Artifact simulating subarachnoid and intraventricular hemorrhage on single-shot, fast spin-echo fluid-attenuated inversion recovery images caused by head movement: A trap for the unwary

BACKGROUND AND PURPOSE

Single-shot, fast spin-echo, fluid attenuated inversion recovery (SS-FSE-FLAIR) images are frequently used to detect disease in the brain and subarachnoid space in confused or uncooperative patients who may move during the examination. In some of these patients, high signal intensity areas are seen on good-quality images in the subarachnoid space and ventricular system in locations not associated with high CSF flow. These artifacts may simulate hemorrhage or leptomeningeal disease. The purpose of this article was to determine the cause of these artifacts, describe ways to recognize them, and find methods to reduce or eliminate them.

METHODS

Healthy volunteers were studied on 6 occasions with conventional multisection FSE-FLAIR images and SS-FSE-FLAIR images while at rest and while nodding and rotating their heads at different speeds. In addition, SS-FSE-FLAIR images with different section widths of the initial inverting pulse and a non-section-selective initial inversion pulse were performed with the subjects moving their heads in the same way. The scans of 30 successive patients with acute neurologic syndromes who had been studied with SS-FSE-FLAIR sequences were reviewed for evidence of high signal intensity in the CSF in regions not associated with high CSF flow.

RESULTS

Each of the volunteers showed areas of increased signal intensity in CSF at sites apart from those associated with rapid pulsatile CSF flow on SS-FSE-FLAIR images acquired during head motion. The images were otherwise virtually free of motion artifact. The use of a wider initial inversion pulse section and a non-section-selected initial inversion pulse reduced the extent of these artifacts. Nineteen of the 30 patients showed areas of high signal intensity in the CSF in regions not associated with highly pulsatile CSF flow. Six of these patients had negative lumbar punctures for blood and xanthochromia and normal CSF protein levels.

CONCLUSION

High signal intensity artifacts may be seen in CSF as a result of head movement on otherwise artifact-free images when imaging uncooperative patients with SS-FSE-FLAIR sequences. These artifacts have a different mechanism and distribution from those caused by CSF pulsation and may simulate subarachnoid and intraventricular hemorrhage. Artifact recognition is aided by signs of patient motion during the examination. The artifacts can be reduced by use of increased section width and non-section-selective initial inversion pulses. Recognition of these artifacts is important, because the circumstances in which the SS-FSE-FLAIR sequence is used and the particular properties of the sequence may conspire to produce a trap for the unwary.

Imaging of the Pineal Region and Spine: Self-Assessment Module

The educational objectives for this self-assessment module on imaging of the pineal region and spine are for the participant to exercise, self-assess, and improve his or her understanding of the evaluation of patients with brain tumors, particularly solid masses of the pineal region; gain familiarity with the clinical entity of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and its radiologic appearance; and gain familiarity with the clinical entity of spinal dural arteriovenous fistula (DAVF) and its radiologic appearance.

ADC measurements in various patterns of multiple sclerosis lesions

OBJECTIVE

To determine the difference of mean apparent diffusion coefficients (ADC) among different patterns of focal multiple sclerosis (MS) lesions, to compare mean lesion ADC between 2 clinical subgroups and to correlate mean lesion ADC with disability.

MATERIAL AND METHOD

Thirty seven patients (26 with relapsing-remitting multiple sclerosis (MS) and 11 with secondary-progressive MS) underwent both conventional and diffusion-weighted MR imaging of the brain. After creating ADC maps, region identification was done by using b = 0 images and T2-weighted images. ADC values were measured for MS lesions and (NAWM).

RESULTS

A total of 288 lesions were identified on the images. The mean ADC for the lesions was significantly higher than that of NAWM Hypointense T1 lesions (n = 221) had a significantly higher mean ADC than isointense T1 lesions (n = 67) in both nonenhancing lesions (n = 250) and enhancing lesions (n = 38). The enhanced rim of ring-enhancing lesions (n = 18) had lower ADC than the central nonenhanced portions. Confluent lesions (n = 62) had a substantially higher mean ADC than discrete lesion (n = 226). Mean lesion ADC of secondary progressive MS was significantly higher than relapsing remitting MS. No correlation between mean lesion ADC and (EDSS) score was found

CONCLUSION

Quantitative diffusion-weighted imaging is useful to elucidate the heterogeneous pathological substrate of MS in different patterns of MS lesions, to differentiate 2 major clinical subgroups.

