Elevated lactate and alkalosis in chronic human brain infarction observed by 1H and 31P MR spectroscopic imaging.

The goal of this study was to investigate lactate and pH distributions in subacutely and chronically infarcted human brains. Magnetic resonance spectroscopic imaging (MRSI) was used to map spatial distributions of 1H and 31P metabolites in 11 nonhemorrhagic subacute to chronic cerebral infarction patients and 11 controls. All six infarcts containing lactate were alkalotic (pHi = 7.20 +/- 0.04 vs. 7.05 +/- 0.01 contralateral, p less than 0.01). This finding of elevated lactate and alkalosis in chronic infarctions does not support the presence of chronic ischemia; however, it is consistent with the presence of phagocytic cells, gliosis, altered buffering mechanisms, and/or luxury perfusion. Total 1H and 31P metabolites were markedly reduced (about 50% on average) in subacute and chronic brain infarctions (p less than 0.01), and N-acetyl aspartate (NAA) was reduced more (approximately 75%) than other metabolites (p less than 0.01). Because NAA is localized in neurons, selective NAA reduction is consistent with pathological findings of a greater loss of neurons than glial cells in chronic infarctions.

Contrast-enhanced magnetic resonance angiography of cerebral arteries. A review.

The loss of blood vessel visibility due to the signal saturation of slow flow can be partially overcome by the T1 reduction that occurs with the use of contrast agents such as Gd-DTPA during magnetic resonance angiography (MRA) studies. Dynamic-imaging techniques that have been applied successfully in abdominal imaging may also be useful for intracranial applications. However, the time between arterial and venous enhancement is very short during intracranial circulation. This limits the spatial resolution that can be obtained between arterial and venous enhancement. Fortunately, the blood-brain barrier and the relatively long duration of significant decrease in blood T1 has led to the development of very high resolution intracranial MRA techniques. Knowledge of the contrast-agent dilution factors and the ultimate resulting relaxation rates can be used to optimize the imaging parameters to maximize vessel signal relative to the background signal (the signal-difference-to-noise ratio). The additional venous vascular detail in the contrast-enhanced study can be spatially resolved in the 3D image data and determined by incorporating information from both high-resolution precontrast and postcontrast studies. In this article, the history, development and application of contrast agents in MRA are presented.

MR detection of intracranial calcification: a phantom study.

To make a comparative analysis of calcium detection between MR and CT, anhydrous, insoluble calcium carbonate spheres varying in size from 1.5-7.0 mm were embedded in three physiologic tissue phantoms: low-protein gelatin (3 gm%), high-protein gelatin (6 gm%), and heavy mineral oil. The calcium-containing phantoms were scanned by CT and MR, using both T1- and T2-weighted sequences, with a slice thickness varying from 5-7 mm. Partial volume artifacts were determined by abutting phantoms with and without calcium and by varying the slice position to include different proportions of the calcium- and noncalcium-containing phantoms. Contrast-detail curves, expressed as a ratio of contrast to noise, were determined for varying sizes of calcification and degrees of partial voluming. As expected, the CT conspicuity of calcification (positive contrast) markedly surpasses that of MR (negative contrast). The difference was two orders of magnitude. When the calcification filled more than half the slice on MR, the conspicuity depended on the contrast of the matrix material; i.e., increased matrix intensity caused increased conspicuity. However, as the size of the calcification decreased, partial volume effects increased; i.e., increased matrix intensity caused decreased conspicuity. Conspicuity of small calcifications is independent of matrix material, since contrast and partial volume effects balance. We conclude that CT is clearly the method of choice for identifying small foci of calcification.

Effects of magnetic susceptibility artifacts and motion in evaluating the cervical neural foramina on 3DFT gradient-echo MR imaging.

The purpose of this study was to evaluate in vitro the effects of magnetic susceptibility and motion on the estimation of neural foraminal diameter with three-dimensional Fourier transformation (3DFT) gradient-recalled MR imaging as compared with CT. A cervical spine phantom was constructed from desiccated human cervical vertebral bodies embedded in a water-based proteinaceous gel. The phantom was imaged with thin-section 1.5-mm axial CT and 1.5-mm axial 3DFT gradient-recalled MR using a constant TR (35 msec) and flip angle (5 degrees), while the TE was varied from 11 to 22 msec. During imaging, the phantom either was kept stationary or underwent subtle, intermittent motion. Compared with CT, MR consistently underestimated the diameters of the neural foramina, leading to overestimation of neural foraminal stenosis. The degree of over-estimation varied directly with increasing TE values, from 8% (TE = 11 msec) to 27% (TE = 22 msec). Motion artifacts also increased foraminal overestimation and mimicked osseous hypertrophy. The effect of image degradation due to motion was noted to increase with longer TE values. Image degradation caused by magnetic susceptibility and motion artifacts can be minimized by using the shortest TE possible. We do not recommend the use of 3DFT gradient-recalled MR imaging for the evaluation of cervical radiculopathy if patient motion is anticipated.

