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PubMed2004

Head-to-head comparison between contrast-enhanced magnetic resonance imaging and dobutamine magnetic resonance imaging in men with ischemic cardiomyopathy.

Contrast-enhanced magnetic resonance imaging (MRI) can predict functional recovery after revascularization. Segments with small, subendocardial scars have a large likelihood of recovery, and segments with transmural infarction have a small likelihood of recovery. Segments with an intermediate extent of infarction have an intermediate likelihood of recovery, and therefore, additional information is needed. Accordingly, the transmurality of infarction on contrast-enhanced MRI was compared with low-dose dobutamine MRI to further define viability in 48 patients. Regional contractile dysfunction was determined by cine MRI at rest (17-segment model), and contractile reserve was determined using low-dose dobutamine infusion. Contrast-enhanced MRI was performed to assess the extent of scar tissue. A total of 338 segments (41%) were dysfunctional, with 61% having contractile reserve. Most segments (approximately 75%) with small, subendocardial scars (hyperenhancement scores 1 or 2) had contractile reserve, whereas contractile reserve was not frequently (17%) observed in segments with transmural infarction (hyperenhancement score 4) (p <0.05). Of segments with an intermediate infarct transmurality (hyperenhancement score 3), contractile reserve was observed in 42%, whereas 58% did not have contractile reserve. In conclusion, the agreement between contrast-enhanced MRI and low-dose dobutamine MRI is large in the extremes (subendocardial scars and transmural scars), and contrast-enhanced MRI may be sufficient to assess the likelihood of the recovery of function after revascularization. However, 61% of segments with an intermediate extent of scar tissue on MRI have contractile reserve and 39% lack contractile reserve. In these segments, low-dose dobutamine MRI may be needed to optimally differentiate myocardium with large and small likelihoods of functional recovery after revascularization.

Adult↗
PubMed2005

Evaluating hip labral tears using magnetic resonance arthrography: a prospective study comparing hip arthroscopy and magnetic resonance arthrography diagnosis.

PURPOSE: To evaluate the sensitivity and accuracy of magnetic resonance arthrography (MRA) with true sagittal scout image mapped radial reformation in localizing hip labral tears. TYPE OF STUDY: Case series. METHODS: Thirty patients were examined with hip MRA because of suspected labral tears. Every patient underwent normal hip arthrography and MR examinations using a 1.5-T scanner with a 3D-FLASH pulse sequence. Multiplanar reformation using double oblique technique produced radial reformatted rotation images with 10 degrees increment on the acetabular rim. Labral tears were annotated as anterior-superior (AS), anterior-inferior (AI), posterior-superior (PS), and posterior-inferior (PI) quadrant based on the cranial-caudal axis in true sagittal reformatted scout localizing image. Patients with positive MRA findings were counseled to have the arthroscopic hip procedure. RESULTS: Five patients showed no MRA indication of labral tear. Of 25 patients who had MRA evidence of labral tear, 17 underwent arthroscopic hip surgery. One patient had only synovial process in the hip joint near the suspected MRA area. The remaining 16 operated patients had labral tears with a total of 21 quadrant lesions on arthroscopy (distributed as AS, 14; AI, 3; PS, 2; and PI, 2). Radial reformatted images revealed accurate mapping with arthroscopic findings in 21 of the 22 quadrant lesions. The sensitivity and accuracy of MRA for the diagnosis of hip labral tear were 100% and 94%, respectively, and the sensitivity and accuracy of radial reformatted MRA for mapping the tear location were 100% and 96%, respectively. CONCLUSIONS: MRA using radial reformatted images with a true sagittal localizer may achieve superior success rates in diagnosing hip labral lesions and in guiding the arthroscopist in portal selection, thus rendering location of hip labral tears simpler in surgery. It supplied detailed preoperative information to the surgeon, avoiding unnecessary surgery for patients if the diagnosis was unconfirmed. LEVEL OF EVIDENCE: Level III.

Acetabulum↗
PubMed2006

Discrimination of myocardial acute and chronic (scar) infarctions on delayed contrast enhanced magnetic resonance imaging with intravascular magnetic resonance contrast media.

