Biomedical Engineering Reference
In-Depth Information
nondestructive technique. Thus there is no sample preparation requirement. Similar to ultrasound,
OCT scan will produce a clear internal cross-section image. However, OCT can obtain a much
higher resolution compared with ultrasound without direct contact with the specimen, which elimi-
nates the contamination of sample and provides a valuable feature for monitoring specimens under
sterile conditions. Not requiring any labeling or contrast agent in OCT measurement is another
remarkable feature. Unlike confocal microscopy, OCT image is based on the backscattering and
not on fl uorescence. There is no fl uorescent labeling required. Due to the nondestructive, direct,
and noncontact measurement features, the monitoring of scaffolds can be performed along the
time under sterile conditions. In fact, we have applied OCT to monitor the scaffold degradation and
cell growth within scaffolds in our laboratory, 153 which requires the quantifi cation of pore size and
porosity variation.
To establish a quantitative estimation of porosity, we have developed two methods. The fi rst one
is the local porosity. Variations of scaffold porosity, occurring as a result of the original polymer/
salt ratio, and various culture conditions were quantifi ed using Matlab software (Mathworks Inc.).
A local porosity analysis, in which large and continuous defects (i.e., pore size
500 µm) were
excluded, was adopted to quantify the porosity of the construct. For each scan, a threshold was set
to discriminate between true empty pores and the pore walls. After binarization, the local porosity
was calculated by a block processing method, 154 and the results were displayed as a gradient color
map as shown in Figure 3.13. Block size was chosen in order to take into account inside construct
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FIGURE 3.13 Demonstration of how to calculate local porosity based on an OCT image: (a) OCT image
of a blank PLLA scaffold, (b) the threshold image by block processing, and (c) the local porosity map after
binarization.
 
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