Biomedical subjects

M E Moseley

Publications and source records attributed to M E Moseley.

At least 19 recordsLinked to original sources

PubMed2001

Comparison of diffusion, blood oxygenation, and blood volume changes during global ischemia in rats.

Rapid diffusion, blood oxygenation, and blood volume weighted echo planar imaging was used to monitor global cerebral ischemia by cardiac arrest in rats. Serial CBV measurements used intravascular iron oxide contrast media (iron dextran). ADC dropped by 5% within 20 sec of cardiac arrest, then continued to decay slowly until a larger rapid drop after 2 min. After iron oxide injection, the initial 5% drop was not observed. The transverse relaxation rate (R(2), R(*)(2) no iron injection) increased rapidly after cardiac arrest, peaking at about 30 sec, then declining towards baseline. The CBV dropped by about 50% within 20 sec. The initial 5% ADC drop may be a vascular artifact. The rapidity of the CBV-weighted signal drop suggests a flow-mediated contribution to the iron oxide contrast mechanism. Magn Reson Med 45:10-16, 2001.

Animals↗

PubMed2000

Diffusion- and perfusion-weighted magnetic resonance imaging of focal cerebral ischemia and cortical spreading depression under conditions of mild hypothermia.

In a model of experimental stroke, we characterize the effects of mild hypothermia, an effective neuroprotectant, on fluid shifts, cerebral perfusion and spreading depression (SD) using diffusion- (DWI) and perfusion-weighted MRI (PWI). Twenty-two rats underwent 2 h of middle cerebral artery (MCA) occlusion and were either kept normothermic or rendered mildly hypothermic shortly after MCA occlusion for 2 h. DWI images were obtained 0.5, 2 and 24 h after MCA occlusion, and maps of the apparent diffusion coefficient (ADC) were generated. SD-like transient ADC decreases were also detected using DWI in animals subjected to topical KCl application (n=4) and ischemia (n=6). Mild hypothermia significantly inhibited DWI lesion growth early after the onset of ischemia as well as 24 h later, and improved recovery of striatal ADC by 24 h. Mild hypothermia prolonged SD-like ADC transients and further decreased the ADC following KCl application and immediately after MCA occlusion. Cerebral perfusion, however, was not affected by temperature changes. We conclude that mild hypothermia is neuroprotective and suppresses infarct growth early after the onset of ischemia, with better ADC recovery. The ADC decrease during SD was greater during mild hypothermia, and suggests that the source of the ADC is more complex than previously believed.

Animals↗

PubMed2000

Yield of diffusion-weighted MRI for detection of potentially relevant findings in stroke patients.

OBJECTIVE: To determine whether diffusion-weighted imaging (DWI) could identify potentially clinically relevant findings in patients presenting more than 6 hours after stroke onset when compared with conventional MRI. METHODS: MRI with both conventional (T2 and proton density images) and echoplanar imaging (DWI and apparent diffusion coefficient maps) was performed 6 to 48 hours after symptom onset (mean, 27 hours) in 40 consecutive patients with acute stroke. All acute lesions were identified first on conventional images, then on DWI, by a neuroradiologist who was provided with the suspected lesion location, based on a neurologist's examination before imaging. Abnormalities were rated as potentially clinically relevant if they were detected only on DWI and 1) confirmed the acute symptomatic lesion to be in a different vascular territory than suspected clinically, 2) revealed multiple lesions in different vascular territories suggestive of a proximal source of embolism, or 3) clarified that a lesion, thought to be acute on conventional imaging, was not acute. RESULTS: The initial clinical impression of lesion localization was incorrect in 12 patients (30%). Clinically significant findings were detected by DWI alone in 19 patients (48%). DWI demonstrated the symptomatic lesion in a different vascular territory than suspected clinically or by conventional MRI in 7 patients (18%) and showed acute lesions in multiple vascular distributions in 5 patients (13%). In 8 patients (20%), DWI clarified that lesions thought to be acute on conventional MRI were actually old. CONCLUSION: In patients imaged 6 to 48 hours after stroke onset, DWI frequently provided potentially clinically relevant findings that were not apparent on conventional MRI.