OBJECTIVES: The purpose of this study was to examine the potential of intravascular gadolinium (Gd)-chelates in discriminating acute from chronic myocardial infarctions (MIs). BACKGROUND: A potential limitation of delayed contrast enhanced magnetic resonance imaging with standard extracellular Gd-chelates is its inability to distinguish acute from chronic MIs. METHODS: Eight pigs with MIs were studied at 3 days and 8 weeks. Inversion recovery gradient echo (IR-GRE), T(1)-turbo spin echo (TSE), and T(2)-TSE images were acquired before and after administration of intravascular and extracellular Gd-chelates. Triphenyltetrazolium chloride (TTC) was used to delineate infarctions at postmortem. Masson's trichrome and Biotinylated Bandeiria simplicifolia Isolectin B4 stains were used to characterize scarred myocardium. Analysis of variance was used to compare signal intensity (SI) ratios and determine differences in infarct extent. RESULTS: The intravascular agent produced differential enhancement of acute infarctions at 3 days (SI ratio 5.8 +/- 1.3) but not at 8 weeks (1.6 +/- 0.4, p < 0.01). The extracellular agent provided differential enhancement of both acute (SI ratio 7.7 +/- 1.4) and chronic (7.5 +/- 0.9) infarctions. The extents of enhanced regions in acute infarctions were not different after intravascular (16.0 +/- 1.3%) or extracellular (17.1 +/- 1.7%) agents; at 8 weeks the extent of extracellular enhanced and TTC regions were smaller (13.2 +/- 1.4% and 12.0 +/- 1.5%, respectively). Masson's trichrome stain demonstrated dense scar tissue, signaling the complete healing of infarction. The vascular stain showed that scar tissue contained fewer microvessels oriented in a haphazard array. CONCLUSIONS: The combination of intravascular and extracellular Gd-chelates discriminates acute from chronic infarctions on delayed images. This double contrast agent approach can be used to determine the age and extent of infarctions.

Animals↗
PubMed2004

Clinical application of magnetic resonance sialographic 3-dimensional reconstruction imaging and magnetic resonance virtual endoscopy for salivary gland duct analysis.

PURPOSE: In a previous study, we showed that the new and fast sequence 3-dimensional (3D)-fast asymmetric spin-echo sequencing could be applied in magnetic resonance (MR) sialographic 3D reconstruction imaging of the parotid gland ducts and in producing virtual endoscopic views of the parotid gland with MR data. MATERIALS AND METHODS: In the present study, we examined the clinical application of these MR sialographic 3D reconstruction imaging and virtual endoscopy of the salivary gland ducts using MR data sets with 3D-fast asymmetric spin-echo sequencing. RESULTS: The MR sialographic 3D reconstruction images showed a complete view in the branch paths from all angles, and the MR virtual endoscopic views showed conditions in the endoluminal tracts of the large branches in 20 patients with salivary gland duct abnormalities, including Sjögren syndrome, cyst, tumor, sialadenitis, and salivary calculi. CONCLUSION: The clinical use of MR sialographic 3D reconstruction imaging and MR virtual endoscopy for salivary gland ducts may enhance understanding of the 3D relationship between the ducts and the surrounding tissue, as well as the endoluminal circumstance within ducts. Possible future applications abound, and further investigation in this field is expected.

Adolescent↗
PubMed2005

Preoperative evaluation of venous systems with 3-dimensional contrast-enhanced magnetic resonance venography in brain tumors: comparison with time-of-flight magnetic resonance venography and digital subtraction angiography.

