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PubMed1993

A chemical shift selective inversion recovery sequence for fat-suppressed MRI: theory and experimental validation.

Fat-suppression techniques are used extensively in routine proton nuclear magnetic resonance imaging to produce images free from chemical shift artifacts and dynamic range problems. A hybrid fat-suppression sequence is studied which combines the principle of short time inversion recovery with chemical shift selective imaging. The aim of this study is to provide a theoretical understanding of the role of the sequence parameters, as well as to compare this hybrid sequence with its most closely related conventional fat-suppression techniques, namely selective pre-saturation and short time inversion recovery (STIR) imaging. The hybrid technique is shown to be robust in normal use, and more tolerant than the conventional methods to mis-settings of parameters such as inversion time, as well as tip angle and frequency bandwidth of the fat selective pulse.

Abdomen↗
PubMed1999

Bilateral mesial temporal sclerosis: MRI with high-resolution fast spin-echo and fluid-attenuated inversion-recovery sequences.

We report a retrospective analysis of MRI in 206 patients with intractable seizures and describe the findings in bilateral mesial temporal sclerosis (MTS) on fast spin-echo (FSE) and fast fluid-attenuated inversion-recovery (fFLAIR) sequences. Criteria for MTS were atrophy, signal change and loss of the digitations of the head of the hippocampus. In patients with bilateral MRI signs of MTS, correlation with clinical electro, volumetric MRI data and neuropsychological tests, when available, was performed. Bilateral MTS was observed in seven patients. Bilateral loss of the digitations and signal change on fFLAIR was seen in all seven. In three, bilateral atrophy was obvious. In two patients, mild bilateral atrophy was observed and in two others, the hippocampi were: asymmetrical, with obvious atrophy on only one side. Volumetric data confirmed bilateral symmetrical atrophy in five patients, and volumes were at the lowest of the normal range in the other two. The EEG showed temporal abnormalities in all patients, unilateral in five and bilateral in two. All patients had memory impairment and neuropsychological data confirmed visual and verbal memory deficits; two patients failed the Wada test on both sides. High-resolution T2-weighted FSE and fFLAIR sequences allow diagnosis of bilateral MTS, which has important therapeutic and prognostic implications.

Adult↗
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↗
PubMed1996

[Cholangiopancreatography with magnetic resonance. Clinical use of a new "inversion-recovery" sequence].

This study was aimed at correlating the yield of a three-dimensional (3D) inversion-recovery (IR) turbo spin-echo MR cholangiopancreatography (MRCP) sequence with that of ERCP and PTC in the imaging of the normal and abnormal biliopancreatic tract. Thirty patients with suspected biliary and pancreatic diseases were examined with MRCP first and then with ERCP or PTC; they were also submitted to US, CT and conventional MR studies and in 5 of them CT cholangiography was also performed. Five patients were normal and 25 had various obstructive abnormalities: 5 patients had gallbladder stones, 8 common bile duct stones, 5 a cholangiocarcinoma and 7 an adenocarcinoma of the pancreatic head or papilla. MRCP was performed with a superconductive magnet at 0.5 T, with volumetric images on coronal planes acquired using an IR turbo SE sequence (TR 2500, TE 1000, TF 89, 4 NEX) with respiratory triggering and vascular presaturation. Segmental intrahepatic bile ducts were correctly depicted in all the patients with benign or malignant obstruction of the common bile duct, but with some respiratory artifacts. Common bile duct stones were correctly depicted in 7 of 8 patients, but studying also the single coronal slices. With this method, the stones were clearly demonstrated in 22 examined gallbladders. Neoplastic obstruction and the obstruction level were correctly identified in all patients. Pancreatic ducts were shown in normal patients and in 8 of 13 patients with neoplastic or lithiasic obstruction of the common bile duct mainly on the pancreatic head. ERCP was carried out successfully in 5 patients with common bile duct stones and in 7 patients with neoplastic obstruction; in the other cancer patients, PTC was necessary. To conclude, respiratory-triggered 3D IR turbo spin-echo MRCP is a noninvasive technique to study mostly biliary conditions which yields similar information to ERCP and PTC in a large number of patients. Moreover, this sequence can be used with midfield MR units to study the obstruction of the biliary and pancreatic ducts not only when invasive techniques fail, but also routinely.

Adult↗
PubMed1994

The value of the short tau inversion recovery sequence in magnetic resonance imaging of thyroid eye disease.

