Cerebral Perfusion Studies
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Defines Aetna's coverage stance for cerebral CT and MRI perfusion studies, including when they are medically necessary versus considered experimental/investigational, for providers and claim reviewers.
No material clinical or coverage changes in this revision.
Coverage Criteria
inv-01: Medically necessary indications
Aetna considers the following cerebral perfusion studies medically necessary when ALL listed conditions are met (grouped by modality and indication):
CT perfusion for acute cerebral ischemia (acute stroke)
- CT perfusion clinical options: Option A: CT perfusion is used as a supplement to non-contrast head CT; Option B: Magnetic resonance imaging is unavailable or contraindicated
inv-02: Experimental / Investigational (Not medically necessary)
The following indications are considered experimental and investigational because effectiveness has not been established:
inv-03: Clinical indications supported by cited evidence
Evidence-supported clinical uses and supporting findings (study-level):
Supported by Wang et al (2010) and guideline summaries; multimodal CT described as useful when MRI unavailable (chunks 18, 22).
Michel et al (2012) pilot randomized feasibility study (chunk 21).
Cremers 2014, Mir 2014, meta-analyses (chunks 25, 26, 33).
Afat et al (2018) retrospective study reported sensitivity 99.0% and specificity 99.5% (chunk 29).
Adebayo & Culpan (2020) systematic review and related prognostic reviews (chunks 51, 54).
Bendinelli et al (2017) prospective study (chunk 36).
Lansberg et al (CRISP) multicenter cohort findings (chunk 38).
inv-04: Descriptive coverage-relevant evidence summaries
Clinical situations where CTP has supporting evidence:
Single-center observational study; larger studies recommended (chunk 36).
CRISP multicenter cohort (chunk 38) with limitations including lack of randomized control group.
Adebayo & Culpan (2020) and related systematic reviews (chunk 51).
inv-05: Evidence summaries with coverage implications
Evidence-based statements and performance estimates from systematic reviews/meta-analyses
Xu et al (2017) and Suh et al (2019) meta-analyses (chunks 91, 93).
Meta-analysis pooled estimates and limitations (chunk 96).
Kwee & Kwee (2020) meta-analysis (chunk 99).
Meta-analysis of 20 studies (chunk 102).
Systematic review (Ahmadian et al 2021) (chunk 104).
Examples of ICD-10 diagnoses referenced in the policy as not covered for the investigational indications include: B00.4 (Herpesviral encephalitis), C71.0–C71.9 (Malignant neoplasm of brain; glioma), G93.82 (Brain death), G31.84 (Mild cognitive impairment), and G20 (Parkinson's disease). These codes appear in the document lists of diagnoses for which perfusion imaging is identified in the investigational/not-covered context.
Use of cerebral CT or MRI perfusion studies for the indications listed in the policy’s Experimental/Investigational section is considered not medically necessary because effectiveness has not been established. The policy explicitly states that cerebral CT perfusion and cerebral MRI perfusion studies are not medically necessary for the many investigational indications enumerated (see policy lists), and claims for those indications may be denied when billed for those diagnoses.
CT and MRI perfusion are identified as not covered for a range of investigational indications. Examples include perfusion imaging for confirmation of brain death, evaluation and grading of cerebral gliomas (including differentiation from lymphoma, metastases, and abscess), assessment of response to angiogenesis inhibitors in glioblastoma, diagnosis of recurrent brain metastases after radiotherapy, and evaluation of moyamoya, traumatic brain injury, cognitive impairment, idiopathic normal pressure hydrocephalus, and Parkinson’s disease biomarker use. The policy states these uses are experimental/investigational because effectiveness has not been established and are considered not medically necessary.
