Single Spin Echo Research Articles

Use of spin echo T(2) BOLD in assessment of cerebral misery perfusion at 1.5 T.

Inadequate blood supply relative to metabolic demand, a haemodynamic condition termed as misery perfusion, often occurs in conjunction with acute ischaemic stroke. Misery perfusion results in adaptive changes in cerebral physiology including increased cerebral blood volume (CBV) and oxygen extraction ratio (OER) to secure substrate supply for the brain. It has been suggested that the presence of misery perfusion may be an indication of reversible ischaemia, thus detection of this condition may have clinical impact in acute stroke imaging. The ability of single spin echo T(2) to detect misery perfusion in the rat brain at 1.5 T owing to its sensitivity to blood oxygenation level dependent (BOLD) contrast was studied both theoretically and experimentally. Based on the known physiology of misery perfusion, tissue morphometry and blood relaxation data, T(2) behaviour in misery perfusion was simulated. The interpretation of these computations was experimentally assessed by quantifying T(2) in a rat model for cerebral misery perfusion. CBF was quantified with the H(2) clearance method. A drop of CBF from 58+/-8 to 17+/-3 ml/100 g/min in the parieto-frontal cortex caused shortening of T(2) from 66.9+/-0.4 to 64.6+/-0.5 ms. Under these conditions, no change in diffusion MRI was detected. In contrast, the cortex with CBF of 42+/-7 ml/100 g/min showed no change in T(2). Computer simulations accurately predicted these T(2) responses. The present study shows that the acute drop of CBF by 70% causes a negative BOLD that is readily detectable by T(2) MRI at 1.5 T. Thus BOLD may serve as an index of misery perfusion thus revealing viable tissue with increased OER.

Optimized MR imaging for polyacrylamide gel dosimetry

Polyacrylamide gels are a powerful tool to measure radiation dose by quantifying the NMR T2 relaxation times of the irradiated gel. The exploitation of these radiation sensitive gels in clinical radiotherapy requires accurate mapping of T2 values. This paper describes the optimization strategy used to identify accurate and practical methods of measuring the range of T2 values typical of gel dosimeters (140-700 ms). The MR imaging techniques used to measure T2 values and the choice of image acquisition parameters are described. Four sequences are compared and the results are analysed in terms of accuracy, signal-to-noise ratio and acquisition time. A multiple spin echo sequence was found to yield the most accurate results (98.9%). Single spin echo sequences, such as Hahn spin echo and EPI spin echo, were found to measure gel T2 values with an accuracy of 90.1%. This paper reports the importance of careful selection and optimization of the MR imaging sequences for accurate and reliable polyacrylamide gel dosimetry.

Strong field behavior of the NMR signal from magnetically heterogeneous tissues

A theory for the behavior of the nuclear magnetic resonance (NMR) signal obtained from magnetically heterogeneous tissues is developed for the limit of a strong external magnetic field. If BO is the magnitude of the external magnetic field, it is found that a free-induction signal decays in a time scaling as 1/Bo, a single-spin echo signal decays in a time scaling as 1/Bo(2/3), and a multiple-spin echo signal decays in a time scaling as 1/Bo(2). Moreover, it is shown that the form of the signal decay for a multiple-spin echo sequence may deviate significantly from an exponential. Numerical results for a model consisting of randomly distributed magnetic spheres are used to confirm the theory. In addition, good agreement is demonstrated between the theory and experimental measurements obtained with particle suspensions. The validity and application of the theory to biological tissues are discussed.

Burst excitation for quantitative diffusion imaging with multiple b-values.

A quantitative imaging sequence has been developed to exploit the intrinsic sensitivity of Burst NMR data to molecular diffusion. In the scan time of a single spin echo experiment, it is possible to acquire many images of the same slice, with a different T(2) and diffusion weighting. Under favorable conditions, it is possible to obtain both the diffusion coefficient and T(2) from the same experiment; or, by correcting for T(2) relaxation using a control image, more precise diffusion coefficients may be measured. The quantitative values in rat brain are in agreement with those from conventional experiments. The major gains of this method are the potentially reduced scan time, the higher number of acquired images corresponding to different diffusion weightings, the reduced sensitivity to inter-scan motion artifact and to local variations in magnetic susceptibility, and an automatic co-registration between T(2) and diffusion images. Problems with the sequence include a lower signal-to-noise ratio than is achievable with diffusion-weighted spin-echo imaging, the limitation of measuring only in-plane components of diffusion and, at present, single-slice acquisition.

