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PubMed2001

MexR repressor of the mexAB-oprM multidrug efflux operon of Pseudomonas aeruginosa: identification of MexR binding sites in the mexA-mexR intergenic region.

The MexR repressor of the mexAB-oprM multidrug efflux operon of Pseudomonas aeruginosa was purified as a C-terminal histidine-tagged protein by metal chelate affinity chromatography. The purified protein was shown to bind ca. 200 bp upstream of mexA, at two sites, each of which contains a repeat of the nucleotide sequence GTTGA in inverse orientation. DNA sequence analysis identified mexA and mexR promoters within the MexR binding regions, consistent with the previously observed negative regulation of mexR and mexAB-oprM expression by MexR. Transcription of mexA from the promoter originating within the MexR binding site II was confirmed and shown to be markedly enhanced in a nalB (i.e., mexR) mutant of P. aeruginosa. A second mexA promoter was also identified, ca. 70 bp upstream of mexAB-oprM, and transcription from this promoter appeared to occur in both the wild type and a nalB mutant. Production of MexAB-OprM in wild-type cells may be due to expression from a constitutively expressed proximal promoter, while MexAB-OprM hyperexpression in nalB mutants is due to the additional expression from a MexR-regulated distal promoter.

Bacterial Outer Membrane Proteins↗
PubMed2004

Right-lower-quadrant pain and suspected appendicitis in pregnant women: evaluation with MR imaging--initial experience.

PURPOSE: To determine if there is a role for magnetic resonance (MR) imaging in evaluation of pregnant women with acute right-lower-quadrant pain in whom acute appendicitis is suspected. MATERIALS AND METHODS: Informed consent and institutional review board approval were obtained. Images obtained with a 1.5-T MR imager and medical records of 23 pregnant women (age range, 19-34 years; mean age, 24.7 years) who presented with acute right-lower-quadrant pain were retrospectively reviewed. MR protocol included use of transverse, coronal, and sagittal noncontiguous T2-weighted single-shot fast spin-echo (SE) sequences; transverse fat-suppressed T2-weighted fast SE sequences; transverse T1-weighted gradient-recalled-echo sequences; and transverse and coronal short inversion time inversion-recovery sequences performed through the lower abdomen and pelvis. MR findings were evaluated by two radiologists and compared with surgical and pathologic findings and clinical follow-up data. RESULTS: Appendix was detected in 20 (86.9%) of 23 patients. Seven patients underwent surgery; four had acute appendicitis, and three had ovarian torsion. Two patients with pelvic abscesses not related to appendicitis underwent percutaneous drainage. Fourteen patients were treated medically. Dilated thick-walled appendix and periappendiceal inflammation were detected in three (75%) of four patients with acute appendicitis. In one patient with appendicitis, the appendix could not be visualized, but inflammation was present in the right lower quadrant. In three patients with ovarian torsion, MR imaging demonstrated right adnexal mass or inflammation. MR imaging was used to correctly identify pelvic abscesses and healthy appendix in two patients. A healthy appendix was depicted in 17 (89.5%) of 19 patients without acute appendicitis. CONCLUSION: MR imaging shows promise for evaluation of pregnant women in whom acute appendicitis is suspected by enabling diagnosis of other possible causes of right-lower-quadrant pain, including ovarian torsion or pelvic abscesses, and demonstrating a healthy or unhealthy appendix.

Abdominal Abscess↗
PubMed1991

Magnetic resonance imaging of the upper airway in obstructive sleep apnea before and after chronic nasal continuous positive airway pressure therapy.