Covered Indications (Detailed)
inv-77: Acute cerebral ischemia (acute stroke)
Acute cerebral ischemia (acute stroke): top-level coverage node
inv-78: Appropriate clinical indications and supporting evidence for cerebral CTP
Appropriate clinical indications and supporting evidence for cerebral CTP — summarized top-level items
inv-79: Indications supported by evidence summaries in document
Indications supported by evidence summaries in the document:
inv-80: Clinical and research indications described in evidence summaries
Clinical and research indications described in evidence summaries:
inv-81: Selected clinical uses of cerebral perfusion MRI
Selected clinical uses of cerebral perfusion MRI summarized from evidence:
inv-82: Appropriate uses with evidence caveats
Appropriate uses with evidence caveats — items with caveats and conditional interpretation:
inv-83: CT and MR perfusion imaging indications summarized from cited literature
CT and MR perfusion imaging indications summarized from cited literature:
Coding
| 0042T | Cerebral perfusion analysis using computed tomography with contrast administration, including post-processing of parametric maps with determination of cerebral blood flow, cerebral blood volume, and mean transit time. |
| 37195 | Thrombolysis, cerebral, by intravenous infusion. |
| 61623 | Endovascular temporary balloon arterial occlusion, head or neck (extracranial/intracranial) including selective catheterization of vessel to be occluded, positioning and inflation of occlusion balloon, concomitant neurological monitoring, and radiologic supervision and interpretation of all angiography required for balloon occlusion and to exclude vascular injury post occlusion. |
| 70450 | CT, head or brain; without contrast material. |
| 70460 | CT, head or brain; with contrast material. |
| 70470 | CT, head or brain; without and with contrast material. |
| 70496 | Computed tomographic angiography, head, with contrast material(s), including noncontrast images, if performed, and image post-processing. |
| I63.00 - I63.9 | Cerebral infarction. |
| I65.01 - I65.9 | Occlusion and stenosis of precerebral arteries, not resulting in cerebral infarction. |
| I66.01 - I66.9 | Occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction. |
| B00.4 | Herpesviral encephalitis. |
| C71.0 - C71.9 | Malignant neoplasm of brain (glioma). |
| G93.82 | Brain death. |
| G31.84 | Mild cognitive impairment, so stated. |
| G20 | Parkinson's disease. |
| No codes listed |
Provider Actions / Billing Guidance
Prior Authorization / Administrative Authorization Not Specified
Prior authorization not specified in this section. The policy text does not state a formal prior authorization (PA) requirement for cerebral CT or MR perfusion studies; there is no explicit administrative authorization or step-therapy described in these excerpts. Providers should verify member benefits and any PA requirements with the payer before performing non-emergent studies.
- No prior authorization language present in provided excerpts
- No step therapy requirements described
Consider PA for Extended‑Window or Nonstandard CTP Use
Consider prior authorization when CTP is used outside standard indications or time windows (for example, selection for endovascular therapy beyond conventional windows or other nonstandard/extended-window uses). Because evidence and methods are heterogeneous and evolving, additional review may be required and PA can help ensure the indication, protocol, and processing meet clinical criteria before approval.
- Recommended: obtain PA for extended-window or nonstandard CT perfusion use (e.g., selection for endovascular therapy beyond usual windows)
- PA especially prudent when institutional protocols or thresholds are not standardized
Prior Authorization: Ensure Indication and Protocol Documentation
When prior authorization is required (per payer or plan-specific rules), documentation should explicitly include clinical indication and the imaging protocol. Required elements include indication for the perfusion study, time from symptom onset (or rationale if time unknown), relevant clinical scores (eg, NIHSS), results of non-contrast CT or MRI when available, and whether MRI is unavailable or contraindicated when CT is used as a substitute.
- Document indication and reason CTP is being used (supplement to NCCT or MRI unavailable/contraindicated)
- Include time window or justification for extended-window use
- Include relevant clinical severity scores (eg, NIHSS)
Required Documentation Elements
Required clinical and imaging documentation should include indication, time window, clinical severity scores (eg, NIHSS), core/penumbra estimates, imaging modality used, and processing details. Processing outputs from automated perfusion software (eg, RAPID or equivalent) should be saved and available to support interpretation and utilization for treatment decisions.
