Biomedical subjects
Publications and source records attributed to D B Hackney.
We report a case of multiple aneurysms with subarachnoid hemorrhage in which CT was inconclusive as to the source of bleeding and in which the angiographic criteria were misleading. Magnetic resonance demonstrated a focal subarachnoid hematoma adjacent to the ruptured aneurysm.
Ten patients with intracerebral metastases from malignant melanoma were evaluated with magnetic resonance (MR) imaging performed at 1.5 T using spin-echo techniques. On the basis of histopathologic findings in three of 10 cases and CT appearances in all 10 cases, three patterns were identified on analysis of MR signal intensities in both short repetition time/echo time (TR/TE) and long TR/TE spin-echo scans. In comparison to normal cortex, nonhemorrhagic melanotic melanoma appeared markedly hyperintense on short TR/TE images and isointense, mildly hypointense on long TR/TE images. Nonhemorrhagic, amelanotic melanoma appeared isointense or mildly hypointense on short TR/TE and isointense or mildly hyperintense on long TR/TE images. Hemorrhagic melanoma varied in appearance, depending on the stage of hemorrhage. Melanotic, nonhemorrhagic melanoma can be distinguished from early and late subacute hemorrhage by its signal intensity on long TR/TE images. Spin-echo MR appears to be the method of choice for diagnosing melanotic metastases.
This is a report of the magnetic resonance study in a case of orbital metastasis from a carcinoid tumor. A rather unusual feature of this lesion was its relatively short T2 as compared with other metastatic orbital lesions.
Fast low-angle multiecho (FLAME) imaging uses partial flip angles of less than 90 degrees with 180 degrees radiofrequency refocusing pulses. The partial flip angle permits imaging with shorter repetition time (TR) values on the order of 750-1,000 ms for 30 degrees angles with image contrast characteristics identical to those obtained with conventional 90-180 degrees schemes and TRs on the order of 2,500 ms. The approximately threefold reduction in imaging time is accompanied by a decrease in signal-to-noise ratio. In many circumstances, however, this trade-off may produce entirely acceptable images of the CNS at a significant reduction in imaging time.
OBJECTIVE: This study was conducted to determine the association between lesion length measured on MRI and the severity of mechanical injury in a rat model of spinal cord trauma. MATERIALS AND METHODS: Sprague-Dawley rats were subjected to a modified Allen weight drop injury and killed 4 h after injury. Their fixed, exercised cords were studied with MRI at 1.9 T. RESULTS: There were strong correlations between lesion length on MR images and weight drop height and square root of drop height (r2 = 0.55, p < 0.0001 and r2 = 0.63, p < 0.0001, respectively). The lesion length differences were significant versus controls for all drop heights at p values of < or = 0.002 and for the 2.5 cm animals versus the 5 and 15 cm animals (p = 0.01 and p = 0.0002, respectively), but the lengths of the 5 vs. 15 cm groups only approached significance (p = 0.06). CONCLUSION: These results suggest that lesion length determined on MR images is a reliable indicator of the severity of trauma among animals subjected to weight drop injury.
Three cases of seizures and marked behavioral changes that occurred after intrathecal metrizamide administration are reported. In each case a cranial computed tomographic scan obtained within 24 hours of the ictus showed hyperdensity of the gray matter, and created an optical illusion of diffuse white matter edema. The literature on adverse reactions and their pathogenesis and on brain parenchymal penetration of metrizamide is reviewed.
The purpose of this study was to compare CT and MR for the detection of cervical disk herniations. Nineteen patients suspected of harboring degenerative disk disease of the cervical spine underwent thin contiguous section CT myelography (CTM) and thin contiguous section three-dimensional Fourier transform (3DFT) gradient echo MR at 67 disk levels. Blinded readings of a high intensity CSF MR technique for the presence or absence of disk herniation were performed by three neuroradiologists. The intraobserver CT-MR concordances ranged from 84 to 89%. Using CTM as the paragon test, MR demonstrated a sensitivity of 79-91% and a specificity of 82-88% for disk herniation. Mean MR-CT concordance (86%) was nearly equivalent to that of CT-CT intraobserver concordance (88%). When consensus readings were considered, the MR-CT concordance (91%) was slightly higher than that of CT-CT intraobserver concordance (88%). We conclude that thin section 3DFT gradient echo MR with high intensity CSF is a reliable method to screen for degenerative disk disease in the cervical spine, since the agreement between MR and CTM is comparable with the intraobserver agreement of CTM.
