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M T Modic

Publications and source records attributed to M T Modic.

At least 37 records · Page 2Linked to original sources
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 degree 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↗
PubMed1989

Intracranial circulation: pulse-sequence considerations in three-dimensional (volume) MR angiography.

The technique and feasibility of magnetic resonance (MR) angiography of intracranial vessels were studied in 35 healthy volunteers. Variations in image orientation, repetition time (TR), and flip angle were evaluated to determine their effects on flow-related enhancement. Gradient modifications--including echo time (TE), motion compensation, bandwidth, and field of view--were also studied in an effort to reduce motion-induced phase shifts. Results indicated that a FISP (fast imaging with steady precession) sequence with a TR of 50 msec, TE of 15 msec, velocity compensation in the read and section-select directions, acceleration compensation in the read direction, anisotropic volume, and a 1.25-mm partition thickness produced three-dimensional angiographic MR images that were accurate and reproducible in the depiction of the major intracranial vessels. Difficulties with field of view, persistent signal void secondary to higher-order motion, and spatial resolution remain major problems requiring additional study.

Adult↗
PubMed1989

Intracranial circulation: preliminary clinical results with three-dimensional (volume) MR angiography.

The authors assessed the clinical utility of a magnetic resonance angiography technique in the evaluation of intracranial circulation. Eighteen patients with a low likelihood of cerebrovascular disease (control group) and 40 patients with suspected cerebrovascular disease were imaged with a FISP (fast imaging with steady precession) sequence (repetition time of 50 msec, echo time of 15 msec, velocity compensation in the read and section-select directions with acceleration compensation in the read direction, 15 degrees anisotropic volume, and a 1.25-mm partition thickness). Ninety-four percent of images in the control group and 72% of images in the group with cerebrovascular disease were considered useful for diagnosis. This technique can provide accurate images of intracranial circulation and can be performed in conjunction with two-dimensional spin-echo or gradient-echo imaging. It was most useful in the evaluation of patent intracranial aneurysms, vessel displacement, and large-vessel occlusive disease. Disadvantages included limited field of view, persistent signal voids, limited spatial resolution, and inadequate depiction of lesions with slow flow.

Adolescent↗
PubMed1989

Three-dimensional (volume) gradient-echo imaging of the carotid bifurcation: preliminary clinical experience.

This study was designed to test the accuracy of magnetic resonance (MR) imaging with a FLASH (fast low-angle shot) 40 degrees volume pulse sequence by comparing it with intraarterial digital subtraction angiography (DSA) in patients with suspected carotid artery stenoses. Fifteen patients referred for evaluation of anterior circulation in cerebrovascular disease composed the pilot group. Twelve patients underwent correlative intraarterial DSA examinations. The FLASH volume sequence, with an echo time of 7.7 seconds, produced high-signal-intensity vascular images for 28 of 30 bifurcations. Of the 24 carotid bifurcations studied with DSA, 22 were depicted with MR angiography. Among the depicted bifurcations, 21 showed good correlation with the DSA images. These included four of four normal bifurcations, three of three with mild stenosis, four of four with moderate stenosis, eight of nine with severe stenosis, and two of two with occlusions. With respect to ulceration, three of four MR angiographic studies showed good correlation with DSA images. This preliminary experience indicates that the method is reproducible and capable of delineating carotid lesions in patients and that it can be performed in conjunction with conventional spin-echo imaging of the brain with only a small increase in patient examination time.

Adult↗
PubMed1989

Extracorporeal membrane oxygenation in infants: angiographic and parenchymal evaluation of the brain with MR imaging.

The authors report their preliminary experience with intracranial three-dimensional Fourier transform magnetic resonance (MR) angiography and T2-weighted MR imaging of the brain parenchyma in 15 neonates less than 1 week old after extracorporeal membrane oxygenation (ECMO) with permanent ligation of the right common carotid artery and internal jugular vein, four 1-year-old infants after ECMO with carotid ligation, and four neonates less than 1 week old after ECMO with reanastomosis of the same artery. MR angiography was technically satisfactory in 20 of the 23 patients and documented patency of the right internal carotid artery proximal to the ophthalmic artery in nine of 16 patients with permanent carotid ligation and in all four patients with reanastomosis. This study suggests MR angiography is feasible in newborns and infants and that, in combination with parenchymal MR imaging, it provides a sensitive, noninvasive method to assess vessel patency and follow cerebrovascular and parenchymal changes in infants after ECMO.

Brain↗
PubMed1989

Magnetic resonance angiography of the extracranial carotid arteries and intracranial vessels: a review.

