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At least 271 records · Page 15Linked to original sources
PubMed1997

Magnetic resonance renography: optimisation of pulse sequence parameters and Gd-DTPA dose, and comparison with radionuclide renography.

The aim of this study was to assess the feasibility of magnetic resonance renography (MRR) using gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) in comparison with conventional radionuclide renography (RR) using technetium-99m-DTPA (99mTc-DTPA). MRR has many advantages over RR, including lack of ionising radiation, increased spatial resolution, and visible background anatomy. By optimising the pulse sequence, we developed an MRR protocol in which signal intensity is linear with Gd-DTPA concentration over a clinically relevant range. Twenty-nine patients and a volunteer were studied using this protocol. Magnetic resonance renography was performed using three different doses of Gd-DTPA: 0.1 mmol kg-1 (n = 13), 0.05 mmol kg-1 (n = 7), and 0.025 mmol kg-1 (n = 9). Each patient was also assessed using radionuclide renography. The resulting renograms were assessed in terms of time to peak signal intensity, signal decrease after peak, and kidney function ratios calculated from both the areas underneath and the slopes of the uptake curves. We have shown that the MR renograms obtained using low dose Gd-DTPA correlate best with the radionuclide renograms. Remaining discrepancies may be explained by variations in the injection procedures (hence in arterial input functions) and the limited coverage of the three MRR slices compared to the whole body projection of RR. Furthermore, at high local concentrations, signal becomes independent of T1 and is dominated by T2.

Adult↗
PubMed1998

Quantum logic gates and nuclear magnetic resonance pulse sequences.

There has recently been considerable interest in the use of nuclear magnetic resonance (NMR) as a technology for the implementation of small quantum computers. These computers operate by the laws of quantum mechanics, rather than classical mechanics and can be used to implement new quantum algorithms. Here we describe how NMR in principle can be used to implement all the elements required to build quantum computers, and draw comparisons between the pulse sequences involved and those of more conventional NMR experiments.

Magnetic Resonance Spectroscopy↗
PubMed2001

[Dynamic MR imaging of the upper abdomen: timing optimization and pulse sequence selection].

Since breath-hold gradient-echo MR imaging was introduced, dynamic MR study has played an important role in the MR investigation of the upper abdomen. In this article, the importance of tailoring imaging delay in each individual patient is stressed, with special attention given to a logical aspect of setting delay time based upon the bolus transfer time obtained by test injection. Also discussed is the importance of selecting types and parameters of pulse sequence to maximize the enhancement effect. It should be noted that alteration of gadolinium concentration in vivo following intravenous injection could result in a large change in signal intensity change on one sequence but little change on another. Double-dose 3DFISP with tailored delay time utilizing the test injection method, which is currently used for dynamic MR imaging in our institute, is presented.

Carcinoma, Hepatocellular↗
PubMed2005

Improving pulse sequences for 3D DOSY: convection compensation.

Signal overlap in the NMR dimension significantly complicates the construction and analysis of 2D diffusion-ordered (DOSY) spectra. Such problems can often be reduced or even eliminated by extending the NMR domain of a DOSY experiment into two dimensions, giving a 3D-DOSY spectrum. To date such experiments have generally sacrificed some signal-to-noise ratio and have required extensive and time-consuming phase cycling. A new family of pulse sequences with internal diffusion encoding (IDOSY) has been introduced which avoids both of these problems. It is often straightforward to incorporate convection compensation in such sequences at no cost in signal-to-noise ratio. Here, some of the problems caused by convection in DOSY are described and illustrated, and the efficacy of convection compensation in the 2DJ-IDOSY and COSY-IDOSY experiments is demonstrated.

Acyclic Monoterpenes↗
PubMed2001

Noncontrast MR imaging and MR arthrography of the ulnar collateral ligament of the elbow: prospective evaluation of two-dimensional pulse sequences for detection of complete tears.

