Search PubMed⌕ Search

Biomedical subjects

T J Masaryk

Publications and source records attributed to T J Masaryk.

At least 19 recordsLinked to original sources
PubMed1992

Intracranial magnetic resonance imaging.

Magnetic resonance angiography (MRA) is currently being incorporated into the routine MR evaluations of patients with suspected cerebrovascular disease. Currently, MRA serves as a useful adjunct to routine parenchymal spin-echo imaging of the head. Intracranial MRA is predominantly used as a screening test for cerebrovascular disease in situations where the clinical suspicion and/or the patient's physical condition does not warrant a conventional arteriogram. Clinical experience to date suggests that MRA can play a significant role in the evaluation of patients with suspected intracranial aneurysms, arteriovenous fistulae, large vessel occlusive disease, and dural sinus occlusion/thrombosis. MRA has not yet reached the point where it can replace conventional catheter angiography. This is most apparent when trying to evaluate 1) larger vessels which are typically difficult to visualize due to higher order motion terms (eg, carotid siphon); 2) the smaller cortical branches with relatively slow flow that would be necessary to see in patients with suspected vasculitis; and 3) any situation in which dynamic information is important such as with mass lesions or vascular malformations. These limitations must be taken into account when deciding on the appropriate imaging study for an individual patient. Large-scale, well-controlled prospective clinical trials will ultimately determine the role intracranial MRA will play in the evaluation of patients with suspected cerebrovascular disease.

Brain↗
PubMed1992

Ischemic brain disease, vascular brain disease, and magnetic resonance angiography.

Rapid, accurate diagnosis and successful implementation of new stroke therapies will depend on the refinement and skilled use of neuroimaging. Because a variety of MR techniques offer information on local brain biochemistry, blood flow, perfusion, vascular integrity, ischemia, edema or free water, infarction, and hemorrhage, there is intense interest in their application to cerebrovascular disease. This review highlights recent advances in MR technology as they relate to conventional MR imaging, MR angiography, and basic MR research into the use of diffusion, perfusion, and spectroscopic techniques.

Brain Ischemia↗
PubMed1991

Cerebrovascular abnormalities in pediatric stroke: assessment using parenchymal and angiographic magnetic resonance imaging.

Three-dimensional (volume) magnetic resonance angiography is a noninvasive technique that images the intracranial and cervical arterial vasculature without contrast agents. Twenty-four children with strokes had combined parenchymal magnetic resonance imaging and magnetic resonance angiography 1 day to 4 years after acute presentation. Eight had had prior intra-arterial angiography. Eighteen magnetic resonance angiographic studies showed arterial stenosis or occlusion in the vascular distribution of magnetic resonance image-defined brain infarction and, in 7 children, in the same location as previously defined abnormalities on intra-arterial angiography. One child had a normal intra-arterial angiogram and magnetic resonance angiogram. The other 5 children with normal magnetic resonance angiographic studies included 3 with presumed embolic disease, 1 with meningitis, and 1 with Crohn's disease-related vasculitis. Collateral flow patterns could be determined in 4 children. Artifact presenting as filling defects in vessels was present in 10 studies, but did not interfere with interpretation of 8 studies. Combined magnetic resonance imaging/magnetic resonance angiography provides a screening technique to evaluate noninvasively brain parenchyma and vasculature in children with suspected large-vessel abnormalities, allowing selection for intra-arterial angiography and serial monitoring of vascular abnormalities over time and during therapeutic intervention.

Anemia, Sickle Cell↗
PubMed1991

3DFT MR angiography of the carotid bifurcation: potential and limitations as a screening examination.