MRI is uniquely suited for evaluation of vascular structures due to its sensitivity to a variety of flow-related phenomena. Recent work has demonstrated that high quality magnetic resonance angiograms (MRA) of the carotid arteries and intracranial vasculature can be achieved by using gradient-echo techniques with short echo times. These MRAs are displayed like conventional arteriograms, but are acquired in a noninvasive fashion with a minimal increase in examination time. We used MRA to visualize 50 of 54 carotid bifurcations tested, with good correlation to the intra-arterial angiograms. We examined the intracranial vasculature in over 40 patients, and demonstrated aneurysms, vascular malformations, and occlusions.

Blood Vessels↗
PubMed1989

Herniation of the suprasellar visual system and third ventricle into empty sellae: morphologic and clinical considerations.

Intrasellar herniation of the optic nerve, optic chiasm, optic tract (suprasellar visual system, SVS), and anteroinferior third ventricle can occur into primary or secondary empty sellae. The anatomic part of this study evaluated the appearance of the SVS in subjects with normal sellae (n = 52), the patterns and prevalence of SVS herniation in enlarged primary empty sellae (n = 24), and the patterns of intrasellar herniation of the SVS in secondary empty sellae (n = 8). The clinical part of this study was to correlate the visual status with the anatomic patterns of the intrasellar herniated SVS. High-resolution MR and CT were used to define the anatomy. MR was superior to CT in all groups in defining accurately the SVS relationship to the sella turcica. In the normal group, the SVS invariably had a straight-line appearance formed by the optic nerve, optic chiasm, and floor of the third ventricle and was above the sella. The SVS was herniated in three of 24 enlarged primary empty sellae. A difference in the appearance of the hypothalamic and infundibular recesses in the primary empty sella group with SVS herniation (dilated recesses and formation of an obtuse angle) and in the secondary empty sella group with SVS herniation (nondilated recesses and formation of an acute angle) was observed. Visual disturbances in primary empty sellae with SVS herniation were present in two of three subjects. Visual disturbances may be absent or minimal in primary empty sellae and secondary empty sellae with herniation of the SVS. Progression of the symptoms--visual field defects, optic atrophy, and loss of vision--is not inevitable. There was no correlation between the severity of visual symptoms and the degree of herniation of the SVS in either the primary or secondary sellae. We found that intrasellar herniation of the SVS into a primary or secondary empty sella is well delineated with MR, and MR should facilitate decisions concerning surgery or therapy. Visual disturbances proved to be an unreliable indicator of herniation.

Adult↗
PubMed1989

Gadolinium-DTPA-enhanced MR imaging of the postoperative lumbar spine: time course and mechanism of enhancement.

To define the time course and mechanism of enhancement of epidural fibrosis after gadolinium-DTPA (Gd-DTPA) injection, we undertook a three-part study in humans and dogs with epidural scar after spine surgery. First, the dynamic in vivo contrast-enhancing properties of epidural scar were assessed by using sequential fast (18-sec) spin-echo sequences after contrast injection. Epidural scar in dogs rapidly enhanced; peak enhancement (101%) was 6 min after injection, with a slower decline toward baseline to 45% after 44 min. Epidural fibrosis in patients followed a similar pattern, with a maximum enhancement of 73% after 5 min. Paraspinal muscle had a lower peak enhancement in both patients (36%) and dogs (22%). Second, vascular injection in two dogs with India ink demonstrated multiple small vessels throughout the epidural scar. Third, light and electron microscopy was performed on epidural scar obtained at reoperation in both patients and dogs. Light microscopy showed multiple small capillaries scattered throughout a background of collagen. Electron microscopy demonstrated a wide variation in the junctions between endothelial cells ranging from "tight" to "loose." Regions of endothelial discontinuity were also visualized. This study suggests that Gd-DTPA diffuses rapidly into the extravascular space in epidural scar, with a slower, net movement toward the intravascular compartment as the agent is renally filtered. The contrast agent transgresses the endothelium through "leaky" intercellular junctions and areas of endothelial discontinuity.

Animals↗
PubMed1989

Gradient-echo MR imaging of the cervical spine: evaluation of extradural disease.

A prospective study was undertaken on 204 consecutive patients comparing low flip angle gradient-echo and T1-weighted spin-echo techniques in the MR evaluation of cervical extradural disease. Four patient groups were studied with varying gradient-echo TEs (6 or 13 msec) and flip angles (10 degrees or 60 degrees). Images were evaluated independently for contrast behavior and anatomy, then directly compared for conspicuity of lesions. The FLASH sequences (especially with a 10 degrees flip angle) produced better conspicuity of disease in half the imaging time. T1-weighted spin-echo sequences were more sensitive to marrow changes and intradural disease. The short TE sequence (6 msec) did not produce any diagnostic advantage over the longer TE sequence (13 msec). A fast and sensitive MR examination for cervical extradural disease combines a sagittal T1-weighted spin-echo acquisition with sagittal and axial FLASH 10 degrees sequences.