OBJECTIVE: To compare MR imaging techniques with differing contrast and spatial resolution for evaluation of complete disruption of the ulnar collateral ligament (UCL) anterior bundle in a cadaveric elbow model. DESIGN: Complete UCL tears were surgically created at the typical location for clinical tears in eight of 28 fresh frozen cadaveric elbow specimens. All specimens underwent 1.5 T MR imaging in the oblique coronal plane, using an extremity coil. The sequences employed were: T1-weighted spin echo (T1 SE), proton density-weighted (PD) fast spin echo (FSE), fat-suppressed T2-weighted FSE (T2 FSE), gradient recalled echo (GRE) with a high matrix, PD FSE with a high matrix (HRPD), and fat suppressed T1-weighted SE with intra-articular gadolinium (MRAr). Two radiologists independently graded the UCL with separate and side-by-side assessments. RESULTS: Sensitivity/specificity pairs were as follows for reader A and reader B, respectively: T1 SE: 0.25/0.95, 0.50/0.95; PD FSE: 0.38/1.00, 0.25/1.00; T2 FSE: 0.50/0.95, 0.63/0.95; GRE: 0.63/0.85, 0.63/0.60; MRAr: 0.88/1.00, 1.00/0.80; HRPD: 0.50/1.00, 0.88/0.80. Kappa statistics for measuring interobserver reliability for each sequence were poor under T1 SE (-0.13) and GRE (0.19), moderate under HRPD (0.41) and T2 FSE (0.44) and good under MRAr (0.62) and PD FSE (0.78). For both readers, the rating for overall image quality was highest for HRPD, and the rating for UCL lesion conspicuity was the highest for MRAr. CONCLUSIONS: Of the MR imaging pulse sequences tested, MRAr showed the greatest ability to identify complete ligamentous injuries with good agreement between readers and had the highest subjective preference for lesion conspicuity. However, HRPD had the least interobserver variability and the highest subjective preference for overall image quality.

Aged↗
PubMed2001

Evaluation of pulse sequences used for magnetic resonance sialography.

OBJECTIVES: To determine the most appropriate sequences for the visualization of small parotid ducts in MR sialography. METHODS: MR images of a phantom consisting of distilled water in polyethylene tubes were obtained with turbo-spin echo (TSE), single-shot turbo-spin echo (SSTSE), half-fourier acquisition, single-shot turbo-spin echo (HASTE) and turbo gradient-spin echo (TGSE) pulse sequences and compared visually and quantitatively. MR sialograms obtained from healthy volunteers and patients with Sjögren's syndrome (SS) were obtained using the same four sequences. RESULTS: In the phantom, TSE images were best and the contrast-noise ratio (CNR) highest. In the volunteers, the main ducts were especially clearly visualized with TSE and in SSTSE; however, the majority of secondary and/or tertiary parotid ducts were not depicted by any of the sequences used. In SS patients, images of small main ducts and small pseudocysts were clearer using TSE. However, TSE could not depict the narrow main ducts or peripheral ducts or very small pseudocysts. CONCLUSIONS: TSE is considered the most suitable MR sequence for assessing small parotid gland ducts. However, further improvement is needed since it does not always visualize them sufficiently.

Adult↗
PubMed1999

Fat suppression magnetic resonance imaging of the triangular fibrocartilage complex. Comparison with spin echo, gradient echo pulse sequences and histology.

Magnetic resonance imaging (MRI) of the triangular fibrocartilage complex (TFCC) of the wrist was performed in ten healthy volunteers using spin echo T1-weighted (SE-T1), fast spin echo T2-weighted (FSE-T2), gradient echo T2-weighted (GRE-T2) and fat suppression spin echo T1-weighted (FS-T1) images. The images were obtained in the coronal plane and were compared to the corresponding histological coronal sections obtained from five fresh frozen cadavers. In our analysis, the FS-T1 pulse sequence visualized the details of the TFCC best, followed by the GRE-T2 images. Delineation of the TFCC on the SE-T1 and the FSE-T2 was poor. The coronal morphology of the TFCC represented on the fat suppression image was almost identical to the corresponding histological sections. We conclude that the fat suppression MRI clearly shows the complex structure of the TFCC and is useful for the morphological evaluation of the TFCC.

Adult↗
PubMed1989

Improved MR images of the brain with use of a gated, flow-compensated, variable-bandwidth pulse sequence.

