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Signal Difference (signal + difference)

Distribution by Scientific Domains

Medical Sciences	80%

Selected Abstracts

Functional perfusion imaging using continuous arterial spin labeling with separate labeling and imaging coils at 3 T

MAGNETIC RESONANCE IN MEDICINE, Issue 5 2003
Toralf Mildner
Abstract Functional perfusion imaging with a separate labeling coil located above the common carotid artery was demonstrated in human volunteers at 3 T. A helmet resonator and a spin-echo echo-planar imaging (EPI) sequence were used for imaging, and a circular surface coil of 6 cm i.d. was employed for labeling. The subjects performed a finger-tapping task. Signal differences between the condition of finger tapping and the resting state were between ,0.5% and ,1.1 % among the subjects. The imaging protocol included a long post-label delay (PLD) to reduce transit time effects. Labeling was applied for all repetitions of the functional run to reduce the sampling interval. Magn Reson Med 49:791,795, 2003. © 2003 Wiley-Liss, Inc. [source]

Picoliter-volume aqueous droplets in oil: Electrochemical detection and yeast cell electroporation

ELECTROPHORESIS, Issue 10 2006
Chunxiong Luo
Abstract An electrochemical detection method was introduced for aqueous droplet analysis in oil phase of microfluidic devices. This method is based on the electrochemical signal difference between aqueous and oil. Applying a low alternating current,(AC) voltage to a couple of Au microelectrodes, this method can offer size information and ion concentration range from 0.02,mmol/L to 1,mol/L of tens of picoliter to nanoliter aqueous droplets. Alternatively, applying a relative high AC voltage (18,Vpp) at a frequency of 1,kHz leads to electroporation of yeast cells encapsulated into picoliter droplets. We believe that this simple technique is useful for a number of aqueous droplet-based chemical and biological analyses as well as cell electroporation. [source]

3D flow-independent peripheral vessel wall imaging using T2 -prepared phase-sensitive inversion-recovery steady-state free precession

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2010
Jingsi Xie BS
Abstract Purpose: To develop a 3D flow-independent peripheral vessel wall imaging method using T2 -prepared phase-sensitive inversion-recovery (T2PSIR) steady-state free precession (SSFP). Materials and Methods: A 3D T2 -prepared and nonselective inversion-recovery SSFP sequence was designed to achieve flow-independent blood suppression for vessel wall imaging based on T1 and T2 properties of the vessel wall and blood. To maximize image contrast and reduce its dependence on the inversion time (TI), phase-sensitive reconstruction was used to restore the true signal difference between vessel wall and blood. The feasibility of this technique for peripheral artery wall imaging was tested in 13 healthy subjects. Image signal-to-noise ratio (SNR), wall/lumen contrast-to-noise ratio (CNR), and scan efficiency were compared between this technique and conventional 2D double inversion recovery , turbo spin echo (DIR-TSE) in eight subjects. Results: 3D T2PSIR SSFP provided more efficient data acquisition (32 slices and 64 mm in 4 minutes, 7.5 seconds per slice) than 2D DIR-TSE (2,3 minutes per slice). SNR of the vessel wall and CNR between vessel wall and lumen were significantly increased as compared to those of DIR-TSE (P < 0.001). Vessel wall and lumen areas of the two techniques are strongly correlated (intraclass correlation coefficients: 0.975 and 0.937, respectively; P < 0.001 for both). The lumen area of T2PSIR SSFP is slightly larger than that of DIR-TSE (P = 0.008). The difference in vessel wall area between the two techniques is not statistically significant. Conclusion: T2PSIR SSFP is a promising technique for peripheral vessel wall imaging. It provides excellent blood signal suppression and vessel wall/lumen contrast. It can cover a 3D volume efficiently and is flow- and TI-independent. J. Magn. Reson. Imaging 2010;32:399,408. © 2010 Wiley-Liss, Inc. [source]

Effect of b value on contrast during diffusion-weighted magnetic resonance imaging assessment of acute ischemic stroke

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2002
Raoul S. Pereira PhD
Abstract Purpose To examine the effect of varying the diffusion encoding strength (b value) on the contrast (signal difference, ,S) between damaged and normal tissue during diffusion-weighted magnetic resonance imaging (DWI) assessment of acute ischemic stroke. Materials and Methods Phantoms with diffusion values approximating those expected in acutely infarcted and normal tissue were constructed from a mixture of agar and formaldehyde and imaged at varying b values (0,3000 mm,2 second). Ten patients were imaged with multiple b values (500,2500 mm,2 second) within 12 hours of stroke onset. Results Theoretical calculations showed that for any combination of diffusion coefficients there existed an optimal b value that was higher than the standard setting of 1000 mm,2 second, and this was confirmed by the phantom studies. In the patients, increasing b from 1000 to 1500 mm,2 second increased ,S (average, 22.4%; P = 0.001), but no consistent benefit was seen at b = 2000 mm,2 second (P = 0.408). This compared favorably with the average optimal b value of 1662 mm, 2 second calculated from the patients. Conclusion These results suggest that increasing the b value from 1000 to 1500 mm,2 second would increase contrast between infarcted and normal tissue in the setting of acute ischemic stroke. J. Magn. Reson. Imaging 2002;15:591,596. © 2002 Wiley-Liss, Inc. [source]

Compartment size estimation with double wave vector diffusion-weighted imaging

MAGNETIC RESONANCE IN MEDICINE, Issue 1 2008
Martin A. Koch
Abstract Double wave vector diffusion weighting uses gradients along two different directions between excitation and acquisition. It has been shown theoretically that for restricted diffusion the signal amplitude in such an experiment can depend on the angle between the two gradient vectors. The highest amplitude is obtained with antiparallel orientation, and the amplitude difference between parallel and antiparallel gradient orientations depends on the compartment size. The validity of this description is experimentally tested for water between polymer beads, for radish, and for porcine spinal cord, using a clinical MR system with limited gradient strength. The results indicate that the phenomenon is observable; however, the size of the signal difference is considerably diminished when compared with theory. This is attributed to violations of the approximating conditions underlying the theoretical description and to free diffusion contributions. It is concluded that the effect could successfully be used as a basis for developing a new noninvasive method for assessing cell size. Magn Reson Med, 2008. © 2008 Wiley-Liss, Inc. [source]