Radiology and 3D Printing: Voxelated Print Characterization, Phantom for Radiotherapy

Category: Blog,From Academia
blank blank Apr 06, 2021

In this issue of “From Academia”, we included two publications that connect the world of radiology and medical 3D printing in very creative ways. In the first article, the authors use an ultrasonic elastography technique that
measures the effective density and the dynamic bulk modulus elastography (EBME) of 3D printed anatomical models using voxelated materials and 3D printed by J750 DAP. This could have important implications for future quality control of 3D printed medical devices using the voxel print technique. In the second article, The researchers demonstrated an inexpensive method of reproducing a full spectrum of adult bone-like anthropomorphic femur phantom slab using a new interlace deposition extrusion method of standard PLA and Fe-PLA filaments. This model can achieve the required CT appearance (based on HU) for a range of bony structures and soft tissues while providing patient-specificity. Such phantom has applications in surgical guidance, diagnostic imaging, as well as end-to-end dosimetry in radiotherapy.

From Academia” features recent, relevant, close to commercialization academic publications in the space of healthcare 3D printing, 3D bioprinting, and related emerging technologies. 

Email: Rance Tino (tino.rance@gmail.com) if you want to pen an Expert Corner blog for us or want to share relevant academic publications with us.

Manufacturing and Characterization of Hybrid Bulk Voxelated Biomaterials Printed by Digital Anatomy 3D Printing

Authored by Hyeonu Heu, Yuqi Jin, David Yang, Christopher Wier, Aaron Minard, Narendra B. Dahotre, Arup Neogi. MDPI Polymers. 30 December 2020

Illustration of Polyjet 3D printing. The printer jetting head moves along the x- and y-axis while printing a digital material on the build tray. The build tray moves up and down along the z-axis during printing. The printed layer is cured by the UV ramps mounted on the printer head. Copyright MDPI Polymers
Illustration of Polyjet 3D printing. The printer jetting head moves along the x- and y-axis while printing a digital material on the build tray. The build tray moves up and down along the z-axis during printing. The printed layer is cured by the UV ramps mounted on the printer head. Copyright MDPI Polymers

Abstract:

The advent of 3D printers has led to the evolution of realistic anatomical organ-shaped structures that are being currently used as experimental models for rehearsing and preparing complex surgical procedures by clinicians.

However, the actual material properties are still far from being ideal, which necessitates the need to develop new materials and processing techniques for the next generation of 3D printers optimized for clinical applications. Recently, the voxelated soft matter technique has been introduced to provide a much broader range of materials and a profile much more like the actual organ that can be designed and fabricated voxel by voxel with high precision.

For the practical applications of 3D voxelated materials, it is crucial to develop the novel high precision material manufacturing and characterization technique to control the mechanical properties that can be difficult using the conventional methods due to the complexity and the size of the combination of materials.

Here we propose the non-destructive ultrasound effective density and bulk modulus imaging to evaluate 3D voxelated materials printed by J750 Digital Anatomy 3D Printer of Stratasys. Our method provides the design map of voxelated materials and substantially broadens the applications of 3D digital printing in the clinical research area.

Nine different constituent materials of Rubik’s cube-like matrix sample printed by J750 Digital Anatomy 3D Printer (DAP) of Stratasys using voxelated digital materials (DMs) (Gel-/Tissue-/Bone-like materials) and 3D printed anatomical models printed using each material (inserts). (a) VeroPureWhite is a base material and has a white color. (b) GelSupport is utilized for printing small blood vessels or porous space in bones. (c) Agilus30Clear is a transparent base material. (d) A DM to represent a degenerative intervertebral disc that is slightly dense. (e) TissueMatrix/AgilusDM400, 400 refers to 400 μm agilus “skin,” representing soft anatomy, commonly things like muscle, fat, and skin. (f) VeroMagenta is a base material having magenta color. (g) General bone represents any bone that is non-vertebrae, skull, long bone, or ribs. (h) A DM to represent a tumor in the bone. (i) A DM to represent a solid internal organ, any solid internal organ. Tech- Labs and Stratasys took the pictures of all anatomical models. Copyright MDPI Polymers
Nine different constituent materials of Rubik’s cube-like matrix sample printed by J750 Digital Anatomy 3D Printer (DAP) of Stratasys using voxelated digital materials (DMs) (Gel-/Tissue-/Bone-like materials) and 3D printed anatomical models printed using each material (inserts). (a) VeroPureWhite is a base material and has a white color. (b) GelSupport is utilized for printing small blood vessels or porous space in bones. (c) Agilus30Clear is a transparent base material. (d) A DM to represent a degenerative intervertebral disc that is slightly dense. (e) TissueMatrix/AgilusDM400, 400 refers to 400 μm agilus “skin,” representing soft anatomy, commonly things like muscle, fat, and skin. (f) VeroMagenta is a base material having magenta color. (g) General bone represents any bone that is non-vertebrae, skull, long bone, or ribs. (h) A DM to represent a tumor in the bone. (i) A DM to represent a solid internal organ, any solid internal organ. Tech- Labs and Stratasys took the pictures of all anatomical models. Copyright MDPI Polymers

