Reduce Data Acquisition Time Research Articles

Spatially uniform sampling in 4-D EPR spectral-spatial imaging

Four-dimensional EPR imaging involves a computationally intensive inversion of the sampled Radon transform. Conventionally, N-dimensional reconstructions have been carried out with N−1 stages of 2-D backprojection to exploit a dimension-dependent reduction in execution time. The huge data size of 4-D EPR imaging demands the use of a 3-stage reconstruction each consisting of 2-D backprojections. This gives three orders of magnitude reduction in computation relative to a single stage 4-D filtered backprojection. The multi-stage reconstruction, however, requires a uniform angular sampling that yields an inefficient distribution of gradient directions. We introduce a solution that involves acquisition of projections uniformly distributed in solid angle and reconstructs in three 2-D stages with the spatial uniform solid angle data set converted to uniform linear angular projections using 2-D interpolation. Images were taken from the two sampling schemes to compare the spatial resolution and the line width resolution. The degradation in the image quality due to the additional interpolation was small, and we achieved ∼30% reduction in data acquisition time.

Microfluidic Flow-Flash: Method for Investigating Protein Dynamics

We report a new method, microfluidic flow-flash, for measuring protein reaction kinetics. The method couples a microscope imaging detection system with a microfluidic flow cell to reduce data acquisition times and sample consumption. This combination allows for the simultaneous collection of spectral and temporal information. The microfluidic flow cell design utilizes three-dimensional sheath flow to reduce sample dispersion and minimize sample consumption. The ability to alter the flow rates in the microfluidic flow cells allows a variety of time scales to be studied with submillisecond time resolution. The imaging detection system can be coupled with several spectroscopic probes including fluorescence and UV/visible absorbance spectroscopy. Here, we utilize the microfluidic flow-flash method to probe the kinetics of CO recombination or O2 binding to myoglobin after the laser-induced photolysis of CO from myoglobin by UV/visible absorbance spectral imaging.

Spectral reconstruction methods in fast NMR: Reduced dimensionality, random sampling and maximum entropy

The need to reduce data acquisition times of multidimensional NMR experiments has fostered considerable interest in novel data acquisition schemes. A recurring theme is that of reduced dimensionality experiments, in which time evolutions in the indirect dimensions are incremented together, rather than independently. Spectral analysis of such data is carried out using methods such as filtered back-projection, GFT, or parametric signal modeling. By using Maximum Entropy reconstruction of reduced-dimensionality data, we show that the artifacts that arise in reduced dimensionality experiments are intrinsic to the data sampling, and are not, in general, the result of the methods used to compute spectra. Our results illustrate that reduced dimensionality is a special case of non-uniform sampling in the time domain. We show that MaxEnt reconstruction yields more accurate spectra for reduced dimensionality data than back-projection reconstruction and that randomly choosing time increments based on an exponentially weighted distribution is more efficient, with fewer artifacts, than the systematic coupling of time increments used in most reduced dimensionality approaches.

Fast spectroscopic imaging using online optimal sparsek‐space acquisition and projections onto convex sets reconstruction

Long acquisition times, low resolution, and voxel contamination are major difficulties in the application of magnetic resonance spectroscopic imaging (MRSI). To overcome these difficulties, an online-optimized acquisition of k-space, termed sequential forward array selection (SFAS), was developed to reduce acquisition time without sacrificing spatial resolution. A 2D proton MRSI region of interest (ROI) was defined from a scout image and used to create a region of support (ROS) image. The ROS was then used to optimize and obtain a subset of k-space (i.e., a subset of nonuniform phase encodings) and hence reduce the acquisition time for MRSI. Reconstruction and processing software was developed in-house to process and reconstruct MRSI using the projections onto convex sets method. Phantom and in vivo studies showed that good-quality MRS images are obtainable with an approximately 80% reduction of data acquisition time. The reduction of the acquisition time depends on the area ratio of ROS to FOV (i.e., the smaller the ratio, the greater the time reduction). It is also possible to obtain higher-resolution MRS images within a reasonable time using this approach. MRSI with a resolution of 64 x 64 is possible with the acquisition time of the same as 24 x 24 using the traditional full k-space method.

