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PubMedDate not supplied

Characterization of focal fatty change in the liver with a fat-enhanced inversion-recovery sequence.

A T1-weighted inversion-recovery (IR) sequence was used to study 15 patients with possible fatty change in the liver. The inversion time (TI) was calculated for optimal suppression of normal liver signal (t-null). Conventional spin-echo (SE) and short TI IR (STIR) sequences were also performed. For seven documented benign focal fatty liver lesions, the T1-weighted IR (fat-enhanced) sequence clearly enabled differentiation of normal from fat-infiltrated liver, whereas three of these lesions were isointense to normal liver with all other sequences. The livers of the other nine patients (two normal, one with diffuse fatty change, two with metastatic disease, one with hemangioma, one with focal nodular hyperplasia, one with simple cyst, and one with micronodular cirrhosis) showed homogeneous reduction of liver signal with the fat-enhanced IR sequence.

Adolescent↗
PubMed1983

NMR anatomy of the brain using inversion-recovery sequences.

The use of NMR inversion-recovery (IR) sequences to demonstrate brain anatomy is illustrated. The high level of grey-white matter contrast is of value in localising anatomical structures and demonstrating myelination during childhood. While the resemblance of IR scans to gross anatomical sections in different planes is close, it is limited by the spatial resolution of the NMR scanner, artefacts and partial volume effects.

Adult↗
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↗
PubMed2000

Two peptides from CD23, including the inverse RGD sequence and its related peptide, interact with the MHC class II molecule.

The human CD23 molecule (low affinity receptor for IgE) has a C-type lectin domain, a reversed Arg-Gly-Asp (RGD) sequence near the C-terminus, and an "RGD-binding inhibitory peptide" at the root of the N-sugar chain. Three peptides were synthesized to determine their functions, i.e., #1, including an inverse RGD sequence near the C-terminus; #2, RGD-binding inhibitory peptides in the gpIIIa chain of platelet integrin gpIIb/IIIa; and #3, the inverse sequence located at the root of the N-sugar chain of CD23 which has homology to peptide 2. Among the three peptide, only peptide 3 inhibited aggregation of L-KT9 cells. Isotope-labeled peptides 1 and 3 bound to MHC class II molecules but peptide 1 did not bind to CD23 molecules. Peptide 3 showed a higher affinity to MHC class II than did peptide 1. Both peptides in CD23, therefore, seem to have interesting and important functions in relation to MHC class II molecules and also to CD23 molecules when CD23 on EBV-transformed B cells acts as a lectin in homotypic cell aggregation. The physiological function of CD23 was discussed from an evolutional point of view.

Amino Acid Sequence↗
PubMed1996

[Fluid attenuated inversion recovery sequences: indications in neuroradiology].

The acronym FLAIR refers to fluid attenuation inversion recovery sequences, which are T2-weighted MR pulse sequences with liquor signal saturation by a long TI. They are characterized by long TR and TE and therefore the acquisition time is very long in the conventional mode, while fast imaging (the Turbo mode) reduces acquisition time to less than 2 minutes. Our study was aimed at codifying the use of this type of sequence in neuroradiologic studies. All the exams were performed with an MR unit with a 1-Tesla magnetic field. We carried out 150 neuroradiologic exams with this pulse sequence on patients with cerebral, medullary or orbital conditions. This technique is very useful to study periventricular or cortical lesions in multiple sclerosis and in other multifocal cerebral conditions (e.g., multiple metastases or lacunar infarcts), but we pointed out the following other advantages: better definition of the extent of infiltrative white matter lesions (i.e., gliomatosis cerebri and lymphomas), better differentiation of cystic from necrotic cavities and exact characterization of cortical damage in cerebral ischemic lesions (useful also for the differential diagnosis). Moreover, FLAIR pulse sequences could diagnose some globe conditions, such as amelanotic uveal melanomas and malformations with no need of contrast agent administration. In contrast, they were useless to study deep ischemic areas, solid neoplasms, hemorrhagic lesions, poroencephalic areas, intrinsic medullary lesions and intra-orbital and extra-ocular conditions. In conclusion, the FLAIR technique is a major diagnostic tool in neuroradiologic MR studies because they overcome such limitations of Turbo SE PD sequences as blurring artifacts; moreover, their acquisition time is always very short. In some cases, FLAIR images are decisive for the diagnosis.

Brain Diseases↗
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↗
PubMed1996

Adult cerebrovascular disease: role of modified rapid fluid-attenuated inversion-recovery sequences.

PURPOSE: To compare a rapid fluid-attenuated inversion-recovery (FLAIR) sequence with T1-weighted, fast spin-echo proton density-weighted, and T2-weighted images in the evaluation of cerebrovascular disease. METHODS: All patients underwent standard T1-, proton density-, and T2-weighted fast spin-echo and fast FLAIR MR imaging at 1.5 T. Images were compared for lesion size, location, and conspicuity. RESULTS: Forty-five infarctions were identified on T2-weighted and fast FLAIR sequences. Lesion size was comparable on the proton density-weighted, fast T2-weighted, and fast FLAIR sequences, although lesion conspicuity was superior on the fast FLAIR images in 43 (96%) of the lesions. Associated periventricular and pontine hyperintensities were more extensive on the fast FLAIR images. CONCLUSION: Our modified fast FLAIR technique provided improved conspicuity of infarctions and white matter disease as compared with T1-, proton density-, and T2-weighted spin-echo images, and a reduced scan time compared with conventional FLAIR sequences in patients with cerebrovascular disease.

