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Biomedical subjects

J S Tsuruda

Publications and source records attributed to J S Tsuruda.

At least 55 records · Page 3Linked to original sources
PubMed1989

Color Doppler imaging of intracranial vessels in the neonate.

This study was performed to examine the effectiveness of color Doppler imaging (CDI) in demonstrating the neonatal intracranial vessels and altered intracranial flow patterns and to determine the optimal approach in imaging and intracranial vasculature. The study was conducted in two parts. First, 14 neonates were examined with CDI by using a standard approach through the anterior fontanel. Whenever possible, views through the posterior fontanel and the temporal bone were obtained also. The anterior cerebral, M1 segment of the middle cerebral, distal internal carotid, and basilar arteries were demonstrated consistently. Portions of the vertebral distal middle cerebral, and posterior cerebral arteries were frequently visualized. In the second part of the study, we examined 10 neonates who had undergone extracorporeal membrane oxygenation. In this group of patients, CDI was able to demonstrate occlusion of the right internal carotid artery and the reversal of flow through the ipsilateral A1 segment. Increased flow on the contralateral side and in the basilar artery was observed in several patients. The anterior fontanel approach was shown to be the most useful in identifying most of the major intracranial arteries and veins with CDI. In addition, the body weights and gestational ages of the neonates were found to significantly influence the success rate in visualizing the intracranial vasculature.

Basilar Artery↗
PubMed1988

Low-artifact intravascular devices: MR imaging evaluation.

Flow-phantom magnetic resonance (MR) imaging, with use of both spin-echo (SE) and gradient-echo (GRE) techniques at 1.5 T, was performed on the percutaneous Greenfield (beta-III titanium alloy [TMA wire]), Amplatz (MP32-N alloy), and Simon nitinol filters and TMA wire facsimiles of the bird's nest, Gunther, new retrievable, and Amplatz vena caval filters. SE imaging allowed detection of thrombi as small as 5 X 5 mm trapped within the percutaneous Greenfield, Simon nitinol, and TMA-wire facsimile filters; with the MP32-N Amplatz filter, a larger volume of thrombus (10 X 20-mm clots) was necessary for clot detection. GRE imaging allowed detection of intraluminal tilting of the percutaneous Greenfield and facsimile Amplatz (TMA-wire) filters. GRE imaging was useful for demonstrating postfilter turbulence due to clots, which was greatest for the Amplatz filter. Imaging of facsimile vascular devices made of tantalum or TMA wire did not cause the severe "black-hole" MR artifacts typical of the stainless-steel devices. SE and GRE imaging were very useful for determining caval patency in two patients with previously placed Mobin-Uddin filters. Noninvasive MR evaluation of blood vessels in the presence of a variety of low-artifact intravascular devices appears feasible.

Blood Vessel Prosthesis↗
PubMed1988

MR evaluation of large intracranial aneurysms using cine low flip angle gradient-refocused imaging.

MR imaging has proved to be useful in evaluating large intracranial aneurysms. The parent artery and patent lumen can be identified as flow voids and differentiated from thrombus. However, in the presence of slow flow, even-echo rephasing, and motion artifact, increased intraluminal signal may be present, which may be difficult to distinguish from thrombus. Aneurysms are also dynamic lesions and exert pulsatile mass effect on adjacent structures. Further definition of vascular anatomy and physiology may aid in therapeutic planning and assessment. Cine MR is a new technique using a movie loop of sequential GRASS (gradient-recalled acquisition in the steady state) images obtained during various points in the cardiac cycle. The combination of GRASS images and cardiac gating thus allows cinegraphic display of vascular structures. A comparison of this method with routine T1- and T2-weighted MR imaging and angiography was made in a group of 13 patients with intracranial aneurysms greater than 1.5 cm in diameter. Eight of these patients underwent transvascular detachable balloon occlusion. With cine MR, flowing blood has high intensity due to flow-related enhancement. Turbulent and high-velocity flow can be recognized on the basis of signal loss, which occurs during systole. Thrombus demonstrated variable signal intensity, which remained unchanged during the cardiac cycle. Compared with routine MR sequences, there was less image degradation from phase-encoding artifacts and improved visualization of the neck of the aneurysm. Pulsatile mass effect was uniquely assessed. After transvascular embolization, cine MR demonstrated improved conspicuity of acute thrombus and higher contrast between flowing blood and the occlusion balloon when compared with routine MR. Confirmation of flow within the parent vessel, residual aneurysm lumen, and distal arterial branches is possible. If the parent vessel was occluded, cine MR yielded greater information than angiography. Cine MR provides additional anatomic and physiologic data in the evaluation and assessment of therapy of intracranial aneurysms. Information can be obtained that is not available with either routine MR or angiography. The inherent limitations of this new technique include partial-volume artifacts, less than optimal flow-related enhancement or spatial resolution, and poor data acquisition due to cardiac arrhythmias.

