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PubMed1985

In vitro metabolism of [2-13C]-ethanol by 1H NMR spectroscopy using 13C decoupling with the reverse dept polarization-transfer pulse sequence.

The metabolism of [2-13C]-ethanol by alcohol dehydrogenase purified from Drosophila melanogaster has been observed by proton nuclear magnetic resonance spectroscopy (NMR). The reverse-DEPT pulse sequence, with composite pulse 13C decoupling to simplify and increase the signal-to-noise of spectra, has been used to eliminate the strong water signal while still observing the proton signals of metabolites of interest. Using these techniques the rates of synthesis of acetaldehyde, its diol and acetate from [2-13C] ethanol by alcohol dehydrogenase were measured simultaneously.

Acetaldehyde↗
PubMed1997

T1-weighted spoiled gradient-echo MR imaging of focal hepatic lesion: comparison of in-phase vs opposed-phase pulse sequence.

The goal of our prospective study was to compare quantitatively and qualitatively in-phase and opposed-phase T1-weighted breath-hold spoiled gradient-recalled-echo (GRE) MR imaging technique for imaging focal hepatic lesion. Thirty-eight patients with 53 focal hepatic lesions had in-phase (TR = 12.3 ms, TE = 4.2 ms) and opposed-phase (TR = 10.1 ms, TE = 1.9 ms) GRE (flip angle = 30 degrees , bandwidth +/- 32 kHz, matrix size 256 x 128, one signal average) MR imaging at 1.5 T. Images were analyzed quantitatively by measuring the lesion-to-liver contrast and for lesion detection. In addition, images were reviewed qualitatively for lesion conspicuity. Quantitatively, lesion-to-liver contrast obtained with in-phase (3. 22 +/- 1.86) and opposed-phase pulse sequence (3.72 +/- 2.32) were not statistically different (Student's t-test). No difference in sensitivity was found between in-phase and opposed-phase pulse sequence (31 of 53, sensitivity 58 % vs 30 of 53, sensitivity 57 %, respectively). Two lesions not seen with opposed-phase imaging were detected with in-phase imaging. Conversely, one lesion not seen on in-phase imaging was detected on opposed-phase imaging so that the combination of in-phase and opposed-phase imaging yielded detection of 32 of 53 lesions (sensitivity 60 %). Qualitatively, lesion conspicuity was similar with both techniques. However, in-phase images showed better lesion conspicuity than opposed-phase images in 9 cases, and opposed-phase images showed better lesion conspicuity than in-phase images in 7 cases. No definite advantage (at a significant level) emerged between in-phase and opposed-phase spoiled GRE imaging. Because differences in lesion conspicuity and lesion detection may be observed with the two techniques in individual cases, MR evaluation of patients with focal hepatic lesion should include both in-phase and opposed-phase spoiled GRE imaging.

Adult↗
PubMedDate not supplied

Differentiation between hepatic cavernous hemangioma and malignant tumor with T2-weighted MRI: comparison of fast spin-echo and breathhold fast spin-echo pulse sequences.

PURPOSE: The goal of our study was to compare a T2-weighted breathhold fast spin-echo (BHFSE) technique with T2-weighted nonbreathhold fast spin-echo (FSE) technique for characterizing cavernous hemangioma of the liver and differentiating this entity from malignant tumor. MATERIALS AND METHODS: Eighteen patients with cavernous hemangiomas and 18 patients with malignant hepatic tumors were studied with T2-weighted MRI with a nonbreathhold FSE technique with and without fat suppression and with a BHFSE technique without fat suppression. Hepatic lesions were analyzed quantitatively using signal intensity (SI) and contrast-to-noise (C/N) ratio. In addition, images were qualitatively compared for accuracy in characterizing hepatic lesion. RESULTS: Quantitatively, hemangioma had significantly higher SI and C/N ratios than did the malignant tumor on every pulse sequence (P < 0.01). Qualitatively, all malignant tumors were correctly categorized; differentiation between cavernous hemangioma and malignant tumor was impossible in three cases of cavernous hemangioma with the three pulse sequences (92% accuracy, 100% sensitivity, and 83% specificity). CONCLUSION: T2-weighted FSE and BHFSE MRI shows comparable levels of accuracy for differentiating between hepatic cavernous hemangioma and malignant tumor. Because overlap may exist using quantitative measurement, morphologic patterns must be carefully analyzed, supporting that quantitative analysis and morphologic evaluation are complementary.