BACKGROUND: Recent developments in magnetic resonance (MR) technology now enable the use of MR venography, providing 3-dimensional (3D) images of intracranial venous structures. The purpose of this study was to assess the usefulness of 3D contrast-enhanced MR venography (CE MRV) in the evaluation of intracranial venous system for surgical planning of brain tumors. METHODS: Forty patients underwent 3D CE MRV, as well as 25 patients, 2-dimensional (2D) time-of-flight (TOF) MR venography in axial and sagittal planes; and 10 patients, digital subtraction angiography. We determined the number of visualized sinuses and cortical veins. Degree of visualization of the intracranial venous system on 3D CE MRV was compared with that of 2D TOF MR venography and digital subtraction angiography as a standard. We also assessed the value of 3D CE MRV in the investigation of sinus occlusion or localization of cortical draining veins preoperatively. RESULTS: Superficial cortical veins and the dural sinus were better visualized on 3D CE MRV than on 2D TOF MR venography. Both MR venographic techniques visualized superior sagittal sinus, lateral sinus, sigmoid sinus, straight sinus, and internal cerebral vein and provided more detailed information by showing obstructed sinuses in brain tumors. Only 3D CE MRV showed superficial cortical draining veins. However, it was difficult to accurately evaluate the presence of cortical collateral venous drainage. CONCLUSION: Although we do not yet advocate MR venography to replace conventional angiography as the imaging standard for brain tumors, 3D CE MRV can be regarded as a valuable diagnostic method just in evaluating the status of major sinuses and localization of the cortical draining veins.

Adolescent↗
PubMed2001

Comparison of magnetic resonance real-time imaging of left ventricular function with conventional magnetic resonance imaging and echocardiography.

This study analyzes the accuracy of a new real-time magnetic resonance imaging (MRI) technique (acquisition duration, 62 ms/image) and echocardiography for the determination of left ventricular (LV) end-diastolic volume, end-systolic volume, ejection fraction, and muscle mass when compared with turbo gradient echo imaging as the reference standard. Thirty-four patients were examined with digital echocardiography, standard, and real-time MRI. A close correlation was found between the results of real-time imaging and the reference standard for end-diastolic volume, end-systolic volume, and ejection fraction (r >0.95), with a lower correlation for LV muscle mass (r = 0.81). Correlations between echocardiography and the reference standard were lower for all parameters. Real-time MRI enables the acquisition of high-quality cine loops of the entire heart in minimal time without electrocardiographic triggering or breath holding. Thus, patient setup and scan time can be reduced considerably. Results are similar to the reference standard and superior to echocardiography for determining LV volumes and ejection fraction. This technique is a valid alternative to current approaches and can form the basis of every cardiac MRI examination.

Adult↗
PubMed1997

Abnormalities of auditory evoked magnetic fields and structural changes in the left hemisphere of male schizophrenics--a magnetoencephalographic-magnetic resonance imaging study.

Functional and structural changes in 10 DSM-III-R male schizophrenics and 10 healthy volunteers were investigated using magnetoencephalographically (MEG) detected long-latency (N100 m) auditory evoked fields (AEFs) and magnetic resonance imaging (MRI). The AEFs were characterized by single moving equivalent dipoles, which were superimposed on MRIs. There were significant differences in dipole orientations and in AEF latencies in the left hemisphere of schizophrenics, when compared to the controls. The MEG-detected alterations were found to be associated with a bilateral volume reduction of the posterior superior temporal gyrus (pSTG), which was more pronounced in the left hemisphere. Separate analysis of white and gray matter has shown that the pSTG volume reduction resulted from decreased gray matter volumes without white matter changes. Both the functional and the morphological data indicate a left-hemispheric disturbance in our patients.

Adult↗
PubMed1983

Assignment of the 1H nuclear magnetic resonance spectrum of the proteinase inhibitor IIA from bull seminal plasma by two-dimensional nuclear magnetic resonance at 500 MHz.

The assignment of the 1H nuclear magnetic resonance (n.m.r.) spectrum of the protease inhibitor IIA from bull seminal plasma is described and documented. The assignments are based entirely on the amino acid sequence and on two-dimensional n.m.r. experiments at 500 MHz. Individual assignments were obtained at 18 degrees C and 45 degrees C for the backbone protons of all 57 amino acid residues, with the single exception of the N-terminal pyroglutamate amide proton. The amino acid side-chain resonance assignments are complete, with the exception of 17 long side-chains, i.e. Pro13, Met43 and all the Glu, Gln, Lys and Arg, where only one or two resonances of C beta H2 and in some cases C gamma H2 could be identified. The sequential assignments showed that the order of the two C-terminal residues in the previously established primary structure had to be changed; this was then confirmed by chemical methods. The chemical shifts for the assigned resonances at 18 degrees C and 45 degrees C are listed for an aqueous solution at pH 4.9. A preliminary characterization of the polypeptide secondary structure was obtained from the observed patterns of sequential connectivities.

