B Davis

M Lord

Todd C Pataky

English

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Pataky Todd C

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Journal of Foot and Ankle Research

Spatial resolution and peak-pressure-change measurement accuracy

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ORAL PRESENTATION Open Access
Spatial resolution and peak-pressure-change
measurement accuracy
Todd C Pataky
From 3rd Congress of the International Foot and Ankle Biomechanics Community
Sydney, Australia. 11-13 April 2012
Background
It has been suggested that plantar pressures should be
measured at ~6.2 mm to accurately characterize local
maxima [1], and it has been shown that sensor widths
of 10 mm can cause a 30% pressure underestimation at
the metatarsal heads [2]. However, these results assume
that pressure maxima, not maxima changes, are of pri-
mary interest. The purpose of this study was to examine
how spatial resolution affects accuracy when measuring
local maxima vs. changes in local maxima.
Methods and materials
A pressure pulse model (Figure 1) was generalized from
[2] for force (F) and wavelength (l) as:
f x y
F
x y, cos cos    






 









2 1
2
1
2
(1)
where the maximum pressure (p*) is 4Fl-2, and the
measured pressure (p) has an analytical solution depen-
Correspondence: tpataky@shinshu-u.ac.jp
Department of Bioengineering, Shinshu University, Ueda, Nagano, 386-8567,
Japan
Figure 1 Pressure model (Eqn.1). Example pulses of l=20 and 25 mm, with maxima of p*=1000 kPa and 640 kPa, Total force = 100 N.
Pataky Journal of Foot and Ankle Research 2012, 5(Suppl 1):O30
http://www.jfootankleres.com/content/5/S1/O30
JOURNAL OF FOOT
AND ANKLE RESEARCH
© 2012 Pataky; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
dent on sensor width w. The measurement accuracy of
local-maxima and local-maxima-changes are p/p* [2],
and (p1-p2)/(p*1-p*2), respectively, where ‘1’ and ‘2’
denote pulses with different wavelengths. To mimic
insole-padding intervention, where total force is not
expected to change, F was a constant 100 N and l was
varied from 20 mm [2]. Numerical optimization was
used to find the critical sensor width that yielded var-
ious target accuracies for both local-maxima and a vari-
ety of local-maxima-changes (-100% to +100% change).
Results
Results reveal that a target accuracy of 90% requires 5
mm resolution for local peak pressures (Figure 2), and
that pressure-changes at 90% accuracy require resolu-
tions of 4.1 mm and 3.2 mm, for changes of -50% and
+50%, respectively. The reason is intuitive: the true dif-
ference pulse has higher frequency components than the
original pulses, so pressure-change accuracy will be
lower for all changes >-100%.
Conclusion
This study has shown that, to achieve a given measure-
ment accuracy, higher spatial resolutions are needed to
measure local-pressure-maxima-changes than single-
maxima. The main limitations are that pressure pulses
are not, in general, constrained to have constant force
and that broader (i.e. non-local) pressure changes were
not considered.
Published: 10 April 2012
References
1. Davis B, Cothren R, Quesada P, Hanson SB, Perry JE: Frequency content of
normal and diabetic plantar pressure profiles: implications for the
selection of transducer sizes. J Biomech 1996, 29:979-983.
2. Lord M: Spatial resolution in plantar pressure measurement. Med Eng
Phys 1997, 19:140-14.
doi:10.1186/1757-1146-5-S1-O30
Cite this article as: Pataky: Spatial resolution and peak-pressure-change
measurement accuracy. Journal of Foot and Ankle Research 2012 5(Suppl
1):O30.
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Figure 2 Critical sensor width needed to achieve given accuracies for local maxima (solid dots), and maxima changes (solid lines).
Pataky Journal of Foot and Ankle Research 2012, 5(Suppl 1):O30
http://www.jfootankleres.com/content/5/S1/O30
Page 2 of 2


Crossref

JE: Frequency content of normal and diabetic plantar pressure profiles: implications for the selection of transducer sizes.

Spatial resolution in plantar pressure measurement. Med Eng Phys 1997, 19:140-14. doi:10.1186/1757-1146-5-S1-O30 Cite this article as: Pataky: Spatial resolution and peak-pressure-change measurement accuracy.

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Spatial resolution and peak-pressure-change measurement accuracy

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