Sound power measurement techniques for powered hand tools

As part of a project to reduce noise induced hearing loss in the construction industry, NIOSH developed a database of sound power level measurements of electric powered hand tools typically used in the construction industry. The tool testing jigs and setups specified and illustrated in ANSI S12.15 were modified to accommodate the higher precision ten‐microphone arrangement used in ISO 3744. ANSI S12.15 is sometimes vague regarding the tool testing jig design, so test jigs were designed to supplement existing specifications in the standard. In the course of the project, test jigs were designed, techniques were devised to improve repeatability of measurements, to reduce waste materials, to reduce measurement setup time, and to reduce data acquisition time. Several types of tools were tested including circular saws, grinders, screw drivers, drills, jig saws, reciprocating saws, miter saws, hammer drills, belt sanders, and impact wrenches. The test jig designs and measurement techniques may help others to save time, reduce waste material, and improve measurement repeatability. Additionally, a microphone was placed in the nominal hearing zone of the tool operator to acquire a time series to assess other sound metrics.

Field mapping system for cyclotron magnet

This paper presents a Hall probe mapping system for measuring a cyclotron magnet, which has been fabricated for the 13 MeV cyclotron at the Korea Institute of Radiological and Medical Sciences. Two Hall probes are mounted on a precision mechanical x– y stage and map magnetic field in the Cartesian coordinate system. The mapping system uses the ‘flying’ mode field mapping method to reduce data-acquisition time. The time required for mapping the whole gap-area of the cyclotron magnet is ∼60 min. The relative measurement error for the averaged magnetic field along beam orbit is less than 0.02%. The cyclotron magnet has been corrected using field measurement data, and the achieved total phase excursion of the cyclotron after correction is less than ±15°, which is within the tolerance of ±20° for the total phase excursion.

Parallel acquisition techniques for accelerated volumetric interpolated breath‐hold examination magnetic resonance imaging of the upper abdomen: Assessment of image quality and lesion conspicuity

To evaluate the impact of parallel acquisition techniques (PATs) on image quality and detection of liver metastases using three-dimensional volumetric interpolated breath-hold examination (VIBE) for clinical liver imaging. Forty-nine patients with various primary malignancies underwent abdominal dynamic contrast-enhanced three-dimensional VIBE magnetic resonance imaging (MRI) (1.5 T) using a standard phased array coil. Recently introduced Generalized Autocalibrating Partially Parallel Acquisition (GRAPPA) and SENSitivity Encoding (mSENSE) PAT reconstruction algorithms were added to reduce scan time twofold. Overall image quality, motion, and aliasing artifacts were classified on a 5-point scale. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) measurements were performed for quantitative comparison. All sequences were evaluated concerning the number of detected lesions. PAT resulted in a reduction of data acquisition time from 23 to 13 seconds. Both GRAPPA and mSENSE data sets yielded 30% less SNR (34.8 +/- 14.1 and 33.1 +/- 13.3, P < 0.001) and 35% less CNR (21.2 +/- 15.0 and 20.9 +/- 12.7, P < 0.05) in comparison to unaccelerated VIBE (SNR = 50.8 +/- 20.3/CNR = 32.5 +/- 19.1). Similarly, PAT revealed lower-image-quality scores than unaccelerated VIBE. GRAPPA resulted in more fold-over artifacts than mSENSE. mSENSE revealed slightly fewer motion artifacts than no PAT. The unaccelerated late-venous-phase VIBE sequence revealed 146 lesions in the same patients. Accelerated images with mSENSE reconstruction detected 138 lesions. GRAPPA revealed 127 lesions, and thus performed inferior to mSENSE. At least for arrays with small numbers of elements, such as arrays used in this study, the PAT-induced reduction in scanning times must be weighed against compromises in image quality, which translate into poorer diagnostic performance regarding detection of small hepatic lesions. Thus, the PAT implementations tested in this study should probably be reserved for patients unable to hold their breaths for regular three-dimensional VIBE data sets.