Magnetic resonance imaging (MRI) provides high-resolution images of the upper airway and is useful for assessing conditions associated with increased tissue water content. To determine whether nasal continuous positive airway pressure (CPAP) changes awake upper airway morphology in obstructive sleep apnea (OSA), we performed awake upper airway MRI scans on five male patients with moderate to severe OSA before and after 4 to 6 wk of nasal CPAP therapy. MRI scans were performed using spin echo pulse sequences to examine detailed anatomy and inversion recovery sequences to assess mucosal water content. Patients did not have nasal CPAP applied during the MRI scans. Axial and sagittal images were obtained, and tracings were made of the upper airway, tongue, and soft palate. Utilizing computer graphics, cross-sectional areas and volumes were calculated for each anatomic structure. A subjective grading system was used to assess upper airway mucosal water content. Pharyngeal volume and minimum pharyngeal cross-sectional area increased (p less than 0.05) and tongue volume decreased (p less than 0.01) following chronic nasal CPAP therapy. The increase in pharyngeal volume occurred mainly in the oropharynx (p less than 0.01). Upper airway mucosal water content decreased in the oropharynx (p less than 0.05). We conclude that chronic nasal CPAP therapy during sleep in patients with OSA produces changes in awake upper airway morphology. These changes may be due to resolution of upper airway edema. The upper airway of patients with OSA can be accurately and repeatedly assessed using MRI.

Adult↗
PubMed2004

Cloning and overexpression of the Exiguobacterium sp. F42 gene encoding a new short chain dehydrogenase, which catalyzes the stereoselective reduction of ethyl 3-oxo-3-(2-thienyl)propanoate to ethyl (S)-3-hydroxy-3-(2-thienyl)propanoate.

Exiguobacterium sp. F42 was screened as a producer of an enzyme catalyzing the NADPH-dependent stereoselective reduction of ethyl 3-oxo-3-(2-thienyl)propanoate (KEES) to ethyl (S)-3-hydroxy-3-(2-thienyl)propanoate ((S)-HEES). (S)-HEES is a key intermediate for the synthesis of (S)-duloxetine, a potent inhibitor of the serotonin and norepinephrine uptake carriers. The responsible enzyme (KEES reductase) was partially purified, and the gene encoding KEES reductase was cloned and sequenced via an inverse PCR approach. Sequence analysis of the gene for KEES reductase revealed that the enzyme was a member of the short chain dehydrogenase/reductase family. The probable NADPH-interacting site and 3 catalytic residues (Ser-Tyr-Lys) were fully conserved. The gene was highly expressed in Escherichia coli, and the gene product was purified to homogeneity from the recombinant E. coli by simpler procedures than from the original host. The molecular mass of the purified enzyme was 27,500 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and 55,000 as determined by gel filtration chromatography. Our results show that this enzyme can be used for the practical production of (S)-HEES.

Amino Acid Sequence↗
PubMed2006

[Magnetic resonance imaging of the brain in phenylketonuria].

To investigate the correlation between the abnormalities of magnetic resonance imaging (MRI) of the brain and blood phenylalanine (Phe) levels in phenylketonuria (PKU) and hyperphenylalaninemia (HPA), we reviewed MRIs from 16 patients with early treated PKU and HPA. Their ages ranged from 4-24 years and were found by mass screening and treated from early infancy, and 5 patients with late detected PKU who were aged 24-33 years. The former patients had no remarkable neurological signs or symptoms. One patient of the latter had severe mental retardation and 3 patients had mild to border mental retardation. Axial T1-weighted and T2-weighted spin echo sequences, fluid attenuated inversion recovery MR sequences (FLAIR) through the brain were performed. The scans were graded according to the extent of increased signal intensity of white matter on T2-weighted and FLAIR sequences. To investigate the influence of plasma Phe levels, three approaches were used. Firstly an average of all yearly serial blood Phe concentration was calculated for each patient, then Phe was determined for a period of 6 months and 12 months prior to MRI, and also for their lifetime up to their age at the time this study began. These average blood Phe levels were classified into four categories: group A:Phe level below 5 mg/dl, group B:5-8 mg/dl, group C:9-12 mg/dl, group D:above 12 mg/dl. MRI findings were not significant in group A. Remarkable high signals of white matter were obtained in group C and D, except for one patient in group D whose MRI finding was normal. MRI findings correlated to long-term dietary control stronger than those of 6 months prior to MRI. The clinical significance of MRI abnormalities is still unclear, and further study is required to clarify the relationship of the MRI findings and clinical conditions.

Adolescent↗
PubMedDate not supplied

The added gradient echo pulse sequence technique: application to imaging of fluid in the temporomandibular joint.

