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At least 217 records · Page 12Linked to original sources

Characterization of crystals of Penicillium purpurogenum acetyl xylan esterase from high-resolution x-ray diffraction.

Acetyl xylan esterase from Penicillium purpurogenum, a single-chain 23 kDa member of a newly characterized family of esterases that cleaves side chain ester linkages in xylan, has been crystallized. The crystals diffract to better than 1 A resolution at the Cornell High Energy Synchrotron Source (CHESS) and are highly stable in the synchrotron radiation. The space group is P2(1)2(1)2(1) and cell dimensions are a = 34.9 A, b = 61.0 A, C = 72.5 A.

Acetylesterase↗

1H MR spectroscopy detection of lipids and lactate in metastatic brain tumors.

1H MR spectroscopy was used to correlate the metabolite signals in 66 untreated metastatic brain tumors with the results of Gd-DTPA enhanced MRI. Cubic volumes containing brain metastases of lung cancer (n = 17), mammary carcinoma (n = 24), melanoma (n = 12) and those originating from other tumors (n = 13) were examined using the double spin echo technique with CHESS pulses for water suppression and TE = 135 ms. Apart from trends toward reduced signals of choline-containing compounds (Cho) and reduced post-Gd MRI contrast in lung cancer compared with the other pathology groups, the four tumor groups had similar MRI and MRS characteristics. Metastases without lipid or lactate (Lact) signal in the 1H MR spectra were comparatively small in size with homogeneous post-Gd MRI enhancement (33 +/- 5%, means +/- SEM; n = 24) and elevated Cho signals compared with normal contralateral brain tissue (70 +/- 5% of contralateral N-acetyl aspartate signal; p < 0.001). The other metastases showed either unambiguous lipid signals (n = 30) or MRS detectable Lact (n = 12) and were heterogeneous on MRI with divergent signals of Gd-enhancement (49 +/- 5% vs 14 +/- 8%, p < 0.001) and Cho (88 +/- 10 vs 47 +/- 8% of contralateral NAA; p = 0.02). Those with Lact were significantly larger compared with both other groups (p < 0.02, both). It is concluded that brain metastases can be categorized into early stage (Cho), intermediate stage (lipid, higher Cho) and late stage metastases (Lact, lower Cho).

Brain Neoplasms↗

NAA-weighted imaging of the human brain using a conventional readout gradient.

An imaging sequence incorporating two complementary forms of water suppression was used in conjunction with conventional readout and phase-encoding gradients to acquire images of N-acetylaspartate (NAA) in human brain. The sequence consisted of CHESS water suppression pulses followed by dual echo sequence to select the imaging volume and frequency-selective refocusing pulses with asymmetric crushers to further reduce the water signal. Spectra and conventional spectroscopic images acquired with the sequence demonstrated robust suppression of water and other resonances down field from the 2.0-ppm NAA resonance with 98% of the brain signal resulting from the 3.0-ppm to 2.0-ppm region. The technique was found to provide NAA maps with a large (256 x 128) imaging matrix and to allow a flexible tradeoff between signal to noise ratio (SNR), matrix size, data acquisition window length, and imaging time. Since spectral information is not directly obtained, the length of the data acquisition window is not determined by the spectral resolution needed to resolve the components of the brain spectrum, allowing a significantly shorter readout period. The shorter acquisition window could potentially facilitate the acquisition of multi-echo or multi-slice brain NAA maps.

Artifacts↗

Clinical application of BASING and spectral/spatial water and lipid suppression pulses for prostate cancer staging and localization by in vivo 3D 1H magnetic resonance spectroscopic imaging.