Adolescent↗
PubMed1987

Radiation effects on cerebral white matter: MR evaluation.

The purpose of this study was to evaluate the white-matter changes associated with cranial radiation by MR imaging. The MR scans of 95 patients receiving conventional external beam radiation for a wide variety of central nervous system tumors were reviewed. Moderately T2-weighted spin-echo images with a 2000-msec repetition time and 56-msec-echo time were analyzed for white-matter abnormalities without knowledge of the patient's history. These were correlated with radiation dose, port, and time interval since completion of therapy, and then compared with an age-matched control group of 180 patients with nonirradiated, space-occupying, intracranial lesions. Radiation-related lesions were characterized as symmetric, high-signal foci in the periventricular white matter. Relative sparing of the posterior fossa, basal ganglia, and internal capsules was noted. In patients older than 20 years, these changes paralleled those seen in ischemia but were more prevalent (p less than .005). In 25 patients with sequential MR scans, these findings remained stable. In those patients with limited treatment fields, for example, pituitary adenomas, no statistical differences were seen between radiation-treated and nontreated groups. Cerebral white-matter changes that mimic deep white-matter infarction are frequently seen in response to therapeutic radiation. There is a variable incidence of radiation effects, becoming more marked in older patients. MR interpretation must consider the neuropathologic consequences of therapeutic radiation, which include demyelination, microvascular occlusion, and blood-brain barrier breakdown.

Adult↗
PubMed1987

MR sequence parameter optimization: an algorithmic approach.

The MR pulsing sequence is often described by terms such as spatial resolution, signal-to-noise, coverage, acquisition time, and contrast. These might be considered "secondary" parameters because they are not set directly but are instead specified indirectly by setting the "primary" parameters: field of view; projections (phase-encoded or readout); slice thickness and gap; number of excitations; and the sequence parameter times--repetition, echo delay, and inversion. Together, the primary and secondary parameters specify the MR pulsing sequence. Many of these parameters are interrelated such that setting one parameter indirectly affects another. Parameter specification is thus an iterative procedure that involves compromises to achieve an optimum relative to some predefined criteria. In this article, we examine the interrelationships between the primary and secondary parameters that specify the spin-echo pulsing sequence and suggest an algorithmic approach for selecting the best sequence parameters.

Algorithms↗
PubMedDate not supplied

Application of a connected-voxel algorithm to MR angiographic data.

A connected-voxel algorithm (CVA) that improves the contrast and conspicuity of blood vessels in maximum-intensity-projection (MIP) magnetic resonance (MR) angiography is described. Images from a variety of anatomic regions in healthy volunteers were calculated with either an MIP procedure alone or with data that had first been processed with the CVA. A low-signal-intensity threshold is first applied to separate groups of voxels associated with different vessels from one another and to eliminate the contribution from low-intensity stationary material. The remaining voxels are grouped by a connectivity criterion into discrete "objects." Vessels are represented by extended objects, and small objects are discarded. The CVA, therefore, reduces the full three-dimensional data set into a small number of discrete objects. It is a powerful technique that can be used to remove signal from vessels overlying the vessel of interest, to separate objects representing arterial flow from those representing venous flow, to eliminate flow artifact from projection images, and to more completely retain signal within the vascular lumen. This technique has been successfully demonstrated with MR angiography in healthy volunteers.