PURPOSE: To assess the value of an added gradient echo in the same pulse sequence with a T1-weighted spin echo for determining the presence of an abnormal fluid collection in the temporomandibular joint with no additional imaging time. MATERIALS AND METHODS: Using a standard T1-weighted sequence used in cine temporomandibular joint imaging, a readout gradient reversal was added and the resulting gradient echo collected. This image was compared with standard T1- and T2-weighted sequences, a short inversion recovery imaging sequence, and a small flip angle fast low-angle shot gradient-echo sequence. RESULTS: The T1-weighted spin echo preceding the added gradient echo is not affected by the gradient reversal, but the additional gradient echo adds T2* contrast information that displays fluid as bright as and compares favorably with other fluid detection sequences. CONCLUSION: The added gradient-echo technique adds sensitivity for the detection of an abnormal increase in fluid in the temporomandibular joint without adding to the overall imaging time of a routine T1-weighted sequence.

Humans↗
PubMed1995

Renal vasculature in potential renal transplant donors: comparison of MR imaging and digital subtraction angiography.

PURPOSE: To compare magnetic resonance (MR) angiography with a selective inversion-recovery sequence and digital subtraction angiography (DSA) in renal transplant donors. MATERIALS AND METHODS: Thirteen potential donors underwent MR imaging at 1.5 T and conventional angiography. Blinded evaluation of imaging findings was performed. A selective inversion-recovery sequence was used to obtain MR arteriograms. RESULTS: Eight accessory vessels were present; MR angiography showed 100% sensitivity in accessory vessel detection. Both studies depicted early arterial branching in two vessels, mild fibromuscular dysplasia in one patient, normal renal size in all patients, and prominent fetal lobulation in two kidneys. A small cyst was detected with MR imaging only. Minor venous anomalies were noted in three patients, though these were not surgically confirmed owing to contralateral surgery. CONCLUSION: Despite the small study population, MR angiography with this sequence appears to have potential value in pretransplantation evaluation of the kidney. Advantages include short examination time, noninvasiveness, avoidance of iodinated contrast media, no radiation, and lower cost than DSA.

Adult↗
PubMed1984

The NMR diagnosis of cerebral tumors.

The results of NMR examinations in 52 patients with histological or clinical diagnoses of cerebral tumor are reviewed. An increase in relaxation time was recognized in all tumors but problems were experienced in distinguishing the margin of tumors from surrounding edema. Mass effects were well demonstrated as a result of the high level of gray-white matter contrast available with inversion-recovery sequences and the use of coronal and sagittal imaging planes. In general repeated FID sequences were less sensitive in detecting tumors than inversion-recovery or spin-echo sequences. Periventricular edema was well demonstrated with spin-echo sequences and was of importance in recognizing acute or subacute hydrocephalus. Radiation therapy was associated with increased relaxation times particularly within white matter. Problems in the recognition of tumor recurrence following treatment are outlined. The opportunities and challenges that NMR imaging is now providing for physicists and radiologists are discussed.

Brain Neoplasms↗
PubMed2003

Comparison of magnetic resonance imaging and transesophageal echocardiography in detection of thrombus in the left atrial appendage.

BACKGROUND AND PURPOSE: A noninvasive technique of visualizing the left atrial appendage (LAA) and its thrombus in patients with atrial fibrillation would be of great interest. This study examined the utility of MRI for the assessment of thrombus in the LAA. METHODS: We evaluated 50 subjects with nonrheumatic continuous atrial fibrillation and a history of cardioembolic stroke. Each patient received an MRI and a transesophageal echocardiography (TEE) on the same day for thrombus detection in the LAA. Both double- and triple-inversion recovery sequences were used for the MRI evaluations. RESULTS: In all subjects, the LAA was readily visualized with MRI. High-intensity masses in the LAA were clearly distinguishable from the LAA wall in the triple-inversion recovery sequences. Concordance between detection of high-intensity mass with MRI and thrombus with TEE was high: no mass (MRI), no thrombus (TEE), 31 patients; mass (MRI), thrombus (TEE), 16 patients; and mass (MRI), no thrombus (TEE), 3 patients (overall kappa=0.876, SE=0.068). CONCLUSIONS: MRI is a noninvasive and reproducible modality for thrombus detection in the LAA of patients with nonrheumatic continuous atrial fibrillation and previous cardioembolic stroke.

