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Biomedical subjects

M Reiser

Publications and source records attributed to M Reiser.

At least 55 records · Page 3Linked to original sources
PubMed2000

Energy transfer in nonequilibrium space-charge-dominated beams

Space-charge modes similar to those observed in recent experiments appear in simulations of nonequilibrium charged particle beams with anisotropy. The modes couple degrees of freedom, causing energy transfer and equipartitioning without halo formation in just a few betatron wavelengths. The rate depends on a single free parameter quantifying the space-charge intensity of the final state. Traditional stability analyses are shown not to apply to high-intensity laboratory beams originating with a large perturbation from equilibrium.

Journal Article↗
PubMed2000

A comparison of paracentesis and transjugular intrahepatic portosystemic shunting in patients with ascites.

BACKGROUND: In patients with cirrhosis and ascites, creation of a transjugular intrahepatic portosystemic shunt may reduce the ascites and improve renal function. However, the benefit of this procedure as compared with that of large-volume paracentesis is uncertain. METHODS: We randomly assigned 60 patients with cirrhosis and refractory or recurrent ascites (Child-Pugh class B in 42 patients and class C in 18 patients) to treatment with a transjugular shunt (29 patients) or large-volume paracentesis (31 patients). The mean (+/-SD) duration of follow-up was 45+/-16 months among those assigned to shunting and 44+/-18 months among those assigned to paracentesis. The primary outcome was survival without liver transplantation. RESULTS: Among the patients in the shunt group, 15 died and 1 underwent liver transplantation during the study period, as compared with 23 patients and 2 patients, respectively, in the paracentesis group. The probability of survival without liver transplantation was 69 percent at one year and 58 percent at two years in the shunt group, as compared with 52 percent and 32 percent in the paracentesis group (P=0.11 for the overall comparison, by the log-rank test). In a multivariate analysis, treatment with transjugular shunting was independently associated with survival without the need for transplantation (P=0.02). At three months, 61 percent of the patients in the shunt group and 18 percent of those in the paracentesis group had no ascites (P=0.006). The frequency of hepatic encephalopathy was similar in the two groups. Of the patients assigned to paracentesis in whom this procedure was unsuccessful, 10 received a transjugular shunt a mean of 5.5+/-4 months after randomization; 4 had a response to this rescue treatment. CONCLUSIONS: In comparison with large-volume paracentesis, the creation of a transjugular intrahepatic portosystemic shunt can improve the chance of survival without liver transplantation in patients with refractory or recurrent ascites.

Adult↗
PubMed2000

Nonlinear behavior of localized space-charge waves in space-charge dominated electron beams

We present experimental observations of the abnormal growth of localized nonlinear space-charge waves in space-charge dominated electron beams passing through a resistive channel. The energy width of the space-charge waves is measured on both ends of the channel. Previous experiments had shown that, for small initial perturbations, the energy width of the slow waves increases, while the energy width of the fast waves decreases, in agreement with linear theory. We report that in the nonlinear regime (large initial perturbations), the energy width of the fast wave increases, which is unexpected, and, to the best of our knowledge, no theory exists that would predict this phenomenon.

Journal Article↗
PubMed2000

Effect of gradient and section orientation on quantitative analysis of knee joint cartilage.

The object of this study was to determine the influence of the gradient and section orientation on cartilage thickness and volume measurements in the knee joint. Eight specimens were imaged with a fat-suppressed gradient-echo sequence, applying sagittal, transverse, and coronal section orientations. Images were additionally acquired with exchanged gradient directions, and with computed tomography (CT) arthrography. After segmentation and three-dimensional (3D) reconstruction, the volume, the mean, and the maximal 3D cartilage thickness were computed. No effect of changes in the gradient orientation was found, suggesting that susceptibility-induced geometric distortion is not a relevant problem in quantitative cartilage imaging. Sagittal images produced similar data to that obtained with transverse (patella) or coronal (tibia) sections, demonstrating that all knee joint cartilages can be accurately quantified from a single sagittal data set. Whereas no significant systematic deviation between magnetic resonance imaging (MRI) and CT arthrography was recorded in the patella, there was a 10%-15% underestimation of tibial cartilage thickness in MRI.

Cartilage, Articular↗
PubMed2000

Electromyography in MRI--first recordings of peripheral nerve activation caused by fast magnetic field gradients.