Peripheral gating and first-order flow compensation were compared for their ability to improve the quality of second-echo (echo time = 80 msec) brain images obtained with a T2-weighted spin-echo sequence. The contrast-to-noise ratios (C/Ns) for interfaces between brain and cerebrospinal fluid, gray and white matter, and lesion and white matter were measured; the C/N was highest for the combination of gating and flow compensation. This combination of motion compensation also reduced motion artifacts more than did either technique alone. Further improvement in C/N was sought by using a variable-bandwidth pulse sequence, which was compared to a conventional spin-echo sequence. The variable-bandwidth technique increased the C/N of the second-echo image by 27%. The combined use of gating, flow compensation, and the variable-bandwidth option produced high-resolution brain images with a single excitation and retained flexibility in number of sections, number of echoes, and echo times.

Brain↗
PubMed1993

[Real-time flow--determination of inferior vena cava on 2 different levels using RACE pulse sequence in MRI. Assessment of the total hepatic vein flow volume as an indirect parameter of liver perfusion].

A new and simple parameter for quantitative evaluation of liver perfusion is outlined: post-sinusoidal quantitative measurement of the entire liver venous flow: This is a result of the differences in evaluated flow volumes at two different levels in the inferior V. cava. The first level ist the height of diaphragm, and the second is situated just cranial of the renal vessels. Normal values obtained from a group of healthy volunteers are presented. A gradient-echo pulse sequence called RACE, enabling flow measurements in real-time, is outlined.

Adult↗
PubMed2004

Incidental liver lesions: diagnostic value of cadence contrast pulse sequencing (CPS) and SonoVue.

The widespread use of modern imaging modalities has led to an increase in the frequency of detecting coincidental focal liver lesions (cysts, haemangiomas, focal nodular hyperplasia, adenoma, focal fatty sparing and infiltration) in patients with no symptoms of liver disease. A positive diagnosis is needed to avoid overinvestigation or protracted follow-up. The limitations of conventional sonography have led to the use of other imaging modalities and invasive or costly procedures such as CT, MRI or biopsy. The availability of real-time contrast-enhanced ultrasound imaging (CEUS) has changed the strategy in the characterization of such lesions without inconvenience for the patient. Cadence contrast pulse sequencing (CPS) gives strong contrast signals as well as simultaneous acquisition of conventional scans for a perfect match of these two images. In our personal experience, in comparison with reference imaging, CPS with SonoVue has differentiated benign from malignant lesions in all cases and has accurately characterized 96% of lesions. These results are slightly better than those reported in the literature, probably because of the higher sensitivity of CPS in detecting bubbles, whether flowing or stationary, and also because of the possibility of matching simultaneously recorded contrast and conventional images which reinforces confidence in lesion assessment. The high diagnostic value of CEUS makes this method a candidate to be considered a reference imaging modality for incidental lesions.

Contrast Media↗
PubMed2000

Simulations of NMR pulse sequences during equilibrium and non-equilibrium chemical exchange.

The McConnell equations combine the differential equations for a simple two-state chemical exchange process with the Bloch differential equations for a classical description of the behavior of nuclear spins in a magnetic field. This equation system provides a useful starting point for the analysis of slow, intermediate and fast chemical exchange studied using a variety of NMR experiments. The McConnell equations are in the mathematical form of an inhomogeneous system of first-order differential equations. Here we rewrite the McConnell equations in a homogeneous form in order to facilitate fast and simple numerical calculation of the solution to the equation system. The McConnell equations can only treat equilibrium chemical exchange. We therefore also present a homogeneous equation system that can handle both equilibrium and non-equilibrium chemical processes correctly, as long as the kinetics is of first-order. Finally, the same method of rewriting the inhomogeneous form of the McConnell equations into a homogeneous form is applied to a quantum mechanical treatment of a spin system in chemical exchange. In order to illustrate the homogeneous McConnell equations, we have simulated pulse sequences useful for measuring exchange rates in slow, intermediate and fast chemical exchange processes. A stopped-flow NMR experiment was simulated using the equations for non-equilibrium chemical exchange. The quantum mechanical treatment was tested by the simulation of a sensitivity enhanced 15N-HSQC with pulsed field gradients during slow chemical exchange and by the simulation of the transfer efficiency of a two-dimensional heteronuclear cross-polarization based experiment as a function of both chemical shift difference and exchange rate constants.

