Contrast-enhanced MR imaging of brain lesions: a large-scale intraindividual crossover comparison of gadobenate dimeglumine versus gadodiamide.

BACKGROUND AND PURPOSE: The higher relaxivity of gadobenate dimeglumine compared with gadodiamide is potentially advantageous for contrast-enhanced brain MR imaging. This study intraindividually compared 0.1-mmol/kg doses of these agents for qualitative and quantitative lesion enhancement. MATERIALS AND METHODS: Adult patients with suggested or known brain lesions underwent 2 identical MR imaging examinations at 1.5T, one with gadobenate dimeglumine and the other with gadodiamide. The agents were administered in randomized order separated by 3-14 days. Imaging sequences and postinjection acquisition timing were identical for the 2 examinations. Three blinded readers evaluated images qualitatively for diagnostic information (lesion extent, delineation, morphology, enhancement, and global preference) and quantitatively for contrast-to-noise ratio (CNR). RESULTS: One hundred thirteen of 138 enrolled patients successfully underwent both examinations. Final diagnoses were intra-axial tumor, metastasis, extra-axial tumor, or other (47, 27, 18, and 21 subjects, respectively). Readers 1, 2, and 3 demonstrated global preference for gadobenate dimeglumine in 63 (55.8%), 77 (68.1%), and 73 (64.6%) patients, respectively, compared with 3, 2, and 3 patients for gadodiamide (P < .0001, all readers). Highly significant (P < .0001, all readers) preference for gadobenate dimeglumine was demonstrated for all qualitative end points and for CNR (increases of 23.3%-34.7% and 42.4%-48.9% [spin-echo and gradient-refocused echo sequences, respectively] for gadobenate dimeglumine compared with gadodiamide). Inter-reader agreement was good for all evaluations (kappa = 0.47-0.69). Significant preference for gadobenate dimeglumine was demonstrated for all lesion subgroup analyses. CONCLUSION: Significantly greater diagnostic information and lesion enhancement are achieved on brain MR imaging with 0.1-mmol/kg gadobenate dimeglumine compared with gadodiamide at an equivalent dose.

Quantitative analysis of the effects of physiologic brain motion on point-resolved spectroscopy.

BACKGROUND AND PURPOSE: Although single-voxel proton MR spectroscopy is a noninvasive method that enables measurement of brain metabolite concentrations, it has been shown that physiologic brain motion causes inaccuracies in measurement of metabolite concentrations and increases the overall SD of the measurements when the stimulated echo acquisition mode (STEAM) is used. We tested the hypothesis that the point-resolved spectroscopy (PRESS) technique is less sensitive to physiologic brain motion than the STEAM technique. METHODS: In 10 healthy subjects, spectra were obtained from a voxel located in the left basal ganglia by using the PRESS sequence with cardiac gating and without water suppression to assess global phase change as a function of physiologic brain motion. This was accomplished by acquiring data at various time delays from the R wave throughout the cardiac cycle. Subsequently, spectra were obtained in 10 healthy subjects by using PRESS both without and with cardiac gating, and with water suppression, to determine whether brain motion resulted in a statistically significant difference in mean and SD of measured metabolite concentration. RESULTS: At various time delays from the R wave throughout the cardiac cycle, no significant global phase difference was noted in water signal intensity. In addition, when PRESS data were obtained both without and with cardiac gating (by using an optimal delay obtained from previously published data by using STEAM), no significant difference was seen in measured metabolite concentrations and SDs. CONCLUSION: The PRESS technique is relatively insensitive to physiologic brain motion.

Contrast-enhanced MR angiography of spinal vessels.

Compared to routine spin-echo images, contrast-enhanced MR angiography provides improved characterization of the spinal vasculature. This technique can help narrow the differential diagnosis and guide further treatment in patients with radiculopathy or myelophathy. The most useful application to date has been in screening for spinal dural fistulae. The fast, three-dimensional method offers the possibility of distinguishing the largest spinal arteries and veins, although additional technical improvements and clinical experience are needed to accomplish this goal.

MR imaging and localized proton spectroscopy of the precentral gyrus in amyotrophic lateral sclerosis.

