Search PubMed⌕ Search

Biomedical subjects

M Essig

Publications and source records attributed to M Essig.

At least 55 records · Page 3Linked to original sources
PubMed1999

Topography of callosal atrophy reflects distribution of regional cerebral volume reduction in Alzheimer's disease.

It has been suggested that regional corpus callosum atrophy in Alzheimer's disease (AD) may serve as an in vivo index of neuronal loss in the neocortex. In this study total and regional size of the corpus callosum was evaluated with respect to the volumes of the frontal, temporal, and parietal lobes in 38 patients with AD (NINCDS-ADRDA criteria) using quantitative magnetic resonance imaging. Twenty healthy subjects matched for age and gender served as a control group. All quantitative measurements were performed by manual tracing using personal computer-based software. Both total size and the five measured regional subsections were significantly smaller in AD when compared to the control subjects. The severity of dementia was significantly correlated with the size of the middle sections of the corpus callosum (rostral body and midbody). Within the AD group, the rostral body of the corpus callosum was significantly correlated with the frontal lobe volumes, the midbody was correlated with the temporal lobe volumes, and size of the splenium was correlated with the parietal lobe volumes. We conclude that callosal atrophy in AD reflects the severity and pattern of cortical neuronal damage. Correlations between regional callosal atrophy and severity of dementia indicate that interhemispheric cortico-cortical disconnection may contribute to the dementia syndrome.

Aged↗
PubMed1999

MR microcirculation assessment in cervical cancer: correlations with histomorphological tumor markers and clinical outcome.

This article reviews the experience available to date on microcirculation assessment in cancer of the cervix including correlation studies of magnetic resonance (MR) microcirculatory parameters with histo-morphometric predictors and direct correlation with patient outcome. The data suggest that MR microcirculation parameters do not always correlate with histo-morphometric parameters, while there is evidence that MR parameters predict patients' treatment outcome. These observations raise the issue that perhaps the histo-morphometric parameters, accepted gold standards for tumor angiogenesis and prognostic factors, reflect anatomical information at a "static" single time point and may not always provide sufficient information on the "dynamic" microcirculation function of the tumor. MR microcirculation assessment reflects both anatomical and functional information and may provide this additional information on the "dynamic" angiogenic and metabolic status of a tumor. Therefore, assessment of tumor microcirculation may augment the individual risk profile in cervical cancer patients and has the potential to impact on therapy selection and treatment outcome.

Contrast Media↗
PubMed1999

Comprehensive MR evaluation of renovascular disease in five breath holds.

To detect a renal artery stenosis and assess its hemodynamic and functional significance in five breath holds. In a single MR exam, T1 weighted FLASH and T2 weighted fast spin echo techniques are used to assess renal morphology, multiphase 3D gadolinium (Gd) MRA to evaluate the renal arteries, and a segmented EPI cine phase-contrast technique to measure renal artery blood flow. A standardized image analysis is performed to assess kidney size, corticomedullar differentiation (CMD), parenchymal enhancement, the degree of renal artery stenosis, abnormalities in blood flow pattern, and any associated abdominal vascular disease. Multiphase 3D-Gd-MRA accurately assesses atherosclerotic renal artery disease particularly in the presence of an associated aortic aneurysm. Delayed parenchymal enhancement, loss of CMD, and decrease in kidney size can be detected. In combination with decreased systolic velocity components, the diagnosis of a hemodynamically and functionally significant stenosis can be made. High-resolution single-phase 3D-Gd-MRA is preferable for evaluation of fibromuscular dysplasia or hypoplastic vessels. The combination of different breath hold techniques in a single, standardized MR exam allows to detect the hemodynamic and functional significance of a renal artery stenosis.

Aged↗
PubMed1999

Motor dysfunction and sensorimotor cortex activation changes in schizophrenia: A study with functional magnetic resonance imaging.

Recent studies demonstrate a diminished activation of the sensorimotor cortex and supplementary motor area (SMA) in schizophrenia which may be involved in the pathogenesis of neurological soft signs (NSS). Yet, the question whether a retarded motor performance may account for these changes remained to be clarified. Twelve DSM-III-R schizophrenics and 12 healthy controls were included. All subjects were right-handed. Nine patients received clozapine, two conventional neuroleptics, and one was drug-free. Functional magnetic resonance imaging (fMRI) was obtained in a resting condition and during pronation/supination at three speed levels (low, medium, and high) with motor performance recorded simultaneously using a pronation/supination device. While measures of motor retardation (i.e., repetition rate and amplitude of the movements) did not differ between patients and controls, the variability of performance was significantly (P < 0.05) increased in the patients' group. In addition, patients with schizophrenia showed a significantly (P < 0.05) decreased activation of the sensorimotor cortices. Similar, although nonsignificant (P = 0.09) activation changes were observed in the SMA. Activation differences were more pronounced at a slow speed and in the drug-free patient. These results confirm a diminished sensorimotor cortex and SMA activation and indicate that variability of performance rather than retarded performance per se may correspond to these changes.

