# 📐 L2 Spec — PET-MR Fusion (molecular + multi-contrast soft tissue) Mismatch-Only Spec
**ID:** `L2-157-001` · **Status:** ⊙ Testnet (genesis catalog)
**Parents:** ⬆ Principle [`L1-157`](/artifact/l1/L1-157)
> **🎯 Tolerance (ε):** expression
> **⚖ Difficulty score:** 0.55 · **Delta tier:** 5
> **⛓ On-chain block:** 41554245
---
## 1. Domain Ω
**Type:** `range`
| Parameter | Unit | Range |
|---|---|---|
| H | px | 128 |
| W | px | 128 |
| Z | — | 32 – 512 |
| Snr db | dB | 0.0 – 35.0 |
| Truncation | — | 0.0 – 0.3 |
| Motion between scans | — | 0.0 – 10.0 |
| Susceptibility distortion | — | 0.0 – 0.3 |
| Mr based attenuation error | — | 0.0 – 0.3 |
## 2. Tolerance (ε)
**Type:** `fn`
```
16.0 + 0.3 * SNR_dB - 10.0 * mr_based_attenuation_error - 0.5 * motion_between_scans - 6.0 * susceptibility_distortion
```
## 3. Difficulty
| Property | Value |
|---|---|
| Difficulty score | 0.55 |
| Delta tier | 5 |
## 4. Fingerprint
`476061e3f141d5052102cfc0eeaa622c9a804b0750b09c6b5f0987d0993142b6`
## 5. On-chain Registration
- **Chain hash:** `0xbd36d634c026e42536b2e2f50adc745e780d55f69c03d7775b4486519487e477`
- **Chain tx hash:** `0x5459614e9fbce28ea918955a3cf1666e525a6609a87a7f1ac45b57560cd56b7f`
- **Chain block:** `41554245`
---
## File Mapping
This bundle consists of: `L2-157-001.md`, `L2-157-001.json`.
| File | Role | How to regenerate |
|------|------|-------------------|
| `L2-157-001.md` | Source of truth — edit this | Human or LLM |
| `L2-157-001.json` | Structured metadata for the registry | LLM regenerates from the sections above |
**Prompt for your LLM after editing this Markdown:**
> Read the attached Markdown. Regenerate the sibling `.json` so every field matches.
> Preserve the schema documented in the rows above.
> Output each file in its own fenced code block tagged with the filename.
> Output only the JSON object.
_This Markdown was auto-synthesized from the catalog row for `L2-157-001`._
_Edit it, regenerate the JSON, and submit at [/submit](/submit) to claim the artifact._