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NEXUS Head CT

Apply the Mower 2017 NEXUS Head CT eight-criterion decision instrument and return whether the patient is low-risk (all eight caller-assigned criteria absent). CT may be omitted by this instrument when low-risk. Does not order a CT.

LIVE $0.005 USDC GET /api/calc/nexus_head_ct

Markdown: /docs/nexus-head-ct.md · Canonical: https://magentlab.com/docs/nexus-head-ct

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

What it computes

Apply the Mower 2017 NEXUS Head CT eight-criterion decision instrument and return whether the patient is low-risk (all eight caller-assigned criteria absent). CT may be omitted by this instrument when low-risk. Does not order a CT.

When to use

When an agent has caller-assigned findings after blunt head injury and needs the published NEXUS Head CT decision instrument, not Hoffman 2000 NEXUS C-spine and not the Canadian CT Head Rule.

When not to use

• Not a medical device. Not a diagnosis. magent does not examine the patient.
• Not a CT order. Low-risk means CT may be omitted by this instrument. Presence of a criterion does not mandate CT. Do not order a CT from this tool.
• This tool is the Mower 2017 eight-criterion NEXUS Head CT decision instrument (derivation Mower 2005 J Trauma). It is not the Hoffman 2000 NEXUS C-spine rule, not NEXUS Chest CT, and not the Canadian CT Head Rule.
• Age 65 or older is a high-risk criterion as published; age 64 is not high-risk on age alone. magent takes adult age 18-120. The caller assigns the seven clinical flags.

Formula

low_risk iff age < 65 and no skull_fracture and no scalp_hematoma and no neurologic_deficit and no altered_alertness and no abnormal_behavior and no coagulopathy and no persistent_vomiting

Citation

Title

Validation of the sensitivity of the National Emergency X-Radiography Utilization Study (NEXUS) Head computed tomographic (CT) decision instrument for selective imaging of blunt head injury patients: An observational study

Authors

Mower WR, Gupta M, Rodriguez R, Hendey GW

Source

PLoS Med. 2017;14(7):e1002313

DOI

10.1371/journal.pmed.1002313

Worked example

Also searched as

• NEXUS Head CT
• NEXUS Head CT decision instrument
• Mower NEXUS Head CT
• NEXUS II Head CT
• National Emergency X-Radiography Utilization Study Head CT
• blunt head injury CT rule
• Mower 2017 Head CT
• NEXUS eight-criterion Head CT

Try

Opens the live endpoint. Unpaid browser requests show the paywall; agents should send Accept: application/json.

/api/calc/nexus_head_ct?age=40&skull_fracture=false&scalp_hematoma=false&neurologic_deficit=false&altered_alertness=false&abnormal_behavior=false&coagulopathy=false&persistent_vomiting=false

Full URL: https://api.magentlab.com/api/calc/nexus_head_ct?age=40&skull_fracture=false&scalp_hematoma=false&neurologic_deficit=false&altered_alertness=false&abnormal_behavior=false&coagulopathy=false&persistent_vomiting=false

Call

Expect HTTP 402 until you retry with PAYMENT-SIGNATURE. Incomplete query params return HTTP 400 before any quote or charge.

curl -i -H "Accept: application/json" "https://api.magentlab.com/api/calc/nexus_head_ct?age=40&skull_fracture=false&scalp_hematoma=false&neurologic_deficit=false&altered_alertness=false&abnormal_behavior=false&coagulopathy=false&persistent_vomiting=false"

Parameters

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.

POST /api/calc/nexus_head_ct Max 25 unit_amount + extra_item_amount * (n - 1) extra $0.002 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 (fixture)

{
  "items": [
    {
      "abnormal_behavior": "false",
      "age": "40",
      "altered_alertness": "false",
      "coagulopathy": "false",
      "neurologic_deficit": "false",
      "persistent_vomiting": "false",
      "scalp_hematoma": "false",
      "skull_fracture": "false"
    },
    {
      "abnormal_behavior": "false",
      "age": "40",
      "altered_alertness": "false",
      "coagulopathy": "false",
      "neurologic_deficit": "false",
      "persistent_vomiting": "false",
      "scalp_hematoma": "false",
      "skull_fracture": "false"
    }
  ]
}

Open bulk paywall →

Opens a two-item fixture on the API host. Unpaid browsers get the same MetaMask paywall as GET; Pay retries POST with those items.

