# Question about Real-time Ultrasound Volume Reconstruction using SteamVR Tracker

**URL:** <https://discourse.slicer.org/t/question-about-real-time-ultrasound-volume-reconstruction-using-steamvr-tracker/41846>\
**Category:** Support\
**Tags:** openigtlink\
**Created:** [February 23, 2025, 10:42am UTC](https://discourse.slicer.org/t/question-about-real-time-ultrasound-volume-reconstruction-using-steamvr-tracker/41846 "2025-02-23T10:42:33Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![MasatoshiOBA](https://avatars.discourse-cdn.com/v4/letter/m/b487fb/32.png) [@MasatoshiOBA](https://discourse.slicer.org/u/MasatoshiOBA)\
**Post date:** [February 23, 2025, 10:42am UTC](https://discourse.slicer.org/t/question-about-real-time-ultrasound-volume-reconstruction-using-steamvr-tracker/41846/1 "2025-02-23T10:42:33Z")

</div>

### **Question:**

#### **Overview:**

I am planning to perform **ultrasound volume reconstruction** using a SteamVR-compatible tracker.  
Currently, I have successfully used `pyigtl` to send tracking data to Slicer, and Slicer receives it as a `Transform node`.

* * *

### **Problems I want to solve:**

#### **(1) Issue with Volume Reslice Driver Settings**

- I set the `Red slice driver` of the `Volume Reslice Driver` to the transform node from the tracker (`Tracker_reference`) and set the mode to `"Transverse"`. However, only a single line appears on the screen.
- On the other hand, if I apply the `Tracker_reference` **directly to the Image** , the image is displayed (see the attached screenshot).
- In various **real-time ultrasound reconstruction tutorials** , I did not find any mention of needing to apply the transform to the `Image` itself.
- **Is this procedure correct?**  
If it is incorrect, could you please advise on the correct way to configure it?

#### **(2) Changing the Reference Point of the Transform**

- As shown in the attached image, when I apply the tracker-derived `Transform node (Tracker_reference)`, the **origin (0,0,0) of the transform node is aligned with Slicer’s global origin**.
- However, I would like the **center of the transform to be the center of the ultrasound probe** (the second tracker center position in the image).
- **Is it possible to shift the reference point of the transform?**  
If so, how can I achieve this?

* * *

### **Things I have tried:**

I attempted to nest the transform nodes in the following structure:

pgsql

コピーする編集する

```auto
Tracker_reference
|
|_ Transform_0 (A transform to move Tracker_reference to the upper center of the Image, which is intended to represent the center of the probe)
   |
   |_ Image (The volume I want to manipulate)

```

However, even with this setup, when I activate the `Volume Reslice Driver`, **Tracker\_reference still behaves as if its reference point is at the lower left center of the screen** , which is not the intended behavior.

* * *

### **Environment Information:**

- **Slicer Version:** 5.8.0
- **Extensions Used:** OpenIGTLink, SlicerIGT, etc.
- **OpenIGTLink / pyigtl Version:** (if applicable, please specify)
- **Tutorials or References Used:** (if applicable, please provide links)
- **Other Settings or Attempts:** As described above

I truly appreciate your time in reading my post and any insights or advice you can provide.  
Your expertise and support mean a lot, and I am grateful for this amazing community that makes learning and problem-solving so much easier.

Thank you in advance!

 ![transform](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/a/c/acf895548fa2a06b42b9a5533f94455a18408421.jpeg)