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PubMed1989

Nucleotide sequences required for Tn3 transposition immunity.

The Tn3 transposon inserts at a reduced frequency into a plasmid already containing a copy of Tn3, a phenomenon known as transposition immunity. The cis-acting site on Tn3 responsible for immunity was mapped by deletions from each side to be within the terminal 38-base-pair sequence that is inversely repeated at the ends of Tn3. Two palindromic sequences are present in the essential part of this region. Some deletions conferred only partial immunity, and others conferred negative immunity. Multiple copies of partially immune ends conferred additional immunity. No other part of Tn3 was necessary for immunity.

Base Sequence↗
PubMed2001

Oxygen-enhanced MR ventilation imaging of the lung: preliminary clinical experience in 25 subjects.

OBJECTIVE: The purpose of this study was to show the feasibility of oxygen-enhanced MR ventilation imaging in a clinical setting with correlation to standard pulmonary function tests, high-resolution CT, and (81m)Kr ventilation scintigraphy. SUBJECTS AND METHODS: Seven healthy volunteers, 10 lung cancer patients, and eight lung cancer patients with pulmonary emphysema were studied. A respiratory synchronized inversion-recovery single-shot turbo-spin-echo sequence (TE, 16; inversion time, 720 msec; interecho spacing, 4 msec) was used for data acquisition. The following paradigm of oxygen inhalation was used: 21% oxygen (room air), 100% oxygen, 21% oxygen. MR imaging data including maximum mean relative enhancement ratio and mean slope of relative enhancement were correlated with forced expiratory volume in 1 sec, diffusing lung capacity, high-resolution CT emphysema score, and mean distribution ratio of (81m)Kr ventilation scintigraphy. RESULTS: Oxygen-enhanced MR ventilation images were obtained in all subjects. Maximum mean relative enhancement ratio and mean slope of relative enhancement of lung cancer patients were significantly decreased compared with those of the healthy volunteers (p < 0.0001, p < 0.0001). The mean slope of relative enhancement in lung cancer patients with pulmonary emphysema was significantly lower than that of lung cancer patients without pulmonary emphysema (p < 0.0001). Maximum mean relative enhancement ratio (r(2) = 0.81) was excellently correlated with diffusing lung capacity. Mean slope of relative enhancement (r(2) = 0.74) was strongly correlated with forced expiratory volume in 1 sec. Maximum mean relative enhancement had good correlation with the high-resolution CT emphysema score (r(2) = 0.38). The maximum mean relative enhancement had a strong correlation with the distribution ratio (r(2) = 0.77). CONCLUSION: Oxygen-enhanced MR ventilation imaging in human subjects showed regional changes in ventilation, thus reflecting regional lung function.

Adult↗
PubMed1997

Comparison of T2-weighted and fluid-attenuated inversion-recovery fast spin-echo MR sequences in intracerebral AIDS-associated disease.

PURPOSE: To compare the value of fast fluid-attenuated inversion-recovery (FLAIR) with T2-weighted fast spin-echo MR imaging in the detection of acquired immunodeficiency virus (AIDS)-related lesions of the brain. METHODS: Forty-four human immunodeficiency virus (HIV)-positive patients were examined with both sequences on either a 1.0-T or a 1.5-T MR system. The number, size, location, and conspicuity of the lesions were evaluated by two independent observers. Contrast ratios between lesions and normal brain/cerebrospinal fluid were determined, and contrast-to-noise ratios were calculated. RESULTS: FLAIR was found to be superior to T2-weighted fast spin-echo in detection of small lesions and of lesions located in cortical/subcortical regions and deep white matter. The two techniques were equal in delineation of lesions larger than 2 cm and for lesions located in the basal ganglia and posterior fossa. In 24 patients, more lesions were detected with the FLAIR fast spin-echo technique. Lesion/cerebrospinal fluid contrast ratios and contrast-to-noise ratios were significantly higher for the FLAIR fast spin-echo sequences than for the T2-weighted fast spin-echo sequences. CONCLUSION: FLAIR allows early detection of small lesions in subcortical and cortical locations, especially in HIV encephalitis. Because of its improved lesion detection rate and greater overall lesion conspicuity, we believe FLAIR is useful in the evaluation of subtle changes in the brains of AIDS patients with central nervous system disease, and could even replace the T2-weighted fast spin-echo technique.

