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At least 1,801 records · Page 100Linked to original sources
PubMed2001

Limits of detection of regional differences in vasodilated flow in viable myocardium by first-pass magnetic resonance perfusion imaging.

BACKGROUND: Perfusion imaging techniques intended to identify regional limitations in coronary flow reserve in viable myocardium need to identify 2-fold differences in regional flow during coronary vasodilation consistently. This study evaluated the suitability of current first-pass magnetic resonance approaches for evaluating such differences, which are 1 to 2 orders of magnitude less than in myocardial infarction. METHODS AND RESULTS: Graded regional differences in vasodilated flow were produced in chronically instrumented dogs with either left circumflex (LCx) infusion of adenosine or partial LCx occlusion during global coronary vasodilation. First-pass myocardial signal intensity-time curves were obtained after right atrial injection of gadoteridol (0.025 mmol/kg) with an MRI inversion recovery true-FISP sequence. The area under the initial portion of the LCx curve was compared with that of a curve from a remote area of the ventricle. Relative LCx and remote flows were assessed simultaneously with microspheres. The ratio of LCx and remote MRI curve areas and the ratio of LCx and remote microsphere concentrations were highly correlated and linearly related over a 5-fold range of flow differences (y=0.96 x+/-0.07, P<0.0001, r(2)=0.87). The 95% confidence limits for individual MRI measurements were +/-35%. Regional differences of >/=2-fold were consistently apparent in unprocessed MR images. CONCLUSIONS: Clinically relevant regional reductions in vasodilated flow in viable myocardium can be detected with 95% confidence over the range of 1 to 5 times resting flow. This suggests that MRI can identify and quantify limitations in perfusion reserve that are expected to be produced by stenoses of >/=70%.

Animals↗
PubMed1995

Identification of an idiotypic peptide recognized by autoantibodies in human immunodeficiency virus-1-infected individuals.

Antibodies against HIV-1 proteins in HIV-1-infected individuals share a cross-reactive idiotype defined by the monoclonal antiidiotypic antibody 1F7 (5). Using a computer algorithm based on the molecular recognition theory, regions of inverse hydropathy between the variable sequence of 1F7 and human monoclonal anti-HIV-1 antibodies were identified, which are assumed to be involved in idiotype-antiidiotype contacts. A peptide was designed from the proposed contact in the variable heavy chain framework 3-complementarity determining region 3 (FR3-CDR3) of human antibodies and was synthesized. This peptide is recognized by the antiidiotype 1F7 and inhibits the binding of 1F7 to human anti-HIV-1 antibodies which express the 1F7 idiotype. A survey of normal and HIV-1-infected sera revealed the presence of antibodies in infected sera which bind to the FR3-CDR3 peptide. The biological relevance of autoantibodies against a self idiotope associated with HIV-1 infection is discussed in the context of the regulation of the antibody response to HIV-1.

Algorithms↗
PubMed2004

Standardized whole brain mapping of tubers and subependymal nodules in tuberous sclerosis complex.

Tuberous sclerosis complex is associated with radiologically visible abnormalities of brain structure, principally tubers and subependymal nodules. We reviewed the literature on neuroimaging of tubers and subependymal nodules and found qualitative evidence of bilateral, predominantly frontal distribution of tubers and bilateral, predominantly subcortical distribution of subependymal nodules in prior studies of pediatric samples. We studied 25 high-functioning adults with tuberous sclerosis complex and normal IQ, acquiring both dual spin-echo and fluid-attenuated inversion recovery magnetic resonance imaging sequences to optimize radiologic diagnosis of tubers and nodules. Individual lesion maps were then coregistered in a standard stereotactic space to facilitate construction of lesion density maps and estimation of lesion density in cortical and subcortical regions reliably defined by a parcellated template image. We found the highest frequency of tubers in frontal lobes and the highest density of tubers in parietal regions. There was significant regional variation in tuber density but no significant lateralization of frequently bilateral tubers. Nodules were located predominantly in the caudate nucleus and were not significantly lateralized. Tuber and nodule volumes were significantly positively correlated. Tuber volume was larger, on average, in patients with a lifetime history of epilepsy, but there was no correlation between IQ and these measures of lesion load. Contemporary image processing tools can be used to enhance quantitative, whole brain analysis of lesion load in patients with tuberous sclerosis complex.

