Biomedical subjects

S E Fischer

Publications and source records attributed to S E Fischer.

31 records · Page 2Linked to original sources

PubMed1997

Target choice determinants of the Tc1 transposon of Caenorhabditis elegans.

The Tc1 transposon of Caenorhabditis elegans always integrates into the sequence TA, but some TA sites are preferred to others. We investigated a TA target site from the gpa-2 gene of C.elegans that was previously found to be preferred (hot) for Tc1 integration in vivo . This site with its immediate flanks was cloned into a plasmid, and remained hot in vitro , showing that sequences immediately adjacent to the TA dinucleotide determine this target choice. Further deletion mapping and mutagenesis showed that a 4 bp sequence on one side of the TA is sufficient to make a site hot; this sequence nicely fits the previously identified Tc1 consensus sequence for integration. In addition, we found a second type of hot site: this site is only preferred for integration when the target DNA is supercoiled, not when it is relaxed. Excision frequencies were relatively independent of the flanking sequences. The distribution of Tc1 insertions into a plasmid was similar when we used nuclear extracts or purified Tc1 transposase in vitro , showing that the Tc1 transposase is the protein responsible for the target choice.

Animals↗

PubMed1997

[Determining heart muscle perfusion by magnetic resonance tomography progressing to clinical application].

Magnetic resonance imaging detects the flow of contrast-enhanced blood and even allows the quantitative assessment of myocardial perfusion. The clinical application of this method is being held back by the difficulties in image evaluation and the limitation of standard techniques to the acquisition of a single slice per heart beat cycle. Recent developments in scanner hardware as well as in image acquisition techniques open up the possibility of assessing myocardial perfusion over the entire heart with a spatial resolution in the range of 2 mm. As an example of such a new scanning strategy, a segmented gradient-echo recalled echo planar imaging sequence with preceding saturation is discussed and results in a patient with an infarction are presented. The clinical use of perfusion assessment covering the entire heart for the diagnosis of coronary artery disease is enhanced by the flexibility of magnetic resonance imaging for the assessment of functional cardiac parameters.

Computer Systems↗

PubMed1997

High-frequency ultrasonic detection of thrombi with a targeted contrast system.

Site-targeted acoustic contrast agents used in conjunction with high-frequency intravascular ultrasound have the potential to localize and characterize intravascular pathology. The present study quantifies the utility of a novel, site-targeted ultrasonic contrast agent with high-frequency ultrasound (30 to 50 MHz) and demonstrates the feasibility of the new agent for augmenting detection of targeted pathology with intravascular ultrasonic catheters. High-frequency acoustic microscopy was used to image avidinconjugated nitrocellulose membranes after exposure to a control or biotinylated contrast agent. Increases (p < 0.05) in backscattered power of approximately 66 dB (4-fold) were found for the biotinylated, but not the control contrast agent. Intravascular ultrasonic images (30 MHz nominal center frequency) of plasma clots after exposure to the targeted contrast agent were brighter (p < 0.05) than in controls. These results demonstrate high-frequency acoustic enhancement with a novel targeted contrast agent and may extend the potential diagnostic spectrum of intravascular ultrasound.

Avidin↗

PubMed1997

Effect of prolonged dissociation on the subjective measurement of near heterophoria.

Previous studies have demonstrated that vergence adaptation resulting from the prolonged decay of slow fusional vergence may prevent the accurate assessment of oculomotor deviations. Continuing changes in heterophoria have been reported after 27 days of monocular occlusion. However, since most slow fusional vergence will decay within the first few minutes of dissociation, a clinical assessment of both vergence adaptation and heterophoria could be made more rapidly. This report documents two investigations which examined changes in near horizontal heterophoria during 30 min and 180 min of continuous dissociation, respectively. Seven out of the 16 subjects exhibited significant changes in heterophoria during the 30 min dissociation period, with a mean increase in exophoria of 3.4 delta. The decay of slow fusional vergence took approximately 25 min to reach completion. Thus in the clinical setting, both the degree of vergence adaptation and a more accurate assessment of heterophoria may be obtained by maintaining dissociation for 25 min. Furthermore, the presence of vergence adaptation can be assessed after just 5 min of dissociation.

Adult↗

PubMed1996

Massive intracranial immature teratoma. Report of a case with polyhidramnios and intense pelvic pain.