MR features of cerebral aspergillosis in an immunocompetent patient: correlation with histology and elemental analysis

We report an unusual case of cerebral aspergillosis in a young immunocompetent patient who also had dissemination to other end organs. The patient presented with a large mass in the left cerebral hemisphere. Elemental analysis of biopsy specimens revealed elevated levels of iron, magnesium, zinc, calcium, chromium, and nickel that correlated with a peripheral rim of hypointensity on T2-weighted images.

Intracranial meningeal disease: comparison of contrast-enhanced MR imaging with fluid-attenuated inversion recovery and fat-suppressed T1-weighted sequences

BACKGROUND AND PURPOSE

Contrast-enhanced fluid-attenuated inversion recovery (FLAIR) imaging has been reported to have higher sensitivity for detecting leptomeningeal disease compared with contrast-enhanced T1-weighted MR imaging. The purpose of this study was to compare contrast-enhanced T1-weighted MR images with fat suppression to contrast-enhanced FLAIR images to determine which sequence was superior for depicting meningeal disease.

METHODS

We reviewed MR images of 24 patients (35 studies) with a variety of meningeal diseases. The MR imaging protocol included contrast-enhanced T1-weighted MR images with fat suppression (FS) and contrast-enhanced fluid-attenuated inversion recovery (FLAIR) images that were reviewed by three neuroradiologists and were assigned a rating of positive, equivocal, or negative for abnormal meningeal enhancement. The two sequences were compared side by side to determine which better depicted meningeal disease.

RESULTS

Abnormal meningeal enhancement was positive in 35 contrast-enhanced T1-weighted MR images with FS and in 33 contrast-enhanced FLAIR studies. In the first group, which had the T1-weighted sequence acquired first (21 of 33 studies), contrast-enhanced T1-weighted images with FS showed superior contrast enhancement in 11 studies (52%), inferior contrast enhancement in six studies (29%), and equal contrast enhancement in four studies (19%) compared with the contrast-enhanced FLAIR images. In the second group, which had the FLAIR sequence acquired first (12 of 33), contrast-enhanced T1-weighted images with FS showed superior contrast enhancement in seven studies (58%), inferior contrast enhancement in two studies (17%), and equal contrast enhancement in three studies (25%).

CONCLUSION

Contrast-enhanced T1-weighted MR imaging with FS is superior to contrast-enhanced FLAIR imaging in most cases for depicting intracranial meningeal diseases.

Axial load—dependent cervical spinal alterations during simulated upright posture: a comparison of healthy controls and patients with cervical degenerative disease

Object. The objectives of this study were to simulate the upright loading condition in the cervical spine by applying a new compression device during supine posture and to assess intervertebral angles and cross-sectional areas of the spinal cord and dural tube before and during axial compression.

Methods. A magnetic resonance (MR) imaging-compatible device was developed to create axial compression with the patient in the supine position. Lateral radiographs were obtained in upright and supine positions with an axial load of 0% (supine) and by applying a cervical compression device at 7, 10, and 13% of body weight (BW) in 18 control individuals and seven symptomatic patients with cervical degenerative disc disease (DDD). Additionally, cervical MR images acquired in 17 controls and 12 patients were compared before and during an axial load of 8.4% BW in terms of anteroposterior diameter and cross-sectional area of the dural sac.

The supine intervertebral angles with loads of 0, 7, 10, and 13% of the individuals' BW relative to upright posture were −8.1 ± 1.3, −2.3 ± 1.4, 1.3 ± 1.9, and 2.8 ± 2°, respectively. Subsequent axial force was interpolated as 8.9% of BW to simulate upright cervical spine alignment. Under an axial loading similar to that created by the upright posture, the dural sac narrowed at the C5–6 interspace in asymptomatic individuals and at the C6–7 interspace in patients with cervical DDD.