Adult↗
PubMed2006

[Evaluation of three-dimensional fast spoiled gradient recalled acquisition in the steady state (FSPGR) using ultra magnetic field 3-Tesla MRI for optimal pulse sequences of T1-weighted imaging].

The advantage of the higher signal-to-noise ratio (SNR) of 3-Tesla magnetic resonance imaging (3TMRI) contributes to the improvement of spatial and temporal resolution. However, T1-weighted images of the brain obtained by the spin-echo (SE) method at 3T MR are not satisfactory for clinical use because of radiofrequency (RF) field inhomogeneity and prolongation of the longitudinal relaxation time (T1) of most tissues. We evaluated optimal pulse sequences to obtain adequate T1 contrast, high gray matter/white matter contrast, and suitable postcontrast T1-weighted images using the three-dimentional (3D) fast spoiled gradient recalled acquisition in the steady state (FSPGR) method instead of the SE method. For the optimization of T1 contrast, the Ernst angle of the optimal flip angle (FA) was obtained from the T1 value of cerebral white matter with the shortest TR and TE. Then the most appropriate FA, showing the maximum contrast-to-noise ratio (CNR) and SNR, was obtained by changing the FA every 5 degrees at about the level of the Ernst angle. Image uniformity was evaluated by a phantom showing similar T1 and T2 values of cerebral white matter. In order to evaluate the effect of the contrast enhancement, signal intensity was compared by the same method using a phantom filled with various dilutions of contrast media. Moreover, clinical studies using full (0.1 mmol/kg) and half (0.05 mmol/kg) doses of Gd-DTPA were carried out with the most appropriate parameters of the 3D-FSPGR method. These studies indicated that the optimal pulse sequences for obtaining an adequate T1-weighted image of the brain using 3D-FSPGR are 9/2 msec (TR/TE) and 13 degrees (FA).

Adult↗
PubMed1985

Theoretical description of depth pulse sequences, on and off resonance, including improvements and extensions thereof.

A general mathematical description of depth pulse sequences in terms of rotation matrices permits a single matrix, known as a cycle matrix, to be written down for each phase-cycled pulse in the overall sequence, such that the result for the total phase-cycled sequence is the product of the individual cycle matrices. It is straightforward to include the effect of the tilted rf axis off resonance and obtain exact solutions. The two types of phase-cycled pulse used in a depth pulse scheme are 2 theta [+/- x] and 2 theta [+/- x, +/- y] and for the general off-resonance case, four of the off-diagonal elements in the 2 theta [+/- x] cycle matrix, and all of the off-diagonal elements in the 2 theta [+/- x, +/- y] cycle matrix, are zero. These simplifications enable important improvements of depth pulse schemes for the elimination of high-flux signals, the reduction of signals from sample regions experiencing pulse angles differing from 90 degrees, and the avoidance of deleterious off-resonance effects such as the production of dispersion signals. In all cases, the dependence of signal intensity off resonance can be easily and exactly calculated. There are important applications in in vivo spectroscopy.

Magnetic Resonance Spectroscopy↗
PubMed1991

MR imaging of liver metastases at 1.5 T: similar contrast discrimination with T1- and T2-weighted pulse sequences.