In previous in situ point-resolved spectroscopy (PRESS) three-dimensional (3D) 1H magnetic resonance (MR) spectroscopic imaging studies, it has been demonstrated that the ratio of prostatic metabolites can noninvasively discriminate prostate cancer from surrounding normal tissue. However, in these studies, conventional chemical shift selective suppression (CHESS) and short-time inversion recovery (STIR) techniques often resulted in inadequate water and lipid suppression. To improve suppression and spatial coverage, the newly developed T1 insensitive dual band selective inversion with gradient dephasing (BASING) Bandstop Filter and dual phase-compensating spectral/spatial spin-echo pulses have been implemented in a clinical setting. In phantom studies, no change in metabolic profiles was observed with application of either BASING or spectral/spatial pulses. In a study of 17 prostate cancer patients, the use of either BASING or spectral/spatial pulses allowed for suppression of water (BASING 99.80 +/- 0.14% and spectral/spatial 99.73 +/- 0.47%) and lipid (BASING 98.56 +/- 1.03% and spectral/spatial 98.44 +/- 1.90%) without a significant difference in the prostatic metabolite ratios. Spectral/spatial suppression has the added advantage of reducing the chemical shift dependence of the PRESS volume, but optimal performance requires high-speed gradients with negligible eddy current effects. BASING suppression is less reliant on accurate pulse and gradient timings and can be implemented easily with no loss in performance on clinical MR scanners with conventional gradients.

Adenocarcinoma↗

Reduced (1)H-NMR visibility of creatine in isolated rat hearts.

The aim of this study was to measure the concentration of creatine in Langendorff perfused rat hearts, both by quantitative (1)H-MRS and by high-pressure liquid chromatography (HPLC). First, the relaxation times and other parameters affecting absolute quantification by MRS were determined. At 11.75 T, the relaxation times of myocardial creatine were T(1) = 1.1+/-0.29 sec (mean +/- SD, n = 5) and T(2) = 56.4+/-6.2 ms (n = 9). In phantom experiments the MRS measurements gave accurate values for the known relative concentrations of the detected substances. In glucose-perfused rat hearts, the creatine concentration measured by HPLC was 14.2+/-1.9 mmol/kg wet weight (n = 8), in good agreement with literature values. The (1)H-MRS measurements, however, resulted in creatine concentrations of only approximately 60% of this value. The application of CHESS-pulses for water suppression led to a further 30% reduction of the creatine MRS signal. These results indicate a reduced (1)H-NMR visibility of creatine in the myocardium, which suggests a compartmentation of myocardial creatine into various pools.

Animals↗

Electronic support groups for breast carcinoma: a clinical trial of effectiveness.

BACKGROUND: A recent Pew Charitable Trust study found that 52,000,000 individuals used the Internet to obtain health/medical information. Clinical trials of face-to-face breast carcinoma support groups show evidence of 1) improvement in quality of life, 2) reduction of psychologic symptoms, 3) improvement in coping responses, and 4) a reduction in pain. To the authors' knowledge, a few studies published to date have investigated Internet-delivered electronic support groups (ESGs) for cancer. The most sophisticated is the Comprehensive Health Enhancement Support System (CHESS) program, which provides integrated information, referral, and a newsgroup-based social support program. However, to the authors' knowledge, no studies published to date have examined the impact of a breast carcinoma ESG in a clinical trial. METHODS: Sixty-seven women completed the initial baseline questionnaires, 32 of whom accepted the authors' invitation and began the groups. With regard to geographic location, 49% lived in rural/small towns, 41% lived in medium-sized cities, and 10% lived in large cities. Diagnostic stages of disease were: Stage I, 22%; Stage II, 56%; Stage III, 12%; and other forms, 10%. There were 4 intervention groups, of which 8 participants led by trained Wellness Community (TWC) (a national agency) leaders met for 1.5 hours once a week for 16 weeks. Student t tests for paired outcome data were computed using baseline and postgroup scores. RESULTS: The results of the current study indicated that breast carcinoma patients significantly reduced depression (Center for Epidemiologic Studies-Depression [CES-D] scale) and Reactions to Pain. They also demonstrated a trend toward increases on The Posttraumatic Growth Inventory (PTGI) in two subscales: New Possibilities and Spirituality. Counterintuitively, breast carcinoma patients appeared to demonstrate an increase in emotional suppression. Postinterview results indicated that approximately 67% of patients found the group to be beneficial. Those who withdrew from the groups (20%) demonstrated low scores in their ability to contain anxiety and appeared to be more likely to suppress their thoughts and feelings regarding their illness. CONCLUSIONS: The findings of the current study are encouraging, particularly because it was conducted through TWC, a national agency willing to make this type of intervention readily available at no cost. A limitation of the current study was the lack of randomization and a control group comparison. Although the authors were not able to demonstrate effectiveness without the addition of a control condition, the analysis of pregroup and postgroup outcomes suggests that a randomized trial is worthwhile. Women with a devastating disease will join and commit themselves to an online support group. In addition, because a large percentage of these women were from rural locations, this type of intervention may hold promise for those who have limited access to support groups.