The Interlace Deposition Method of Bone Equivalent Material Extrusion 3D Printing for Imaging in Radiotherapy

Authored by Rance Tino, Adam Yeo, Milan Brandt, Martin Leary, Tomas Kron. Materials & Design. 1 February 2021

Illustration of interlace deposition method of standard PLA and Fe-PLA filament using a slicer software. Copyright Materials & Design
 Illustration of interlace deposition method of standard PLA and Fe-PLA filament using a slicer software. Copyright Materials & Design

Abstract:

Existing material extrusion 3D printing methods of bone-equivalent phantoms for Computed Tomography (CT) imaging in Radiotherapy is limited by the geometrical inaccuracies and the achievable density ranges. The interlace deposition method proposed in this research facilitates the production of densities within the range of polylactic-acid (PLA) and iron-reinforced PLA (Fe-PLA) taking advantage the dual-extrusion printing in an interlacing pattern with variable layer thickness to fine-tune mean Hounsfield Unit (HU) within a volume of interest.

Results show an achieved HU from 63 to 4130 using clinical CT protocols; this result is consistent for all specimen orientations. The proposed method enables the emulation of bone-like HU; as is demonstrated by the manufacture of a patient-specific femur phantom with a mean HU of 173±62 for red bone marrow, 400±64 for cancellous, 1102±182 for cortical, and 56±30 HU for soft tissues. This research demonstrates an inexpensive and clinically-ready approach to constructing bone-equivalent phantoms for imaging and may allow for personalized dosimetry for treatment planning in Radiotherapy.

CT results of manufactured phantom scanned at 140 kVp with 2 mm slice thickness. CT images illustrated here uses a contrast window level of 427 and a window width of 1885. (a) transverse CT images of the manufactured phantom at varying specimen orientations including specimen parallel to the gantry axis at 0∘, 45∘, 90∘ and specimen perpendicular to the couch plane, 90∘, b) the rigid registration of patient CT dataset with the manufactured phantom CT dataset (scanned at 90∘ to emulate the patient orientations, illustrating transverse, sagittal and frontal patient planes, overlaid with the manufactured phantom CT dataset inside bounding box. Generated HU profiles from dashed yellow line profiles are shown in Fig. 9. Volumetric regions of interests were generated using user-defined thresholding for each tissue segments (tissue contours) to extract mean HU and SD of the enclosed CT voxels (Table 2). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.). Copyright Materials & Design
CT results of manufactured phantom scanned at 140 kVp with 2 mm slice thickness. CT images illustrated here uses a contrast window level of 427 and a window width of 1885. (a) transverse CT images of the manufactured phantom at varying specimen orientations including specimen parallel to the gantry axis at 0∘, 45∘, 90∘ and specimen perpendicular to the couch plane, 90∘, b) the rigid registration of patient CT dataset with the manufactured phantom CT dataset (scanned at 90∘ to emulate the patient orientations, illustrating transverse, sagittal and frontal patient planes, overlaid with the manufactured phantom CT dataset inside bounding box. Generated HU profiles from dashed yellow line profiles are shown in Fig. 9. Volumetric regions of interests were generated using user-defined thresholding for each tissue segments (tissue contours) to extract mean HU and SD of the enclosed CT voxels (Table 2). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.). Copyright Materials & Design

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