# NEXUS Chest CT

NEXUS Chest CT

Status: LIVE
Price: $0.005 USDC
`GET /api/calc/nexus_chest_ct`
HTML: https://magentlab.com/docs/nexus-chest-ct
Markdown: https://magentlab.com/docs/nexus-chest-ct.md

Not a medical device. Not a diagnosis, dose, or listing recommendation.

## What it computes

Apply the Rodriguez 2015 NEXUS Chest CT-Major and Chest CT-All decision instruments and return whether each is negative (all of that instrument's caller-assigned criteria absent). Does not order a CT.

## When to use

When an agent has caller-assigned findings after blunt trauma and needs the published NEXUS Chest CT selective-CT instruments, not the NEXUS Chest CXR instrument and not Hoffman 2000 NEXUS C-spine.

## When not to use

- Not a medical device. Not a diagnosis. magent does not examine the patient or read a radiograph.
- This tool is the Rodriguez 2015 Chest CT-Major and Chest CT-All instruments only. It is not the NEXUS Chest CXR seven-item instrument (nexus-chest) and not the Hoffman 2000 NEXUS C-spine rule.
- Derivation and validation enrolled blunt trauma age >14 undergoing chest imaging at eight US level I trauma centers. magent does not take numeric age; the caller assigns all flags, including abnormal_cxr.
- These are one-way rule-out instruments. Presence of a criterion does not mandate CT. Do not order a CT from a positive instrument.

## Formula

```
ct_major_negative iff no abnormal_cxr and no distracting_injury and no chest_wall_tenderness and no sternal_tenderness and no thoracic_spine_tenderness and no scapular_tenderness; ct_all_negative iff Major-negative and no rapid_deceleration_mechanism
```

## Citation

[Derivation and Validation of Two Decision Instruments for Selective Chest CT in Blunt Trauma: A Multicenter Prospective Observational Study (NEXUS Chest CT)](https://doi.org/10.1371/journal.pmed.1001883)
Rodriguez RM, Langdorf MI, Nishijima D, Baumann BM, Hendey GW, Medak AJ, Raja AS, Adelman EE, Mower WR
PLoS Med. 2015;12(10):e1001883
DOI: [10.1371/journal.pmed.1001883](https://doi.org/10.1371/journal.pmed.1001883)

## Worked example

### All seven criteria absent

Given: `abnormal_cxr=false, chest_wall_tenderness=false, distracting_injury=false, rapid_deceleration_mechanism=false, scapular_tenderness=false, sternal_tenderness=false, thoracic_spine_tenderness=false`

1. No abnormal CXR, no distracting injury, no chest-wall tenderness, no sternal tenderness, no thoracic-spine tenderness, no scapular tenderness, no rapid deceleration mechanism
2. Chest CT-Major negative and Chest CT-All negative; this tool does not order a CT


### Rapid deceleration alone leaves Major negative

Given: `abnormal_cxr=false, chest_wall_tenderness=false, distracting_injury=false, rapid_deceleration_mechanism=true, scapular_tenderness=false, sternal_tenderness=false, thoracic_spine_tenderness=false`

1. All six Chest CT-Major findings are absent; rapid deceleration mechanism is present
2. Chest CT-Major is negative; Chest CT-All is not negative. Presence of this criterion does not mandate CT


## Also searched as

- NEXUS Chest CT
- NEXUS Chest CT-Major
- NEXUS Chest CT-All
- Rodriguez Chest CT
- selective chest CT blunt trauma
- Chest CT-Major
- Chest CT-All
- NEXUS Chest CT decision instrument

