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PubMed2004

Correlative MR imaging and histopathology in porcine neurocysticercosis.

PURPOSE: To examine whether all the histopathologically seen features of cysticercus cysts excised from brain of swine naturally infected with neurocysticercosis during its evolution are actually visible on magnetic resonance imaging (MRI). MATERIALS AND METHODS: Five swine naturally infected with cerebral cysticercosis were subjected to fast spin-echo (SE) T2, SE T1, fluid attenuated inversion recovery imaging, T1-weighted magnetization transfer (MT), and postcontrast T1-weighted MT sequences on MRI. These animals were sacrificed after imaging and ex vivo imaging of the intact excised brain using the same imaging protocol was also performed. Grossing of these brains was done similar to the ex vivo imaging planes. Numeral density and external appearance of each cyst and scolex were evaluated on each pulse sequence. Amount of pericystic edema, if present, was also assessed. On histopathology, cellular characteristics, inflammatory response, and the extent of edema, if present, in the brain parenchyma around the cysts were graded. Cysts were categorized into viable, early, and late degenerated on histopathology. The MRI features of each cyst were correlated with their histopathologic findings. RESULTS: Out of 31 cysts, eight were found to be viable, 13 early degenerated, and 10 late degenerated on histopathology. T2-weighted imaging demonstrated all the cysts while T1-weighted imaging showed 97% of the cysts. Scolex was seen in 90.3% and 93.5% of the cysts on T2- and T1-weighted images, respectively. Minimal edema (grade I) and inflammation in degenerating cysts present on histopathology was not visible on MRI. All but one of eight degenerated cysts, which showed enhancement on postcontrast MRI, had edema on imaging as well as on histopathology. CONCLUSION: T2-weighted MRI demonstrated all the cysts that were visible on histopathology. Non-enhancement of some of the degenerated cysts along with absence of edema on MRI is likely to underestimate the staging of neurocysticercosis evolution, and these early degenerating cysts may be misdiagnosed as in viable stage.

Animals↗
PubMed1994

Magnetic resonance imaging of transfusional hepatic iron overload.

The transfusional iron overload in 11 adult patients suffering from haematological malignancy was studied in 14 consecutive 1.0 Tesla magnetic resonance imaging (MRI) studies. Routine T1- and T2-weighted spin echo sequences and a fat suppressed sequence (STIR) were used. The ratio from a region of interest of the liver parenchyma and from a manganese chloride reference phantom was measured. There was a definite difference between the signal ratio from the haematological patient group and the control group (p = 0.0001). The patients showed a diminished signal ratio in all pulse sequences used. There was a statistically significant inverse linear correlation between the number of transfused red cell units and the signal ratio in the T1-weighted (p = 0.03) and the T2-weighted (p = 0.03) images. A definite decrease of the effect is found after 20-30 red cell unit transfusions in T2-weighted and STIR images.

Adult↗
PubMedDate not supplied

Theoretical analysis of gadopentetate dimeglumine enhancement in T1-weighted imaging of the brain: comparison of two-dimensional spin-echo and three-dimensional gradient-echo sequences.

By using a theoretical model, the signal difference-to-noise ratios between simulated lesions and normal white matter and gray matter were calculated as a function of lesion concentration of gadopentetate dimeglumine (GD) for two-dimensional (2D) T1-weighted spin-echo (SE), three-dimensional (3D) steady-state spoiled gradient-echo (GRE) (FLASH [fast low-angle shot]), and 3D magnetization-prepared rapid gradient echo (MP-RAGE) pulse sequences. The 3D GRE sequences provided greater contrast enhancement at relatively high [GD], and the 2D SE sequence demonstrated greater enhancement and a higher rate of enhancement at low [GD]. The results predict that at low [GD], certain lesions could probably be detected with the 2D SE sequence but possibly not with one or both of the 3D GRE sequences. At high [GD], certain lesions could probably be detected with one or both of the 3D GRE sequences but possibly not with the 2D SE sequence. This provides a potential explanation for the clinical observation that certain contrast agent-enhanced lesions appear less conspicuous on 3D GRE images than on 2D SE images and vice versa. Modified parameter values were derived for the 3D FLASH and 3D MP-RAGE sequences that are predicted to produce contrast enhancement behavior equivalent or superior to that of a conventional 2D SE sequence.