Example 200 (fixture)

{
  "count": 2,
  "path": "/api/calc/nexus_head_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": "Mower WR, Gupta M, Rodriguez R, Hendey GW",
        "doi": "10.1371/journal.pmed.1002313",
        "id": "mower-2017",
        "pmid": "28700585",
        "source": "PLoS Med. 2017;14(7):e1002313",
        "title": "Validation of the sensitivity of the National Emergency X-Radiography Utilization Study (NEXUS) Head computed tomographic (CT) decision instrument for selective imaging of blunt head injury patients: An observational study"
      },
      "formula": "nexus_head_ct",
      "formula_expression": "low_risk iff age < 65 and no skull_fracture and no scalp_hematoma and no neurologic_deficit and no altered_alertness and no abnormal_behavior and no coagulopathy and no persistent_vomiting",
      "criteria": [
        {
          "value": 40,
          "factor": "age_lt_65",
          "met": true
        },
        {
          "factor": "no_skull_fracture",
          "met": true
        },
        {
          "factor": "no_scalp_hematoma",
          "met": true
        },
        {
          "factor": "no_neurologic_deficit",
          "met": true
        },
        {
          "factor": "no_altered_alertness",
          "met": true
        },
        {
          "factor": "no_abnormal_behavior",
          "met": true
        },
        {
          "factor": "no_coagulopathy",
          "met": true
        },
        {
          "factor": "no_persistent_vomiting",
          "met": true
        }
      ],
      "low_risk": 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": "Mower WR, Gupta M, Rodriguez R, Hendey GW",
        "doi": "10.1371/journal.pmed.1002313",
        "id": "mower-2017",
        "pmid": "28700585",
        "source": "PLoS Med. 2017;14(7):e1002313",
        "title": "Validation of the sensitivity of the National Emergency X-Radiography Utilization Study (NEXUS) Head computed tomographic (CT) decision instrument for selective imaging of blunt head injury patients: An observational study"
      },
      "formula": "nexus_head_ct",
      "formula_expression": "low_risk iff age < 65 and no skull_fracture and no scalp_hematoma and no neurologic_deficit and no altered_alertness and no abnormal_behavior and no coagulopathy and no persistent_vomiting",
      "criteria": [
        {
          "value": 40,
          "factor": "age_lt_65",
          "met": true
        },
        {
          "factor": "no_skull_fracture",
          "met": true
        },
        {
          "factor": "no_scalp_hematoma",
          "met": true
        },
        {
          "factor": "no_neurologic_deficit",
          "met": true
        },
        {
          "factor": "no_altered_alertness",
          "met": true
        },
        {
          "factor": "no_abnormal_behavior",
          "met": true
        },
        {
          "factor": "no_coagulopathy",
          "met": true
        },
        {
          "factor": "no_persistent_vomiting",
          "met": true
        }
      ],
      "low_risk": true
    }
  ]
}

Response

Example JSON

Machine form of the same example. Frozen fixture. Not a live lookup.

{
  "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": "Mower WR, Gupta M, Rodriguez R, Hendey GW",
    "doi": "10.1371/journal.pmed.1002313",
    "id": "mower-2017",
    "pmid": "28700585",
    "source": "PLoS Med. 2017;14(7):e1002313",
    "title": "Validation of the sensitivity of the National Emergency X-Radiography Utilization Study (NEXUS) Head computed tomographic (CT) decision instrument for selective imaging of blunt head injury patients: An observational study"
  },
  "formula": "nexus_head_ct",
  "formula_expression": "low_risk iff age < 65 and no skull_fracture and no scalp_hematoma and no neurologic_deficit and no altered_alertness and no abnormal_behavior and no coagulopathy and no persistent_vomiting",
  "criteria": [
    {
      "value": 40,
      "factor": "age_lt_65",
      "met": true
    },
    {
      "factor": "no_skull_fracture",
      "met": true
    },
    {
      "factor": "no_scalp_hematoma",
      "met": true
    },
    {
      "factor": "no_neurologic_deficit",
      "met": true
    },
    {
      "factor": "no_altered_alertness",
      "met": true
    },
    {
      "factor": "no_abnormal_behavior",
      "met": true
    },
    {
      "factor": "no_coagulopathy",
      "met": true
    },
    {
      "factor": "no_persistent_vomiting",
      "met": true
    }
  ],
  "low_risk": true
}

Client errors (HTTP 400)

Invalid params return 400 without charge. Shared HTTP 402 and 503 meanings: Payments.

Related tools

• NEXUS C-spine — Apply the Hoffman 2000 NEXUS C-spine rule and return whether the five low-risk criteria all hold (imaging not indicated by this rule).
• Canadian CT Head Rule — Apply the Stiell 2001 Canadian CT Head Rule and return whether CT is indicated from caller-assigned high-risk and medium-risk findings after minor blunt head injury.

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. Unpaid valid requests return HTTP 402 with a base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote: retry the same PAYMENT-SIGNATURE. Full handshake and shared payment errors: Payments. Stdio MCP: /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.