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Background and Purpose: Total spine MRIs are requested by the emergency department when focused imaging can not be ordered on the basis of history or clinical findings. However, their efficacy is not known. We assessed the following: 1) major radiologic and clinical outcomes of total spine MR imaging performed by the emergency department, and 2) whether the presence of a high-risk clinical profile and/or neurologic findings impacts the clinical outcomes., Materials and Methods: Total spine MRIs requested by the emergency department during a 28-month period were evaluated for major radiologic (cord compression, cauda equina compression, and other significant findings) and major clinical outcomes (hospital admission during the visit followed by an operation, radiation therapy, or intravenous antibiotics or steroids). Associations between a high-risk clinical profile (cancer, infection, coagulopathy) and/or the presence of neurologic findings and outcomes were assessed., Results: After we excluded trauma or nondiagnostic studies, 321/2047 (15.7%) MRIs ordered during study period were total spine MR imaging; 117/321 (36.4%) had major radiologic and 60/321 (18.6%) had major clinical outcomes (34/60 in <24 hours); and 58/117(49.6%) with major radiologic outcome were treated compared with 2/205 (1.0%) without (OR = 99, P  < .001). The presence of both a high-risk clinical profile and neurologic findings concurrently in a patient (142/321) increased the likelihood of major clinical outcomes during the same visit (OR = 3.1, P  < .001) and in <24-hours (OR = 2.6, P  = .01) compared with those with either a high-risk clinical profile or neurologic findings alone (179/321)., Conclusions: Total spine MR imaging ordered by our emergency department has a high radiologic and significant clinical yield. When a high-risk clinical profile and neurologic findings are both present in a patient, they should be prioritized for emergent total spine MR imaging, given the increased likelihood of clinical impact., (© 2020 by American Journal of Neuroradiology.)

Background and Purpose: Fast spin-echo short τ inversion recovery sequences have been very useful for MR imaging-guided deep brain stimulation procedures in Parkinson disease. However, high-quality fast spin-echo imaging deposits significant heat, exceeding FDA-approved limits when patients already have undergone deep brain stimulation and need a second one or a routine brain MR imaging for neurologic indications. We have developed a STIR sequence with an ultra-low specific absorption rate that meets hardware limitations and produces adequate tissue contrast in cortical and subcortical brain tissues for deep brain stimulation recipients., Materials and Methods: Thirteen patients with medically refractory Parkinson disease who qualified for deep brain stimulation were imaged at 1.5T with a fast spin-echo short τ inversion recovery sequence modified to meet conditional MR imaging hardware and specific absorption rate restrictions. Tissue contrast-to-noise ratios and implant localization were objectively and subjectively compared by 2 neuroradiologists, and image quality for surgical planning was assessed by a neurosurgeon for high and low specific absorption rate images., Results: The mean contrast-to-noise ratio for cerebral tissues without including the contrast-to-noise ratio for ventricular fluid was 35 and 31 for high and low specific absorption rate images. Subjective ratings for low specific absorption rate tissue contrast in 77% of patients were identical to (and in a few cases higher than) those of high specific absorption rate contrast, while the neurosurgical coordinates for fusing the stereotactic atlas with low specific absorption rate MR imaging were equivalent to those of the high specific absorption rate for 69% of patients., Conclusions: Patients with Parkinson disease who have already had a deep brain stimulation face a risk of neural injury if routine, high specific absorption rate MR imaging is performed. Our modified fast spin-echo short τ inversion recovery sequence conforms to very conservative radiofrequency safety limits, while it maintains high tissue contrast for presurgical planning, postsurgical assessment, and radiologic evaluations with greater confidence for radiofrequency safety., (© 2014 by American Journal of Neuroradiology.)

Background and Purpose: Spinal cord atrophy is a common feature of MS. However, it is unknown which cord levels are most susceptible to atrophy. We performed whole cord imaging to identify the levels most susceptible to atrophy in patients with MS versus controls and also tested for differences among MS clinical phenotypes., Materials and Methods: Thirty-five patients with MS (2 with CIS, 27 with RRMS, 2 with SPMS, and 4 with PPMS phenotypes) and 27 healthy controls underwent whole cord 3T MR imaging. The spinal cord contour was segmented and assigned to bins representing each C1 to T12 vertebral level. Volumes were normalized, and group comparisons were age-adjusted., Results: There was a trend toward decreased spinal cord volume at the upper cervical levels in PPMS/SPMS versus controls. A trend toward increased spinal cord volume throughout the cervical and thoracic cord in RRMS/CIS versus controls reached statistical significance at the T10 vertebral level. A statistically significant decrease was found in spinal cord volume at the upper cervical levels in PPMS/SPMS versus RRMS/CIS., Conclusions: Opposing pathologic factors impact spinal cord volume measures in MS. Patients with PPMS demonstrated a trend toward upper cervical cord atrophy. However patients with RRMS showed a trend toward increased volume at the cervical and thoracic levels, which most likely reflects inflammation or edema-related cord expansion. With the disease causing both expansion and contraction of the cord, the specificity of spinal cord volume measures for neuroprotective therapeutic effect may be limited.

In order to obtain high resolution images of fixed excised rat spinal cords we have developed a technique using a 6-mm bore, two-turn saddle coil, with a usable imaging length of approximately 4 cm. MR imaging is performed on a prototype 31-cm bore, 1.9-T system with a 1.5-mm section thickness and 7.6-mm field of view.

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.

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.

An animal model of acute cerebrovascular thromboembolism was developed to evaluate the feasibility of selective fibrinolysis. In 20 Flemish Giant rabbits, autologous clot was deposited via selected catheterization of the distal end of the common carotid artery. The rates of clot lysis with streptokinase were compared in eight control rabbits and after three different dosage regimens in four rabbits each. Group A received selective infusion of 5000 U/hr; group B received 4000 U/min for 1 hr, 3000 U/min for 2 hr, and 5000 U/hr for 2 hr; and group C was treated similar to group B plus receiving an initial 20,000 U bolus of streptokinase. Lysis was evaluated by serial angiograms obtained hourly for up to 6 hr after the clot was deposited. Five proximal vessels arising from the common carotid artery were chosen for the angiographic grading system. The control group showed beginning lysis after 5-6 hr. Group A appeared to show a slight improvement about 4 hr after clotting. Group B demonstrated an early and greater improvement at 2 hr that appeared to be sustained throughout the experiment. Group C showed no difference compared with the control group. The Dunnet t procedure and the Kruskel-Wallis nonparametric analysis of variance were used for comparing the angiograms of the treatment groups with those of the control group at corresponding study times. The results of these animal experiments do not indicate a definite benefit of streptokinase treatment alone over no treatment. Further controlled studies are needed before the value of streptokinase in routine clinical practice can be determined.

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.

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.

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.

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.