Adult↗

PubMed2000

Advantages of adding diffusion-weighted magnetic resonance imaging to conventional magnetic resonance imaging for evaluating acute stroke.

BACKGROUND: Accurate localization of acute ischemic lesions in patients with an acute stroke may aid in understanding the etiology of their stroke and may improve the management of these patients. OBJECTIVE: To determine the yield of adding diffusion-weighted magnetic resonance imaging (DWI) to a conventional magnetic resonance imaging (MRI) protocol for acute stroke. DESIGN: A prospective cohort study. SETTING: A referral center. PATIENTS AND METHODS: Fifty-two patients with a clinical diagnosis of acute stroke who presented within 48 hours after symptom onset were included. An MRI scan was obtained within 48 hours after symptom onset. A neuroradiologist (A.M.N.) and a stroke neurologist (G.W.A.) independently identified suspected acute ischemic lesions on MRI sequences in the following order: (1) T2-weighted and proton density-weighted images, (2) fluid-attenuated inversion recovery images, and (3) diffusion-weighted images and apparent diffusion coefficient maps. MAIN OUTCOME MEASURES: Diagnostic yield and interrater reliability for the identification of acute lesions, and confidence and conspicuity ratings of acute lesions for different MRI sequences. RESULTS: Conventional MRI correctly identified at least one acute lesion in 71% (34/48) to 80% (39/49) of patients who had an acute stroke; with the addition of DWI, this percentage increased to 94% (46/49) (P<.001). Conventional MRI showed only moderate sensitivity (50%-60%) and specificity (49%-69%) compared with a "criterion standard." Based on the diffusion-weighted sequence, interrater reliability for identifying acute lesions was moderate for conventional MRI (kappa = 0.5-0.6) and good for DWI (kappa = 0.8). The observers' confidence with which lesions were rated as acute and the lesion conspicuity was significantly (P<.01) higher for DWI than for conventional MRI. CONCLUSION: During the first 48 hours after symptom onset, the addition of DWI to conventional MRI improves the accuracy of identifying acute ischemic brain lesions in patients who experienced a stroke.

Acute Disease↗

PubMed2000

Changes in baseline cerebral blood flow in humans do not influence regional cerebral blood flow response to photic stimulation.

The effect of changes in baseline regional cerebral blood flow (rCBF) values on the cerebral blood flow response during neuronal activation was studied with functional magnetic resonance imaging (fMRI). Using a breath-holding challenge as a hypercapnic stimulus, rCBF alterations during photic stimulation under normo- and hypercapnia were determined in nine volunteers. With breath-holding, baseline rCBF in areas corresponding to the visual cortex significantly increased from 54 +/- 5 ml/100 g/min to 85 +/- 9 ml/100 g/min (P < 0.001). Despite this significant change in baseline flow values, the rCBF increase during visual stimulation was very similar under normo- and hypercapnic conditions (28 +/- 8 ml/100 g/min versus 26 +/- 8 ml/100 g/min, respectively). This study supports the notion that within wide physiologic variations, task-induced cerebral blood flow changes are independent of baseline rCBF values.

Adult↗

PubMed2000

MRI of focal cerebral ischemia using (17)O-labeled water.