Adolescent↗
PubMed2001

Intra-observer, inter-observer and inter-scanner variations in brain MRI volume measurements in multiple sclerosis.

INTRODUCTION: Measurement of brain volume on magnetic resonance imaging (MRI) scans is regarded as an objective marker of multiple sclerosis (MS) severity with the potential to monitor treatment efficacy accurately. This study was performed to assess the variability of brain MRI volume measurements. PATIENTS AND METHODS: We studied nine patients with relapsing-remitting MS, who were imaged on two occasions (separated by an interval of 24 h) using two different MR scanners and fast fluid-attenuated inversion recovery (fast-FLAIR) sequences. The whole brain volume computed from each image was measured three times by three observers using a seed-growing technique based on signal intensity thresholding. Intra-observer, inter-observer and inter-scanner variabilities were expressed as coefficients of variations (COVs). The inter-scanner variability included not only the intra-observer variation but also the repositioning variability and the variation in observed brain volume caused by different scanner hardware and sequence implementations. RESULTS: There was no statistically significant difference in patients' brain volume values between observers (P=0.82) or between scanners (P=0.30). The mean intra-observer COV was 1.2% (s.e.=0.4%), the mean inter-observer COV was 1.8% (s.e.=0.8%) and the mean inter-scanner COV was 2.4% (s.e.=1.2%). The intra-observer variance was not statistically different from those found between observers (P=0.83) or scanners (P=0.44). CONCLUSION: The intra-observer variability in brain volume measurements found in this study was within the range of intra-observer variability found in previous studies. This study shows that the use of different observers and MR scanners has only a small influence on the measured brain volume and does not affect the reproducibility of this measurement greatly.

Adult↗
PubMed2000

A conventional and magnetization transfer MRI study of the cervical cord in patients with MS.

OBJECTIVE: To evaluate the contribution made by cervical cord damage, assessed using a fast short-tau inversion recovery (fast-STIR) sequence and magnetization transfer ratio (MTR) histogram analysis to the clinical manifestations of MS. BACKGROUND: Previous studies have failed to show significant correlations between the number and extent of T2 spinal cord lesions and the clinical status of patients with MS. Fast-STIR is more sensitive than T2-weighted imaging for detecting cervical cord MS lesions. MTR histogram analysis provides estimates of the overall disease burden in the cervical cord with higher pathologic specificity to the more destructive aspects of MS than T2-weighted scans. METHODS: We obtained fast-STIR and magnetization transfer (MT) scans from 96 patients with MS (52 with relapsing-remitting [RRMS], 33 with secondary progressive [SPMS], and 11 with primary progressive [PPMS] MS) and 21 control subjects. Dual-echo scans of the brain were also obtained and lesion load measured. RESULTS: Eighty-one of the patients with MS had an abnormal cervical cord scan. Patients with SPMS had more cervical cord lesions and more images with visible cervical cord damage than did patients with RRMS or PPMS (p = 0.04). The entire cohort of patients with MS had lower average MTR of the cervical cord (p = 0.006) than control subjects. Compared to control subjects, patients with RRMS had similar cervical cord MTR histogram-derived measures, whereas those with PPMS had lower average MTR (p = 0.01) and peak height (p = 0.02). Patients with SPMS had lower histogram peak height than did those with RRMS (p = 0.03). The peak position and height of the cervical cord MTR histogram were independent predictors of the probability of having locomotor disability. We found no correlation between brain T2 lesion load and any of the cervical cord MTR histogram metrics. CONCLUSIONS: This study shows that the amount and severity of MS pathology in the cervical cord are greater in the progressive forms of the disease. An accurate assessment of cervical cord damage in MS gives information that can be used in part to explain the clinical manifestations of the disease.

Adult↗
PubMed2000

[Comparison of whole-body MR imaging and bone scintigraphy in the detection of bone metastases from breast cancer].