Breast Neoplasms↗

Silicone-fat differentiation in the breast: exploiting the bright-fat phenomenon in fast spin-echo MR imaging.

Selective suppression of silicone or fat with chemical shift-selective (CHESS) pulses is difficult because of the small chemical shift difference between the primary lipid signal and the primary silicone signal at 1.5 T. Differentiation of these chemically distinct species is, however, an important clinical task in assessing implant rupture and silicone migration in breast tissue. A method uniquely suited for silicone-fat differentiation with fast spin-echo (FSE) sequences is reported. It is based on the dependence of fat signal on echo spacing in FSE imaging and results show that it may provide a clinically robust method for silicone-fat differentiation in magnetic resonance imaging of the breast.

Adipose Tissue↗

Localized 2D J-resolved 1H MR spectroscopy of human brain tumors in vivo.

Application of two-dimensional (2D) J-resolved MR spectroscopy, fully localized in three dimensions to monitor the metabolites in human brain tumors in vivo on a whole body MR scanner is presented. A modified PRESS sequence with [90 degrees - 180 degrees - t1/2 - 180 degrees - t1/ 2-acquisition] was used for voxel localization (2D J point-resolved spectroscopy [PRESS]); chemical shift selective (CHESS) sequence was used for suppression of water. The incremental delay (t1/2) added to the intervals before and after the last slice-selective 180 degrees RF pulse allowed the monitoring of the J-evolution in a localized 2D NMR spectrum. The addition of the second frequency dimension in 2D J-resolved spectroscopy to encode the indirect spin-spin coupling allowed the visualization of lactate peaks not observed in the 1D MR spectrum because of severe overlap with lipid peaks. 2D spectra of a two-layer phantom with 100 mM alanine and corn oil and also from three patients with tumors are presented here. The 2D spectra show that the J-coupled lactate peaks could be separated even when the lipids peaks severely overlap.

Adult↗

Neurochemistry of late-life major depression: a pilot two-dimensional MR spectroscopic study.

PURPOSE: To evaluate a two-dimensional localized chemical shift correlated spectroscopy (L-COSY) sequence in elderly patients with major depression. MATERIALS AND METHODS: A total of 33 healthy elderly subjects and 15 elderly patients with major depression were investigated. A voxel size of 3 x 3 x 3 cm3 was chosen in the dorsolateral prefrontal region with predominantly white matter, with the use of three slice-selective radiofrequency (RF) pulses (90 degrees , 180 degrees , and 90 degrees). A chemical shift-selective (CHESS) sequence was used prior to volume localization for the presaturation of water. The two-dimensional raw data matrix consisted of 1024 complex points along the detection period (t2), and 100 increments along the evolution period (t1), resulting in a total acquisition time of approximately 27 minutes per acquisition. The metabolite ratios were calculated using the two-dimensional peak volumes with respect to the diagonal peak volume of total creatine (Cr) at 3.0 ppm. RESULTS: In the 33 elderly subjects, the mean ratio of choline (Cho) to Cr was 10% higher in men compared to women (P < 0.05), consistent with earlier findings obtained by one-dimensional MRS. When the metabolite ratios were compared in a subsample of 16 elderly female controls and 12 depressed female patients, the depressed geriatric patients had higher levels of myoinositol (mI), phosphoethanolamine (PE), and glutamate/glutamine (Glx) than the controls, although the differences were not statistically significant. CONCLUSION: Our pilot study shows the feasibility of performing two-dimensional L-COSY successfully in elderly subjects and patients with late-life mood disorders. These findings are consistent with and expand on our earlier findings in major depressive disorder (MDD) detected with one-dimensional MRS.