Adult↗
PubMed1999

[Fluid-attenuated-inversion-recovery (FLAIR) imaging in the diagnosis of cerebral gliomas and metastases].

This study demonstrates the value of a fast fluid-attenuated inversion-recovery (FLAIR) technique in the assessment of cerebral gliomas and metastases. Thirty-five patients with cerebral gliomas and 12 patients with a total of 39 cerebral metastases were examined by T2/proton density-weighted fast spin echo, fast FLAIR with and without contrast medium and contrast-enhanced T1-weighted spin echo using identical slice parameters. The images were evaluated using quantitative and qualitative criteria. Quantitative criteria were tumor-to-background and tumor-to-cerebrospinal fluid contrast and contrast-to-noise. The qualitative evaluation was performed as a multireader analysis concerning lesion detection, lesion delineation and image artifacts. In the qualitative evaluation, all readers found fast FLAIR to be superior to fast spin echo in the exact delineation of cerebral tumors (P < 0.001) and the delineation of enhancing and non-enhancing tumor parts. Fast FLAIR was superior in the delineation of cortically located and small lesions but was limited in lesions adjacent to the ventricles. Fast FLAIR provided significantly better tumor-to-CSF contrast and tumor-to-CSF contrast-to-noise (P < 0.001). The tumor-to-background contrast and tumor-to-background contrast-to-noise of the fast FLAIR images were lower than that of T2-weighted spin-echo images but were significantly increased after the application of contrast medium. FLAIR images had a more image artifacts, but these influenced the image interpretation in only two patients. Signal hyperintensities at the ventricular border were present in 92% of the patients. These are common findings in fast FLAIR and should be included in image interpretation.

Brain Neoplasms↗
PubMed1999

[MRI of the kidneys. New diagnostic strategies].

AIM: New diagnostic strategies for evaluation of the kidney by fast MR imaging techniques. MATERIAL AND METHODS: A comprehensive morphologic and functional evaluation of the kidney is proposed using fast MR imaging of renal morphology, multiphase 3D gadolinium MR angiography, MR urography and MR flow measurements. A single MR examination is designed to grade renovascular disease and assess the hemodynamic and functional significance, detect and characterize renal lesions and evaluate the urinary tract. RESULTS: The combined analysis of morphologic and functional data allows reliable assessment of renal artery stenosis, benign and malignant renal masses and diseases of the renal collecting system and ureters, as well as congenital abnormalities in good agreement to the results of conventional imaging modalities. The improved tissue contrast and additional functional information compensates for the disadvantage of a lower spatial resolution. CONCLUSION: Combined morphologic and functional MR examination represents a reliable, non-invasive and cost-effective alternative imaging modality for comprehensive diagnostic evaluation of renal disease.

Acute Kidney Injury↗
PubMed1999

Comparison of diffusion anisotropy measurements in combination with the flair-technique.

Fluid-attenuated inversion recovery (FLAIR) technique offers an effective tool to diminish partial-volume averaging effects from cerebrospinal (CSF) signal with in vivo magnetic resonance imaging. CSF-suppressed and unsuppressed direction-dependent diffusion-weighted (DW) images are obtained with a DW spin-echo EPI sequence in a single acquisition scheme. Comparison of unsuppressed and CSF-suppressed apparent diffusion coefficient (ADC) maps yields consistent values for brain tissue in volunteers when no partial-volume effects are expected, but differs considerably at borders of parenchyma to ventricles and sulci. From theory and phantom studies, a corrected anisotropy index is introduced considering differences of statistical fit errors. Anisotropy of white matter is observed in normal brain of volunteers. Anisotropy index maps reveal destruction of fiber tracts in pathologic areas. Results of a preliminary study on 12 patients with intra-axial tumors indicate an improved delineation of tumor boundaries of FLAIR ADC maps against unsuppressed acquisition.

Adult↗
PubMed1999

High-resolution MR venography of cerebral arteriovenous malformations.

