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3D Printing in Interventional Radiology
Introduction
Interventional radiology (IR) is a subspecialty of radiology in which radiologists perform minimally invasive operations to diagnose, treat, and cure a variety of conditions. As compared to traditional surgeries, IR procedures can reduce surgical risks, operating and recovery time, costs, and at times lead to improved patient outcomes. The range of diseases and organ systems amenable to IR procedures are extensive and include vascular, oncologic, hepatobiliary, gastrointestinal, genitourinary, pulmonary, musculoskeletal, and neurologic intervention. IR procedures broadly involve angioplasty and stenting, thrombolysis, embolization, ablation, biopsy, drainage, injection, and retrieval.
Three-dimensional (3D) printing technologies are already well established in the surgical domain. In fact, even before the advent of this technology, researchers across the world were creating 3D objects for surgical planning by milling structures from foam, plastic, and other materials using a subtractive approach. , A glimpse into its role in surgical fields may substantiate parallel use cases within IR. Complex procedures require preoperative evaluation, and often, practice, to ensure a successful outcome. The role of 3D printing in surgery is usually for the purpose of illustrating anatomy in a relatable 3D method to surgeons, to create an anatomically accurate environment for hands-on simulation of a procedure, to serve as an intraoperative reference tool, to create customized equipment, and to develop tailored devices for a certain patient or procedure. This technology has been shown to reduce surgical time, increase operator confidence, and lead to improved operative results.
There is growing evidence that physical 3D printed models aid clinicians in improving patient management and allow for improved patient outcomes. These models can add value to clinical practice by allowing preprocedural planning or fabrication of custom devices and can have a large impact on trainee education and patient understanding. These use cases lay the foundation for several applications of 3D printing within IR. In this chapter, we will address printing techniques and workflow relevant to IR, use cases of this technology in IR, and the future of 3D printing in IR.
3D Printing Workflow
The general workflow to fabricate a 3D printed anatomic model involves image acquisition, segmentation, post-processing with computer-aided design (CAD) software, printing, and model post-processing, as exemplified in Fig. 11.1 . As these topics have been discussed in detail in previous chapters, we will not go into depth here. However, it must be noted that a model's accuracy depends on how well the targeted structures can be clearly distinguished from surrounding tissues on the initial imaging. The study of choice should provide the maximum contrast differentiation between the anatomy of interest and surrounding structures, which depends on size, shape, density, and magnetic resonance characteristics of tissue.
IR procedures vary widely by organ system, specific intervention, and age group, warranting unique imaging needs which should be considered when printing a model. For example, computed tomography (CT) may be the preferred modality when characterizing a complex inferior vena cava (IVC) filter retrieval due to the spatial resolution and ability to delineate metallic material. Certain tumors may have borders which are better defined on magnetic resonance imaging (MRI) and can aid in planning approach to a biopsy or complex ablation. Technical factors such as signal-to-noise ratio and contrast-to-noise ratio can, respectively, impact the ability to resolve fine structures such as small vessels and the ability to distinguish different materials such as pleural effusion from adjacent atelectasis.
Once an anatomic model has been segmented and prepared for printing using CAD software, the many different options for 3D printing must be considered. The International Organization for Standardization and American Society of Testing and Materials have categorized these techniques under seven standardized headings including vat photopolymerization, material extrusion, directed energy deposition, powder bed fusion, binder jetting, material jetting, and sheet lamination. The unique aspects of each of these techniques are discussed separately in Chapter 5 entitled “3D Printing Principles and Technologies.” Techniques most relevant to use cases that arise in IR include vat photopolymerization, material extrusion, binder jetting, and material jetting. Once printing is complete, the part and the build plate are removed. The part is cleaned and support structures, if present, are removed ( Fig. 11.2 ). For IR planning purposes, hollowed vasculature models may be required. It is important to note that for these models, technologies with dissolvable support materials are preferred.
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