Thermal Perfusion Probe for Monitoring Regional Cerebral Blood Flow

Number: 0703

Table Of Contents

Applicable CPT / HCPCS / ICD-10 Codes


Aetna considers a thermal perfusion probe for monitoring regional cerebral blood flow experimental and investigational because there is insufficient evidence of the clinical value of these approaches in the management of individuals with acute neurological disorders (e.g., head injury, subarachnoid hemorrhage, or following neurosurgery) or for other indications. 

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CPT Codes / HCPCS Codes / ICD-10 Codes

Code Code Description

Information in the [brackets] below has been added for clarification purposes.   Codes requiring a 7th character are represented by "+":

Other CPT codes related to the CPB:

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
61000 - 64999 Nervous System/Surgery

ICD-10 codes not covered for indications listed in the CPB (not all-inclusive):

E75.00 - E75.19, E75.23
E75.25, E75.29, E75.4
Disorders of sphingolipid metabolism and other lipid storage disorders
G00.0 - G09 Inflammatory diseases of the central nervous system
G11.0 - G12.9
Systemic atrophies primarily affecting the central nervous system
G20 - G26 Extrapyramidal and movement disorders
G30.0 - G32.8 Other degenerative diseases of the nervous system
G35 - G43.919 Demyelinating diseases of the cental nervous system and episodic and paroxysmal disorders
G45.0 - G45.9 Transient cerebral ischemic attacks and related syndromes
G46.0 - G46.8 Vascular syndromes of brain in cerebrovascular diseases
G80.0 - G83.9 Cerebral palsy and other paralytic syndromes
G90.01 - G91.9, G93.7, G93.89, G93.9
G94, G95.0 - G95.9, G99.0, G99.2
Other disorders of the nervous system
I60.00 - I66.9, I67.1 - I67.2
I67.4 - I69.998
Cerebrovascular diseases
S02.0xx+ - S02.413+
S02.60x+ - S02.92x+
Fracture of skull and facial bones, with or without intracranial injury
S06.0X0A - S06.A1XS Intracranial injury, excluding those with skull fracture
Z13.850 Encounter for screening for traumatic brain injury
Z13.858 Encounter for screening for other nervous system disorders


Cerebral blood flow (CBF) is essential for normal metabolism of the brain.  Ischemic brain injury occurs when CBF is insufficient to meet metabolic demand, which can occur in acute neurological disorders (e.g. head injury, subarachnoid hemorrhage, or following neurosurgery).

Various imaging techniques have been attempted to identify individuals at risk for secondary ischemic brain injury and manage response to therapies.  Some of these techniques are still evolving (e.g., stable-xenon-enhanced computed tomography (XeCT), perfusion computed tomography, perfusion magnetic resonance imaging, single photon emission computed tomography (SPECT) and positron emission tomography (PET)).  While these techniques can provide regional information about CBF, the data provided is a single snap shot in time.  Methods for the continuous measurement of CBF have been investigated and are now commercially available.  One such method is a thermal perfusion probe, which is placed intra-cerebrally via a burr hole in the vascular area of interest in the brain.  The probe is connected to a monitor that displays CBF data. 

The QFlow 500 probe (Hemedex, Inc, Cambridge, MA) is an example of a commercially available thermal perfusion probe that has received 510(k) marketing clearance from the Food and Drug Administration (FDA).  It is used along with the Bowman Perfusion Monitor, Model 500 (Hemedex, Inc, Cambridge, MA).  According to the manufactures website, one potential application of the device is for monitoring CBF in patients with traumatic brain injury to help identify secondary ischemic injury to the brain.  The manufacturer states that, by measuring continuous, real-time CBF, clinicians may identify cerebral edema and measure tissue blood flow response to therapies.  Another potential neurological application is monitoring CBF following neurosurgery (e.g., aneurysm and subarachnoid hemorrhage procedures).

