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Biomedical subjects

P W Schaefer

Publications and source records attributed to P W Schaefer.

At least 19 recordsLinked to original sources
PubMed2006

First-pass quantitative CT perfusion identifies thresholds for salvageable penumbra in acute stroke patients treated with intra-arterial therapy.

BACKGROUND AND PURPOSE: The purpose of this study was to determine whether, in acute stroke patients treated with intra-arterial (IA) recanalization therapy, CT perfusion (CTP) can distinguish ischemic brain tissue destined to infarct from that which will survive. METHODS: Dynamic CTP was obtained in 14 patients within 8 hours of stroke onset, before IA therapy. Initial quantitative cerebral blood volume (CBV) and flow (CBF) values were visually segmented and normalized in the "infarct core" (region 1: reduced CBV and CBF, infarction on follow-up), "penumbra that infarcts" (region 2: normal CBV, reduced CBF, infarction on follow-up), and "penumbra that recovers" (region 3: normal CBV, reduced CBF, normal on follow-up). Normalization was accomplished by dividing the ischemic region of interest value by that of a corresponding, contralateral, uninvolved region, which resulted in CBV and CBF "ratios." Separate CBV and CBF values were obtained in gray matter (GM) and white matter (WM). RESULTS: Mean CBF ratios for regions 1, 2, and 3 were 0.19 +/- 0.06, 0.34 +/- 0.06, and 0.46 +/- 0.09, respectively (all P < .001). Mean CBV ratios for regions 1, 2, and 3 were similarly distinct (all P < .05). Absolute CBV and CBF values for regions 2 and 3 were not significantly different. All regions with CBF ratio <0.32, CBV ratio <0.68, CBF <12.7 mL/100 g/min, or CBV <2.2 mL/100 g infarcted. No region with CBF ratio >0.44 infarcted. GM versus WM CBF and CBV values were significantly different for region 2 compared with region 3 (P < .05). CONCLUSIONS: In acute stroke patients, quantitative CTP can distinguish ischemic tissue likely to infarct from that likely to survive.

Adult↗
PubMed2002

Diffusion-weighted MRI in diffuse axonal injury of the brain.

The goal of this study was to identify and describe the different types and patterns of tissue injury which are encountered by diffusion-weighted imaging (DWI) in diffuse axonal injury (DAI) of the brain. The DWI data sets of 98 patients who suffered from a closed-head injury were retrospectively evaluated. Medical records were reviewed to rule out pre-existing neurological diseases. Lesions were studied for their DWI signal characteristics and lesion size or extension. Traumatic lesions were classified into three categories depending on their signal characteristica on DWI and apparent diffusion coefficient (ADC) maps: type 1, DWI- and ADC-hyperintense most likely representing lesions with vasogenic edema; type 2, DWI-hyperintense, ADC-hypointense indicating cytotoxic edema; type 3, central hemorrhagic lesion surrounded by an area of increased diffusion. According to the size and extent of lesions, injury was classified into three groups: group A, focal injury; group B, regional/confluent injury; and group C, extensive/diffuse injury. Our study showed that diffusion-weighted imaging differentiates between lesions with decreased and increased diffusion in patients with DAI. Different degrees of tissue injury extent were noticed. Future prospective studies should study if this additional information can be used as a predictor of injury reversibility, final outcome and prognosis.

Adolescent↗
PubMed2001

Applications of DWI in clinical neurology.

Echo planar diffusion-weighted imaging (EP DWI) provides information about the physiologic state of the brain that is not available on conventional magnetic resonance (MR) images. Specifically, it provides signal proportional to the molecular diffusion of water molecules. It has proven highly sensitive in the detection of acute infarction and it is reliable in differentiating acute stroke from other diseases that mimic acute stroke clinically and on conventional MR images. With perfusion imaging, diffusion-weighted imaging is useful in predicting final infarct size and patient outcome. Diffusion MR is also becoming increasingly useful in the evaluation of a wide variety of other disease processes including neoplasms, intracranial infections and traumatic brain injury. Because acute stroke is common in the differential diagnosis of the majority of patients who present with acute neurologic deficits, diffusion-weighted imaging has become an essential sequence.

Brain↗
PubMed2001

Comparison of diameter and perimeter methods for tumor volume calculation.