This work presents a novel approach for quantifying low concentrations of H(2)(17)O in vivo and explores its utility for assessing cerebral ischemia. Oxygen-17 enriched water acts as a T(2) shortening contrast agent whose effect can be suppressed by decoupling at the (17)O frequency during TE interval in a spin-echo MR image. Serial T(2)-weighted echo planar images were acquired in phantoms and rat brain with decoupler power alternated every eight images. The resulting periodic signal change (proportional to H(2)(17)O concentration) was detected by cross-correlating the square-wave decoupler power timecourse with the signal intensity in each voxel. Natural abundance (0.037 atom%) images of H(2)(17)O in rat brain were generated. The transverse relaxivity of H(2)(17)O in brain was estimated, R(2) = 2.4+/-0.5 s(-1)(atom%)(-1). After bolus injection of 1 ml of 10 atom% H(2)(17)O, brain H(2)(17)O concentration was estimated at 0.06+/-0.01 atom%. In the rat focal ischemia model, (17)O cross-correlation maps compared well with diffusion and Gd-DTPA perfusion images to indicate infarct location. Magn Reson Med 43:876-883, 2000.

Animals↗

PubMed2000

Spreading waves of transient and prolonged decreases in water diffusion after subarachnoid hemorrhage in rats.

Diffusion-weighted MRI (DWI), which can detect cortical spreading depressions (SDs) as propagating waves of reduced apparent diffusion coefficient (ADC) of water, was used to investigate whether spreading depression occurs after subarachnoid hemorrhage (SAH) induced by endovascular perforation in the rat. Eleven rats underwent SAH while positioned in the magnet. The ADC measurements had a temporal resolution of 12 sec. Transient decreases in ADC to 74 +/- 5% of pre-SAH values were observed in three rats after SAH, which propagated over the cortex with an average speed of 4.2 +/- 0. 6 mm/min, consistent with an SD wave. Furthermore, in all 11 rats, a wavefront of reduced ADC, which did not resolve within the 12 min observation period, spread at a speed of 3.2 +/- 1.7 mm/min in the ipsilateral cortex, and again is consistent with the speed of SD propagation. Therefore, spreading depression-like cellular depolarization is a consequence of acute subarachnoid hemorrhage in rats. Magn Reson Med 44:110-116, 2000.

Animals↗

PubMed2000

Condition number as a measure of noise performance of diffusion tensor data acquisition schemes with MRI.

Diffusion tensor mapping with MRI can noninvasively track neural connectivity and has great potential for neural scientific research and clinical applications. For each diffusion tensor imaging (DTI) data acquisition scheme, the diffusion tensor is related to the measured apparent diffusion coefficients (ADC) by a transformation matrix. With theoretical analysis we demonstrate that the noise performance of a DTI scheme is dependent on the condition number of the transformation matrix. To test the theoretical framework, we compared the noise performances of different DTI schemes using Monte-Carlo computer simulations and experimental DTI measurements. Both the simulation and the experimental results confirmed that the noise performances of different DTI schemes are significantly correlated with the condition number of the associated transformation matrices. We therefore applied numerical algorithms to optimize a DTI scheme by minimizing the condition number, hence improving the robustness to experimental noise. In the determination of anisotropic diffusion tensors with different orientations, MRI data acquisitions using a single optimum b value based on the mean diffusivity can produce ADC maps with regional differences in noise level. This will give rise to rotational variances of eigenvalues and anisotropy when diffusion tensor mapping is performed using a DTI scheme with a limited number of diffusion-weighting gradient directions. To reduce this type of artifact, a DTI scheme with not only a small condition number but also a large number of evenly distributed diffusion-weighting gradients in 3D is preferable.

Algorithms↗

PubMed2000

Assessment of hemodynamic response during focal neural activity in human using bolus tracking, arterial spin labeling and BOLD techniques.