Adult↗
PubMed1997

MR of the spine with a fast T1-weighted fluid-attenuated inversion recovery sequence.

PURPOSE: To optimize a T1-weighted fast fluid-attenuated inversion recovery (FLAIR) sequence using computer-simulated data and to study its clinical utility for imaging the spine. METHODS: Relative signal intensities and contrast of relevant normal and pathologic tissues in the spine were computed using an inversion recovery equation modified to account for a hybrid RARE (rapid acquisition with relaxation enhancement) readout. A range of inversion time (TI) and repetition time (TR) pairs that null the signal from CSF was generated. A contrast-optimized heavily T1-weighted fast FLAIR sequence, based on the generated data, was qualitatively compared with conventional T1-weighted spin-echo sequences for imaging various spinal abnormalities. RESULTS: A T1/TR pair of approximately 862/2000 was extracted from the computer-generated data to produce effective nulling of CSF signal, to achieve heavy T1 weighting, and to optimize contrast between abnormal tissues and cord/bone marrow. Clinical implementation of the optimized T1-weighted fast FLAIR sequence revealed superior contrast at the CSF-cord interface, better conspicuity of lesions of the spinal cord and bone marrow, and reduced hardware-related artifacts as compared with conventional T1-weighted spin-echo sequences. CONCLUSION: The optimized T1-weighted fast FLAIR technique has definite advantages over spin-echo sequences for imaging the spine. Comparable acquisition times render the FLAIR sequence the method of choice for T1-weighted imaging of the spine.

Adult↗
PubMedDate not supplied

Experience with MR cholangiopancreatography with use of a fast inversion recovery sequence during a single breath-hold period.

The purpose of this study was to evaluate the single breath-hold fast inversion recovery sequence (FIR) for depicting the biliary tract. A prospective study was performed in 40 patients with suspected diseases in the biliary tract. MRCP (magnetic resonance cholangiopancreatography) including cholecystograms of diagnostic quality was carried out in 35 patients. Impacted common duct stones were able to be distinguished from malignancies because of their characteristic shapes of obstruction in four of five cases. FIR with thick slices can provide a shorter acquisition time and fewer artifacts with better signal to noise ratio and contrast to noise ratio than MIP images obtained by means of gradient echo methods. MRCP with FIR was a useful adjunctive tool for non-invasive evaluation of patients with obstructive jaundice.

Biliary Tract↗
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↗
PubMed1997

[Fast spin echo and fast fluid attenuated inversion recovery sequences in multiple sclerosis].

Fast spin echo (FSE) and fast fluid attenuated inversion recovery (fast-FLAIR) MR sequences were compared with conventional spin echo (CSE) in quantitating multiple sclerosis (MS) lesion burden. For each sequence, the total number and volume of MS lesions were calculated in 38 remitting MS patients using a semiautomated lesion detection program. CSE, FSE and fast-FLAIR images were reported on randomly and at different times by two expert observers. Interobserver differences, the time needed to quantitate MS lesions and lesion signal intensity (contrast-to-noise ratio and overall contrast) were considered. The lesions were classified by site into infratentorial, white matter and cortical/subcortical. A total of 2970 lesions with a volume of 961.7 cm3 was calculated on CSE images. FSE images depicted fewer (16.6%; p < .005) and smaller (24.9%; p < .0001) lesions and the differences were statistically significant. Despite an overall nonsignificant reduction for fast-FLAIR images (.5% and 4.8% for lesion number and volume, respectively), significantly lower values (lesion number: p < .01; volume: p < .04) were observed for infratentorial lesions, while significantly higher values were seen for cortical/subcortical lesions (lesion number: p < .01; volume: p < .02). A higher lesion/white matter contrast (p < .002), a significant time saving for lesion burden quantitation (p < .05) and very low interobserver variability were found in favor of fast-FLAIR. Our data suggest that, despite the limitations regarding infratentorial lesions, fast-FLAIR sequences are indicated in MS studies because of their good identification of cortical/subcortical lesions, almost complete interobserver agreement, higher contrast-to-noise ratio and the limited time needed for semiautomated quantitation.

Adult↗
PubMed1996

Determining depth of invasion of advanced colorectal cancer using MRI short inversion time inversion recovery sequences.

To examine the usefulness of magnetic resonance imaging (MRI) in the preoperative determination of cancerous invasion, we examined 39 patients with advanced colorectal cancer with 0.5T MRI. We employed short inversion time inversion recovery (STIR) sequences, in addition to ordinary spin echo sequences for T1- and T2-weighted images. Preoperatively, the estimated depth of tumor invasion was classified into three grades according to MRI findings, and confirmed on the basis of surgical and histopathologic results. The depth of tumor invasion estimated preoperatively using STIR sequences corresponded well with the surgical and histopathologic results in 85% of the cases. In contrast, assessments based on T1-weighted images corresponded well in only 62% of the cases and T2-weighted images corresponded well in only 64%.

Colon, Sigmoid↗
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↗