical correlation and a long-term follow-up study will be needed.

Adolescent↗
PubMed2006

Effect of injection rate of contrast material on CT of hepatocellular carcinoma.

OBJECTIVE: The purpose of this study was to assess the effect of two injection rates of contrast material (3 mL/sec and 5 mL/sec) in hepatic arterial dominant phase MDCT for the detection of small (< 2 cm) hepatocellular carcinomas. MATERIALS AND METHODS: The injection rates 3 mL/sec and 5 mL/sec were used prospectively in imaging examinations of patients with the suspected diagnosis of hepatocellular carcinoma. Each group consisted of 30 patients by chance. The group that received injections at 3 mL/sec had 35 hepatocellular carcinoma lesions, and the 5 mL/sec group had 41 lesions. In all patients the dose and concentration of contrast material were 100 mL and 350 mg/mL iodine (total dose of iodine, 35 g). In each patient a mini-test-bolus technique was used with an additional 15 mL of contrast material to determine optimal scan delay after administration of contrast material. Receiver operating characteristic analysis was used to assess diagnostic performance with the two injection rates of contrast material. RESULTS: There were no statistically significant differences between the two groups in regard to area under the curve and sensitivity. These values for the 3 mL/sec group were 0.97 and 28/35 (80%) and for the 5 mL/sec group were 0.96 and 36/41 (88%). However, the specificity and positive predictive values at 3 mL/sec (236/250 [95%] and 28/42 [67%]) were significantly higher than those at 5 mL/sec (227/265 [86%] and 36/73 [49%]) (p < 0.05). These results suggest there were more false-positive findings of contrast-enhanced lesions in cirrhotic livers on hepatic arterial dominant phase images obtained after injection of contrast material at 5 mL/sec than on images obtained after injection at 3 mL/sec. CONCLUSION: In the detection of small hypervascular hepatocellular carcinoma in cirrhotic liver, the risk of false-positive findings of lesions on hepatic arterial dominant phase images is significantly greater with the higher injection rate (5 mL/sec) than with the medium rate (3 mL/sec).

Adult↗
PubMed2005

The magnetic resonance Matas test: Feasibility and comparison with the conventional intraarterial balloon test occlusion with SPECT perfusion imaging.

PURPOSE: To evaluate a new MR Matas test that uses a form of contrast-enhanced MR angiography (MRA) with temporary manual occlusion of the common carotid artery whose internal carotid artery (ICA) is to be permanently sacrificed. MATERIALS AND METHODS: The MR Matas test was performed on eight patients using an open type MR imager (Signa Profile 0.2 Tesla ver. 7.5, GE-YMS, Tokyo, Japan). Conventional balloon occlusion Matas test and single-photon emission computed tomography (SPECT) of the brain were performed in all cases within a week before or after the MR Matas test. RESULTS: The MR Matas test was successful in all eight patients without any complications. The image quality of the MR Matas test was generally sufficient to confirm cross-flow from the patent side to the occluded side in comparison with selective intraarterial digital subtraction angiography (IADSA) except in one case. CONCLUSION: Brain perfusion information using MR Matas test is comparable to brain SPECT.

Aged↗
PubMed2005

Line-scan diffusion tensor MR imaging at 0.2 T: feasibility study.

PURPOSE: To investigate and measure apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values using data obtained with line-scan diffusion-weighted imaging (DWI) of human brains on a 0.2 Tesla MR imager. MATERIALS AND METHODS: Diffusion-tensor imaging (DTI) was performed on eight healthy volunteers. The signal-to-noise ratios (SNRs) of white matter and cerebrospinal fluid were measured. ADC and FA were also measured from the data obtained from all subjects. Three-dimensional corticospinal fiber tracts were reconstructed from the DT images and a qualitative evaluation was done. RESULTS: The total scan time was 52 minutes 30 seconds for 18 slices with full-tensor images covering the whole brain. The ADCs and FAs show the appropriate values, in comparison with values obtained at high field strength in previous studies. Corticospinal fibers were demonstrated more clearly on images obtained at 0.2 T than at 1.5T. CONCLUSION: DTI at low field strength may be feasible for clinical use to estimate the white matter of brain with limited coverage, which often may be sufficient.

Adult↗
PubMed2004

Comparison of true FISP with turbo SE in ovarian imaging.