Flow Injection Analysis↗
PubMed1999

Pulse sequences for measurement of one-bond (15)N-(1)H coupling constants in the protein backbone.

A set of three improved two-dimensional (2D) NMR methods for measuring one-bond (15)N-(1)H coupling constants in the protein backbone is presented. They are tailored to suit the size of the TROSY effect, i.e., the degree of interference between dipolar and chemical shift anisotropy relaxation mechanisms. The methods edit 2D spectra into two separate subspectra corresponding to the two possible spin states of the coupling partner. Cross talk between the two subspectra is a second order effect in the difference between the actual coupling constants and the one used in setting the pertinent delays of the pulse sequences. This relatively high degree of editing accuracy makes the methods useful for applications to molecules subjected to weak alignment where the one-bond coupling constants are linear combinations of a scalar J and a residual dipolar contribution containing important structural information. A demonstration of the new methods is shown for the (15)N-labeled protein chymotrypsin inhibitor 2 in a lipid bicelle mixture.

Hydrogen↗
PubMedDate not supplied

Optimization of contrast-enhanced MR angiography of the hands with a timing bolus and elliptically reordered 3D pulse sequence.

Our objective was to optimize bolus administration and sequence setting in gadolinium-enhanced magnetic resonance (MR) angiography of the hands. Elliptically reordered three-dimensional (3D) spoiled gradient-echo sequence with non-slab-selective radio frequency excitation was optimized according to the measurements of arterial and venous time-signal curves in 21 patients. Great variations in bolus arrival time and arterio-venous transit time could be observed. In most patients high-quality arterial depiction could be obtained with minor venous contamination. Contrast-to-noise, spatial resolution, and selective arterial filling is still a challenge for 3D MR angiography of the hand but can be optimized using Gadolinium-BOPTA and a dedicated pulse sequence setting with exact bolus timing.

Adolescent↗
PubMed1985

Benign and malignant breast disease: magnetic resonance and radiofrequency pulse sequences.

Thirty patients with suspected abnormality of the breasts on mammography were evaluated with magnetic resonance imaging (MRI) in a blind fashion. Spin-echo (SE) 250/30 msec scans were used to screen the examined breast. At the location of the suspected abnormality, inversion recovery (IR) 1000/30/300, SE 1000/30, and SE 1000/120 scans were performed. On the basis of these magnetic resonance images and experience with 70 previously studied patients, abnormalities of the breasts were grouped into five patterns. Ten malignant lesions exceeded 1 cm in diameter and were all correctly diagnosed by mammography and MRI. Of the remaining 20 benign conditions, four were suspicious for malignancy on MRI compared to eight with mammography. The shape of the lesion and the change in its signal intensity with different MR radiofrequency pulse sequences allows differentiation between a benign and a malignant process. On the basis of this preliminary experience, it seems MRI may have an adjunctive role to screening mammography. SE 1000/120 scans show higher signal intensity from carcinoma than from normal duct tissue, fibrocystic disease, and fibroadenoma. In this respect, it may allow some tissue specification in the breast.

Adenofibroma↗
PubMed1989

MR characterization of adrenal masses: field strength and pulse sequence considerations.

The authors evaluated the ability of magnetic resonance (MR) imaging at 1.5 T to characterize 28 adrenal masses, using several variables: signal intensity ratios (adrenal/liver and adrenal/fat) on T2- and T1-weighted images, and the calculated T2 relaxation time of the adrenal mass. Signal intensity ratios were unreliable in distinguishing adenomas from nonadenomas. The calculated T2 relaxation time was more useful: All 15 adrenal masses with a T2 of less than 60 msec were adenomas. A T2 greater than 60 msec was less specific and included six metastases, two pheochromocytomas, one adrenal carcinoma, two adrenal hemorrhages, and two nonhyper-functioning adenomas. Therefore, T2 values are more accurate than signal intensity ratios for characterization of adrenal masses at 1.5 T. The unsuitability of previously published criteria determined with 0.35- and 0.5-T systems may reflect the change of T1 and T2 relaxation times with field strength, altering the relative T1 and T2 weighting by a given pulse sequence.