The authors evaluated soft-tissue contrast on spin-echo (SE) proton density-weighted, SE T2-weighted, SE short-echo-time (TE) T1-weighted, and gradient-echo (GRE) images of 34 patients with known hepatic tumors who underwent high-field-strength (1.5-T) magnetic resonance imaging. For solid liver tumors, the difference in the mean lesion-liver contrast-to-noise ratios (C/Ns) with T1- (GRE and SE) and T2-weighted pulse sequences was not statistically significant (P greater than .05). For nonsolid liver tumors, the T2-weighted images provided significantly greater (P less than .05) mean lesion-liver C/N than T1-weighted GRE images. Mean liver signal-to-noise ratio was significantly greater on T1-weighted GRE (P less than .0001) and T1-weighted SE (P less than .05) images than on T2- and proton density-weighted images. Qualitative analysis of T1-weighted (SE and GRE) images and proton density- plus T2-weighted images showed that lesion conspicuity was similar in 25 of 32 patients (78%). The results suggest that liver tumor imaging at high field strength can be performed with short-TE T1-weighted (SE or GRE) or conventional T2-weighted pulse sequences.

Humans↗
PubMed2004

Detecting intermolecular NOEs by means of a novel DPFGSE pulse sequence. Application to the solvation of carbohydrates in binary mixtures.

We present a pulse sequence based on solute-to-solvent NOE enhancement and aimed at the detection of intermolecular NOE's. Thus, a W3 pulse cluster is used to selectively filter the solvent signals in a DPFGSE sequence. The sequence has been tested on a sample of glucose dissolved in two binary aqueous mixtures (water-acetonitrile and water-DMSO). We show how the resulting enhancements may derive from intermolecular cross-relaxation or, in the water-DMSO sample, also from chemical exchange. In each case, a quantitative interpretation of the data is also supplied, both in terms of local enrichment in one specific solvent (preferential solvation), and by means of a kinetic model for a two-site chemical exchange.

Acetonitriles↗
PubMedDate not supplied

Pulse sequence generated oblique magnetic resonance imaging: applications to cardiac imaging.

A pulse sequence procedure for producing oblique magnetic resonance images is described. Using this procedure we present a new, accurate method to obtain true short-axis views and true long-axis views (both parallel and perpendicular to the septal plane) of the heart. The method is accurate regardless of the orientation of patient's heart. The method does not require the patient to be rotated, nor otherwise moved, and does not require any additional hardware. The method is experimentally verified with both human and phantom studies. The phantom study indicates accuracy of approximately 1 degree with a commercial scanner that reports angular measurements to a precision of 1 degree. Application of the short-axis views to measurement of left ventricular volume, and possible advantages of Gauss-Legendre integration for this measurement are discussed. Finally, multiphase oblique cardiac images are presented.

Biophysical Phenomena↗
PubMed1996

Some new observations on pulse sequence dependent diffusion related edge enhancement in MR microscopy.

Self-diffusion of nuclear spins has been suggested to cause edge enhancement in images especially on a microscopic scale. According to previously published work, theory suggests that edge enhancement is caused by motional narrowing due to the boundaries and spin self-diffusion during the data acquisition period. More careful examination reveals that edge enhancement due to motional narrowing develops only under a few specific conditions. This lack of generality of motional narrowing theory, as well as experimental observations, indicate that edge enhancement due to effects other than motional narrowing alone can exist. It is found that edge enhancement depends greatly on the data acquisition mode; therefore, the images obtained are different depending on the pulse sequence employed. For example, excessive attenuation of DC components due to diffusion can result in edge enhancement in the spin echo signal. However, in the case of FID-like signals, DC components are preserved while positive high frequency parts are attenuated, thereby degrading resolution. The new phenomenon observed has been termed selective spectral suppression since the observed edge enhancement results from the selective attenuation of certain frequency components in the nuclear signals due to diffusion-dependent signal attenuation for a given pulse sequence.

Diffusion↗
PubMed2006

[Basic evaluation of the new pulse sequence for simultaneous acquisition of T1- and T2-weighted images].

A novel pulse sequence that enables simultaneous acquisition of T1-weighted (T1W) and T2-weighted (T2W) images is presented. In this new technique, the inversion recovery (IR) pulse of conventional fast inversion recovery (Fast IR) is replaced with a pulse train that consists of a fast spin echo (FSE) and 180 (y) +90 (x) for driven inversion (DI). By using a shorter TI and independent k-space ordering, the first part of the sequence provides T2W images and the second part provides T1W images, thereby enabling simultaneous acquisition in a single scan time comparable to that of Fast IR. Signal simulation also was conducted, and this was compared with conventional scanning techniques using normal volunteers. In the human studies, both T1W and T2W images showed the same image quality as conventional images, suggesting the potential for this technique to replace the combination of Fast IR and T2W FSE for scan-time reduction.