AIDS Dementia Complex↗
PubMed2001

Reduction of CSF and blood flow artifacts on FLAIR images of the brain with k-space reordered by inversion time at each slice position (KRISP).

BACKGROUND AND PURPOSE: Our purpose was to test a new variant of the fluid-attenuated inversion-recovery (FLAIR) sequence that was designed to reduce CSF and blood flow artifacts by use of a non-slice-selective inversion pulse and k-space reordered by inversion time at each slice position (KRISP). METHODS: With the KRISP FLAIR sequence, the slice order was cycled so that each inversion time (TI) was associated with a region of k-space rather than a particular slice, and the effective inversion time (TI(eff)) was chosen to null the signal from CSF. Scans were obtained with both conventional and KRISP FLAIR sequences. Studies were performed in 20 adult patients with a variety of brain diseases. Images were evaluated for artifacts from patient motion, CSF, and blood flow, and scored on a four-point scale. The conspicuity of the cortex, meninges, ventricular system, brain stem, and cerebellum was evaluated, as was lesion number and conspicuity. RESULTS: The KRISP FLAIR sequence showed more patient motion artifacts but had a pronounced advantage over the conventional sequence in control of CSF artifacts around the foramen of Munro, in the third ventricle, aqueduct, and fourth ventricle, as well as in the basal cisterns and around the brain stem and cerebellum. Blood flow artifacts from the internal carotid, basilar, and vertebral arteries were also much better controlled. Spurious high signal in the sylvian branches of the middle cerebral artery was eliminated. The meninges, cortex, ventricular system, brain stem, and cerebellum were better seen due to improved artifact suppression and an edge enhancement effect. CONCLUSION: The KRISP FLAIR sequence can suppress CSF and blood flow artifacts and improve the conspicuity of the meninges, cortex, brain stem, and cerebellum. Its major disadvantage is its duration, which may be reducible with a fast spin-echo version.

Adolescent↗
PubMed2001

Localization of post-traumatic trochlear nerve palsy associated with hemorrhage at the subarachnoid space by magnetic resonance imaging.

PURPOSE: To report evaluation of traumatic trochlear nerve palsy using head magnetic resonance imaging. DESIGN: Observational case reports. METHODS: We examined two cases involving trochlear nerve palsy after closed head injury. RESULTS: Using a fluid attenuated inversion recovery pulse sequence, MRI showed a high-intensity lesion consistent with subarachnoid hemorrhage at the trochlear nerve area in the ambient cisterns. CONCLUSION: An impact force directed toward the tentorium can be a mechanism of injury in some post-traumatic trochlear nerve palsies. Fluid attenuated inversion recovery pulse sequence is a sensitive method for detection of abnormalities in cases associated with head injury.

Adolescent↗
PubMed2005

Long inversely oriented subunits form a complex monomer of Tribolium brevicornis satellite DNA.

Highly abundant satellite DNA named TBREV is detected and characterized in the beetle Tribolium brevicornis (Insecta: Coleoptera). An outstanding peculiarity of the TBREV satellite monomer is its complex structure based on the two approximately 470-bp-long subunits, inversely oriented within a 1061-bp-long monomer sequence. The proposed evolutionary history demonstrates a clear trend toward increased complexity and length of the TBREV satellite monomer. This tendency has been observed on three levels: first as direct and inverted duplications of short sequence motifs, then by inverse duplication of the approximately 470-bp sequence segment, and, finally, by spread of inversely duplicated elements in a higher-order register and formation of extant monomers. Inversely oriented subunits share a similarity of 82% and have a high capacity to form a thermodynamically stable dyad structure that is, to our knowledge, the longest ever described in any satellite monomer. Analysis of divergences between inversely oriented subunits shows a tendency to a further reduction in similarity between them. Except in its centromeric localization, the TBREV satellite does not show similarity to other known Tribolium satellites, either in nucleotide sequence or in monomer length and complexity. However, TBREV shares common features of other Tribolium satellites that might be under functional constraints: nonconstant rate of evolution along the monomer sequence, short inverted repeats in the vicinity of an A+T tract, nonrandom distribution of A or T >/=3 tracts, and CENP-B box-like motifs. Although long inverted subunits might reinforce structural characteristics of the satellite monomer, their nucleotide sequence does not seem to be under constraints in order to preserve the dyad structure.

