Biological mimics or phantoms play an important role both in the use and in the development of medical technologies for diagnosis, treatment and characterization of biological tissues and fluids:
- They are an essential tool to guide the development of instrumentation and characterize its specifications and performance.
- They allow to calibrate measurement and diagnostic biomedical devices, prior to its use with people or animals, providing the equipment with greater security.
- They serve as a training tool for users who have to handle measurement and diagnostic equipment, in a safe environment and without the pressure of the consequences derived from possible errors during this learning phase.
There is a wide variety of materials used for the manufacture of phantoms, taking into account the physical properties of the tissues to be reproduced, durability, manufacturing requirements, price, etc.
Polyvinyl alcohol (PVA) is one of our preferred materials for making tissue similes due to its excellent qualities of strength, durability and similarity to different biological tissues. Furthermore, the possibility of using additives in its formulation enables a fine adjustment of properties to those of the materials to be simulated. In addition to PVA, we work with other polymeric materials such as some PVC elastomers (plastisols), silicones, wax gels, agar, etc. In addition, the incorporation of 3D printing into the production process of tissue mimics provides great flexibility both to make molds and bone tissue mimics.
PVA allows molding of materials with many different shapes. It is remarkable the possibility of molding PVA gels in fairly thin sheets (0.2-1mm) without breaking, to simulate epithelial tissues and make coatings, resulting in a fairly resistant material.
Regarding the tissues simulated with PVA, different proposals have been carried out in our group, such as the phantom of the upper part of the head of a newborn, simulating skin, meninges, upper part of the brain and cerebrospinal fluid. The skull made of PLA (Polylactic Acid) by 3D printing was also included in the phantom.
We are currently working on phantoms for breast tomography. In particular, a calibration phantom to adjust the tomography device before each scan, has been designed and manufactured. The phantom is essentially a cylindrical piece with an elliptical section that includes inserts of different sizes, speeds and attenuations, in the ranges of the main breast tissues (1450-1550 m/s for velocity and 1.5- 5dB/cm at 3.5MHz for attenuation).
Additionally, we are currently working on an anthropomorphic breast phantom to assess the sensitivity of the system and fine-tune the image analysis and image formation algorithms. This phantom simulates the lactophorous ducts, as well as the fatty and fibroglandular tissues of the breast, which are predominant in proportion. In them we insert elements that simulate different lesions: tumors, cysts, fibroadenomas and microcalcifications.
Related papers
—Luis Elvira, Carmen Durán, Ricardo T. Higuti, Marcelo M. Tiago, Alberto Ibañez, M. Parrilla, Eva Valverde, Javier Jiménez y Quique Bassat. Development and characterization of medical phantoms for ultrasound imaging based on customizable and mouldable polyvinyl alcohol cryogel-based materials and 3-D printing: Application to high frequency cranial ultrasonography in infants. Ultrasound in Medicine and Biology, Vol 45, No 8, pp 2226-2241; https://doi.org/10.1016/j.ultrasmedbio.2019.04.030. Agosto 2019.
—Trabajo de fin de máster: Optimización del proceso de fabricación de criogeles de polivinil alcohol (PVA) para la simulación de tejidos biológicos. Autora: Yasmine Bahagi. Director: Luis Elvira Segura. Escuela Técnica Superior de Ingeniería Industriales (UPM). 25/10/2021.
