摘要:

AbstractTo achieve optimal image quality and highest spatial resolution for inner ear imaging with a 3D gradient echo sequence, it is necessary to minimize susceptibility dephasing effects by using very short TE. Fractional RF pulses and echoes can yield short TE for moderate spatial resolution; however, for voxel size of less than 1 mm, TE is limited by the phase encode gradients. We present a method to obtain very short effective TE by using short triangular shaped phase encode gradients to sample the central portions of k‐space and progressively longer trapezoidal gradients for the outer portions of k‐space. A 3D pulse sequence employing the modified phase encoding scheme for both in‐plane and slice phase encoding directions was implemented and tested on phantoms andin vivo.The effective TE equals the minimal TE used for the central k‐space portions. Submillimeter resolution (0.35 x 0.35 x 0.7 mm3) images of the inner ear were obtained with effective TE of 3.2 ms and were compared with standard 3D images with TE of 8 ms. With this pronounced TE reduction, the susceptibility artifacts at air/fluid interfaces are significantly

ISSN:0740-3194    

DOI:10.1002/mrm.1910330112

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractA model system of a paramagnetic lymphotropic MR contrast agent (Gd‐DTPA labeled polyglucose associated macrocomplex, PGM) for T1‐weighted MR imaging of lymph nodes in rats and rabbits was evaluated. Pharmacokinetic (tissue accumulation) and MR imaging data (optimal dose and timing parameters) were obtained in normal rats (n= 88) after subcutaneous (SC) injection of paramagnetic, radiolabeled [111In]Gd‐DTPA‐PGM. A rabbit model of lymph node metastases (n= 8) was ultimately used to demonstrate the potential of MR imaging with Gd‐DTPA‐PGM for nodal tumor detection. Maximum concentrations of Gd‐DTPA‐PGM were found in popliteal and paraaortic lymph nodes within 24 h after SC administration, and highest lymph node SNR values were obtained by MR imaging at this time point. The optimum imaging dose was 6–12 μmol Gd/kg. Tumor‐lymph node contrast increased from 0.0 ± 1.2 precontrast to 19.2 ± 6.5 (spoiled gradient echo sequence,TR50/TE7/flip angle 60°) postcontrast and conspicuity of nodal metastases was improved. Gd‐DTPA‐PGM accumulates in lymph nodes after SC administration and significantly enhances lymph node signal intensity of normal animals but

ISSN:0740-3194    

DOI:10.1002/mrm.1910330113

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractWhen red blood cells are deoxygenated, hemoglobin, which is then transformed into deoxyhemoglobin or methemoglobin, becomes paramagnetic. The transverse nuclear magnetic relaxation rate of water protons is considerably enhanced by this chemical transformation. A general agreement exists about the origin of the phenomenon—local field inhomogene‐ities induced by paramagnetic centers randomly distributed within the cell—but the localization of the region that dominates the relaxation is unclear. We addressed this problem with a computer simulation devoted to the determination of transverse magnetic relaxation of water protons in the presence of superparamagnetic MRI contrast agent candidates. The simulation confirms an earlier experimental result that shares equitably the responsibility for the observed relaxation between intracellular and extracellular

ISSN:0740-3194    

DOI:10.1002/mrm.1910330114

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractAn improved multi‐slice, multi‐spin‐echo proton spectro‐scopic imaging method for human brain is presented. The technique allows the reconstruction of lactate images, along with choline plus creatine, N‐acetylaspartate, and lipid images from one single data set processed in three separate ways. The discrimination between resonances of lipid protons and lactate methyl protons is based on homonuclear spin‐spin coupling. The reliability of the separation of the lipid and lactate contribution depends on the T2 of the lipid resonances. Measurements were performed on a standard 1.5 Tesla clinical scanner on healthy volunteers and a patient with high grade CNS lymphoma, demonstrating the ability to obtain high quality metabolite maps wi

ISSN:0740-3194    

DOI:10.1002/mrm.1910330115

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractQuantification of MRS signals obtained with surface coils is difficult due to the inhomogeneous response of these coils. This inhomogeneity results in the measured signal from a defined volume of interest (VOI) being spatially dependent. To account for the sensitivity variation with position from the surface coil, we have developed a method of calculating correction factors for defined VOIs based on an experimentally obtained 3D sensitivity coil map. These factors may then be applied to spectra obtained from these VOIs to accurately take into consideration the varying coil sensitivity resulting in a reduction of measured signal. This method is demonstrated here to be able to correct for the inhomogeneity of surface coils over a range of two coil radii to within 4% accuracy.