## Parameters

- `abnormal_cxr` (boolean, required): Abnormal chest radiograph as assigned by the caller (paper: any thoracic injury including clavicle fracture, or a widened mediastinum). true means the finding is present and Chest CT-Major is not negative. true or false. magent does not read a radiograph.
- `distracting_injury` (boolean, required): Painful, distracting injury as assigned by the caller. true means a distracting injury is present and Chest CT-Major is not negative. true or false. magent does not examine the patient.
- `chest_wall_tenderness` (boolean, required): Chest-wall tenderness to palpation as assigned by the caller. true means tenderness is present and Chest CT-Major is not negative. true or false. magent does not palpate the chest.
- `sternal_tenderness` (boolean, required): Sternal tenderness to palpation as assigned by the caller. true means tenderness is present and Chest CT-Major is not negative. true or false. magent does not palpate the sternum.
- `thoracic_spine_tenderness` (boolean, required): Thoracic-spine tenderness to palpation as assigned by the caller. true means tenderness is present and Chest CT-Major is not negative. true or false. magent does not palpate the thoracic spine.
- `scapular_tenderness` (boolean, required): Scapular tenderness to palpation as assigned by the caller. true means tenderness is present and Chest CT-Major is not negative. true or false. magent does not palpate the scapula.
- `rapid_deceleration_mechanism` (boolean, required): Rapid deceleration mechanism as assigned by the caller (paper: fall from >20 feet or motor vehicle crash >40 mph with sudden deceleration). true means the finding is present and Chest CT-All is not negative. true or false. magent does not classify mechanism.

## Bulk (POST)

POST the same path with a JSON items array. The first item is the GET unit; each additional item is $0.002. Invalid items return HTTP 400 before settlement.

Method: `POST /api/calc/nexus_chest_ct`
Max items: 25
Price: unit_amount + extra_item_amount * (n - 1) (unit 5000 atomic, extra 2000 atomic)
Status: PREVIEW

- 1 to 25 items. Each item uses the same keys as the GET query parameters.
- POST of 1 item costs the same as GET. Lists longer than 25: chunk into multiple POSTs. Extra items still execute; do not pad dummy rows.
- The first invalid item fails the whole request (index in the 400 JSON). You are not charged.
- HTTP 200 is {count, path, items}. Each items[i] is the GET 200 body for that row.
- Catalog misses (empty matches, found=false) stay paid 200s inside that slot.
- x402 resource URL is this path plus n and body_sha256. Browsers that prefer text/html get the same paywall as GET; Pay retries POST with the same items.

Example request:

```json
{
  "items": [
    {
      "abnormal_cxr": "false",
      "chest_wall_tenderness": "false",
      "distracting_injury": "false",
      "rapid_deceleration_mechanism": "false",
      "scapular_tenderness": "false",
      "sternal_tenderness": "false",
      "thoracic_spine_tenderness": "false"
    },
    {
      "abnormal_cxr": "false",
      "chest_wall_tenderness": "false",
      "distracting_injury": "false",
      "rapid_deceleration_mechanism": "false",
      "scapular_tenderness": "false",
      "sternal_tenderness": "false",
      "thoracic_spine_tenderness": "false"
    }
  ]
}
```

Human paywall (two-item fixture): https://api.magentlab.com/paywall/bulk/nexus-chest-ct

