Imaging of the MTP joint: Developing an imaging protocol optimised for damage detection and 3D modelling

Sammanfattning: Walking without pain in the toe has a significant impact on a person’s well-being. Human mobility will be impaired in osteoarthritis of the big toe, and pain will occur during walking. By replacing the cartilage or bone injury with an individualised implant, osteochondral injuries to the knee and ankle can be treated. One company that develops and produces these implants together with associated surgical instruments is called Episurf Medical AB. The company can evaluate a lesion and design the individual implant with its associated instrument based on magnetic resonance imaging or computed tomography images. Episurf currently has a production of implants with associated surgical instruments for the knee and ankle but wants to expand further to implants for the metatarsophalangeal joint (MTP joint), commonly named the big toe joint. In order to perform the work process and create the implant and the surgical instruments, Episurf needs qualitative images taken with MRI or CT. Episurf has specific protocols for CT and MRI for imaging the knee and ankle, but no protocol exists yet for the MTP. In this project, CT and MRI have been used to scan the MTP, where various parameters such as foot position, image plane, slice thickness, slice increment and FOV were tested. For CT, different tube currents and tube voltages and their effect on image quality was also tested. In MRI, different sorts of sequences to use when taking pictures of MTP were evaluated. In addition to CT, a scan was also performed with cone-beam computed tomography(CBCT) to see if it could be an additional imaging modality. When evaluating the images for all imaging modalities, Signal to Noise Ratio(SNR), spatial resolution and contrast were considered. For CT, the radiation was evaluated against image quality, and for MRI, the time aspect was evaluated. For images taken with a CT, the parameter setting for the slice thickness should be 0.5-0.8 mm, and the slice increment should be 50% of the slice thickness. As the foot is not a radiation-sensitive region, the radiation can be high. Since the radiation is recommended to be high and the only critical area to evaluate is the big toe, it is enough to include only the forefoot. Finally, the patient’s foot should be in the standing position to have the best possible evaluation opportunities. MRI needs additional tests to find the best relationship between time, SNR, slice increment and slice thickness. More tests also need to be performed for CBCT, where its technology is examined to create an acceptable segmented 3D model, as it was difficult in this project.