PURPOSE: Lesion volume is often used as an end point in clinical trials of oncology therapy. We sought to compare the common method of using orthogonal diameters to estimate lesion volume (the diameter method) with a computer-assisted planimetric technique (the perimeter method). METHODS: Radiologists reviewed 825 magnetic resonance imaging studies from 219 patients with glioblastoma multiforme. Each study had lesion volume independently estimated via the diameter and perimeter methods. Cystic areas were subtracted out or excluded from the outlined lesion. Inter- and intrareader variability was measured by using multiple readings on 48 cases. Where serial studies were available in noncystic cases, a mock response analysis was used. RESULTS: The perimeter method had a reduced interreader and intrareader variability compared with the diameter method (using SD of differences): intrareader, 1.76 mL v 7.38 mL (P < .001); interreader, 2.51 mL v 9.07 mL (P < .001) for perimeter and diameter results, respectively. Of the 121 noncystic cases, 23 had serial data. In six (26.1%) of those 23, a classification difference occurred when the perimeter method was used versus the diameter method. CONCLUSION: Variability of measurements was reduced with the computer-assisted perimeter method compared with the diameter method, which suggests that changes in volume can be detected more accurately with the perimeter method. The differences between these techniques seem large enough to have an impact on grading the response to therapy.

Brain↗
PubMed2001

Reproductive character displacement in Lymantria monacha from northern Japan?

Our objective was to test the hypothesis that the pheromone blend and/or diel periodicity of pheromonal communication differ in populations of the nun moth, Lymantria monacha (Lepidoptera: Lymantriidae), from eastern Asia (northern Honshu, Japan) and Central Europe (Bohemia, Czech Republic). Coupled gas chromatographic-electroantennographic detection (GC-EAD) analyses of pheromone gland extract of female L. monacha from Japan confirmed the presence of compounds previously identified in pheromone extracts of L. monacha from Bohemia, as follows: (Z)-7-octadecene, 2-methyl-(Z)-7-octadecene (2me-Z7-18Hy), cis-7,8-epoxy-octadecane (monachalure), and cis-7,8-epoxy-2-methyloctadecane (disparlure). Field experiments in Honshu suggested that (+)-monachalure is the major pheromone component of L. monacha. 2me-Z7-18Hy significantly enhanced attractiveness of (+)-monachalure. Addition of (+)-disparlure to (+)-monachalure plus 2me-Z7-18Hy in Honshu and Bohemia increased attractiveness of lures by 1.2 and 20 times, respectively, indicating that (+)-disparlure is of least and most significance in the respective L. monacha populations. Moreover, capture of male L. monacha in pheromone-baited traps between 18:00 and 24:00 hr in Bohemia and 2:00 and 5:00 hr in Honshu revealed a markedly different diel periodicity of pheromonal communication. Pheromonal communication late at night and use of (+)-monachalure, rather than (+)-disparlure, as the major pheromone component by L. monacha in Honshu may have resulted from interspecific competition with coseasonal L. fumida, which uses the early night for pheromonal communication and (+)-disparlure as major pheromone component. Whether communication channel divergence of L. monacha in Honshu indeed constitutes a case of reproductive character displacement is difficult to prove. The evolution of such divergence in sympatric populations of L. fumida and L. monacha would have to be demonstrated.

Animal Communication↗
PubMed2001

Unilateral temporal lobe stroke causing ischemic transient global amnesia: role for diffusion-weighted imaging in the initial evaluation.

Ischemia has been proposed as a cause of transient global amnesia (TGA), but proof has been lacking. The authors performed magnetic resonance imaging on a 77-year-old woman with classic TGA at 4 hours and at 6 days after the onset of symptoms. Her initial diffusion-weighted imaging (DWI) and apparent diffusion coefficient imaging suggested an acute infarct in the left mesial temporal lobe. Follow-up T2-weighted imaging at 6 days confirmed the lesion as an ischemic infarct, despite resolution of her symptoms. DWI permits early detection of small ischemic lesions and may identify patients with ischemic TGA who should be evaluated for potential sources of emboli.

Aged↗
PubMed2001

Diagnostic value of apparent diffusion coefficient hyperintensity in selected patients with acute neurologic deficits.