The aim of this study was to investigate the usefulness of whole body MR imaging (WB-MRI) in the detection of bone metastases from breast cancer and to compare the results with those from bone scintigraphy. In 21 patients with suspected bone metastasis from breast cancer, both bone scintigraphy and WB-MRI were performed. With WB-MRI, coronal images were obtained using a body coil in an FOV of 48 cm, and sequences of fast short TI inversion recovery (STIR) and gadolinium-enhanced fast spoiled GRASS (SPGR) were used in three parts: from the head to the thorax, the abdomen to the pelvis, and the lower extremities. Of the total 105 metastatic bone lesions, 65 (61.9%) were detected by bone scintigraphy, 98 (93.3%) by fast STIR, and 74 (70.5%) by fast SPGR. Thus, the detection of bone metastases by WB-MRI was excellent. However, detectability in the ribs was lower for WB-MRI than for bone scintigraphy. Contrast-enhanced MRI was useful in the differentiation of osteosclerotic lesions, in which high signal intensity is rare, pleural effusion, which has high signal intensity on STIR, and bone metastatic lesions. In conclusion, WB-MRI showed high reliability in the detection of bone metastatic lesions from breast cancer.

Adult↗
PubMed2000

Many multipotential gene-marked progenitor or stem cell clones contribute to hematopoiesis in nonhuman primates.

Retroviral insertion site analysis was used to track the contribution of retrovirally transduced primitive progenitors to hematopoiesis after autologous transplantation in the rhesus macaque model. CD34-enriched mobilized peripheral blood cells were transduced with retroviral marking vectors containing the neo gene and were reinfused after total body irradiation. High-level gene transfer efficiency allowed insertion site analysis of individual myeloid and erythroid colony-forming units (CFU) and of highly purified B- and T-lymphoid populations in 2 animals. At multiple time points up to 1 year after transplantation, retroviral insertion sites were identified by performing inverse polymerase chain reaction and sequencing vector-containing CFU or more than 99% pure T- and B-cell populations. Forty-eight unique insertion sequences were detected in the first animal and also in the second animal, and multiple clones contributed to hematopoiesis at 2 or more time points. Multipotential clones contributing to myeloid and lymphoid lineages were identified. These results support the concept that hematopoiesis in large animals is polyclonal and that individual multipotential stem or progenitor cells can contribute to hematopoiesis for prolonged periods. Gene transfer to long-lived, multipotent clones is shown and is encouraging for human gene therapy applications.

Animals↗
PubMedDate not supplied

Fluid-attenuated inversion recovery intraarterial signal: an early sign of hyperacute cerebral ischemia.

BACKGROUND AND PURPOSE: Early detection of arterial occlusion and perfusion abnormality is necessary for effective therapy of hyperacute cerebral ischemia. We attempted to assess the utility of the fast fluid-attenuated inversion recovery (fast-FLAIR) sequence in detecting occluded arteries as high signal (referred to as intraarterial signal) and to establish the role of fast-FLAIR in detecting ischemic penumbra of hyperacute stroke within 24 hours after ictus. METHODS: We studied 60 patients with hyperacute cerebral ischemia caused by occlusion of intracranial major arteries. We compared intraarterial signal on FLAIR images with time of flight (TOF) on MR angiograms, flow voids on T2-weighted images, hyperintense lesions on diffusion-weighted images, and results of follow-up CT or MR scans. RESULTS: In 58 (96.7%) patients, FLAIR detected intraarterial signals as early as 35 minutes after stroke onset. In 48 (80.0%) patients, intraarterial signal on FLAIR images coincided with lack of TOF on MR angiograms. In 41 (74.5%) of 55 patients, the intraarterial signals of fast T2-weighted imaging depicted occlusion better than did deficient flow void on T2-weighted images. In 25 (41.7%) of 60 patients, the area of intraarterial signal distribution was larger than the hyperintense lesion measured on diffusion-weighted images. Areas of final infarction had sizes between those of intraarterial signal distribution on FLAIR images and lesions measured on diffusion-weighted images. In 35 (87.5%) of 40 patients, areas of intraarterial signal distribution were equal to regions of abnormal perfusion. CONCLUSION: Intraarterial signal on FLAIR images is an early sign of occlusion of major arteries. FLAIR combined with diffusion-weighted imaging can be helpful to predict an area at risk for infarction (ischemic penumbra). FLAIR plays an important role for determining whether a patient should undergo perfusion study.