Conclusions. This cervical compression device may be a useful tool to simulate upright cervical spinal alignment. The results of this study help in understanding the pathophysiology of symptoms related to cervical degenerative disorders in upright posture.

Cerebello-Pontine angle (CPA) lymphoma with perineural extension into the middle fossa: case report

BACKGROUND

Tumors of the cerebello-pontine angle are most commonly schwannoma and meningioma. Primary central nervous system (CNS) lymphoma usually presents deep within the cerebral hemispheres, occasionally is found in the cerebellum, and rarely occurs in the cerebello-pontine angle. We report a rare case of primary CNS lymphoma involving the right cerebello-pontine angle and the middle cranial fossa mimicking a tentorial meningioma.

METHODS

A 21-year-old woman presented with right sided hearing loss and a facial droop. Computed tomography (CT) and magnetic resonance imaging (MRI) were performed, followed by cerebral angiography to assess vascularity.

RESULTS

Imaging revealed a bilobed mass involving the right cerebello-pontine angle and middle fossa. The labyrinthine segment of the facial nerve canal was enlarged, and some bony erosion was seen along the petrous bone anteriorly. The mass was hypointense on both T1 and T2-weighted MRI and exhibited heterogenous enhancement. It was distinctly hypovascular on angiography. At surgery, a B-cell lymphoblastic lymphona was found that infiltrated along the 7(th) and 8(th) nerve complexes into the internal auditory canal.

CONCLUSION

Imaging and surgery disclosed a cerebello-pontine lymphoma with perineural extension along the 7(th) nerve to reach the middle cranial fossa. Because of the unusual imaging characteristics of this tumor, as well as special considerations with respect to treatment, preoperative consideration of this entity is important in planning direct surgical biopsy rather than an extensive resection.

Effects of age on tissues and regions of the cerebrum and cerebellum

Normal volunteers, aged 30 to 99 years, were studied with MRI. Age was related to estimated volumes of: gray matter, white matter, and CSF of the cerebrum and cerebellum; gray matter, white matter, white matter abnormality, and CSF within each cerebral lobe; and gray matter of eight subcortical structures. The results were: 1) Age-related losses in the hippocampus were significantly accelerated relative to gray matter losses elsewhere in the brain. 2) Among the cerebral lobes, the frontal lobes were disproportionately affected by cortical volume loss and increased white matter abnormality. 3) Loss of cerebral and cerebellar white matter occurred later than, but was ultimately greater than, loss of gray matter. It is estimated that between the ages of 30 and 90 volume loss averages 14% in the cerebral cortex, 35% in the hippocampus, and 26% in the cerebral white matter. Separate analyses were conducted in which genetic risk associated with the Apolipoprotein E epsilon4 allele was either overrepresented or underrepresented among elderly participants. Accelerated loss of hippocampal volume was observed with both analyses and thus does not appear to be due to the presence of at-risk subjects. MR signal alterations in the tissues of older individuals pose challenges to the validity of current methods of tissue segmentation, and should be considered in the interpretation of the results.

Neuroimaging of AIDS. I. Viral infections

Viral infections of the brain and spinal cord cause significant morbidity and mortality in patients afflicted with AIDS. Debate continues over the specific mechanisms and pathways of how HIV-1 manifests itself in the brain and spinal cord. Attempts to predict which seropositive patients develop neurocognitive deficits caused by HIV-1 and how soon these deficits will occur in the course of disease have had limited success. The neuropathologic changes of HIV-1 must be distinguished from other viral infections, such as cytomegalovirus, JC papovavirus (progressive multifocal leukoencephalopathy), herpes simplex virus type 1, and varicella-zoster virus. In addition to cerebral spinal fluid sampling and serum testing, some specific features are seen with contrast-enhanced CT, MR imaging, proton MR spectroscopy, SPECT, and PET.

Quantitative analysis of signal intensities and contrast after fat suppression in contrast-enhanced magnetic resonance imaging of the spine

RATIONALE AND OBJECTIVES

We studied the effect of fat suppression on signal intensity and contrast on contrast-enhanced magnetic resonance (MR) images of the spine.