22 patients with thyroid eye disease were examined with magnetic resonance imaging (MRI) and the results compared with 10 controls. Imaging was performed on a 1.0 T scanner using a head coil. All patients were examined using both T1W and short tau inversion recovery (STIR) sequences. The relative signal intensity (SI) of individual extraocular muscles were quantified by comparison with SI from the adjacent temporalis muscle to give a signal intensity ratio (SIR). The results were compared with clinical disease activity assessed by the Werner grading system. Visual evaluation of muscle size and calculated SIRs showed an increase when compared to normals in 15 of the 22 patients. This difference was significant in patients with high grade (4-6) clinical disease. The known histological changes in this disease suggest that this increase in signal is caused by oedema secondary to acute inflammation. STIR sequences suppress the retro-orbital fat and thus enhance these changes both in the muscles and in the fat itself. The MR findings suggest that the STIR sequence can be used to predict those patients that will respond to anti-inflammatory treatment.

Adult↗
PubMed1999

Brain lesions: when should fluid-attenuated inversion-recovery sequences be used in MR evaluation?

PURPOSE: To compare qualitatively and quantitatively the contrast of brain lesions detected with fluid-attenuated inversion-recovery (FLAIR) and intermediate-weighted sequences at magnetic resonance (MR) imaging. MATERIALS AND METHODS: In this prospective study, 47 patients suspected of having a brain lesion underwent MR imaging with FLAIR, intermediate-weighted, and T2-weighted sequences. Qualitative assessment was performed of lesion conspicuity, detection, overall image artifact, and additional clinical information. Contrast and contrast-to-noise ratio (CNR) were calculated between lesions and the normal brain or cerebrospinal fluid (CSF). RESULTS: FLAIR images were equal to intermediate-weighted images for overall lesion conspicuity and detection but were associated more often with image artifacts. Lesion-to-background contrast was significantly higher on FLAIR than on intermediate-weighted images. FLAIR images failed to demonstrate multiple sclerosis (MS) plaques located in the basal ganglia and brain stem. CONCLUSION: Although FLAIR images provided additional information in some cases, they did not have distinct advantages over intermediate-weighted images. When cases of MS are evaluated, intermediate-weighted images are preferable to FLAIR images. Except in cases of MS, either FLAIR or intermediate-weighted sequences should be added to T2-weighted sequences at MR imaging.

Adolescent↗
PubMed2006

Comparative analysis of the bovine MHC class IIb sequence identifies inversion breakpoints and three unexpected genes.

The bovine major histocompatibility complex (MHC) or BoLA is organized differently from typical mammalian MHCs in that a large portion of the class II region, called class IIb, has been transposed to a position near the centromere on bovine chromosome 23. Gene mapping indicated that the rearrangement resulted from a single inversion, but the boundaries and gene content of the inverted segment have not been fully determined. Here, we report the genomic sequence of BoLA IIb. Comparative sequence analysis with the human MHC revealed that the proximal inversion breakpoint occurred approximately 2.5 kb from the 3' end of the glutamate-cysteine ligase, catalytic subunit (GCLC) locus and that the distal breakpoint occurred about 2 kb from the 5' end from a divergent class IIDRbeta-like sequence designated DSB. Gene content, order and orientation of BoLA IIb are consistent with the single inversion hypothesis when compared with the corresponding region of the human class II MHC (HLA class II). Differences with HLA include the presence of a single histone H2B gene located between the proteasome subunit, beta type, 9 (PSMB9) and DMB loci and a duplicated TAP2 with a variant splice site. BoLA IIb spans approximately 450 kb DNA, with 20 apparently intact genes and no obvious pseudogenes. The region contains 227 simple sequence repeats (SSRs) and approximately 167 kb of retroviral-related repetitive DNA. Nineteen of the 20 genes identified in silico are supported by bovine EST data indicating that the functional gene content of BoLA IIb has not been diminished because it has been transposed from the remainder of BoLA genes.

Animals↗
PubMed2005

Comparative evaluation of magnetization transfer contrast and fluid attenuated inversion recovery sequences in brain tuberculoma.

AIM: To compare T1-weighted magnetization transfer (MT) with fluid attenuated inversion recovery (FLAIR) imaging for evaluating conspicuity and number of lesions in individuals with brain tuberculoma. MATERIALS AND METHODS: In all 28 patients with brain tuberculoma underwent MR examination using fast spin-echo (FSE) T2, spin-echo (SE) T1, T1-weighted MT and FLAIR imaging. Post-contrast T1-weighted MT imaging was taken as the gold standard for assessing the number of lesions. Tuberculomas detected both on T1-weighted MT and FLAIR imaging were examined for the wall to be defined, and were divided into two groups on the basis of presence (group 1) or absence (group 2) of perilesional oedema visible on FLAIR imaging. The mean signal intensity of the wall of the lesions and adjacent oedema or brain parenchyma was analyzed qualitatively and quantitatively. RESULTS: The number of lesions detected on T1-weighted MT was higher than on FLAIR imaging (209 versus 163). Conspicuity in both groups was better on T1-weighted MT images qualitatively as well as quantitatively. The difference in the signal intensity of the wall of the lesion and perilesional oedema was statistically significant only on T1-weighted MT images in group 1 (p=0.0003 versus 0.3), whereas in group 2 it was statistically significant both on T1-weighted MT and FLAIR imaging (p=0.009 versus 0.05). CONCLUSION: FLAIR imaging is not helpful in the examination of brain tuberculomas compared with T1-weighted MT imaging, as it neither contributes to the characterization of lesion nor assesses the true disease load.

