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Biomedical subjects

A Haase

Publications and source records attributed to A Haase.

At least 163 records · Page 9Linked to original sources
PubMed1990

Snapshot FLASH MRI. Applications to T1, T2, and chemical-shift imaging.

Snapshot FLASH magnetic resonance imaging techniques have been developed to enable real-time imaging of MR parameters. The first realization of the method is based on a 64 X 128 FLASH tomogram acquired within 200 ms, using improved MR system hardware conditions. The soft tissue contrast obtained in FLASH MRI almost disappears by using flip angles of less than 5 degrees and repetition times of 3 ms. This work describes extensions of FLASH MRI placing conventional MR experiments before the whole imaging sequence. This creates images of any desired contrast without changing the measuring time. Examples of inversion-recovery T1, spin-echo T2, chemical-shift-selective, and spectroscopic FLASH MRI are presented. Further extensions to real-time MRI of blood vessels, diffusion coefficients, combination with two-dimensional MR spectroscopy experiments, and other nuclei are discussed.

Humans↗
PubMed1990

3D-snapshot flash NMR imaging of the human heart.

SNAPSHOT-FLASH is a recently developed, ultrafast imaging technique, based on conventional FLASH imaging. The application of this new variant to 3D imaging allows the acquisition of a 128 x 128 x 32 data set in 12.5 seconds without triggering, or for cardiac imaging with gating within 32 heartbeats. Compared to standard 3D-FLASH this is 128 times faster, because triggering is only required when the 3D phase-encoding gradient is incremented. The method depicts for the first time fast three-dimensional views of the human heart without motional artifacts. The images are spin-density weighted. Using suitable prepulses any desired T1- or T2-contrast may be achieved. The generation of 3D movies is possible without an increase of the total scan time.

Heart↗
PubMed1990

Nucleotide sequence analysis of a provirus derived from an individual with tropical spastic paraparesis.

Human T-cell lymphotropic virus type 1 (HTLV-1), the cause of inapparent infections and T-cell leukemias and lymphomas, has also been implicated in two chronic neurological diseases, tropical spastic paraparesis (TSP) and HTLV-1 associated myelopathy (HAM). We initiated a search for a neurotropic variant of HTLV-1 that might be responsible for these chronic progressive myelopathies by cloning and sequencing a provirus from a T-cell line from an individual with TSP. The LTRs and genes of the TSP provirus differ from HTLV-1 by 20-30 nucleotides in each region, but none of the substitutions ostensibly affect functional sites with the exception of the env gene. We document one substitution in the region encoding gp46 common to TSP and HAM proviruses and a mutation that introduces two stop codons in the region encoding gp21. The latter should delete about 100 amino acids from the transmembrane anchor, and, for this reason, the progeny of the sequenced provirus are likely to be defective viruses, maintained in the culture through coinfection of cells with wild-type non-defective HTLV-1. While defective viruses could be responsible for persistent infection of the nervous system in TSP, this cannot be generally the case as we show that HTLV-1 DNA amplified from cell lines from two other individuals with TSP lacked the stop codons. Similarly, comparisons of DNA amplified from HTLV-1 DNA in cases of ATL, HAM, and TSP did not establish a correlation between the mutation in gp46 and neurological disease. The issue of neurotropic variants in HTLV-1 associated neurological disease thus remains an open one which may be resolved in the future by examining proviruses in cells in the lesions in the nervous system; or proviruses in ATL and HAM/TSP which differ in their ability to replicate in glial or neuronal cells.

Amino Acid Sequence↗
PubMed1990

Cardiac and vascular imaging with an MR snapshot technique.