Adult↗
PubMed2004

FASCINATE: a pulse sequence for simultaneous acquisition of T2-weighted and fluid-attenuated images.

A pulse sequence that enables simultaneous acquisition of T2-weighted and fluid-attenuated images is presented. This sequence is referred to as FASCINATE (Fluid-Attenuated Scan Combined with Interleaved Non-ATtEnuation). In this new technique, the inversion pulse of conventional fast fluid-attenuated inversion recovery (FLAIR) is replaced with a fast spin echo (FSE) acquisition that has an additional 180(y)-90(x) pulse train for driven inversion. By using appropriate scan parameters, the first part of the sequence provides T2-weighted images and the second part provides fluid-attenuated images, thus allowing simultaneous acquisition in a single scan time comparable to that of fast FLAIR. FASCINATE was compared with conventional scanning techniques using a normal volunteer and a patient. A signal simulation was also conducted. In the human study, both T2-weighted and fluid-attenuated images from FASCINATE showed the same image quality as conventional images, suggesting the potential for this technique to replace the combination of fast FLAIR and T2-weighted FSE for scan time reduction.

Brain↗
PubMed2005

Quantifying CBF with pulsed ASL: technical and pulse sequence factors.

We summarize here current methods for the quantification of CBF using pulsed arterial spin labeling (ASL) methods. Several technical issues related to CBF quantitation are described briefly, including transit delay, signal from larger arteries, radio frequency (RF) slice profiles, magnetization transfer, tagging efficiency, and tagging geometry. Many pulsed tagging schemes have been devised, which differ in the type of tag or control pulses, and which have various advantages and disadvantages for quantitation. Several other modifications are also available that can be implemented as modules in an ASL pulse sequence, such as varying the wash-in time to estimate the transit delay. Velocity-selective ASL (VS-ASL) uses a new type of pulse labeling in which inflowing arterial spins are tagged based on their velocity rather than their spatial location. In principle, this technique may allow ASL measurement of cerebral blood flow (CBF) that is insensitive to transit delays.

Arteries↗
PubMed1988

Cervical spine: MR imaging with a partial flip angle, gradient-refocused pulse sequence. Part I. General considerations and disk disease.

A magnetic resonance imaging pulse sequence with a short repetition time (TR), short echo time (TE), partial flip angle, and gradient refocused echo was evaluated for the detection of cervical disk disease in a prospective study of 90 patients. These parameters were manipulated to adjust signal-to-noise ratio (S/N) and contrast: flip angle (3 degrees-18 degrees), TR (22-60 msec), and TE (12.5-25 msec). Flip angle had the greatest effect on S/N and contrast; its effect differed between axial and sagittal imaging. Cerebrospinal fluid S/N reached a peak at a smaller flip angle in sagittal imaging than in axial imaging. The useful range of flip angles depended on TR. Increasing TR had minimal direct effect on S/N or contrast, but because a longer TR allowed the use of larger flip angles for both axial and sagittal imaging, higher S/N could be achieved with similar contrast. This effect of increasing TR had to be balanced against increased imaging time and increased probability of motion artifact. Increasing TE decreased S/N, increased contrast, and increased magnetic susceptibility artifacts. For the diagnosis of cervical disk disease, the best sequence appears to be one with a very short TR, short TE, and small flip angles within a narrow range.

Cervical Vertebrae↗
PubMed1986

Optimizing pulse sequences for magnetic resonance imaging of the musculoskeletal system.

On the surface, pulse sequence optimization seems like a difficult problem because of the many variables involved. In practice, however, the simple strategy of obtaining both T1- and T2-weighted images of the body part in question is adequate in most musculoskeletal imaging. This strategy virtually guarantees the production of images with adequate contrast between normal and abnormal tissue, no matter which of the common background tissues is considered. Although intravenous contrast agents can improve the already excellent contrast between musculoskeletal tissues, it is too early to tell the exact role they will play in the work-up of musculoskeletal disease.

