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Biomedical subjects

O Takizawa

Publications and source records attributed to O Takizawa.

18 recordsLinked to original sources
PubMed2001

Moving-table reduced-dose gadolinium-enhanced three-dimensional magnetic resonance angiography: velocity-dependent method with three-phase gadolinium infusion.

The purpose of this study was to develop a method for reducing gadolinium dose and suppressing venous overlap in moving-table three-dimensional (3D) magnetic resonance (MR) angiography from the abdomen to the feet. Thirty-one patients underwent three-phase infusion of 16-18 mL of gadolinium: infusion rates and imaging times were determined after taking into account mean blood flow velocity, so that image acquisition was synchronized with peak arterial enhancement at both the first and third stations (velocity-dependent method). Twenty-three other patients underwent slow infusion of 38 mL of gadolinium with fixed acquisition time (high-dose method). The image quality for the two methods was compared. The velocity-dependent method produced good image quality with significantly less venous overlap than the high-dose method, especially in the below-the-knee region (P <.001). The velocity-dependent method provides satisfactory MR angiograms using 16-18 mL of gadolinium in patients having various blood flow velocities.

Adult↗
PubMed2001

Measurement of in-vivo local shear modulus by combining multiple phase offsets mr elastography.

To provide realistic surgical simulation, haptic feedback is important. In the existing surgical simulators, the fidelity of the deformation and haptic feedback is limited because they are based on the subjective evaluation of the expert-user and not on an objective model-based evaluation. To obtain elastic modulus of in-vivo human tissues, magnetic resonance elastography (MRE) was developed. MRE is a phase-contrast- based method that can visualize propagating strain waves in materials. The quantitative values of shear modulus can be calculated by estimating the local wavelength of the wave pattern. Low frequency mechanical motion must be used for soft tissue-like materials, because strain waves rapidly attenuate at higher frequency. Therefore, wavelength in MRE is long. It is difficult to estimate local wavelength with high spatial resolution especially from noisy MRE. In the MRE sequence, motion-sensitizing gradient (MSG) are synchronized with the mechanical cyclic motion. MRE with multiple initial phase offsets can be generated with increasing delays between the MSG and mechanical excitation. In this paper, we describe a method of measuring local wavelength with high spatial resolution by combining multiple phase offsets MRE. To confirm the reliability of this method, a computer simulation and phantom study were performed. The shear modulus measured with various elastic objects was well consistent with the value obtained by MRE and the mechanical method. The shear moduli of excised porcine liver and in-vivo human calf muscle were also analyzed by this method. on the subjective evaluation of an expert-user and not on objective model-based methods.

Acoustic Stimulation↗
PubMed2000

Sensible human projects: haptic modeling and surgical simulation based on measurements of practical patients with MR elastography--measurement of elastic modulus.

To provide realistic surgical simulation, 3D visualization and haptic feedback are important. In the existing surgical simulators, the fidelity of the deformation and haptic feedback is limited because they are based on the subjective evaluation of the expert-user and not on an objective model-based evaluation. To obtain accurate elastic modulus of whole human tissues, we have started a new project called the Sensible Human Project (SHP). This paper deals with establishing the measurement of elastic modulus by the magnetic resonance elastography (MRE) technique, as a first step of the SHP Project.

Computer Simulation↗
PubMed1999

[Three-phase gadolinium infusion in moving-table three-dimensional MR angiography].

Moving-table three-dimensional (3D) MR angiography provides images of long segments of arteries. However, deep veins are sometimes superimposed on the arteries below the knee, and peripheral arteries sometimes fail to be visualized. We have developed an imaging method with three-phase gadolinium infusion according to the mean blood flow velocity of the leg. Nineteen patients with various blood flow velocities were studied. Eighteen of the patients had no venous superimposition. All 19 patients showed good configuration of peripheral arteries with 16-18 ml of gadolinium. This method is useful for better visualization of peripheral arteries without venous superimposition.

Adult↗
PubMed1998

[Characteristics and detectability of RARE technique].

RARE is a kind of fast spin echo technique with large number of echo train and long TE. Because of long TE, signal from parenchyma is vanished and only liquid with long T2, such as bile, pancreatic juice, is detected. Compared to HASTE, signal from vessels like portal or hepatic vein is vanished either. Acquisition time of RARE is extremely short because it is single shot technique. So, on MRCP examination, RARE is good method for easily understanding of whole structure of biliary system because it is usually used as a projection image with thick slice. On the other hand, one should pay attention for shorter T2 bile and pancreatic juice. If their T2 is short, biliary system may not be shown with RARE.