Rapid T2-weighted MR imaging of uterine leiomyomaand adenomyosis

To compare three rapid T2-weighted pulse sequences with high-resolution turbo spin-echo (SE) magnetic resonance (MR) imaging for the diagnosis of leiomyoma and adenomyosis. Eighteen patients referred for evaluation of suspected leiomyoma or adenomyosis underwent imaging at 1.5 T with a phased-array multicoil. Non-breath-hold, fat-saturated sagittal images of 4-7 mm, with equivalent voxel size, were obtained through the pelvis with the following three rapid pulse sequences: segmented, half-Fourier single shot turbo SE (HASTE), turboGRASE (TGSE) and turbo SE MR images. Mean acquisition times were 17 s (HASTE), 37 s (TGSE), and 42 s (turbo SE). These images were compared, in a blinded fashion, to high resolution turbo SE MR images, which are considered the "standard" for pelvic MRI. The three rapid pulse sequences, HASTE, TGSE and turbo SE, provided equivalent diagnostic information when compared with high-resolution turbo SE MR images. There was no significant difference in image quality, detection and localization of leiomyoma or in diagnosis of adenomyosis among the three rapid sequences. HASTE imaging demonstrated the least ghosting. Diagnostic T2-weighted images of benign uterine pathology may be obtained in as little as 17 s.

5543709 Magnetic resonance imaging method and apparatus for generating a plurality of single spin echoes

An object is repeatedly excited by a 90-degree pulse and a plurality of spin echoes are obtained by a 180-degree pulse each time the excitation is repeated. The spin echoes are differently phase-encoded and the spin echoes thus generated are assigned to a substantial half portion of a raw image data space in a phase-encoding direction, the remaining substantial half of data being estimated from the data in that portion. The data covering the raw image data space are used to produce a corresponding image of the object.

Comparison of conventional single echo and multi‐echo sequences with a fast spin‐echo sequence for quantitative T2 mapping: Application to the prostate

The accuracy of water T2 maps generated from a fast spin-echo (FSE) sequence was compared with data obtained by conventional single and multi-echo spin-echo pulse sequences using a commercial gel phantom. Spatially localized stimulated echo acquisition mode (STEAM) proton spectroscopy was also used to confirm the reported water T2 values of the gels contained in the phantom. The FSE sequence was shown to be superior in accuracy to both the single and multi-echo spin echo sequences and comparable to STEAM, producing results that were within 10% of known values. The effectiveness of the FSE sequence was further demonstrated by generating T2 maps of the normal and diseased prostate in clinically acceptable imaging times, resulting in comparable T2 values to those obtained using STEAM. Accurate quantitative T2 maps can be produced with the FSE sequence.

Alternate k-space sampling in EPI: compensation for T2* and adjustable T2 weighting.

In this work, preliminary results are described for a modification of the MBEST sampling scheme such that image resolution can be increased while preserving image contrast. In this new approach, a single spin-echo is used in sampling k-space. The basic idea relies on acquiring a conventional EPI image from the center of k-space and applying a pi pulse to permit the acquisition of the two outer edges of k-space. Using this new approach, it is possible to obtain an enhancement in EPI image resolution, while reducing the extent of T2* weighting. As a result, the resulting images possess reduced T2* contrast and suffer less signal loss from T2* effects such as spatial variations in susceptibility and field inhomogeneity.