In this study, the hemodynamic response and changes in oxidative metabolism during functional activation were measured using three functional magnetic resonance imaging (fMRI) techniques: the blood oxygenation level-dependent (BOLD) technique, flow-sensitive alternating inversion recovery (FAIR), and bolus tracking (BT) of an MR contrast agent. With these three techniques we independently determined changes in BOLD signal, relative cerebral blood flow (rCBF), and cerebral blood volume (rCBV) associated with brain activation in eight healthy volunteers. In the motor cortex, the BOLD signal increased by 1.8 +/- 0.5%, rCBF by 36.3 +/- 8.2% (FAIR), and 35.1 +/- 8.6% (BT), and rCBV by 19.4 +/- 4.1% (BT) in response to simultaneous bilateral finger tapping. In the visual cortex, BOLD signal increased by 2.6 +/- 0.5%, rCBF by 38.5% +/- 7.6 (FAIR), and 36.9 +/- 8.8% (BT), and rCBV by 18.8 +/- 2.8% (BT) during flickering checkerboard stimulation. Comparing the experimentally measured rCBV with the calculated rCBV using Grubb's power-law relation, we conclude that the use of power-law relationship results in systematic underestimate of rCBV.

Adult↗

PubMed2000

Diffusion- and perfusion-weighted MRI in a patient with a prolonged reversible ischaemic neurological deficit.

We report acute and follow-up diffusion- and perfusion-weighted MRI (DWI, PWI) findings in a patient with a prolonged reversible ischaemic neurological deficit. PWI 12 h after the patient was last seen to be without symptoms revealed a large perfusion deficit in the left posterior MCA territory with a relatively inconspicuous and much smaller abnormality on DWI. Follow-up showed resolution of abnormalities on both DWI and PWI, and conventional MRI was normal, apart from a very slight abnormality, visible only on FLAIR images, at the centre of the initially DWI-positive region. These findings demonstrate the utility of PWI when be used in combination with DWI to investigate the pathophysiology of transient ischemic syndromes.

Aged↗

PubMed2000

Quantification of cerebral blood flow by bolus tracking and artery spin tagging methods.

This study deals with perfusion quantification in healthy volunteers using two types of dynamic magnetic resonance imaging (MRI) methods. Absolute cerebral blood flow (CBF) measurements were performed in 11 subjects by applying both bolus tracking of exogenous contrast agent and non-invasive arterial spin labeling MRI techniques. Both methods produced CBF images with good tissue contrast and CBF values are in good agreement with literature data. The correlation between cerebral blood volume (CBV) and CBF is also discussed.

Arteries↗

PubMed2000

Microstructure of temporo-parietal white matter as a basis for reading ability: evidence from diffusion tensor magnetic resonance imaging.

Diffusion tensor magnetic resonance imaging (MRI) was used to study the microstructural integrity of white matter in adults with poor or normal reading ability. Subjects with reading difficulty exhibited decreased diffusion anisotropy bilaterally in temporoparietal white matter. Axons in these regions were predominantly anterior-posterior in direction. No differences in T1-weighted MRI signal were found between poor readers and control subjects, demonstrating specificity of the group difference to the microstructural characteristics measured by diffusion tensor imaging (DTI). White matter diffusion anisotropy in the temporo-parietal region of the left hemisphere was significantly correlated with reading scores within the reading-impaired adults and within the control group. The anisotropy reflects microstructure of white matter tracts, which may contribute to reading ability by determining the strength of communication between cortical areas involved in visual, auditory, and language processing.

Adult↗

PubMed2000

Spreading depression-induced expression of c-fos and cyclooxygenase-2 in transgenic mice that overexpress human copper/zinc-superoxide dismutase.

Spreading depression (SD) is a wave of sustained depolarization challenging the energy metabolism of cells without causing irreversible damage. SD is a major mechanism of gene induction that takes place in cortical injury, including ischemia. We studied the role of oxygen radicals in SD-induced c-fos and cyclooxygenase-2 (COX-2) induction using transgenic (Tg) mice that overexpress copper/zinc-superoxide dismutase (SOD1). The frequency, amplitude and duration of SD waves were similar in the Tg mice and wild-type littermates. c-fos and COX-2 mRNAs were strongly induced 1 and 4 h after SD. The induction of both genes was slightly but significantly less at 4 h in the Tg mice. The results indicate that even a mild, noninjurious metabolic stimulation increases the concentration of oxygen radicals to the level that contributes to gene expression.

