Appendix for Lorrca® MaxSis
Lorrca Maxsis User Manual Page 205
Version 5.04 MRN-231-EN
2. If only one diffraction pattern is analysed, which can be configured, e.g., for RBC-stability
testing, parameter accuracy will be estimated using the Bootstrap method. (References 47
16
,
60
17
) This method takes M random data points from the set of N that remained after outlier
rejection. M is normally taken equal to N resulting in a new hypothetical data set in which some
data points appear more than once while others are omitted. By repeatedly (300x) generating
these hypothetical data sets from the original set, and by fitting each set to the equation of a
tilted ellipse, a distribution is obtained for each of the five ellipse parameters. The average
value is a good estimate of the true parameter while the standard error serves to indicate the
accuracy of the estimate.
Normally, the diffraction pattern is displayed on an orthogonal base and the orientation angle ()
will not be of value in ektacytometry. Therefore, A is taken the axis closest to the vertical and B is
taken the axis closest to the horizontal. With this definition EI can be negative when the diffraction
pattern is rotated over 90º, which happens when the cells orient differently in shear flow, e.g., in
sickle cell anemia (Reference 9
18
) or elliptocytosis. (References 18
19
, 15
20
)
Note that the accuracy of the fit also depends on the number of edge coordinates that are
extracted from the image. The number of edge coordinates can be increased by fitting more than
one intensity level, at the cost of computational speed.
11.6.2.2. RBC-aggregation and –relaxation measurements
The state of RBC (dis-)aggregation is shear rate dependent: at high shear rates, all red cells in
normal human blood are dispersed and deformed. At very low shear rates or at stasis, aggregates
(rouleaux) will form. RBC aggregation behaviour can be studied from light intensity measurements;
both changes in light absorption and in light back scatter can be used. The LoRRca applies a light
back scatter system.
Various aggregation indices can be determined in whole blood by means of back scatter
measurements. A diode laser, which is mounted inside the BOB, serves as light source. Light that
is back scattered by the layer of blood in the gap is collected by two photodiodes inside the static
BOB and is converted into an electrical signal (Figure 5).
16
Press W.H., Teukolsky A.A., Vetterling W.T., Flannery B.P., Quick-and-dirty monte carlo: The bootstrap
method, in: Numercal recipes in C, The art of scientific computing, Cambridge University Press, 2nd ed., pp.
691-694, 1992 (ISBN: 0-521-43108-5).
17
Thomas G.E., Use of the bootstrap in robust estimation of location, The Statistician, vol. 49:(1), pp. 63-77,
2000.
18
Bessis M., Mohandas, N., Feo C., Automated ektacytometry: A new method of measuring red cell
deformability and red cell indices, Blood cells, vol. 6, pp. 315-327, 1980.
19
Dobbe J.G.G., Hardeman M.R., Streekstra G.J., Strackee J., Ince C., Grimbergen C.A., Analyzing red
blood-cell deformability distributions, Blood Cells, Molecules, and Diseases, vol. 28:(3), pp. 373-384,
May/Jun 2002.
20
Dobbe J.G.G., Engineering developments in hemorheology, PhD Thesis, University of Amsterdam, Sept.
2002.
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