Aged↗

Gradient reversal technique and its applications to chemical-shift-related NMR imaging.

The chemical-shift effect often degrades slice selectivity thereby degrading the contrast and spatial resolutions in a high-field NMR imaging. We propose a new pulse sequence which can compensate for this chemical-shift effect during slice selection. This technique provides correct slice definition as well as clear separation between water and lipid protons in high-field proton NMR imaging. Particular applications of this technique are 2D imaging with a thin-slice selection and chunk 3D imaging, where correction of the chemical-shift effect in slice selection is important. Another interesting application of the technique is chemical-shift-selective (CHESS) imaging. This technique does not require spectral-selective rf pulses and it takes advantage of the chemical-shift effect during slice selection. The latter is found to be useful for human in vivo chemical-shift imaging in high-field NMR. In this paper, the theoretical derivation of the proposed gradient reversal technique, its applications, and related experimental results are presented.

Humans↗

Localized high-resolution proton NMR spectroscopy using stimulated echoes: initial applications to human brain in vivo.

Water-suppressed localized proton NMR spectroscopy using stimulated echoes has been successfully applied to detect metabolites in the human brain in vivo. The STEAM spectroscopy sequence allows single-step localization by exciting three intersecting slices. Water suppression is achieved by preceding chemical-shift-selective (CHESS) rf pulses. High-resolution (0.05 ppm) proton NMR spectra of healthy volunteers have been High-resolution (0.05 ppm) proton NMR spectra of healthy volunteers have been obtained on a conventional 1.5-T whole-body MRI system (Siemens Magnetom). Volumes-of-interest (VOI) of 64 ml (4 x 4 x 4 cm3) were localized in the occipital area of the brain and spectra were recorded within measuring times ranging from 1 s (single scan) to about 10 min. The experimental procedure is described in detail. Resonance assignments include acetate, N-acetyl aspartate, gamma-amino butyrate, glutamine, glutamate, aspartate, creatine and phosphocreatine, choline-containing compounds, taurine, and inositols. Cerebral lactate was found to be at a maximum concentration of 0.5 mM when assuming N-acetyl aspartate in white matter to be 6 mM.

Adenine Nucleotides↗

In vivo 1H chemical shift imaging of silicone implants.

In order to study the aging process (i.e., silicone migration, fat infiltration) of silicone (polydimethylsiloxane, PDMS) based biomaterials in living subjects by NMR imaging, a hybrid 1H selective excitation and saturation chemical shift imaging technique (IR/CHESS-CSSE) has been developed. This sequence allows selective mapping of the distribution of silicone protons in vivo, while suppressing the contributions of fat and water. Our results indicate that a combined inversion recovery and CHESS pulse, followed by a spoiler gradient, must be applied to suppress all contributions of fat protons to the NMR signal. The sensitivity of our experiments allows the detection of a chemically unchanged silicone concentration of 5% in a voxel of 0.9 mm3 at a signal/noise ratio of 2.

Adipose Tissue↗

Chemical shift imaging from simultaneous acquisition of a primary and a stimulated echo.

