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Sourcing Machined Tungsten Collimators for Medical Imaging

Updated September 26, 2026 · Reviewed September 26, 2026

A collimator is one of the more precision-demanding parts machined in tungsten heavy alloy, since its function depends on an aperture that is both correctly sized and correctly aligned. This guide covers what matters when sourcing one, from grade and tolerance to the questions a shop will ask before it quotes.

What a collimator does

A collimator shapes a radiation beam, in imaging or therapy equipment, by absorbing radiation everywhere except through a defined aperture or set of apertures. The tungsten body provides the shielding mass, and the aperture geometry, size, shape and alignment, determines the beam that reaches the target or detector. Because the aperture is doing the functional work, its tolerance matters more than almost any other dimension on the part.

Collimator types and what they mean for machining

“Collimator” covers a range of geometries, and the type used in your equipment affects how the part gets quoted and machined.

• Pinhole collimators use a single small aperture, often with a tapered or conical bore, used where a magnified or minified projection is needed. The taper angle and the entrance and exit diameters are usually the critical dimensions.
• Parallel-hole collimators, common in gamma cameras and some nuclear medicine equipment, use a dense array of many small parallel holes separated by thin septa. Hole diameter, septal thickness and hole-to-hole consistency across the array are the features that matter most, and this geometry is usually the most machining-intensive of the group.
• Fan-beam and cone-beam collimators, used in CT and some radiography systems, use a slot or a small number of larger apertures shaped to spread the beam in a defined pattern rather than a single narrow path.
• Multi-leaf collimators, used in radiotherapy, are built from a stack of individually machined leaves that move to shape the treatment field. Each leaf is a separate part, and the edges that form the aperture when the leaves are assembled carry the tightest tolerance on the whole set.

Tell your shop which of these you are sourcing early. A parallel-hole array and a single pinhole bore are both “collimators,” but they are very different machining jobs, and the quote depends on which one you mean.

Grade selection

Tungsten heavy alloy, typically W-Ni-Fe per ASTM B777, is the standard material for collimators, chosen for the same reasons it is standard for shielding generally: high density in a machinable, structurally sound form. Where the collimator sits near equipment sensitive to magnetic fields, W-Ni-Cu is the non-magnetic alternative at a similar density. Pure tungsten is used less often for collimators, since heavy alloy’s easier machining is usually preferable when the part does not also need pure tungsten’s heat resistance.

Aperture tolerance and alignment

The aperture is typically the tightest-toleranced feature on a collimator, since its size directly affects how much radiation passes through and its alignment affects where the beam lands. Depending on the imaging system, apertures may need tolerances at the tighter end of what heavy alloy can achieve by milling, sometimes finished by grinding or EDM for the smallest or most precise apertures. Confirm the actual tolerance requirement against your equipment’s design specification rather than assuming a standard number, since collimator tolerance requirements vary significantly by application and imaging modality.

Alignment between multiple apertures, or between an aperture and an external mounting feature, is often as important as the aperture size itself. State any alignment requirement clearly on the drawing, including the datum structure the shop should machine to.

Typical dimensional ranges by application

These figures are typical starting points to plan around, not specifications for any particular piece of equipment. Confirm every number against your own design before it goes on a drawing.

Feature	Diagnostic imaging (parallel-hole or pinhole)	Radiotherapy (multi-leaf or block)
Aperture or hole diameter	Often well under 5 mm, sometimes sub-millimeter	Typically larger, from several millimeters to tens of millimeters
Wall or septal thickness	Thin septa between holes, driven by shielding math for the isotope used	Thicker walls, driven by the higher beam energy involved
Aperture-to-aperture consistency	Very high, especially across a dense hole array	Fewer apertures, so consistency is checked leaf-to-leaf instead
Typical machining route	Milling and drilling, EDM for the finest holes	Milling, with grinding on mating leaf edges

Other design considerations

• Wall thickness around the aperture needs to provide enough shielding mass without unnecessary bulk, which is a design tradeoff specific to your imaging system’s requirements.
• Mounting features for integrating the collimator into the equipment, dimensioned to the same tolerance standards as any precision mechanical interface.
• Multiple-aperture geometries, common in multi-leaf or adjustable collimator designs, which add machining complexity and usually justify tighter process control from the shop.
• Aperture surface finish, since a rough bore wall can scatter radiation at the edges of the beam. If this matters for your application, specify a finish requirement rather than leaving it to the shop’s default.

Blanks and quantity

Collimators for prototype or low-volume equipment are typically machined from standard heavy alloy bar or plate stock. For production quantities, a near-net sintered blank can reduce machining time on the bulk of the shielding mass, leaving the precision aperture work as the main machining operation. Ask your shop whether this makes sense for your expected volume.

Certification and documentation

Medical imaging equipment often has documentation requirements tied to its regulatory pathway, which varies by market and application. We do not determine or claim regulatory status on your behalf. State clearly what material certification, dimensional inspection or other documentation your project requires, and we match you only with shops able to provide it.

Common mistakes buyers make on a collimator RFQ

A shop quoting a collimator usually has to ask about a few things when they are missing from the RFQ. Answering them upfront speeds up the quote:

1. Not stating the collimator type. “Collimator” alone does not tell a shop whether they are quoting one pinhole bore or an array of two hundred parallel holes. Say which.
2. Leaving aperture tolerance as “standard” or blank. There is no universal standard aperture tolerance. State the actual number from your design, even if it is provisional.
3. Omitting alignment requirements between apertures or mounting features. If two apertures must line up within a stated value, put that value and its datum on the drawing, not just a note that says “align.”
4. Assuming the shop knows your regulatory pathway. Shops do not infer FDA, CE or other regulatory documentation needs from the part type. State the actual documents required.
5. Not flagging magnetic sensitivity. If the collimator sits near an MRI or another field-sensitive system, say so explicitly and specify W-Ni-Cu, since a shop defaults to standard W-Ni-Fe otherwise.

What to include in the RFQ

1. Grade and binder, W-Ni-Fe unless there is a magnetic constraint.
2. Collimator type, pinhole, parallel-hole array, fan-beam or multi-leaf, so the shop understands the actual geometry.
3. Aperture dimensions and tolerance, confirmed against your equipment’s design specification.
4. Alignment and datum requirements, if the part has multiple apertures or critical mounting features.
5. Surface finish inside the aperture, if beam edge scatter matters for your application.
6. Documentation requirements, stated explicitly for your regulatory pathway.
7. Quantity and expected repeat volume.

When your drawing is ready, send your RFQ and we match it with shops experienced in precision shielding work. For the broader shielding category, see tungsten radiation shielding parts. For tolerance expectations across tungsten grades generally, see what tolerance and finish you can hold on a tungsten part.

See also: tungsten collimators for imaging and NDT, for collimator types, aperture routes and tolerances.

Frequently asked questions

Sources

• Wikipedia - Collimator
• Wikipedia - Radiation protection
• Wikipedia - Nuclear medicine

Keep reading

• MIL-T-21014 vs ASTM B777: How to Convert an Old Tungsten Heavy Alloy Callout
• How to Source Machined Tungsten Shielding and Counterweights