Biliary Tract↗
PubMed1997

[Dynamic susceptibility contrast MRI with echo planar imaging using 1.0T system: comparison of different EPI sequences].

Dynamic susceptibility contrast MRI has been performed using the gradient echo sequence on conventional MR imagers. On echo planar imaging (EPI) devices, not only gradient-echo EPI but also spin-echo EPI allow for the monitoring of contrast agent-induced changes in susceptibility. The purpose of this study was to evaluate the contribution of each EPI pulse sequence to susceptibility-induced delta R2(*) through the first pass of a bolus of Gd-DTPA. Thirty healthy volunteers were examined with a 1.0T superconducting MRI unit (IMPACT, Siemens) using EPI. For dynamic susceptibility contrast MRI, we used gradient echo EPI (TE = 60), spin echo EPI (TE = 60) and asymmetric spin echo EPI (TE = 88). Regional relative CBV (rrCBV) maps were generated. On the rrCBV map generated with gradient echo EPI, the high-intensity area of the brain surface was more conspicuous than that generated with spin echo EPI. The rrCBV map generated with asymmetric spin echo EPI represented the contrast between those generated with spin echo EPI and gradient echo EPI. The rrCBV rate between gray matter and white matter with gradient echo EPI was significantly higher than that with spin echo EPI. We suggest that the rrCBV map calculated with spin echo EPI tends to reflect capillary blood volume and the rrCBV map calculated with gradient echo EPI tends to reflect total blood volume.

Adult↗
PubMed1995

[Contrast-enhanced 3D MR angiography of the chest and abdomen with breath-holding using phase reordering].

This report presents the feasibility of phase-recordered contrast-enhanced three-dimensional MR angiography in 32 consecutive patients with vascular abnormalities in the chest and abdomen. To suppress motion artifacts due to respiratory corruption, a phase-reordering technique was introduced so that the low frequency components of the phase data were obtained first during the imaging period. Image quality and degree of motion suppression were assessed by four radiologists independently without information on breath-holding time. Abnormalities were detected in 30 cases (93.8%), and their extent was correctly assessed in 28 cases (87.5%). More confident assessment was possible in abnormalities of the pulmonary vessels and thoracic aorta than in those of the abdominal aorta and portal venous system. With phase reordering, more than 20 seconds of breath-holding ensured image quality sufficient to correctly assess the vascular abnormalities. While this technique is easy and requires only single breath-holding, it can provide excellent MRA without slice-to-slice spatial misregistration.

Aortic Aneurysm, Abdominal↗
PubMed1995

[Breath-holding three-dimensional MR imaging: evaluation of phase reordering for motion artifact suppression].

To suppress image degradation due to respiratory corruption during breath holding, a method of reordering of phase encoding was introduced in three-dimensional MR imaging. Without trade-offs in SNR, CNR, and examination time, the method provided a significant reduction of respiratory motion-induced artifacts both in phantom and in vivo experiments. More than twenty seconds of breath holding ensured acceptable image quality regardless of respiratory motion thereafter. Signal intensity change during data acquisition altered the obtained image contrast compared with that of standard sequential linear phase encoding. This technique can be readily implemented on standard two-and three-dimensional pulse sequences and will improve image quality when a patient cannot hold his/her breath during the whole imaging period.

Artifacts↗
PubMed1994

Single breath-holding three-dimensional magnetic resonance portography with bolus injection of Gd-DTPA in subjects with normal liver: a comparison with two-dimensional time-of-flight technique.

Two-dimensional time-of-flight (2D-TOF) magnetic resonance (MR) portography tends to produce general image degradation owing to the phase discrepancy caused by multiple breath-holding. To solve this problem, three-dimensional (3D)-MR portographies were reconstructed from image data acquired with a bolus injection of Gd-DTPA with single breath-holding in 20 subjects with normal liver function. 2D-TOF MR portographies were obtained beforehand for the comparison. All the images were displayed in a cine mode for the two MR angiographic techniques. Visualization was assessed as positive when the vessel was visualized without disruption. 3D-MR portography produced a positive rate of over 80% for all but the left first-order branch. With the 2D-TOF techniques, however, only the portal trunk and left second-order branches were visualized at this rate. The positive rate for most portal branches was significantly higher with 3D-MR portography than with the 2D-TOF technique. In conclusion, 3D-MR portography makes it possible to depict the portal venous system without disruption using a short measurement time with single breath-holding and has the potential to become a powerful method for abdominal MR angiography.