BACKGROUND AND PURPOSE: A pattern of decreased intensity on apparent diffusion coefficient (ADC) maps is useful in the early detection of ischemic brain injury. Less information exists with regard to patients with acute neurologic deficits in whom there is abnormal conventional magnetic resonance imaging (MRI) and increased ADC intensity. METHODS: The authors identified 13 patients with acute neurologic deficits who underwent diffusion MRI and had calculated ADC maps demonstrating hyper-intensity in regions characterized by computed tomography hypodensity and MRI T2 hyperintensity. The initial and follow-up imaging characteristics and clinical syndromes were recorded. RESULTS: Clinical syndromes included hypertensive encephalopathy, posterior leukoencephalopathy, hyperperfusion following carotid endarterectomy, venous sinus thrombosis, HIV encephalopathy, and brain tumor. Diffusion-weighted imaging (DWI) was hyperintense in 3 of 13 patients, isointense in 4 of 13 patients, heterogeneous in 3 of 13 patients, and hypointense in 3 of 13 patients. The ADC values in these regions were significantly higher than those in control regions (P < .0001). At early follow-up, MRI abnormalities resolved completely in 3 of 13 patients and partially in 9 of 13 patients. MRI abnormalities were unchanged in 1 patient. CONCLUSIONS: In the evaluation of patients with acute neurologic deficits, ADC hyperintensity may identify a subset of patients with vasogenic edema of nonischemic etiology. Frequently, these conditions are potentially reversible if appropriately managed. DWI and conventional images alone are not sufficient to identify these neurologic conditions.

Acute Disease↗
PubMed2001

Ischemic stroke: effects of etiology and patient age on the time course of the core apparent diffusion coefficient.

PURPOSE: To determine whether the evolution of the core apparent diffusion coefficient (ADC) of water in ischemic stroke varies with patient age or infarct etiology. MATERIALS AND METHODS: One hundred forty-seven patients with stroke underwent 236 diffusion-weighted magnetic resonance imaging examinations. Etiologies of lesions were classified according to predefined criteria; in 224 images, the diagnosis of lacune could be firmly established or excluded. ADC was measured in the center of each lesion and in contralateral normal-appearing brain. A model was used to describe the time course of relative ADC (rADC), which is calculated by dividing the lesion ADC by the contralateral ADC, and to test for age- or etiology-related differences in this time course. RESULTS: Transition from decreasing to increasing rADC was estimated at 18.5 hours after stroke onset. In subgroup analysis, transition was earlier in nonlacunes than in lacunes (P =.02). There was a trend toward earlier transition in patients older than the median age of 66.0 years, compared with younger patients (P =.06). Pseudonormalization was estimated at 216 hours. Among nonlacunes, the rate of subsequent rADC increase was more rapid in younger patients than in older patients (P =.001). Within the smaller sample of lacunes, however, no significant age-related difference in this rate was found. CONCLUSION: Differences in ADC depending on the patient's age and infarct etiology suggest differing rates of ADC progression.

Adult↗
PubMed2001

Frequency and clinical context of decreased apparent diffusion coefficient reversal in the human brain.

PURPOSE: To determine the probability that regions of decreased apparent diffusion coefficient (ADC) return to normal without persistent symptoms or T2 change and the settings in which these ADC reversals occur. MATERIALS AND METHODS: Three hundred magnetic resonance (MR) imaging studies were selected at random from a database of 7,147 examinations to determine the probability of a pathologically decreased ADC. In cases with decreased ADC, the clinical history was recorded and, if available, follow-up MR imaging findings were evaluated. Five cases of ADC reversal became known during the same period and were evaluated to determine the initial ADC decrease, clinical outcome, and findings at follow-up imaging. RESULTS: Findings in 116 of 300 MR imaging studies revealed regions of decreased ADC. In 49 of 116 studies, follow-up MR imaging examinations were performed at least 4 weeks after the onset of symptoms; ADC did not reverse. Five cases of ADC reversal were identified in the same period, giving an estimated 0.2%-0.4% probability of ADC reversal. Clinical settings were venous sinus thrombosis and seizure (n = 3), hemiplegic migraine (n = 1), and hyperacute arterial infarction (n = 1). Both white matter (n = 3) and gray matter (n = 3) regions were involved. CONCLUSION: Reversal of ADC lesions is rare, occurs in complicated clinical settings, and can involve white or gray matter.

Adolescent↗
PubMed2001

Unique linear and nodular MR enhancement pattern in schistosomiasis of the central nervous system: report of three patients.