Three-dimensional time-of-flight MR angiography in the evaluation of intracranial aneurysms treated by endovascular balloon occlusion.

The authors share their experience with MRA in the assessment of cerebral aneurysms. Despite its limitations--spatial resolution, insensitivity to slow flow states, subacute thrombus artifacts--they believe the technique shows potential.

Dural sinus occlusion: evaluation with phase-sensitive gradient-echo MR imaging.

The purpose of this study was to evaluate the usefulness of limited-flip-angle, phase-sensitive velocity imaging with gradient-recalled-echo (VIGRE) MR when combined with spin-echo MR in the diagnosis of dural sinus thrombosis. The VIGRE sequence consists of a rapid single-slice acquisition, 50/15/2 (TR/TE/excitations), and 30 degrees flip angle. At each slice position, a total of four images were reconstructed; these consisted of one magnitude image and three images sensitive to proton motion in each orthogonal direction. The flow direction and flow velocity (cm/sec) were obtained from each of the phase images, and results were correlated with data obtained from a phantom experiment. In normal controls, dural sinus velocities ranged from a mean of 9.9 to 14.4 cm/sec for the transverse and superior sagittal sinuses, respectively. Three patients with proved dural sinus occlusion were studied with spin-echo images at 1.5 T. Three-dimensional time-of-flight MR angiography was also performed in one patient. The presence of dural sinus occlusion was determined by the lack of flow void on the spin-echo images, the absence of phase shift on the VIGRE study, and the presence of retrograde flow on the phase image in the sinus proximal to the occluded segment. Time-of-flight angiography overestimated the extent of the thrombosis caused by spin saturation. Follow-up VIGRE studies detected the formation of collateral flow in one patient and recanalization with the establishment of normal antegrade sinus flow in the other. We conclude that phase-sensitive MR imaging is helpful in establishing the diagnosis and extent of dural sinus occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)

The value of MR neurography for evaluating extraspinal neuropathic leg pain: a pictorial essay.

SUMMARY: Fifteen patients with neuropathic leg pain referable to the lumbosacral plexus or sciatic nerve underwent high-resolution MR neurography. Thirteen of the patients also underwent routine MR imaging of the lumbar segments of the spinal cord before undergoing MR neurography. Using phased-array surface coils, we performed MR neurography with T1-weighted spin-echo and fat-saturated T2-weighted fast spin-echo or fast spin-echo inversion recovery sequences, which included coronal, oblique sagittal, and/or axial views. The lumbosacral plexus and/or sciatic nerve were identified using anatomic location, fascicular morphology, and signal intensity as discriminatory criteria. None of the routine MR imaging studies of the lumbar segments of the spinal cord established the cause of the reported symptoms. Conversely, MR neurography showed a causal abnormality accounting for the clinical findings in all 15 cases. Detected anatomic abnormalities included fibrous entrapment, muscular entrapment, vascular compression, posttraumatic injury, ischemic neuropathy, neoplastic infiltration, granulomatous infiltration, neural sheath tumor, postradiation scar tissue, and hypertrophic neuropathy.

Incidental detection of hippocampal sclerosis on MR images: is it significant?

BACKGROUND AND PURPOSE: The prevalence of hippocampal sclerosis in the general nonepileptic patient population is not well described. While reports of its association with partial complex seizures are abundant, its absence in nonafflicted patients is generally presumed but not well documented. To test the hypothesis that hippocampal sclerosis is specific for epilepsy, we reviewed the MR imaging studies of 207 patients referred for hearing loss to determine whether high-resolution MR imaging could detect unsuspected hippocampal sclerosis in nonepileptic patients. METHODS: Our institution screens patients with hearing loss by using high-resolution coronal and axial temporal bone MR imaging that includes the hippocampus within the imaging volume. We retrospectively reviewed 207 studies randomly selected from this database. RESULTS: The hippocampus was normal in 205 patients; in the remaining two patients we identified one or more primary determinants for hippocampal sclerosis. Subsequent retrospective chart review revealed that both patients had had previously diagnosed seizure disorders. CONCLUSION: The imaging determinants of hippocampal sclerosis are not prevalent in nonepileptic patients. Incidental identification of hippocampal sclerosis on MR images is uncommon and significant, and should prompt further clinical investigation to exclude a seizure disorder.