Algorithms↗
PubMedDate not supplied

Techniques for high-resolution MR imaging of atherosclerotic plaque.

Atherosclerotic cardiovascular disease is the most common cause of death in the United States. Investigation of atherosclerotic plaque morphology and composition is important because the findings may be useful in predicting prognosis or response to therapy. This study presents high-resolution magnetic resonance (MR) imaging techniques developed on a 1.5-T whole-body imager with a custom-built surface coil, for characterizing the composition and morphology of plaque removed at carotid endarterectomy. The initial comparison of MR imaging and histologic results showed good correlation. In conjunction with MR angiography, these techniques could be used in in vivo imaging to define the size, location, and contents of atherosclerotic plaque at the carotid bifurcation.

Artifacts↗
PubMedDate not supplied

Multislab three-dimensional T2-weighted fast spin-echo imaging of the hippocampus: sequence optimization.

Three-dimensional (3D) fast spin-echo (FSE) imaging can produce contiguous thin sections for high-quality multiplanar reconstructions. Such reformatted images may be useful in the evaluation of three-dimensionally complex, curvilinear anatomic structures such as the hippocampus. The authors describe a 3D FSE protocol for T2-weighted imaging of the hippocampus. The protocol uses an overlapping-multiple-slab imaging strategy to decrease imaging times and a modified refocusing radio-frequency pulse train to improve the reformatted images. The authors describe their parameter optimization, discuss the benefits and limitations of the new sequence, and present representative images of healthy volunteers.

Artifacts↗
PubMedDate not supplied

Partial volume effects in volume-localized phased-array proton spectroscopy of the temporal lobe.

MRS techniques can aide in confirming the location of seizure foci in temporal lobe epilepsy. N-acetyl aspartate (NAA), creatine plus phosphocreatine, choline-containing compounds, and lactate are most often the clinically relevant metabolites in these studies. We examined the importance of partial volume effects from tissue heterogeneity in temporal lobe spectroscopy on the metabolite ratios. Our study shows that localized spectroscopy, using three different voxel sizes, centered on the anterior body of the hippocampus, produces significantly different values for the NAA to the creatine ratio. The spectroscopy was performed at 1.5 T using the PRESS pulse sequence and a phased-array coil system specifically designed for the temporal lobe. The data exhibits a clear trend of increasing NAA to creatine ratios with increasing voxel size. This trend demonstrates that partial volume effects can contribute to variation of NAA to creatine ratios in healthy subjects.

Artifacts↗
PubMedDate not supplied

Phased-array magnetic resonance imaging of the carotid artery bifurcation: preliminary results in healthy volunteers and a patient with atherosclerotic disease.

A high resolution MR imaging technique using a custom designed flexible phased-array surface coil was developed to examine the wall of the carotid artery bifurcation in vivo. The phased-array consisted of two overlapping coils which increased the image signal-to-noise ratio at the depth of the carotid artery by approximately 70%, relative to a similarly sized single loop coil. The imaging protocol included a 2D T1-weighted (T1W) spin-echo scan and cardiac gated T2-weighted and proton density-weighted (PDW) fast spin-echo (FSE) scans. Images were obtained of six healthy volunteers and of one patient with known atherosclerotic disease several days before carotid endarterectomy. On T1W and PDW images of the healthy volunteers, the carotid arterial wall appeared to be comprised of two concentric rings; a high signal inner ring and a lower signal outer ring. The MR images of the patient revealed a calcified carotid bifurcation plaque which was confirmed during surgery. The endarterectomy specimen was imaged in vitro with MR and then sectioned histologically for correlation with the patients in vivo images. Our preliminary findings indicate that a high resolution technique may provide a noninvasive technique to study atherosclerosis of the carotid bifurcation.

Arteriosclerosis↗
PubMedDate not supplied

Atherosclerosis of the carotid artery: evaluation by magnetic resonance angiography.