Prior studies on the evaluation of stimulation by MRI were based on the subjective feeling of the volunteers. A wide variety of stimulation thresholds between the subjects was observed. In order to exclude subjective perception levels as a cause of this variation, we developed a method to investigate the activation of peripheral nerves after gradient switching by electromyography (EMG) within the MR-imager. Five healthy volunteers were positioned in the MR-scanner with the bridge of the nose at isocenter. The amplitude of sinusoidal pulse trains of the anterior-posterior gradient (rise-times: 200 or 300 micros, various numbers of oscillations) was increased stepwise. Four surface electrodes were placed on the region where a muscle-twitch was reported. Electric activity of the muscle during stimulation experiments was recorded with an MR-compatible electro-physiologic amplifier. Stimulation thresholds were defined by the appearance of an EMG-signal. Thresholds were sharp and consistent with the report of the subjects.

Adult↗
PubMed2000

Optimization and evaluation of the signal intensity change in multisection oxygen-enhanced MR lung imaging.

The behavior of the signal intensity in MRI of human lungs was investigated during inhalation of pure oxygen. Nine volunteers were examined, five using a breath-hold and four using a non-breath-hold technique. Four coronal slices were acquired in each volunteer using an inversion recovery turbo spin-echo sequence. The inversion time of the sequence was optimized for maximum contrast. Breathing of pure oxygen and room air was alternated in the volunteers. Breath-hold and non-breath-hold cases were compared. Breathing pure oxygen lead to a statistically significant signal intensity increase (up to 18%) compared to breathing room air. In addition, T(1) maps were acquired during breathing 100% oxygen and room air. Inhalation of pure oxygen reduced the mean T(1) time of the lungs from 1280 (+/-85) msec to 1224 (+/-139) msec without breath-hold and from 1219 (+/-176) to 1074 (+/-92) msec with breath-hold. Therefore, an optimized sequence and measurement protocol provided significant signal intensity changes utilizing 100% oxygen. Magn Reson Med 43:860-866, 2000.

Adult↗
PubMed2000

Elastic registration of 3D cartilage surfaces from MR image data for detecting local changes in cartilage thickness.

The objective of this work was to develop and validate a computational method for the registration (matching) of 3D cartilage plates from MR image data sets. The technique tracks local cartilage thickness changes over time. A 3D elastic registration technique was applied that identifies corresponding points of the bone-cartilage interface in MR data sets of 3D-reconstructed cartilage plates. In a first rigid preregistration step, the surfaces are aligned, using the principal axes decomposition to correct for different joint positions and orientations in the MR scanner. In a second step, the surfaces are deformed elastically, based on geometric surface features, until they are sufficiently similar to identify corresponding surface points. The method was validated against artificially corrupted cartilage surfaces and MR data obtained from in vivo and in vitro compression experiments. The in vivo reproducibility was tested on patellar data sets of volunteers, with repositioning of the joint in between replicate acquisitions.

Cartilage, Articular↗
PubMed2000

Electroencephalography during functional echo-planar imaging: detection of epileptic spikes using post-processing methods.

EEG has been used to trigger functional MRI of patients with focal epilepsy, but EEG can be obscured by artifacts during MR data acquisition, and no continuous correlation of EEG and MRI has been possible without limiting the image time. Artifacts caused by an MRI sequence were investigated in five healthy subjects, and an EEG of five patients with epileptic discharges was recorded during echo-planar imaging. All interfering frequencies in the EEG were discrete and defined by loop structures in the MRI sequence. In post-processing of the EEG interfering frequencies were automatically detected by comparing the frequency spectra of the EEG recorded before and during imaging. After elimination of interfering frequencies by filters in the time domain or by Fourier transform, reliable spike detection in the EEG recorded during MR data acquisition became feasible, without loss of EEG quality.

Algorithms↗
PubMed2000

Citrulline immunohistochemistry for demonstration of NOS activity in vivo and in vitro.

Nitric oxide (NO), a biomolecule with major cytotoxic potency, is generated by NO synthases (NOS) utilizing l-arginine as substrate and citrulline is formed as a "side product." In brain tissue, citrulline is considered to be produced exclusively by NOS, due to the incomplete urea cycle in the brain. We aimed to characterize NOS activity by citrulline immunostaining in different cell types of the brain under in situ conditions and in slice and culture experiments. NOS-positive neurons and activated microglial cells were the most prominent citrulline-positive structures. Lack of citrulline immunoreaction in neurons of nNOS knockout mice emphasizes the dependency of citrulline positivity on NOS activity, and likewise there was no citrulline staining after application of the NOS inhibitors 7-nitroindazole and NIL. Interestingly, only a portion of NOS-containing neurons costained for citrulline. The inhibition of argininosuccinate synthetase by alpha-methyl-dl-aspartate increased the number of citrulline-positive cells, apparently due to reduction of the turnover rate of citrulline. Cells positive for NOS but negative for citrulline may indicate that the enzyme is either not activated or inhibited by cellular control mechanisms. The fact that not all citrulline-positive cells were NOS positive may be explained by an insufficient detection sensitivity or by disparate sites of citrulline production and recycling. The present results show that citrulline immunocytochemistry offers a viable and convenient means for studying NOS activity at the single-cell level to elicit its posttranslational control under physiological and pathophysiological conditions.

