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At least 19 recordsLinked to original sources
PubMed1990

[Magnetic resonance tomographic diagnosis of retrobulbar neuritis using inversion recovery sequences].

Inversion recovery sequences with short inversion periods (STIR sequences) are particularly suitable for the examination of the intra-orbital and intracanalicular portion of the optic nerve, since they selectively suppress interference from neighbouring fat. This technique makes possible direct demonstration of retrobulbar neuritis that had to be diagnosed exclusively by clinical criteria up to now. As evidence of inflammatory changes in 15 out of 18 patients with acute retrobulbar neuritis, there were areas of increased signal intensity in the affected nerve; in six cases the nerve was also swollen. In eight normals and five patients with healed retrobulbar neuritis, the signal and calibre of the optic nerves were normal.

Adult↗
PubMed1988

Analysis of the termini of the DNA of bovine parvovirus: demonstration of sequence inversion at the left terminus and its implication for the replication model.

The distribution of terminal-sequence orientations in the viral DNA of bovine parvovirus (BPV), an autonomous parvovirus, was studied by end labeling and restriction enzyme digestion and also by cloning. The left (3') end of the minus strand of BPV was found in two alternative sequence orientations (designated as flip and flop, which are reverse complements of each other), with a 10-fold excess of flip. This is in contrast to the autonomous rodent parvoviruses which encapsidate minus-strand DNA with only the flip orientation at this end. The right (5') end of the minus strand of BPV contained both sequence orientations with equal frequencies, as in the rodent parvoviruses. Sequence inversions were also detected at both ends of the plus strand, which makes up about 10% of the encapsidated BPV DNA. Each terminus of BPV DNA had a characteristic ratio of flip to flop forms, and this ratio was restored in the progeny DNA resulting from transfection with genomic clones of different defined terminal conformations. Replicative-form DNA showed the same distribution of terminal-sequence orientations as the reannealed plus and minus virion DNAs, suggesting that the distribution of flip and flop forms observed in virion DNA is not due to selective encapsidation, but rather to the specific distribution of replicative forms. The current replication model for autonomous parvoviruses, which was based on the available data for the rodent parvoviruses, cannot account for the observed distribution of BPV DNA. An alternative model is suggested.

Animals↗
PubMed1987

Proton exchange and base-pair lifetimes in a deoxy-duplex containing a purine-pyrimidine step and in the duplex of inverse sequence.

Using proton relaxation and magnetization transfer from water we have measured the imino proton exchange kinetics in two dodecadeoxynucleotide duplexes. One is formed by the self-complementary sequence 5'-d(C-C-T-T-T-C-G-A-A-A-G-G), the other by the inverse sequence. The imino proton exchange rates are found to depend on the concentration of ammonia or imidazole, acting as basic catalysts of proton exchange. Extrapolation of exchange times to infinite catalyst concentration yields the base-pair lifetimes, for instance 40 milliseconds for the central G.C base-pair of the 5'-d(C-C-T-T-T-C-G-A-A-A-G-G) duplex and four milliseconds for its A.T neighbour, at 15 degrees C. These results differ markedly from those reported by other laboratories for similar deoxy compounds. An explanation of the discrepancy has been proposed recently. Differences between base-pair lifetimes indicate that opening is not co-operative. From the catalyst efficiency relative to exchange from isolated nucleosides, we estimate the dissociation constant of each base-pair, e.g. 0.3 x 10(-6) and 1.5 x 10(-5) at 15 degrees C, for the same G.C and A.T base-pairs. The lifetime and dissociation constant of corresponding base-pairs of the two duplexes are similar, except for the central G.C base-pair. This correlates with differences in the solution structures reported by others. We have completed the assignments of the imino protons and of the six cytosine amino protons of the 5'-d(G-G-A-A-A-G-C-T-T-T-C-C) 12-mer. A new base-pair numbering scheme is proposed.

Base Composition↗
PubMed1988

Genomic clones of bovine parvovirus: construction and effect of deletions and terminal sequence inversions on infectivity.

