---
license: cc-by-4.0
tags:
  - diffusion-mri
  - monte-carlo
  - replay-pack
  - microstructure
pretty_name: dmrai-lab substrate bank
---

# dmrai-lab substrate bank

Compressed Monte-Carlo **replay packs** (`.rpk`) for diffusion-MRI microstructure. Each pack is one master walk on a substrate plus the physics channels needed to **replay** any acquisition inside its certified envelope — *one walk, every acquisition* — in the open [Replay Pack Specification](https://github.com/dmrai-lab/replay-pack-spec) format.

```python
from dmipy_sim import bank
pack = bank.pull("<id>", repo_id="dmrai-lab/substrate-bank")
S = pack.replay(waveform, relaxation=True)
```

## Substrates

`Field σ` = off-resonance field inhomogeneity (Hz @3 T, B0 ⊥ fibre); `Fibre axis` = the substrate's intrinsic orientation in stored coordinates (B0/gradient directions are defined relative to it — see each card). Both are intrinsic, so you can pick a substrate *without downloading* it.

| Substrate | Replay tiers | Field σ (Hz@3T) | ICVF | Fibre axis | Size | License |
|---|---|---|---|---|---|---|
| [`cactus-axons/single-bundle-g070-icvf061`](cactus-axons/single-bundle-g070-icvf061.md) | C0 C1 C2 C3 C4 | 0.97 | 0.61 | [+1.00, +0.01, -0.00] | 46.65 MB | CC-BY-4.0 |
| [`canonical-wm/g070-f055-3T`](canonical-wm/g070-f055-3T.md) | C0 | — | — | — | 18.23 MB | CC-BY-4.0 |

Each substrate links to its own **substrate card** with geometry, provenance, fidelity and load/replay instructions. Tier legend: C0 gradient · C1 bulk relaxation · C2 surface relaxivity · C3 field · C4 magnetization transfer.