Cervical Vertebrae↗
PubMed1989

Magnetic resonance imaging of the spine.

The role of magnetic resonance imaging (MRI) for the evaluation of the spine is expanding rapidly. In addition to being noninvasive, MRI offers high soft-tissue contrast and multiplanar imaging capability. MRI examinations of the spine usually include a T1-weighted spin-echo and a T2-weighted spin-echo and/or a gradient-echo sequence. As in other parts of the body, the use of surface coils results in higher-quality examinations. Various methods are employed to reduce the motion artifacts that are particularly troublesome in spine imaging. Paramagnetic contrast agents are used to enhance soft-tissue lesions. The contrast sensitivity of MRI provides a unique means to assess the intervertebral disc, and MRI is rapidly becoming the method of choice for evaluation of disc disease. It is also very sensitive and accurate in the detection of osteomyelitis of the spine. MRI has improved the evaluation of failed back surgery syndrome, and the administration of gadolinium-diethylene trimene pentacidic acid helps to differentiate postsurgical scar from recurrent disc herniation. MRI is an unparalleled tool for the detection and evaluation of intramedullary lesions including syringomyelia, gliomas, hematomas, and lesions associated with dysraphism. It is also useful in many extramedullary intradural processes. In summary, MRI is the best first examination for spinal disease.

Epidural Space↗
PubMed1989

Imaging of degenerative disease of the cervical spine.

The introduction of new techniques to the magnetic resonance imaging (MRI) armamentarium is beginning to provide an MRI examination that overcomes many of the disadvantages noted in earlier reports. An analysis of the various advantages and disadvantages of MRI, plain film myelography, and computed tomographic myelography points to a potential revision of the sequence of diagnostic studies and the workup of cervical degenerative disease. MRI might now be the appropriate first test for the evaluation of the cervical spine in a patient with symptoms referable to degenerative disease when therapeutic intervention is considered. An initial T1-weighted sagittal image with a 3-mm slice thickness will provide excellent contrast evaluation of the vertebral body marrow, disc space height, neural canal, and spinal cord. Disc herniation, canal stenosis, subluxation, and malalignment can be appreciated. Next, a fast, variable flip angle, gradient-echo sequence can be performed to increase the signal density of the cerebrospinal fluid relative to the extradural elements and cord. This provides an increased conspicuousness of extradural disease. Axial gradient-echo fast sequences, with low flip angles, will provide a second orthogonal plane with increased conspicuousness of extradural changes relative to the neural foramen and thecal sac. If necessary, additional oblique views through the neural foramen can be obtained. Finally, if intramedullary disease is considered in the differential, a gated, refocused, T2-weighted examination in the sagittal plane will provide the necessary soft-tissue contrast to detect pathology without unwanted artifact. Thus, unlike plain film or computed tomographic myelography, an examination of the entire cervical region including the osseous structures, extradural cerebrospinal fluid interface, and the spinal cord can be obtained with a single modality in an outpatient setting and in a noninvasive fashion. MRI can certainly replace plain film myelography for the overwhelming majority of situations. If surface-coil MRI fails to demonstrate an abnormality responsible for the patient's clinical symptoms, then a high-resolution computed tomographic scan with or without intrathecal contrast can be obtained. While the cost at first may seem prohibitive, the additional information that MRI is capable of providing in a noninvasive outpatient setting more than compensates for the expense.

Cervical Vertebrae↗
PubMed1988

Degenerative disk disease: assessment of changes in vertebral body marrow with MR imaging.

The authors reviewed magnetic resonance (MR) images of 474 consecutive patients referred for lumbar spine MR imaging. Type 1 changes (decreased signal intensity on T1-weighted spin-echo images and increased signal intensity on T2-weighted images) were identified in 20 patients (4%) and type 2 (increased signal intensity on T1-weighted images and isointense or slightly increased signal intensity on T2-weighted images) in 77 patients (16%). In all cases there was evidence of associated degenerative disk disease at the level of involvement. Histopathologic sections in three cases of type 1 change demonstrated disruption and fissuring of the end plates and vascularized fibrous tissue, while in three cases of type 2 change they demonstrated yellow marrow replacement. In addition, 16 patients with end-plate changes documented with MR were studied longitudinally. Type 1 changes in five of six patients converted to a type 2 pattern in 14 months to 3 years. Type 2 changes in ten patients remained stable over a 2-3-year period. These signal intensity changes appear to reflect a spectrum of vertebral body marrow changes associated with degenerative disk disease.

