PixelPrint: three-dimensional printing of patient-specific soft tissue and bone phantoms for CT

Abstract

Patient-based CT phantoms, with realistic image texture and densities, are essential tools for assessing and verifying CT performance in clinical practice. This study extends our previously presented 3D printing solution (PixelPrint) to patient-based phantoms with soft tissue and bone structures. To expand the Hounsfield Unit (HUs) range, we utilize a stone-based filament. Applying PixelPrint, we converted patient DICOM images directly into FDM printer instructions (G-code). Density was modeled as the ratio of filament to voxel volume to emulate attenuation profiles for each voxel, with the filament ratio controlled through continuous modification of the printing speed. Two different phantoms were designed to demonstrate the high reproducibility of our approach with micro-CT acquisitions, and to determine the mapping between filament line widths and HU values on a clinical CT system. Moreover, a third phantom based on a clinical cervical spine scan was manufactured and scanned with a clinical spectral CT scanner. CT image of the patient-based phantom closely resembles the original CT image both in texture and contrast levels. Measured differences between patient and phantom are around 10 HU for bone marrow voxels and around 150 HU for cortical bone. In addition, stone-based filament can accurately represent boney tissue structures across the different x-ray energies, as measured by spectral CT. This study demonstrates the feasibility of our 3D-printed patient-based phantoms to be extended to soft-tissue and bone structure while maintaining accurate organ geometry, image texture, and attenuation profiles for spectral CT.

Design and fabrication of 3D-printed patient-specific soft tissue and bone phantoms for CT imaging

“…Continuing our previously published research on the PixelPrint lung phantom [18], [19], this study not only extended the types of human tissue printed, but also enhanced the resolution and stability of PixelPrint. Filament line spacing was reduced from 1.0 to 0.5 mm, potentially doubling the resolution capabilities of the printed phantoms.…”

“…Altering the line width by varying the extrusion rate alone does not provide sufficient spatial resolution due to the inherently slow response time of the extrusion process. Our group recently developed PixelPrint [18], a methodology that combines a software tool as well as a standard FDM printer to create phantoms [19]- [23]. In PixelPrint, DICOM images of the original patient are directly converted into G-code on a pixel-by-pixel basis.…”

“…The filament ratio is continuously modified by varying the printing speed. Polylactic acid (PLA), a common printing filament, allows a print range approximately from -850 to 200 HU at different filament ratios, and has been used to print various patient-based lung phantoms [19].…”

Design and fabrication of 3D-printed patient-specific soft tissue and bone phantoms for CT imaging

“…Altering the line width by varying the extrusion rate alone does not provide su cient spatial resolution due to the inherently slow response time of the extrusion process. Our group recently developed PixelPrint [18], a methodology that combines a software tool as well as a standard FDM printer to create phantoms [19]- [23]. In PixelPrint, DICOM images of the original patient are directly converted into G-code on a pixel-by-pixel basis.…”

“…The lament ratio is continuously modi ed by varying the printing speed. Polylactic acid (PLA), a common printing lament, allows a print range approximately from − 850 to 200 HU at different lament ratios, and has been used to print various patient-based lung phantoms [19].…”