Genomic clones of the autonomous parvovirus bovine parvovirus (BPV) were constructed by blunt-end ligation of reannealed virion plus and minus DNA strands into the plasmid pUC8. These clones were stable during propagation in Escherichia coli JM107. All clones tested were found to be infectious by the criteria of plaque titer and progressive cytopathic effect after transfection into bovine fetal lung cells. Sequencing of the recombinant plasmids demonstrated that all of the BPV inserts had left-end (3')-terminal deletions of up to 34 bases. DNA isolated from progeny virions arising from transfected infectious clones was found to be indistinguishable from wild-type DNA by restriction enzyme analysis. Defective genomes could also be detected in the progeny DNA even though the infection was initiated with homogenous, cloned DNA. Full-length genomic clones with 3' flip and 3' flop conformations were constructed and were found to have equal infectivity. Analysis of low-molecular-weight DNA isolated from lysates of cells transfected with these clones demonstrated that rescue and replication of BPV DNA could be detected 3 to 8 days after transfection. Expression of capsid proteins from transfected genomes was demonstrated by hemagglutination, indirect immunofluorescence, and immunoprecipitation of [35S]methionine-labeled cell lysates. Use of appropriate antiserum for immunoprecipitation showed the synthesis of BPV capsid and noncapsid proteins after transfection. Independently, a series of genomic clones with increasingly larger 3'-terminal deletions was prepared from separately subcloned 3'-terminal fragments. Transfection of these clones into bovine fetal lung cells revealed that deletions of up to 34 bases at the 3' end lowered but did not abolish infectivity, while deletions of greater than 52 bases were lethal. End-label analysis showed that the 34-base deletion was repaired to wild-type length in the progeny virus.

Amino Acid Sequence↗
PubMedDate not supplied

High signal regions in normal white matter shown by heavily T2-weighted CSF nulled IR sequences.

Inversion recovery (IR) sequences with an inversion time (TI) designed to markedly reduce or null the signal from CSF (TI of approximately 2,100 ms at 1.0 T) and a very long echo time (TE) of 240 ms were used to image the brain of two normal adult volunteers, one 34-year-old man with an intrinsic tumor, and one 3-month-old infant with an infarct. Using these very heavily T2-weighted pulse sequences, adult gray and white matter showed similar signal intensity in many areas of the brain, but normal white matter in regions of the centrum semiovale, posterior internal capsule, parietopontile tract, occipitothalamic radiation, and brain stem showed a much higher signal intensity than surrounding gray or white matter. The infant displayed a low signal intensity in myelinated regions in the internal capsule and occipitothalamic radiation and a high signal in unmyelinated white matter. In many of the images there were strong similarities to the distribution of high signal within white matter seen with pulsed gradient spin echo sequences (TE 130 ms) designed to demonstrate effects due to anisotropic diffusion. Arguments are advanced to support the view that the high signal intensity in white matter tracts is due to one or more long T2 components that may be associated with unmyelinated or sparsely myelinated fibres within white matter. The resemblance to diffusion weighted images may reflect the fact that both employ long TEs and both produce a low signal from CSF. If myelin possessed a different susceptibility from axoplasm so that magnetic field gradients were generated around nerve fibres when their orientation was not parallel to B0, diffusion of water might then produce the observed dependence on fibre direction. The high signal regions in white matter are a potential source of confusion in image interpretation, and measurements of T2 in white matter need to be made with these regional variations in mind. The concept of normal appearing white matter also needs to be applied with a knowledge of these differences. The IR sequences used in this study provide a very high T2 dependence with a low signal from CSF and may be useful for detecting disease in the CNS of adults and children.

Adult↗
PubMedDate not supplied

MR imaging: clinical use of the inversion recovery sequence.

The properties of the inversion recovery (IR) sequence are considered and its use in clinical practice is illustrated. The effect of changing repetition time, inversion time (TI), and echo time; the method of data encoding; the type of data collection; and the method of image processing are analysed. Normal appearances and clinical examples in the central nervous system and the remainder of the body are used to illustrate the many options available with this sequence. The short TI IR sequence has advantages in magnetic resonance imaging of the body, and medium TI sequences are of value in localisation in the brain and in demonstrating contrast enhancement. Long TI sequences can be used in pediatrics and for separating tumour and oedema. Suppression or partial suppression of fat and fluid signals are two useful options with IR sequences.

Astrocytoma↗
PubMedDate not supplied

Endorectal surface coil MR imaging of prostatic carcinoma with the inversion-recovery sequence.