Animals↗
PubMed2000

Diagnosing enteroceles using dynamic magnetic resonance imaging.

PURPOSE: Enteroceles are in part difficult to detect but a frequent finding in pelvic floor disorders. The aim of this study was to evaluate magnetic resonance colpocystorectography in the diagnosis of enteroceles. METHODS: In this prospective study 11 volunteers and 55 patients with pelvic floor descent were examined. In addition to magnetic resonance colpocystorectography, a dynamic cystoproctography was performed on 34 patients. Opacification of organs was used. An enterocele was assessed in relationship to the pubococcygeal reference line (magnetic resonance colpocystorectography) or the width of the rectovaginal space (dynamic cystoproctography). A clinical gynecologic examination served as reference. RESULTS: The clinical examination diagnosed an enterocele in 43, magnetic resonance colpocystorectography in 49, and dynamic cystoproctography in 14 cases. Magnetic resonance colpocystorectography further subdivided the enteroceles according to their contents (mesenteric fat or fluid, 12; small bowel, 32, large bowel, 3; and rectosigmoidocele, 2). Magnetic resonance colpocystorectography proved statistically significantly superior to dynamic cystoproctography (15 cases) and the reference. Sensitivity and specificity of magnetic resonance colpocystorectography were 100 percent each. It was able to reveal clinically missed enteroceles as being peritoneoceles associated with a rectocele or a uterovaginal prolapse (10 cases). CONCLUSION: Magnetic resonance colpocystorectography is a promising method for diagnosis of enteroceles, because hernial canal, sac, and contents are reliably identified.

Adult↗
PubMed2000

[Diagnostic imaging in cardiac diagnosis].

PURPOSE: Cardiac imaging includes determination of the size and structure of the cardiac chambers, valves, great vessels and the coronary arteries, chamber and valvular function, myocardial perfusion, viability and metabolism. MATERIAL AND METHODS: Chest roentgenography, angiography, echocardiography and nuclear imaging are commonly used but computed tomography and magnetic resonance imaging also offer a promising potential. RESULTS: Coronary angiography is the gold standard in assessing coronary anatomy. Fast CT technologies such as electron-beam and multi-low-CT are promising non-invasive imaging modalities in the assessment of coronary artery disease. With intravascular ultrasound early stages of coronary atherosclerosis can be detected. For the assessment of myocardial perfusion and viability as well as cardiac function, scintigraphic methods are widely accepted. However, MRI methods have also reached a high degree of accuracy. Evaluation of chamber and valvular function is, due to its wide availability, the field of echocardiography. CONCLUSIONS: In clinical routine chest roentgenography, angiography, echocardiography and nuclear imaging are well established. The value of computed tomography and magnetic resonance imaging in the evaluation of coronary artery disease, myocardial perfusion, viability and metabolism is yet to be defined.

Coronary Disease↗
PubMed2000

[Myocardial perfusion at rest and during stress. MR signal characteristics of persistent and reversible myocardial ischemia].

AIM: Performance of combined rest/stress MR perfusion studies and the analysis of qualitative signal intensity parameters in comparison with 99mTc-SestaMIBI SPECT in patients with known coronary artery disease (CAD). METHODS: Sixteen patients with CAD underwent MR myocardial perfusion assessment at rest and after dipyridamole-induced hyperemia. Qualitative parameters (SI increase, SI upslope) of the SI time-curves were evaluated and characteristics of normal, reversible and persistent hypoperfused myocardium as assessed by 99mTc-SestaMIBI SPECT were compared. RESULTS: Compared with the rest values, normal myocardium showed a significant increase of the SI upslope during hyperemia (P < 0.001), whereas persistent (P = 0.07) and reversible (P = 0.15) hypo-perfusions showed only minor changes. SI increase over baseline also showed a significant increase only in normal myocardium (P < 0.001). At rest, reversible ischemic areas showed no significant differences from normal myocardium, whereas during hyperemia SI increase was significantly lower (P = 0.02). CONCLUSIONS: Qualitative SI parameters of a combined rest/stress MR myocardial perfusion study allow to differentiate normal from reversibly or persistently hypoperfused myocardium.

Adult↗
PubMed2000

[Virtual coloscopy with multi-slice computerized tomography. Preliminary results].