Aged↗
PubMed1999

Optimization of gray/white matter contrast with fast inversion recovery for myelin suppression: a comparison of fast spin-echo and echo-planar MR imaging sequences.

We compared two MR imaging sequences, fast inversion recovery for myelin suppression (FIRMS) and echo-planar FIRMS (EP-FIRMS), for depicting gray/white matter contrast. In 18 patients, the frequency bandwidth (BW) was optimized for each sequence; in nine patients, the BW was held constant. In the BW-optimized group, the mean contrast-to-noise ratio (C/N) was three times higher with the FIRMS sequence. In the BW-constant group, the mean C/N was 27% higher with the EP-FIRMS sequence; however, geometric distortion degraded the EP-FIRMS images excessively. For optimal gray/white contrast, FIRMS appears to be the superior pulse sequence.

Brain Diseases↗
PubMed2002

Characterization of hematopoietic bone marrow in male professional cyclists by magnetic resonance imaging of the lumbar spine.

PURPOSE: To prospectively evaluate hematopoietic bone marrow of male professional cyclists in relation to performance data and laboratory data, and in comparison to age-matched healthy volunteers. MATERIALS AND METHODS: Twenty male cyclists and 44 volunteers (27 males and 17 females) were prospectively studied by magnetic resonance imaging (MRI) at high-field strength. A sagittal T1-weighted (T1-w) spin-echo (SE) sequence, a gradient-echo (GE) sequence with an echo time (TE) for out-of-phase (OOP) imaging, and a turbo inversion-recovery sequence with short inversion time (TIRM) for fat suppression was used. The averaged bone marrow signal intensity (SI) of three adjacent vertebrae was related to the signal of an adjacent nondegenerative disk. RESULTS: The cyclists revealed a significantly different SI as compared to male volunteers in the OOP (0.34 +/- 0.14 vs. 0.28 +/- 0.09, P < 0.05) and T1-w sequences (1.62 +/- 0.19 vs. 1.77 +/- 0.30, P < 0.05). Only in TIRM was there a significant difference compared to female volunteers (0.36 +/- 0.08 vs. 0.44 +/- 0.04, P < 0.01). MRI data of cyclists did not correlate to hemoglobin, erythrocyte, or reticulocyte counts; ferritin, relative heart volume, relative maximal power (rPmax; W/kg bw), or relative maximal oxygen consumption (VO(2)max). A borderline linear correlation was found for hematocrit (OOP: r = 0.42, P = 0.06; TIRM: r = 0.44, P = 0.06). CONCLUSION: Bone marrow hyperplasia is observed in male professional cyclists in the axial skeleton. The MR findings are probably independent of mechanically induced marrow edema. A multifactorial cause must be considered, as single laboratory and performance data did not appear to contribute significantly to these results.

Adult↗
PubMed2002

[Evaluation of t(1)-weighted black blood imaging using triple inversion recovery].

The black blood sequence, in which the blood signal is suppressed, fundamentally provides T(2)-weighted images. We developed a T(1)-weighted black blood sequence. This new sequence improved the triple IR sequence that uses three inversion pulses by continuously providing three inversion pulses. By so doing, the sequence lengthens the time from the third inversion pulse to data sampling. The new sequence sets the flip angle of the third inversion pulse to 95-110 degrees. Consequently, the difference in T(1) is emphasized in favor of the longitudinal magnetization component with the null point of blood. Data sampling uses the fast spin-echo sequence of a wide sampling bandwidth. The wide bandwidth shortens echo space. T(1)-weighted black blood images were obtained by these methods. Fat suppression is possible by using a CHESS pulse before data sampling.

Brain↗
PubMed1988

Conservative intrachromosomal recombination between inverted repeats in mouse cells: association between reciprocal exchange and gene conversion.