Brain↗
PubMed2006

Characterization of the lipopolysaccharide and beta-glucan of the fish pathogen Francisella victoria.

Lipopolysaccharide (LPS) and beta-glucan from Francisella victoria, a fish pathogen and close relative of highly virulent mammal pathogen Francisella tularensis, have been analyzed using chemical and spectroscopy methods. The polysaccharide part of the LPS was found to contain a nonrepetitive sequence of 20 monosaccharides as well as alanine, 3-aminobutyric acid, and a novel branched amino acid, thus confirming F. victoria as a unique species. The structure identified composes the largest oligosaccharide elucidated by NMR so far, and was possible to solve using high field NMR with cold probe technology combined with the latest pulse sequences, including the first application of H2BC sequence to oligosaccharides. The non-phosphorylated lipid A region of the LPS was identical to that of other Francisellae, although one of the lipid A components has not been found in Francisella novicida. The heptoseless core-lipid A region of the LPS contained a linear pentasaccharide fragment identical to the corresponding part of F. tularensis and F. novicida LPSs, differing in side-chain substituents. The linkage region of the O-chain also closely resembled that of other Francisella. LPS preparation contained two characteristic glucans, previously observed as components of LPS preparations from other strains of Francisella: amylose and the unusual beta-(1-6)-glucan with (glycerol)2phosphate at the reducing end.

Alanine↗
PubMed1990

Hypointense MR signal in chronically inspissated sinonasal secretions.

Six patients with chronically obstructed sinuses were examined with computed tomography (CT) and magnetic resonance (MR) imaging prior to surgical decompression. In all six patients, hypointense signal was present on all MR sequences despite CT evidence of the presence of high-attenuation material filling the sinus. At surgery, all specimens were viscid or pastelike with no evidence of hemorrhagic products as a cause for the MR findings. Sinonasal secretions may have a spectrum of MR signal intensity, ranging from hyperintense to signal void with all pulse sequences. These findings must be kept in mind when interpreting images of patients with suspected chronic sinusitis.

Adult↗
PubMed2003

Fast proton spectroscopic imaging using steady-state free precession methods.

Various pulse sequences for fast proton spectroscopic imaging (SI) using the steady-state free precession (SSFP) condition are proposed. The sequences use either only the FID-like signal S(1), only the echo-like signal S(2), or both signals in separate but adjacent acquisition windows. As in SSFP imaging, S(1) and S(2) are separated by spoiler gradients. RF excitation is performed by slice-selective or chemical shift-selective pulses. The signals are detected in absence of a B(0) gradient. Spatial localization is achieved by phase-encoding gradients which are applied prior to and rewound after each signal acquisition. Measurements with 2D or 3D spatial resolution were performed at 4.7 T on phantoms and healthy rat brain in vivo allowing the detection of uncoupled and J-coupled spins. The main advantages of SSFP based SI are the short minimum total measurement time (T(min)) and the high signal-to-noise ratio per unit measurement time (SNR(t)). The methods are of particular interest at higher magnetic field strength B(0), as TR can be reduced with increasing B(0) leading to a reduced T(min) and an increased SNR(t). Drawbacks consist of the limited spectral resolution, particularly at lower B(0), and the dependence of the signal intensities on T(1) and T(2). Further improvements are discussed including optimized data processing and signal detection under oscillating B(0) gradients leading to a further reduction in T(min).