Real-time vascular and cardiac magnetic resonance (MR) imaging has been reported only with echo-planar imaging. In this study, the fast low-angle shot (FLASH) MR imaging sequence was reduced to repetition times of 3 msec and echo times of less than 1.3 msec with use of an improved MR imaging system. The resulting 200-msec MR images (64 X 128 pixels) are called snapshot FLASH images. They allow measurements from dynamic series of MR images depicting processes such as relaxation behavior and the cardiac cycle in the absence of motion and flow artifacts. In animal studies (at 4.7 T) and in studies of human volunteers (at 2.0 T), vascular and cardiac snapshot FLASH images were obtained as a single shot, as reconstructed motion, and as real-time movies. The arbitrary and fast T1 contrast of these images and the reduction of motion artifacts result in favorable applications for the depiction of myocardial and great-vessel anatomy. These clinical applications can be performed on conventional MR imagers with minor technical modifications.

Animals↗
PubMed1990

The 3'-flanking region shared by the human apolipoprotein AI and CIII gene regulates gene expression in cooperation with 5'-flanking elements.

The genes of the apolipoproteins AI and CIII are localized in opposite orientation on chromosome 11 in close vicinity, separated from each other by a non-coding intergenic region of 2.1 kb. The interdependence of their expression has been studied in cotransfection experiments in Hep G2 cells. An expression vector harboring the intergenic region with CAT as reporter gene and likewise pUC 19 derivatives with the putative cis-elements were constructed. Inhibition of gene expression by 5'-flanking elements of the apo AI and CIII gene was observed. Four proteins have been identified in nuclear extracts of Hep G2 cells that bind to several sequences of the intergenic domain but not to the 5'-flanking regions of apo AI or CIII gene. These proteins might be responsible for the silencer effect. The pathway of the regulation of apo CIII and AI expression derived from the experiments described here is supported by mutations in the intergenic region, leading to the phenotype of hypertriglyceridemia, and the stimulatory effect of cholesterol on apo AI transcription in Hep G2 cells.

Apolipoprotein A-I↗
PubMed1990

[Diagnosis of oropharyngeal function with FLASH-MR tomography].

Magnetic resonance imaging (MRI) has several advantages over conventional X-ray methods: the patient is not exposed to radiation; images of any chosen level can be taken without changing the position of the patient; soft tissues are well differentiated; and artefacts due to dental materials are avoided. Thus, in certain fields of ENT diagnosis MRI is superior to computed tomography, for example, in the imaging of acoustic neuromas, glomus tumours and tumours of the parotids, oropharynx and orbit. The measuring time per slice image, which was previously measured in minutes, has been reduced by a factor up to 1000 by the FLASH (fast low angle shot) technique. Thus, it is now possible to follow human physiological processes on an MRI film with a frame speed of 5 pictures using a whole-body magnet. Films of speech, tongue movements and the act of swallowing reveal the value of this technique for the functional diagnosis of disease of the oropharynx. Precise imaging of the anatomical and functional situation, especially of soft tissues, is superior to that of previous methods such as ultrasound, X-ray, and endoscopy.

Deglutition↗
PubMed1989

Variable excitation angle AFP pulses.

RF pulses employing the principle of adiabatic fast passage are finding increasing application with surface coils. A small modification to existing AFP pulses that allows the excitation angle to be chosen largely independently of B1 strength is described here. Rapid 3D imaging applications of such pulses are presented.

Diagnostic Imaging↗
PubMed1988

31P FLASH NMR imaging.

A method of 31P FLASH NMR imaging is described using a low flip angle excitation pulse and three-dimensional Fourier transform spectroscopic imaging (3DFT). In vivo high-resolution 31P NMR spectra are obtained for each of 32 x 32 image elements using a minimum measuring time of 1.5 min. 31P FLASH images of a rat showing the spatial distribution of phosphocreatine, alpha-, beta-, and gamma-ATP have been measured in a 4.7-T magnet with a spatial resolution of 6 mm.

Adenosine Triphosphate↗
PubMed1988

Expression of the human serum apolipoprotein AI and AII genes in Xenopus laevis oocytes. Lipid-associated secretion of gene products.