Diffusion-weighted MR imaging of the brain: value of differentiating between extraaxial cysts and epidermoid tumors.

This study demonstrates the use of diffusion-weighted MR imaging in improving the specificity of the diagnosis of extraaxial brain tumors. Three surgically proved lesions (one arachnoid cyst and two epidermoid tumors) and two nonsurgically proved lesions (arachnoid and ependymal cysts) were evaluated with T1- and T2-weighted spin-echo studies followed by intravoxel incoherent motion (IVIM) MR imaging. The IVIM images of the lesions were displayed as an apparent diffusion coefficient (ADC) image obtained at 0.65 G/cm (maximum gradient b value = 100 sec/mm2) and compared with external oil and water phantoms. The ADC of arachnoid cysts was similar to stationary water whereas the ADC of epidermoid tumors was similar to brain parenchyma, indicating the solid nature and the slower diffusion rate of the epidermoid tumors. Cisternal CSF demonstrated uniformly high ADC, primarily because of bulk flow, which enhanced image contrast. Improved delineation of postsurgical changes was also possible. Our preliminary results show that diffusion-weighted MR imaging can be useful in distinguishing between arachnoid cysts and epidermoid tumors.

Three-dimensional gradient-recalled MR imaging as a screening tool for the diagnosis of cervical radiculopathy.

The purpose of the study was to implement and assess a fast-screening, three-dimensional Fourier transformation (3DFT) MR sequence for the cervical spine. This sequence maintains adequate signal-to-noise and image contrast similar to gradient-recalled echo two-dimensional Fourier transformation (2DFT) imaging. Thirty patients with radiculopathy were examined with 3DFT gradient-recalled echo imaging. The data set consisted of 60 contiguous 1.5- to 2.0-mm-thick axial slices with a total coverage of 9 to 12 cm. In 10 patients, comparison was made with 4-mm-thick axial T1-weighted spin-echo 2DFT or gradient-recalled echo 2DFT studies. With the use of a volume acquisition, adequate signal-to-noise and image contrast similar to T2*-weighted gradient-recalled echo 2DFT acquisitions were obtainable. Coverage was improved despite the use of thinner sections without interslice gap. Thin-section 3DFT provided superior detail of acquired foraminal and spinal canal stenosis and disk morphology. Limitations included increased sensitivity to patient motion and "wraparound" artifact in the slice-select direction. Overall, diagnostic confidence was improved with 3DFT owing to the reduction of partial volume artifact. We have adopted this technique as the primary screening method for diagnosing cervical radiculopathy.

Phased-array surface coil MR of the orbits and optic nerves.

PURPOSE: To devise a practical technique for high-resolution evaluation of the anterior optic apparatus using a phased-array surface coil system, and to evaluate this system in patients with suspected optic pathway abnormalities. METHODS: A four-element phased-array coil pair was placed on each side of the head, and signal-to-noise measurements were obtained using a head phantom. Comparison between the phased-array coil, the quadrature coil, and a single-turn 12.7-cm (5-in) surface coil was done. T1 spin-echo and T2 fast spin-echo sequences were obtained in the oblique axial and oblique sagittal planes, to approximate the long axis of the optic nerves and the nonoblique coronal plane. RESULTS: The phantom signal-to-noise measurements at simulated locations of the optic nerve head, optic canal, and optic chiasm revealed an improvement of at least 30% using the phased-array system. Of 24 imaged cases, 9 had trauma, 5 had suspected neoplasms, and 2 had optic neuritis. In 3 patients, an unexpected diagnosis of optic pathway contusion or infarction was made. The remaining 8 patients had various suspected visual pathway lesions. CONCLUSION: Phased-array surface coils allow rapid, thin-section imaging of the entire anterior optic pathway, with improved signal-to-noise ratio. This may improve evaluation of optic pathway lesions over conventional techniques.

Terson syndrome: CT evaluation in 12 patients.

PURPOSE: Terson syndrome may be overlooked in the acute setting and often requires ophthalmologic intervention to prevent long-term visual loss. In this syndrome, vitreous or retinal hemorrhage results from an abrupt rise in intracranial pressure, leading to retinal venous hypertension and intraocular hemorrhage. Our objective was to determine whether imaging findings could be discovered that might facilitate an earlier diagnosis. METHODS: Our inpatient medical record data base for 1991-1996 listed 11 patients with Terson syndrome. The medical records of these 11 patients were reviewed retrospectively and compared with their noncontrast head CT scans and with scans of 10 control subjects. One additional case was discovered prospectively, for a total of 12 patients. Three radiologists unaware of the patients' history evaluated CT scans of the orbits for evidence of intraocular hemorrhage. RESULTS: CT findings in eight patients were suggestive of retinal hemorrhage manifested by a retinal crescent or nodule that was slightly hyperdense relative to the vitreous humor. There was a high degree of concordance between the retrospective and independent reviews. CONCLUSION: Retinal nodularity and crescentic hyperdensities are evident on CT scans in the majority of patients with Terson syndrome. Although findings are subtle and not present in all cases, in the setting of subarachnoid hemorrhage they suggest retinal hemorrhage and warrant detailed fundoscopic evaluation.