The in vitro behavior of various states of hemoglobin was examined over a wide range of concentrations. Solutions of increasing concentrations of oxyhemoglobin displayed significant increases in T1 and T2 relaxation rates that were insensitive to pH values between 6.0 and 6.9. Bovine serum albumin, which displayed a relaxation behavior nearly identical to that of oxyhemoglobin, was used to normalize for the protein concentration of the deoxyhemoglobin and methemoglobin samples. Concentrated protein solutions with increasing proportions of deoxyhemoglobin yielded little change in the T1 relaxation rate. In these samples, however, the T2 relaxation rate displayed a parabolic dependence on the concentration of intracellular deoxyhemoglobin paralleling the inhomogeneity of the sample; this was not observed with extracellular deoxyhemoglobin. Similar T2 relaxation behavior was observed for intracellular methemoglobin, except that the magnitude of the T2 shortening was smaller than that for deoxyhemoglobin. The magnitude of the T2 shortening was pH dependent, roughly paralleling the change in the equilibrium between the high-spin acid form of methemoglobin and the low-spin basic form of methemoglobin. Marked increase in the T1 relaxation rate is observed with increasing concentrations of methemoglobin, again with greater relaxation enhancement at lower pH. The results of our study emphasize the importance of normalizing for protein concentration when assessing the effects of paramagnetic forms of hemoglobin.
Routine evaluation of axial MR images of the cervical spine with high-intensity CSF (long TR/TE spin-echo or gradient-echo images) revealed apparent narrowing of the cord's anteroposterior diameter when these images were compared with corresponding postmyelography CT scans. This discrepancy was believed to be due to the truncation artifact at the CSF-cord boundary. To examine the truncation effect, we compared cord diameters in 12 patients on postmyelography CT scans and MR images and then compared these with MR scans of normal volunteers and of an agar-saline spine phantom. There was an artifactual diminution of the cord diameter in the 128-step phase-encoding axis of the 128 x 256-matrix MR scan as compared with the diameter of the cord in the patients' postiohexol CT scans and in the 256 phase-encoded axis MR scan in the volunteer study. A similar discrepancy was noted in the spine phantom study, in which the cord diameter in the 256-step phase-encoded MR scan, the CT scan, and direct measurement exceeded that in the 128-step phase-encoded axis MR scan. The range of differences between the measurements was as large as 2.3 mm (patients), 1.7 mm (volunteers), and 1.8 mm (phantom) for the three studies. In all three studies, varying the photographic window width and level produced variation in the apparent cord diameter of up to 1.5 mm. To eliminate this effect, the cord diameters in the phantom and the normal control subjects were measured at identical window levels. The truncation artifact, coupled with standard window settings used in photography, may lead to inaccurate display of the diameter of the cervical spinal cord.
Human and rat cervical spinal cords were imaged with high-resolution spin-echo and inversion-recovery pulse sequences in an experimental 1.9-T MR system. The gross morphology of the cord was easily discernible in fresh and fixed specimens, including the white and gray commissures, dorsal and ventral horns, and lateral and posterior funiculi. The T1, T2, and spin-density values for gray and white matter were determined from these images and were found to be 914 msec, 114 msec, and 71% for white matter other than the dorsal columns, and 946 msec, 87 msec, and 80% for gray matter in human spinal cords. These values are reduced considerably after formalin fixation: T1 to 56% (white matter) and 54% (gray matter) of prefixation values, T2 to 52% (white matter) and 70% (gray matter) of fresh values, and spin density to 90% (white matter) and 96% (gray matter) of prefixation values. Interestingly, the central gray matter demonstrates higher signal intensity than the white matter on both short and long TR/TE images. This intensity difference was observed for both human and rat spinal cords, before and after fixation, and can be explained by the relatively small T1 differences between gray matter and white matter and the gray matter-white matter spin-density ratios: 1.127 for fresh and 1.203 for fixed specimens.