Animals↗
PubMed1994

HNCCH-TOCSY, a triple resonance experiment for the correlation of backbone 13C alpha and 15N resonances with aliphatic side-chain proton resonances and for measuring vicinal 13CO,1H beta coupling constants in proteins.

A 3D triple resonance experiment has been designed to provide intraresidual and sequential correlations between amide nitrogens and alpha-carbons in uniformly 13C/15N-labeled proteins. In-phase 13C alpha magnetization is transferred to the aliphatic side-chain protons via the side-chain carbons using a CC-TOCSY mixing sequence. Thus, the experiment alleviates the resonance assignment process by providing information about the amino acid type as well as establishing sequential connectivities. Leaving the carbonyl spins untouched throughout the transfer from 13C alpha to 1H beta leads to E.COSY-type cross peaks, from which the 3JH beta CO coupling constants can be evaluated. The pulse sequence is applied to oxidized Desulfovibrio vulgaris flavodoxin.

Carbon Isotopes↗
PubMed1999

Quality assessment of localization technique performance in small volume in vivo 1H MR spectroscopy.

A new phantom and evaluation method for experimental evaluation of 1H-magnetic resonance spectroscopy single volume localization techniques regarding signal contamination (C), defined as the part of the signal originating outside the volume of interest, is presented. The quality assessment method is based on a spherical phantom with an oil/water interface in order to reduce susceptibility effects, and applied for stimulated-echo acquisition method (STEAM) and spin-echo (SE) sequences, echo times of 270, 135, and 10 ms, and cubic volumes of interest (VOI) of 1(3), 1.5(3), 2(3), 2.5(3), and 3(3) cm3. To be able to mimic measurements of the contamination in three dimensions the physical gradients representing the three orthogonal directions for slice selection were shifted in the pulse sequences. Contamination values in one dimension differed between 6.5% and 8.4% in SE sequences, and between 0.7% and 13.8% in STEAM sequences. In STEAM sequences a decrease of C with increasing VOI size was observed while SE sequences showed comparable C values for the different VOI sizes tested. The total contamination in three dimensions were 19% and 18% in SE and STEAM sequences with a TE of 270 ms, and 7% in a STEAM sequence with a TE of 10 ms, respectively. The presented evaluation method is easily applied to the new phantom and showed high reproducibility.

Artifacts↗
PubMed1996

Cardiac magnetic resonance fluoroscopy.

A technique is described for high speed interactive imaging of the heart with either white or black blood contrast. Thirty-two views of a segmented, magnetization-prepared gradient echo sequence are acquired during diastole. Using three-quarter partial Fourier sampling, data for a complete 128 x 128 image are acquired in three cardiac cycles. High speed reconstruction provides an image update of each cardiac cycle 159 ms after measurement. An independent graphical user interface facilitates interactive control of section localization and contrast by permitting pulse sequence parameter modification during scanning. The efficiency and image quality of the cardiac MR fluoroscopy technique were evaluated in 11 subjects. Compared with the conventional graphic prescription method, the cardiac fluoroscopy technique provides an approximate eightfold reduction in the time required to obtain subject-specific double oblique sections. Image quality for these scout acquisitions performed during free breathing was sufficient to identify small cardiac structures.

Coronary Angiography↗
PubMed2006

Optimum spin-state selection for all multiplicities in the acquisition dimension of the HSQC experiment.

Most conventional heteronuclear spin-state-selective (S(3)) NMR experiments only work for a specific multiplicity, typically IS spin systems. Here, we introduce a general and efficient IPAP strategy to achieve S(3) editing simultaneously for all multiplicities in the acquisition dimension of the HSQC experiment. Complementary in-phase (HSQC-IP) and anti-phase (HSQC-AP) data are separately recorded with a simple phase exchange of two 90 degrees proton pulses involved in the mixing process of the F2-coupled sensitivity-improved HSQC pulse sequence. Additive and subtractive linear combination of these IP/AP data generates simplified F2-alpha/beta-spin-edited HSQC subspectra for all IS, I(2)S, and I(3)S spin systems and combines enhanced and optimized sensitivity with excellent tolerance to unwanted cross-talk contributions over a considerable range of coupling constants. Practical aspects such as pulse phase settings, transfer efficiency dependence, inter-pulse delay optimization, and percentage of cross-talk are theoretically analyzed and discussed as a function of each I(n)S multiplicity. Particular emphasis on the features associated to spin-editing in diastereotopic I(2)S spin systems and application to the measurement of long-range proton-carbon coupling constants are also provided.