Carotid artery atherosclerotic plaques (APs) can lead to brain ischemia, an event shown to correlate with both the degree of stenosis and the composition of the AP. Currently, accurate estimates of stenosis can be obtained by either x-ray angiography or three-dimensional time-of-flight (TOF) magnetic resonance angiography (MRA). Our purpose was to determine whether three-dimensional TOF MRA images could also provide information on plaque location, morphology, and composition. Seven pre-endarterectomy patients underwent three-dimensional TOF MRA. After endarterectomy, plaque histology was evaluated. Three-dimensional TOF MRA images contained sufficient soft tissue contrast to differentiate the plaques from the surrounding tissues in all cases. Estimation of plaque morphology had 80% correlation with histology. Finally, intraplaque hemorrhage and calcification were deplicted as regions of moderately high and very low intensity, respectively. These preliminary results suggest that three-dimensional TOF MRA may be useful in studying the development and progression of carotid atherosclerosis.

Aged↗
PubMedDate not supplied

Gradient-echo MR imaging of the lumbar spine: comparison with spin-echo technique.

Gradient-echo (GRE) magnetic resonance (MR) imaging has been advocated as the imaging modality of choice for evaluating radiculopathy in the cervical spine. Axial GRE images of the lumbar spine in 50 patients were compared with similar images obtained using spin-echo (SE) technique on a 1.5 T MR system. The SE images were superior to GRE images in the evaluation of the neural foramina, epidural fat, and disk herniation. The GRE images obtained were inadequate for lumbar spine imaging due to an unacceptable level of chemical shift artifacts. The GRE technique does provide the advantages of rapid acquisition of T2* images and decreased motion artifact. Axial GRE images may play an increasingly important role in lumbar spine imaging with continued changes in software and improvements in technology.

Adolescent↗
PubMedDate not supplied

Three-dimensional time-of-flight MR angiography in the evaluation of cerebral aneurysms.

We review our preliminary experience with the use of three-dimensional (3D) time-of-flight (TOF) magnetic resonance (MR) angiography (MRA) in the assessment of intra- and extracranial aneurysms. Six patients were examined: Five had intracranial aneurysms and one had a cervical carotid pseudoaneurysm. A 3D rephased gradient recalled echo pulse sequence and maximum intensity projection (MIP) reconstruction algorithm were used. Magnetic resonance angiography, spin echo MR, and conventional angiography were retrospectively reviewed with specific regard to individual vessel visualization, aneurysm depiction, and presence of artifact related to acquisition techniques or MIP reconstruction. All aneurysms were detected on MRA, and anatomical correlation with conventional angiography was excellent. Significant problems included loss of visualization of small vessels, intraluminal signal loss in large vessels, subacute thrombus simulating flow on MIP reconstructions, and limited projections obtainable with MIP techniques. Adequate MRA assessment of aneurysms can be obtained using a combination of T1-weighted spin echo images and 3D TOF MRA. Review of all components of the MRA is required. MRA may be useful in screening asymptomatic patients for intracranial aneurysms as well as in the follow-up of patients treated with balloon occlusion.

Adult↗
PubMedDate not supplied

Quantitative comparison of conventional spin echo and fast spin echo during brain myelination.

PURPOSE: Fast SE (FSE) sequences have largely replaced conventional SE (CSE) T2-weighted sequences in the brain and have been generally accepted as qualitatively comparable. The purpose of the present study was to subject these sequences to a quantitative comparative analysis in the brain. METHOD: A quantitative analysis of relative signal intensities of white and gray matter was performed comparing CSE and FSE T2-weighted sequences in brains of 20 children at varying stages of myelination. RESULTS AND CONCLUSION: At all ages in individual patients, white matter had less signal intensity (SI) relative to gray matter on FSE than CSE, though the relative difference in SI was small. This resulted in white matter appearing slightly more myelinated on FSE than CSE. This difference is attributed to differences in magnetization transfer. In myelinated brain (white matter hypointense to gray matter), contrast-to-noise was greater with FSE, while in unmyelinated brain, contrast-to-noise was greater with CSE.

Brain↗
PubMedDate not supplied

Effects of magnetic susceptibility artifacts and motion in evaluating the cervical neural foramina on 3DFT gradient-echo MR imaging.