METHODS

Contrast-enhanced T1-weighted MR images were obtained at identical levels with and without fat suppression. Signal intensity and contrast were measured in regions of interest in fat, muscle, spinal bone marrow, and enhancing lesions. The differences in the mean values of these signal intensities and the mean values of contrast between enhanced tissues and bone marrow, fat, and muscle were subjected to statistical validation.

RESULTS

Mean signal intensity of the extraspinal fat and bone marrow was lower after fat suppression (70% and 46% reduction, p < .001 and p < .05, respectively), whereas the signal intensity of muscle showed no significant change (p < .9). Enhancing spinal lesions showed a difference in mean signal intensity after fat suppression (22% increase, p < .2). Contrast between enhanced lesions and bone marrow and fat was higher after fat suppression (78% increase, p < .01 for bone marrow; 8% increase, p < .001 for fat).

CONCLUSION

In contrast-enhanced MR examinations of the spine, the use of fat suppression may increase the signal intensity of the enhancing lesion by expanding the dynamic gray scale of the image and increases the contrast between the lesion and adjacent bone marrow and suppressed fat.

Normal computed tomography and magnetic resonance imaging anatomy of the globe, orbit, and visual pathways

The presence of bone and fat in the orbit provide high contrast with normal structures on both CT and MR images. In patients with visual deficits or oculomotor paralysis, imaging studies should include the intracranial cavity to evaluate the visual pathways back to the occipital cortex and the cranial nerves within the cavernous sinuses and brainstem. Magnetic resonance images display the intracranial anatomy in exquisite detail. Fat-suppressed magnetic resonance sequences should be used in conjunction with gadolinium enhancement.

MR imaging of spinal nerve roots: techniques, enhancement patterns, and imaging findings

The purpose of this report was to review the MR techniques, contrast enhancement patterns, and MR imaging findings for the spinal nerve roots. The phenomenon of contrast enhancement of the nerve roots and its relationship to disk disease and failed-back-surgery syndrome are discussed. The MR imaging findings for various inflammatory and neoplastic disorders affecting the spinal nerve roots are described and illustrated.

Fat-suppression contrast-enhanced MRI in the failed back surgery syndrome: a prospective study

We examined 25 patients with recurrent pain after lumbar disk surgery with MRI to evaluate the usefulness of gadolinium (Gd)-enhanced fat-suppression (FS) imaging in patients with failed back surgery. Pulse sequences included T1-weighted (T1W) images, Gd-enhanced T1W images, and Gd-enhanced T1W images with FS. The addition of FS to Gd-enhanced T1W images improved visualization of enhancing scar in all cases, helped distinguish scar from recurrent herniated disk, and showed more clearly the relationship of scar to the nerve roots and thecal sac. The images also demonstrated enhancement of the facet joints and theca in 23 and 11 cases, respectively. Intradural nerve roots were more conspicuous with FS in 21 cases. The combination of unenhanced and Gd-enhanced T1W images with FS is recommended for routine examination of the postoperative back.

MR detection of white matter disease of the brain in patients with HIV infection: fast spin-echo vs conventional spin-echo pulse sequences

OBJECTIVE

Although fast spin-echo images and slower spin-echo images have similar contrast characteristics, the two techniques have not yet been shown to be equivalent in all aspects of brain imaging. To determine if the two sequences are equivalent, we compared detection of white matter lesions, image quality, and artifact degradation on fast spin-echo and spin-echo proton density-weighted and T2-weighted MR images of the brain in prospectively selected patients who were seropositive for HIV.

SUBJECTS AND METHODS

Fast spin-echo and spin-echo MR images of the brain were obtained in 153 consecutive subjects. The images were reviewed independently by three experienced neuroradiologists. The size, number, and location of white matter lesions were compared for the two techniques. Image quality, motion artifact, CSF flow artifact, and gray-white matter differentiation were graded on a five-point scale.