OBJECTIVE: The purpose of this paper is to describe the unique MR imaging appearance of schistosomiasis of the central nervous system (CNS). CONCLUSION: Contrast-enhanced T1-weighted MR images in all three patients with CNS schistosomiasis revealed a central linear enhancement surrounded by multiple enhancing punctate nodules, forming an "arborized" appearance. Pathologically, this enhancement pattern correlated with a host granulomatous response to Schistosoma species ova. Although the pattern is not present in all cases of CNS schistosomiasis, when it is observed, a diagnosis of CNS schistosomiasis should be considered.

Adult↗
PubMed2000

Diffusion-weighted magnetic resonance imaging identifies the "clinically relevant" small-penetrator infarcts.

BACKGROUND: Most patients initially seen with a clinical syndrome consistent with a small-penetrator infarct (SPI) also harbor multiple, chronic, hyperintense, white matter lesions on conventional magentic resonance imaging (ie, T2-weighted image [T2WI] and fluid-attenuation inversion recovery [FLAIR] imaging). Diffusion-weighted imaging (DWI) can identify the clinically relevant "index infarction" in such circumstances, since it differentiates between acute and chronic lesions. OBJECTIVE: To determine the clinical and radiological predictors associated with misidentification of an SPI as acute using T2WI and FLAIR images in patients with an acute SPI seen on DWI. PATIENTS: Sixty-seven consecutive patients who had an SPI. METHODS: Two independent examiners, provided with brief clinical information, but blinded to DWI findings, sought a clinically appropriate lesion on T2WI and FLAIR imaging in 67 consecutive patients found to have an SPI seen on DWI. RESULTS: The index infarction based on evaluation of T2WI or FLAIR images was in a different location than the acute lesion as identified by DWI in 9 (13%) and 11 (16%) of 67 patients, respectively. Both T2WI and FLAIR imaging were rated normal in another 9% of the patients. Multivariate analysis showed that small lesion size (<10 mm) was the only predictor of misidentifying the clinically appropriate lesion on conventional magnetic resonance imaging (P<.01). CONCLUSIONS: T2-weighted imaging and FLAIR imaging fail to identify the clinically relevant SPI in almost one quarter of the patients found to have a lesion on DWI. The characteristics of DWI make it well suited for the detection of acute small infarcts. Diffusion-weighted imaging is necessary to consistently define the clinical-anatomical relations in patients initially seen with SPIs.

Adult↗
PubMed2000

Mitochondrial DNA variation among worldwide populations of gypsy moths, Lymantria dispar.

Gypsy moth populations from Japan, mainland Asia, Europe, Tunisia, and North America were analyzed for variation in mitochondrial DNA (mtDNA) sequences from three gene regions. These samples resolve into four groups, representing gypsy moths from (1) Okinawa, Japan, (2) Hokkaido, Japan, (3) Honshu and Kyushu, Japan and mainland Asia, and (4) Europe, Tunisia, and North America. Some patterns of geographic variation observed for mtDNA (for example, the distinctiveness of gypsy moths from Hokkaido, Japan) coincide with those observed by Goldschmidt from analyses of morphology, life history, and intersexuality. Other patterns (relative sequence homogeneity across Asia, Honshu, and Kyushu and reduced levels of variation in mainland Japan) do not.

Animals↗
PubMed2000

Magnetic resonance imaging of cerebral hemorrhagic stroke.

Despite a traditional perception of reliance on computed tomography and lack of acceptance of magnetic resonance imaging (MRI) for detecting acute hemorrhage, MRI appears to be used increasingly in hemorrhagic stroke. This review addresses the MRI findings of acute hemorrhagic stroke obtained using relatively new imaging techniques. These new techniques have resulted in more acute stroke patients undergoing MRI examination. New information about the frequency and appearance of hemorrhage is emerging: for example, approximately 15-26% of cases of acute cerebral infarctions appear to be complicated by intracerebral hemorrhage. The MRI appearances of hemorrhagic transformation of ischemic infarction, as well as acute hypertensive intracerebral hemorrhage, are discussed based on clinical, biochemical, and technical aspects.

Brain Ischemia↗
PubMed2000

Diffusion-weighted imaging as a problem-solving tool in the evaluation of patients with acute strokelike syndromes.