- Indication and time since symptom onset
- Clinical scores (eg, NIHSS) and pertinent exam findings
- Non-contrast CT/CTA or MRI findings if available
- CTP/MRP processed outputs and maps (eg, CBF, CBV, MTT, Tmax)
Processing Documentation
Processing documentation: automated perfusion-processing outputs and mismatch metrics (eg, core and penumbra volumes, Tmax thresholds, rCBV values) should be recorded and retained in the medical record. When automated software is used, include the software name/version and the quantitative outputs used to make treatment decisions.
- Record software name and version (eg, RAPID)
- Save parametric maps and numeric outputs (CBF, CBV, MTT, Tmax)
- Report core and penumbra volumes and thresholds used
Record Perfusion Metric and Threshold
Record perfusion metrics and thresholds used in studies and clinical decision-making. Reported thresholds in the literature vary (for example, rCBV thresholds for tumor vs necrosis or rCBV ranges reported in meta-analyses). If thresholds are used to guide therapy, specify the metric (eg, rCBV, Tmax, CBF) and the numeric threshold applied.
- Specify metric(s) used (eg, rCBV, CBF, Tmax) and numeric thresholds
- Include threshold ranges where relevant (eg, rCBV ranges reported in studies)
Evidence Limitations May Trigger Additional Review / Non‑standardized Methods Risk Denial
Evidence limitations and non-standardized methods may trigger additional review or denial. The literature shows heterogeneity in acquisition, post-processing, and reported thresholds; such variability and risk of bias can prompt case-by-case review and denial if prespecified thresholds or standardized methods are not documented.
- Heterogeneity of methods and thresholds increases likelihood of additional review
- Lack of prespecified thresholds or standardized processing may prompt denial
Limitations and Cost‑Effectiveness Considerations
Limitations of CTP should be noted in documentation. CTP is unreliable for lacunar (small subcortical) infarcts and should not be relied on alone in that context. For transient ischemic attack (TIA) workups, routine MR DWI is not always cost‑effective; include consideration of cost‑effectiveness and appropriateness of MR versus CT in the record when pertinent.
- CTP has limited sensitivity for lacunar/RSSI infarcts — avoid sole reliance on CTP for these diagnoses
- MR DWI is not universally cost‑effective for TIA; consider timing and clinical context
Administrative Notes / Not‑Applicable Items
Not applicable / None specified: In the provided document excerpts there are no explicit step‑therapy requirements, no explicit administrative authorization workflow, and no preoperative-specific authorization steps described. For use in preoperative evaluation or other unlisted indications, obtain prior benefit verification and document clinical rationale; these indications may be considered investigational and risk denial.
- No step therapy requirements described in provided text
- No explicit administrative authorization or preoperative authorization instructions in excerpts
- Investigational indications listed in policy risk denial if used outside listed medically necessary criteria
Contrast Use and Modality Selection
CT perfusion requires IV iodinated contrast for dynamic acquisition and post‑processing
CT perfusion requires intravenous administration of iodinated contrast for dynamic acquisition and post‑processing to derive perfusion parameters—document contrast use in reports and claims.
- Contrast agent administration is integral to CTP acquisition and should be documented
CTA/CTP for brain death ancillary testing require iodinated contrast and variable protocols
When CTA/CTP are used as ancillary tests for brain death confirmation, note that iodinated contrast is required and protocols and sensitivities vary across institutions; document the protocol used.
- CTA/CTP are more invasive than MRA because of contrast injection; sensitivity in studies has been variable
DSC MR perfusion requires contrast bolus and deconvolution processing (document methods)
DSC MR perfusion uses a contrast bolus and deconvolution algorithms to derive CBV, CBF, and MTT; document contrast administration and post‑processing methods when billing or requesting prior authorization.
- Document the processing approach (deconvolution, AIF selection) and software if relevant
Use ASL when contrast is contraindicated or in pediatric cases; document rationale
If contrast is contraindicated or in pediatric patients, ASL (a non‑contrast MR technique) may be used to quantify CBF; document the rationale for choosing ASL over contrast techniques.