Generalized Rank Annihilation Method Applied to a Single Multicomponent Pulsed Gradient Spin Echo NMR Data Set

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTGeneralized Rank Annihilation Method Applied to a Single Multicomponent Pulsed Gradient Spin Echo NMR Data SetBrian Antalek and Willem WindigView Author Information Imaging Research and Advanced Development Eastman Kodak Company Rochester, New York 14650-2132 Cite this: J. Am. Chem. Soc. 1996, 118, 42, 10331–10332Publication Date (Web):October 23, 1996Publication History Received27 June 1996Published online23 October 1996Published inissue 1 January 1996https://doi.org/10.1021/ja962172vCopyright © 1996 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views259Altmetric-Citations79LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (105 KB) Get e-AlertsSUBJECTS:Animal derived food,Diffusion,Mixtures,Nuclear magnetic resonance spectroscopy,Quantum mechanics Get e-Alerts

Low-temperature (4.2 K) 23Na and 27Al swept-field nuclear magnetic resonance spectroscopy of zeolites: observation of framework and non-framework aluminum sites

A new method for acquiring 23Na and 27Al nuclear magnetic resonance (NMR) spectra of zeolites is introduced. The key features are operation at low temperature, 4.2 K, and the ability to scan across large spectral regions. In this method, the magnetic field is slowly swept through the resonance condition as the line shape is recorded by a lowpower single pulse or spin echo pulse sequence. A single crystal and powder sample of andalusite are studied to verify the spectral response features of the pulse sequences. Then, four hydrogen faujasites are studied; the samples have different amounts of non-framework aluminum. By acquiring the spectra at 4.2 K, the motion of ions and water molecules is suppressed and the NMR spectra are obtained in the static limit. We compare these spectra to simulations based on 27Al quadrupole coupling constants previously obtained in room temperature studies. There is partial agreement, but the 4.2 K spectra appear to show more 27Al sites than are observed at room temperature.

Excitation Sculpting in High-Resolution Nuclear Magnetic Resonance Spectroscopy: Application to Selective NOE Experiments

Selective pulses are key elements in high-resolution NMR experiments, so great effort has been put into designing pulse shapes with desirable properties.'-' In this communication we describe a selective excitation technique which, judged by the usual criteria, outdistances existing methods. Our method gives constant phase and amplitude excitation over an easily adjustable bandwidth, can achieve given selectivity in a shorter time than existing methods, has no out-of-band sidelobes, and in exciting a multiplet, refocuses the evolution of scalar coupling. The method is tolerant of radio-frequency (fl field inhomogeneity, and altering the net flip angle is easy. The use of pulsed field gradients (PFGS)~,~ results in these crucial properties being achieved in a single scan, without difference spectroscopy or phase cycling: magnetization from outside the desired bandwidth is destroyed, thus simplifying the subsequent manipulation of the excited magnetization. While PFGs have been used to tailor spectral response using single spin echoes, for example with the WATERGATE sequence,I0 and while selective 180 pulses have been used for selective excitation in conjunction with difference spectroscopy, the approach described here is more general. The heart of the method is the double PFG spin echo (DPFGSE) sequence (-GI -S-GI-G~-S-G~-), in which S is any sequence of 13'pulses of any kind and the Gi are PFGs. S induces the unitary transformation Us = R-,(/f?) R-y(t9) R,(a) R,(@ R,@) where, e.g., R,(y) represents a rotation through an angle y about an axis E , and a, @, and 8 are arbitrary angles. It can be shownI2 that applying a DPFGSE to isolated spins transforms a magnetization vector m = (m,,m,,m,) into a vector M with components

Large angle spin-echo imaging

A study was undertaken to assess the use of excitation flip angles greater than 90 degrees for T1 weighted spin-echo (SE) imaging with a single 180 degrees refocusing pulse and short TR values. Theoretical predictions of signal intensity for SE images with excitation pulse angles of 90-180 degrees were calculated based on the Bloch equations and then measured experimentally from MR images of MnCl2 phantoms of various concentrations. Liver signal-to-noise ratios (SNR) and liver-spleen contrast-to-noise ratios (CNR) were measured from breathhold MR images of the upper abdomen in 16 patients using 90 and 110 degrees excitation flip angles. The theoretical predictions showed significant improvements in SNR with excitation flip angles > 90 degrees, which were more pronounced at small TR values. The phantom studies showed reasonably good agreement with the theoretical predictions in correlating the excitation pulse angle with signal intensity. In the human imaging studies, the 110 degrees excitation pulse angle resulted in a 7.4% (p < .01) increase in liver SNR and an 8.2% (p = .2) increase in liver-spleen CNR compared to the 90 degrees pulse angle at TR = 275 ms. Increased signal intensity resulting from the use of large flip angle excitation pulses with a single echo SE pulse sequence was predicted and confirmed experimentally in phantoms and humans.