PURPOSE: To compare the signal pattern of True FISP (true fast imaging with steady state precession) with that of T2-weighted TSE (turbo spin echo) sequencing in several ovarian pathologies and to clarify the pathologies that may be misdiagnosed when True FISP is used as a fast T2-weighted MR (magnetic resonance) imaging technique. METHODS: A total of 56 patients with 58 ovarian lesions were prospectively studied. The histopathological diagnoses were surgically confirmed in all patients. All MR images were acquired with a 1.5T MR scanner. After routine MR examination (T2-weighted sagittal imaging with a turbo spin echo sequence and T1 and T2 transverse imaging with a spin echo and turbo spin echo sequence, respectively), True FISP was performed in the sagittal plane with a fat-saturation technique. The acquisition times for the True FISP and TSE techniques were 27 s and 4 min, 42 s, respectively. Three radiologists interpreted all images according to three grading scores and with particular reference to the difference in signal pattern between the two sequences (1=similar signal patterns in the ovarian lesions in both True FISP and TSE images; 2=partially different signal patterns in both True FISP and TSE images; and 3=conflicting signal patterns in both True FISP and TSE images). RESULTS: Those assigned a score of "1" included 30 patients with 30 ovarian lesions (12 malignant lesions and 18 benign lesions); those assigned a score of "2" included 10 patients with 10 lesions (two malignant and eight benign); and those assigned a score of "3" included 16 patients with 18 ovarian lesions (two malignant and 16 benign). With the influence of the fat-suppression technique excluded, eight ovarian lesions showed conflicting signal patterns between the two sequences and high signal intensity of hemorrhaging in the corresponding lesion in T1-weighted images. Lesions of both high and low signal intensity in TSE images appeared as lesions of high signal intensity in True FISP images. About 14% (8/56 lesions) of the True FISP and TSE signal patterns in ovarian pathology were conflicting in this study. CONCLUSION: The results indicate that the True FISP technique cannot replace the T2-weighted TSE technique in the evaluation of ovarian pathology. T1-weighted images with or without fat suppression are required for the evaluation of ovarian lesions with FISP images.

Adolescent↗
PubMed2004

[Principles of diffusion-weighted MR imaging and application to clinical neurology].

Diffusion-weighted Imaging (DWI) is a advantageous method for early detection of cerebral ischemia. DWI with echo-planar sequence (EP-DWI) offers multisectional images sensitive to cytotoxic edema in a very short aquisition time and is almost free from motion artifact. However, the susceptibility artifacts and low spatial resolution of EP-DWI must be improved. In estimation of DWI, influence of T2 must be considered, because DWI is almost always based on T2-weighted imaging. DWI is applied to other cerebral disorders such as degenerative and demyelinating disease, infectious disease, tumors or so. In order to demonstrate water diffusion precisely, diffusion tensor imaging (DTI) must be introduced and applied to anisotropy indices such as fractional anisotropy (FA) and depiction of neurofiber direction, tractography. Measurements of FA in various degenerative diseases may contribute to differentiation in normal appearing white matter. Diffusion tensor tractography may provide more information about relationship of major white matter tract such as corticospinal tract with brain lesion. Furthermore, DWI and DTI are expected to demonstrate diffusion of protons of aminoacids such as choline, creatine, NAA and provide more pertinent information of regional pathologic state of the brain in future.

Animals↗
PubMed2003

T1-weighted fluid-attenuated inversion recovery at low field strength: a viable alternative for T1-weighted intracranial imaging.

BACKGROUND AND PURPOSE: T1-weighted spin-echo imaging has been widely used to study anatomic detail and abnormalities of the brain; however, the image contrast of this technique is often poor, especially at low field strengths. We tested a new pulse sequence, T1-weighted fluid-attenuated inversion recovery (FLAIR), which provides good contrast between lesions, surrounding edematous tissue, and normal parenchyma at low field strengths and at acquisition times comparable to those of T1-weighted spin-echo imaging. METHODS: Thirteen patients with brain lesions underwent T1-weighted spin-echo and T1-weighted FLAIR imaging during the same imaging session. T1-weighted spin-echo and T1-weighted FLAIR images were compared on the basis of four quantitative (lesion-white matter [WM] contrast-to-noise ratio [CNR], lesion-CSF CNR, gray matter-WM CNR, and WM-CSF CNR) and three qualitative criteria (conspicuousness of lesions, image artifacts, and overall image contrast). RESULTS: CNRs obtained with T1-weighted FLAIR were comparable but statistically superior to those obtained with T1-weighted spin-echo imaging. In general, T1-weighted FLAIR and T1-weighted spin-echo imaging produced comparable image artifacts. Conspicuousness of lesions and the overall image contrast were judged to be superior on T1-weighted FLAIR images. CONCLUSION: T1-weighted FLAIR imaging may be a valuable alternative to conventional T1-weighted imaging, because the former technique offers superior image contrast at low field strengths and comparable acquisition times.

Adult↗
PubMed2003

[Improving diffusion-weighted imaging of liver with SENSE technique: a preliminary study].

Diffusion-weighted imaging (DWI) has not commonly been performed for assessment of the liver because of technical and physiologic problems. The sensitivity-encoding (SENSE) technique enables the acquisition time to be shortened and reduces artifacts on DWI. We compared the DWI without SENSE, with SENSE only, and with SENSE and half-Fourier technique using a 1.5 Tesla MRI unit. In general, imaging quality was improved and fewer artifacts were observed in DWI with SENSE. DWI of liver with SENSE is expected to be a useful tool for clinical application.

Aged↗
PubMed2002

Velocity-coded colour magnetic resonance angiography and perfusion-weighted magnetic resonance imaging for the evaluation of extracranial-to-intracranial arterial bypass surgery.