Amino Acid Sequence↗
PubMed1998

Risk and safety of repetitive transcranial magnetic stimulation: report and suggested guidelines from the International Workshop on the Safety of Repetitive Transcranial Magnetic Stimulation, June 5-7, 1996.

Single-pulse transcranial magnetic stimulation (TMS) is a safe and useful tool for investigating various aspects of human neurophysiology, particularly corticospinal function, in health and disease. Repetitive TMS (rTMS), however, is a more powerful and potentially dangerous modality, capable of regionally blocking or facilitating cortical processes. Although there is evidence that rTMS is useful for treating clinical depression, and possibly other brain disorders, it had caused 7 known seizures by 1996 and could have other undesirable effects. In June 1996 a workshop was organized to review the available data on the safety of rTMS and to develop guidelines for its safe use. This article summarizes the workshop's deliberations. In addition to issues of risk and safety, it also addresses the principles and applications of rTMS, nomenclature, and potential therapeutic effects of rTMS. The guidelines for the use of rTMS, which are summarized in an appendix, cover the ethical issues, recommended limits on stimulation parameters, monitoring of subjects (both physiologically and neuropsychologically), expertise and function of the rTMS team, medical and psychosocial management of induced seizures, and contra-indications to rTMS.

Brain Diseases↗
PubMed2002

In vivo monitoring of age-related changes in rat brain using quantitative diffusion magnetic resonance imaging and magnetic resonance relaxometry.

Diffusion-weighted magnetic resonance imaging (MRI) has been proven to be a sensitive diagnostic tool to examine age associated acute and chronic changes in brain tissue. The aim of our study was to examine whether there are differences in brain diffusion and transverse relaxation time between young and adult rats. In an experimental MR scanner, 24 young (age: 3 months) and 26 adult rats (age: 12 months) were examined using diffusion-weighted and transverse relaxation time (T2)-weighted MRI sequences. There were no differences in the T2 relaxation time between the two animal groups, either local or global. However, the mean apparent diffusion coefficient (ADC) within the whole brain was significantly lower (P<0.0005) in the adult animals (765+/-35 x 10(-6) mm(2)/s) than in the young animals (829+/-45 x 10(-6) mm(2)/s). ADC decrease was mainly found in the cerebral cortex. These results can be attributed to an activity-related or central nervous system damage-related internal water shift from the extracellular to the intracellular space without a net increase in water content in brain tissue. Our study also shows that age-related changes in diffusion should be considered when performing longitudinal studies in rats.

Aging↗
PubMed1997

Calculation of electric fields induced near metal implants by magnetic resonance imaging switched-gradient magnetic fields.

Electric (E) fields induced near metal implants by MRI switched-gradient magnetic fields are calculated by a new equivalent-circuit numerical technique. Induced E-field results are found for a metallic spinal-fusion implant consisting of two thin wires connected to the metallic case of a current generator as well as for its subsections: a bare U-shaped wire, an insulated U-shaped wire, a cut insulated wire, and a generator. The presence of the metallic implants perturbs the E field significantly. Near the ends of the bare U-shaped wire, the E field is 89.7 times larger than in the absence of the wire. The greatest E field concentration occurs near the ends of the cut insulated wire, where the E field is 196.7 times greater than in the absence of the wire. In all cases, the perturbation of the induced E field by the implanted wire is highly localized within a few diameters of the wire.

Bone Wires↗
PubMed1998

Generation of depth-perception information in stereoscopic nuclear magnetic resonance imaging by non-linear magnetic field gradients.

Stereoscopic NMR images have been produced in the past. However, because of the gradients are linear, only isometric projections can be produced, i.e., they do not carry correct depth-perception information. The resulting stereoscopic image will not have correct relative sizes at different depths. This paper gives an analysis of what perception information is needed and shows that it can be produced by a non-linear magnetic field gradient. The concept is exemplified by simulations and its implementation is demonstrated successfully by experiments. The depth-encoding gradient can be generated by static steel pieces or by current loops. The procedure can be incorporated into any existing hardware and pulse sequences, and has potential application in surgery.