Animals↗

PubMed2000

High speed diffusion magnetic resonance imaging of ischemia and spontaneous periinfarct spreading depression after thromboembolic stroke in the rat.

Spontaneous episodes of transient cell membrane depolarization (spreading depression [SD]) occur in the surroundings of experimental stroke lesions and are believed to contribute to infarct growth. Diffusion-weighted imaging (DWI) is capable of detecting the water shifts from extracellular to intracellular space associated with SD waves and ischemia, and can make in vivo measurements of these two features on a pixel-by-pixel basis with good temporal resolution. Using continuous high speed DWI with a temporal resolution of 12 seconds over a period of 3 hours, the in vivo contribution of spontaneous SDs to the development of ischemic tissue injury was examined in 8 rats using a thromboembolic stroke model. During the observation period, the initial lesion volume increased in 4 animals, remained unchanged in 1 animal, and decreased in 3 animals (most likely because of spontaneous clot lysis). Irrespective of the lesion evolution patterns, animals demonstrated 6.5 +/- 2.1 spontaneous SDs outside of the ischemic core. A time-to-peak analysis of apparent diffusion coefficient (ADC) changes for each SD wave demonstrated multidirectional propagation patterns from variable initiation sites. Maps of the time constants of ADC recovery, reflecting the local energy supply and cerebral blood flow, revealed prolonged recovery times in areas close to the ischemic core. However, repetitive SD episodes in the periinfarct tissue did not eventually lead to permanent ADC reductions. These results suggest that spontaneous SD waves do not necessarily contribute to the expansion of the ischemic lesion volume in this model.

Animals↗

PubMed2000

Relationship between apparent diffusion coefficient and subsequent hemorrhagic transformation following acute ischemic stroke.

BACKGROUND AND PURPOSE: A method for identifying patients at increased risk for developing secondary hemorrhagic transformation (HT) after acute ischemic stroke could be of significant value, particularly in patients being considered for thrombolytic therapy. We hypothesized that diffusion-weighted MRI might aid in the identification of such patients. METHODS: We retrospectively analyzed 17 patients with ischemic stroke who received diffusion-weighted MRI within 8 hours of symptom onset and who also received follow-up neuroimaging within 1 week of initial scan. The apparent diffusion coefficient (ADC) for each pixel in the whole ischemic area was calculated, generating a histogram of values. Areas subsequently experiencing HT were then compared with areas not experiencing HT to determine the relationship between ADC and subsequent HT. RESULTS: A significantly greater percentage of pixels possessed lower ADCs (</=550x10(-)(6) mm(2)/s) in HT lesions compared with non-HT lesions (47% versus 19%; P:<0.001). Moreover, >40% of the pixels possessed values </=550x10(-)(6) mm(2)/s in all lesions experiencing secondary HT, compared with <31% of the pixels in the non-HT-destined lesions. CONCLUSIONS: HT-destined stroke regions possess a significantly great percentage of low ADC values than non-HT-destined regions. Early measurement of ADC values may be a useful tool for assessing secondary HT risk.

Aged↗

PubMed2000

Is early ischemic lesion volume on diffusion-weighted imaging an independent predictor of stroke outcome? A multivariable analysis.

