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PubMedDate not supplied

Efficacy of contrast medium use for neuroimaging at 3.0 T: utility of IR-FSE compared to other T1-weighted pulse sequences.

As inversion-recovery (IR) technique improves T1 contrast at high field strength, signal enhancement by T1-shortening contrast media may be affected. To clarify the different enhancement properties at 3.0 T, the authors compared T1-weighted sequences. Twelve contrast-enhancing lesions were investigated by spin-echo (SE), inversion recovery fast spin-echo (IR-FSE), two-dimensional gradient-echo (2D GE), and magnetization-prepared three-dimensional gradient-echo (3D GE) sequences and evaluated by comparing signal-intensity enhancements within the lesions. In addition, signal-to-noise-ratios (SNR) and contrast-to-noise-ratios (CNR) were measured. On average, signal enhancement of the lesions amounted to 60% for SE, 57% for IR-FSE, 32% for 2D GE, and 35% for 3D GE images. CNR of gray matter versus white matter was significantly higher for IR SE and GE imaging than for genuine SE and 2D GE acquisitions (Wilcoxon test), while 2D GE imaging alone had an excellent SNR. As IR-FSE images provide an excellent CNR for gray and white matter in the brain and contrast enhancement performs almost similarly well compared with SE imaging, this technique appears to be well suited for T1-weighted neuroimaging without and with contrast enhancement at 3.0 T. However, the inherent blurring of the IR-FSE can lead to poor performance for very small lesions.

Adult↗
PubMed1985

Theory of localized polarization transfer.

Because polarization transfer from one type of nucleus to another can occur only when both types of nuclei are excited, it is possible, by using two separate rf coils for the excitation, to restrict the spatial region of the sample from which a signal can be received to a specific volume of overlap of the two inhomogeneous field patterns. In this paper we develop the theory of this method of localization in a homogeneous static field. The polarization transfer is achieved by a generalized phase-cycled DEPT sequence, in which case the method has the additional advantage of a gain in sensitivity of a 13C signal associated with the maximum polarization-transfer enhancement. Localization by means of the inverse-DEPT sequence is also studied, and off-resonance effects are calculated. Experimental confirmation of the theoretical expressions is given.

Magnetic Resonance Spectroscopy↗
PubMed2000

[Karyotype of the midge Chironomus heterodentatus Konstantinov from the group Obtusidens (Diptera, Chironomidae)].

The karyotype of Chironomus heterodentatus, belonging to the obtusidens-group described by Konstantinov from the Volga in 1956, was studied in detail. Combinations of chromosomal arms are AB, CD, EF and G (cytocomplex thummi). The Ch. heterodentatus karyotype cleary differs from those of other members of the obtusidens-group with a species-specific banding pattern in arms A, B, C and D. Chromosomal polymorphism on homo- and heterozygous inversions was found in arms, A, B, D, E and G. 19 inversion banding sequences and their 27 genotypic combinations have been recorded. The shortest arm G is highly polymorphic. Heterozygotes on the Balbiani ring activity were found in arm G along with homo- and heterozygotes on inversions. B-chromosomes with a frequency equal to 2.7-25.0% were recorded in some Volga populations.

Animals↗
PubMed1986

FLP site-specific recombinase of yeast 2-micron plasmid. Topological features of the reaction.

The 2-micron plasmid of the yeast Saccharomyces cerevisiae encodes a site-specific recombinase (FLP) that promotes inversion across a unique site contained in each of the 599-base-pair inverted repeats of the plasmid. We have studied the topological changes generated in supercoiled substrates after exposure to the purified FLP protein in vitro. When a supercoiled substrate bearing two FLP target sequences in inverse orientation is treated with FLP, the products are multiply knotted structures that arise as a result of random entrapment of interdomainal supercoils. Likewise, a supercoiled substrate bearing two target sequences in direct orientation yields multiply interlocked catenanes as the product. Both types of substrate seem to be able to undergo repeated rounds of recombination that result in products of further complexity. The FLP protein also acts as a site-specific topoisomerase during the recombination reaction.

Binding Sites↗
PubMed1988

Ultrasound, CT, and MRI comparison in primary and secondary tumors of the liver.