The value of inversion-recovery (IR) sequences in the diagnosis and staging of prostatic carcinoma with magnetic resonance (MR) imaging was studied. Twenty-six patients with carcinoma of the prostate were imaged at 1.5 T with an endorectal surface coil and with a variety of IR sequences and a set of spin-echo (SE) sequences for comparison. Ex vivo prostate specimens were imaged again at the same field strength. The two images were correlated with histologic sections. Cancer was identified with MR imaging in 96% of patients. Of the tumors more than 4 mm in diameter, 87% were identified on T2-weighted SE images, whereas only 26% were identified on IR images. However, IR images may be more useful in local staging of carcinoma. Gross capsular infiltration was present in only two patients; however, it was detectable (and excluded in five other patients) by means of IR images. It was not detectable on SE images. The high quality of images obtained with the endorectal coil was confirmed. The authors conclude that addition of the IR sequence to MR imaging with the endorectal coil may improve the usefulness of this examination.

Adult↗
PubMedDate not supplied

MR imaging of the liver using short TI inversion recovery sequences.

Use of the short inversion time inversion recovery (STIR) sequence in magnetic resonance (MR) imaging of the liver is illustrated in 20 patients. The sequence provides high contrast images of the liver with relatively little degradation due to motion. Lesions appeared more extensive than with X-ray CT in 14 cases and equal in six. Additional areas of presumed atrophy, fatty infiltration, edema, or vascular insufficiency were only seen with MR. The STIR sequence may be valuable in screening of the liver for metastatic disease.

Evaluation Studies as Topic↗
PubMed1987

The design of a multiple inversion recovery sequence for T1 measurement.

Inversion recovery has the potential to be a powerful method of determining the values of T1 in in vivo studies. However, because of its relative slowness it is not practical to undertake several experiments with different values of the interval between the magnetization inverting 180 degree pulse and the interrogating 90 degree one. The multiple inversion recovery method described here uses a series of sampling pulses, most much less than 90 degrees, to produce a series of images. It is shown that slice shape is relatively reproducible from one sample to another and that, largely as a result, the accuracy of the sequence in measuring T1 is encouraging.

Brain↗
PubMed1987

Magnetic resonance imaging of midline brain tumors using inversion recovery sequences at 0.08 T (3.4 MHz).

The use of inversion recovery sequences to highlight intracranial tumors in children is illustrated. The effect of changing the inversion time (TI) to produce the best spatial resolution and to highlight the contrast resolution between different tumors and normal brain is analyzed. The normal appearances and clinical examples in the central nervous system are used to illustrate the options that are available using IR sequences. Variation of TI for providing a means of differentiating short T1 lesions from long T1 lesions is discussed, short TI sequences being best for demonstrating gliomas and astrocytomas whilst medium/long TI sequences are best for demonstrating vascular abnormalities and short T1 tumors. Inversion recovery imaging is considered to be an accurate alternative to spin-echo imaging as currently applied.

Adolescent↗
PubMed1992

Fast and accurate measurements of T1 using a multi-readout single inversion-recovery sequence.

TOMROP is a multiple readout single inversion-recovery sequence which may potentially allow the measurement of multi-exponential T1 recoveries in vivo by NMR imaging. It is shown that several important modifications must be made to this sequence to permit T1 to be measured accurately and reliably. With these modifications it is possible to measure T1 with a mean systematic error of -1.5% (-0.3% for samples with T1 greater than 300 ms), a mean accuracy of 3.1% (2.1% for samples with T1 greater than 300 ms) and a mean repeatability of 1.4% (1.4% for samples with T1 greater than 300 ms), using data collected in 6.4 min from sixteen 128 x 128 matrix images.

Algorithms↗
PubMedDate not supplied

MR characterization of hepatic lesions by t-null inversion recovery sequence.

Tissue characterization of focal hepatic lesions was performed employing an inversion recovery sequence with short repetition time and short inversion time (TI) values. Different and specific TI values, correlated to the in vivo measured T1 relaxation times, were used to null the signal intensity of each type of lesion. In 40 patients studied, we observed the nulling effect of normal liver in 10 of 10 cases with a TI of 136 ms, of metastases in 7 of 8 cases with a TI of 175 ms, of hemangiomas in 15 of 16 cases with a TI of 200 ms, and of cysts in 6 of 7 cases with a TI of 235 ms. A quantitative analysis of the nulled signal was performed by measuring the signal/noise values. A further qualitative and quantitative characterization was carried out by evaluating the signal intensity of hepatic lesions at the null point of normal liver. The method provided the possibility of discriminating different focal lesions with specificity values of 83-94%, according to the type of lesion.

Adult↗
PubMed1989

[MR characterization of breast pathology using inversion recovery sequence].