Adipose Tissue↗
PubMed2004

Pulse sequence for multislice T1rho-weighted MRI.

A 2D multislice spin-lock (MS-SL) MR pulse sequence is presented for rapid volumetric T1rho-weighted imaging. Image quality is compared with T1rho-weighted data collected using a single-slice (SS) SL sequence and T2-weighted data from a standard MS spin-echo (SE) sequence. Saturation of longitudinal magnetization by the application of nonselective SL pulses is experimentally measured and theoretically modeled as T2rho decay. The saturation data is used to correct the image data as a function of the SL pulse duration to make quantitative measurements of T1rho. Measurements of T1rho using the saturation-corrected MS-SL data are nearly identical to those measured using an SS-SL sequence. The MS-SL sequence produces quantitative T1rho maps of an entire sample volume with the high-SNR advantages conferred by SE-based sequences.

Animals↗
PubMed1997

Assessment of parotid masses: which MR pulse sequences are optimal?

The objective of this paper is to determine which MR pulse sequences are optimal for delineation of lesion and predicting pathologic nature of lesion with signal intensity. A prospective study was performed in 53 parotid masses (39 benign and 14 malignant lesions) in 53 patients. Signal intensity of lesion was visually assessed and lesion/parotid contrast-to-noise ratios were measured. On visual assessment, detection sensitivity was 100% for nonenhanced nonfat-suppressed T1-weighted images, 91% for nonfat-suppressed fast spin-echo (FSE) T2-weighted images, 83% for gadolinium-enhanced fat-suppressed T1-weighted images, and 75% for fat-suppressed FSE T2-weighted images. The highest contrast-to-noise ratios were obtained with nonenhanced T1-weighted images. Hypointensity of lesion relative to the parotid gland on nonfat-suppressed FSE T2-weighted images was seen in 11 of 14 malignancies, 12 of 15 Warthin tumors, and two of 18 pleomorphic adenomas. Cystic portion of hyperintensity on nonenhanced T1-weighted images was solely seen in benign tumors (n = 11). Thus, the highest accuracy (81%) (79% sensitivity and 82% specificity) for predicting malignancy was obtained with a criterion of hypointensity on nonfat-suppressed FSE T2-weighted images plus absence of cystic portion of hyperintensity on nonenhanced T1-weighted images. Nonenhanced T1-weighted images combined with nonfat-suppressed FSE T2-weighted images is optimal for delineation of lesion and prediction of pathologic nature of parotid masses.

Adolescent↗
PubMed1988

Interactions of paramagnetic contrast agents and the spin echo pulse sequence.

The theoretical equations for paramagnetic contrast agent effects and the spin echo pulse sequence are combined to graph magnetic resonance (MR) intensity as a function of paramagnetic contrast agent concentration for various tissues. Analysis of the graphs and equations demonstrate several technical and clinical implications. These include: (1) positive enhancement is most likely to occur with short TEs and TRs; (2) changes in machine parameters TE and TR will change the concentration of agent at which the peak enhancing MR intensity will occur; (3) there is an absolute maximum MR intensity that can be reached with contrast enhancement; (4) the maximum MR intensity reached with enhancement is dependent on the tissues' T2 and, to a lesser degree, T1 relaxation times; (5) certain TE and TR combinations will cause no enhancement; (6) if positive enhancement does occur, it will usually occur only over a limited range of agent concentration; and (7) the tissues' T1 relaxation time but not its T2 time determines whether positive enhancement will occur and the relative amount of enhancement.

Contrast Media↗
PubMedDate not supplied

Pulse sequence design for volume selective excitation in magnetic resonance.

The design of a pulse sequence for volume localization in magnetic resonance spectroscopy is described in detail. The sequence is based on the volume selective excitation technique (VSE) proposed by Aue et al. [J. Magn. Reson. 56, 350 (1984)] and overcomes the high rf power requirements of VSE. The implications of various design stages are demonstrated experimentally and by computer simulations.

Biophysical Phenomena↗