Adult↗
PubMed1988

Carotid bifurcation: MR imaging. Work in progress.

To devise and implement an in-plane magnetic resonance angiography examination of the carotid bifurcation capable of producing high-resolution images, the authors examined 19 normal carotid arteries and 14 patients with angiographically documented disease with two flow-correction techniques: a three-gradient, velocity-refocused technique with spin-echo (SE) and gradient-echo sequences, and a four-gradient velocity- and acceleration-corrected SE technique. With use of three equal gradients in the read direction, velocity-related phase changes were minimized by placing the dephasing gradient after the 180 degree pulse and near the read gradient. Acceleration effects were minimized through the use of short echo times and cardiac gating. Both velocity- and acceleration-produced phase changes were corrected with the four-gradient scheme but at the expense of some limitations in spatial resolution. Both techniques consistently produced satisfactory images of the carotid bifurcation in healthy individuals. However, the results indicate that the present gradient-phase modulation techniques have several drawbacks, including susceptibility to patient motion, overlapping with the jugular vein, and inability to image carotid stenosis accurately due to turbulence.

Blood Flow Velocity↗
PubMed1988

Fast three-dimensional MR imaging of the knee: comparison with arthroscopy.

Twenty patients with suspected internal derangement of the knee were examined with fast, three-dimensional (3D) magnetic resonance (MR) imaging and arthroscopy with a numerical classification system designed for use by both the radiologist and orthopedist. MR volume acquisitions allowed delineation of all arthroscopically diagnosed meniscal tears and high-grade meniscal degeneration. All arthroscopically visible ligamentous injuries, including partial cruciate tears, were detected with MR imaging. There was excellent correlation for high-grade cartilaginous lesions, although MR imaging appeared insensitive to small cartilage irregularities. Additionally, MR imaging allowed diagnosis of ten bone abnormalities not accessible to arthroscopic evaluation. The high accuracy of MR imaging that was found in this study was in large part due to the thin, contiguous sections generated in volume imaging. With the added advantage of high patient throughput, fast volume MR imaging is an accurate and efficient method for evaluation of knee abnormality.

Arthroscopy↗
PubMed1988

Lumbar spine: postoperative MR imaging with Gd-DTPA.

Thirty patients with failed back surgery syndrome were studied to evaluate the effectiveness of magnetic resonance (MR) imaging with gadolinium-diethylenetriaminepentaacetic acid/dimeglumine (Gd-DTPA) in differentiating postoperative epidural fibrosis (scar) from recurrent disk herniation. Pre- and postcontrast MR images were interpreted without access to other diagnostic, surgical, or pathologic findings. Seventeen patients had surgical and pathologic correlation of the MR findings at 19 disk levels. The precontrast studies had a sensitivity, specificity, and accuracy of 100%, 71%, and 89%, respectively. The enhanced MR studies correctly depicted the character of abnormal epidural soft tissue in 17 patients at all 19 levels. Scar showed heterogeneous enhancement on the early T1-weighted spin-echo images obtained within 10 minutes after contrast material administration. Herniated disk did not show significant enhancement on the early studies but showed variable degrees of enhancement on delayed images in nine of 12 cases. Other criteria were found to be less useful than the pattern of enhancement. Results indicate that precontrast and early postcontrast T1-weighted spin-echo studies are highly accurate in separating epidural fibrosis from herniated disk.

Adult↗
PubMed1988

Epidural fibrosis and recurrent disk herniation in the lumbar spine: MR imaging assessment.

Twenty patients were enrolled in a prospective study to evaluate MR imaging in the differentiation of epidural scar and herniated disk material. Fourteen patients had surgical verification of imaging findings. In 12 (86%) of these patients, the MR interpretations fully agreed with the observations at surgery. Careful integration of the findings on sagittal and axial T1-weighted images with more T2-weighted axial images was important for analysis. Anterior and lateral recess scars were hypo- or isointense on T1-weighted sequences and hyperintense on more T2-weighted sequences relative to the "parent" anulus intensity. Free fragments demonstrated a slightly hyperintense signal intensity on T1-weighted images relative to epidural fibrosis but had a similar hyperintense signal intensity on T2-weighted sequences. Prolapsed or extruded disk fragments were hypo- or isointense relative to the parent anulus on all sequences. Morphology, epidural location, mass effect, and often signal intensity were the important parameters by which scar and herniated disk could be differentiated with MR.

Adolescent↗