SUBJECT: Using multi-slice computed tomography (MSCT) large body areas can scanned with high spatial resolution. In this study, MSCT was employed for virtual colonoscopy in various pathologies of the colon. MATERIALS AND METHODS: For MSCT a Somatom Plus 4, Volume Zoom scanner, (Siemens, Forchheim) was employed, equipped with four parallel detector rows. Twenty-five patients were included in this trial, prior to colonoscopy or partial colon resection. After cleaning the colon, distension was achieved by insufflation of room air using a rectal tube. The parameters of acquisition and reconstruction were as follows: collimation 4 x 1 mm and 4 x 2.5 mm respectively; tube charge per slice: 140-160 mAs; pitch 5-6; i.v. contrast medium: 120 ml Ultravist 300 (Schering) with a flow rate of 3 ml/s; delay: 35 s. For 3D reconstruction we used edge-enhanced volume rendering, virtual colonoscopy and extraluminal views of volume-rendered images. RESULTS: Nine polyps and four of five colon carcinomas were detected using MSCT virtual colonoscopy. In three patients with ulcerative colitis virtual coloscopy revealed morphological alterations compatible with this disease. In two of four patients with multiple diverticula of the colon the true extent of the disorder could be assessed in virtual colonoscopy. CONCLUSION: Utilizing virtual MSCT colonoscopy polyps and cancer of the colon can be reliably detected, if proper cleaning and distension is provided. On axial images alone smaller polyps may be assessed. The high z-axis resolution of MSCT offers superior conditions for CT-based virtual colonoscopy.

Colitis, Ulcerative↗
PubMed2000

[Functional MRI of the pelvic floor: its normal anatomy and pathological findings].

PURPOSE: Functional MRI of the pelvic floor allows mapping and definition of different forms of pelvic floor dysfunction. METHODS: We performed functional MRT of the pelvic floor in 39 healthy nulliparas and 324 patients. The diagnosis of a pathological organ descent was made if certain landmarks of the pelvic floor compartments descended below the pubococcygeal reference-line (PC-line). RESULTS: If there was no organ descent below the PC-line on straining and if the pelvic floor muscles hardly changed position, a normal finding was diagnosed. 70% of organ prolapses came in the combined form. The generally gradual development of an organ descent led to a change of the main finding in 21.6%. The masking of a cystocele (48.6%) or of an enterocele (34.3%) by a rectocele was most frequent in these cases. DISCUSSION: The use of functional MRI of the pelvic floor appears to be especially useful in young patients, in cases of divergent clinical and sonographic or radiological findings and if the presence of a predominant hernial sac with or without enterocele/rectocele is supposed.

Adolescent↗
PubMed2000

[Functional MRI of the pelvic floor. The methods and reference values].

PURPOSE: Functional cine MRI of the pelvic floor is a yet another modality in addition to various radiological fluoroscopic techniques. This article describes our own method in view of the recent literature and provides morphometric reference values. MATERIAL AND METHOD: We examined 20 nulliparous women (range of age: 25-51 years) with normal findings in the gynecological and urodynamic examination. Functional cine MRI was performed on a 1.5 Tesla equipment after opacification of the vagina and rectum. We used a T2-weighted gradient-echo sequence (Ture-FISP) to determine the position of the reference organs at rest and during straining/defecation. Two different reference lines were used. In addition 29 morphometric and functional parameters were measured, all of them being observer independent. RESULTS: Functional cine MRI was able to show the extent and interaction of the pelvic floor organs in all cases with the reference organs always remaining above the pubococcygeal reference line. The depth of the rectocele was 2 cm. With the exception of the diameter of urogenital hiatus the different parts of the levator ani muscle could not be determined. DISCUSSION: Functional cine MRI using an appropriate organ opacification and slice positioning is an objective, unifying diagnostic approach of the pelvic floor. The reference data given can be of help to distinguish normal from abnormal findings.

Adult↗
PubMed2000

[Chronic infections of the skeletal system. Their imaging diagnosis].

The diagnosis of chronic osteomyelitis is made on the basis of clinical, radiologic and histologic findings. The role of imaging in patients with known chronic osteomyelitis is to detect and to delineate areas of active infection. To correctly interpret the imaging findings, it is essential to take both the individual clinical findings and previous imaging studies into account. Reliable signs of active infection are bone marrow abscess, sequestra and sinus tract formation. Only the combined evaluation of bony changes together with alterations of the adjacent soft tissues provides good diagnostic accuracy. Projection radiography gives an overview of the condition of the bone, which provides the basis for follow-up and the selection of further imaging modalities. Computed tomography can be used to evaluate even discrete or complex bony alterations and to guide percutaneous biopsy or drainage. Magnetic resonance imaging achieves the best diagnostic sensitivity and specificity and provides superior contrast as well as anatomical resolution in both bone marrow and soft tissues. In this paper the features and clinical relevance of imaging in primary chronic osteomyelitis, posttraumatic osteomyelitis, tuberculous spondylitis and osteomyelitis of the diabetic foot are reviewed, with particular respect to MRI.

Bone Diseases↗