Adolescent↗
PubMed2001

Analysis of integrated hepatitis B virus DNA and flanking cellular sequence by inverse polymerase chain reaction.

Although hepatitis B virus (HBV) DNA has been detected in the human hepatoma cell line, HAGS 2.1, viral and cellular junction sequences have not been investigated fully. To facilitate the analysis of HBV DNA integration sites in HAGS 2.1 cells, a combination of conventional polymerase chain reaction (PCR) and inverse PCR (IPCR) was carried out to identify the junction between the viral and the cellular gene. The HBV integrant and its cellular counterpart sequence were cloned and analyzed. The sequencing data indicated that the breakpoints on the HBV integrant are at nucleotide 2111 of the C gene and nucleotide 1558 of the X gene. The length of the integrated HBV DNA in HAGS 2.1 was approximately 2.6 kb, which includes partial C, P, and X genes and an intact S gene. The cellular sequence flanking the integrated HBV gene was very similar to a human satellite III repetitive sequence with 43 and 56 of GGAAT repeats on the left- and right-hand side, respectively. Although the findings on the viral-cellular junction in HAGS 2.1 cells cannot explain the liver tumorigenesis, the current study shows that by choosing the nearest restriction site, which can be determined by conventional PCR rather than using a unique site within the integrated viral sequence to do IPCR, gives a higher successful rate for cloning and the subsequent analysis of the viral-cellular junctions.

Cloning, Molecular↗
PubMed1996

[Advantages and disadvantages of fast fluid-attenuated inversion recovery sequence in the evaluation of brain infarction].

This study was performed to determine the advantages and disadvantages of fast fluid attenuated inversion recovery (fast FLAIR) images in diagnosing brain infarction compared with fast spin-echo (fast SE) images. Fast FLAIR and fast SE images were obtained in 32 patients with brain infarction. Infarctions close to the sulci were difficult to differentiate from the real sulci on fast SE images, but were clearly depicted on FLAIR images. Linear foci along with cortex were especially well demonstrated on FLAIR images. On the other hand, foci that showed high signal intensity on fast SE images were sometimes appeared as having low or iso signal intensity on FLAIR images. These foci, suspected of being cystic lesions, were sometimes difficult to identify on fast FLAIR images. For the above reasons, we concluded that fast FLAIR and fast SE each have advantages and disadvantages in the detection of brain infarctions.

Cerebral Infarction↗
PubMed2002

Multislice double inversion pulse sequence for efficient black-blood MRI.

Over the last several years there has been a rapidly growing interest in high-resolution MRI of the vascular wall to assess the extent of atherosclerotic lesions. Vessels of particular clinical relevance are the carotid and coronary arteries. Currently, the preferred imaging sequence for these studies is a "black-blood" technique based on the double-inversion scheme to null the blood signal. A critical drawback of the black-blood technique, however, has been its single-slice nature, as there is only one point in time during the recovery of the blood magnetization from inversion at which the signal is completely nulled. Consequently, the total scan time can become prohibitively long, particularly when an imaging protocol includes several series of these datasets. In this work, a multiple-slice double-inversion technique is described that can reduce the scan time by a factor of two or more. It is demonstrated in vivo with examples from carotid and coronary arteries that one can acquire multiple slices with sufficient nulling of blood, following a single set of inversion pulses.

Adult↗
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↗
PubMed1997

Assembly and dissociation of human insulin and LysB28ProB29-insulin hexamers: a comparison study.