Thirty-five patients with surgically removed or percutaneous biopsy-proven tumors were examined by ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI). This retrospective study describes the appearance of the primary tumors and metastases and compares the sensitivity and specificity of the 3 imaging methods. Ultrasound, CT, and MRI examinations as well as clinical, operative, and/or histologic data were available for all 35 patients. Paramagnetic contrast agent gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) was used in 23 patients and a short TI inversion recovery MRI sequence was used in 23 patients, in addition to various spin echo MRI sequences. Thirteen patients were examined using both Gd-DTPA and the short TI inversion recovery sequence. Our comparative study--based on the following criteria: detection, size, location of the tumor, and portal vein involvement and bile duct dilatation--demonstrated an advantage of MRI over ultrasound in 16 of 35 cases, equal results in 17 of 35 cases and a disadvantage of MRI compared to ultrasound in 2 of 35 cases. With the identical criteria, MRI proved to be more informative than CT in 10 of 35 cases, equal in 21 of 35 cases, and less informative in 4 of 35 cases.

Adolescent↗
PubMed1980

Polymorphism in mitochondrial DNA of humans as revealed by restriction endonuclease analysis.

Mitochondrial DNA samples from each of 21 humans of diverse racial and geographic origin were digested with each of 18 restriction endonucleases. The sizes of the resulting DNA fragments were compared after gel electrophoresis. No differences among the samples were detected in digest with 7 of the enzymes. Analysis of digests with the remaining enzymes showed one or more differences. Each of the 21 samples could be characterized individually on the basis of these digests. All between-sample differences could be explained by single base substitutions. No evidence for sequence rearrangements (inversions, transpositions) was obtained. Fourteen of the site alterations were shared by two or more samples; six of these were shared between races. The data indicate that individuals differ from a postulated ancestral mtDNA sequence at 0.18% of their base pairs. On the basis of an estimated rate for base substitution of 1% per 10(6) years [Brown, W. M., George, M., Jr. & Wilson, A. C. (1979) Proc. Natl. Acad. Sci. USA 76, 1967-1971], Homo sapiens could have speciated or passed through a severe population constriction as recently as 180,000 years ago. The data suggest that group-specific patterns of cleavage exist. The high resolution and precision afforded by this method of analysis makes possible the investigation of many questions concerning human population genetics, evolution, and recent history.

Asia↗
PubMed1989

Experimental approaches to image localized human 31P NMR spectroscopy.

Experimental procedures for obtaining localized 31P NMR spectra of humans by means of the ISIS sequence are discussed in detail. The technique is optimized for use with volume coils and with surface coils in order to measure localized 31P NMR spectra of different tissues and organs. Selective frequency-modulated (FM) inversion and excitation pulses are applied for optimal inversion or excitation despite B1 inhomogeneity. Pulse imperfection may lead to spurious signal contributions from outside the selected volume; this contamination is reduced by using long pulse intervals, by properly ordering the ISIS acquisitions, and by using FM excitation pulses. Simultaneous measurement of multiple volumes was implemented by including an additional selective inversion pulse, and an extension of the ISIS addition/subtraction scheme. Localized T1 measurements with surface coils are implemented by using a B1-insensitive inversion pulse in the inversion recovery sequence. The quantitative reproducibility of localized 31P NMR spectra was verified. Absolute metabolite concentration can be determined after a suitable calibration of the 31P NMR spectrum. Localized shimming is required to obtain localized 31P NMR spectra of excellent spectral resolution. This is done by monitoring the 1H NMR signal from water by a single-shot localization technique. The techniques discussed can be applied to obtain spectra of brain, liver, heart, and other organs. 31P NMR spectra of intracranial tumors demonstrate its applicability in the examination of patients.

Brain↗
PubMed1999

Disappearance of hypointense multiple sclerotic lesions on FLAIR MRI.