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This study attempts to determine the magnitude of change in the concentration of a nonparamagnetic protein (human serum albumin) required to effect a detectable change in signal intensity on a clinical imaging unit. For a range of protein concentrations from 0-6100 mg/dl the concentration could not be predicted by inspecting the images. Measurement of displayed signal intensity failed to distinguish concentrations of 0.09-3700 mg/dl, while 6100 mg/dl gave slightly higher intensity signals. Although this low sensitivity represents expected behavior for low concentrations, the failure to differentiate the higher concentrations implies limitations imposed by clinical imaging techniques. Our results suggest that additional factors, such as paramagnetic material and motion as well as differences in protein concentration, may be involved in the MR signal intensities observed in pathologic CSF and cystic CNS collections.
High-field MRI is capable of differentiating acute, subacute, and chronic hemorrhagic cortical infarctions. In eight of nine patients, hemorrhage occurred in a vascular watershed zone. Acute hemorrhagic cortical infarction produces mild cortical low intensity on T2-weighted images outlined by subcortical edema (high intensity) and isointensity with normal cortex on T1-weighted images. Subacute hemorrhagic cortical infarction shows cortical high intensity first on T1-weighted images and later on T2-weighted images; it is also associated with subcortical edema. In the chronic stage, there is a marked persistent cortical low intensity on T2-weighted images. This is most prominent in the deeply infolded cortical gyri. The low intensity noted in acute and chronic hemorrhagic cortical infarction with T2 weighting appears to be related to two separate underlying histochemical states. The characteristic cortical low intensity observed on T2-weighted images in acute and chronic hemorrhagic cortical infarction is proportional to the square of the magnetic field strength.
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Internuclear ophthalmoplegia is a gaze disorder characterized by impaired adduction on the side of a lesion involving the medial longitudinal fasciculus with dissociated nystagmus of the abducting eye. Eleven patients with internuclear ophthalmoplegia (nine with clinical multiple sclerosis, two with clinical infarction) underwent MR imaging with spin-echo techniques on a 1.5-T system. Nine patients also had CT. MR showed focal or nodular areas of high signal intensity on T2-weighted images in the region of the medial longitudinal fasciculus in 10 of 11 patients. In one of four patients with internuclear ophthalmoplegia who had MR after intravenous gadolinium-DTPA, an enhancing ring lesion was seen in the region of the medial longitudinal fasciculus on short TR/TE images, indicating active blood-brain-barrier disruption, which correlated with this patient's recent-onset internuclear ophthalmoplegia. CT failed to show the lesions in all nine patients examined. This report demonstrates the superiority of MR in evaluating gaze disorders attributable to brainstem dysfunction, such as internuclear ophthalmoplegia, and correlates MR findings with the relevant neuroanatomy of the medial longitudinal fasciculus.
The relationship between tumor mass and vascular involvement as seen on MR imaging was examined in 11 patients with masses in the parasellar region, and the findings were correlated with CT and angiography. In six cases, MR was superior to CT and angiography in depicting the relationship of the tumor to adjacent blood vessels. In these cases, MR demonstrated tumor surrounding the blood vessel without changing the diameter of its lumen. Angiography did not reveal encasement in these cases. In four cases, both MR and angiography showed signs of vascular encasement with narrowing of the vessel's lumen. In two cases, MR was equivocal while angiography revealed vascular encasement in one case and was negative for encasement in the other. CT was less sensitive than MR in defining vascular encasement since there is usually little contrast between an enhancing tumor and the major blood vessels. Coronal scanning appeared to be the best plane of imaging and correlated well with the anteroposterior angiogram. We propose that MR is the method of choice for evaluating arterial encasement by tumors and may obviate the need for angiography in those cases in which MR is positive for a basal lesion.
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