Acute Disease↗
PubMed2004

Magnetic resonance imaging of myocardial infarction using gadolinium-based contrast agent.

OBJECTIVES: To evaluate myocardial infarcts using a segmented inversion-recovery prepared gradient echo sequence on a 1.5 Tesla MR scanner after injection of a gadolinium-based contrast agent. METHODS: Fourteen patients were prospectively offered a cardiac MR exam between November 2003 and February 2004. Six patients had a history of anterior wall MI, six had a history of inferior wall MI and two patients had MI of undetermined location. RESULTS: Delayed enhancement indicating the presence of scarring was visualized in all fourteen patients. The scarring was transmural in ten patients and non-transmural in four patients. CONCLUSION: Delayed enhancement of infarcted areas in the myocardium after injection of gadolinium-based contrast agent represents scarring and adequate resolution exists to distinguish transmural from non-transmural scarring. This technique is useful in determining viability of infarcted myocardium, may detect infarcts missed by SPECT and may help in the selection of patients for implantation of defibrillators.

Contrast Media↗
PubMed1987

Assessment of multiple sclerosis lesions by magnetic resonance imaging.

Fifty patients clinically suspected to have multiple sclerosis (MS), who were classified by Schumacher's criteria into three clinical categories (definite, probable, or possible MS), underwent complete brain magnetic resonance (MR) scans. The T2-weighted spin echo (SE) pulse sequence was more sensitive than inversion recovery (IR) in detecting MS lesions. Greater than 50% of the lesions demonstrated by SE were missed on the corresponding IR slices. However, lesions in the brainstem were more readily assessed using IR. MS lesions appeared larger on SE than on IR. Fifty-five percent of SE-demonstrated lesions were 1 to 2 cm or larger in size, while only 32% of IR-demonstrated lesions were greater than 1 cm. Axial and coronal planes of study demonstrated the same number, size, and location of lesions.

Adult↗
PubMed1985

[Nuclear spin resonance tomography and its anatomic-pathological correlates].

NMR examination of a preserved head was performed using different Inversion Recovery and Spin Echo sequences. Correlations were made between the MR and the macroscopic pathological and later, the histological appearances of the specimen at corresponding slices. Normal anatomical structures and the multiple pathological lesions were all clearly demonstrated by MRI.

Aged↗
PubMed1982

Changes in gene order and gene expression.

Studies on changes in gene position in germ line and somatic cell chromosomes during evolution and differentiation have led biologists to abandon the static view of chromosomes as invariant linear arrays of hereditary information. Prokaryotic cells contain several classes of DNA insertion elements which move from place to place in the genome and mediate chromosome rearrangements. Similar elements exist in a wide variety of eukaryotic organisms (yeasts, insects, plants, and vertebrates). In addition, both reversible and irreversible changes of chromosome primary structure provide developmental controls on gene activity in bacteria, bacteriophages, yeasts, trypanosomes, and mammalian lymphocytes. At least five recombination mechanisms are known to catalyze chromosome changes: 1) general homologous, 2) site-specific reciprocal, 3) illegitimate, 4) DNA splicing, and 5) replicative. Various combinations of these mechanisms can explain many different chromosome rearrangements and changes in gene dosage. Changes in gene position can alter gene expression in many ways, some of which we understand (such as insertional mutation and inversion of coding and regulatory sequences) and some of which are still unexplained. The activities of DNA insertion elements and somatic rearrangement systems are subjects to controls at several levels by specific regulatory systems, natural selection, and connection to cell lineage. Despite the recent increase in knowledge about the biological importance of changes in gene order on chromosomes, there are far more questions than answers, particularly about the mechanisms that coordinate recombination events and cell division in higher organisms.

Animals↗
PubMed1994

Analysis of the translational initiation region on the Euglena gracilis chloroplast ribulose-bisphosphate carboxylase/oxygenase (rbcL) messenger RNA.