BACKGROUND AND PURPOSE: The heterogeneity of stroke makes outcome prediction difficult. Neuroimaging parameters may improve the predictive value of clinical measures such as the National Institutes of Health Stroke Scale (NIHSS). We investigated whether the volume of early ischemic brain lesions assessed with diffusion-weighted imaging (DWI) was an independent predictor of functional outcome. METHODS: We retrospectively selected patients with nonlacunar ischemic stroke in the anterior circulation from 4 prospective Stanford Stroke Center studies evaluating early MRI. The baseline NIHSS score and ischemic stroke risk factors were assessed. A DWI MRI was performed within 48 hours of symptom onset. Clinical characteristics and early lesion volume on DWI were compared between patients with an independent outcome (Barthel Index score >/=85) and a dependent outcome (Barthel Index score <85) at 1 month. A logistic regression model was performed with factors that were significantly different between the 2 groups in univariate analysis. RESULTS: Sixty-three patients fulfilled the entry criteria. One month after symptom onset, 24 patients had a Barthel Index score <85 and 39 had a Barthel Index score >/=85. In univariate analysis, patients with independent outcome were younger, had lower baseline NIHSS scores, and had smaller lesion volumes on DWI. In a logistic regression model, DWI volume was an independent predictor of outcome, together with age and NIHSS score, after correction for imbalances in the delay between symptom onset and MRI. CONCLUSIONS: DWI lesion volume measured within 48 hours of symptom onset is an independent risk factor for functional independence. This finding could have implications for the design of acute stroke trials.

Adult↗

PubMed2000

Serial MRI after transient focal cerebral ischemia in rats: dynamics of tissue injury, blood-brain barrier damage, and edema formation.

BACKGROUND AND PURPOSE: With the advent of thrombolytic therapy for acute stroke, reperfusion-associated mechanisms of tissue injury have assumed greater importance. In this experimental study, we used several MRI techniques to monitor the dynamics of secondary ischemic damage, blood-brain barrier (BBB) disturbances, and the development of vasogenic edema during the reperfusion phase after focal cerebral ischemia in rats. METHODS: Nineteen Sprague-Dawley rats were subjected to transient middle cerebral artery occlusion of 30 minutes, 60 minutes, or 2.5 hours with the suture occlusion model. MRI, including diffusion-weighted imaging (DWI), T2-weighted imaging, perfusion-weighted imaging, and T1-weighted imaging, was performed 5 to 15 minutes before reperfusion, as well as 0.5, 1.5, and 2.5 hours and 1, 2, and 7 days after withdrawal of the suture. Final infarct size was determined histologically at 7 days. RESULTS: In the 30-minute ischemia group (and partially also after 60 minutes), DWI abnormalities reversed transiently during the early reperfusion period but recurred after 1 day, probably due to secondary ischemic damage. After 2.5 hours of ischemia, DWI abnormalities no longer reversed, and signal intensity on both DWI and T2-weighted images increased rapidly in the previously ischemic region due to BBB damage (enhancement on postcontrast T1-weighted images) and edema formation. Early BBB damage during reperfusion was found to be predictive of relatively pronounced edema at subacute time points and was probably related to the increased mortality rates in this experimental group (3 of 7). CONCLUSIONS: Reperfusion after short periods of ischemia (30 to 60 minutes) appears to be mainly complicated by secondary ischemic damage as shown by the delayed recurrence of the DWI lesions, whereas BBB damage associated with vasogenic edema becomes a dominant factor with longer occlusion times (2.5 hours).

Animals↗

PubMed2000

New magnetic resonance imaging methods for cerebrovascular disease: emerging clinical applications.

During the 1990s, novel magnetic resonance imaging (MRI) techniques have emerged that allow the noninvasive and rapid assessment of normal brain functioning and cerebral pathophysiology. Some of these techniques, including diffusion-weighted imaging and perfusion-weighted imaging, have already been used extensively in specialized centers for the evaluation of patients with cerebrovascular disease. Evidence is now rapidly accumulating that both diffusion- and perfusion-weighted imaging, particularly when used in combination with high-speed MR angiography, will lead to improvements in the clinical management of acute stroke patients. Other novel MR techniques, such as spectroscopic imaging, diffusion tensor imaging, and blood oxygenation level-dependent functional MRI, have not yet assumed a definitive role in the diagnostic evaluation of cerebrovascular disease. However, they are promising research tools that provide noninvasive data about infarct evolution as well as mechanisms of stroke recovery. In this article, we review the basic principles underlying these novel MRI techniques and outline their current and anticipated future impact on the diagnosis and management of patients with cerebrovascular disease.

Brain↗