Carbon Isotopes↗
PubMed2003

Self-diffusion measurements by a constant-relaxation method in strongly inhomogeneous magnetic fields.

The simple pulse sequence thetax-tau1-2thetay-tau1+tau2-2thetay-tau2-Hahn echo used to measure the self-diffusion coefficient D under constant-relaxation condition, i.e., for tau1+tau2=const. was investigated in the presence of strongly inhomogeneous static as well as radiofrequency magnetic fields. The encoding of the Hahn-echo amplitude by the pulse flip angle and diffusion was evaluated by taking into account the spatial distribution of the off-resonance field, the strength and orientation of the local field gradients, and the pulse flip angles by a computer simulation program. As input files, this program uses maps of static and radiofrequency fields, and the D coefficient can be evaluated from the time dependence of the Hahn-echo amplitude. The method was applied to a mobile one-sided NMR sensor, NMR-MOUSE with a bar magnet by measuring D for a series of liquids with different viscosities. The method was shown to be particularly useful for measuring D of solvents in elastomers without the need for measurements of the transverse relaxation rates. The self-diffusion coefficient of toluene in a series of crosslinked natural rubber samples was measured and correlated with the crosslink density. Finally, the method was applied to measure the diffusion anisotropy of free water in bovine Achilles tendon.

Algorithms↗
PubMed1996

Three-dimensional contrast-enhanced MR angiography.

Three-dimensional contrast-enhanced magnetic resonance (MR) angiography is a relatively new technique that uses the transient shortening in blood T1 following the intravenous injection of gadolinium chelates to image blood vessels irrespective of flow. For many applications, 3D contrast-enhanced MR angiography is developing into a safe, fast, and cost-effective alternative to conventional diagnostic angiography. One of its biggest advantages over other MR angiography techniques (and CT angiography) is the ability to image in a plane parallel to the vessel of interest. This feature, combined with the inherent properties of a 3D gradient refocused sequence, make 3D contrast-enhanced MR angiography intrinsically fast, high resolution and free from saturation and turbulence-related artifacts. This article is designed to familiarize the reader with the theory of 3D contrast-enhanced MR angiography and the application of the technique to different vascular territories. Contrast agents, relaxation effects, contrast bolus effects, pulse sequences, artifacts, and post-processing, as well as the present state of thinking with regard to optimal contrast injection timing/detection and Fourier space mapping are discussed. Patient preparation and techniques and imaging parameters for body applications of gadolinium-enhanced MR angiography, including aorta, renal arteries, mesenteric arteries, portal venous system, pelvis and legs, pulmonary arteries, and carotid arteries are included.

Fourier Analysis↗
PubMed1998

Regulation of cell volume and diffusion of intracellular water in salivary acinar cells.

The regulation of acinar cell volume and the properties of intracellular water were investigated in perfused rat mandibular salivary glands by proton nuclear magnetic resonance (NMR) spectroscopy. Using an inversion-recovery pulse sequence, and an extracellular relaxation reagent (10 mM Gd-DTPA) to suppress the proton NMR signal from extracellular water, acinar cell volume (intracellular water content) in unstimulated glands was shown to depend upon Cl- uptake by basolateral Na+-K+-2Cl- cotransport. Muscarinic and beta-adrenoceptor stimulation induced shrinkage and swelling respectively. In pulsed-field-gradient NMR experiments, the diffusion coefficient of intracellular water was found to be more than an order of magnitude smaller than that of extracellular water. Using this intrinsic difference in diffusivity between the two compartments, cell volume regulation was investigated in intact, perfused glands in the absence of relaxation reagents. Using both NMR techniques, acinar cells in perfused glands were observed to behave like simple osmometers in response to anisosmotic media, and did not show the volume regulatory responses described in dissociated acinar cells.

