Robert J. Sevick

Magnetic resonance imaging at 3.0 Tesla: challenges and advantages in clinical neurological imaging.

MR imaging at very high field (3.0 T) is a significant new clinical tool in the modern neuroradiological armamentarium. In this report, we summarize our 40-month experience in performing clinical neuroradiological examinations at 3.0 T and review the relevant technical issues. We report on these issues and, where appropriate, their solutions. Issues examined include: increased SNR, larger chemical shifts, additional problems associated with installation of these scanners, challenges in designing and obtaining appropriate clinical imaging coils, greater acoustic noise, increased power deposition, changes in relaxation rates and susceptibility effects, and issues surrounding the safety and compatibility of implanted devices. Some of the these technical factors are advantageous (eg, increased signal-to-noise ratio), some are detrimental (eg, installation, coil design and development, acoustic noise, power deposition, device compatibility, and safety), and a few have both benefits and disadvantages (eg, changes in relaxation, chemical shift, and susceptibility). Fortunately solutions have been developed or are currently under development, by us and by others, for nearly all of these challenges. A short series of 1.5 T and 3.0 T patient images are also presented to illustrate the potential diagnostic benefits of scanning at higher field strengths. In summary, by paying appropriate attention to the discussed technical issues, high-quality neuro-imaging of patients is possible at 3.0 T.

The use of magnetic resonance imaging to noninvasively detect genetic signatures in oligodendroglioma.

Background: Some patients with low-grade glioma have extraordinarily long survival times; current, early treatment does not prolong their lives. For this reason, therapies that sometimes have neurologic side effects are often deferred intentionally. Methods: In a study of oligodendrogliomas, we used a quantitative method of MR analysis based on the S-transform to investigate whether codeletion of chromosomes 1p and 19q, a marker of good prognosis, could be predicted accurately by measuring image texture. Results: Differences in texture were seen between tumors with codeletion of chromosomes 1p and 19q and those with intact 1p and 19q alleles on contrast-enhanced T1-weighted and T2-weighted MR images. Quantitative MR texture on T2 images predicted codeletion of chromosomes 1p and 19q with high sensitivity and specificity. Conclusions: This new method of MR image interpretation may have the potential to augment the diagnostic assessment of patients with suspected low-grade glioma.

Spontaneous Thrombosis of an Unruptured Anterior Communicating Artery Aneurysm An Unusual Cause of Ischemic Stroke

BACKGROUND Stroke caused by spontaneous thrombosis of an unruptured intracranial aneurysm is a rare event. CASE DESCRIPTION A 66-year-old woman experienced a transient ischemic attack and cerebral infarctions due to spontaneous thrombosis of an unruptured anterior communicating artery aneurysm. Extension of thrombus into both anterior cerebral arteries and the left middle cerebral artery, resulting in ischemic infarction in all three vascular territories, was diagnosed by CT scanning, MRI, and cerebral angiography and confirmed at autopsy. CONCLUSIONS This case illustrates a rare complication of an unruptured saccular aneurysm with neuroimaging and pathological correlation. Morphological and hemodynamic factors that may have precipitated aneurysm thrombosis are discussed with reference to experimental models.

Calgary experience with West Nile virus neurological syndrome during the late summer of 2003

BACKGROUND Between August 25 and September 25, 2003 seven patients with West Nile virus neurological manifestations were identified through the hospital neurology consultation services in Calgary, Alberta, Canada. Three of the seven patients were treated with interferon alpha-2b (IFN alpha-2b). In this report we document the clinical characteristics of these seven cases. METHODS Clinical and laboratory information was obtained from a retrospective review of patient hospital and clinic charts. Patients were included if they had serological evidence of West Nile virus infection and had clinical evidence of aseptic meningitis, encephalomyelitis, cerebellar syndrome or motor neuronopathy. Three patients received a treatment course of three million units IFN alpha-2b, administered by subcutaneous injection once per day for 14 days. RESULTS Four patients had cerebellar signs without change in consciousness, two had both encephalitis and neuromuscular weakness, and one patient had focal lower motor neuron arm weakness. The mean age was 52 (range 24 - 73). All patients had flu-like illness and fever as presenting symptoms and six had severe headaches. Two patients were immunocompromised prior to infection. Two patients with cerebellar signs (one with opsoclonus-myoclonus) improved spontaneously and exhibited only mild residual deficits on discharge. The other two patients with cerebellar findings developed brainstem involvement, one coinciding with and one subsequent to the cerebellar symptoms. Within one week of treatment with IFN alpha-2b these latter two patients showed marked improvement. One patient with encephalitis and neuromuscular weakness, was treated with IFN alpha-2b and subsequently recovered. INTERPRETATION In this case review of seven patients, multiple neurological symptoms occurred in each patient and the neurological presentation was varied. Four patients had predominant cerebellar findings and one patient had opsoclonus-myoclonus, not previously reported. The marked improvement in three patients who received IFN alpha-2b raises preliminary optimism towards this potential treatment.

MR angiography compared to conventional selective angiography in acute stroke.