The purpose of this study was to evaluate the diagnostic potential of a high-resolution magnetic resonance (MR) venography technique in patients with cerebral arteriovenous malformations (AVMs). A high-resolution 3D gradient echo sequence was used with a long echo time TE to obtain venous information down to sub-pixel sized vessel diameters of several hundred microns. The method is based on the paramagnetic property of deoxyhemoglobin, and the resulting developing phase difference between veins and brain parenchyma at long echo times which leads to signal cancellation. The reconstructed venograms were compared with time-of-flight (TOF)-MR angiography using qualitative and quantitative criteria with the conventional digital subtraction angiography serving as the reference gold standard. In 17 patients with angiographically proven cerebral AVMs, the method indicates its potential in clinical applications. Venography was able to detect all AVMs whereas TOF-MRA failed in three patients. In the delineation of venous drainage patterns MR venography was superior to TOF-MRA, however, the method failed in the detection of about half of the main feeding arteries, as expected. Due to susceptibility artifacts at air/tissue boundaries and interference with paramagnetic hemosiderin, venography was limited with respect to the delineation of the exact nidus sizes and shapes in ten patients with AVMs located close to the skull base or having suffered from previous bleeding. Although the visualization of draining veins represents an important prerequisite in the surgical and radiosurgical treatment planning of cerebral AVMs, application of high resolution MR venography may be limited in the diagnostic work-up in some of these patients. On the other hand, it may be of special importance in the early detection and assessment of small AVMs that are difficult to diagnose with other MR methods.

Adolescent↗
PubMed1999

Effect of lipid-lowering strategies on tubular cell biology.

BACKGROUND: Interstitial fibrosis and the development of renal cysts are crucial phenomena in renal disease progression. While 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors has been shown to reduce the progression of several experimental nephropathies, the mechanism of their potential protective effect remaines unclear. METHODS: The antiproliferative, apoptotic, and fibrinolytic effects of HMG-CoA reductase inhibitors were assessed in primary cultured rat (rPTCs) and mouse proximal tubule cells (mPTCs), in isolated rat proximal tubules, and in vivo in 5/6 nephrectomized rats (Nx). RESULTS: In vitro, lovastatin inhibited rPTC proliferation in a manner selectively prevented by mevalonate, farnesyl-, or geranylgeranyl-pyrophosphate (FPP or GGPP). Lovastatin reduced membrane-bound p21ras and fetal calf serum-induced c-fos and c-jun protein expression. Gel shift assay showed that lovastatin reduced activated protein-1 (AP-1) binding activity. In vivo, lovastatin inhibited tubular cell proliferation after Nx, as measured by proliferative cell nuclear antigen staining. Lovastatin-treated mPTCs displayed nucleus cleavage and DNA ladder formation, which were prevented by GGPP. Like C3 exoenzyme, lovastatin induced actin filament disruption, which preceded evidence of apoptosis. Lovastatin increased tissue-type plasminogen activator (PA) and decreased PA inhibitor activities and antigens; these effects were prevented by mevalonate and GGPP but not FPP, and were reproduced by C3 exoenzyme in a manner insensitive to GGPP. CONCLUSIONS: HMG-CoA reductase inhibitors decreased proliferation, increased apoptosis, and enhanced fibrinolytic activity of renal tubular cells via modulation of different isoprenylated proteins. These effects could participate to reduce the progression of renal diseases.

Animals↗
PubMed1999

[The simultaneous determination of the arterial input function for dynamic susceptibility-weighted magnetic resonance tomography of the A. carotis interna and the A. cerebri media].

PURPOSE: The determination of the arterial input function (AIF) is necessary for absolute quantification of the regional cerebral blood volume and blood flow using dynamic susceptibility contrast MRI. The suitability of different vessels (ICA--internal carotid artery, MCA--middle cerebral artery) for AIF determination was compared in this study. METHODS: A standard 1.5 T MR system and a simultaneous dual FLASH sequence (TR/TE1/TE2/alpha = 32/15/25/10 degrees) were used to follow a bolus of contrast agent. Slice I was chosen to cut the ICA perpendicularly. Slice II included the MCA. Seventeen data sets from ten subjects were evaluated. RESULTS: The number of AIF-relevant pixels, the area under the AIF and the maximum concentration were all lower when the AIF was determined from the MCA compared to the ICA. Additionally, the mean transit time (MTT) and the time to maximum concentration (TTM) were longer in the MCA, complicating the computerized identification of AIF-relevant pixels. Data from one subject, who was examined five times, demonstrated that the intraindividual variance of the measured parameters was markedly lower than the interpersonal variance. CONCLUSIONS: It appears to be advantageous to measure the AIF in the ICA rather than the MCA.

Adult↗
PubMed1999

Abdominal aortic aneurysm. Detection of multilevel vascular pathology by time-resolved multiphase 3D gadolinium MR angiography: initial report.