RESULTS

No statistical difference was found in gray-white matter differentiation. Overall image quality, CSF flow artifacts, and motion artifacts were slightly worse on the fast spin-echo images (p < .05). Although some variability existed in the detection of lesions less than 5 mm in diameter, the differences was small, and all larger lesions were detected by both techniques. Agreement between fast spin-echo and conventional spin-echo techniques was nearly exact with respect to characterizing findings in brain as either normal or abnormal.

CONCLUSIONS

Fast spin-echo and spin-echo MR of the brain produce images of similar quality and show white matter lesions equally well. These results support the replacement of slower, conventional spin-echo pulse sequences with faster fast spin-echo sequences.

MR imaging of the spine: recent advances in pulse sequences and special techniques

A number of new techniques have been developed to enhance MR imaging of the spine. Fat-suppression techniques used in conjunction with gadolinium-based contrast material improve visualization of enhancing inflammatory and neoplastic diseases. Fast spin-echo (FSE) sequences can be used to decrease imaging times, to increase resolution, or to improve signal-to-noise ratios on T2-weighted images. In general, FSE images provide a better myelographic effect with reduced magnetic susceptibility compared with gradient-recalled echo (GRE) techniques. With volume GRE sequences, thin contiguous sections can be obtained, and images can be reformatted into multiple planes from a single data set. High-contrast imaging can be accomplished by using three-dimensional (3D) turbo-fast low-angle shot (FLASH) or magnetization prepared rapid acquisition gradient-echo (MP RAGE) techniques with gadolinium contrast enhancement. Finally, CSF flow dynamics within the subarachnoid space and within cystic lesions can be elucidated with phase-contrast techniques. Judicious selection of these methods and other innovative MR techniques is necessary to maximize the potential of MR in diagnosis of spinal disease.

Blood flow dynamics in the vertebrobasilar system: correlation of a transparent elastic model and MR angiography

PURPOSE

To describe the flow patterns in a model of the vertebrobasilar artery and use these observations to explain the appearance of the flow on the MR images.

METHODS

We created an anatomically precise, transparent elastic model of the human vertebrobasilar artery containing a basilar tip aneurysm and perfused the model with non-Newtonian fluid which has similar rheologic properties to blood. Flow patterns in the vessels were directly observed. MR angiogram images were obtained with commercially available two-dimensional time-of-flight, three-dimensional time-of-flight, and 3-D phase-contrast MR angiographic pulse sequences, and they were correlated with the directly seen flow patterns. Quantitative flow velocity measurements were performed with 2-D cine phase-contrast MR angiography and correlated with the flow measured with an electromagnetic flow meter.

RESULTS

Visualization studies showed the dye stream patterns in the vertebrobasilar arteries to be extremely complex and variable. During the MR experiments we found that often the same segment of a vessel could appear very different depending on the pulse sequence. In some instances, the model experiments helped to explain the MR appearance of the vessels. Flow profiles measured with 2-D cine phase contrast were found to be consistent with those measured directly with an electromagnetic flow meter.

CONCLUSION

Clear elastic models can be used to duplicate the flow in human cranial vessels and thus provide a unique means to observe these flow patterns directly. The flow patterns helped to explain the variation in appearance of the vessels and the artifacts with different MR angiography pulse sequences. The artifacts depend on both the geometry of the vessel and the flow pattern within it. Two-dimensional cine phase-contrast MR provides temporal flow field information that is directly related to physiological information about flow volumes and velocity patterns.

Evaluation of fat suppression in contrast-enhanced MR of neoplastic and inflammatory spine disease

PURPOSE

To determine the benefit of fat suppression in conjunction with gadolinium enhancement for evaluating neoplastic and inflammatory diseases of the spine.

METHODS

Contrast-enhanced T1-weighted images were compared with the corresponding contrast-enhanced T1-weighted images with fat suppression in 14 patients with various neoplastic and inflammatory spine diseases.

RESULTS

Contrast-enhanced T1-weighted images with fat suppression showed enhancing lesions in all cases of vertebral disease (five cases), but in one case some metastases did not enhance. Paravertebral (nine lesions), epidural (seven lesions), and intradural-extramedullary (six lesions) were delineated better with contrast-enhanced fat suppression. In the 14 cases (29 lesions), nine lesions were seen only on contrast-enhanced images with fat suppression. Integrity of the vertebral end plates was assessed more accurately on fat-suppressed images.

