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Monitoring of Regional Cerebral Blood Flow Using an Implanted Cerebral Thermal Perfusion Probe

Policy Number: MP-214

Latest Review Date: October 2019

Category: Medicine

Policy Grade: Effective June, 2011: Active Policy but no longer scheduled for regular literature reviews and updates.


Monitoring of regional cerebral blood flow using an implanted cerebral thermal perfusion probe is considered not medically necessary and investigational.


Assessment of cerebral perfusion is considered an important component of the management of patients with head trauma, post neurological surgery or strokes of a variety of etiologies, including subarachnoid hemorrhage. For example, cerebrovasospasm leading to decreased cerebral blood flow and ischemia and delayed neurological deterioration is one of the major causes of morbidity and mortality after subarachnoid hemorrhage (SAH). All patients with SAH are initially treated with the calcium channel blocker nifedipine to prevent vasospasm, which typically occurs between Day 5 and Day 14 after the initial bleed. Ongoing assessment of vasospasm is performed during this period to determine the need for additional treatment. If vasospasm is detected, patients may be treated with “Triple H” therapy, consisting of induced hypertension, hypervolemia with colloids and hemodilution. If the vasospasm is marked, persistent, focal, or associated with neurological defects, then the patient may undergo angiogram and angioplasty. Neurological deterioration is an important clinical sign of vasospasm, but neurologic assessment is obviously difficult in sedated or comatose patients.

Bedside transcranial doppler (TCD) is the technique most commonly used to assess cerebral perfusion, but this technique is technically difficult, can take over an hour, visualizes a small proportion of vessels, and not infrequently, cannot be done at all if temporal bone windows are dense. A variety of other techniques have been investigated to measure cerebral perfusion, including numerous protocols for CT scans, PET scans or other radionuclide studies. A major limitation of these techniques is the fact that they cannot be performed at the bedside.

Recently, a cerebral thermal perfusion probe has been investigated, which has the additional advantage of being able to provide continuous bedside monitoring. In contrast to other techniques like TCD, which can assess the entire brain, the thermal perfusion probe will assess regional cerebral blood flow. The Qflow 500™ Perfusion Monitoring System is a cerebral thermal perfusion probe that received FDA clearance through the 510(k) process in 2000. The labeled indication for the device is as follows:

“The QFlow™ is intended for extravascular monitoring of microcirculation blood flow in buried tissues. Examples of this application include (but are not limited to) 1) the monitoring of buried muscle or esophagus following free muscle transfer or esophageal free muscle transfer or esophageal reconstruction, 2) monitoring soft tissue microcirculation following reconstructive surgery, such as oral and facial reconstruction, and 3) monitoring cerebral blood flow during and following neurosurgery for head trauma.”

The device consists of two thermistors embedded at the distal tip of the probe, which is placed intracerebrally via a burr hole in the vascular area of interest in the brain. The probe is connected to a probe monitor that continuously displays the perfusion data. The power dissipated in the thermistor provides a measure of the ability of the tissue to carry heat by both thermal conduction within the tissue and by thermal convection due to tissue blood flow.

As noted above, the labeled indication for the device is not limited to its intracerebral use. However, this policy is only focused on the intracerebral use of the device to assess cerebral perfusion.


The most recent literature search was performed through October 8, 2019.


There is no gold standard technology for currently measuring cerebral perfusion. While angiography might be considered the gold standard, this test is not routinely performed; rather a variety of noninvasive tests are used to determine the need for angiography. Transcranial Doppler (TCD) is the most commonly performed noninvasive test; however, in the published literature, the diagnostic performance of the cerebral thermal perfusion probe was correlated to xenon-enhanced CT scan (Xe-CT), since this test also provides an absolute measure of cerebral blood flow. The impact of the test on the management of the patient primarily focuses on triaging the patient to various treatment strategies of increasing complexity. For example, in the instance of subarachnoid hemorrhage (SAH), assessment of cerebral perfusion may dictate whether or not the patient requires more aggressive therapy, including the invasive procedures of angiography and angiogram. Finally, the ability of an implanted cerebral infusion probe creates the unique opportunity of providing continuous real time data. The ultimate health outcomes are the morbidity and mortality related to the underlying event, i.e., residual neurologic defects or death.

