Comparison of Printed versus Machined Tungsten Pyramidal Collimators

Advances in additive manufacturing techniques are creating new opportunities for collimator design in nuclear medicine. In this work we assess the relative merits of fabricating aperture components via printing with tungsten powder versus machining with tungsten alloys. We report on experiences with a variety of metal printing approaches and describe the ranges of material density we have achieved, as well as the figure and finish of raw and polished parts.We also report on the direct comparison of pyramid-shaped collimators, for a dedicated cardiac SPECT system being developed at Massachusetts General Hospital, that we fabricated via both approaches. Illumination with 99mTc point sources is used to create shadow images on an iQID imaging station from which general leakage and pinhole-edge penetration could be experimentally determined.We find that the flexibility in design, for example the ability to easily create skewed clearance cones in arrays of focused pinholes with printed fabrication, must be balanced against higher material density and uniformity in machined tungsten alloy parts. However, as new printing and machining methods are being introduced, the physical tradeoffs are likely to become less significant.