The authors compared the three-dimensional Fourier transform (3DFT) time-of-flight magnetic resonance (MR) angiograms in 38 patients initially studied with selective intraarterial digital subtraction angiography (DSA) for suspected arteriosclerotic disease of the carotid bifurcation. MR angiograms were successfully obtained in 65 of the 75 carotid arteries (87%) visualized with DSA. DSA and MR angiographic studies were assessed for percentage area stenosis by two independent observers on two occasions. Statistical tests indicated consistency in interpretation for each observer as well as between observers. No significant difference was found between the two modalities in ability to depict changes in percentage area stenosis. For the 32 right carotid arteries in the comparison, the median for the difference between MR angiography and intraarterial DSA was 1.83% (range, -22.38% to 55.60%); for the 33 visualized left carotid arteries, it was 0.00% (range, -20.55% to 49.95%). Receiver operating characteristic analysis indicated that technically adequate MR angiography may be a sensitive screening examination for stenoses.

Angiography, Digital Subtraction↗
PubMed1991

Neoplastic disease of the spine.

In summary, MR imaging has become the single most effective modality for the evaluation of spinal neoplasms by virtue of its ability to image the spinal cord directly and noninvasively. In this fashion, one can localize mass lesions relative to the spinal cord; in conjunction with the patient's clinical history, it is thus possible to provide a brief yet accurate differential diagnosis. Intravenous paramagnetic contrast enhancement also may prove extremely useful in further delineating such lesions. In addition, it has demonstrated a high sensitivity to primary and secondary tumors of the bony spine through its ability to detect subtle T1 signal changes in the vertebral marrow space.

Bone Cysts↗
PubMed1991

Flow, radiofrequency pulse sequences, and gradient magnetic fields: basic interactions and adaptations to angiographic imaging.

The basic process of MRI consists of two essential, relatively independent components: (1) excitation in the form of a radiofrequency pulse sequence, and (2) signal sampling and localization, that is, forming the MR image through the use of field gradients. The presence of motion (blood flow) during either excitation or sampling results in two types of corresponding effects: (1) time-of-flight effects, and (2) spin phase phenomena. These effects can be manipulated through the use of special coils, pulse sequences, gradients, and postprocessing techniques to provide angiographic images in which simple motion provides the basis for contrast.

Cerebral Angiography↗
PubMed1991

Magnetic resonance angiography of the carotid bifurcation.

MRA methods may be categorized into TOF or PC techniques. TOF techniques utilize flow related enhancement to provide high signal intensity blood. Two common TOF methods to visualize the bifurcations are sequential 2D or 3D imaging. In 2D imaging, the carotid bifurcation is visualized by obtaining a series of thin 2D axial gradient echo images. This stack of images may then be subjected to postprocessing to show just the vessel geometry, with the background stationary tissue suppressed. Advantages of 3D techniques include a reduction of T2* effects and a theoretical increase in signal to noise. While the scan time is increased with 3D imaging with the additional direction of phase encoding, overall imaging times are comparable for 3D and sequential 2D techniques, with both being shorter than the 3D PC technique. Advantages of PC angiography include direct and effective suppression of background tissues and definition of slow flow states. This method also has the potential for quantitative flow measurements. Because the signal of blood from this technique depends on flow induced phase change, signal loss from more complex flow is more problematic than with TOF methods. It is apparent from the plethora of methods available that no single MRA technique can answer all clinical questions and situations. Specific techniques and parameters will have to be tailored to individual patient needs. While this makes the routine application of MRA more complex, it also will ensure that the maximum diagnostic yield is achieved.

Carotid Arteries↗
PubMed1991

Magnetic resonance angiography of the intracranial vasculature.