As yet, a valid tissue characterization of human breast diseases has not been possible with conventional MR techniques. On the basis of the experimental thesis according to which fibroadenomas and carcinomas have a slight, though significant, difference in T1 relaxation times, we employed specific inversion recovery sequences at the T null of the breast glandular and adipose tissues, to enhance the differences in the signal intensities of the various pathologies. We examined 16 (6 cystic dysplasias, 5 fibroadenomas, 3 carcinomas, and 1 phylloid fibroadenoma) selected patients with the above-mentioned sequences in addition to the routine T1- and T2-weighted spin echo sequences. The following conclusions were reached by evaluating the characteristic signal intensities: MR spin echo sequences allow solid lesions to be distinguished from cystic ones; MR inversion recovery sequences allow fibroadenomas to be distinguished from carcinomas with 88% accuracy.

Adenofibroma↗
PubMed1991

Structure of the gas vesicle plasmid in Halobacterium halobium: inversion isomers, inverted repeats, and insertion sequences.

Halobacterium-halobium NRC-1 harbors a 200-kb plasmid, pNRC100, which contains a cluster of genes for synthesis of buoyant gas-filled vesicles. Physical mapping of pNRC100 by using pulsed-field gel electrophoresis showed the presence of a large (35 to 38-kb) inverted repeat (IR) sequence. Inversion isomers of pNRC100 were demonstrated by Southern hybridization analysis using two restriction enzymes, AflII and SfiI, that cut asymmetrically within the intervening small single-copy region and the large single-copy region, respectively, but not within the large IRs. No inversion isomers were observed for a deletion derivative of pNRC100 lacking one IR, which suggests that both copies are required for inversion to occur. Additionally, the identities and approximate positions of 17 insertion sequences (IS) in pNRC100 were determined by Southern hybridization and limited nucleotide sequence analysis across the IS element-target site junctions: ISH2, a 0.5-kb element, was found in four copies; ISH3, a 1.4-kb heterogeneous family of elements, was present in seven copies; ISH8, a 1.4-kb element, was found in five copies; and ISH50, a 1.0-kb element, was present in a single copy. The large IRs terminated at an ISH2 element at one end and an ISH3 element at the other end. pNRC100 is similar in structure to chloroplast and mitochondrial genomes, which contain large IRs and other large halobacterial and prokaryotic plasmids that are reservoirs of IS elements but lack the large IRs.

Base Sequence↗
PubMed1988

Magnetic resonance imaging of the parotid glands using inversion-recovery sequences at 0.08 T.

One hundred and eight examinations on 103 patients with suspected disease of the salivary glands were studied using a 0.08 T resistive magnet and inversion-recovery pulse sequences. Sixty-eight patients who had a mass lesion within a salivary gland later had surgery, and specimens were obtained for histological diagnosis. The remaining 35 patients were diagnosed on clinical grounds. In all cases the clinical findings were compared with the appearances on magnetic resonance imaging (MRI). The use of inversion-recovery pulse sequences allowed accurate localization of all tumour masses and, because of the clarity with which blood vessels were displayed, the precise relationship of any parotid mass to the retromandibular vessels and hence the facial nerve was possible. Whilst MRI did not display any pathognomonic features to allow the differentiation of malignant cell types or the differentiation of invasive malignant tumours from chronic inflammatory disease, it was possible to differentiate parotitis from Mikulicz's disease and to diagnose cysts and pleomorphic adenomas by their appearances on MRI.

Cysts↗
PubMed1985

The short TI inversion recovery sequence--an approach to MR imaging of the abdomen.

Initial clinical experience with magnetic resonance imaging (MRI) of the abdomen using short TI inversion-recovery (STIR) pulse sequences is described and compared with X-ray CT in a variety of abdominal disease. The extent of abnormality shown with MRI was greater than that with CT in 21 of 30 cases and equal in 9 cases. Lesion contrast was greater with MRI in 15 cases, equal in 14 and less in 1. The level of artefact was equal in 27 cases and greater with MRI in 3 cases. The STIR pulse sequence has significant advantages in producing high soft-tissue contrast, controlling respiratory artefact, avoiding confusion with intra-abdominal fat and identifying bowel loops.

Abdomen↗
PubMed1988

Simple assay for quantitation of Tn5 inversion events in Escherichia coli and use of the assay in determination of plasmid copy number.

In this report, we describe a simple method for measuring the frequency of sequence inversion in the transposable element Tn5 as a result of recombination across its duplicated IS50 elements. The structure of Tn5 was manipulated so that the neomycin phosphotransferase gene of the transposon would be expressed only if a sequence inversion event occurred. This highly sensitive assay also served as the basis for a novel means of estimating plasmid copy number.

Chromosome Inversion↗