Animals↗
PubMed2005

Intracranial meningeal disease: comparison of contrast-enhanced MR imaging with fluid-attenuated inversion recovery and fat-suppressed T1-weighted sequences.

BACKGROUND AND PURPOSE: Contrast-enhanced fluid-attenuated inversion recovery (FLAIR) imaging has been reported to have higher sensitivity for detecting leptomeningeal disease compared with contrast-enhanced T1-weighted MR imaging. The purpose of this study was to compare contrast-enhanced T1-weighted MR images with fat suppression to contrast-enhanced FLAIR images to determine which sequence was superior for depicting meningeal disease. METHODS: We reviewed MR images of 24 patients (35 studies) with a variety of meningeal diseases. The MR imaging protocol included contrast-enhanced T1-weighted MR images with fat suppression (FS) and contrast-enhanced fluid-attenuated inversion recovery (FLAIR) images that were reviewed by three neuroradiologists and were assigned a rating of positive, equivocal, or negative for abnormal meningeal enhancement. The two sequences were compared side by side to determine which better depicted meningeal disease. RESULTS: Abnormal meningeal enhancement was positive in 35 contrast-enhanced T1-weighted MR images with FS and in 33 contrast-enhanced FLAIR studies. In the first group, which had the T1-weighted sequence acquired first (21 of 33 studies), contrast-enhanced T1-weighted images with FS showed superior contrast enhancement in 11 studies (52%), inferior contrast enhancement in six studies (29%), and equal contrast enhancement in four studies (19%) compared with the contrast-enhanced FLAIR images. In the second group, which had the FLAIR sequence acquired first (12 of 33), contrast-enhanced T1-weighted images with FS showed superior contrast enhancement in seven studies (58%), inferior contrast enhancement in two studies (17%), and equal contrast enhancement in three studies (25%). CONCLUSION: Contrast-enhanced T1-weighted MR imaging with FS is superior to contrast-enhanced FLAIR imaging in most cases for depicting intracranial meningeal diseases.

Adolescent↗
PubMedDate not supplied

Design and implementation of magnetization transfer pulse sequences for clinical use.

The transfer of magnetization between a free and a bound pool of spins is described in terms of the respective longitudinal relaxation times and the life times of spins in each pool. The effect of an off resonance radiofrequency (RF) pulse in producing saturation in the bound pool and a consequent decrease in both the available longitudinal magnetization and the T1 of spins in the free pool is described. The effects of increasing duration of the saturating RF pulse on image pixel signal intensity were used to determine values for the decrease in both T1 and the available magnetization in gray and white matter of the brain as well as in muscle, fat, and CSF. At 0.15 T the available magnetization of muscle was reduced by approximately 60% and its T1 was decreased from 350 to 150 ms. The available magnetization of white and gray matter was reduced by 40% and their values of T1 were reduced by 80-110 ms. The reduction in available magnetization was used to increase contrast on proton density weighted or T2-weighted SE pulse sequences. These changes were also used to design inversion recovery (IR) pulse sequences with particular contrast properties. A short inversion time (TI) magnetization transfer (MT) IR (MT-STIR) pulse sequence was used to reduce the signal from normal muscle to zero to produce an angiographic effect in the leg. Increased tissue contrast was observed with a T2-weighted (MT-SE) sequence in a patient with bilateral cerebral infarction and with an MT-IR pulse sequence in a patient who had an intracranial hematoma. Three patients with cerebral tumors showed high lesion contrast with MT-STIR sequences. Components within two tumors were changed to different degrees by MT and in one case change in the brain attributable to recent radiotherapy treatment was only identified with an MT-STIR sequence. Magnetization transfer can be used to manipulate both the available longitudinal magnetization and the T1 of normal and abnormal tissues. The changes in tissue contrast produced by this can be very substantial and are likely to be of importance in clinical imaging.

Adult↗
PubMed1998

Fast FLAIR MRI in childhood white-matter abnormalities.

We compared a fast fluid-attenuated inversion recovery (FLAIR) pulse sequence with a dual-echo short tau fast inversion-recovery (DESTTIR) sequence in 20 children with white matter abnormalities. Although the overall image quality of DESTTIR images was better, the lesion-to-background contrast was significantly higher with the fast FLAIR pulse sequence and lesion detection was more accurate.

