Multiple ion detection system with miniscan facilities and expanded mass range for magnetic sector mass spectrometers.

A new four-channel multiple ion detection (MID) system is described. By adding a A V of up to 1100 volts to the nominal accelerating voltage ( V ) , a mass range of about 3 0 % ( V = 3600 volts) to 9 0% ( V = 1200 volts) can be covered, thus providing a remarkably wide range compared to other MID units. The system incorporates a ramp voltage, which added to V allows a small scan around each one of the peaks fo- cused, as well as holding amplifiers in each channel. These features combined with the excellent stability of the Ionization chamber against voltage changes mlnlmlre the errors due to defocusing effects, permitting the addition of voltages as high as those described. The scan time is continuously adjustable between 0.5 and 12 s and the swltching time between two adjacent channels is 50 ms. The circuit design, its operation, and some aspects of the performance of this unit are described.Peer reviewe

Multiple ion detection system with miniscan facilities and expanded mass range for magnetic sector mass spectrometers.

A new four-channel multiple ion detection (MID) system is described. By adding a A V of up to 1100 volts to the nominal accelerating voltage ( V ) , a mass range of about 3 0 % ( V = 3600 volts) to 9 0% ( V = 1200 volts) can be covered, thus providing a remarkably wide range compared to other MID units. The system incorporates a ramp voltage, which added to V allows a small scan around each one of the peaks fo- cused, as well as holding amplifiers in each channel. These features combined with the excellent stability of the Ionization chamber against voltage changes mlnlmlre the errors due to defocusing effects, permitting the addition of voltages as high as those described. The scan time is continuously adjustable between 0.5 and 12 s and the swltching time between two adjacent channels is 50 ms. The circuit design, its operation, and some aspects of the performance of this unit are described.Peer reviewe

Systolodiastolic variations of blood flow during central retinal vein occlusion: exploration by dynamic angiography

Background/aim: In patients with acute central retinal vein occlusion (CRVO), dynamic angiography may reveal the presence of pulsatile flow (termed here pulsatile venular outflow, PVO) within first order veins (that is, the large veins). The main goal of this study was to investigate the mechanism underlying PVO. Methods: 10 patients with CRVO and PVO were included. Quantitative and qualitative analysis of venous flow on dynamic angiograms allowed the correlation, temporally, of second and first order vein flow on the one hand, and venous flow and systolic cycle on the other. Results: Analysis of the time-velocity curve showed that (1) the onset of arterial systole preceded the onset of PVO by less than 0.08 seconds (n = 5); (2) PVO onset was simultaneous to the time of onset of minimal flow (V(min)) in first order veins (n = 10); (3) the time of onset of maximal flow (V(max)) in first order veins occurred 0.20–0.44 seconds after the onset of PVO (n = 6). Conclusions: During CRVO with severe reduction in blood flow, the presence of PVO is the result of the existence of a distinct haemodynamic regimen in first and second order veins. These data support the hypothesis that second order veins flow is synchronous with the arterial flow, while the delayed peak flow in first order veins may reflect the consequences of the delayed IOP curve and/or of intermittent venous compression