OBJECTIVE: To evaluate multiphasic 3D gadolinium-enhanced magnetic resonance angiography (3D-Gd-MRA) for detection of vascular pathology at multiple levels of the aorta and iliac arteries. METHODS: In 18 patients with abdominal aortic aneurysm (n = 13), dissection (n = 3), or both (n = 2), multiphase 3D-Gd-MRA was performed acquiring five consecutive (6.8 seconds) 3D data sets in a single breath-hold. In each of the five time-resolved phases, vessel visibility of the abdominal aortic branches and iliac arteries was assessed. The extent of vessel involvement by the aneurysm or dissection seen on multiphase 3D-Gd-MRA was compared with standard imaging and surgical findings. Digital subtraction angiography was available for comparison in 4 cases, CT angiography in 10 cases. RESULTS: Due to the delayed filling of the aortic aneurysm, the proximal aortic branches and the aneurysm neck demonstrated an inversely related enhancement compared with the distal abdominal and iliac vessels (P < 0.001). Review of all five phases of multiphase 3D-Gd-MRA allowed optimal visualization of each vessel segment without any artifacts due to parenchymal or venous overlay. In dissections, review of three phases was required (P < 0.001) for diagnostic evaluation of the true and false lumens. Substantially more vessel involvement was detected on multiphase 3D-Gd-MRA; this was surgically confirmed in 10 of 11 cases and affected therapy management in 11 of 18 cases. CONCLUSIONS: Multiphase 3D-Gd-MRA is a convenient, robust, and safe technique for presurgical anatomic mapping of complex aortic aneurysms and dissections.

Aortic Dissection↗
PubMed1999

Hepatic lesions: morphologic and functional characterization with multiphase breath-hold 3D gadolinium-enhanced MR angiography--initial results.

PURPOSE: To investigate multiphase (arterial, portal venous, and late venous phases) breath-hold three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) angiography for the detection and functional characterization of hepatic lesions. MATERIALS AND METHODS: Breath-hold fast spoiled gradient-echo 3D gadolinium-enhanced MR angiography was performed in 18 patients with 35 hepatic lesions. Measurements of signal intensity were obtained for 27 seconds in each phase, with 23-second delays between the three phases. Lesion-liver visibilities at each phase on the MR angiographic, precontrast T1-weighted, T2-weighted, and postcontrast T1-weighted images were compared. The MR angiographic functional lesion characterization was based on the combined assessment of spatial variations and the evolution of contrast material enhancement in all three phases. RESULTS: All 35 lesions were correctly characterized on the MR angiographic images, which is significantly (P < .01) better than the precontrast T1-weighted (n = 14 [40%]), T2-weighted (n = 23 [66%]), and postcontrast T1-weighted (n = 25 [71%]) imaging results. Analysis of the spatial variations and the evolution of contrast material enhancement significantly (P < .01) improved lesion characterization in 66% (23 of 35) of all lesions. CONCLUSION: Multiphase breath-hold 3D gadolinium-enhanced MR angiography is feasible and robust and significantly improves the morphologic detection of benign or malignant lesions during the early arterial phase. It further improves the functional characterization of hepatic lesions, combining an arterial, portal-venous, and late MR angiographic phase of contrast enhancement.

Adult↗
PubMed1999

Cerebral gliomas and metastases: assessment with contrast-enhanced fast fluid-attenuated inversion-recovery MR imaging.

The effect of contrast material on fast fluid-attenuated inversion-recovery (FLAIR) magnetic resonance images was evaluated for 16 patients with enhancing gliomas and 12 patients with cerebral metastases. Because of a marked T1 effect, fast FLAIR imaging provided a marked contrast enhancement, resulting in the highest tumor-to-background contrast ratio compared with standard imaging techniques.

Adult↗
PubMed1999

Renal arteries: optimization of three-dimensional gadolinium-enhanced MR angiography with bolus-timing-independent fast multiphase acquisition in a single breath hold.

PURPOSE: To compare two different three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) angiographic techniques. MATERIALS AND METHODS: In 26 patients suspected of having renal artery stenosis, results with fast multiphase 3D MR angiography were compared to those with standard 3D MR angiography in 37 patients. With both techniques, 31-second breath-hold acquisitions were performed. Multiphase angiography comprised five discrete 6.4-second acquisitions without bolus timing, and standard angiography comprised a single acquisition based on test-bolus timing. Two readers evaluated images obtained with both techniques in terms of image quality, artifacts, and vessel conspicuity. Accuracy of findings on the multiphase 3D MR angiograms for assessment of renal artery stenosis was determined by comparing them to digital subtraction angiograms and surgical findings. RESULTS: In the early arterial phase, multiphase 3D MR angiograms showed no image degradation by venous overlay, whereas standard 3D MR angiograms depicted at least minor overlay in 53 of 83 renal arteries (P < .001). Less parenchymal enhancement in the early arterial phase resulted in a higher vessel conspicuity for the divisions and segmental arteries (P < .001). Both readers detected and correctly graded 18 of 20 stenoses on the multiphase angiograms with almost perfect interobserver agreement (kappa > 0.89). CONCLUSION: Renal multiphase 3D MR angiography is an accurate technique requiring no bolus timing. The performance of early arterial phase imaging leads to improved depiction, particularly of the distal renovascular tree, compared to that with standard single-phase 3D MR angiography.

Adult↗
PubMed1998

Assessment of neuropsychological changes in patients with arteriovenous malformation (AVM) after radiosurgery.

PURPOSE: The purpose of this study was to investigate neuropsychological effects of radiosurgery in patients with cerebral arteriovenous malformation (AVM), with special focus on attention and memory. This report describes the study setup and presents the first results during a follow-up of up to 1 year. MATERIALS AND METHODS: Seventy-nine patients were studied before, acutely after radiosurgery, and during the regular follow-up (subacute phase: Weeks 6-12, chronic phase: Months 6-12). Radiosurgery was performed using a modified linear accelerator (minimum doses to the target volume: 15-22 Gy, median 20 Gy). Estimated whole brain dose was 0.5 to 2 Gy. Neuropsychological testing included assessment of general intelligence (Wechsler Adult Intelligence Scale), attention (modified Trail-Making Test A, Digit Symbol Test, D2 Test, Wiener Determination Machine) and memory (Rey Auditory Verbal Learning Test, Benton Visual Retention Test). During follow-up, alternate test versions were used. Neuropsychological deficits were defined as a test score of at least one standard deviation (SD) below the mean of the normal distribution. RESULTS: The pretherapeutic evaluation revealed marked deviations from the normal population; 24% had deficits in intelligence (range 23-31% in different subtests), attention (35%, 23-59%) and memory (48%, 31-61%). The overall percentage of aberrant results was reduced by 12% (memory) to 14% (attention) in the chronic phase up to 12 months after therapy. The improvement in test scores was significant (p < 0.05) in 3 of 4 subtests of attention functions. CONCLUSIONS: The acute tolerance of radiosurgery seems to be very good in these patients, showing no relevant increase in number of patients with neuropsychological deficits. Although the long-term follow-up needs to be further increased, our data indicate a tendency to slight improvement in the overall neuropsychological performance of AVM patients in the chronic phase after radiosurgery.

Adult↗
PubMed1998

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors increase fibrinolytic activity in rat aortic endothelial cells. Role of geranylgeranylation and Rho proteins.

3-Hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitors (HRIs) have been recently shown to prevent atherosclerosis progression. Clinical benefit results from combined actions on various components of the atherosclerotic lesion. This study was designed to identify the effects of HRI on one of these components, the endothelial fibrinolytic system. Aortas isolated from rats treated for 2 days with lovastatin (4 mg/kg body wt per day) showed a 3-fold increase in tissue plasminogen activator (tPA) activity. In a rat aortic endothelial cell line (SVARECs) and in human nontransformed endothelial cells (HUVECs), HRI induced an increase in tPA activity and antigen in a time- and concentration-dependent manner. In SVARECs, the maximal response was observed when cells were incubated for 48 hours with 50 micromol/L HRI. An increase of tPA mRNA was also in evidence. In contrast, HRI inhibited plasminogen activator inhibitor-1 activity and mRNA. The effects of HRI were reversed by mevalonate and geranylgeranyl pyrophosphate, but not by LDL cholesterol and farnesyl pyrophosphate, and were not induced by alpha-hydroxyfarnesyl phosphonic acid, an inhibitor of protein farnesyl transferase. C3 exoenzyme, an inhibitor of the geranylgeranylated-activated Rho protein, reproduced the effect of lovastatin on tPA and plasminogen activator inhibitor-1 activity and blocked its reversal by geranylgeranyl pyrophosphate. The effect of HRI was associated with a disruption of cellular actin filaments without modification of microtubules. A disrupter of actin filaments, cytochalasin D, induced the same effect as lovastatin on tPA, whereas a disrupter of microtubules, nocodazole, did not. In conclusion, HRI can modify the fibrinolytic potential of endothelial cells, likely via inhibition of geranylgeranylated Rho protein and disruption of the actin filaments. The resulting increase of fibrinolytic activity of endothelial cells may contribute to the beneficial effects of HRI in the progression of atherosclerosis.

Animals↗