Adenoma↗
PubMed1993

Prospective comparison of T2-weighted fast spin-echo, with and without fat suppression, and conventional spin-echo pulse sequences in the upper abdomen.

PURPOSE: To evaluate use of fast spin-echo (FSE) magnetic resonance imaging with and without fat suppression in the liver and upper abdomen. MATERIALS AND METHODS: Conventional spin-echo (SE) T2-weighted, FSE T2-weighted, and fat-suppressed FSE T2-weighted images from 37 patients strongly suspected to have focal hepatic lesions were evaluated. RESULTS: Quantitative analysis demonstrated that fat-suppressed FSE imaging had the highest lesion-liver contrast-to-noise ratio; conventional SE imaging, the lowest. In a qualitative analysis, FSE imaging was preferred. In a rank order analysis, FSE imaging was preferred 83% of the time and fat-suppressed FSE imaging 17% of the time as regards overall image quality; fat-suppressed FSE imaging was preferred 64% of the time, FSE imaging 23% of the time, and conventional SE imaging 13% of the time as regards signal abnormality detection. CONCLUSION: FSE imaging with and without fat suppression is a potentially useful pulse sequence for evaluating the upper abdomen.

Abdomen↗
PubMed1995

Suspected multiple sclerosis: MR imaging with a thin-section fast FLAIR pulse sequence.

PURPOSE: To compare thin-section, sagittal, fast fluid-attenuated inversion-recovery (FLAIR) magnetic resonance (MR) imaging with conventional axial spin-echo (SE) imaging for early detection of multiple sclerosis (MS) in the brain. MATERIALS AND METHODS: Conventional 5-mm axial proton-density- and T2-weighted SE images and sagittal 2-mm fast FLAIR images of the brain in five healthy volunteers and 25 patients with clinically suspected MS were evaluated and graded as normal or as showing possible or probable MS in a double-blind study. RESULTS: Fast FLAIR was judged better than SE in 37% of cases, equal to SE in 63%, and never worse than SE. In 43% of patients considered to have normal SE images, fast FLAIR images showed abnormalities consistent with MS. A subependymal striated appearance observed in several cases is believed to represent early inflammation and/or demyelination around subependymal veins in MS. CONCLUSION: Sagittal thin-section fast FLAIR is superior to conventional axial proton-density- and T2-weighted SE pulse sequences for detection of MS plaques in the brain.

Adult↗
PubMed1993

Dual mechanisms for change in myocardial signal intensity by means of a single MR contrast medium: dependence on concentration and pulse sequence.

To determine whether gadodiamide injection can provide sufficient enhancement on both T1- and T2-weighted spin-echo magnetic resonance (MR) images of the heart and skeletal muscles, anesthetized rats were divided into five groups. Groups 1-3 received 0.1 (n = 9), 0.3 (n = 8), or 0.5 (n = 8) mmol/kg gadodiamide injection, respectively, and T1-weighted images were obtained. Groups 4 and 5 received 0.3 or 0.5 mmol/kg gadodiamide injection, respectively, and T2-weighted images were obtained. Gadolinium concentration was measured in myocardium by means of inductively coupled plasma-atomic emission spectroscopy. On T1-weighted images, the 0.1 and 0.3 mmol/kg doses produced a dose-dependent increase in myocardial signal intensity proportional to gadolinium concentration. A dose of 0.5 mmol/kg, which correlated with higher gadolinium concentration and did not further increase myocardial signal intensity, prolonged the imaging window. On T2-weighted images, the 0.3 mmol/kg dose caused a transient decrease in myocardial signal intensity; the 0.5 mmol/kg dose produced greater and persistent loss of signal intensity. In conclusion, the changes in signal intensity induced by gadodiamide injection depend on the dose, pulse sequence, and type of tissue.

Animals↗