A 3-D printed tungsten pre-clinical X-ray system collimator. The tungsten alloy powder is printed into the form desired and is laser fused so it can be machined and finished. Previously, making collimators from Tungsten was labor intensive because it required working with sheets of the metal to create the collimator matrix.
Inmolecular radiotherapy (MRT)treatment of the thyroid, existing single photon emission computed tomography (SPECT) imaging systemsare unable to accurately measure radiation absorbed by patients during and after treatment. As a consequence, only limited information regarding the success of radiotherapy treatment has been available.
For the last six years, teams from theUniversity of Liverpool’s Department of Physicsand The Royal Marsden and Royal Liverpool University Hospitals have been working to develop an imaging system (known as DEPICT) that would better measure the absorbed radiation dosimetry. The aim is to provide a more accurate treatment and diagnosis of patients.
Central to the imaging system’s scanner is a collimator. This is a device which aligns the beams of radiation emitted from the patient so that they are directed onto a detector. The radioactive iodine is ingested by the patient in liquid or capsule form, and then gamma rays are emitted in all directions through the patient, yet only the rays which are aligned with the collimator holes will make it through to the detector. The data received can then be converted into an image on a computer screen.
以前，铅是准直器的首选材料。然而，钨在屏蔽无用的伽马射线方面比铅效率高得多。增材制造现在允许用钨制造准直器，从而获得病人接受辐射剂量更清晰的图像。
A critical part of the new imaging system is the use of a direct-digital conversion, cadmium-zinc-telluride (CZT) detector. This part is used in conjunction with a parallel hole collimator with an active area comprising an array of 0.6 mm holes. Traditionally made of lead, collimators on the market were not up to the task of supporting the new DEPICT system, because it required a very intricate design that was not possible to create from this relatively soft material. Researchers hit on the idea that high-density tungsten could be the ideal material if they could find a way shape it into the required collimator.
Tungsten Difficult to Work With, But Ideal For Collimators
Tungsten’s density is around 1.7 times that of lead traditionally used in collimators, but it is difficult to work with because it has the highest boiling and melting points of any element known to man. It also means there is no other material in the world capable of holding tungsten as a molten liquid, so it cannot be cast into high precision shapes in the manner of iron, aluminum and other common metals. That is until now.
A group of experts in the U.K. recently began3-D printing钨合金粉末具有复杂的几何形状，是一种新的材料加工方法。汽车和航空零部件制造公司Wolfmet的一个团队开发了这种高度专业化的增材制造冶金工艺，本质上是将钨合金粉末熔合在一起。使用高功率激光器将连续的纯钨粉末层熔接起来，直到形成一个复杂的组件。一旦熔化，粉末被压成零件，烧结，然后加工成所需的形式。
The Wolfmet tungsten team has developed a highly specialized metallurgy process, essentially fusing successive layers of tungsten powder to build a finished component.
The method is ideal for the manufacture of high-precision components such as collimators and radiation shields in CT, SPECT, MR and X-ray imaging systems. Furthermore, the technique allows components to be produced cost effectively in days and weeks rather than months.
该技术也被称为选择性激光熔化(SLM)或直接金属激光烧结(DMLS)，是一种增材制造技术，首次实现了生产具有复杂几何形状的单个金属部件，而不需要特定于零件的模具。增材制造工艺使用高能激光对金属粉末层进行成形，形成三维组件。
The geometries that can be achieved are not possible using traditional machining, otherwise known as subtractive manufacturing. By removing this design limitation, the possibilities are almost endless. When tungsten’s excellent radiation absorption combined with good thermal resistance is added into the mix, the possibilities become genuinely exciting.
The end material is an alloy, of 90-97 percent tungsten depending on the grade. This material retains the unique density and radiation shielding capabilities of pure tungsten however, for the first time, it can also be machined to tight tolerances.
Creating a Complex 3-D Printed Collimator
Wolfmet团队帮助创建了世界上第一个用于描述系统的准直器。经过最近的试验，该小组报告说取得了巨大的成功。由于其优良的衰减特性，钨准直器与相同的铅准直器相比，可显著降低隔膜穿透，从而大大改善图像质量。
“The final product shows great potential to enable better radiotherapy treatment monitoring,” said Samantha Colosimo, Ph.D., project manager,Optimization of Medical Accelerators (OMA) Project,利物浦大学。
The team working on the project is hopeful that the DEPICT imaging system will be available commercially in the next three years.
The implications could be significant; the ability to individualize treatments is expected to reduce healthcare costs by providing speedier and more efficient treatments. Importantly, it is hoped that this development will increase rates of successful cancer treatment, leading to improved quality of life and health for those patients.
Applications Outside of Healthcare
The same principals of 3-D printing tungsten could mean huge advances in other sectors outside of healthcare.
用于检查运输集装箱内物品的机场和货物扫描仪也可以使用钨准直器以同样的方式升级。扫描仪通常有钨栅格，可以筛除杂散的x射线，从而得到更精确的图像。目前，这些网格是由许多单独的钨片手工构建的，但很快就会被单一的SLM部件所取代。
The application of the metallurgy process allows these complex parts to be manufactured as a single component. This results in a much shorter delivery time and eliminates a lot of costly hand assembly work.
可以融入钨的几何细节，现在可能意味着可以创造出越来越复杂的组件。在未来，这意味着有可能提供手持的、轻量级的医疗扫描仪，可以用于锁定单个器官，同时产生同样精确的图像。
钨的特性众所周知，但只有现在才能通过这种新的制造方法更充分地利用它们。
Steve Jeffery is the business development manager forWolfmet's 3-D printed tungsten components division.
August 10, 2022