Animals↗
PubMedDate not supplied

Dynamic subtraction contrast-enhanced MR angiography: technique, clinical applications, and pitfalls.

Rapid advances in techniques of contrast material-enhanced magnetic resonance (MR) angiography have enabled evaluation of the entire aorta and the main arteries. Dynamic subtraction MR angiography consists of first-pass imaging of long segments of arteries by using a three-dimensional fast field echo sequence with multiple rapid bolus injections of a small dose of gadopentetate dimeglumine. Subtraction enables clear demonstration of the enhanced vascular lumen by eliminating background signal. Improved temporal resolution and repeated sequences after gadopentetate dimeglumine administration allow demonstration of arteries and veins separately. Double subtraction postprocessing can be used to eliminate arterial enhancement in demonstration of the portal and systemic veins. Additional postprocessing can be used to demonstrate arteries in a single image in patients with aortic dissection or a prolonged circulation time. To optimize the examination, the pulse sequence, injection dose, injection rate, timing of the start of data acquisition, imaging time, breath holding, section thickness, and coil selection should be considered. This technique is flexible enough to be applied in a variety of clinical settings, including atherosclerotic occlusive disease, aneurysm of aortoiliac arteries, bypass graft, Takayasu arteritis, aortic dissection, antiphospholipid antibody syndrome, renal artery disease, pelvic vascular disease, and the portomesenteric venous system.

Contrast Media↗
PubMed2006

Cardiac pacemaker: in vitro assessment at 1.5 T.

BACKGROUND: In vitro testing is used to determine safe parameters before performing magnetic resonance imaging (MRI) on a patient with an implant. Therefore, the objective of this study was to evaluate a cardiac pacemaker using a 1.5-T magnetic resonance (MR) system. METHODS: A modern cardiac pacemaker (INSIGNIA I PLUS, Model 1298, and FINELINE II, Model 4471, pacing leads; Guidant Corporation, St Paul, MN) was evaluated for magnetic field interactions at 1.5 T. Magnetic resonance imaging-related heating was assessed using 3 different 1.5-T scanners operating at various levels of radio-frequency power and imaging conditions. Functional aspects of the pacemaker were evaluated immediately before and after MRI (9 different pulse sequences). Artifacts were also characterized. RESULTS: Magnetic field interactions for the pacemaker were minor. Temperature changes measured in vitro were at levels that are not expected to pose a risk for specific MR conditions (< 4.0 degrees C). The function of the pacemaker was unaffected by MRI. Artifacts were minor for the leads and relatively large for the implantable pulse generator. CONCLUSION: The findings indicated that this pacemaker exhibited acceptable safety features relative to the use of a 1.5-T MR system. If induced currents do not occur for this device, it may be safe for a patient to undergo MRI by following specific conditions. The results are specific to the pacemaker tested, the MR systems, and conditions used in this evaluation.

Artifacts↗
PubMed1989

NMR studies of mobility within protein structure.

