Abstract
Artifacts in computed tomography (CT) and magnetic resonance imaging (MRI) due to titanium implants in spine surgery are known to cause difficulties in follow-up imaging, radiation planning, and precise dose delivery in patients with spinal tumors. Carbon fiber–reinforced polyetheretherketon (CFRP) implants aim to reduce these artifacts. Our aim was to analyze susceptibility artifacts of these implants using a standardized in vitro model. Titanium and CFRP screw-rod phantoms were embedded in 3% agarose gel. Phantoms were scanned with Siemens Somatom AS Open and 3.0-T Siemens Skyra scanners. Regions of interest (ROIs) were plotted and analyzed for CT and MRI at clinically relevant localizations. CT voxel–based imaging analysis showed a significant difference of artifact intensity and central overlay between titanium and CFRP phantoms. For the virtual regions of the spinal canal, titanium implants (ti) presented − 30.7 HU vs. 33.4 HU mean for CFRP (p < 0.001), at the posterior margin of the vertebral body 68.9 HU (ti) vs. 59.8 HU (CFRP) (p < 0.001) and at the anterior part of the vertebral body 201.2 HU (ti) vs. 70.4 HU (CFRP) (p < 0.001), respectively. MRI data was only visually interpreted due to the low sample size and lack of an objective measuring system as Hounsfield units in CT. CT imaging of the phantom with typical implant configuration for thoracic stabilization could demonstrate a significant artifact reduction in CFRP implants compared with titanium implants for evaluation of index structures. Radiolucency with less artifacts provides a better interpretation of follow-up imaging, radiation planning, and more precise dose delivery.
Highlights
With the development of better diagnostic imaging and new targeted systemic therapies for different tumor entities, the incidence of spinal metastases in oncologic patients increasesNeurosurg Rev (2021) 44:2163–2170 relevant artifacts in computed tomography (CT) and magnetic resonance imaging (MRI) making follow-up diagnostics and adjuvant radiotherapy with radiation planning and precise dose delivery difficult [1, 11, 16].Polyetheretherketon (PEEK) is a radiolucent biomaterial which started to replace metal implants in orthopedics and trauma since the 1990s and is used for interbody fusion cages in spine surgery for several years [17, 26, 33]
In the carbon fiber–reinforced polyetheretherketon (CFRP) constructs, most of the intensity changes were seen at the screw tulip (1192.0 ± 664.3 Hounsfield units (HU) vs. 564.3 ± 171.6 HU (CFRP), p < 0.001) which is still made of titanium and the cross-link (714.7 ± 157.4 HU vs. 81.3 ± 5.4 HU (CFRP) p < 0.001) (Fig. 2a)
For iterative metal artifact reduction (IMAR) CT, there was a significant difference between CFRP with 46.17 ± 89.66 HU compared with titanium with 347.8 ± 136.9 HU (p < 0.001) (Fig. 2b)
Summary
With the development of better diagnostic imaging and new targeted systemic therapies for different tumor entities, the incidence of spinal metastases in oncologic patients increasesNeurosurg Rev (2021) 44:2163–2170 relevant artifacts in CT and MRI making follow-up diagnostics and adjuvant radiotherapy with radiation planning and precise dose delivery difficult [1, 11, 16].Polyetheretherketon (PEEK) is a radiolucent biomaterial which started to replace metal implants in orthopedics and trauma since the 1990s and is used for interbody fusion cages in spine surgery for several years [17, 26, 33]. Over 15 years ago, pedicle screws were started being produced from carbon fiber–reinforced polyetheretherketon (CFRP) coated with porous titanium for better osseointegration. Those special screws are in clinical use with good mechanical stability and present an excellent alternative to titanium in order to reduce imaging artifacts [10, 21, 28]. Several studies evaluated the advantages in imaging of these new implants or concentrated mainly on the advantages in radiation oncology according to improved radiation planning as well as dose calculation and distribution [4, 10, 23, 28]. We analyzed susceptibility artifacts in CT and MR imaging of standardized titanium and CFRP screw-rod constructs for posterior spinal stabilization in agarose gel phantoms in vitro
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