Adolescent↗
PubMed2005

Noninvasive quantification of cerebral blood volume in humans during functional activation.

Like cerebral blood flow (CBF), cerebral blood volume (CBV) is an important physiological parameter closely associated with brain activity and thus, noninvasive quantification of CBV during brain activation provides another opportunity to investigate the relationship between neuronal activity and hemodynamic changes. In this paper, a new method is presented that is able to quantify CBV at rest and during activation. Specifically, using an inversion recovery pulse sequence, a set of brain images was collected at various inversion times (TIs). At each TI, functional images were acquired with a block-design visual stimulation paradigm. A biophysical model comprised of multiple tissue components was developed and was utilized for the determination of CBV using the visual stimulation data. MRI experiments on five healthy volunteers showed that CBV was 5.0 +/- 1.5 ml blood/100 ml brain during rest and increased to 6.6 +/- 1.8 ml blood/100 ml brain following visual stimulation. Furthermore, experiments with visual stimulation at two frequencies (2 and 8 Hz) showed that the increases in CBV correlated with the strength of stimulation. This technique, with its ability to measure quantitative CBV values noninvasively, provides a valuable tool for quantifying hemodynamic signals associated with brain activation.

Algorithms↗
PubMed1999

Two-point method for T1 estimation with optimized gradient-echo sequence.

Relaxation times estimation methods play a central role in various problems, such as magnetic resonance (MR) hardware calibration, tissue characterization, or temperature measurement. Previous studies have proposed optimization criteria to estimate the relaxation time T1 faster than with a multipoint method leading to two-point methods. In this paper, the class of optimized two-point methods is extended to gradient-echo (GE) sequence offering new advantages over spin-echo (SE) or inversion recovery (IR) sequences. Two GE acquisitions, with optimal flip angles theta1 and theta2 minimizing both the total scan time and the variance in the computed T1 image were applied to estimate T1, and the results were compared with those of SE sequence with optimized paired repetition times T(R1) and T(R2). First, phantom studies were carried out with five tissue-like samples on a 0.5T scanner. Then in vivo, human brain T1 image were calculated using both optimized GE and SE two-point methods. More precise T1 GE estimates than those for SE were found thanks to high signal-to-noise ratio (SNR) per unit of time, but with a small bias. These results also concern the temperature variation measurement methods, based on T1 estimation. Preliminary experimental data for temperature measurement are given.

Brain↗
PubMed2005

Implementation of a rapid inversion-prepared dual-contrast gradient echo sequence for quantitative dynamic contrast-enhanced magnetic resonance imaging of the human prostate.

The first step in quantitative pharmacokinetic modeling is to determine the arterial input function (AIF) by deriving the contrast medium (CM) concentration from an appropriate imaging sequence by monitoring changes in either the amplitude or the phase signal of an accommodative artery. The bolus passage is best detected on T2- or T2*-weighted images, while extravasation is best assessed on T1-weighted images. Here, an imaging sequence is used that employs a parallel acquisition technique for the interleaved acquisition of an inversion-prepared T1-weighted image and a T1/T2*-mixed-weighted image for determination of the AIF. The sequence was applied in six patients with prostate cancer. A method is presented for quantifying the AIF derived from the signal intensity-time courses of both the T1/T2*-mixed-weighted and the T1-weighted image. Furthermore, in some patients the signal intensity-time course of the T1-weighted image exhibits flow-induced signal modulations. To reduce the effect of this flow-related signal enhancement the corresponding phase information was used. The sequence presented here has the potential to improve the quantification of the AIF at all time points and pharmacokinetic modeling of the CM dynamics of the prostate.

Algorithms↗
PubMed1991

Sequence of the cDNA encoding ovine tumor necrosis factor-alpha: problems with cloning by inverse PCR.