- ASL is appropriate when gadolinium/iodinated contrast is contraindicated or to avoid contrast in children
Choose DSC/DCE/ASL based on diagnostic question and contrast safety; document selection
Select DSC vs DCE vs ASL based on the diagnostic question and patient factors; document choice of modality and contrast safety considerations in the record.
- Provide acquisition parameters and post‑processing details to support interpretation and potential coverage review
Document pediatric ASL acquisition parameters and known limitations (arterial transit time, blood T1)
In pediatric ASL and CBF quantification, be aware that arterial transit time and assumptions about blood T1 can affect measurements; document relevant acquisition parameters (e.g., PLD) and limitations when reporting CBF values.
- Note potential sensitivity to arterial transit time and T1 of blood especially in pediatric populations
Not Covered / Investigational Indications
The policy lists many additional investigational indications for which CT and MR perfusion are not covered, including but not limited to: evaluation of head and neck cancers, monitoring tumor progression after glioma radiotherapy, differentiation of radiation necrosis from recurrent tumor or pseudo‑progression, evaluation of brain arteriovenous malformations, identification of new infarcts after TIA or minor stroke, and pediatric post‑operative cerebellar mutism syndrome. These indications are included in the policy’s Experimental/Investigational lists and thus are considered not medically necessary.
CT perfusion should not be relied upon as the sole diagnostic test for lacunar (recent small subcortical) infarcts. A systematic review found wide heterogeneity in CTP techniques and low sensitivity for lacunar infarcts (reported sensitivity range 0% to 62.5%), and the authors concluded that CT perfusion cannot reliably diagnose lacunar stroke due to consistent false negative rates; CTP may at best be supportive when a perfusion deficit is seen but is insufficient alone for diagnosis.
Additional investigational exclusions and cautionary notes include: evidence limitations from study heterogeneity, small sample sizes, variable patient populations, and lack of standardized acquisition and post‑processing protocols; the policy emphasizes that non‑standardized methods and lack of prespecified diagnostic thresholds limit generalizability and may lead to denial for investigational uses. The policy also notes decision analyses questioning whether imaging to select patients for some therapies (e.g., induced‑hypertension for suspected DCI) improves outcomes versus treating all patients, reinforcing that such uses remain investigational.
Definitions and Technical Terms
Background and Evidence Summary
Computed tomography perfusion (CTP) acquires sequential CT images during intravenous iodinated contrast administration and, with post‑processing, generates quantitative perfusion maps such as cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT). These derived parameters are used clinically to help distinguish ischemic core from salvageable penumbra in acute ischemic stroke pathways when MRI is unavailable, and to provide rapid, widely available perfusion information to support acute treatment decisions.
inv-03 (supporting evidence): Clinical indications supported by cited evidence
Supporting evidence for clinical indications — grouped evidence nodes:
inv-04: Descriptive coverage-relevant evidence summaries
Descriptive evidence summaries for coverage-relevant clinical situations:
The evidence base for many perfusion applications is limited by substantial heterogeneity in study designs, small sample sizes, variable reference standards, and risk of bias. Systematic reviews have highlighted inconsistent patient selection, differences in acquisition and post‑processing methods, and lack of prespecified diagnostic thresholds, all of which reduce confidence in pooled diagnostic accuracy estimates and limit generalizability of reported thresholds and automated software outputs.
CTP has specific limitations for lacunar (recent small subcortical) infarcts: studies show heterogeneous perfusion patterns and consistently low sensitivity, leading authors to conclude that CT perfusion is unreliable for diagnosing lacunar stroke. Because false negative rates are substantial, reliance on CTP alone may miss recent small subcortical infarcts; larger, prospective, technically homogeneous studies are needed to clarify any role for perfusion imaging in this condition.
Revision History
Policy underwent routine review (Last review recorded).
Policy originally became effective.
Next scheduled policy review date.
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