The two major apolipoproteins of plasma high-density lipoproteins (HDL) are apolipoprotein AI (apo AI) and AII (apo AII). The apo AI and the correctly oriented apo CIII genes separated by 2.6 kb were obtained by fusion of two human lambda-genomic clones. The apo AII gene was isolated as a 3 kb clone. These apolipoprotein genes have been injected independently and together into Xenopus laevis oocytes and their expression studied. Both apolipoprotein genes were transcribed and translated into their preproforms and processed in Xenopus laevis oocytes to their proforms. They were secreted into the medium associated with newly synthesized phospholipids and neutral lipids as particles floating in the high-density lipoprotein range between 1.12 and 1.21 g/ml. Secreted apo AI is associated mainly with newly synthesized phosphatidylethanolamine and little triglyceride, apo AII with phosphatidylethanolamine, lysophosphatidylethanolamine and neutral lipids. Simultaneous injection of the apo AI and apo AII genes led to the secretion of both apoproteins which separated into two bands during CsCl-density gradient centrifugation. The heavier particles were associated with proapo AI and AII, phosphatidylethanolamine (greater than 90%) and traces of lysophosphatidylethanolamine as lipid components. Proapo AII was immunoprecipitated from the less dense fraction and found to be mainly associated with lysophosphatidylethanolamine. Radiolabelled newly synthesized apolipoproteins in secreted particles were characterized by immunoprecipitation after delipidation of the secreted lipoprotein particles. The oocyte-system proved very suitable for studies of the expression of serum apolipoprotein genes, the assembly of the apolipoproteins with specific lipids to lipoprotein particles and their secretion.

Animals↗
PubMed1987

SYS-FLASH. Systemic saturation in FLASH MR imaging.

A simple modification of FLASH (Fast Low Angle SHot) MR imaging, which results in a variable reduction of the intensity of flowing blood and flow artifacts in transaxial tomograms, is reported. Here a nonselective radiofrequency pulse of variable flip angle is used before the acquisition of each projection in FLASH imaging to saturate flowing blood within the whole volume (SYstemic Saturation = SYS-FLASH).

Abdomen↗
PubMed1987

Flow suppression in rapid FLASH NMR images.

Rapid FLASH (fast low angle shot) NMR images are very sensitive to flow phenomena. In particular, a steady reflow of unsaturated spins from outside the imaging plane results in high image intensities which depend on the flip angle, the repetition time, and the flow velocity. Here we describe a technique that suppresses these signals by saturating remote spins prior to entering the imaging plane, e.g., by intercalating the FLASH sequence with slice-selective 1-2-1 pulse packages. Experiments have been carried out on phantoms and human extremities. Flow artifacts in the phase-encoding direction of the images are strongly reduced. Vascular structures may be easily delineated using difference images obtained with and without flow suppression.

Arm↗
PubMed1987

ECG-triggered arterial FLASH-MR flow measurement using an external standard.

In ECG-triggered FLASH-MR images, the inflow of unsaturated spins into the imaging plane results in the reproducible delineation of time variant flow in the arterial system. With the additional acquisition of an external reference image upstream the arterial vessel under investigation, the quantification of flow is possible with the FLASH-MR sequence in one measurement. The method allows the rapid measurement of arterial flow at least in great vessels.

Aorta, Abdominal↗
PubMed1987

Biophysica and medical aspects of fast NMR-imaging.

Nuclear magnetic resonance (NMR) imaging is a promising new technique for non-invasive medical diagnosis. Following a decade of technical improvements and preliminary medical experiences, the measuring time of several minutes remained the major drawback of the method. The recent development of a fast NMR-imaging technique, the so-called FLASH (Fast Low Angle SHot) method, opens a new field of medical applications. This article deals with a few applications and aspects of FLASH imaging. Using the technique cross-sectional images can be taken within a few seconds without loss in spatial resolution. Therefore dynamic investigations of the function of internal organs and images of blood vessels become possible. Furthermore three-dimensional volume imaging of the whole object provides the full anatomical information. FLASH imaging is also applicable in combination with localized NMR-spectroscopy. Thus, biochemical information from NMR-spectroscopy and structural and functional information from NMR-tomography can easily be combined.

Fourier Analysis↗