BACKGROUND AND PURPOSE: In the search for a diagnostic test for amyotrophic lateral sclerosis (ALS), especially upper motor neuron (UMN) involvement, MR imaging and proton spectroscopy techniques have each received attention, but their findings have not been correlated. The purpose of this study was to identify relationships among the results of current techniques, taking into account the severity of clinical UMN disease, so that objective measures of the pathogenesis of ALS may be established. METHODS: Eighteen subjects with clinically diagnosed ALS and 12 healthy volunteers underwent MR imaging of the brain and localized proton MR spectroscopy. Water-suppressed spectra from the left precentral gyrus and from the left cuneus gyrus were analyzed with the LCModel method, yielding concentrations for N-acetyl (NA), total creatine (Cr), choline (Cho), glutamate (Glu), glutamine (Gin), and myo-inositol (Ins) metabolic substrates. Signal intensities of the precentral gyrus on T2-weighted images were assessed qualitatively in a blinded fashion. RESULTS: For the precentral gyrus, mean Cho (1.3 mM) and Ins (3.25 mM) for the ALS group were significantly increased. After adjustment for Cr covariance, mean Glu (5.08 mM) and NA (6.31 mM) were decreased. For the cuneus gyrus, no difference in metabolite concentrations between groups was observed. Trend analysis of the precentral gyrus metabolite concentrations revealed significant increases in Cho and Ins and decreases in NA and Glu with respect to the severity of clinical UMN signs. Metabolic changes were greater in the subset of ALS patients with precentral gyrus signal changes on imaging, and significantly increased Ins was associated with cortical hypointensity on fast spin-echo images. CONCLUSION: Mean metabolite concentrations determined from precentral gyrus spectra reflect clinical and pathologic changes that occur in ALS. Imaging findings, while related to the spectral and clinical results, are not specific to ALS.

1H-magnetic resonance spectroscopy in amyotrophic lateral sclerosis.

1H-magnetic resonance spectroscopy (MRS) is potentially a powerful tool for the investigation of the chemicals of the brain in vivo in health and disease. Levels of N-acetyl-aspartate (NAA) in the motor cortex and brainstem of patients with amyotrophic lateral sclerosis (ALS) have been reported to be reduced by up to 68%, and in one report the level of glutamate in the brainstem was increased by 58%. We studied levels of metabolites in the cerebral cortex and brainstem of 20 ALS patients and 14 age-matched controls with a 1.5 Tesla Picker magnet using MRS. We used the same spectra for determining both the area of the metabolite peaks expressed as a ratio of the area of the creatine (Cr) peak, and the absolute concentrations using the Provencher LC model. These produced different results. With the LC model, the NAA content of the motor cortex of ALS patients was reduced by 7.7% (P=0.015), and that of the brainstem was reduced by 21.5% (P=0.035), compared with controls. The degree of reduction of NAA was related to the severity of upper motor neuron abnormalities. No effect of treatment with anti-glutamate agents on NAA concentration could be detected. Concentrations of other metabolites were not affected in ALS. It appears that MRS is a technique that is still in development, and that further refinement is required before it can be used to understand disease mechanisms and investigate treatment in ALS.

Vascular anatomy and disorders of the lumbar spine and spinal cord.

The design and interpretation of MR imaging studies of patients with suspected spinal vascular disease are based on a knowledge of arterial and venous anatomy. This article describes the major intradural vessels and their appearance on spin-echo MR images and gadolinium-enhanced MR angiography. Current gadolinium-enhanced MR techniques primarily detect veins, which may be increased in apparent number, size, or tortuosity in the pathological conditions discussed. These characteristics of abnormal veins have yet to be quantified, and differentiation between normal and abnormal is sometimes difficult. Familiarity with the appearance of normal veins on MR angiography facilitates recognition of abnormal vessels and thus the formulation of a more accurate differential diagnosis in the patient with a conus or cauda equina lesion. In the future, gadolinium-enhanced 3D MR angiography may achieve adequate spatial and temporal resolution to differentiate spinal arteries from spinal veins. This differentiation could further simplify the diagnosis of vascular lesions, depending or the complexity of the vascular pattern observed. Also, the combination of MR angiography and diffusion imaging of the cord may finally provide the information needed for characterization by MR imaging of clinically suspected arterial infarction.