We have cloned and sequenced the ovine tumor necrosis factor-alpha (TNF-alpha)-encoding cDNA, using gene amplification by polymerase chain reaction (PCR) technology, to aid studies of assorted diseases in this species. We used primers selected from published TnfA sequences of other species on a cDNA template prepared from lipopolysaccharide-stimulated ovine alveolar macrophages, to generate a product representing the central region of the molecule. We then used a novel method based on 'inverse PCR' to generate a product containing the 5' and 3' ends of the molecule. Here, we present the complete sequence of the ovine TNF-alpha cDNA and compare it with other published TNF sequences. The cloned cDNA has a leader sequence of 156 bp followed by a protein-coding sequence of 702 bp and a 3'-untranslated region of 800 bp. The protein product of the gene is a protein of Mr = 25,586, 79% homologous to human TNF-alpha. An mRNA produced by alveolar macrophages, which hybridises to the cloned gene, is induced greatly, with a peak induction time of approx. 135 min, in response to stimulation by lipopolysaccharide and to plating on plastic. We also discuss the resolution of some artefacts of the inverse PCR technique.

Amino Acid Sequence↗
PubMed2000

Visualization of subthalamic nuclei with cortex attenuated inversion recovery MR imaging.

There is a significant amount of interest in studying the thalamus because of its central location in the brain and its role as a gatekeeper to higher centers of cognition. Imaging and measuring of the individual subnuclei of the thalamus has proven extremely difficult in MR because of the contrast-to-noise (CNR) of the MR sequences used. This report describes a novel MR pulse sequence known as cortex attenuated inversion recovery (CAIR), which increases the CNR in images and allows the individual subnuclei of the thalamus to be visualized by selectively nulling the gray matter in the brain using an inversion recovery sequence with an inversion time of 700 ms at 1.5 T.

Adult↗
PubMed1989

Characterization of normal brain tissue using seven calculated MRI parameters and a statistical analysis system.

A statistical analysis system for classifying normal brain tissue has been applied to the analysis of MRI scans on 45 volunteers. The Bayes Maximum Likelihood method was used to achieve a discrimination accuracy of 84% for 13 tissue types among three age group sets, with classification accuracies for individual regions ranging from 50 to 100%. In order to attain this level of discrimination a set of seven derived relaxation-type parameters was used to categorize the tissue types. Values for these experimentally estimated parameters were derived from the MRI intensities of eight images in the following pulse sequences: (1) a Carr-Purcell-Meiboom-Gill (CPMG) four-echo train, (2) a single-echo inversion recovery, and (3) three single-echo sequences with varying repetition times, TR, and echo delays, TE. The T2 values derived from ratios of single-echo intensities showed better discrimination power than those from the four-echo CPMG train. The general precision of the seven estimated parameters was excellent, with percentage standard deviations ranging from 4 to 18% for the various regions studied. The tissue discrimination achieved by use of just three relaxation parameters, T1, T2, and proton density, calculated from intensities of images from a four-echo sequence, an inversion recovery sequence, and a short TR single-echo sequence, was not as good, being only 55%.

Adult↗
PubMed1989

The use of an improved inversion pulse with the spin-echo/inversion-recovery sequence to give increased accuracy and reduced imaging time for T1 measurements.

The hyperbolic secant inversion pulse has been incorporated into the interleaved saturation-recovery/inversion-recovery sequence to provide T1 measurements combining high precision with a significantly reduced imaging time (a mean accuracy of 2% over a T1 range of 300 to 1650 ms for standard gel phantoms, with Tr1 = Tr2 = 2.0 s, Ti = 0.67 s).

Humans↗
PubMed1992

Magnetic resonance imaging of the parotid gland using the STIR sequence.

The object of this study was to determine the efficiency of the short tau inversion recovery (STIR) sequence in the assessment of salivary disease. Sixteen patients with tumours either in or adjacent to the parotid gland were imaged using a 1.5T Philips Gyroscan, with a standard head coil. T1-weighted spin-echo and STIR sequences were obtained in multiple planes and assessed independently by each of the authors. Positive fine needle aspiration cytology or histological proof of the nature of the imaged lesions was obtained for every patient. T1-weighted spin-echo images were most useful for visualizing anatomical structures and for identification of the facial nerve. All lesions were visible with T1-weighted images but were very much more conspicuous in the STIR sequences, for which a minimal lesion resolution of 6 mm was achieved. No contrast enhancement was required. It was not possible to determine the pathological nature of the lesion by scan appearance only. Our conclusion is that a combination of T1-weighted spin-echo and STIR sequences in the axial and coronal planes is the preferred protocol for salivary gland imaging.

Adolescent↗