Depth Perception↗
PubMed1983

Nuclear magnetic resonance studies of amino acids and proteins. Rotational correlation times of proteins by deuterium nuclear magnetic resonance spectroscopy.

We show that measurement of the spin-lattice (T1) and spin-spin (T2) relaxation times (or line widths) of irrotationally bound 2H nuclei in macromolecules undergoing isotropic rotational motion outside of the extreme narrowing limit (i.e., for the case omega 02 tau R2 much greater than 1) permits determination of both the rotational correlation time (tau R) of the macromolecule and the electric quadrupole coupling constant (e2qQ/h) of the 2H label. The technique has the advantage over 13C nuclear magnetic resonance (NMR) that no assumptions about bond lengths (which appear to the sixth power in 13C relaxation studies) or relaxation mechanisms need to be made, since relaxation will always be quadrupolar, even for aromatic residues at high field. Asymmetry parameter (eta) uncertainties are shown to cause negligible effects on tau R determinations, and in any case it is shown that both e2qQ/h and eta may readily be determined in separate solid-state experiments. By way of example, we report 2H NMR results on aqueous lysozyme (EC 3.2.1.17) at 5.2 and 8.5 T (corresponding to 2H-resonance frequencies of 34 and 55 MHz). Interpretation of the results in terms of the isotropic rigid-rotor model yields e2qQ/h values of approximately equal to 170 or approximately equal to 190 kHz, respectively, for the imidazolium and free-base forms of [epsilon 1-2H] His-15 lysozyme in solution, in excellent agreement with e2qQ/h values of approximately 167 and approximately 190 kHz obtained for the free amino acids in the solid state. In principle, the method may in suitable cases permit comparison between the dynamic structures of proteins in solution and in the crystalline solid state.

Amino Acids↗
PubMed1984

Nuclear magnetic resonance studies of amino acids and proteins. Deuterium nuclear magnetic resonance relaxation of deuteriomethyl-labeled amino acids in crystals and in Halobacterium halobium and Escherichia coli cell membranes.

We have obtained deuterium (2H) Fourier transform nuclear magnetic resonance (NMR) spectra of zwitterionic L-[beta-2H3]alanine, DL-[gamma-2H6]valine, DL-[beta, gamma-2H4]threonine, L-[delta-2H3]leucine, and L-[alpha, beta, gamma, gamma', delta-2H10]isoleucine in the crystalline solid state and have determined the deuteriomethyl group spin-lattice relaxation rates as a function of temperature. The results yield the Arrhenius activation energies (delta E) for methyl rotation, and through use of a suitable mathematical model, rotational correlation times, tau c. For alanine, valine, threonine, leucine, and isoleucine at 37 degrees C, tau c and delta E values are 780, 100, 40, 38, and 18 ps and 22, 14.0, 17.6, 15.5, and 8.6 kJ, respectively. For L-[beta-2H3]alanine in the zwitterionic lattice, a spin-lattice relaxation time (T1) minimum of 2.1 +/- 0.3 ms is observed (at 0 degree C), in excellent agreement with the 1.92-ms prediction of the mathematical model. Similar tau c and delta E measurements are reported for bacteriorhodopsin in the purple membrane of Halobacterium halobium R1 and for Escherichia coli cell membranes. Overall, our results demonstrate a great similarity between the dynamics in amino acid crystals and in membrane proteins. However, threonine exhibits a nonlinear Arrhenius behavior in bacteriorhodopsin, and in the valine-, leucine-, and isoleucine-labeled membrane samples at higher temperatures (approximately greater than 37 degrees C), there is evidence of an additional slow side-chain motion. The lipid phase state in E. coli does not appear to influence, on the average, the dynamics of the valine side chains. These results indicate that the sensitivity of the deuterium NMR technique is now adequate to study in moderate detail the dynamics of most types of amino acids in a membrane protein and that adequate sensitivity, in some instances, should be available for the study of individual amino acids in suitably labeled membrane proteins.

Amino Acids↗
PubMed1989

A magnetization-transfer nuclear magnetic resonance study of the folding of staphylococcal nuclease.

