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Biomedical subjects

A Haase

Publications and source records attributed to A Haase.

At least 91 records · Page 5Linked to original sources
PubMed1998

[3-dimensional echo-enhanced transcranial Doppler ultrasound diagnosis].

Echo-enhancing agents improve the signal intensity of transcranial Doppler signals, enabling a novel approach of three-dimensional transcranial vascular imaging by Doppler ultrasound. The basic principle, system requirements and early clinical results with a custom built system are described. Transcranial color Doppler imaging was performed through the temporal bone acoustic window. During i.v. administration of the transpulmonary stable, galactose-based echo-enhancer Levovist (Schering) the video output of the ultrasound scanner was digitized and the spatial position of the recorded frames was simultaneously registered using a mechanical position sensor. After automatic segmentation of the color information, the 3D datasets were reconstructed offline using a Unix-based workstation (Silicon Graphics). Visualization was achieved by maximum intensity projection or surface visualization techniques. Administration of Levovist resulted in good enhancement of the vascular Doppler signal intensity, enabling acquisition of a 3D dataset of the complete circle of Willis with an imaging window of approximately 3-5 min for one i.v. injection. The vascularity of tumors could be recorded as a 3D dataset and further analyzed. The power Doppler technique with echoenhancement proved a valuable tool for 3D dataset recording. 3D datasets clearly facilitated the diagnosis of the vascular anatomy and lesion vascularity and provided additional information on localization of feeders, vascular displacement and extent of tumor vascularity.

Blood Flow Velocity↗
PubMed1998

Functional magnetic resonance imaging in intact plants--quantitative observation of flow in plant vessels.

Quantitative magnetic resonance (MR) images of flow velocities in intact corn plants were acquired using magnetization-prepared MR microscopy. A phase contrast flow imaging technique was used to quantitate water flow velocities and total volume flow rates in small xylem vessels. The simultaneous measurement of the transpiration of the whole plant was achieved by using a closed climate chamber within the MR magnet. The total volume flow rate and the transpiration values were in close correlation. Functional magnetic resonance imaging in intact plants was performed by light stimulation of the transpiration inside of the magnet. The change in the flow velocities in the xylem vessels of single vascular bundles was in correlation with the changes in the transpiration. Significant differences were observed between the xylem vessels in different vascular bundles. Furthermore, flow velocity measurements were performed on excised plant stems and visualized by the uptake of the MR contrast agent, gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA). A comparison between the phase contrast flow imaging and the contrast media uptake showed to be in good agreement with each other.

Hydroponics↗
PubMed1998

Partial respecification of nasotemporal polarity in double-temporal chick and chimeric chick-quail eyes.

In chick embryos, naso-temporal polarity of the retina becomes established before Hamburger-Hamilton stage 10. To examine the plasticity of the early eye anlage, double-temporal eyes were made using stage 10-11 (E1.5) chick embryos and stage 8-9 quail embryos. In vivo and in vitro experiments revealed that these double-temporal compound eyes were not completely temporal but nasal in a large peripheral part of the graft. Four hours after transplantation, the nasal-specific fork head transcription factor CBF1 was not expressed in double-temporal eyes but was clearly detectable 24 h later. This suggests that in the peripheral part of the graft, temporal positional values were changed into nasal positional values by a respecification process.

Animals↗
PubMed1998

In vitro analysis of the initial tooth mobility in a novel optomechanical set-up.

An optomechanical set-up was developed to accurately measure displacement/force curves of the initial tooth mobility in vitro. The system presented is capable of recording all six components of a tooth movement resulting from an applied orthodontic force system, and consists of a laser diode-based optical part and a six degree of freedom mechanical part. Three laser diodes were mounted in orthogonal arrangement on the tooth of a specimen and their light (lambda = 670 nm) was focused on the surfaces of three position sensing detectors. The laser beams thus defined a cartesian rigid body coordinate system and the movements of the tooth could directly be derived from the movements of the laser spots on the surfaces of the optical detectors. The force system was applied and simultaneously measured via a three-dimensional force-torque transducer mounted on a six-axis positioning table. Measuring accuracy of the tooth displacements was in the range of 9.0 microns and 0.022 deg for translations and rotations, respectively. Resolution and accuracy of the mechanical system was approx. 0.02 N for the measurement of forces and 0.5 Nmm for torques. Displacement/force diagrams of the specimen of a swine's mandible are presented, showing the relationships between applied force system and tooth displacement of the lower first premolar. The accuracy reached proved to be sufficient for the verification of numerical (Finite Element) models of the initial tooth mobility.

Alveolar Process↗
PubMed1998

Evaluation of PCR for diagnosis of melioidosis.

