Search PubMed⌕ Search

Biomedical subjects

M T Modic

Publications and source records attributed to M T Modic.

At least 19 recordsLinked to original sources
PubMed1992

Short echo time proton spectroscopy of human brain using a gradient head coil.

Short echo time, single voxel localized proton spectroscopy was accomplished using a stimulated echo (STEAM) sequence running on a Siemens 1.5-T system with a head coil incorporating the Z and Y gradients. Spectra from the temporal lobe, the cerebellum and mid brain were acquired from a group of normal volunteers using the following parameters: voxel size = 8 ml, TE = 22 msec, 512 signal averages and TR = 1.7 sec. STEAM spectra acquired with the small diameter gradients showed significantly fewer artifacts at short TE, allowing the observation of glutamate/glutamine, GABA, taurine, and inositol in addition to the prominent resonance of choline, creatine/phosphocreatine and N-acetylaspartate (NAA). The levels of chlorine, creatine and NAA were found to be significantly different in the three regions of the brain examined.

Adult↗
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

Current assessment of spinal degenerative disease with magnetic resonance imaging.

Radiography (plain roentgenography, myelography, computed tomography (CT), computed tomographic myelography) has been used to identify morphologic changes involving the various components of the diskovertebral unit. Added to this armamentarium of imaging techniques is magnetic resonance (MR) imaging, with its superior ability to define anatomy, its improved contrast sensitivity, and its potential to provide unique biochemical and physiologic information. The authors review the current use of MR imaging in defining degenerative changes in the spine including the various patterns of herniation, annular tears, canal stenosis, and the use of gadolinium-diethylenetriamine-pentaacetic acid for previously unoperated and operated patients. Prospective studies have compared surface-coil MR imaging, CT, and myelography in the evaluation of disk herniation and stenosis and found an 82.6% accuracy between MR imaging and surgical findings for the type and location of the disease. Recent experience with precontrast and postcontrast MR imaging in the postoperative lumbar spine indicated that it was 96% accurate in differentiating scar from disk in 44 patients at 50 reoperated levels. Three-dimensional imaging is, more and more, becoming an integral part of routine MR imaging. The theoretical and practical advantages of three-dimensional imaging are several and include a theoretical increase in the signal-to-noise ratio over two-dimensional imaging (by the square root of the number of partitions selected), the ability to obtain thin contiguous slices from the volume without the problem of cross-talk found in two-dimensional imaging, more accurate slice thickness than that achieved in two-dimensional imaging, and a reduction in susceptibility artifacts. Different three-dimensional techniques are capable of providing either high or low signal intensity cerebrospinal fluid (CSF), with excellent suppression of CSF pulsation artifacts. Certain sequences provide a high enough signal intensity that a computer algorithm may be used to display the CSF in a rotating three-dimensional manner, similar to a myelogram. This three-dimensional myelographic image has the potential of providing the clinician with a global assessment of the CSF spaces, an advantage previously lacking with other imaging techniques.

Contrast Media↗
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

Magnetic resonance imaging in the evaluation of low back pain.

Many observers believe that magnetic resonance has become the procedure of choice for lumbar spine imaging. This article includes discussions of technique, normal anatomy, degenerative disc disease, and the use of paramagnetic contrast agents. Numerous figures are provided to illustrate explanations.

Back Pain↗
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

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

Steady-state free precession imaging in the presence of motion: application for improved visualization of the cerebrospinal fluid.

The authors discuss the appropriate FISP (fast imaging with steady-state precession) sequence structure to maintain constant phase at the radio-frequency pulse in the presence of motion. They present preliminary results of its application to head and spine imaging in an effort to maintain contrast between the cerebrospinal fluid (CSF) and the soft tissue. In the usual application of these FISP-like sequences, the gradient structure is modified to avoid unwanted signal (and contrast) variations due to field inhomogeneities. This change makes the signal sensitive to motion with a resulting decrease in signal intensity for moving tissue. The expected high contrast at large flip angles for tissues with low T1/T2 ratios such as CSF is not obtained. The technique discussed here overcomes the effects of field inhomogeneities and compensates for moving spins so that the transverse steady-state equilibrium and hence high contrast are obtained simultaneously.

Cerebrospinal Fluid↗
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↗
PubMed1990

Intracranial aneurysms: evaluation by MR angiography.

The purpose of this study was to compare the accuracy of a volume gradient-echo MR angiography (MRA) technique with that of intraarterial digital subtraction angiography (IA DSA) in the identification of intracranial aneurysms. The intracranial vasculature was examined in 47 patients by MRA and compared with IA DSA findings in 19 of these patients who had saccular or giant intracranial aneurysms. The remaining 28 patients, in whom no aneurysm was found, served as a control group. MRA was performed with the use of a velocity-compensated gradient-echo sequence (TR = 40-50/TE = 7-15) with a 15 degrees flip angle. The sensitivity and specificity were calculated for the evaluation of the cine 3D reconstructions (cine MRA) only, cine MRA + inspection of the individual partitions, and cine MRA + individual partitions + spin-echo studies. Of 21 aneurysms, of which three were missed in two patients, the sensitivity varied from 67% for cine MRA only to 86% for the cine MRA + partitions + spin-echo studies; of the 19 patients, among whom it was assumed that the diagnosis of any one aneurysm in a patient would lead to angiography and detection of additional aneurysms, the sensitivity varied from 73% for the cine MRA only to 95% for the cine MRA + partitions + spin-echo studies. The results of this study suggest that MRA can define the circle of Willis sufficiently to allow detection of intracranial aneurysms as small as 3-4 mm. MRA holds promise as a truly noninvasive screening examination of intracranial vasculature in patients at risk for aneurysms.

Adolescent↗
PubMed1990

MR imaging of the postoperative lumbar spine: assessment with gadopentetate dimeglumine.

This study defines the accuracy of gadopentetate-dimeglumine-enhanced MR imaging in patients with failed back surgery syndrome by comparing the imaging studies with surgical findings in a large patient population. From June 1988 to March 1989, 193 postoperative patients had MR imaging of the lumbar spine both with and without contrast administration. Of this group, 27 had repeat surgery at 31 levels: these patients comprise the study group. Postcontrast MR diagnoses were as follows: scar only (n = 4), disk only (n = 13), scar and disk (n = 9), and no aberrant epidural tissue (n = 5). Surgical diagnoses differed from the MR diagnoses in two patients at two levels. In one patient, disk was diagnosed on MR while osteophyte was present at surgery. In the other patient, scar only was diagnosed by MR but disk and scar were present at surgery. These data, when combined with the authors' previous experience, give pre- and postcontrast MR a 96% accuracy in differentiating scar from disk in 44 patients at 50 reoperated levels. For patients 6 or more weeks past surgery, sagittal and axial T1-weighted MR imaging before and after administration of gadopentetate dimeglumine is an effective method of evaluating the postoperative lumbar spine.

Adult↗