A case of massive intracranial immature teratoma in a female stillborn is reported. She was the product of the second pregnancy of a 25-year-old healthy woman. The pregnancy was unremarkable until the 25th week of gestation when the mother noticed a rapid enlargement of her abdomen and intense pelvic pain. Because of the pain, a cesarean section was indicated, and a stillborn weighing 2750g with macrocephaly was delivered. The cranial contents weighed 1350g and showed a huge tumoral mass with only a rim of normal brain. A histologic diagnosis of immature teratoma was made. Massive intracranial teratomas are rare tumors and their occurrence in intrauterine life is even rarer. Their histogenesis is unknown, and there is no explanation for their continuous growth during embryogenesis. A prenatal diagnosis of this rare condition can be made by ultrasound, computed tomography, or magnetic resonance imaging.

Adult↗

PubMed1995

Limitations of stimulated echo acquisition mode (STEAM) techniques in cardiac applications.

Stimulated echoes are widely used for imaging functional tissue parameters such as diffusion coefficient, perfusion, and flow rates. They are potentially interesting for the assessment of various cardiac functions. However, severe limitations of the stimulated echo acquisition mode occur, which are related to the special dynamic properties of the beating heart and flowing blood. To the well-known signal decay due to longitudinal relaxation and through-plane motion between the preparation and the read-out period of the stimulated echoes, additional signal loss is often observed. As the prepared magnetization is fixed with respect to the tissue, this signal loss is caused by the tissue deformation during the cardiac cycle, which leads to a modification of the modulation frequency of the magnetization. These effects are theoretically derived and corroborated by phantom and in vivo experiments.

Blood Flow Velocity↗

PubMed1994

True myocardial motion tracking.

Myocardial tagging is a powerful tool for the assessment of in-plane cardiac motion. However, for previous myocardial tagging techniques, the imaged slice is fixed with respect to the magnet coordinate system. Thus, images acquired at different heart phases do not always represent the same slice of the myocardium. A new myocardial tagging technique is presented, which takes the through-plane motion into consideration. It involves tagging of the desired myocardial slice and applying a subtraction imaging technique to image just that part of the myocardium. The examination time can be reduced considerably by the acquisition of two one-dimensionally tagged images. To increase the signal-to-noise ratio especially at later heart phases, variable imaging RF excitation flip angles are applied. To reduce motion artifacts a repetitive breathhold scheme was applied. In vivo results demonstrate that the tags can be accurately tracked within the entire heart period with a temporal resolution of 35 ms, even at a top basal level of the heart and right ventricle.

Algorithms↗

PubMed1994

Real-time image reconstruction system for interventional magnetic resonance surgery.

Interventional surgery techniques under the control of fast acquired magnetic resonance (MR) images may become important in interventional radiology in the near future. One of the components needed for an interventional MR scanner is the real-time reconstruction of the acquired MR images. However up to now no real-time reconstruction systems are readily available for MR images. Therefore a reconstruction device was developed, which allows reconstruction and display of MR images with a delay of less than 50 ms. Additional to the high performance, the main characteristics of the presented device are its full compatibility with different MR acquisition techniques and its moderate cost. The device can be operated with most types of commercial scanners. It is especially suited for interventional MR systems but has also applications with conventional MR scanners.

Cost-Benefit Analysis↗

PubMed1993

Improved myocardial tagging contrast.

Myocardial tagging is a new noninvasive MRI method that allows the study of myocardial motion with high accuracy. However, with conventional tagging techniques tagging contrast is impaired at later heart phases due to longitudinal relaxation. An improved method, called Complementary SPAtial Modulation of Magnetization (CSPAMM), which separates the component of the magnetization with the tagging information from the relaxed component by subtraction of two measurements with first a positive and then a negative tagging grid, is presented. This technique improves the grid contrast and greatly facilitates the automatic evaluation of the myocardial motion. Thus the motion assessment of the entire heart cycle becomes possible. The improvements are documented by numerical simulations and by experiments on phantoms and on human volunteers.

Heart↗

PubMed1992

Evaluation of left ventricular segmental wall motion in hypertrophic cardiomyopathy with myocardial tagging.