Recombination in mammalian cells is thought to involve both reciprocal and nonreciprocal modes of exchange, although rigorous proof is lacking due to the inability to recover all products of an exchange. To investigate further the relationship between these modes of exchange, we have analyzed intrachromosomal recombination between duplicated herpes simplex virus thymidine kinase (HSV tk) mutant alleles arranged as inverted repeats in cultured mouse L cells. In crosses between inverted repeats, a single intrachromatid reciprocal exchange leads to inversion of the sequence between the crossover sites and recovery of both genes involved in the event. The majority of recombinant products do not display such inversion and are thus consistent with a nonreciprocal mode of recombination (gene conversion). The remaining products display the sequence inversion predicted for intrachromatid reciprocal exchange. In light of the fact that intrachromatid exchanges occur, the rarity of intrachromatid double reciprocal exchanges strengthens the interpretation that the majority of events in this and previous investigations involve gene conversion. Furthermore, in accord with prediction, one-third of the reciprocal recombinants (inversions) display associated gene conversion. This association suggests that reciprocal and nonreciprocal modes of exchange are mechanistically related in mammalian cells. Finally, the occurrence of inversion recombinants suggests that intrachromosomal recombination can be a conservative (nondestructive) process.

Animals↗
PubMed1997

A simplified sequence for observing deoxymyoglobin signals in vivo: myoglobin excitation with dynamic unexcitation and saturation of water and fat (MEDUSA).

This paper describes a new, simplified pulse sequence for observing NMR signals from deoxymyoglobin in vivo. Paramagnetically shifted resonances from deoxymyoglobin can be exploited to noninvasively calculate intracellular oxygen tension in striated muscle. However, special sequences are required to observe these weak signals against the larger water and fat signals encountered in vivo. The pulse sequence described here, which is based on inversion recovery sequences, efficiently suppresses both water and fat resonances and can be implemented with short repetition rates. Moreover, it is perfectly suited for studies with surface coils, where RF inhomogeneities render other popular suppression sequences ineffective.

Humans↗
PubMed1996

Age-related magnetic resonance imaging morphology of the menisci in asymptomatic individuals.

In 82 asymptomatic subjects aged 8-62 years we evaluated the menisci by magnetic resonance imaging (MRI). Using a 1.0-tesla imager spin-echo sequences (SE 700/20), partial-saturation sequences (500/10), and short-time inversion-recovery sequences (1600/130/30) were performed. For grading the degeneration of the meniscus, a standard classification (grades 0-4) was used. Positive MRI findings correlated with the patients' age. In SE sequences, a grade 0 meniscus was found in 45.5% of all cases, grade 1 in 33.2%, grade 2 in 16.1%, grade 3 in 4.5%, and grade 4 in 0.7%. In PS sequences, we found grade 0 in 23.9%, grade 1 in 27.5%, grade 2 in 31.5%, grade 3 in 15.9%, and grade 4 in 1.1%. In STIR sequences, we found grade 0 in 56%, grade 1 in 25.4%, grade 2 in 11.1%, grade 3 in 6%, and grade 4 in 1.6%. Correlation of meniscus degeneration with subjects' age showed an increase of grade 3 and 4 lesions with advancing age. Subjects older than 50 years presented with grade 3 and 4 lesions in the SE sequence in 28.5% of the cases, in PS sequences in 40.7%, and in STIR sequences in 25%. In asymptomatic subjects, MRI shows an increasing prevalence of meniscal alterations which correlates with age. Especially in subjects older than 50 years, a significant number of meniscal tears must be expected. This shows the potential danger of the use of MRI alone as a basis for the determination of surgical intervention.

Adolescent↗
PubMed1999

A new psbA mutation yielding an amino-acid exchange at the lumen-exposed site of the D1 protein.