Reduced data acquisition time in multi-dimensional NMR spectroscopy using multiple-coil probes

A new hardware-based approach is presented to reduce data acquisition times in multi-dimensional NMR spectroscopy using a multiple-coil probe. Using a four-coil setup, two-dimensional COSY and TOCSY spectra were acquired in one-quarter the time of conventional spectra by simultaneous acquisition of different effective t 1 evolution times for each coil. Data processing consists of simple phase-shifting and intensity normalization of the individual data sets, and results in spectra almost identical to those acquired in a conventional manner. This method can potentially be integrated with other new data acquisition and processing schemes for further increases in data acquisition speed.

Scan-plane reduction techniques for planar near-field antenna measurements [AMTA corner

In this work, two planar near-field scan-plane reduction techniques are considered and results are presented. It is shown how truncation based on field-intensity contours, instead of simple geometric truncation, can in some cases improve the efficiency of the truncation process. Both techniques are applied to measured data sets, and it is shown how these methods can be used to reduce data-acquisition times, while also assessing the impact of the total acquisition surface reduction on the far-field radiation-pattern integrity.

High resolution photodetachment spectroscopy of negative ions via slow photoelectron imaging.

A technique for high resolution anion photodetachment spectroscopy is presented that combines velocity map imaging and anion threshold photodetachment. This method, slow electron velocity-map imaging, provides spectral line widths of better than 1 meV. Spectra over a substantial range of electron kinetic energies are recorded in a single image, providing a dramatic reduction of data acquisition time compared to other techniques with comparable resolution. We apply this technique to atomic iodine and the van der Waals cluster I.CO2 as test systems, and then to the prereactive Cl.D2 complex where partially resolved structure assigned to hindered rotor motion is observed.

(3,2)D GFT-NMR experiments for fast data collection from proteins.

High throughput structure determination of proteins will contribute to the success of proteomics investigations. The G-Matrix Fourier Transformation NMR (GFT-NMR) method significantly shortens experimental time by reducing the number of the dimensions of data acquisition for isotopically labeled proteins (Kim, S. and Szyperski, T. (2003) J. Am. Chem. Soc. 125, 1385). We demonstrate herein a suite of ten 3D-->2D or (3,2)D GFT-NMR experiments using (13)C/(15)N-labeled ubiquitin. These experiments were completed within 18 hours, representing a 4- to 18-fold reduction in data acquisition time compared to the corresponding conventional 3D experiments. A subset of the GFT-NMR experiments, (3,2)D HNCO, HNCACB, HN(CO)CACB, and 2D (1)H-(15)N HSQC, which are necessary for backbone assignments, were carried out within 6 hours. To facilitate the analysis of the GFT-NMR spectra, we developed automated procedures for viewing and analyzing the GFT-NMR spectra. Our overall strategy allows (3,2)D GFT-NMR experiments to be readily performed and analyzed. Nevertheless, the increase in spectral overlap and the reduction in signal sensitivity in these fast NMR experiments presently limit their application to relatively small proteins.

Focal volume confinement by submicrometer-sized fluidic channels.

Microfluidic channels with two lateral dimensions smaller than 1 microm were fabricated in fused silica for high-sensitivity single-molecule detection and fluorescence correlation spectroscopy. The effective observation volumes created by these channels are approximately 100 times smaller than observation volumes using conventional confocal optics and thus enable single-fluorophore detection at higher concentrations. Increased signal-to-noise ratios are also attained because the molecules are restricted to diffuse through the central regions of the excitation volume. Depending on the channel geometries, the effective dimensionality of diffusion is reduced, which is taken into account by simple solutions to diffusion models with boundaries. Driven by electrokinetic forces, analytes could be flowed rapidly through the observation volume, drastically increasing the rate of detection events and reducing data acquisition times. The statistical accuracy of single-molecule characterization is improved because all molecules are counted and contribute to the analysis. Velocities as high as 0.1 m/s were reached, corresponding to average molecular residence times in the observation volume as short as 10 micros. Applications of these nanofabricated devices for high-throughput, single-molecule detection in drug screening and genomic analysis are discussed.