CONCLUSION

Although noncontrast T1-weighted images are sufficient to screen for vertebral disease, contrast-enhanced images with fat suppression may detect additional lesions. Fat suppression should be used in conjunction with gadolinium for evaluating epidural, paravertebral, and intradural-extramedullary spinal lesions.

Extraspinal abnormalities detected on MR images of the spine

Surface-coil MR imaging of the spine is one of the most commonly performed MR imaging procedures. As the spine is the region of interest in these studies, extraspinal abnormalities may be overlooked. Such lesions can be difficult to perceive because they are out of the area of interest or distant from the surface coil. MR studies may be interpreted without other radiographic studies for comparison, as the other studies often have been performed elsewhere. Consequently, it is important for radiologists to be aware of the extraspinal anatomy and the appearances of extraspinal abnormalities. We describe the appearances of some common extraspinal diseases and normal variants detected with surface-coil MR imaging of the spine.

MR of the spine in Guillain-Barré syndrome

MR examination of the spine after injection of gadopentetate dimeglumine showed enhancement of the cauda equina in a case of Guillain-Barré syndrome. These MR observations may help confirm the diagnosis of Guillain-Barré syndrome.

HIV-associated psychosis: a study of 20 cases. San Diego HIV Neurobehavioral Research Center Group

OBJECTIVE

Psychosis is an uncommon but serious complication of infection with HIV. This article presents the results of a study of HIV-infected individuals with psychosis.

METHOD

The authors evaluated 20 HIV-infected men who had noniatrogenic new-onset psychosis without delirium, current substance abuse, or previous psychotic episodes. Clinical, neuropsychological, CSF, magnetic resonance imaging, and neuropathologic assessments were made. A comparison group consisting of 20 nonpsychotic HIV-infected men matched to the psychotic subjects with respect to age, race, years of education, and Centers for Disease Control HIV stage was also evaluated.

RESULTS

The psychotic patients differed from the nonpsychotic comparison subjects in having significantly higher rates of past stimulant and sedative/hypnotic abuse or dependence and, at follow-up, a significantly higher rate of mortality. They also showed a trend toward greater global neuropsychological impairment.

CONCLUSIONS

New-onset psychosis may be, at least in part, a manifestation of an HIV-associated encephalopathy.

Cine magnetic resonance imaging and color Doppler flow mapping displays of flow velocity, spatial acceleration, and jet formation: a comparative in vitro study

To study the effects of flow acceleration and high-velocity jets on the display characteristics of cine magnetic resonance imaging compared with color Doppler flow mapping, a custom-designed in vitro flow model was developed. This model consisted of a funnel segment tapering to an orifice (0.78 cm2) that leads into a confined receiving chamber with a second, discrete orifice (0.78 cm2) at its distal end. Cine magnetic resonance images obtained at varying flow rates (1.5 to 27.2 L/min) demonstrated loss of signal intensity throughout the tapering zone of spatial acceleration and a small zone of more marked signal loss immediately proximal to the second orifice (always < 50% of the signal intensity within the tapering funnel zone) associated with more rapid spatial acceleration. A formed jet was imaged distal to the first orifice, and the turbulence area surrounding the laminar central jet core correlated well with flow rate (r = 0.98), as did the distance from the orifice to the subsequent onset of flow relaminarization (r = 0.96). A turbulent spray area was always seen distal to the second, discrete orifice. Comparative observations with color Doppler flow mapping and continuous wave Doppler demonstrated that signal intensity on cine magnetic resonance imaging is reduced by both spatial acceleration, and the high-velocity and turbulent jets associated with obstructive and regurgitant lesions. In vitro evaluation of cine magnetic resonance imaging allows comparative observations to be made about the flow characteristics of cine magnetic resonance imaging and color Doppler flow mapping and provides a more rational basis for the interpretation of cine magnetic resonance imaging in the clinical setting.