In the FDA Summary of Safety and Effectiveness of the QFlow 500™ Perfusion Monitoring System, the manufacturer indicates that the device is essentially similar to other perfusion monitors. Measurement of perfusion using thermistors is an established and accepted technology. However, the technical challenge of the cerebral perfusion probe is related to the necessity of distinguishing between thermal conduction and convection. Data analysis of the QFlow 500™ device relies on data reduction algorithms to make this distinction. An additional issue of technical feasibility is the ability to accurately place the probe in the area of vascular interest such that the cerebral perfusion is measured in the critical area. Vasospasm may not be predictably associated with the area of SAH, and may even occur contralateral to the bleed. This aspect of technical feasibility is not specifically addressed in the published literature.

There are minimal published data regarding the diagnostic performance of the cerebral perfusion probe. As noted above, Vajkoczy studied the correlation of the probe compared to xenon-enhanced CT scan. The microprobe was implanted subcortically into 16 brain-injured patients, and cerebral blood flow was assessed simultaneously with the thermal perfusion probe and xenon-enhanced CT scans. The 2 values were highly correlated (R= 0.89). However, it should be noted that the probe was implanted contralateral to the vascular area of interest, and thus, in this validation study, was not intended to provide clinically relevant information. Aside from a correlation with a gold standard, diagnostic performance is based on sensitivity, specificity, and positive and negative predictive values for the presence, absence, or severity of vasospasm, which in turn depend on cut off values to distinguish between a positive and negative test. There is minimal discussion of these diagnostic parameters in the published literature. For example, the availability of continuous monitoring, compared to monitoring with episodic TCD, creates the possibility of assessing the evolution and severity of vasospasm, in contrast to its presence or absence. Cut off values are important to determine when vasospasm is clinically relevant in order to guide treatment decisions.

No published studies were identified that used data from a cerebral thermal perfusion probe to guide treatment decisions. Thome et al used a thermal perfusion probe as a technique for intraoperative monitoring in 20 patients undergoing aneurysm surgery that required temporary arterial occlusion. However, it does not appear that treatment decisions were based on probe data. Vajkoczy et al used a thermal diffusion probe in 14 patients with high grade SAH treated operatively, implanting 2 probes in the vascular territories deemed at highest risk for developing vasospasm. Again, treatment decisions were not based on data from the cerebral perfusion probe.

There are inadequate data to permit scientific conclusions concerning the effect of the technology on health outcomes, and whether or not the use of a cerebral thermal perfusion probe results in an improvement in the net health outcome.

Two small studies were identified that used a thermal diffusion probe for experimental monitoring of cerebral blood flow following traumatic brain injury or subarachnoid hemorrhage. One was a case study and the other was a study with 8 patients. No studies were identified that would alter the coverage statement of this policy.


Cerebral perfusion, cerebral thermal perfusion probe, Qflow 500™ Perfusion Monitoring System, subarachnoid hemorrhage, transcranial doppler (TCD)


The Qflow 500™ Perfusion Monitoring System is a cerebral thermal perfusion probe that received FDA clearance through the 510(k) process in 2000.


Coverage is subject to member’s specific benefits. Group specific policy will supersede this policy when applicable.

ITS: Home Policy provisions apply

FEP contracts: FEP does not consider investigational if FDA approved and will be reviewed for medical necessity. Special benefit consideration may apply. Refer to member’s benefit plan.


CPT Codes:

There are no specific CPT codes for cerebral thermal perfusion probes. It is likely they are reported with:

61107 Twist drill hole(s) for subdural, intracerebral, or ventricular puncture; for implanting ventricular catheter, pressure recording device, or other intracerebral monitoring device

61210 Burr hole(s); for implanting ventricular catheter, reservoir, EEG electrode(s), pressure recording device, or other cerebral monitoring device (separate procedure)


CPT Codes:

0077T Implanting and securing cerebral thermal perfusion probe, including twist or burr hole, to measure absolute cerebral tissue perfusion


  1. Barth M, Capelle HH, et al. Effects of the selective endothelin A (ER(A)) receptor antagonist Clazosentan on cerebral perfusion and cerebral oxygenation following severe subarachnoid hemorrhage – preliminary results from a randomized clinical series. Acta Neurochir 2007; 149(9): 911-918.