ISSN:0740-3194    

DOI:10.1002/mrm.1910330116

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractMeasurements of the transverse relaxation time T2are usually conducted with the Carr Purcell Meiboom Gill (CPMG) pulse sequence, which causes T2‐weighted magnetization. Diffusion effects are a common source of error in measurements of this kind, because the incoherent motion of spins in external magnetic field gradients distorts T2weighting of the transverse magnetization. As a result, inaccurate T2‐values are obtained. In this work, we present a method which completely compensates for the effect of diffus

ISSN:0740-3194    

DOI:10.1002/mrm.1910330117

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe inability to return the heart to the same position for all breath‐holds during 2D coronary MR imaging can result in imaging different locations than desired. This can lead to problems such as (i) missing a whole vessel, or a part of it, (ii) misaligning segments of vessels imaged in different breath‐holds, and (iii) degrading image quality when a single slice is acquired in multiple breath‐holds. To reduce inconsistencies in the breath‐hold level, we designed a respiratory feedback monitor (RFM) that uses a bellows to monitor the circumference of the subject's chest. When the circumference of the subject's chest is within preset limits, an audio signal alerts subjects to hold their breath at that position. Use of the RFM significantly reduces the problems caused by inconsistent breath‐holds and the number of breath‐holds for an examination in 2D coronary

ISSN:0740-3194    

DOI:10.1002/mrm.1910330118

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractWe describe a technique to increase the velocity‐to‐noise ratio (VNR) of phase‐contrast magnetic‐resonance velocity images based on making three measurements/flow encoding axis rather than the usual two. A phase‐aliased high first moment data set and a nonaliased low first moment data set are acquired, and the high‐moment data are phase unwrapped using the low‐moment data. The VNR of the resulting measurement is given by that of the high‐moment measurement and increases linearly with the first moment. A factor of 4 gain in VNR was observed with only a 50% increase in scan time. Thus, this method is a much more efficient way to increase VNR than s

ISSN:0740-3194    

DOI:10.1002/mrm.1910330119

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractLong echo time (272 ms)1H magnetic resonance spectro‐scopic imaging was used to measure the relative magnitudes of the N‐acetylaspartate (NAA) signal in a variety of anatomically defined brain structures (centrum semiovale, thalamus, medial frontal cortex, and genu of the corpus callosum) composed primarily of gray matter or white matter. Six normal young adult humans aged 30–40 were studied. With a 95% level of statistical confidence, the white matter in the centrum semiovale (CSO) produced a more intense NAA signal than did the gray matter in the thalamus and the frontal cortex. Differences between the white matter regions were also noted. The CSO white matter's NAA signal yielded a larger NAA signal than did the white matter of the genu of the corpus callosum. Possible reasons for the anatomical variation in the cerebral NAA signal intensity are disc

ISSN:0740-3194    

DOI:10.1002/mrm.1910330120

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractUsing sodium multiple quantum filtered methods, we have, for the first time, demonstrated the presence of residual quadrupolar interaction in human skeletal muscle and brainin vivo.Surface coils were used in both skeletal muscle and brain studies on healthy human volunteers. Theoretical analysis shows that even with arbitrary flip angles the double quantum filter retains filtering capability; it passes even rank two quantum coherence more efficiently than odd rank two quantum coherence. Multiple quantum filtered spectra were obtained from the gastrocnemius muscle in the leg and from the parietal lobe region of the brain. In double quantum filtered spectra, we observed different proportions of narrow and broad components with preparation time, while the line shape of triple quantum filtered spectra remained similar to the one observed in isotropic environment. These results suggest that, in human skeletal muscle and brain, sodium ions are bound to some ordered structures.

ISSN:0740-3194    

DOI:10.1002/mrm.1910330121

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY