Correlation of optical coherence tomography measurements with dissolution

Optical coherence tomography (OCT) uses a low-wavelength light beam to penetrate materials and reveal structural properties beneath the surface. Due to its fast scanning and processing speed, OCT is an optimal technology for the in-line monitoring of processes.

The compressed tablets produced by AMS were measured with OCT under a spinning disk to obtain many images of the same tablet. In these images, structural patterns can be seen beneath the surface of the biconvex tablets. However, the tablets from the nine investigated batches appear to be the same visually.

We could quantify pixel patterns in these images using advanced image analysis methods. These pixel patterns are the result of the light-scattering behavior of the OCT light beam when it hits each tablet’s surface and structure around 100-200 µm beneath its surface. An area of interest is detected automatically and evaluated in several ways.

This way, we obtained several OCT values associated with each image and an average value for every tablet. After OCT measurement, tablets were tested for dissolution, and each tablet’s release profile of the active pharmaceutical ingredient (API) was documented.

We hypothesized that the light-scattering behavior corresponds with the porosity properties of the tablet. In past studies, such structural properties correlate with dissolution behavior. We were able to establish a clear correlation between OCT measurements and dissolved API. In particular, the average penetration depth of the scattering behavior was determined and demonstrated an excellent visual correlation with the dissolved API.

With this part of the project, we have built the foundation for using OCT as an in-line monitoring solution for tableting lines, where on average, 10 to 20 tablets per second can be scanned and evaluated. A test trial with an OCT installation at the tablet press is currently ongoing at RCPE.