Linear analyzers

Linear Analyzer. The linear analyzer was developed for the measurement of beta-emitting radionuclides and was introduced in 1980 by Berthold Analytical Instruments (Filthuth 1986). It operates as a position-sensing proportional counter, measuring a fixed number of channels along the length of the chromatographic plate. The system is equipped with analytical software for quantification. 

The linear analyzer and the digital autoradiograph may be used with any radionuclide... 

A comparison of four different methods of quantification is shown in Fig. 9.1.1.3. A phantom chromatographic plate with increasing amounts of radioactivity (0.25, 1.0, 4.0, 16.0, and 64.0 kBq) spotted at exact intervals was measured by A. linear analyzer, B. conventional scanner, C. cut/measure, and D. ionization chamber (Capintec). The highest sensitivity was achieved with A. and C., the best resolution with B. and C. Using the ionization chamber indicated low detection efficiency of radioactivity below 20 kBq (peaks 1, 2, 3, and 4). 

Linear analyzers and conventional TLC scanners are standard equipment in nuclear medicine. These instruments offer high detection efficiency and resolution characteristics combined with speed of analysis, which is required for the analysis of short-lived radiopharmaceuticals. 

Quantification of labeled components. Each chromatogram is measured (TEC linear analyzer or gamma counter), and the regional radioactivities are expressed as a percentage of the total recovered counts ... 

Among explicit symplectic Partitioned Runge-Kutta methods this is the maximum stability threshold [74]. In a similar way one can analyze the stability of the Verlet and other methods and one thus obtains conditions on the stepsize that must hold for the equilibrium points to be stable in the linearization. Analyzing the stability of both continuous and discrete iteration is much more compUcated for... 

Linear Analyzers and Imaging-Proportional Counter Scanners... 

The Berthold Linear Analyzer LB 285 (Figure 13.1) is a position-sensitive... 

Figure 13.1 Berthold Linear Analyzer LB 285 with IBM-AT computer. [Reproduced with permission of Wiley-Interscience from Filthuth (1990).]...

Comparisons of the various TLRC methods are summarized in Tables 13.1 (Shul-man, 1983 Shulman and Weaner, 1991) and 13.2 (Clark and Klein, 1996). Linear analyzers are still widely used in many laboratories because they offer reasonable speed, resolution, sensitivity and quantitative accuracy that is adequate for many applications and are less expensive than the newer detection instruments. When the highest level of sensitivity, quantification, and resolution are required, use of a multiwire proportional counter or phosphor imager is in order despite their high price. The field appears to be moving rather quickly toward much wider use of phosphor imagers, and it is likely this trend will continue at the expense of proportional counters. 

Parameters Autoradiography Zonal analysis Linear analyzer MWPC detector Phosphor imager... 

Filthuth, H. (1990). Detection of radioactivity distribution with position-sensitive detectors, linear analyzer, and digital autoradiograph. Chem. Anal. (NY) 108 167-183. 

Another major step forward for radio-TLC came in the early 1980s when the so-called linear analyzer was introduced. This instrument was easier to use and more sensitive than the old scanners and was automated to the extent that up to four plates could be run overnight. More details are given below. As a consequence, improved quantitative results were obtained and analysis time was shortened. However, resolution was still not as good as that obtained by using autoradiography, and two-dimensional plates could not be easily evaluated. 

The linear analyzer fundamentally functions in a completely different way compared to the preceding radioscanners in that the components of one entire track of the TLC plate are simultaneously measured without movement of the detector head. Inherently this affords the linear analyzer far greater sensitivity and thus greatly increases the speed of measurement and hence the throughput of samples. 

Figure 1 Schematic diagram of a linear analyzer detector with a resistive anode wire.

There are three principal techniques for the analysis of radioactive components on TLC plates, autoradiography, zonal analysis, and mechanical detectors (e.g. linear analyzers, phosphor imagers, MWPC detectors). The technique of choice depends on a number of parameters but of primary consideration are sensitivity and resolution. Other parameters that are to be considered are quantitation, linear dynamic range, speed, sample throughput, and preservation of the sample. A comparative sununary of the detection methods with respect to these parameters is shown in Table 2. 

Both autoradiography and zonal analysis have a number of drawbacks, including sensitivity and resolution, but primarily both techniques are extremely time consuming. Linear analyzers offer a good compromise among speed, resolution, and quantitative accuracy. However, the performance of the linear analyzers falls well below that of the currently available MWPC detectors and phosphor imagers in all respects. Sensitivity, quantitation, and particularly resolution are significantly superior... 

In general, as the newer range of detectors were brought onto the market they were very expensive in comparison to the linear analyzers. However, as competition and technological developments occur the prices are slowly coming down. A further consideration is that in the authors own institute, for example, one Bioimaging Analyser has replaced approximately ten linear analyzers. 

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