Determination of tacrine metabolites in microsomal incubate by high performance liquid chromatography–nuclear magnetic resonance/mass spectrometry with a column trapping system

A column trapping system has been incorporated into high performance liquid chromatography–nuclear magnetic resonance–mass spectrometry (HPLC–NMR–MS) to reduce data acquisition time of NMR experiments. The system uses a trapping column to capture analytes after the HPLC column and back flush trapped analyte to the flow cell of the NMR probe for detection. A dilution solvent is mixed with eluent from HPLC column to reduce the influence of the organic content in the mobile phase before column trapping. The trapping column is also coupled with a mass spectrometer (MS) to get complementary MS data on the same peak. Studies on 1-hydroxylated 9-amino-1,2,3,4-tetrahydro-acridine (1-OH tacrine), indomethacin and testosterone with the column trapping system showed good recovery of analytes and over 3-fold mean increase in UV–VIS signal intensity. The time saving on NMR experiments with the column trapping system was demonstrated by the analysis of dog microsomal incubate with tacrine.

Improving resolution in fast rotating-frame experiments.

The rapid rotating-frame technique allows significant reduction in data-acquisition time compared with the two-dimensional method by stroboscopic observation of the nuclear magnetization during its evolution in the rotating frame. A onefold reduction in the dimensionality of the original rotating-frame experiment is achieved by using a train of strong radiofrequency pulses separated by short acquisition windows. The penalty for shortening experimental time is a reduction in spectral resolution compared with the two-dimensional method due to relaxation of transverse magnetization components during the observation windows. A variant of the rapid-rotating frame technique for improving spectral resolution based on undersampling and self-phase encoding is presented. An M-fold resolution improvement requires M experiments, thus, making possible a tradeoff between spectral resolution and experimental time. The technique was applied for spatial localization of quadrupole nuclei in powder solids, and resolution improvement is demonstrated on one- and two-dimensional NQR images.

Tuning of X-ray phase retarder for magnetic EXAFS spectroscopy in helicity modulation mode.

A technique for polarization tuning over a wide energy range has been developed for magnetic EXAFS spectroscopies using a dia mond x-ray phase retarder in helicity modulation mode. A quick rocking scan using a piezo stage enabled us to tune the angle of retarder crystal with the precision of +/-2 arcsecond within 1 s. Available energy range of circular dichroism measurements has been extended to 6-16 keV by adopting not only undulator gap scan but also the present tuning technique. This technique has been applied to magnetic EXAFS measurements in pure iron at the Fe K-edge. Higher signal-to-noise ratio was obtained in reduced data acquisition time.

Breath-hold 3D MR coronary angiography with a new intravascular contrast agent (feruglose)—first clinical experiences

Demonstration of the initial results of breath-hold 3D MR coronary angiography with patients using a new intravascular contrast agent (feruglose). Contrast-enhanced 3D MR-coronary angiography was performed in 5 patients with coronary artery disease after administration of feruglose in three different doses (0.5 (n = 3), 2, 5 mg Fe/kg body weight for each patient). MR coronary angiography was performed with an ECG-triggered 3D-FLASH-sequence during breath-hold at 1.5 T (TR 6.8 ms, TE 2.5 ms, flip-angle 30°). To reduce data acquisition time, only the two anterior elements of the phased-array body coil were activated. The data acquisition window within the cardiac cycle ranged between 217–326 ms depending on the matrix. Signal-to-noise (SNR) and contrast-to-noise ratios (CNR) of the coronary arteries were analyzed, and the results for the detection of coronary artery stenoses were compared with those obtained by conventional coronary angiography. SNR and CNR revealed an improved image quality at a dose of 2 mg Fe/kg compared with the lower dose, but no further improvement was obtained by rising the dose to 5 mg Fe/kg. Except for the left circumflex artery of one patient, at minimum the proximal parts of all four main coronary arteries could be imaged for all patients. Within the visible parts of the coronary arteries, six of eight significant coronary stenoses were identified correctly. Imaging of the proximal parts of the coronary arteries including detection of stenoses is possible during breath-hold using an intravascular contrast agent.