Previously published PCR-based diagnostic tests for melioidosis were evaluated for clinical usefulness. A Burkholderia pseudomallei 16S rRNA-derived primer set had a sensitivity approaching 100% for clinical samples from 22 culture-confirmed cases of melioidosis and enabled diagnosis of 3 culture-negative cases. However, samples from 10 of 30 inpatients from Royal Darwin Hospital with other diagnoses were positive by PCR, giving a specificity of 67% and a positive predictive value of only 70%. Although there are a number of intriguing possible explanations for our results, concerns of inappropriate therapy resulting from a positive result by PCR have led us to forgo the advantage of rapid PCR diagnosis for melioidosis until a better system is validated.

Humans↗
PubMed1998

A cluster of latently expressed genes in Kaposi's sarcoma-associated herpesvirus.

Infection with Kaposi's sarcoma-associated herpesvirus (KSHV) is closely associated with Kaposi's sarcoma (KS) and primary effusion lymphoma, with viral genomes present in a latent state in the majority of tumor cells. Here we describe a cluster of latently expressed viral genes whose mRNAs are generated from a common promoter. Two mRNAs in this region encode the latency-associated nuclear antigen, the product of open reading frame 73 (ORF73). The larger RNA, of 5.8 kb, is an unspliced transcript that includes ORF72 and -71 at its 3' end; it initiates at nucleotides (nt) 127880 to 127886 from a promoter lacking recognizable TATA elements. A less abundant mRNA, of 5.4 kb, is a variant of this transcript, in which 336 nt of 5' noncoding information has been removed by RNA splicing. A third, more abundant RNA is generated from the same promoter region via splicing from the common splice donor at nt 127813 to an acceptor 5' to ORF72; this transcript is the presumed mRNA for ORF72, which encodes the viral cyclin D homolog. All three RNAs are 3' coterminal. In situ hybridization analysis with probes that can detect all three transcripts shows that the RNAs are detectable in a large fraction of BCBL-1 cells prior to lytic induction and in >70% of KS spindle cells in primary KS tumors. This confirms that these transcripts are indeed latent RNAs and suggests a role for their products in viral persistence and/or KSHV-associated proliferation.

Alternative Splicing↗
PubMed1997

Quantitative magnetic resonance imaging of capillary water permeability and regional blood volume with an intravascular MR contrast agent.

A novel method is presented to simultaneously measure the permeability surface area product of water (PS), also known as capillary diffusion capacity, and the regional blood volume (RBV). It is based on magnetic resonance imaging of the longitudinal relaxation times of tissue and blood at different concentrations of an intravascular MR contrast agent. PS and RBV were measured in vivo in different regions of the brain and the skeletal muscle of the rat. The average PS values (n = 5) obtained in cerebral cortex, corpus callosum, hippocampus, thalamus, jaw muscle, and tongue muscle were 3.31 +/- 0.20, 1.81 +/- 0.25, 3.37 +/- 0.36, 3.68 +/- 0.44, 10.6 +/- 1.1, and 14.1 +/- 2.51 ml x min(-1) x g(-1), respectively. The corresponding average RBV values were 1.63 +/- 0.18, 1.22 +/- 0.25, 3.30 +/- 0.37, 3.03 +/- 0.36, 1.66 +/- 0.30, and 1.38 +/- 0.33 ml x 100 g(-1). These results are in good agreement with previously reported literature values obtained by means of autoradiography.

Animals↗
PubMed1997

Real time monitoring of laser-induced thermal changes in cartilage in vitro by using snapshot FLASH.

Snapshot FLASH imaging has been applied to study the spatial and temporal spreading of thermal changes caused by a Holmium:YAG laser in patella cartilage in vitro at 7 T. The temperature dependence of the proton resonance frequency was used to demonstrate the thermal energy deposition. A series of cartilage images, with a time resolution of 512 ms and a spatial resolution of 400 x 200 microm, showed dynamic changes of the temperature-related image phase in the regions irradiated by the laser.

Cartilage, Articular↗
PubMed1997

Motion-adapted gating based on k-space weighting for reduction of respiratory motion artifacts.

A new modified type of gating is presented that shows the ability to reduce the total scan time with almost conserved image quality compared with conventional gating. This new motion-adapted gating approach is based on a k-space-dependent gating threshold function. MR data acquired are only accepted if the motion-induced displacements measured from a reference position are below the chosen gating threshold function. During the MR measurement the scanner analyses respiratory motion decides in real-time which data in k-space could be measured according to the gating threshold function and performs data acquisition. In the present paper the approach will be described and discussed. Simulations based on in vivo data and initial in vivo experiments are presented to compare different variants of the new approach mutually and to the conventional technique. The analysis given is focused on spin warp type sequences, which are the best candidates for this approach.

Abdomen↗
PubMed1997

The effect of perfusion on T1 after slice-selective spin inversion in the isolated cardioplegic rat heart: measurement of a lower bound of intracapillary-extravascular water proton exchange rate.

Many NMR measurements of cardiac microcirculation (perfusion, intramyocardial blood volume) depend on some kind of assumption of intracapillary-extravascular water exchange rate, e.g., fast exchange. The magnitude of this water exchange rate, however, is still unknown. The intention of this study was to determine a lower limit for this exchange rate by investigating the effect of perfusion on relaxation time. Studies were performed in the isolated perfused cardioplegic rat heart. After slice-selective inversion, the spin lattice relaxation rate of myocardium within the slice was studied as a function of perfusion and compared with a mathematical model which predicts relaxation rate as a function of perfusion and intracapillary-extravascular exchange rate. A linear relationship was found between relaxation rate T(-1) and perfusion P normalized by perfusate/tissue partition coefficient of water, lambda: deltaT(-1) = m x deltaP/lambda with 0.82 < or = m < or = 1.06. Insertion of experimental data in the model revealed that a lower bound of the exchange rate from intra- to extravascular space is 6.6 s(-1) (4.5 s(-1), P < 0.05), i.e., the intracapillary lifetime of a water molecule is less than 150 ms (222 ms, P < 0.05). Based on this finding, the T1 mapping after slice-selective inversion could become a valuable noncontrast NMR method to measure variations of perfusion.

Animals↗
PubMed1997

Study of microcirculation by coloured microspheres and NMR-microscopy in isolated rat heart: effect of ischaemia, endothelin-1 and endothelin-1 antagonist BQ 610.

Although the investigation of coronary microcirculation is of great importance, available methods have severe restrictions. They do not allow the study of vasodynamics of resistance vessels and microscopic conductance vessels simultaneously in the isolated beating rat heart. We now demonstrate that the combined measurement of perfusion which reflects the state of resistance vessels and cross-sections of microscopic conductance vessels is feasible in the model of the isolated constant flow perfused rat heart. Perfusion measurement was based on injection of coloured microspheres. Cross-sections of microscopic conductance vessels (diameter >140 micron) were determined by NMR-microscopy by flow weighted imaging. Both methods were established recently by our group. The combined measurement was applied to hearts which were subjected to ischaemia and reperfusion (group 1: n=5, 15 min ischaemia/group 2: n=7, 30 min ischaemia/measurements before ischaemia and 15/30 min after reperfusion), 200 pmol endothelin-1 bolus application (group 3: n=6/measurements before and 5 min after drug application), continuous infusion of the endothelin-1 antagonist BQ 610 (group 4: n=6/measurements before and 20 min after onset of infusion), and 200 pmol endothelin-1 application superimposed on 20 min of continuous BQ 610 infusion (group 5: n=7/combined measurement before BQ 610 infusion and 5 min after endothelin-1 application). In group 1, 15 min reperfusion restored the pre-ischaemic perfusion state, whereas conductance vessels were dilated (80.8+/-2.6%), after 30 min reperfusion pre-ischaemic conditions were also restored for conductance vessels. In group 2, a redistribution of perfusion from left ventricular endocardium to the right ventricular wall was observed. Post-ischaemic rhythm disturbances made NMR-imaging in this group impossible. In group 3, a shift of perfusion from the left ventricular myocardium to the right ventricular wall was observed. Similarly, the cross-section of left ventricular conductance vessels decreased (-32.6+/-2.1%), whereas size of right ventricular vessels increased. In group 4, BQ 610 had no effect on perfusion nor on vessel size and antagonized the effect of endothelin-1 on perfusion and vessel size in group 5.

Animals↗
PubMed1997

Theoretical evaluation and comparison of fast chemical shift imaging methods.

Magnetic resonance chemical shift imaging (CSI) is becoming the method of choice for localized NMR spectroscopic examinations, allowing simultaneous detection of NMR spectra from a large number of voxels. The main limitation of these methods is their long experimental duration. A number of fast CSI experiments have been presented, promising to reduce that duration. In this contribution the criteria for evaluating and optimizing the sensitivity of fast CSI experiments are elaborated. For a typical experiment in the human brain, the performance of various methods is compared. While conventional CSI provides optimal sensitivity per unit time, it is shown in which circumstances fast sequences allow a shorter experimental duration. Using these results, the best method for any experimental requirements can be selected.

Brain Chemistry↗