Preliminary experience has shown that MRA can provide useful clinical information that complements the more traditional SE brain evaluation of patients with cerebrovascular disease. MRA is particularly appealing in that it provides a relatively rapid, noninvasive alternative to the existing vascular imaging modalities and the capability to evaluate the brain parenchyma directly. This can often be done without repositioning the patient or significantly prolonging the examination time. MRA sequences have been applied in the evaluation of patients with intracranial aneurysms, vascular malformations, vasoocclusive disease, neoplasms, and dural sinus thrombosis. The MRA study design and acquisition parameters are crucial and need to be optimized to maximize sensitivity and specificity of the examination based on the individual clinical presentation. The results of the SE and MRA studies should be evaluated together to obtain a definitive diagnosis or to determine whether conventional angiography is needed. As with any other diagnostic procedure, it is important to recognize the strengths and limitations of these techniques. Despite its advantages, MRA will not replace conventional catheter angiography in the near future. Rather, it will complement existing indications for conventional MR studies. Spatial resolution and intravascular signal loss due to rapid, complex flow continue to be the most limiting factors in intracranial MRA imaging. Significant improvements in these areas are currently being realized.

Brain↗
PubMed1990

Parenchymal and vascular magnetic resonance imaging of the brain after extracorporeal membrane oxygenation.

Three-dimensional (volume) magnetic resonance angiography is a new and noninvasive method for imaging the intracranial vasculature. The combination of magnetic resonance angiography and conventional magnetic resonance imaging was used to evaluate brain parenchyma and vessels in 30 survivors of extracorporeal membrane oxygenation. Magnetic resonance imaging findings were abnormal in 33% of the patients, with no increased frequency of right hemispheric lesions. Magnetic resonance angiography demonstrated good intracranial flow in all infants and demonstrable right internal carotid arterial flow in 35% of those patients with permanent carotid ligation. An abnormal magnetic resonance imaging study was found more often in infants with abnormal predischarge neurologic examination results. These techniques have several advantages over other neuroimaging modalities, including better definition of deep structures, myelin formation, and intracranial vasculature, the absence of bone artifact, and the elimination of catheter or contrast use.

Brain↗
PubMed1990

Optimizing blood vessel contrast in fast three-dimensional MRI.

Magnetic resonance angiography has matured to the point where clinically useful images can be acquired in half an hour or less. In this paper, the role of 3D imaging techniques is primarily considered. Specifically, the optimal imaging parameters, sequences, and reconstruction techniques are evaluated for moving spins. A variant of FISP known as ROAST with low flip angles, short repeat times, and a thick slab has been found to yield the best 3D survey scan of the cranial vessels with roughly 1 X 1 X 1-mm3 resolution in each of the processed images (slices). For the faster flowing carotids, a sagittal scout with as short a TE as possible is required to avoid spin dephasing. Localization is accomplished in both cases by acquiring thin slab 3D, thin partition, larger flip angle, longer repeat time FLASH sequences. Different choices of dephase/rephase sequences and directions are also reviewed. These choices are discussed from a practical and theoretical perspective. In particular, improvements in contrast and resolution are evaluated using half-Fourier, 512 acquisition, small fields of view and constrained reconstruction for both rephased gradient echo sequences and dephased thin slice long TR spin-echo sequences. A resolution of 0.5-0.75 mm is recommended to obtain sufficient image quality for consistent clinical interpretation of stenoses and vessel abnormalities.

Blood Flow Velocity↗
PubMed1990

Carotid-CNS MR flow imaging.

The authors present their 1-year experience with the use of 3DFT, time-of-flight MR angiography for the evaluation of vascular diseases of the head and neck. Their experience with over 150 patients indicates that this examination may be performed in conjunction with standard spin-echo imaging with only a minimal increase in patient examination time. This combined examination is most applicable to atherosclerotic disease of the carotid bifurcation, arterial occlusions of the primary and secondary branches of the intracranial circulation (particularly in pediatric patients such as those following ECMO or with sickle cell anemia), and patients with saccular berry aneurysms. This type of static, angiographic technique adds little to standard spin-echo imaging in patients with arteriovenous fistulae, neoplasms, and giant intracranial aneurysms. Limitations of the present technique include the inability to visualize slow flow lesions (e.g., giant aneurysms) and selected high flow states (arteriovenous fistulae, some severe stenoses).

Algorithms↗
PubMed1990

Diagnosis of cerebrovascular disease in sickle cell anemia by magnetic resonance angiography.