Liver iron quantification: Studies in aqueous iron solutions, iron overloaded rats, and patients with hereditary hemochromatosis

For the noninvasive liver iron quantification by MRI in human iron overload diseases, fundamental proton relaxation mechanisms were studied in aqueous solutions with ferritin and other iron compounds, in experimentally iron overloaded rats, and in patients with iron overload diseases. MR-relaxation rates as a function of iron concentrations in the range of 0–7.5 mg Fe/g aqueous iron solutions, 0–5.4 mg Fe/g rat liver in vivo, and 0.16–4.9 mg Fe/g human liver in vivo were determined from multi- and sets of single-spin echo sequences (1.5 T imager). As predicted by theory, transverse relaxation rates ( 1 T 2 ) in aqueous iron solution, in liver tissue of rats, and in human liver tissue increased linearly with the iron concentration. A preliminary calibration for the liver iron quantification by MRI was performed from in vivo measurements of liver 1 T 2 - relaxation rates and liver iron quantification by atomic absorption spectroscopy in biopsies from 13 patients. With the single spin-echo method, precise in vivo liver iron quantification in humans also above 2.0 mg Fe/g liver tissue ( T 2<15 ms) should be accomplished on any imager with shortest spin-echo time available, at least TE < 20 ms.

T1, T2 and proton density measurements in the grading of cerebral gliomas

The possibility that cerebral tumours may be graded by measuring T1 or T2 with magnetic resonance (MR) imaging was studied. A consecutive series of patients with subsequently verified gliomas was enrolled, and studied with MR. Patients who had prior surgical, chemotherapeutic or steroid treatment were excluded. Single slice multiple saturation recovery and multiple spin echo techniques were used to measure T1, T2 and proton density in the tumour. In 33 patients with cerebral gliomas there were 5 grade I, 12 grade II, 7 grade III and 9 grade IV. T1 and T2 values tended to be smaller in grade I gliomas than in grades II, III and IV gliomas. Relaxation parameters overlapped considerably in tumours with different grades. Proton density values did not show much change between different grades of gliomas. Relaxation parameters cannot be used to determine tumour grade reliably.

Multiple spin echoes in a high-resolution spectrometer

The Hahn spin-echo pulse sequence 90°—τ-90° normally results in a single spin echo at time 2τ; however, several workers (e.g., Einzel et al., Phys. Rev. Lett. 53, 2312, 1984; Bowtell et al., J. Magn. Reson. 88, 643, 1990) have reported that its application to liquid samples with strong signals in high magnetic fields can result in multiple spin echoes (MSEs) at times 2τ, 3τ, 4τ, …. In this paper a simplified explanation of the MSE phenomenon is offered, and it is shown that extended trains of strong multiple echoes can be produced easily in a conventional high-resolution spectrometer.

A spatial editing of NMR spectra by use of heteronuclear multiple spin echoes

NMR mu ltiple spin echoes (MSEs), observed when the Hahn spin-echo pulse sequence 90°-7-90’ (1) is applied to samples with strong equilibrium polarizations (for example, 3He or water) in a linear field gradient (2-d)) may also be seen in heteronuclear experiments. This allows a novel form of spatial editing of heteronucleus NMR spectra, restricting signals to those from heteronuclei spatially coincident with high proton concentrations. The sequence 90°-7-90° normally produces a single spin echo at time 7 following the second pulse. However, mu ltiple spin echoes, occurring at times nr (n = 2, 3, 4, . . . ) following the second pulse, are observed when the same sequence is applied to samples with large equilibrium magnetizations in a linear field gradient, G . The echoes arise from the partial cancellation of the applied field gradient by the dipolar field generated by the z component of the nuclear magnet ism (5). Heteronuclear mu ltiple spin echoes ( HMSEs ) can be observed at times n ( yn / y x )7 for signals of dilute heteronuclei X in samples with high proton concentrations if the heteronucleus signal is measured following a 90°-r-90’ sequence applied to protons. F igure 1 shows the first two of a train of such echoes obtained for a solution of Na2HP04 in HZ0 using the sequence (I):

