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Clin Biomech (Bristol, Avon). 1997 Apr;12(3):S15.

Assessment of pedar and F-Scan revisited.


INTRODUCTION:: Previous experimental results have suggested that the PEDAR system (Novel Electronics, Inc.) for plantar pressure measurement was able to measure known static pressures more accurately than the F-Scan system (Tekscan, Inc.). These measurements, however, were made prior to two recent developments of the F-Scan system (the release of new resistive ink sensor insoles and software allowing for calibration via an air pressure bladder). We sought to address the following questions: (a) Which system measures known pressure more accurately? (b) Which system is more repeatable? (c) Which system has lower measurement variance across a uniform distribution? (d) Is F-Scan repeatability improved with recalibration? METHODS:: Pressure measurements were made using a pair of PEDAR insoles and a pair of new ink, F-Scan insoles. All measurements were made in a Novel air bladder, which provided generated known, uniform pressure distributions. The PEDAR insoles were calibrated using the standard protocol involving the air bladder. This calibration was used for all PEDAR measurements. F-Scan insoles were calibrated on each of three testing days using the new bladder calibration technique. The second testing day was one day after the first, while the third testing day occurred four days following the first. Each set of measurements involved placing both insole pairs (one on top of the other) in the bladder and loading the bladder, at 100 kPa intervals (100 up to 500 kPa and 500 down to 100 kPa). Data were recorded at each interval and the bladder was emptied between each recording. One set of data was collected on the first testing day. On each of the remaining test days, one data set was collected with the F-Scan system using the calibration from the first day, and another set was collected using a calibration obtained that day. For each recording we computed the average and standard deviation of pressure values across sensors in a 3 cm x 3 cm area in the 'forefoot' region. RESULTS:: Across all data sets and all conditions, the mean absolute differences between the area average pressure and the bladder pressure gauge value were 10 and 86 kPa for the PEDAR and F-Scan systems, respectively. The mean absolute differences for the five sessions were 10.7, 5.5, 11.5, 3.3, and 10.5 kPa for the PEDAR insoles. For the F-Scan insoles the means were 110, 104 and 83 kPa with the first day calibration, and 110, 73 and 60 kPa with same day calibrations. The mean standard deviations across the indicated region were 9 and 19 kPa, respectively. DISCUSSION:: The results obtained appear to suggest that the PEDAR insole system still measures uniform pressure more accurately and with greater repeatability than does the F-Scan system with new resistive ink insoles and with calibration via a bladder. The PEDAR system also demonstrated lower variance across sensors, suggesting that sensor to sensor random errors were lower in the PEDAR system. These findings, generally, indicate that applications requiring the greatest accuracy and/or repeatability would be best performed with a PEDAR system. It was noted, however, that repeatability of the F-Scan system was improved when a calibration from a single day was used across days. This finding has beneficial implications for F-Scan users in clinical settings, as it would suggest that trends over time could be better detected if the insoles initially used by a patient are not discarded or recalibrated. CONCLUSIONS:: In summary, we must concur with previous reports that the PEDAR system is likely the system of choice when the greatest accuracy and repeatability are desired; however, for some common clinical applications, F-Scan users can improve the utility of their data by using the new insoles, calibrating via bladder, and retaining patients' initial insoles and calibration files.

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