Adult↗
PubMed1994

Three-dimensional black blood MR angiography of the liver during breath holding. A comparison with two-dimensional time-of-flight MR angiography.

In 2-D time-of-flight MR angiography (2-D TOF MRA) of the liver, artifacts caused by respiratory motion are unavoidable. Therefore, a 3-D black blood MRA of the liver was attempted in 7 healthy volunteers, using a 3-D gradient echo sequence which allows imaging during breath holding. 2-D TOF MRA was performed as well. In all subjects, 3-D MRA allowed visualization of the trunk, 1st-, and 2nd-order branches of the portal vein without interruption. Right 3rd-order branches were visualized without interruption in 6 of 7 subjects (85%). However, with 2-D MRA, the transverse portion of the left main portal vein could not be visualized in any subject, and the periphery of the portal vein was less clear than with 3-D MRA.

Adult↗
PubMed1989

[Clinical evaluation of regurgitant blood flow by rapid cine magnetic resonance imaging in patients with valvular heart disease].

The clinical usefulness of magnetic resonance imaging (MRI) for evaluating regurgitant blood flow in patients with valvular heart disease was studied. The study subjects comprised three healthy volunteers and nine patients with valvular heart disease (aortic regurgitation 3, mitral regurgitation 2, tricuspid regurgitation 2, and pulmonary regurgitation 2). Five were men and seven were women, ranging in age from 31 to 85 years. Valvular heart disease was diagnosed by two-dimensional Doppler echocardiography. MRI was performed using a 1.5 tesla super-conductive magnet system (MAGNETOM, Siemens AG). A rapid MRI technique (fast low-angle shot [FLASH], flip angle = 30 degrees, TR = 65-90 msec, TE = 10-38 msec) was used to generate 11 frames throughout one cardiac cycle in the transaxial, coronal and oblique planes. These sequential frames were displayed in cine mode on a CRT. 1. Intracavitary blood was imaged as a high signal intensity on gradient echo images, while surrounding cardiac structures had somewhat lower signal intensities. 2. In healthy volunteers, systolic ejection blood flow from the left ventricle was observed on coronal images in the cine mode display. The influx of atrial blood into the left and right ventricles was also clearly observed on transaxial cine images. 3. Aortic regurgitant flow was observed as areas of no signal intensity within the left ventricular cavity during diastole on coronal images. 4. Mitral and tricuspid regurgitations were observed within the left and right atria, respectively, as areas of no signal intensity on transaxial images. The extent of regurgitant flow was determined in the vertical long-axis plane, equivalent to the right anterior oblique projection. 5. The vertical oblique scan was suitable for detecting pulmonary regurgitant flow. These results indicate that the rapid cine MRI technique is a useful tool for noninvasively determining regurgitant blood flow in patients with various valvular heart diseases.

Adult↗
PubMedDate not supplied

Use of magnetization transfer contrast to improve single breath-hold three-dimensional MR-portography with bolus injection of gadopentetate dimeglumine: a preliminary report.

We investigated whether better visualization of the intrahepatic portal system could be obtained by adding magnetization transfer contrast (MTC) to three-dimensional MR portography (3D-MRP). In 15 healthy volunteers, 3D fast low-angle shot images combined with an off-resonance pulse were obtained after bolus injection of gadopentetate dimeglumine during one period of breath-holding. Within 1 week after injection, MR images without MTC were obtained using the same scanning condition. MRPs with and without the MTC pulse were compared quantitatively and qualitatively. The contrast-to-noise ratio of the portal vein-liver was significantly higher in the group imaged with the addition of MTC. Qualitatively, the use of MTC improved peripheral portal branch depiction on maximum-intensity projection images. Even when the MTC pulse was added to the conventional method of 3D data collection, it was possible to obtain images within one period of breath-holding. In conclusion, the use of MTC can substantially enhance the quality of 3D-MRPs.

Adult↗
PubMedDate not supplied

Use of three-dimensional segmented FLASH sequence with magnetization transfer contrast to improve Gd-DTPA-enhanced intrahepatic MR portography.

