More often than you'd think, I get a request to create a 3D-printed medical model, and then discover the CT simply isn't good enough. The quality of a 3D model starts long before printing. It starts at the imaging stage.

This is the first part of a short series on the planning stages of a 3D medical model. Stage one: the scan. Below are four practical rules that can save you real frustration, cost, and time.

1. Slice thickness

This is probably the single most critical variable. For most models, and especially when there are small structures or internal cavities, you want a slice thickness of roughly 0.7 to 1 mm. Thicker slices (3 to 5 mm) cause a significant loss of detail.

On MRI, thickness is usually higher, so it's worth confirming in advance that the structure is even clearly visible. And a small extra tip: in most cases there's no need to go below 0.7 mm, both because of the computational load and because 1 mm already yields anatomy detailed enough to work with.

2. A protocol matched to the anatomy

Match the type of scan to the anatomy and to the goal. A hip-joint protocol is not the same as a cardiac scan. The right protocol for the target region makes the difference between usable data and a scan that looks fine but can't carry a model.

3. Artifact prevention

Motion, implants, or technical errors will distort the model, even when the slice resolution is excellent. It's worth knowing that dedicated protocols often exist to reduce noise and metal artifacts, for example MAR (Metal Artifact Reduction) on CT, which can substantially improve scan quality for patients with implants.

4. Check the scan is complete

This may sound trivial, but I've run into scans that partially cut off the region of interest. Want a model of the heart? If the left atrium is clipped at the top edge, the model won't be usable. Check that all the required anatomy actually appears across the slices.

When data is missing, it can sometimes be rebuilt

Even when information is missing from the scan, there's always the option to complete the missing detail manually, by digitally reconstructing it during the file-building stage. Two important caveats:

  • In surgical models you must not alter the anatomy, so the accuracy of the surgical plan is never put at risk.
  • In educational, marketing, or structure-demonstration models, you can absolutely adapt the anatomy to your needs.

Keep in mind that manual editing can raise the cost of the model. But if you're planning to adapt it anyway, a less-than-perfect scan is sometimes enough.

In summary

A 3D model is the result of a chain of processes. If you start with missing data or poor imaging quality, even the most advanced printing technology won't produce a quality model. Get the scan right, and everything downstream gets easier.

Next in the series: segmentation, how you move from a raw scan to a 3D model, and which tools exist for it (including the ones from my day-to-day work).