The purpose of this study was to evaluate in vitro the effects of magnetic susceptibility and motion on the estimation of neural foraminal diameter with three-dimensional Fourier transformation (3DFT) gradient-recalled MR imaging as compared with CT. A cervical spine phantom was constructed from desiccated human cervical vertebral bodies embedded in a water-based proteinaceous gel. The phantom was imaged with thin-section 1.5-mm axial CT and 1.5-mm axial 3DFT gradient-recalled MR using a constant TR (35 msec) and flip angle (5 degrees), while the TE was varied from 11 to 22 msec. During imaging, the phantom either was kept stationary or underwent subtle, intermittent motion. Compared with CT, MR consistently underestimated the diameters of the neural foramina, leading to overestimation of neural foraminal stenosis. The degree of over-estimation varied directly with increasing TE values, from 8% (TE = 11 msec) to 27% (TE = 22 msec). Motion artifacts also increased foraminal overestimation and mimicked osseous hypertrophy. The effect of image degradation due to motion was noted to increase with longer TE values. Image degradation caused by magnetic susceptibility and motion artifacts can be minimized by using the shortest TE possible. We do not recommend the use of 3DFT gradient-recalled MR imaging for the evaluation of cervical radiculopathy if patient motion is anticipated.

Cervical Vertebrae↗
PubMedDate not supplied

Dural sinus occlusion: evaluation with phase-sensitive gradient-echo MR imaging.

The purpose of this study was to evaluate the usefulness of limited-flip-angle, phase-sensitive velocity imaging with gradient-recalled-echo (VIGRE) MR when combined with spin-echo MR in the diagnosis of dural sinus thrombosis. The VIGRE sequence consists of a rapid single-slice acquisition, 50/15/2 (TR/TE/excitations), and 30 degrees flip angle. At each slice position, a total of four images were reconstructed; these consisted of one magnitude image and three images sensitive to proton motion in each orthogonal direction. The flow direction and flow velocity (cm/sec) were obtained from each of the phase images, and results were correlated with data obtained from a phantom experiment. In normal controls, dural sinus velocities ranged from a mean of 9.9 to 14.4 cm/sec for the transverse and superior sagittal sinuses, respectively. Three patients with proved dural sinus occlusion were studied with spin-echo images at 1.5 T. Three-dimensional time-of-flight MR angiography was also performed in one patient. The presence of dural sinus occlusion was determined by the lack of flow void on the spin-echo images, the absence of phase shift on the VIGRE study, and the presence of retrograde flow on the phase image in the sinus proximal to the occluded segment. Time-of-flight angiography overestimated the extent of the thrombosis caused by spin saturation. Follow-up VIGRE studies detected the formation of collateral flow in one patient and recanalization with the establishment of normal antegrade sinus flow in the other. We conclude that phase-sensitive MR imaging is helpful in establishing the diagnosis and extent of dural sinus occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

Diffusion-weighted MR imaging of the brain: value of differentiating between extraaxial cysts and epidermoid tumors.

This study demonstrates the use of diffusion-weighted MR imaging in improving the specificity of the diagnosis of extraaxial brain tumors. Three surgically proved lesions (one arachnoid cyst and two epidermoid tumors) and two nonsurgically proved lesions (arachnoid and ependymal cysts) were evaluated with T1- and T2-weighted spin-echo studies followed by intravoxel incoherent motion (IVIM) MR imaging. The IVIM images of the lesions were displayed as an apparent diffusion coefficient (ADC) image obtained at 0.65 G/cm (maximum gradient b value = 100 sec/mm2) and compared with external oil and water phantoms. The ADC of arachnoid cysts was similar to stationary water whereas the ADC of epidermoid tumors was similar to brain parenchyma, indicating the solid nature and the slower diffusion rate of the epidermoid tumors. Cisternal CSF demonstrated uniformly high ADC, primarily because of bulk flow, which enhanced image contrast. Improved delineation of postsurgical changes was also possible. Our preliminary results show that diffusion-weighted MR imaging can be useful in distinguishing between arachnoid cysts and epidermoid tumors.

Adult↗