Magnetic resonance neurography for cervical radiculopathy: a preliminary report.

Magnetic resonance neurography was used to directly image cervical spinal nerves in patients with clinical and radiographic evidence of cervical radiculopathy. A magnetic resonance imaging phased-array coil system was used to obtain high-resolution coronal T1-weighted spin echo, coronal/axial T2-weighted fast spin echo with fat saturation, and coronal/axial fast short tau inversion recovery weighted images of the cervical spine and spinal nerves. Three patients with neck and upper extremity pain and one asymptomatic volunteer were studied. The T2-weighted and the fast short tau inversion recovery images demonstrated markedly increased signal in the proximal portion of the affected spinal nerves. In two patients, contrast-to-noise measurements of the affected spinal nerves showed a markedly increased intensity compared with that of the noninvolved spinal nerves. Our findings demonstrate that phased-array coils used in conjunction with magnetic resonance neurography sequences can detect signal abnormalities within compressed cervical spinal nerves in patients with corresponding radicular symptoms and findings. This technique may prove to be helpful in evaluating patients with multilevel disc and/or spondylotic disease of the cervical spine.

Magnetic resonance imaging signal changes in denervated muscles after peripheral nerve injury.

The evaluation of peripheral nerve disorders has traditionally relied on a clinical history, physical examination, and electrodiagnostic studies. Recent studies have used magnetic resonance imaging (MRI) to evaluate a variety of both nerve and muscle disorders. In this article, we describe the use of MRI, using short-tau inversion recovery (STIR) sequences, to evaluate muscle signal characteristics in a variety of peripheral nerve disorders. A total of 32 patients were studied, and 12 representative cases are discussed in detail. Increased STIR signal in muscle was seen in cases of severe axonotmetic injuries involving the transection of axons producing severe denervation changes on electromyography. The increased STIR signal in denervated muscles was seen as early as 4 days after the onset of clinical symptoms, which is significantly earlier than changes detected on electromyography. The MRI signal changes were reversible when the recovery of motor function occurred as a result of further muscle innervation. In cases of neurapraxic nerve injuries, characterized by conduction block without axonal loss, the STIR signal in muscle was normal. These findings show that MRI using STIR sequences provides a panoramic visual representation of denervated muscles useful in localizing and grading the severity of peripheral nerve injury secondary to either disease or trauma. MRI using STIR sequences may therefore play an important role in the prediction of clinical outcome and the formulation of appropriate therapy early after peripheral nerve injury.

Intraneural perineurioma of the common peroneal nerve. Case report and review of the literature.

Intraneural perineurioma, or localized hypertrophic mononeuropathy (LHM), is a focal lesion that produces a slowly progressive mononeuropathy in a peripheral nerve. The authors describe the clinical presentation, magnetic resonance (MR) neurography characteristics, and pathological characteristics of a perineurioma involving the peroneal nerve. Although there has been much debate surrounding the cause of this lesion, a literature review supports the argument that this is a neoplastic lesion, best referred to as intraneural perineurioma. Surgical management includes excision to prevent progression of palsy and placement of a nerve graft if clinically indicated. A 28-year-old woman presented with a 2-year history of progressive painless right peroneal nerve palsy. Magnetic resonance neurography revealed a right common peroneal nerve mass. At surgery, the mass was easily excised, leaving significant nerve fascicles intact. Intraoperative biopsy was not performed nor was a nerve graft placed. Pathological investigation demonstrated onion bulb-shaped whorls consistent with the appearance of intraneural perineurioma; immunochemical analysis confirmed the diagnosis. A review of the literature supports the argument that perineurioma, or LHM, is a neoplastic process, making "intraneural perineurioma" the most appropriate name. The authors also demonstrate the utility of MR neurography in the identification isolated nerve tumors and review the surgical management of this lesion.

Application of magnetic resonance neurography in the evaluation of patients with peripheral nerve pathology.

