Explain 3D and 4D medical imaging technologies with applications.

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Accepted Answer

## 3D and 4D Medical Imaging

### 3D imaging
A volume of data (stack of 2D slices from CT, MRI, ultrasound or PET) is processed by a computer to display the anatomy in three dimensions.

```mermaid
flowchart LR
  A[Acquire slices CT MRI] --> B[Segmentation]
  B --> C[Volume or surface rendering]
  C --> D[3D model]
  D --> E[Planning and printing]
```

**Rendering methods:** MPR (multi-planar reformat), MIP (maximum intensity projection), surface rendering, volume rendering.

### 4D imaging
4D = 3D + **time**. The volume is captured continuously, so motion such as breathing, heartbeat or foetal movement is seen.

| Point | 3D imaging | 4D imaging |
|---|---|---|
| Dimensions | x, y, z | x, y, z + time |
| Output | Static volume | Moving volume (cine) |
| Examples | CT angiography, 3D reconstruction of skull | 4D CT for lungs, 4D ultrasound of foetus, cardiac MRI |
| Data size | Large | Very large |

### Applications
- Surgical planning and 3D-printed anatomical models.
- Radiotherapy: 4D CT accounts for tumour motion with respiration.
- Cardiology: heart wall motion, valves, 4D flow MRI.
- Obstetrics: 3D/4D foetal face and movement.
- Orthopaedics, dental implant planning, vascular imaging.

### Exam tip
Define 4D as 3D plus time and give three applications for each.

3D and 4D Medical Imaging

3D imaging

4D imaging

Applications

Exam tip

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