NMR studies of dynamics within structure have revealed that a quite new approach to protein structure and its relation to function is necessary. This approach requires the consideration in detail of the following: 1. Local movements of groups and small segments to allow fast recognition and fitting. The motion concerns on/off rates as well as binding. The observations affect surface/surface recognition, e.g. of antigen/antibody as well as of substrate and protein. 2. Somewhat larger interdomain or N- and C-terminal segments which allow rearrangement. Cases in point are the movement of segments in blood-clotting proteins or in histones. 3. Relative motion of helices in hinges. These actions are likely in such enzymes as kinases and P-450 cytochromes. 4. Relative motion of helices within domains (relative to other helices or sheets) in mechanical devices (triggers) e.g. in calmodulin. 5. General motion in random proteins. Examples extend from rubber-like proteins (entropy sensors), some glycoproteins, to proteins carrying peptide hormones to be generated only after hydrolysis. 6. Order----disorder transitions locally as in osteocalcin and metallothionine. 7. Swinging arm motions associated with special sequences such as (Ala-Pro)n. 8. Of great interest is the power of NMR to look at proteins which are relatively large, up to 50 kDa proteins, and to isolate certain zones of interest. This needs careful temperature dependent studies and analysis of separated domains [72] as well as the use of a great variety of pulse sequences [15] and of nuclei other than protons. 9. In this article I have illustrated the different possibilities using work in my own group. This is done to lessen the burden of extensive review. I fully realise that the range of examples is now large. I would stress though that the production of the necessary technology was the endeavour of several of us within the Oxford Enzyme Group from 1970 to 1985, i.e. from 270-600 MHz Fourier-transform NMR spectroscopy. 10. While all of these features have been demonstrated by NMR methods there are parallel developments both using X-ray diffraction methods and theoretical approaches. All these procedures are changing the view of protein structure to one which incorporates dynamics all the way from conventional vibronic/rotational coupling to the disordered motions characteristic of random polymers. It is the understanding of dynamics that leads to an appreciation of function.

Amino Acid Sequence↗
PubMed1990

Timing of data acquisition determines image quality in femoropopliteal phase-sensitive MR angiography.

To study the effects of timing of data acquisition on quality of femoropopliteal magnetic resonance (MR) angiograms, the authors studied 16 healthy men, mean age 34.3 +/- 6 years, by color Doppler imaging and by phase-sensitive (PS) MR angiography. PS MR imaging was performed at 1.5T using a flow adjustable gradient (FLAG) pulse sequence. The images were graded in a blinded fashion by two independent observers. Of 16 MR angiograms consisting of 141 angiographic images (AI), 45 (31.9%) were diagnostic. At least 1 diagnostic AI was obtained in each subject, and 38 (84.4%) of the diagnostic images were acquired within the first 120 milli-seconds (ms) of the systolic flow pulse. The highest yield of diagnostic images (90.9%) was obtained in the interval of thirty to sixty ms before the peak flow velocity. In healthy man diagnostic PS MR angiography requires triggering to the femoropopliteal systolic flow pulse. The highest yield of diagnostic images is acquired during the flow pulse acceleration.

Adult↗
PubMedDate not supplied

Variation in MR signal intensity across normal human knee cartilage.

Signal intensity (SI) of individual pixels on sagittal magnetic resonance (MR) images of normal human knee cartilage was quantified to investigate whether it was related to cartilage proteoglycan content. In five subjects, images were acquired with spin-echo sequences with a TR msec/TE msec of 1,000 or 700/20 and a three-dimensional gradient-echo (GRE) sequence (60/15). In a sixth subject, the GRE sequence alone was used with 15 degrees, 30 degrees, and 50 degrees flip angles. In all subjects, SI was maximal in pixel layers of the medial zone and minimal at both cartilage edges, resulting in the presence of a bell-shaped curve of interpixel (zonal) SI variation across the cartilage thickness. The magnitude of SI was dependent on the pulse sequence and flip angle, but the bell shape of the SI variation curve was independent of them. For example, in the medial tibial cartilage, the peak SI was highest with the 1,000/20 spin-echo sequence, intermediate with the 700/20 sequence, and lowest with the GRE sequence. The differences were statistically significant. The bell-shaped SI variation curve resembled the curve for zonal variation in cartilage proteoglycan content but not the curves for collagen or free water content. The physiologic basis for this resemblance and the potential usefulness of the findings for early diagnosis of diseases such as osteoarthritis are discussed.

Adult↗