Noninvasive ICP measurement methods

Measurement of intraocular and intracranial pressure: Is there a relationship?

Authors: Kirk T, Jones K, Miller S, Corbett J.

OBJECTIVE: To study whether noninvasive, intraocular pressure (IOP) measurements significantly correlate with standard intracranial pressure (ICP) measurements.

METHODS: This prospective, blinded study enrolled 46 patients who were undergoing medically indicated lumbar puncture (LP). IOP was measured by applanation tonometry immediately prior to measuring LP opening pressure. One patient was excluded due to unsuccessful ICP measurement.

RESULTS: In the 45 patients to successfully undergo IOP and ICP measurement, there was no significant relationship between ICP and average IOP for both eyes (r = -0.005). There was no significant relationship between ICP and IOP in either eye, when studied individually(r = 0.03 ocular dexter , r = -0.05 ocular sinister ). There was no significant relationship between ICP and IOP when the eye best correlated to the patient's ICP was chosen (r = -0.01).

INTERPRETATION: No significant relationship between ICP and IOP was observed. Noninvasive IOP measurements do not predict ICP.ANN NEUROL 2011;

Intracranial pressure: why we monitor it, how to monitor it, what to do with the number and what’s the future?

Authors: Andrea Lavinio and David K. Menon.

Improved ICP probes, antibiotic-impregnated ventricular catheters and multimodality, computerized systems allow ICP monitoring and individualized optimization of brain physiology. Noninvasive technologies for ICP and cerebral perfusion pressure assessment are being tested in the clinical arena. Computerized morphological analysis of the ICP pulse-waveform can provide an indicator of global cerebral perfusion.

Noninvasive intracranial compliance from MRI-based measurements of transcranial blood and CSF flows: indirect versus direct approach

Authors: Tain RW, Alperin N.

Intracranial compliance (ICC) determines the ability of the intracranial compartment to accommodate an increase in volume without a large increase in intracranial pressure (ICP). The clinical utilization of ICC is limited by the invasiveness of current measurement. Several investigators attempted to estimate ICC noninvasively, from magnetic resonance imaging (MRI) measurements of cerebral blood and cerebral spinal fluid flows, either using indirect measures of ICC or directly by measuring the ratio of the changes in intracranial volume and pressure during the cardiac cycle. The indirect measures include the phase lag between the cerebrospinal fluid (CSF) and its driving force, either arterial inflow or net transcranial blood flow. This study compares the sensitivity of phase-based and amplitude-based measures of ICC to changes in ICC. In vivo volumetric blood and CSF flows measured by MRI phase contrast from healthy volunteers and from patients with elevated ICP were used for the comparison. An RLC circuit model of the craniospinal system was utilized to simulate the effect of a change in ICC on the CSF flow waveform. The simulations demonstrated that amplitude-based measures of ICC are considerably more sensitive than phase-based measures, and among the amplitude-based measures, the ICC index provides the most reliable estimate of ICC.

Improved noninvasive intracranial pressure assessment with nonlinear kernel regression

Authors: Peng Xu, Magdalena Kasprowicz, Marvin Bergsneider, Xiao Hu

The only established technique for intracranial pressure (ICP) measurement is an invasive procedure requiring surgically penetrating the skull for placing pressure sensors. However, there are many clinical scenarios where a noninvasive assessment of ICP is highly desirable. With an assumption of a linear relationship among arterial blood pressure (ABP), ICP, and flow velocity (FV) of major cerebral arteries, an approach has been previously developed to estimate ICP noninvasively, the core of which is the linear estimation of the coefficients f between ABP and ICP from the coefficients w calculated between ABP and FV. In this paper, motivated by the fact that the relationships among these three signals are so complex that simple linear models may be not adequate to depict the relationship between these two coefficients, i.e., f and w , we investigate the adoption of several nonlinear kernel regression approaches, including kernel spectral regression (KSR) and support vector machine (SVM) to improve the original linear ICP estimation approach. The ICP estimation results on a dataset consisting of 446 entries from 23 patients show that the mean ICP error by the nonlinear approaches can be reduced to below 6.0 mmHg compared to 6.7 mmHg of the original approach. The statistical test also demonstrates that the ICP error by the proposed nonlinear kernel approaches is statistically smaller than that estimated with the original linear model (p < 0.05). The current result confirms the potential of using nonlinear regression to achieve more accurate noninvasive ICP assessment.

Using MRI of the optic nerve sheath to detect elevated intracranial pressure

Authors: Heidi Harbison Kimberly and Vicki E Noble

The current gold standard for the diagnosis of elevated intracranial pressure (ICP) remains invasive monitoring. Given that invasive monitoring is not always available or clinically feasible, there is growing interest in non-invasive methods of assessing ICP using diagnostic modalities such as ultrasound or magnetic resonance imaging (MRI). Increased ICP is transmitted through the cerebrospinal fluid surrounding the optic nerve, causing distention of the optic nerve sheath diameter (ONSD). In this issue of Critical Care, Geeraerts and colleagues describe a non-invasive method of diagnosing elevated ICP using MRI to measure the ONSD. They report a positive correlation between measurements of the ONSD on MRI and invasive ICP measurements. If the findings of this study can be replicated in larger populations, this technique may be a useful non-invasive screening test for elevated ICP in select populations.

Noninvasive Monitoring of Intracranial Pressure

Authors: Djordje Popovic1,3,*, Michael Khoo1 and Stefan Lee 2

(1Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, CA, 2 Department of Neurosurgery, Keck School of Medicine, University of Southern California, Los Angeles, CA, 3 Advanced Brain Monitoring Inc., Carlsbad, CA)

Recent Patents on Biomedical Engineering 2009, 2, 165-179
Received: April 29, 2009; Accepted: May 6, 2009; Revised: May 9, 2009

Increased intracranial pressure (ICP) is one of the major causes of secondary brain ischemia that accompanies a variety of pathological conditions, most notably, traumatic brain injury (TBI), stroke, and intracranial hemorrhages. However, aside from a few Level I trauma centers, ICP monitoring is rarely a part of the clinical management of patients with these conditions because of the invasiveness of the standard monitoring methods (which require insertion of a catheter into the cranium), additional risks they present for patients, high costs associated with the procedure, and the limited access to trained personnel, i.e., a neurosurgeon. Alternative methods have therefore been sought with which ICP can be measured noninvasively. This article reviews nearly 30 such methods patented over the past 25 years, which included ultrasound “time-of-flight” techniques, transcranial Doppler, methods based on acoustic properties of the cranial bones, EEG, MRI, tympanic membrane displacement, oto-acoustic emission, ophthalmodynamometry, and ultrasound measurements of optic nerve sheath diameter. At present, none of the methods is sufficiently accurate to allow for routine clinical use although several hold promise. Future developments should integrate further refinements of the existing methods, combined use of multiple sensors and/or technologies, and large clinical validation studies on relevant populations.  


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