An imaging method is presented for obtaining chemical shift images from only one acquisition. Images are acquired with the same spatial resolution as in regular spin-echo imaging. The sequence is based on the simultaneous acquisition of a spin echo and a stimulated echo in a single pass. The use of 90 degrees radiofrequency pulse flip angles results in the same proton density, T2 and T1 weighting for the two echoes. Application of this sequence to chemical shift imaging is discussed for three fat suppression techniques (chopper, CHESS, and hybrid). Imaging was performed on phatoms and volunteers. The image quality was the same as those obtained by the chopper and the hybrid methods and the acquisition time was reduced by a factor of two.

Adipose Tissue↗

1H MR spectroscopy in patients with metastatic brain tumors: a multicenter study.

In a cooperative study involving six clinical MR centers, localized 1H MR spectroscopy was used to characterize untreated metastatic brain tumors (40 cases, 45 lesions). Cubic volumes (3.4 or 8 cm3) filled for more than 50% by metastatic brain tissue were examined by single-voxel double spin echo MRS, by using chemical shift selective imaging (CHESS) pulses for water suppression and TE = 135 ms. Choline (Cho), creatine (Cr) and N-acetyl aspartate (NAA) levels in brain metastases of mammary carcinoma (n = 13), lung cancer (n = 11) and melanoma (n = 10) were similar. Metastasis NAA/Cho signal intensity ratio varied between 0.00 and 1.17, compared with 2.68 +/- 0.56 (SD) in lobus occipitalis and 1.94 +/- 0.63 in corpus nuclei caudati region (P < 0.0001, both). 1H MR spectroscopy, although not suited to recognize the primary tumor of metastases, could serve as a clinical test for excluding (metastatic) tumor as cause of solitary focal brain disorders that are hard to diagnose with current imaging methods.

Adult↗

Continuously moving table 3D MRI with lateral frequency-encoding direction.

A method is presented for 3D MRI in an extended field of view (FOV) based on continuous motion of the patient table and an efficient acquisition scheme. A gradient-echo MR pulse sequence is applied with lateral (left-right (L/R)) frequency-encoding direction and slab selection along the direction of motion. Compensation for the table motion is achieved by a combination of slab tracking and data alignment in hybrid space. The method allows fast k-space coverage to be achieved, especially when a short sampling FOV is chosen along the direction of table motion, as is desirable for good image quality. The method can be incorporated into different acquisitions schemes, including segmented k-space scanning, which allows for contrast variation with the use of magnetization preparation. Head-to-toe images of volunteers were obtained with good quality using 3D spoiled gradient-echo sequences. As an example of magnetization-prepared imaging, fat/water separated images were acquired using chemical shift selective (CHESS) presaturation pulses.

Beds↗

Non-invasive temperature imaging with thulium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetramethyl-1,4,7,10-tetraacetic acid (TmDOTMA-).

Non-invasive thermometry using hyperfine-shifted MR signals from paramagnetic lanthanide complexes has attracted attention recently because the chemical shifts of these complexes are many times more sensitive to temperature than the water 1H signal. Among all the lanthanide complexes examined thus far, thulium tetramethyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (TmDOTMA-) appears to be the most suitable for MR thermometry. In this paper, the feasibility of imaging the methyl 1H signal from TmDOTMA- using a frequency-selective radiofrequency excitation pulse and chemical shift-selective (CHESS) water suppression is demonstrated. A temperature imaging method using a phase-sensitive spin-echo imaging sequence was validated in phantom experiments. A comparison of regional temperature changes measured with fiber-optic probes and the temperatures calculated from the phase shift near each probe showed that the accuracy of imaging the temperature with TmDOTMA- is at least 0.1-0.2 degrees C. The feasibility of imaging temperature changes in an intact rat at 0.5-0.6 mmol/kg dose in only a few minutes is demonstrated. Similar to commonly used MRI contrast agents, the lanthanide complex does not cross the blood-brain barrier. TmDOTMA- may prove useful for temperature imaging in many biomedical applications but further studies relating to acceptable dose and signal-to-noise ratio are necessary before clinical applications.