A child is presented who displayed hypointense multiple sclerotic lesions on fluid-attenuated inversion recovery sequences by magnetic resonance imaging, with the possible pathologic tissue changes of these hypointense lesions evaluated. The magnetic resonance imaging results in this patient demonstrated the disappearance of low-signal lesions on fluid-attenuated inversion recovery in multiple sclerosis, and the improvement of this patient's condition was likely compatible with sequential magnetic resonance imaging findings. Some hypointense lesions in the supratentorial white matter that appear on fluid-attenuated inversion recovery images in multiple sclerosis patients may include reversible brain lesions, suggesting extracellular fluid collection not accompanied by axonal loss or gliosis.

Adolescent↗
PubMed2002

Passive catheter tracking using MRI: comparison of conventional and magnetization-prepared FLASH.

PURPOSE: To compare a magnetization-prepared gradient-echo (GRE) sequence with a conventional GRE sequence for visualizing contrast agent-filled catheters. MATERIALS AND METHODS: Passive visualization of endovascular catheters using MRI was compared between two imaging sequences: 1) inversion recovery (IR)-fast low angle shot (FLASH), and 2) conventional FLASH. Two-dimensional projection images of the catheters filled with 4% diluted contrast agent in a phantom and the aorta of swine were obtained with each sequence with a temporal resolution of two frames per second. We compared background suppression and catheter visibility using the catheter-to-background signal ratio and the ratings of two radiologists. RESULTS: In the phantom, IR-FLASH allowed for a 200% increase in catheter-to-background ratio (p < 0.01) and improved depiction of catheters over conventional FLASH. In swine, the IR-FLASH images showed a statistically significant improvement of 80% (p < 0.001) over conventional FLASH in all comparisons of the catheter-to-background signal ratio, and an improvement of 160% (p < 0.05) in comparison with the radiologists' observations. CONCLUSION: This study shows that IR-FLASH is a better technique for passive tracking of contrast agent-filled catheters than conventional FLASH.

Animals↗
PubMed2006

Magnetic resonance imaging technique for the examination of canine mammary tumours.

The aim of this study was to adapt the human magnetic resonance imaging (MRI) sequences for use in the routine examination of canine mammary glands. MRI was performed on 10, middle- to old-aged dogs of different breeds. It was found that T1- and T2-weighted spin echo, short T1 inversion recovery sequences and a gradient echo (GE) dynamic T1-weighted measurement made in the coronal and transversal planes were the most informative MR diagnostic methods for imaging canine mammary tumours. The static MR technique is the most detailed imaging modality for differentiating the tissue types in the substance of the mammary gland. The MRI findings were in close relationship with the histological result (five malignant mixed tumours and five cases of invasive ductal carcinoma). Using the GE dynamic contrast-enhanced sequence the morphological patterns as well as the kinetic parameters proved to be malignant. By the dynamic measurement technique initial information was obtained on the contrast enhancing properties, which are valuable factors during in vivo staging and in the prognostic work.

Animals↗
PubMedDate not supplied

STIR sequence in infectious sacroiliitis in three patients.

Magnetic resonance imaging (MRI) provides the most detailed evaluation of the sacroiliac (SI) joint and surrounding soft tissue. Therefore, this technique represents the most sensitive and specific method in early diagnosis of infectious sacroiliitis. Among three patients diagnosed as having infectious sacroiliitis in our hospital, the short tau inversion recovery sequence (STIR) was found to be more effective than the T1 contrast-enhanced sequence, particularly in delineating all findings of the SI joint inflammation and allowing for the early detection of septic sacroiliitis.

Adult↗
PubMed1987

Proton magnetic resonance imaging of the ocular lens.

Several osmotic cataract models as well as human diabetic lenses were tested by nuclear magnetic resonance spectroscopy and imaging. Both longitudinal (T1) and transverse (T2) relaxation times increased with increase in lens hydration. Therefore proton magnetic resonance imaging (MRI) can be used to detect changes of the biophysical environment of water proton in the lens. T2-weighted imaging sequence (spin-echo) can be used to differentiate lenses with hydrational changes since they exhibit higher signal intensity (because of long T2) than normal lenses at the same TE (echo time). A greater contrast can be achieved with the inversion-recovery sequence, which, in addition to contribution from T2, also incorporates T1 and proton density terms. Proton MRI is potentially useful for the detection of pre-cataractous changes.

Aged↗
PubMed1987

Magnetic resonance imaging in lissencephaly.