Improving high‐resolution MR bold venographic imaging using a T1 reducing contrast agent

Recently, a new imaging method was proposed by Reichenbach et al (Radiology 1997;204:272–277) to image small cerebral venous vessels specifically. This method, referred to as high-resolution blood oxygen level-dependent venography (HRBV), relies on the susceptibility difference between the veins and the brain parenchyma. The resulting phase difference between the vessels and the brain parenchyma leads to signal losses over and above the usual T2* effect. At 1.5 T, a rather long TE (roughly 40 msec) is required for this cancellation to become significant, leading to enhanced susceptibility artifacts and a long data acquisition time. In this study, we examine the utility of incorporating a clinically available T1 reducing contrast agent, Omniscan (Sanofi Winthrop Pharmaceuticals, NY, NY), with the HRBV imaging approach to reduce susceptibility artifacts and imaging time while maintaining the visibility of cerebral veins. Using a double-dose injection of Omniscan, we were able to reduce TE from 40 to 25 msec. This led to a decrease in TR from 57 to 42 msec, allowing a 26% reduction in data acquisition time while maintaining the visibility of cerebral venous vessels and reducing susceptibility artifacts. J. Magn. Reson. Imaging 1999;10:118–123, 1999. © 1999 Wiley-Liss, Inc.

Multi-electrode detection in voltammetry

The effect of the number of electrodes and their relative distribution on the gain of the signal-to-noise ratio (SNR) in a multiplexed voltammetric measurement was evaluated. A voltammetric multi-channel instrument was constructed capable of operating with up to 63 ultramicroelectrodes (mercury coated copper discs , diameter 55 µm). The gain in the SNR was investigated as a function of the number of electrodes (15, 31 and 63) in the array. For each array a design matrix was employed for the multiplexed measurements. The results show that the detection limit for Pb(II) can be improved 5.1-fold by employing 63 electrodes. The overlapping effect of diffusion layers was also evaluated and the results allow the conclusion that, for multiplexed readings obtained at 100 per second, and when the distance between adjacent electrodes is less than 20 times their diameter, the radial component is disturbed, causing a reduction in the faradaic current. On the other hand, by keeping the distance greater than this limit, the multiplex gain can be fully achieved with a substantial reduction in data acquisition time.

Identification of drug metabolites in biological matrices by intelligent automated liquid chromatography/tandem mass spectrometry.

A rapid and systematic strategy for the identification of drug metabolites in biological matrices based on liquid chromatography-tandem mass spectrometry (LC/MS/MS) techniques was utilized for the identification of drug metabolites of the HIV protease inhibitor Indinavir. This strategy integrates intelligent realtime mass spectrometry with HPLC detection and a predictive strategy for detecting metabolites arising from common biotransformations, to rapidly elucidate structures of drug metabolites. Structures of metabolites generated from in vitro incubation mixtures of Indinavir were characterized from a single chromatographic analysis using the automated LC/MS/MS methodology, thus reducing data acquisition time and improving efficiency.

Hadamard Transform Time-of-Flight Mass Spectrometry

A new mode of operation of a time-of-flight mass spectrometer (TOFMS) is described and demonstrated. A continuous ion beam emerging from the ion source is accelerated and then modulated by a pseudorandom sequence of “on” and “off” pulses. The data acquisition period is set to match the period of the modulation sequence, and data are acquired synchronously with the modulation of the ion beam. The modulation sequence is deconvoluted from the data using a fast Hadamard transform (FHT) algorithm to extract the time-of-flight distribution of the ions. This multiplexing scheme increases the ion usage to ∼50% for a single detector instrument and ∼100% for a multiple detector instrument, which improves the signal level considerably over that of conventional TOFMS. The gains in signal lead to an improved signal-to-noise ratio or alternatively reduced data acquisition time, giving HT-TOFMS a major instrumental advantage over conventional TOFMS in a number of applications at little additional cost. Positive mode ele...