  2. Blue Cross Blue Shield Association. Monitoring of regional cerebral blood flow using an implanted cerebral thermal perfusion probe. Medical Policy Reference Manual, March 2008.

  3. Jaeger M, Soehle M and Meixensberger J. Brain tissue oxygen (PtiO2): A clinical comparison of two monitoring devices. Acta Neurochir Suppl 2005; 95: 79-81. (Abstract)

  4. Thome, C., Vajkoczy, P., Horn, P., & et al. Continuous monitoring of regional cerebral blood flow during temporary arterial occlusion in aneurysm surgery. J Neurosurg 2001; 95:402-11.

  5. U.S. Food and Drug Administration. 510(k) Summary of Safety and Effectiveness: QFlow™ 500 Perfusion Monitoring System, May 2002. //

  6. U.S. Food and Drug Administration. 510(k) Summary for CMA Cerebral Tissue Monitoring System. October 2002, //

  7. Vajkoczy, P., Horn, P., Thome, C., & et al. Regional cerebral blood flow monitoring in the diagnosis of delayed ischemia following aneurismal subarachnoid hemorrhage. J Neurosurg 2003; 98:1227-1234.

  8. Vajkoczy, R., Roth, H., Horn, P., & et al. Continuous monitoring of regional cerebral blood flow; experimental and clinical validation of a novel thermal diffusion microprobe. J Neurosurg 2000; 93:265-74.


    Medical Policy Group, December 2005 (4)

    Medical Policy Administration Committee, December 2005

    Available for comment December 23, 2005-February 6, 2006

    Medical Policy Group, December 2006 (1)

    Medical Policy Group, December 2007 (1)

    Medical Policy Group, February 2009 (1)

    Medical Policy Group, June 29, 2011; Active Policy but no longer scheduled for regular literature reviews and updates.

    Medical Policy Group, March 2016 (4): Key Points and Coding section updates. No change to policy statement.

Medical Policy Group (3): 2019 Updates to Key Points. A peer reviewed literature analysis was completed and no new information was identified that would alter the coverage statement of this policy. This policy will remain on biannual reviews.

This medical policy is not an authorization, certification, explanation of benefits, or a contract. Eligibility and benefits are determined on a case-by-case basis according to the terms of the member’s plan in effect as of the date services are rendered. All medical policies are based on (i) research of current medical literature and (ii) review of common medical practices in the treatment and diagnosis of disease as of the date hereof. Physicians and other providers are solely responsible for all aspects of medical care and treatment, including the type, quality, and levels of care and treatment.

This policy is intended to be used for adjudication of claims (including pre-admission certification, pre-determinations, and pre-procedure review) in Blue Cross and Blue Shield’s administration of plan contracts.

The plan does not approve or deny procedures, services, testing, or equipment for our members. Our decisions concern coverage only. The decision of whether or not to have a certain test, treatment or procedure is one made between the physician and his/her patient. The plan administers benefits based on the member’s contract and corporate medical policies. Physicians should always exercise their best medical judgment in providing the care they feel is most appropriate for their patients. Needed care should not be delayed or refused because of a coverage determination.

As a general rule, benefits are payable under health plans only in cases of medical necessity and only if services or supplies are not investigational, provided the customer group contracts have such coverage.

The following Association Technology Evaluation Criteria must be met for a service/supply to be considered for coverage:

1. The technology must have final approval from the appropriate government regulatory bodies;

2. The scientific evidence must permit conclusions concerning the effect of the technology on health outcomes;

3. The technology must improve the net health outcome;

4. The technology must be as beneficial as any established alternatives;

5. The improvement must be attainable outside the investigational setting.

Medical Necessity means that health care services (e.g., procedures, treatments, supplies, devices, equipment, facilities or drugs) that a physician, exercising prudent clinical judgment, would provide to a patient for the purpose of preventing, evaluating, diagnosing or treating an illness, injury or disease or its symptoms, and that are:

1. In accordance with generally accepted standards of medical practice; and

2. Clinically appropriate in terms of type, frequency, extent, site and duration and considered effective for the patient’s illness, injury or disease; and

3. Not primarily for the convenience of the patient, physician or other health care provider; and

4. Not more costly than an alternative service or sequence of services at least as likely to produce equivalent therapeutic or diagnostic results as to the diagnosis or treatment of that patient’s illness, injury or disease.