Diagnostic and surgical management of spinal dural arteriovenous fistulas.

OBJECTIVE: A retrospective review was conducted to compare magnetic resonance (MR) and conventional spinal angiographic images and to investigate the outcome of our treatment protocol for patients with spinal dural arteriovenous fistulas (DAVFs). MATERIALS AND METHODS: Nine patients with a diagnosis of DAVF based on clinical myelopathy and preoperative MR imaging (MRI) and MR angiography (MRA) findings were treated at our institution by the senior author (BAG). All nine patients initially presented with progressive myelopathy. Preoperative MRI revealed T2-weighted signal abnormalities in all patients, and MRA was diagnostic in all patients. Each patient underwent a laminectomy and ligation of the arterialized draining vein. Selective spinal angiograms were used to confirm the level of fistula immediately before the surgical procedure was performed and to document complete obliteration after clip ligation of the medullary draining vein. Follow-up MRI and MRA were performed approximately 2 months postoperatively. RESULTS: MRI T2-weighted signal hyperintensity improved after surgery in all nine patients. Postoperatively, progression of motor weakness and gait difficulty was halted and some improvement was observed in all patients. No patient was neurologically normal, however. To date, there has been no clinical or MRA evidence of recurrence in any patient. CONCLUSION: Preoperative MRA and intraoperative spinal x-ray angiography present as an effective combination for diagnosing and intraoperatively confirming DAVF. Both T1-weighted enhancement and T2-weighted signal hyperintensity on MR images improved after the obliteration of the DAVFs and correlated with clinical improvement in all nine patients. MRA provides adequate visualization and localization of spinal DAVFs and may serve as a useful noninvasive tool for diagnosing and following patients with spinal DAVFs in the future.

MR angiography of the spine.

Postcontrast MR angiography complements the standard spinal MR imaging study by improving detection and display of normal and abnormal intradural vessels, primarily veins. Detection of abnormal veins facilitates diagnosis of spinal vascular malformations and vascular tumors. The most useful application has been in screening for spinal dural arteriovenous fistula, in which MR angiography demonstrates the medullary vein into which the fistula drains, thus allowing noninvasive identification of the spinal level of the fistula.

Spine MR angiography.

The use of MR angiography to evaluate spinal vessels is in an early stage of development. Both time-of-flight (3D) and phase-contrast (2D and 3D) techniques have been applied, and for both types of techniques, the vessels are best visualized following intravenous gadolinium administration. The vessels of interest are the millimeter-sized intradural arteries and veins, which are located on the cord surface and travel from the cord to the epidural space. Only the post gadolinium 3D TOF technique has been shown to display normal intradural vessels (thoracolumbar region), principally veins. Both TOF and PC techniques provide better delineation of enlarged intradural vessels associated with spinal vascular malformations than standard MR imaging alone. PC techniques are much less sensitive in detecting the arterial supply to dural arteriovenous fistula than intramedullary arteriovenous malformation. The TOF technique can predict the foraminal level of a dural fistula when an enlarged medullary vein, resulting from retrograde drainage, is present. MR angiography, in conjunction with MR imaging, is now suggested for screening of suspected spinal vascular malformation. Other applications such as vascular tumors and arterial or venous occlusive disease are under investigation.

Radiation-induced brachial plexopathy: MR and clinical findings.

A 54-year-old man had a slowly progressive bilateral brachial plexopathy 17 months after surgery and radiation therapy for a stage IV supraglottic carcinoma. MR imaging at presentation showed a symmetric pattern of parascalene and interscalene hyperintense signal on T2-weighted images and after contrast enhancement. Although hyperintense signal has been more often associated with recurrent tumor than with delayed radiation injury or fibrosis, the location and pattern of the signal abnormalities suggested a diagnosis of radiation-induced plexopathy. This diagnosis was confirmed by the relative stability of the neurologic and MR findings 30 months after treatment.

Lyme neuroborreliosis masquerading as a brainstem tumor in a 15-year-old.