BACKGROUND AND PURPOSE: Velocity-coded colour magnetic resonance angiography (VCCMRA) and perfusion magnetic resonance imaging (pMRI) were evaluated as methods for investigating the efficacy of extracranial-to-intracranial arterial bypass (EC-IC bypass) by comparing the findings of VCCMRA and those of cerebral angiography and by measuring the improvement ratio after EC-IC bypass by pMRI compared to that by single photon emission computed tomography (SPECT) using the autoradiographic technique. METHODS: Thirteen patients who underwent VCCMRA, angiography, SPECT, and pMRI before and after surgery were analyzed. Findings of VCCMRA were compared to those of angiography. Improvement ratio was calculated compared to the cerebellum for cerebral blood volume, mean transit time (MTT), and regional cerebral blood flow (rCBF) as measured by pMRI and quantitative SPECT. RESULTS: Findings of VCCMRA were in good agreement with those of angiography and clearly showed the direction of bypass flow. No statistically significant correlation was observed between the improvement ratios in CBF in the hemisphere and middle cerebral artery territory on the surgical and non-surgical sides and in rCBF in the same regions of interest (ROIs) (r=-0.574, 0.09). However, a statistically significant correlation was observed between the cerebrovascular reserve capacity (CVRC) in the hemisphere on the surgical side and in MTT in the same ROIs (r=0.955, P<0.001). CONCLUSION: VCCMRA may clearly show the direction of flow in the EC-IC bypass. MIT measured by pMRI may indicate the postoperative state of CVRC. These techniques could replace angiography and positron emission tomography or SPECT in patients undergoing EC-IC bypass.

Adult↗
PubMed2002

Electrophysiological, anatomical and histological remodeling of the heart to AV block enhances susceptibility to arrhythmogenic effects of QT-prolonging drugs.

The present study was designed to investigate what kinds of adaptation occurred in the canine chronic AV block model, which has been used to study torsade de pointes (TdP). Dogs at 7-10 days (acute phase) and 28-56 days (chronic phase) after AV block were assessed. Ventricular effective refractory period and monophasic action potential duration were prolonged in chronic animals compared with acute animals; moreover the electrically vulnerable period was prolonged in chronic animals. Non-specific IKr channel blocker cisapride (1 and 10 mg/kg, p.o.) was administered without anesthesia to estimate the feasibility of QT prolongation. In chronic animals, QT prolongation followed by TdP was induced in one dog by the low dose and in all by the high dose, which was not observed in acute animals. MR images indicated increases of diameter and wall thickness of both ventricles in chronic animals. The degree of hypertrophy was prominent in the right ventricular wall and septal wall. Heart weight of the chronic animals was 1.7 times greater than that of normal control subjects. Photo- and electron-micrograph analyses showed myocardial cell hypertrophy with parallel increases of collagen fiber and extracellular space in chronic animals. These electrophysiological, anatomical and histological adaptations may predispose the chronic AV block heart to drug-induced QT prolongation with enhanced risk of re-entry and early after depolarization, leading to the onset of TdP.

Animals↗
PubMed2002

[Line scan diffusion weighted imaging (LSDI) on 0.2 Tesla MRI of the normal cervical cord in vivo: preliminary study].

Diffusion weighted imaging(DWI) has been widely performed in the brain. However, DWI of the spinal cord is rarely performed because of technical and physiologic problems. Line scan diffusion weighted imaging(LSDI) is spin-echo based and relatively insensitive to susceptibility artifacts. We calculated the apparent diffusion coefficient(ADC) values of the normal cervical spinal cord by LSDI on a 0.2 Tesla MR imager and compared the ADC values with those from 1.5 Tesla MRI previously reported in the literature. The ADC values were adequate, and LSDI on 0.2 Tesla MRI is expected to become a useful tool for clinical application.

Adult↗
PubMedDate not supplied

MR-guided intravascular catheter manipulation: feasibility of both active and passive tracking in experimental study and initial clinical applications.

PURPOSE: To evaluate clinically the feasibility and usefulness of MR-guided intravascular procedures with either active or passive tracking. METHODS: With an active MR tacking system and a 0.2 Tesla open MR imager, real-time and biplane displays of positions of a receive-only coil at the tip of catheters were obtained. For passive tracking, 4 Fr catheters with suitable susceptibility for passive tracking were used. Passive tracking with a 1.5 Tesla MR imager could be performed with parameters of TR 15-50 msec, TE 2.2-2.7 msec, and FA 30 degrees. The temperature of each tracking catheter was monitored in vitro. Clinical trials were performed on six patients (three each). The catheter was introduced to the superior mesenteric artery (SMA) under MR guidance by active or passive tracking to perform MR imaging during arterial portography. RESULTS: The temperature increased minimally. In humans, the SMA and celiac artery could be easily introduced on active tracking. MR-guided manipulation of catheters by active or passive tracking in the model and in dogs' vessels was very successful. Introduction of the catheter into the SMA was successful in two cases of active tracking and in all cases of passive tracking. CONCLUSION: The MR-guided intravascular manipulation of catheters by active or passive tracking may be a clinically feasible method.

Catheterization, Peripheral↗