Current literature on thermal perfusion probes has focused on their clinical feasibility and technical capabilities. Jaeger et al (2005) measured regional cerebral blood flow (rCBF) using the QFlow in patients with severe subarachnoid hemorrhage (n = 5) and traumatic brain injury (n = 3) and compared these results to brain tissue oxygen measurements (P(ti)O(2)) using the Licox (GMS, Kiel-Mielkendorf, Germany) for an average of 9.6 days.  The data indicated a significantcorrelation between CBF and P(ti)O(2) (r = 0.36).  After 400 intervals of 30-min duration, the QFlow and the P(ti)O(2) measurements correlated 72 % of the time when P(ti)O(2) changes were greater than 5 mm Hg (r > 0.6).  In 19 % of the intervals a statistically significant correlation was observed (r < 0.6).  During the remaining 9 %, no correlation was found (r < 0.3).  The authors suggested that the level of P(ti)O(2) is predominately determined by rCBF, since changes in P(ti)O(2) were correlated in 90 % of episodes to simultaneous changes of CBF.  Phases of non-monitoring were mostly due to fever of the patient, when the system does not allow monitoring to avoid overheating of the cerebral tissue. 

Vajkoczy et al (2003) obtained rCBF using thermal-diffusion (TD) microprobes to prospectively diagnose symptomatic vasospasm in 14 patients with high-grade subarachnoid hemorrhage (SAH) who underwent early clip placement for anterior circulation aneurysms.  The TD microprobes were implanted into the white matter of vascular territories that were deemed at risk for developing symptomatic vasospasm.  Data on arterial blood pressure, intracranial pressure, cerebral perfusion pressure, rCBF, cerebrovascular resistance (CVR), and blood flow velocities were collected at the patient's bedside.  The diagnosis of symptomatic vasospasm was based on the manifestation of a delayed ischemic neurological deficit and/or a reduced territorial level of CBF as assessed using stable XeCT scanning in combination with vasospasm demonstrated by angiography.  Bedside monitoring of TD-rCBF and CVR allowed the detection of symptomatic vasospasm.  In the 10 patients with vasospasm, the TD-rCBF decreased from 21 +/- 4 to 9 +/- 1 ml/100 g/min), whereas in the 4 other patients the TD-rCBF value remained unchanged (mean TD-rCBF = 25 +/- 4 compared with 21 +/- 4 ml/100 g/min).  Based on a comparison of the results of TD-rCBF and Xe-enhanced CT studies, as well as the calculation of sensitivities, specificities, predictive values, and likelihood ratios, the investigators identified a TD-rCBF value of 15 ml/100 g/min as a reliable cutoff for the diagnosis of symptomatic vasospasm.  In addition, the investigators found that TD flowmetry was characterized by a more favorable diagnostic reliability than transcranial Doppler ultrasonography.  The authors concluded that TD flowmetry represents a promising method for the bedside monitoring of patients with SAH to detect symptomatic vasospasm.

Tasneem and colleague (2017) stated that neuro-critical care patients are at risk of developing secondary brain injury from inflammation, ischemia, and edema that follows the primary insult.  Recognizing clinical deterioration due to secondary injury is frequently challenging in comatose patients.  Multi-modality monitoring (MMM) encompasses various tools to monitor cerebral metabolism, perfusion, and oxygenation aimed at detecting these changes to help modify therapies before irreversible injury sets in.  These tools include intra-cranial pressure (ICP) monitors, transcranial Doppler (TCD), Hemedex (thermal diffusion probe used to measure regional CBF), micro-dialysis catheter (used to measure cerebral metabolism), Licox (probe used to measure regional brain tissue oxygen tension), and continuous electroencephalography.  Cerebral blood flow can be measured by inserting a thermal diffusion probe (TDP) directly into brain parenchyma.  The commercially available system includes the Hemedex monitoring system, which is not MRI compatible.  It allows regional CBF (rCBF) monitoring by assessing thermal convection due to tissue blood flow.  The probe tip is inserted into white matter of brain and its utility depends on proximity to the area of interest.  Thermal diffusion probe has been validated by Xenon perfusion CT and CBF level below 15 ml/100 g/min is identified as threshold for diagnosis of hypo-perfusion.  Per MMM consensus guidelines, TDP should be placed in vascular territory of ruptured aneurysm to monitor for vasospasm.  Quantification of rCBF with TDP is highly dependent on patient's core body temperature and is significantly altered in conditions of hyperthermia.  To-date, there are no published studies of improved outcome with treatment strategies directed solely by CBF monitoring, however it appears to be a promising tool to use in conjunction with other parameters.  Nevertheless, MMM is now a reality commonly used in advance neuro-critical care units throughout the world.  Although various studies have shown the physiologic feasibility of monitoring various neurologic parameters, there is still no published data from randomized trials to support that targeting any variable improves clinical outcome.  The authors concluded that although further research is needed to demonstrate the impact of MMM on improving clinical outcomes, their contribution to illuminate the black box of the brain in comatose patients is indisputable. 