In eight metribuzin-resistant photoautotrophic cell cultures of Chenopodium rubrum (Thiemann and Barz, 1994 a, b) sequence analyses of a part of the psbA gene coding for the photosystem-II D1 protein had revealed different double and triple mutations within the herbicide binding niche of the protein (Schwenger-Erger et al., 1993). Two pairs of the examined cell lines carried identical mutations within this part of the protein, although their growth performance and their herbicide resistance patterns were different, both at the cellular and the thylakoid level. Starting from the known part of the psbA gene we have amplified the remaining psbA sequences using inverse polymerase chain reaction. Thus the complete sequence of the coding part of the gene was elucidated. After sequence analyses we found an additional amino acid exchange at the position 184 (ile-->asn) of the D1 protein in cell line L1. Metabolic consequences of this mutation are discussed. Partial sequence analyses of the psbD gene of the herbicide resistant cell culture lines revealed no mutation within that part of the D2 protein, which is in direct contact with the D1 protein.

Amino Acid Substitution↗
PubMed2006

[MRI diagnosis of benign sacrococcygeal teratomas of the infants].

OBJECTIVE: To investigate the value of MR imaging in the diagnosis of benign sacrococcygeal teratomas of the infants. METHODS: MR imaging of benign sacrococcygeal teratomas in 6 cases proved by surgery and pathology was retrospectively reviewed. In all patients, a fast imaging sequence, fast spin echo sequence was employed, together with short time inversion recovery sequence and contrast enhancement scanning by intravenous injection of Gd-DTPA. RESULTS: There were 6 benign sacrococcygeal teratomas, which were heterogeneous masses and arose from the distal sacrococcygeal region in the pelvis. The MR imaging appearances of the benign sacrococcygeal teratomas were characteristic, T1- and T2-weighted images demonstrated a large mass containing round, well-defined areas of varying signal intensity representing its cystic, solid, and sometimes fat, calcification within the lesions. CONCLUSION: MR imaging provides definitive information of benign sacrococcygeal teratomas and clearly shows both extra-and intra-pelvic components, and even better anatomic details, which facilitates the surgical planning adequately.

Female↗
PubMed1995

Carpal tunnel syndrome: correlation of magnetic resonance imaging, clinical, electrodiagnostic, and intraoperative findings.

We undertook a prospective study of 43 wrists in 32 patients who had been clinically diagnosed as having carpal tunnel syndrome (study group) and 5 wrists in people who had no symptoms (control group), correlating the clinical, electrodiagnostic, intraoperative, and magnetic resonance imaging (MRI) findings. MRI of the carpal tunnel and thenar eminence was performed, using coronal and axial T1- and T2-weighted, proton density, and short tau inversion recovery sequences. Abnormalities of the median nerve, as revealed by MRI, were found in 43 of 43 (100%) wrists in the study group and in 0 of 5 (0%) wrists in the control group. Increased signal of the median nerve was seen in 41 of 43 (95%) wrists, increased signal of the flexor tendon sheath in 41 of 43 (95%), volar bowing of the flexor retinaculum in 39 of 43 (91%), increased distance between the flexor tendons in 37 of 43 (86%), and abnormal nerve configuration in 28 of 43 (65%). Increased short tau inversion recovery signal of the thenar muscles was found in 5 of 43 (12%) wrists, all of which had undergone severe denervation changes, as revealed by electromyography. Operative release was performed for 27 of 43 (63%) wrists, and follow-up was obtained for 42 of 43 (98%). A good or excellent postoperative outcome resulted for 20 of 27 (74%) patients, a fair outcome for 2 of 27 (7%), and a poor outcome for 4 of 27 (15%), and 1 of 27 (4%) patients was lost to follow-up. For patients undergoing carpal tunnel release whose MRI revealed an abnormal nerve configuration, the outcome was improved, with good or excellent results in 15 of 18 (83%) patients. No association with outcome was seen with median nerve or flexor tendon signal changes, increased interspace between the flexor tendons, or flexor retinaculum bowing. Our results indicate that MRI is a sensitive diagnostic modality that can demonstrate signal and configurational abnormalities of the median nerve in patients diagnosed with carpal tunnel syndrome. Increased signal of the thenar muscles, as revealed by MRI, using short tau inversion recovery sequences, occurs only in muscles that have undergone severe denervation changes, as revealed by electromyography.

Carpal Tunnel Syndrome↗