Magnetic resonance imaging study of the structure of the yolk in the developing avian egg

Magnetic resonance imaging (MRI) techniques were used to study the morphology of the latebra and concentric rings seen in the yolk of White Leghorn eggs during development of the avian embryo. Previous studies of the macroscopic structure of avian yolk have revealed the latebra, a vase-shaped structure beneath the blastoderm composed of white yolk. The bulbous portion in the center of the yolk is termed the body of the latebra. The thinner portion extending toward the blastoderm is referred to as the neck of the latebra. As the neck of the latebra approaches the blastoderm, it flares out to become the nucleus of Pander. The remainder of the yolk often features alternating concentric layers of white and yellow yolk. These layers, which appear as rings in sections, are thought to represent the daily accumulation of yolk during oogenesis. In this study eggs were imaged with a single slice spin echo sequence using MRI parameters that maximized the visualization of the latebra and concentric rings in the egg yolk. Some experiments were conducted for 2 to 3 day periods with eggs kept in the bore of the magnet using a small incubator that was constructed using a temperature-controlled water pump. The concentric rings of the yolk and the body of the latebra flatten and become more elliptical during development. The neck of the latebra becomes shorter and disappears around the 7th day of incubation. The body of the latebra starts to become incorporated into the embryo at about the 7th day of incubation and usually disappears by the 13th day. The concentric rings are no longer visible as distinct entities at this time. Histochemical procedures carried out as a result of MRI findings indicate that the latebra is an iron-rich structure.

Improvement in signal-to-noise ratio and reduction of chemical shift and motion-induced artifacts by summation of gradient and spin echo data acquisition.

Narrow bandwidth magnetic resonance (MR) imaging allows an increase of signal-to-noise ratio (SNR) but causes increased chemical shift and motion-induced artifacts. To obtain MR images with SNR approximately equal to that obtained with narrow bandwidth but with less chemical shift and motion-induced artifact, we introduced triple readout gradient reversal centered around the spin echo. As a result, signals from two gradient echoes and a single spin echo can be collected and summed. Phantom, knee, shoulder, and abdominal MR images were obtained using a 1.5 T GE Signa System at sampling rates ranging from 10 to 60 kHz. Since the bandwidth per pixel was tripled, chemical shift misregistration was reduced by the same factor. The summation image of two gradient echoes and one spin echo had an SNR comparable with that of a single spin echo acquired within the same total sampling interval. Data acquisition at a high sampling ratio also minimizes the dispersion of T2* weighting among three echoes. In addition, summation of the three resulting images decreases motion artifact by effective averaging.

Increased brain water content in pseudotumour cerebri measured by magnetic resonance imaging of brain water self diffusion

Brain water self diffusion was investigated by magnetic resonance scanning in 7 patients fulfilling conventional diagnostic criteria for pseudotumour cerebri. Quantitative diffusion measurements were obtained using single spin echo pulse sequences with pulsed magnetic field gradients of different magnitude. In all patients the diffusion images showed an increased diffusion in various brain regions when compared with the diffusion coefficients for corresponding regions in healthy subjects. In 3 pseudotumour patients the increased self diffusion was localized to the periventricular regions, while 4 patients had increased diffusion in the whole brain. The findings indicate the presence of increased brain water content both intra- and extracellularly suggesting that patients with pseudotumour have two defects of pathogenetical significance: intracellular water accumulation and increased resistance to cerebrospinal fluid (CSF) outflow leading to an interstitial oedema.

The influence of pulse sequence on the relaxation effects of superparamagnetic iron oxide contrast agents.

The effects of different pulse sequences and timing parameters on the increase in transverse relaxation rate produced by superparamagnetic iron oxide particles have been studied. Gradient-echo, single spin-echo, and multiple-echo images recorded at 2.0 T were used to evaluate the reduction in signal intensity per unit concentration of iron oxide for different echo times and in different media. For the same echo time, gradient-echo sequences were found to be more than twice as sensitive to the effects of the agent as single spin-echo imaging sequences, while multiple-echo sequences were much less affected than either. Using measurements of the relative effects on different sequences, the contributions of different relaxation mechanisms have been quantified.