PURPOSE: Investigations into the kinetic assembly and dissociation of hexameric LysB28ProB29-human insulin (LysPro), a rapid-acting insulin analog produced by the sequence inversion of amino acids at positions B28 and B29, were designed to explain the impact that the sequence inversion has on the formulation and pharmacokinetics of the insulin analog. METHODS: The kinetics of phenolic ligand binding to human insulin and LysPro were studied by stopped-flow spectroscopy. The kinetics of R6 hexamer disruption were studied by extraction of Co(II) with EDTA. RESULTS: Phenolic ligand binding to human insulin yielded rate constants for a fast and slow phase that increased with increasing ligand concentration and are attributed to the T6 --> T3R3 and T3R3 --> R6 transitions, respectively. However, the kinetics of phenolic ligand binding with LysPro was dominated by rates of hexamer assembly. The kinetic differences between the insulin species are attributed to alterations at the monomer-monomer interface in the dimer subunit of the LysPro analog. The extraction of Co(II) from both hexameric complexes by EDTA chelation is slow at pH 8.0 and highly dependent on ligand concentration. Cobalt extraction from LysPro was pH dependent. Of the various phenolic ligands tested, the relative affinities for binding to the human and LysPro hexamer are resorcinol > phenol > m-cresol. CONCLUSIONS: The extraction data support the formation of an R6-type LysPro hexamer under formulation conditions, i.e., in the presence of divalent metal and phenolic ligand, that is similar in nature to that observed in insulin. However, the formation kinetics of LysPro identify a radically different monomeric assembly process that may help explain the more rapid pharmacokinetics observed with the hexameric formulation of LysPro insulin relative to human insulin.

Cobalt↗
PubMed1980

Structure of a cloned circular Moloney murine leukemia virus DNA molecule containing an inverted segment: implications for retrovirus integration.

Closed circular Moloney murine leukemia virus (M-MuLV) DNA was prepared from recently infected cells and cloned in a lambda vector. Four classes of cloned M-MuLV inserts were found: Class I, full length 8.8-kilobase (kb) inserts with two tandem long terminal repeats (LTRs) of 600 base pairs; class 2, 8.2-kb inserts with a single copy of a LTR; class 3, M-MuLV DNA inserts with various portions deleted; and class 4, an 8.8-kb insert with an internal sequence inversion. Determination of nucleotide sequence at the junction between the two LTRs from a class 1 insert suggested that circularization occurred by blunt-end ligation of an 8.8-kb linear DNA. The class 4 molecule had an inversion that was flanked by inverted LTRs, each of which had lost two terminal base pairs at the inversion end points. Also, four base pairs that were present only once in standard M-MuLV DNA were duplicated at either end of the inversion. This molecule was interpreted as resulting from an integrative inversion in which M-MuLV DNA has integrated into itself. Its analysis thus provided explicit information concerning the mechanism by which retrovirus DNA integrates into host cell DNA. Models of retrovirus integration based on bacterial DNA transposition mechanisms are proposed.

Bacteriophage lambda↗
PubMed2005

Diagnostic evaluation of magnetic resonance imaging with turbo inversion recovery sequence in head and neck tumors.

The clinical outcome of patients with head and neck cancer depends on many factors such as tumor size, metastatic involvement and angioarchitecture of the tumor. The correct staging of tumor extension, presence of cervical lymph node metastases and evaluation of vascular infiltration are essential diagnostic steps before treatment. The aim of this study was to evaluate the accuracy of turbo inversion recovery magnitude (TIRM) magnetic resonance imaging (MRI) in the diagnosis of head and neck tumors with special attention to tumor size and tumor spread according to the current TNM classification. TIRM sequence with short T1 relaxation and long TE (echo time) improves imaging contrast because of the increased T1-weighting and the inherent fat suppression. In a prospective clinical study, 32 patients underwent preoperative MRI. Diagnosis was confirmed histologically in all cases. Scanning was performed on a 1.0-T unit applying TIRM as well as T1- and T2-weighted turbo spin echo (TSE) sequences. In all sequences, tumor size was overestimated due to reactive inflammatory changes surrounding the tumor tissue. The least overestimation was documented on TIRM and post-contrast T1 TSE. The highest values of relative tumor signal intensities were obtained in TIRM (3.5+/-0.9) and T2 TSE (3.5+/-0.8) followed by post-contrast T1 TSE (1.6+/-0.7) and pre-contrast T1 TSE (1.2+/-0.3). Due to the inherent fat suppression, tumor delineation was most obvious in TIRM. In patients with suspected cancer of the head and neck, TIRM should be considered as a standard and a diagnostically relevant sequence in the MRI staging protocol.

Adult↗
PubMed1991

An optimized multislice acquisition sequence for the inversion-recovery MR imaging.

An optimized multislice data acquisition scheme for inversion-recovery MR imaging is proposed and experimental results are presented. In this new scheme, instead of forming a set of multislice inversion-recovery sequences in series for a given phase encoding step, 180 degrees inversion pulses corresponding to different slices are interwoven with the spin echo data acquisition sequence in an optimal way depending on the desired inversion-recovery time. For example, between the 180 degrees inversion RF pulse and the spin-echo imaging sequence, a number of imaging and inversion sequences are inserted with different slice combinations, i.e., long inversion-recovery time is effectively utilized for the other slice pre-inversion and data acquisition. With the optimized sequence, imaging time has been reduced by as much as a factor of four compared with the existing methods.

Brain↗