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/nexus_chest_ct",
  "items": [
    {
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Rodriguez RM, Langdorf MI, Nishijima D, Baumann BM, Hendey GW, Medak AJ, Raja AS, Adelman EE, Mower WR",
        "doi": "10.1371/journal.pmed.1001883",
        "id": "rodriguez-2015",
        "pmid": "26440607",
        "source": "PLoS Med. 2015;12(10):e1001883",
        "title": "Derivation and Validation of Two Decision Instruments for Selective Chest CT in Blunt Trauma: A Multicenter Prospective Observational Study (NEXUS Chest CT)"
      },
      "formula": "nexus_chest_ct",
      "formula_expression": "ct_major_negative iff no abnormal_cxr and no distracting_injury and no chest_wall_tenderness and no sternal_tenderness and no thoracic_spine_tenderness and no scapular_tenderness; ct_all_negative iff Major-negative and no rapid_deceleration_mechanism",
      "criteria": [
        {
          "factor": "no_abnormal_cxr",
          "met": true
        },
        {
          "factor": "no_distracting_injury",
          "met": true
        },
        {
          "factor": "no_chest_wall_tenderness",
          "met": true
        },
        {
          "factor": "no_sternal_tenderness",
          "met": true
        },
        {
          "factor": "no_thoracic_spine_tenderness",
          "met": true
        },
        {
          "factor": "no_scapular_tenderness",
          "met": true
        },
        {
          "factor": "no_rapid_deceleration_mechanism",
          "met": true
        }
      ],
      "ct_all_negative": true,
      "ct_major_negative": true
    },
    {
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Rodriguez RM, Langdorf MI, Nishijima D, Baumann BM, Hendey GW, Medak AJ, Raja AS, Adelman EE, Mower WR",
        "doi": "10.1371/journal.pmed.1001883",
        "id": "rodriguez-2015",
        "pmid": "26440607",
        "source": "PLoS Med. 2015;12(10):e1001883",
        "title": "Derivation and Validation of Two Decision Instruments for Selective Chest CT in Blunt Trauma: A Multicenter Prospective Observational Study (NEXUS Chest CT)"
      },
      "formula": "nexus_chest_ct",
      "formula_expression": "ct_major_negative iff no abnormal_cxr and no distracting_injury and no chest_wall_tenderness and no sternal_tenderness and no thoracic_spine_tenderness and no scapular_tenderness; ct_all_negative iff Major-negative and no rapid_deceleration_mechanism",
      "criteria": [
        {
          "factor": "no_abnormal_cxr",
          "met": true
        },
        {
          "factor": "no_distracting_injury",
          "met": true
        },
        {
          "factor": "no_chest_wall_tenderness",
          "met": true
        },
        {
          "factor": "no_sternal_tenderness",
          "met": true
        },
        {
          "factor": "no_thoracic_spine_tenderness",
          "met": true
        },
        {
          "factor": "no_scapular_tenderness",
          "met": true
        },
        {
          "factor": "no_rapid_deceleration_mechanism",
          "met": true
        }
      ],
      "ct_all_negative": true,
      "ct_major_negative": true
    }
  ]
}
```

## Response fields

- `formula` (string): nexus_chest_ct
- `formula_expression` (string): Rodriguez 2015 Chest CT-Major six criteria and Chest CT-All seven criteria
- `ct_major_negative` (boolean): true only when all six Chest CT-Major findings are absent. Does not order a CT. Presence of a criterion does not mandate CT. Not a diagnosis.
- `ct_all_negative` (boolean): true only when the six Major findings and rapid_deceleration_mechanism are absent. Does not order a CT. Presence of a criterion does not mandate CT. Not a diagnosis.
- `criteria` (array): Per-factor rows with factor and met; met is true when that finding is absent (the low-risk item holds)
- `citation` (object): Rodriguez 2015 PLoS Med citation
- `disclaimer` (string): Not-a-device notice

## Example JSON

Frozen fixture. Not a live lookup.