In a patient with clinical manifestations suggestive of brain malformation, computer-assisted tomography (CT) showed lissencephaly: agyria, pachygyria, absent opercularization, and colpocephaly. The patient did not have seizures or a typical EEG of hypsarrhythmia. By magnetic resonance imaging (MRI), using a long inversion-recovery sequence, it was possible to verify the CT-findings and to demonstrate heterotopic grey matter and missing claustrum. By MRI it was much easier to estimate the altered ratio of grey and white matter. High grey-white matter contrast of inversion-recovery scans and the possibility of imaging the brain in sagittal, coronal and transverse planes make MRI the method of choice for the evaluation of lissencephaly and other brain malformations. In this case it helped to verify lissencephaly as one aspect of an unknown clinical entity of type-I-lissencephaly, defective structure of lymphatic nodes, a polyarthritis-like clinical picture, hypodontia, and flaring of the ribs.

Brain↗
PubMed2006

Chromosome evolution in the Thermotogales: large-scale inversions and strain diversification of CRISPR sequences.

In the present study, the chromosomes of two members of the Thermotogales were compared. A whole-genome alignment of Thermotoga maritima MSB8 and Thermotoga neapolitana NS-E has revealed numerous large-scale DNA rearrangements, most of which are associated with CRISPR DNA repeats and/or tRNA genes. These DNA rearrangements do not include the putative origin of DNA replication but move within the same replichore, i.e., the same replicating half of the chromosome (delimited by the replication origin and terminus). Based on cumulative GC skew analysis, both the T. maritima and T. neapolitana lineages contain one or two major inverted DNA segments. Also, based on PCR amplification and sequence analysis of the DNA joints that are associated with the major rearrangements, the overall chromosome architecture was found to be conserved at most DNA joints for other strains of T. neapolitana. Taken together, the results from this analysis suggest that the observed chromosomal rearrangements in the Thermotogales likely occurred by successive inversions after their divergence from a common ancestor and before strain diversification. Finally, sequence analysis shows that size polymorphisms in the DNA joints associated with CRISPRs can be explained by expansion and possibly contraction of the DNA repeat and spacer unit, providing a tool for discerning the relatedness of strains from different geographic locations.

Base Sequence↗
PubMed2002

[Does dynamic contrast-enhanced MRI enable recognition of development of vertebral fractures in multiple myeloma?].

PURPOSE: To compare the value of MRI sequences with dynamic MRI measurements (d-MRT) for the assessment of risk of lumbar vertebral fractures in patients with multiple myeloma. MATERIAL AND METHODS: In 10 patients with multiple myeloma a sagittal T 1 -, T 2 -weighted spin-echo and an inversion-recovery sequence were performed. For dynamic measurements a fast gradient-echo sequence (turbo fast low angle shot 2 D) with machine-controlled Gd-DTPA administration was used. The presence of bone marrow abnormalities was determined and additionally the value of the highest signal increase (amplitude Alpha) was calculated for each of the 50 vertebral bodies. The subsequent development of vertebral fractures was assessed by MRI at a mean time interval of 6.2 months after the initial d-MRI. The pattern of marrow involvement and the amplitudes of the vertebral bodies that collapsed in the observation period were statistically compared with those of the vertebral bodies that did not collapse. RESULTS: During the follow-up period newly or progressive fractures occurred in 6 of 10 patients (7 of 50 vertebral bodies). The degree of pathological signal changes that preceded fractures was not significantly different (p > 0.05) from that of the other contemporary lesions identified in vertebral bodies that did not collapse in follow-up. In contrast, the amplitude of vertebrae that collapsed (A: 33.1 +/- 8.2) was significantly higher (p < 0.0001) than the amplitude of vertebrae that did not collapse (A: 16.7 +/- 4.2). The amplitude was a reliable predictor of vertebrae that collapsed in all cases. CONCLUSION: In contrast to the analysis of marrow lesions detected with non-dynamic MRI, this study suggests that the perfusion-parameter amplitude in dynamic contrast-enhanced MRI is a potentially relevant value to predict the risk of vertebral fractures in patients with multiple myeloma.

Adult↗
PubMed1982

NMR imaging of the brain.