Current literature on thermal perfusion probes has focused on their feasibility and technical capabilities.  Prospective clinical outcome studies are needed to determine their clinical value over other standard methods of identifying individuals at risk for secondary ischemic brain injury (e.g., head injury, subarachnoid hemorrhage, or following neurosurgery) and in monitoring response to therapies.


The above policy is based on the following references:

  1. Barth M, Capelle H-H, Münch E, et al. Effects of the selective endothelin A (ETA) receptor antagonist clazosentan on cerebral perfusion and cerebral oxygenation following severe subarachnoid hemorrhage – preliminary results from a randomized clinical series. Acta Neurochir (Wien) 2007;149(9):911-918.
  2. Bouma GJ, Muizelaar JP. Evaluation of regional cerebral blood flow in acute head injury by stable xenon-enhanced computerized tomography. Acta Neurochir Suppl (Wien). 1993;59:34-40.
  3. De Georgia MA, Deogaonkar A. Multimodal monitoring in the neurological intensive care unit. Neurologist. 2005;11(1):45-54.
  4. Haberl RL, Villringer A, Dirnagl U. Applicability of laser-Doppler flowmetry for cerebral blood flow monitoring in neurological intensive care. Acta Neurochir Suppl (Wien). 1993;59:64-68.
  5. Hemedex, Inc. Bowman Perfusion Monitor [website]. Cambridge, MA: Hemedex; 2002. Available at: Accessed March 9, 2005.
  6. Jaeger M, Soehle M, Schuhmann MU, et al. Correlation of continuously monitored regional cerebral blood flow and brain tissue oxygen. Acta Neurochir (Wien). 2005;147(1):51-56.
  7. Jagoda AS, Cantrill SV, Wears RL, et al. Clinical policy: Neuroimaging and decision making in adult mild traumatic brain injury in the acute setting. Ann Emerg Med. 2002;40:231-249.
  8. Rosenthal G, Sanchez-Mejia RO, et al. Incorporating a parenchymal thermal diffusion cerebral blood flow probe in bedside assessment of cerebral autoregulation and vasoreactivity in patients with severe traumatic brain injury. J Neurosurg. 2011;114(1):62-70.
  9. Steiner LA, Czosnyka M. Should we measure cerebral blood flow in head-injured patients? Br J Neurosurg. 2002;16(5):429-439.
  10. Tasneem N, Samaniego EA, Pieper C, et al. Brain multimodality monitoring: A new tool in neurocritical care of comatose patients. Crit Care Res Pract. 2017;2017:6097265.
  11. 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(3):402-411.
  12. U.S. Food and Drug Administration (FDA), Center for Devices and Radiologic Health (CDRH). QFlow 500 Perfusion Monitoring System. 510(k) Summary of Safety and Effectiveness. 510(k) No. K013376. Rockville, MD: FDA; May 8, 2002.
  13. Vajkoczy P, Horn P, Thome C, et al. Regional cerebral blood flow monitoring in the diagnosis of delayed ischemia following aneurysmal subarachnoid hemorrhage. J Neurosurg. 2003;98(6):1227-1234.
  14. Vajkoczy P, 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(2):265-274.