```json
{
  "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
  "citation": {
    "authors": "Rodriguez RM, Langdorf MI, Nishijima D, Baumann BM, Hendey GW, Medak AJ, Raja AS, Adelman EE, Mower WR",
    "doi": "10.1371/journal.pmed.1001883",
    "id": "rodriguez-2015",
    "pmid": "26440607",
    "source": "PLoS Med. 2015;12(10):e1001883",
    "title": "Derivation and Validation of Two Decision Instruments for Selective Chest CT in Blunt Trauma: A Multicenter Prospective Observational Study (NEXUS Chest CT)"
  },
  "formula": "nexus_chest_ct",
  "formula_expression": "ct_major_negative iff no abnormal_cxr and no distracting_injury and no chest_wall_tenderness and no sternal_tenderness and no thoracic_spine_tenderness and no scapular_tenderness; ct_all_negative iff Major-negative and no rapid_deceleration_mechanism",
  "criteria": [
    {
      "factor": "no_abnormal_cxr",
      "met": true
    },
    {
      "factor": "no_distracting_injury",
      "met": true
    },
    {
      "factor": "no_chest_wall_tenderness",
      "met": true
    },
    {
      "factor": "no_sternal_tenderness",
      "met": true
    },
    {
      "factor": "no_thoracic_spine_tenderness",
      "met": true
    },
    {
      "factor": "no_scapular_tenderness",
      "met": true
    },
    {
      "factor": "no_rapid_deceleration_mechanism",
      "met": true
    }
  ],
  "ct_all_negative": true,
  "ct_major_negative": true
}
```

## Errors

- HTTP 400 `invalid_flag`: boolean clinical flags must be true or false Returned before settlement; you are not charged.
- HTTP 400 `invalid_items`: POST body must be a JSON object with only an items array Returned before settlement; you are not charged.
- HTTP 400 `invalid_item_count`: items must be an array of 1 to 25 objects Returned before settlement; you are not charged.
- HTTP 400 `invalid_item`: each items entry must be a JSON object Returned before settlement; you are not charged.

Shared HTTP 402 and 503: https://magentlab.com/docs/payments

## Related tools

- [NEXUS Chest](https://magentlab.com/docs/nexus-chest) — Apply the Rodriguez 2011 NEXUS Chest decision instrument and return whether the seven low-risk criteria all hold (chest radiography not indicated by this instrument).
- [NEXUS C-spine](https://magentlab.com/docs/nexus) — Apply the Hoffman 2000 NEXUS C-spine rule and return whether the five low-risk criteria all hold (imaging not indicated by this rule).

## Payment

Unpaid requests return HTTP 402 even if query parameters or POST items are missing or invalid, so CDP and agents can index the path. After a PAYMENT-SIGNATURE, invalid params return HTTP 400 JSON before settlement. magent does not charge. Fix the params, then request a new 402 quote for that complete URL. Catalog misses (empty matches, found=false) are valid paid 200s.

- GET the tool with Accept: application/json (do not send Accept: text/html unless you want the human paywall).
- HTTP 402 means you have not paid. Decode the base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote.
- Sign accepts[0] (exact, EIP-3009) with validBefore = now + maxTimeoutSeconds (600 seconds), or accepts[1] (batch-settlement deposit/voucher) on product GET. Ping and POST {items} stay exact. Magent retries transient facilitator 429/5xx before answering.
- Retry the same URL with PAYMENT-SIGNATURE (base64 JSON of accepted and payload). Magent attaches canonical extensions.bazaar on CDP verify/settle; echoing 402 bazaar is optional.
- Success is HTTP 200 JSON plus PAYMENT-RESPONSE. exact settles before the tool. batch-settlement verifies (and deposit-settles) before the tool and commits the charge after HTTP 2xx. HTTP 503: retry the same PAYMENT-SIGNATURE. Mint a new exact nonce only after a new HTTP 402.

- offered `exact` on eip155:8453: Fixed-price USDC on Base. The buyer authorizes the advertised amount (EIP-3009). magent settles before the tool runs (paymentFlow upfront). extra.assetTransferMethod=eip3009 extra.paymentFlow=upfront.
- offered `batch-settlement` on eip155:8453: Payment-channel vouchers claimed later in batches. Exact stays accepts[0]. Same-path POST {items} is still exact. extra.assetTransferMethod=eip3009 extra.paymentFlow=authorization.

- not offered `upto`: Not offered. Usage-based: buyer authorizes a ceiling, seller settles the actual amount after work. Reserved for a future metered tool. Not for current calculators or code search.

Same-path POST {items} is still scheme exact: one EIP-3009 authorization for GET unit plus $0.002 per extra item. That is not x402 batch-settlement (payment channels / vouchers).

Shared HTTP 402 and 503 table: https://magentlab.com/docs/payments

Stdio MCP (one process per host): https://magentlab.com/docs/mcp

## Guarantees

- HTTP 402 is unpaid, including a missing query. After PAYMENT-SIGNATURE, invalid parameters return HTTP 400 before settlement. You are not charged. HTTP 402 never includes the tool JSON.
- exact: settlement finishes before the tool (paymentFlow upfront). batch-settlement: verify/deposit before the tool; chargedCumulativeAmount commits after HTTP 2xx. Uncertain or failed settlement fails closed (HTTP 503). Retry the same PAYMENT-SIGNATURE.
- HTTP 402 is unpaid only. Do not sign a second authorization because of a 503.
- Execution is timeout-bounded and concurrency-capped.
- Calculator inputs are stored encrypted for allowlisted operators (Magent Console). They are not in public logs, SSH lookups, catalog, or rollups. Request logs store path without query.