The basic features of an NMR imaging system are outlined and three pulse sequences which produce images with varying dependence on proton density T1 and T2 are described. The first of these sequences, Repeated Free Induction Decay produces images which demonstrate changes in proton density as well as flow effects. The second sequence, Inversion-recovery, produces images which are dependent on T1 and show a high level of grey, white matter contrast giving considerable anatomical detail. In addition pathological processes such as infarction, haemorrhages, demyelination and malignancy, produce changes in T1 enabling lesions to be localised. The third sequence, Spin-echo, produces images which are dependent on T2. These show very little grey, white matter contrast but demonstrate acute and space occupying lesions as well as cerebral oedema. The high level of grey, white matter contrast, lack of bone artefact, variety of sequences, capacity for multiplanar imaging, sensitivity to pathological change and lack of known hazard make NMR an important addition to existing techniques of neurological diagnosis.

Brain↗
PubMed2001

Cloning, sequencing, and expression of the leukotoxin gene from Fusobacterium necrophorum.

Fusobacterium necrophorum is a gram-negative, rod-shaped, anaerobic bacterium that is a primary or secondary etiological agent in a variety of necrotic purulent infections in animals and humans. Included are diseases of cattle such as liver abscesses and foot rot, which have economically important consequences for the cattle industry. The major virulence factor of this bacterium is leukotoxin, a secreted protein of high molecular weight active against leukocytes from ruminants. The screening of a genomic DNA library with polyclonal antisera raised against native affinity-purified leukotoxin and further extension of the sequence using inverse PCR led to the cloning of the entire leukotoxin gene. The leukotoxin gene open reading frame (ORF; lktA) consists of 9,726 bp and encodes a protein of 3,241 amino acids with an overall molecular weight of 335,956. The leukotoxin does not have sequence similarity with any other bacterial leukotoxin. Five truncated overlapping polypeptides covering the whole lktA ORF were used to immunize rabbits. In Western blot assays, polyclonal antisera raised against all five truncated polypeptides recognized affinity-purified leukotoxin from F. necrophorum culture supernatant in a Western blot assay. Antisera directed against two of the five polypeptides had neutralizing activity against the toxin. The entire leukotoxin ORF was expressed in Escherichia coli. Flow-cytometric analysis showed that the recombinant leukotoxin was active against bovine polymorphonuclear leukocytes and was inhibited with antiserum raised against the F. necrophorum leukotoxin. Southern blot hybridization analysis revealed different patterns of lktA hybridizing bands between isolates of the two subspecies of F. necrophorum.

Animals↗
PubMed1993

The complete nucleotide sequence of a small cryptic plasmid from a rumen bacterium of the genus Butyrivibrio.

The complete nucleotide sequence of a plasmid, designated pRJF1, isolated from a rumen bacterium of the genus Butyrivibrio, has been determined. pRJF1 is a small plasmid (2631 bp) which shows the high AT content (64%) typical of plasmids from gram-positive organisms. Computer analysis of sequence data revealed two major open reading frames encoded on the same strand but in different frames. The smaller, ORF1 (435 bp), is preceded by Shine Dalgarno (SD) and Escherichia coli-10, -35 sequences and is predicted to encode an acidic polypeptide of 145 aa. The putative protein shows little homology to known bacterial proteins except in a small region similar to part of the Pre protein (plasmid recombination enzyme) of Bacillus plasmid pTB913. Pre proteins of the pTB913 family, however, show conservation of several amino acids in the amino terminal region of the protein that may be related to function. This pattern of amino acid conservation is not observed in ORF1. The predicted product of ORF2 (849 bp) is a basic protein of 283 as that shows significant similarity to repA gene products of plasmids from gram-negative (but not gram-positive) bacteria. No typical Shine Dalgarno sequence or -10, -35 sequences precede this coding region. While sequence homologous to nick sites of plasmids from gram-positive organisms that replicate via ssDNA intermediates were also detected in pRJF1, the order of the three consecutive inverted repeats typical of nick sites is not conserved. pRJF1, however, does contain an extended region of directly and inversely repeated sequence motifs reminiscent of theta replication origins.

Amino Acid Sequence↗