Twenty healthy volunteers underwent gadopentetate dimeglumine (gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA))-enhanced MR angiography (MRA) using three-dimensional-segmented fast low angle shot images (FLASH) with magnetization transfer contrast (MTC) pulses. MRA was obtained at 75 seconds (early phase) and 135 seconds (late phase) after bolus injection of Gd-DTPA (MTC+ group) during one period of breath-holding. Within 1 week. MRA without MTC was performed under the same scanning conditions. Visualization of intrahepatic portal branches with these methods was compared in both phases. Portal vein-liver contrast-to-noise ratios were significantly higher in the MTC+ group in both phases. For third- and fourth-order portal branches, visualization was significantly better in the MTC+ group in both phases. Use of three-dimensional-segmented FLASH shortened acquisition time and facilitated imaging during breath-holding and also reduced whole-body average specific absorption rate values. Visualization of intrahepatic portal vein branches was improved by MTC pulses, and effective imaging time was prolonged.

Adult↗
PubMedDate not supplied

Real-time interactive MR imaging system: sequence optimization, and basic and clinical evaluations.

A real-time interactive MR imaging system (real-time MRI) is an MR scanner which has a fast image updating cycle and the ability to freely change slice orientation, just like an ultrasound imaging system. Recently, such a system has been developed and installed on a clinical 1.5-Tesla system. The purpose of this study was to optimize the pulse sequences for clinical use and to evaluate the clinical usefulness and basic functionality of real-time MRI. For T1-weighted imaging, FLASH (fast low angle shot) can be selected, and up to 5 frames per second can be acquired depending on the matrix size. For T2-weighted imaging, true FISP (fast imaging with steady-state precession) can be selected, and up to 4 frames per second can be acquired. Maximum C/N between liver and spleen was obtained at a flip angle of 20 degrees on FLASH. Maximum C/N between cardiac cavity and wall was obtained at a flip angle of 60 degrees on true FISP. Localization of the right and left coronary arteries could be performed within 30 seconds in three volunteers. Although the present real-time MRI system has drawbacks such as low spatial resolution and relatively low contrast resolution, we expect real-time MRI to be one of the most important tools for future clinical MRI.

Adult↗
PubMedDate not supplied

Aortoiliac stenooculusive disease and aneurysms: screening with non-contrast enhanced two-dimensional cardiac gated cine phase contrast MR angiography with multiple velocity encoded values and cardiac gated two-dimensional time-of-flight MR angiography.

PURPOSE: To evaluate the performance of two-dimensional cine phase contrast MRA with multi-velocity encoded values (multi-VENC cine PC) and ECG-gated two-dimensional time-of-flight MRA (ECG-2D-TOF) for the detection of stenoocclusive lesions and aneurysms in the aortoiliac area, when each method was used individually and when the two methods were used together. METHODS: Forty-one patients were included in this study. Multi-VENC cine PC and ECG-2D-TOF were obtained first, then contrast enhanced three-dimensional magnetic resonance angiography (CE-3D-MRA) was performed as the standard of reference. Two observers reviewed the images separately without knowledge of patients' symptoms or histories. Sensitivities and specificities were obtained separately for stenooclusive lesions and aneurysms by two reviewers. RESULTS: When the two methods were applied together, high sensitivities (93.0 by observer 1 and 91.9% by observer 2) and adequate specificities (87.6 and 82.3%) were obtained for stenoocclusive lesions. For aneurysms, moderate to high sensitivities (91.1 and 71.1%) and high specificities (98.8 and 99.4%) were obtained. CONCLUSION: These results suggest that the performance of two non-contrast enhanced MRA techniques may be valuable as a screening tool when the two methods are applied together.

Aged↗
PubMedDate not supplied

31P-NMR spectroscopy of myopathies: clinical application of whole-body MR.

Patients with myopathies were examined by 31P-NMR spectroscopy using a whole body MR system operating at 1.5 T. Spectra from the femoral muscles were measured as a function of time during a post-exercise recovery period. A 4-min scanning time was used to obtain a good S/N ratio and enable us to evaluate the relative intensity and position of each absorption line. The results were expressed by PCr/Pi ratio and pH value and compared with values before exercise. Clear changes were observed in the recovery process after workload depending on the stage of disease. We were able to observe the in vivo dynamic energy metabolism of myopathies by whole-body MR.

Adult↗