BACKGROUND AND PURPOSE Accuracy of intracranial magnetic resonance angiography (MRA) and reliability of interpretation are not well established compared to conventional selective catheter angiography. The purpose of this study was to determine the accuracy of MRA in evaluation of intracranial vessels in acute stroke and transient ischemic attack (TIA) patients METHODS Twenty-nine patients (seven females, 22 males; median age 53) with acute stroke or TIA were enrolled into the study. All patients underwent both MRA using a 3 T clinical magnet and conventional angiography within 48 hours. Median time between MRA and angiography was 263 minutes. Conventional angiography preceded MRA in 15 cases. Fourteen patients received thrombolysis during MRA or angiography. National Institutes of Health Stroke Scale scores were obtained prior to the MR exam. One neuroradiologist rated all conventional angiograms, which were used as gold standard. Five observers, blinded to conventional angiography results and all clinical information except symptom side, rated the MR angiograms. Kappa statistics were used to assess reliability; contingency tables were used to assess accuracy of non-enhanced and enhanced MRA. RESULTS Two hundred and fifty two intracranial vessels were assessed. Agreement between raters was good for both non-enhanced (kappa = 0.50) and gadolinium-enhanced (kappa = 0.46) images. There were a total of 26 vessels occluded by DSA. Overall, the non-enhanced MRA showed sensitivity of 84.2% (95% CI 60.4-96.6) and specificity of 84.6% (95% CI 78.6-89.4). The enhanced MRA showed sensitivity of 69.2 (95% CI 38.6-90.9) and specificity of 73.6 (95% CI 65.5-80.7). CONCLUSIONS Magnetic resonance angiography is a good non-invasive screening tool for assessing intracranial vessel status in acute ischemic stroke. Angiography remains the gold standard for definitive assessment of the intracranial circulation.

A comparison of images generated from diffusion-weighted and diffusion-tensor imaging data in hyper-acute stroke

To compare isotropic (combined diffusion‐weighted image [CMB], apparent diffusion coefficient [ADC], TRACE, exponential ADC [eADC], and isotropically‐weighted diffusion image [isoDWI]) and anisotropic (relative anisotropy [RA], fractional anisotropy [FA], and volume ratio [VR]) diffusion images collected with fast magnetic resonance (MR) diffusion‐weighted (DWI) and diffusion‐tensor (DTI) acquisition strategies (each less than one minute) in hyper‐acute stroke.

Contrast-enhanced MR angiography of the intracranial circulation.

NCE MRA can provide the authors with useful diagnostic information in patients suffering from intracranial vascular disease, often leading to improved or altered treatment decisions. Most centers have used 3D TOF for evaluation of stroke-the most common cerebral vascular disease. Because of slow and disturbed flow, conventional 3D TOF MRA tends to overestimate stenotic lesions and occluded arteries and this can confound neurovascular assessment in stroke patients. Post contrast 3D TOF techniques provide a more robust and more specific method for imaging the intracranial circulation that overcomes the drawbacks of conventional 3D TOF. In the setting of acute ischemic stroke, the authors have found that the combination of conventional and CE 3D TOF MRA improves their overall diagnostic ability. Dynamic and time-resolved CE MRA techniques have evolved rapidly. Time-resolved CE MRA, in particular, is emerging as a useful technique for imaging dynamic vascular pathologies such as AVMs. Unfortunately, time-resolved MRA of the intracranial circulation provides images with low spatial resolution and is currently limited to subsecond frame rate 2D acquisitions, and less than 2 seconds frame rates for 3D acquisitions. Nevertheless, like in other vascular regions, CE MRA represents a milestone for non-invasive intracranial vascular imaging. The continuing development of CE MRA techniques and of new contrast agents will lessen the need for intra-arterial angiography in the future.

Effect ofb value on contrast during diffusion-weighted magnetic resonance imaging assessment of acute ischemic stroke

To examine the effect of varying the diffusion encoding strength (b value) on the contrast (signal difference, ΔS) between damaged and normal tissue during diffusion‐weighted magnetic resonance imaging (DWI) assessment of acute ischemic stroke.

Trigeminal neuropathy: Gd-DTPA enhanced MR imaging.

A review of 17 patients with Gd-DTPA enhancing lesions of the trigeminal nerve (6 patients with benign tumors, 4 with inflammatory disease, 7 with malignant tumors) was conducted to determine if contrast enhanced MR imaging is superior to nonenhanced imaging and to identify imaging characteristics that aid in separating benign and malignant disease. Contrast enhanced imaging appears to be superior to nonenhanced imaging in patients with intrinsic fifth nerve lesions. Malignant lesions are suggested by enlarged, enhancing fifth nerves with irregular margins and benign lesions by minimal or no enlargement with smooth margins. Overlap of imaging findings between benign and malignant disease strongly suggests that follow-up imaging and clinical findings are of utmost importance. Gadolinium-enhanced MR imaging of the fifth nerve is recommended in patients with trigeminal sensory or motor deficits as well as those with atypical trigeminal neuralgia.

Microbleeding on MRI as a Marker for Hemorrhage After Stroke Thrombolysis

To the Editor: We noted with interest the article by Dr Kidwell et al,1 who describe an MRI application that detects microbleeds. Kidwell et al propose that this technique can identify patients who might be at high risk for hemorrhagic complications, if intravenous or intra-arterial thrombolysis is given. We agree that this application merits further study and have recently seen an example of asymptomatic hemorrhage after thrombolysis, in …