The chloroplast mRNAs from Euglena gracilis fall into two classes. One group of mRNs from this organelle contains a Shine-Dalgarno sequence 5' to the start codon, while the other group of mRNAs does not have a conserved sequence signal in the 5'-untranslated region. To investigate the start signals for E. gracilis chloroplast mRNAs that do not carry a Shine-Dalgarno sequence, 30 S initiation complex formation has been studied using a series of transcripts carrying the wild-type translational start site of ribulose-bisphosphate carboxylase/oxygenase (rbcL) or mutated derivatives of this site. Mutation of the start codon of the rbcL gene indicates that the chloroplast 30 S subunit is recognizing only the correct AUG codon. The analysis of the messages from a series of deletion mutants shows that a minimum of delta 20 residues 5' to the AUG codon is required for activity. Maximal activity requires the full 55-base leader sequence. Surprisingly, a transcript carrying the inverse complement of 48 bases in the leader is delta 60% as active as the wild-type message in promoting initiation complex formation. Introduction of a Shine-Dalgarno sequence in the 5'-leader increases the activity of the mRNA only delta 1.4-2-fold. The presence of an oligodeoxynucleotide containing a strong Shine-Dalgarno sequence does not significantly inhibit the formation of initiation complexes at the rbcL start site. Similar results are obtained when initiation complexes are formed with initiation factors from either E. gracilis chloroplasts or Escherichia coli.

Animals↗
PubMed1990

Recombination resulting in unusual features in the polyomavirus genome isolated from a murine tumor cell line.

Polyomavirus-induced tumor formation in the adult natural mouse host has been investigated. Tumors were produced in nude mice with the transformation-defective mutant strain NG18 after a long latency period by apparent activation of a cryptic endogenous transforming viral function. A tumor cell line, designated ScB, was established and characterized. Cells from this morphologically distinct line were unusual in that they grew in soft agar but did not form foci. They were highly tumorigenic. They had a 3.1-kilobase major viral transcript that hybridized to probes derived from regions encoding both the T antigens and the structural proteins. ScB cells expressed polyomavirus small T antigen, a slightly altered middle T antigen, and a truncated large T antigen but no capsid proteins. Middle T antigen preserved its interactions with host proteins of 60 and 37 kilodaltons and with c-src. Analysis of cDNA and genomic clones indicated that the stable viral insert in the ScB genome contained multiple copies of the viral B-enhancer. The genome contained two intragenic inversions which created novel early- to late-strand switches. A simple model for the generation of one inversion is proposed that involves the juxtaposition of two stem-loop structures at an illegitimate recombination site; the location of the inverted segment within the integrated sequence permits use of the viral late polyadenylation signal in early-region transcripts, as confirmed by DNA sequence. A repetitive sequence may facilitate recombination at the other inversion site. Both the biological consequences of the observed rearrangements and the structure of the integrated viral DNA suggest that the recombination events are nonrandom.

Animals↗
PubMed2001

Rearrangements of the DNA in carbon ion-induced mutants of Arabidopsis thaliana.

To elucidate the nature of structural alterations in plants, three carbon ion-induced mutations in Arabidopsis thaliana, gl1-3, tt4(C1), and ttg1-21, were analyzed. The gl1-3 mutation was found to be generated by an inversion of a fragment that contained GL1 and Atpk7 loci on chromosome 3. The size of the inverted fragment was a few hundred kilobase pairs. The inversion was found to accompany an insertion of a 107-bp fragment derived from chromosome 2. The tt4(C1) mutation was also found to be due to an inversion. The size of the intervening region between the breakpoints was also estimated to be a few hundred kilobase pairs. In the case of ttg1-21, it was found that a break occurred at the TTG1 locus on chromosome 5, and reciprocal translocation took place between it and chromosome 3. From the sequences flanking the breakpoints, the DNA strand breaks induced by carbon ions were found to be rejoined using, if present, only short homologous sequences. Small deletions were also observed around the breakpoints. These results suggest that the nonhomologous end-joining (NHEJ) pathway operates after plant cells are exposed to ion particles.

Arabidopsis↗
PubMed1989

Genomic sequencing reveals a 5-methylcytosine-free domain in active promoters and the spreading of preimposed methylation patterns.

