# NEXUS Head CT NEXUS Head CT Status: LIVE Price: $0.005 USDC `GET /api/calc/nexus_head_ct` HTML: https://magentlab.com/docs/nexus-head-ct Markdown: https://magentlab.com/docs/nexus-head-ct.md 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 [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](https://doi.org/10.1371/journal.pmed.1002313) Mower WR, Gupta M, Rodriguez R, Hendey GW PLoS Med. 2017;14(7):e1002313 DOI: [10.1371/journal.pmed.1002313](https://doi.org/10.1371/journal.pmed.1002313) ## Worked example ### All eight criteria absent Given: `abnormal_behavior=false, age=40, altered_alertness=false, coagulopathy=false, neurologic_deficit=false, persistent_vomiting=false, scalp_hematoma=false, skull_fracture=false` 1. Age 40 is < 65; no skull fracture, scalp hematoma, neurologic deficit, altered alertness, abnormal behavior, coagulopathy, or persistent vomiting 2. low_risk is true; CT may be omitted by this instrument. This tool does not order a CT ### Age 65 is not low-risk Given: `abnormal_behavior=false, age=65, altered_alertness=false, coagulopathy=false, neurologic_deficit=false, persistent_vomiting=false, scalp_hematoma=false, skull_fracture=false` 1. Age 65 meets the age ≥ 65 criterion; the seven clinical flags remain absent 2. low_risk is false. Presence of this criterion does not mandate CT ## 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 ## Parameters - `age` (integer, required): Age in years (integer 18-120). Age ≥ 65 is a high-risk criterion; 64 is not high-risk on age alone. Low-risk age criterion holds when age < 65. - `skull_fracture` (boolean, required): Evidence of skull fracture as assigned by the caller. true means a skull-fracture finding is present and low_risk is false. true or false. magent does not examine the patient or read a radiograph. - `scalp_hematoma` (boolean, required): Scalp hematoma as assigned by the caller. true means a scalp hematoma is present and low_risk is false. true or false. magent does not examine the scalp. - `neurologic_deficit` (boolean, required): Neurologic deficit (neurosurgical deficits) as assigned by the caller. true means a deficit is present and low_risk is false. true or false. magent does not examine the patient. - `altered_alertness` (boolean, required): Altered level of alertness as assigned by the caller. true means alertness is altered and low_risk is false. true or false. magent does not assign GCS. - `abnormal_behavior` (boolean, required): Abnormal behavior as assigned by the caller. true means abnormal behavior is present and low_risk is false. true or false. magent does not examine the patient. - `coagulopathy` (boolean, required): Coagulopathy as assigned by the caller. true means coagulopathy is present and low_risk is false. true or false. magent does not interpret a coagulation assay. - `persistent_vomiting` (boolean, required): Persistent vomiting as assigned by the caller. true means persistent vomiting is present and low_risk is false. true or false. magent does not take a vomit count. ## 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_head_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_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" } ] } ``` Human paywall (two-item fixture): https://api.magentlab.com/paywall/bulk/nexus-head-ct Example 200: ```json { "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 fields - `formula` (string): nexus_head_ct - `formula_expression` (string): Mower 2017 eight-criterion NEXUS Head CT decision instrument - `low_risk` (boolean): true only when all eight criteria are absent. CT may be omitted by this instrument when true. 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 low-risk item holds (age < 65 or the named finding is absent). age_lt_65 includes value - `citation` (object): Mower 2017 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": "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 } ``` ## Errors - HTTP 400 `invalid_age`: age must be an integer from 18 to 120 Returned before settlement; you are not charged. - 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 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). - [Canadian CT Head Rule](https://magentlab.com/docs/canadian-ct-head) — 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. - 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.