BACKGROUND: Segmental wall motion was assessed noninvasively in eight patients with hypertrophic cardiomyopathy and six healthy volunteers by magnetic resonance myocardial tagging. METHODS AND RESULTS: Localization scans were performed for determination of the true short-axis views of the left ventricle (double-angulated view). Spatial modulation of magnetization was used to produce a rectangular grid of landmarks. Distortion of the grid was assessed at end diastole, mid systole, and end systole with multiphase gradient echoes. Image sets were acquired at three different planes, namely, the base, the equator, and the apex. Quantitative evaluation was carried out by computer-assisted image analysis. Each individual grid crossing point was identified automatically and the displacement calculated. A polar coordinate system with the center of gravity as motion reference point was chosen to assess fractional rotation and radial displacement at the endocardial, midwall, and epicardial layers of the septal, anterior, posterior, and inferior regions. A wringing motion of the left ventricle with a clockwise rotation of 5.0 +/- 2.4 degrees at the base and a counterclockwise rotation of -9.6 +/- 2.9 degrees at the apex was observed in control subjects. An equal rotation of 5.0 +/- 2.5 degrees at the base and a slightly reduced rotation of -7.3 +/- 5.2 degrees at the apex was found in patients with hypertrophic cardiomyopathy. A transmural gradient in fractional rotation and radial displacement was observed, with the highest values in the endocardial layer. Rotation in patients with hypertrophic cardiomyopathy was significantly less than in normal volunteers in the posterior region of the equatorial and apical planes. Furthermore, radial displacement was significantly reduced in the septum and inferior wall. In the anterior and posterior wall segments, a reduction of the radial displacement was observed only in the epicardium and midwall layers. CONCLUSIONS: Magnetic resonance myocardial tagging allows the noninvasive assessment of regional wall motion. Both in normal volunteers and in patients with hypertrophic cardiomyopathies, cardiac motion occurs in a complex mode, with the base and the apex rotating in opposite directions and the equatorial plane as a transitional zone (wringing motion). A reduced cardiac rotation can be observed in patients with hypertrophic cardiomyopathy mainly in the posterior region, whereas a reduced radial displacement is found in the inferior septal zone.

Adult↗

PubMed1991

Non invasive measurement of myocardial motion using magnetic resonance tagging.

Magnetic resonance imaging has become a key modality within the modern radiology department. In addition to the conventional slice images, three dimensional angiographic images, and quantitative flow measurements can be obtained. More recently methods have been developed which enable one to visualize the motion of objects through the application of magnetic resonance markers or tags. Generally the myocardium appears homogeneous with respect to magnetic resonance imaging. Thus at best the displacement of the myocardial surfaces can be observed, but rotational and shear motions are not discernable. With magnetic resonance tagging this all changing. Tagging involves modifying the ability of the tissue to produce a nuclear magnetic resonance signal, in a spatially dependent manner. Typically the pattern is a grid of reduced signal intensity. The tagging grid is applied prior to the heart contraction. Then images are made during systole and diastole. The rotation and shear of the myocardium can be inferred from the distortions of the tagging grid. Here our work in this field is reviewed.

Heart Diseases↗

PubMedDate not supplied

Acquisition and evaluation of tagged magnetic resonance images of the human left ventricle.

Magnetic resonance myocardial tagging was used to noninvasively analyze the complicated contraction pattern of the human cardiac left ventricle. The tagging and imaging sequence was optimized to obtain three to four double-angulated short-axis views during systole. The image contrast between labeled and unlabeled tissue was sufficient to apply a semiautomatic image evaluation procedure. In accordance with the invasively achieved findings of other groups, the measurements indicate a wringing motion of the left ventricle, with a clockwise twist at the heartbase and a contrary rotation at the apical level.

Cardiomyopathy, Hypertrophic↗

PubMedDate not supplied

Quantification of the local heartwall motion by magnetic resonance myocardial tagging.

Sophisticated magnetic resonance tagging techniques provide powerful tools for the non-invasive assessment of the local heartwall motion towards a deeper fundamental understanding of local heart function. For the extraction of motion data from the time series of magnetic resonance tagged images and for the visualization of the local heartwall motion a new image analysis procedure has been developed. New parameters have been derived which allows quantification of the motion patterns and are highly sensitive to any changes in these patterns. The new procedure has been applied for heart motion analysis in healthy volunteers and in patient collectives with different heart diseases. The achieved results are summarized and discussed.

Algorithms↗