Previous work demonstrated an inverse correlation between methylation at the three 5'-CCGG-3' sequences in positions +24, +6, and -215 relative to the cap site of the late E2A promoter of adenovirus type 2 (Ad2) DNA and its activity. In the study presented here, we used the genomic sequencing method to detect 5-methyl-2'-deoxycytidine (m5dC) residues in 5'-CG-3' sequences other than the 5'-CCGG-3' (Hpa II) sites. The patterns of methylation in all 5'-CG-3' sequences over a region of about 180 base pairs required for gene activity in the late E2A promoter of integrated Ad2 DNA were determined in cell lines that carry this promoter in an active or inactive state. In cell lines HE1 and uc2, the late E2A promoter is active and all thirteen 5'-CG-3' sequences between positions +24 and -160 are unmethylated. In cell line HE2, the same promoter is permanently shut off and all 5'-CG-3' sequences are methylated in both strands. Thus, the inverse correlation is perfect in these cell lines over a region of about 180 base pairs in the late E2A promoter. The same promoter segment was analyzed in cell lines mc23 and mc40, in which a late E2A promoter-chloramphenicol acetyltransferase (CAT) gene construct had been genomically fixed after in vitro 5'-CCGG-3' methylation and subsequent transfection. In cell line mc23, the preimposed methylation pattern was stable and the CAT gene was inactive. Genomic sequencing confirmed the presence of m5dC in the 5'-CCGG-3' sequences and revealed the spreading of methylation to neighboring 5'-CG-3' sequences along the entire promoter. Some of these sites were hemimethylated. In cell line mc40, several of the 120 integrated copies became demethylated in positions +24 and +6, but the promoter was methylated in some of the copies upstream of position -50. Cell line mc40 expressed the CAT gene.

5-Methylcytosine↗
PubMed2006

Remarkable site specificity of local transposition into the Hsp70 promoter of Drosophila melanogaster.

Heat-shock genes have numerous features that ought to predispose them to insertional mutagenesis via transposition. To elucidate the evolvability of heat-shock genes via transposition, we have exploited a local transposition technique and Drosophila melanogaster strains with EPgy2 insertions near the Hsp70 gene cluster at 87A7 to produce numerous novel EPgy2 insertions into these Hsp70 genes. More than 50% of 45 independent insertions were made into two adjacent nucleotides in the proximal promoter at positions -96 and -97, and no insertions were into a coding or 3'-flanking sequence. All inserted transposons were in inverse orientation to the starting transposon. The frequent insertion into nucleotides -96 and -97 is consistent with the DNase hypersensitivity, absence of nucleosomes, flanking GAGA-factor-binding sites, and nucleotide sequence of this region. These experimental insertions recapitulated many of the phenotypes of natural transposition into Hsp70: reduced mRNA expression, less Hsp70 protein, and decreased inducible thermotolerance. The results suggest that the distinctive features of heat-shock promoters, which underlie the massive and rapid expression of heat-shock genes upon heat shock, also are a source of evolutionary variation on which natural selection can act.

Animals↗
PubMed1998

Cloning and molecular characterization of part of a new gene fused to HMGIC in mesenchymal tumors.

Aberrations of the HMGIC gene, encoding an architectural transcription factor and located in the chromosomal region 12q15, are very frequent among benign mesenchymal tumors, such as lipomas, uterine leiomyomas, or pulmonary chondroid hamartomas. These HMGIC aberrations are caused by characteristic structural chromosomal aberrations, either visible by conventional cytogenetics or as cryptic abnormalities. Some of these aberrations of chromosome 12 are not specific for particular tumor entities but can occur in a variety of tumors with HMGIC abnormalities. One such example is the pericentric inversion inv(12)(p11.2q15). Starting from the ectopic sequence derived from an HMGIC fusion transcript of an aggressive angiomyxoma with such an inversion we established three PAC clones covering the breakpoint region 12p11 and cloned part of a yet unknown gene in 12p11.2, which is fused to the third exon of HMGIC. Using fluorescence in situ hybridization with these PACs we were able to show that the same region was involved by 12p11.2 aberrations in lipomas, aggressive angiomyxomas, and pulmonary chondroid hamartomas.

Amino Acid Sequence↗

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