A 15-year-old boy had onset of unilateral facial weakness. A few days later, he experienced mild vertigo, double vision, and headache. Examination confirmed a peripheral right seventh nerve weakness in addition to an internuclear ophthalmoplegia. The neurologic features suggested a pontine glioma. A T2-weighted MRI scan revealed demyelinating lesions in the pons and in several areas of the cerebrum, including the periventricular region. Subsequent history revealed that he had been diagnosed with Lyme arthritis 7 years earlier while living in Connecticut. The radiographic studies favored a diagnosis of multiple sclerosis. However, studies of blood and cerebrospinal fluid established a diagnosis of Lyme neuroborreliosis.

MR angiography of normal intradural vessels of the thoracolumbar spine.

PURPOSE: To identify and describe the normal intradural vessels detected on MR angiograms of the thoracolumbar spine. METHODS: Six adult subjects who had clinical evidence of myelopathy, yet normal findings at spinal digital subtraction angiography (DSA), were also studied without and with contrast-enhanced MR imaging and three-dimensional time-of-flight, single-slab MR angiography. Sagittal and coronal subvolume (targeted) maximum intensity projection images were compared with arterial and venous phase DSA images. Angiographic images were then compared with postmortem, formalin-fixed cord specimens. RESULTS: Recognizable intradural vessels were detected only on contrast-enhanced MR angiograms. These vessels corresponded to the posterior and/or anterior median (midline) veins and the great medullary veins. The median veins had variable but mild tortuosity. The medullary veins, which extended from the median veins and coronal venous plexus on the cord surface to the epidural venous plexus, were relatively straight and usually located at T-12 or L-1. The anterior spinal artery could partially contribute to the anterior midline vascular signal. CONCLUSION: The intradural vessels identified on contrast-enhanced MR angiograms are primarily veins, and these are usually the largest vessels on or near the cord surface. The limited number and minimal tortuosity of these veins may serve as a baseline for the examination of patients with clinically suspected arteriovenous malformation or fistula.

Spinal dural arteriovenous fistulas: evaluation with MR angiography.

PURPOSE: To show that postgadolinium three-dimensional time-of-flight MR angiography shows abnormal intradural vessels associated with spinal dural arteriovenous fistula better than routine MR imaging and provides screening information useful for subsequent diagnostic conventional angiography and/or posttreatment evaluation. METHODS: Precontrast and postcontrast MR imaging and MR angiograms, as well as subsequent digital subtraction angiograms, were obtained for eight patients with dural arteriovenous fistulas, diagnosed with digital subtraction angiography and verified with surgery. In four patients, MR studies also were obtained after surgery. RESULTS: All patients had cord hyperintensity of T2-weighted images and postgadolinium enhancement on T1-weighted images. Five had vessellike signal abnormalities in the subarachnoid space on MR. Abnormal intradural vessels were detected in all eight patients with MR angiography. Comparison with digital subtraction angiography revealed these vessels to be primarily enlarged veins of the coronal venous plexus on the cord surface. In six patients, the medullary vein draining the fistula was demonstrated, indicating the level of the fistula, later identified by digital subtraction angiography. After surgical obliteration of the fistula, the draining medullary vein and most or all of the abnormal coronal veins were no longer demonstrated, with decrease or resolution of cord hyperintensity on T2-weighted images. CONCLUSION: Postgadolinium, spinal MR angiography in cases of suspected dural arteriovenous fistula provides information about intradural veins that supplements the diagnostic value of the MR imaging results, facilitates the subsequent digital subtraction angiography study, and, in treated cases, reflects the success of surgery and/or embolization.

Imaging of the postoperative neck with emphasis on surgical flaps and their complications.

Radiologists are playing an increasingly important role in the management of patients with head and neck cancer. Imaging is often essential in preoperative planning. It is therefore imperative for the radiologist to be familiar with the wide variety of surgical procedures used as well as the normal CT and MR imaging appearance after such procedures. In addition, familiarity with the appearance of tumor recurrence and postoperative complications is essential. This pictorial essay illustrates the appearance of the normal and abnormal postoperative neck on CT scans and MR images, with an emphasis on reconstructive flaps. Postoperative complications evident on imaging studies are depicted, as is the appearance of tumor recurrence. One lymph node classification system is briefly reviewed as a basis for discussion of neck dissection and other surgical procedures.