Animals↗

Evaluation of two-dimensional L-COSY and JPRESS using a 3 T MRI scanner: from phantoms to human brain in vivo.

Localized versions of two-dimensional (2D) magnetic resonance spectroscopic (MRS) sequences, namely JPRESS and L-COSY, have been implemented on a whole-body 3T MRI/MRS scanner. Volume selection was achieved using three slice-selective radio-frequency (RF) pulses: 90 degrees-180 degrees-180 degrees in JPRESS and 90 degrees-180 degrees-90 degrees in L-COSY with a CHESS sequence prior to voxel localization for global water suppression. The last 180 degrees RF pulse was used for resolving the J-coupled cross peaks in JPRESS, whereas the last 90 degrees RF pulse was used for coherence transfer between J-coupled metabolites in L-COSY. A head MRI coil for 'transmission' and a 4 inch receive surface coil for 'reception' or a head coil transmit/receive were used. A total of 16 healthy volunteers were investigated using these 2D MRS sequences. Voxel sizes of 18 and 27 ml were localized in the occipito-parietal gray and white matter regions and the total duration for each 2D signal acquisition was typically 35 min. Compared with 2D L-COSY, reduced spectral width along the second spectral dimension and shorter 2D spectral acquisition were the major advantages of 2D JPRESS. In contrast, increased spectral width along the new spectral dimension in L-COSY resulted in an improved spectral dispersion enabling the detection of several brain metabolites at low concentrations that have not been resolved using the conventional one-dimensional (1D) MRS techniques. Due to increased sampling rate, severe loss of metabolite signals due to T2 during t1 was a major drawback of 2D JPRESS in vivo.

Adult↗

Structure of the oxidized long-chain flavodoxin from Anabaena 7120 at 2 A resolution.

The structure of the long-chain flavodoxin from the photosynthetic cyanobacterium Anabaena 7120 has been determined at 2 A resolution by the molecular replacement method using the atomic coordinates of the long-chain flavodoxin from Anacystis nidulans. The structure of a third long-chain flavodoxin from Chondrus crispus has recently been reported. Crystals of oxidized A. 7120 flavodoxin belong to the monoclinic space group P2(1) with a = 48.0, b = 32.0, c = 51.6 A, and beta = 92 degrees, and one molecule in the asymmetric unit. The 2 A intensity data were collected with oscillation films at the CHESS synchrotron source and processed to yield 9,795 independent intensities with Rmerg of 0.07. Of these, 8,493 reflections had I > 2 sigma and were used in the analysis. The model obtained by molecular replacement was initially refined by simulated annealing using the XPLOR program. Repeated refitting into omit maps and several rounds of conjugate gradient refinement led to an R-value of 0.185 for a model containing atoms for protein residues 2-169, flavin mononucleotide (FMN), and 104 solvent molecules. The FMN shows many interactions with the protein with the isoalloxazine ring, ribityl sugar, and the 5'-phosphate. The flavin ring has its pyrimidine end buried into the protein, and the functional dimethyl benzene edge is accessible to solvent. The FMN interactions in all three long-chain structures are similar except for the O4' of the ribityl chain, which interacts with the hydroxyl group of Thr 88 side chain in A. 7120, while with a water molecule in the other two. The phosphate group interacts with the atoms of the 9-15 loop as well as with NE1 of Trp 57. The N5 atom of flavin interacts with the amide NH of Ile 59 in A. 7120, whereas in A. nidulans it interacts with the amide NH of Val 59 in a similar manner. In C. crispus flavodoxin, N5 forms a hydrogen bond with the side chain hydroxyl group of the equivalent Thr 58. The hydrogen bond distances to the backbone NH groups in the first two flavodoxins are 3.6 A and 3.5 A, respectively, whereas in the third flavodoxin the distance is 3.1 A, close to the normal value. Even though the hydrogen bond distances are long in the first two cases, still they might have significant energy because their microenvironment in the protein is not accessible to solvent.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