The equilibrium between alternative folded states of a globular protein, staphylococcal nuclease, has been investigated by using 1H NMR. Magnetization-transfer experiments have revealed the existence of a related structural heterogeneity of the unfolded state, and quantitative analysis of a series of these experiments has permitted the kinetics of folding and interconversion of the different states to be explored. A model based on cis/trans isomerism at the peptide bond preceding Pro-117 has been developed to account for the results. This model, recently supported by a protein-engineering experiment [Evans et al. (1987) Nature (London) 329, 266], has been used to interpret the kinetic data, providing insight into the nature of the folding processes. The predominance of the cis-proline form in the folded state is shown to derive from a large favorable enthalpy term resulting from more effective overall folding interactions. The kinetics of folding and isomerization are shown to occur on similar time scales, such that more than one pathway between two states may be significant. It has been possible, however, to compare the direct folding and unfolding rates within the cis- and trans-proline-containing populations, with results suggesting that the specific stabilization of the cis peptide bond is effective only at a late stage in the folding process.

Isomerism↗
PubMed1997

pKa measurements from nuclear magnetic resonance for the B1 and B2 immunoglobulin G-binding domains of protein G: comparison with calculated values for nuclear magnetic resonance and X-ray structures.

Two-dimensional homo- and heteronuclear nuclear magnetic resonance (NMR) spectroscopy was used to determine pKa values for all of the acidic residues in the B1 and B2 immunoglobulin G- (IgG-) binding domains of protein G. Due to the stability of protein G over a wide pH range, estimates of ionization constants were also obtained for some basic residues. These experimentally determined ionization constants were compared with values calculated from both X-ray and NMR-derived structures of B1 and B2 using the UHBD algorithm [Antosiewicz, J., et al. (1994) J. Mol. Biol. 238, 415-436]. This algorithm has been found to be predictive for pKa measurements in proteins and, in combination with experimental measurements, allowed some evaluation of the NMR and X-ray structures. Three regions where significant differences exist between the X-ray and NMR structures are (1) the position of the E56 side chain relative to the backbone amides of K10 and D40, (2) residues 33-37 in the helix, and (3) the Y45 side-chain conformation. For all three cases, the experimental pH titration curves are notably more consistent with the X-ray structures than the NMR structures. In contrast, a number of solvent-accessible side chains have experimental pKas more in agreement with mean pKas calculated from families of NMR structures. The conformations of these side chains may be susceptible to crystal packing effects. From titration experiments under basic conditions, it is noteworthy that the chemical shift of the Y45 C epsilonH resonance is invariant up to pDcorr 12. The Y45 side-chain hydroxyl group appears to maintain a nativelike hydrogen bond with D47 at pDcorr 12, even though the protein is approximately 90% unfolded. These results suggest that this short-range (i, i + 2) interaction, located in the beta3-beta4 hairpin, is present in the high-pH denatured state and may therefore form early in the folding of protein G.

Aspartic Acid↗
PubMed1998

Determination of the magnetic axes of cobalt(II) and nickel(II) azurins from 1H NMR data: influence of the metal and axial ligands on the origin of magnetic anisotropy in blue copper proteins.

The orientation and the axial, Deltachiax, and rhombic, Deltachirh, components of the magnetic susceptibility tensor anisotropy for the cobalt(II) and nickel(II) derivatives of azurin from Pseudomonas aeruginosa have been determined from 1H NMR data. For both derivatives, the axial geometry of the system determines the orientation of the chi-tensor, whose z-axis forms an angle of 18.6 and 20.1 degrees with the Cu-OGly45 axial bond in the cobalt(II) and nickel(II) derivatives, respectively. For protons close to this axis, large negative pseudocontact shifts are observed, while those close to the NNS plane of the equatorial ligands experience lower and positive pseudocontact shifts for the same distance. Dipolar shifts are larger in the cobalt derivative, not only because of the larger spin number but also due to its intrinsically higher anisotropy. The contact contribution to the hyperfine shifts for the coordinated residues has been evaluated and analyzed in terms of unpaired spin delocalization mechanisms and geometry considerations. The results are extended to other blue copper proteins whose cobalt derivatives have been studied by 1H NMR. The electronic structure and its implications in the redox properties of the native copper proteins are also commented.

Anisotropy↗