Scanning acquisition

The principle of the acquisition system is to translate the probe into a tube (including hemispherical drilled holes) step by step, every 0.04 mm, after a forwards and backwards 360 rotation of the tube trigging every 0.2° angular step a 360° electronic scanning of tube with the 160 acoustic apertures. During the electronic scanning the tube is assumed to stay at the same place. The acquisition lasts about 30 minutes for a C-scan acquisition with a 14 kHz recurrence frequency. 

Due to their comparatively low costs and easy operation, quadtupole instruments are the most common instruments used for hyphenation in CEC analyses. However, these instruments only operate at low mass resolution. Sensitivity can be enhanced by operating in selected ion monitoring mode instead of full scanning acquisitions. Unfortunately, this leads to the loss of structural information. The expansion of biological applications has been largely accommodated by the TOE, quadtupole mass filter, and ion-trap instruments. The major advantage of TOE is its potential for speed, resolution, and good mass accuracy. 

A scanning calibration enables peaks acquired in a scanning acquisition to be mass measured accurately (scan mode). If only a scanning calibration is performed, the instrument is calibrated correctly only for scanning acquisitions over the same mass range and at the same scan speed as those used for the calibration. The scan speed recommended for the scanning calibration is 100 amu/s. 

LC-ISP-MS has been also successfully applied for the assay of 21 sulfonamides in salmon flesh (121). Separation was achieved in a reversed-phase LC system with gradient elution. Simple positive-ion spectra with an intense protonated molecule and no fragment ions of relevant abundance were displayed by all analytes by operating in the full-scan acquisition and SIM modes. Further application of tandem MS using SRM for increased sensitivity could overcome the lack of structural information presented by the ISP mass spectra. 

P 26] Time-resolved FTIR spectroscopy was performed by operation of an infrared spectrometer in the rapid scan acquisition mode (see Figure 1.59) [110]. The effective time span between subsequent spectra was 65 ms. Further gains in time resolution can be achieved when setting the spectral resolution lower (here 8 cm4) or by using the step-scan instead of rapid-scan mode. 

In lipid analyses with LC-MS, mass scanning methods have included MS full-scan acquisition with accurate mass, acquiring precursor and fragment exact mass data simultaneously with MSe scan, precursor ion scan and MRM. The most popular fragmentation method in MS/MS experiments has been collision-induced dissociation, but also higher energy collision dissociation has been utilized. 

Figure 9.2 Spectra obtained using the Varian 5 mm XSens dual cold probe. (A) 500 MHz H spectrum, 50 pg quinine, 3 mm NMR tube, 1 scan acquisition. (B) 125 MHz 13C spectrum, 50 pg quinine, 3 mm NMR tube, 2.5 hour acquisition (data kindly provided by Varian Inc.).

Figure 12.7 Acquisition and reconstruction of interferograms in stcp-scan acquisition mode.

Preliminary analyses were full-scan acquisitions with a mass range of 150-500 amu/2 sec. Electron multiplier voltage was set at 1500 V. Data were collected, analyzed and plotted with a Finnigan Superlncos data system. 

Figure 9 Full-scan acquisition mode of the quadrupole mass filter.

Low Risk. CTA has a lower rate of patient discomfort, is less expensive, and has considerably lower risk of stroke and other vascular complications compared to conventional catheter angiography. It is also advantageous in situations when MR is contraindicated or cannot be performed. CTA is typically more readily available than MR, especially in emergency settings. CTA, unlike MRA, lends itself to the imaging of acutely ill patients, as there are no restrictions on the type and quantity of associated support equipment, such as intravenous pumps, ventilators, or monitoring hardware. Because CT scan acquisition is more rapid than that of MRA, CTA is less prone to motion artifact. When CTA is combined with CT perfusion (CTP) for the evaluation of acute stroke, quantitative perfusion data can also be obtained, which is not typically possible with MR perfusion imaging. 

Moreover, the CTA-SI dataset, assuming an approximate steady-state level of contrast enhancement during scan acquisition, is intrinsically blood volume weighted. Like DWI, these images can be used to determine tissue with a high likelihood of infarction in the absence of early, complete recanalization [90]. In addition, the extent of hypoattenuation in the CTA-SIs has been shown to be an excellent predictor of functional outcome in ischemic stroke of both the anterior and posterior circulation [91-93]. This topic is discussed more fully in Chap. 5. 

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