Currently, diagnosis and management of disorders involving nerves are generally undertaken without images of the nerves themselves. The authors evaluated whether direct nerve images obtained using the new technique of magnetic resonance (MR) neurography could be used to make clinically important diagnostic distinctions that cannot be readily accomplished using existing methods. The authors obtained T2-weighted fast spin-echo fat-suppressed (chemical shift selection or inversion recovery) and T1-weighted images with planes parallel or transverse to the long axis of nerves using standard or phased-array coils in healthy volunteers and referred patients in 242 sessions. Longitudinal and cross-sectional fascicular images readily distinguished perineural from intraneural masses, thus predicting both resectability and requirement for intraoperative electrophysiological monitoring. Fascicle pattern and longitudinal anatomy firmly identified nerves and thus improved the safety of image-guided procedures. In severe trauma, MR neurography identified nerve discontinuity at the fascicular level preoperatively, thus verifying the need for surgical repair. Direct images readily demonstrated increased diameter in injured nerves and showed the linear extent and time course of image hyperintensity associated with nerve injury. These findings confirm and precisely localize focal nerve compressions, thus avoiding some exploratory surgery and allowing for smaller targeted exposures when surgery is indicated. Direct nerve imaging can demonstrate nerve continuity, distinguish intraneural from perineural masses, and localize nerve compressions prior to surgical exploration. Magnetic resonance neurography can add clinically useful diagnostic information in many situations in which physical examinations, electrodiagnostic tests, and existing image techniques are inconclusive.

MR sequence parameter optimization: an algorithmic approach.

The MR pulsing sequence is often described by terms such as spatial resolution, signal-to-noise, coverage, acquisition time, and contrast. These might be considered "secondary" parameters because they are not set directly but are instead specified indirectly by setting the "primary" parameters: field of view; projections (phase-encoded or readout); slice thickness and gap; number of excitations; and the sequence parameter times--repetition, echo delay, and inversion. Together, the primary and secondary parameters specify the MR pulsing sequence. Many of these parameters are interrelated such that setting one parameter indirectly affects another. Parameter specification is thus an iterative procedure that involves compromises to achieve an optimum relative to some predefined criteria. In this article, we examine the interrelationships between the primary and secondary parameters that specify the spin-echo pulsing sequence and suggest an algorithmic approach for selecting the best sequence parameters.

Magnetic resonance imaging and computed tomography of cerebral vascular disease.

Magnetic resonance imaging has emerged as the primary modality in detection and characterization of cerebrovascular lesions. New applications of existing spin-echo and gradient-recalled echo techniques are described. Functional imaging techniques ranging from the characterization of macroscopic proton motion (diffusion-weighted MR imaging), rapid imaging of intravascular contrast transit times (perfusion MR imaging), fast-flow mapping (MR angiography), and in vivo metabolic assessment (MR spectroscopy) are discussed. CT scanning remains important as an initial screening examination, in identifying acute hemorrhage, and in demonstrating blood flow.

Elimination of eddy current artifacts in diffusion-weighted echo-planar images: the use of bipolar gradients.

Small gradient fields resulting from incompletely canceled eddy currents can cause geometric distortion in echo-planar images. Although this distortion is negligible in most echoplanar applications, the large gradient pulses used in diffusion-weighted echo-planar imaging can result in significant image distortion. In this report, it is shown that this distortion can be significantly reduced by the application of bipolar gradient waveforms. Both bipolar diffusion-sensitizing gradients and an inverted gradient preparatory pulse were examined for minimizing the eddy currents responsible for these distortions.

Three-dimensional time-of-flight MR angiography in the evaluation of cerebral aneurysms.

We review our preliminary experience with the use of three-dimensional (3D) time-of-flight (TOF) magnetic resonance (MR) angiography (MRA) in the assessment of intra- and extracranial aneurysms. Six patients were examined: Five had intracranial aneurysms and one had a cervical carotid pseudoaneurysm. A 3D rephased gradient recalled echo pulse sequence and maximum intensity projection (MIP) reconstruction algorithm were used. Magnetic resonance angiography, spin echo MR, and conventional angiography were retrospectively reviewed with specific regard to individual vessel visualization, aneurysm depiction, and presence of artifact related to acquisition techniques or MIP reconstruction. All aneurysms were detected on MRA, and anatomical correlation with conventional angiography was excellent. Significant problems included loss of visualization of small vessels, intraluminal signal loss in large vessels, subacute thrombus simulating flow on MIP reconstructions, and limited projections obtainable with MIP techniques. Adequate MRA assessment of aneurysms can be obtained using a combination of T1-weighted spin echo images and 3D TOF MRA. Review of all components of the MRA is required. MRA may be useful in screening asymptomatic patients for intracranial aneurysms as well as in the follow-up of patients treated with balloon occlusion.