The study of blood flow by means of magnetic resonance techniques has led to a noninvasive magnetic resonance angiography (MRA) technique for imaging large cerebral vessels. Ten children with sickle cell hemoglobinopathy and a history of acute neurologic syndromes were studied with combined parenchymal magnetic resonance imaging (MRI) and MRA. Six had abnormal MRI findings and MRA-defined luminal lesions in the vascular distribution of these parenchymal infarctions. The three children with previous intraarterial angiography had MRA abnormalities that corresponded with vascular lesions on conventional angiograms. Four had normal MRI and MRA findings. We conclude that a combination of MRI and MRA provides a noninvasive screening test for large-vessel disease in this population.

Anemia, Sickle Cell↗
PubMed1990

Diagnosis of lumbar arachnoiditis by magnetic resonance imaging.

Twenty-four cases of lumbar arachnoiditis were evaluated by magnetic resonance (MR) imaging. The morphologic changes of arachnoiditis by MR were compared in 20 cases with CT myelography (CTM) and plain film myelography (PFM). An abnormal configuration of nerve roots was seen by MR. Three anatomic groups were identified. Group 1 showed conglomerations of adherent nerve roots residing centrally within the thecal sac. Group 2 demonstrated nerve roots adherent peripherally to the meninges, giving rise to an "empty sac" appearance. Group 3 showed a soft tissue mass replacing the subarachnoid space. Magnetic resonance imaging resulted in accurate diagnosis, and had excellent correlation with CT myelography and plain film myelographic findings in the diagnosis of lumbar arachnoiditis.

Arachnoiditis↗
PubMed1990

Assessment of extradural degenerative disease with Gd-DTPA-enhanced MR imaging: correlation with surgical and pathologic findings.

To test whether gadolinium-DTPA-enhanced MR would increase the conspicuity of extradural degenerative disease in the previously unoperated patient, we prospectively studied a group of 30 patients with symptoms suggestive of disk disease. Surgical findings and pathologic correlations were used as an objective measure of accuracy. Gadolinium-DTPA increased the confidence of diagnosis at one of eight operated cervical levels (six patients) and changed the diagnosis from extradural degenerative disease to tumor in one patient. The mechanism of enhancement of the epidural space and peridiskal region appears to be related to accumulation of contrast material within the epidural venous plexus, as well as to epidural fibrosis associated with disk disruption and herniation. While the immediate clinical utility of gadolinium-DTPA for morphologic analysis seems limited to difficult cervical spine cases, the presence of enhancement as a marker of epidural fibrosis and attempted healing may prove to be of great importance in studying the natural history and basic pathophysiology of degenerative disk disease.

Adult↗
PubMed1990

Tears of the anulus fibrosus: assessment with Gd-DTPA-enhanced MR imaging.

T2-weighted images have been shown to be capable of defining anular tears in vitro as increased signal intensity within the normal low-signal-intensity anulus fibrosus. Since growth of granulation tissue into anular tears has been described as part of the healing process, it seemed likely that gadolinium-DTPA should enhance anular tears as it does scar tissue in other parts of the spine. We retrospectively reviewed spinal MR images from 30 previously unoperated patients and correlated areas of increased signal intensity within the anulus on T2-weighted images with areas of enhancement on T1-weighted images, and to a limited extent, with surgical findings. Eighteen separate areas of anular enhancement were found in 12 patients (six cervical, 12 lumbar). Only five of these enhancing areas showed increased signal intensity on T2-weighted images, four of a type II tear pattern and one of a type III tear pattern. Contrast enhancement within the anulus was in a pattern of type II tear in 14 and type III in four. Histology from an enhancing type II anulus demonstrated vascularized granulation tissue within the avascular anulus, without focal herniation. Anular tears may be imaged in vivo not only with T2-weighted images but also with gadolinium-DTPA-enhanced T1-weighted images by virtue of their vascularized granulation tissue.

Back Pain↗