Non-Radiographic Electrical Capacitance Tomography Medical Imaging

An Office of Naval Research funded project.

Project title: Noncontact Tomographic Condition Monitoring of Osseointegrated Prosthesis

Source of support: Office of Naval Research

The loss of a limb is one of the major reasons for disability. Advances in prosthetic devices have improved the quality of life of amputees and is also a main reason for the increase of arthroplasty surgeries in the U.S. over the last few decades. Today, socket prostheses are most widely used, but osseointegrated prostheses are emerging as a highly promising alternative that offers patients greater comfort, improved performance, and quality of life. In short, osseointegration involves anchoring a portion of the prosthesis in bone and consists of a percutaneous element that is attached to the artificial limb. However, one of its challenges is that the tissue-prosthesis interface near the percutaneous abutment is highly susceptible to infection. The objective of this study is to develop a noncontact, noninvasive system for detecting and monitoring subcutaneous infection at the tissue and osseointegrated prosthesis interface. It is known that the local pH of tissue can change due to infection. Therefore, the sensing system integrates two parts, namely, pH-sensitive thin films that can be coated onto prosthesis surfaces prior to them being implanted and an electrical capacitance tomography (ECT) algorithm that can reconstruct the spatial permittivity distribution of a region of space (i.e., in this case the cross-section of the residual stump) in a noncontact fashion. First, it was shown that ECT could be used for mapping the electrical permittivity distribution of biological specimens and was able to resolve differences between bone and tissue. With the system validated, second, pH-sensitive thin films were designed such that its electrical permittivity responded to changes in pH and then spray-coated onto metallic rods. Third, phantoms of the human-prosthesis system were prepared by embedding the film-coated prosthesis in saturated foam (to simulate tissue). Finally, the film-coated rod was exposed to different pH buffer solutions, dried, and then subjected to ECT testing as validation. The results validated that ECT was able to detect and localize permittivity variations correlated to pH changes.

Collaborators:

Prof. Michael D. Todd, UC San Diego
Dr. A. Drew Barnett, Elintrix
Dr. Joseph Reed, Elintrix

Peer-Reviewed Publications:

S. Gupta, H-J. Lee, K. J. Loh, M. D. Todd, J. Reed, and A. D. Barnett, 2018, "Noncontact Strain Monitoring of Osseointegrated Prostheses," Sensors (1424-8220), MDPI, 18(9): 3015. DOI: 10.3390/s18093015
S. Gupta and K. J. Loh, 2018, "Monitoring Osseointegrated Prosthesis Loosening and Fracture using Electrical Capacitance Tomography," Biomedical Engineering Letters (2093-9868), Springer, 8(3): 291-300. DOI: 10.1007/s13534-018-0073-4
S. Gupta and K. J. Loh, 2017, "Noncontact Electrical Permittivity Mapping and pH-Sensitive Thin Films for Osseointegrated Prosthesis and Infection Monitoring," IEEE Transactions on Medical Imaging (0278-0062), IEEE, Early Access. DOI: 10.1109/TMI.2017.2707390
S. Gupta and K. J. Loh, 2017, "Non-Contact Tomographic Imaging and Nanocomposite Films for Monitoring Human-Prosthesis Interfaces," Procedia Engineering (1877-7058), Elsevier, 188: 110-118. DOI: 10.1016/j.proeng.2017.04.464

Fig. 1: This schematic illustrates the test setup used for noncontact interrogation of specimens.

Fig. 3: A lamb shank was used as a representative biological specimen to validate whether or not ECT could reconstruct the difference in permittivity between tissue versus bone.

Fig. 2: The actual ECT test setup is shown.

Fig. 4: The corresponding ECT spatial permittivity map of the lamb shank is shown.

Fig. 5: A film-coated human-prosthesis phantom was subjected to different pH buffer solutions and interrogated by ECT. The results demonstrated that the nanocomposite worked in concert with ECT to reveal the magnitudes and locations of pH changes indicative of subcutaneous infection.

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