This article addresses syndromes that clinically and/or radiologically resemble acute stroke. These syndromes generally fall into four categories. (1) Patients with acute neurological deficits with nonischemic lesions and no acute abnormality on diffusion-weighted images. These patients may have peripheral vertigo, migraines, seizures, dementia, functional disorders, amyloid angiopathy, or metabolic disorders. When these patients present, we can confidently predict that they are not undergoing infarction. (2) Patients with ischemic lesions with reversible clinical deficits. Nearly 50% of patients with transient ischemic attacks have lesions with restricted diffusion. Patients with transient global amnesia may have punctate lesions with restricted diffusion in the medial hippocampus, parahippocampal gyms, and corpus callosum. (3) Vasogenic edema syndromes that may mimic acute infarction clinically and on conventional imaging. These include eclampsia/hypertensive encephalopathy, other posterior leukoencephalopathies, human immunodeficiency virus encephalopathy, hyperperfusion syndrome following carotid endarterectomy, venous sinus thrombosis, acute demyelination, and neoplasm. These syndromes demonstrate elevated diffusion rather than the restricted diffusion associated with acute ischemic stroke. (4) Entities in which restricted diffusion may resemble acute infarction. These include pyogenic infections, herpes virus encephalitis, Creutzfeldt-Jakob disease, diffuse axonal injury, tumors with dense cell packing, and rare acute demyelinative lesions.

Diffusion↗
PubMed2000

Diffusion-weighted MR imaging of the brain.

Diffusion-weighted magnetic resonance (MR) imaging provides image contrast that is different from that provided by conventional MR techniques. It is particularly sensitive for detection of acute ischemic stroke and differentiation of acute stroke from other processes that manifest with sudden neurologic deficits. Diffusion-weighted MR imaging also provides adjunctive information for other cerebral diseases including neoplasms, intracranial infections, traumatic brain injury, and demyelinating processes. Because stroke is common and in the differential diagnosis of most acute neurologic events, diffusion-weighted MR imaging should be considered an essential sequence, and its use in most brain MR studies is recommended.

Animals↗
PubMed2000

Diffusion-weighted imaging in neonatal cerebral infarction: clinical utility and follow-up.

We describe the clinical utility of echo-planar diffusion-weighted imaging in neonatal cerebral infarction. Eight full-term neonates aged 1 to 8 days referred for neonatal seizures were studied. Patients were followed for a mean of 17 months with detailed neurologic examinations at regular intervals. Head computed tomography (CT) and conventional magnetic resonance (MRI) and diffusion-weighted images were obtained. Percent lesion contrast was evaluated for 19 lesions on T2-weighted and diffusion-weighted images. Follow-up conventional MRIs were obtained in seven patients. The findings on diffusion-weighted imaging were correlated with CT and conventional MRI findings as well as with short-term neurodevelopmental outcome. Four patients had focal cerebral infarctions. Four patients had diffuse injury consistent with hypoxic-ischemic encephalopathy. Percent lesion contrast of all 19 lesions was significantly higher on diffusion-weighted images when compared with T2-weighted images. In five patients, there were lesions visualized only with diffusion-weighted imaging. In all patients, there was increased lesion conspicuity and better definition of lesion extent on the diffusion-weighted images compared with the CT and T2-weighted MR images. In seven of eight patients follow-up imaging confirmed prior infarctions. Short-term neurologic outcome correlated with the extent of injury seen on the initial diffusion-weighted imaging scans for all patients. Diffusion-weighted imaging is useful in the evaluation of acute ischemic brain injury and seizure etiology in neonates. In the acute setting, diffusion-weighted imaging provides information not available on CT and conventional MRI. This information correlates with short-term clinical outcome.

Brain↗
PubMed1999

MRI detection of new hemorrhages: potential marker of progression in cerebral amyloid angiopathy.

The authors used serial gradient-echo MRIs to detect new small hemorrhages in patients with previous lobar hemorrhage. Of 24 lobar hemorrhage patients (17 diagnosed with probable and 7 with possible amyloid angiopathy) who prospectively underwent repeat MRI 1.5 years after initial study, 9 (38%) demonstrated additional hemorrhages at follow-up. Interrater agreement was high. New hemorrhages were more frequent in patients with probable amyloid angiopathy (8 of 17, 47%) with more hemorrhages at baseline (p < 0.01). These results suggest a role for gradient-echo MRI in assessing disease progression in amyloid angiopathy.

Aged↗