Estimating the accuracy of optic nerve sheath diameter measurement using a pocket-sized, handheld ultrasound on a simulation model

Non-Invasive Intracranial Pressure Monitoring

(1) Background: Intracranial pressure (ICP) monitoring plays a key role in the treatment of patients in intensive care units, as well as during long-term surgeries and interventions. The gold standard is invasive measurement and monitoring via ventricular drainage or a parenchymal probe. In recent decades, numerous methods for non-invasive measurement have been evaluated but none have become established in routine clinical practice. The aim of this study was to reflect on the current state of research and shed light on relevant techniques for future clinical application. (2) Methods: We performed a PubMed search for “non-invasive AND ICP AND (measurement OR monitoring)” and identified 306 results. On the basis of these search results, we conducted an in-depth source analysis to identify additional methods. Studies were analyzed for design, patient type (e.g., infants, adults, and shunt patients), statistical evaluation (correlation, accuracy, and reliability), number of included measurements, and statistical assessment of accuracy and reliability. (3) Results: MRI-ICP and two-depth Doppler showed the most potential (and were the most complex methods). Tympanic membrane temperature, diffuse correlation spectroscopy, natural resonance frequency, and retinal vein approaches were also promising. (4) Conclusions: To date, no convincing evidence supports the use of a particular method for non-invasive intracranial pressure measurement. However, many new approaches are under development.

Construct Validity and Reproducibility of Handheld Ultrasound Devices in Carotid Artery Diameter Measurement

The construct validity and reproducibility of three commonly used handheld ultrasound (US) devices in measuring carotid arterial diameter was evaluated: Telemed MicrUs EXT-1H (Telemed, Vilnius, Lithuania), Butterfly iQ (Butterfly Network, Inc., Guilford, CT, USA) and Philips Lumify (Philips Healthcare, Best, The Netherlands). An in vitro setup was built to evaluate construct validity, compared with high-end US, and intra-observer variability of handheld US devices. Handheld devices showed a mean difference of 0.023 ± 0.030 cm, 0.012 ± 0.037 cm and 0.009 ± 0.046 cm for, respectively, Telemed, Butterfly and Lumify in comparison with high-end US devices. Intraclass agreement with the high-end system as well as intra-observer variability for handheld US devices was classified as excellent, with all values greater than 0.95. Subsequently, inter-observer variability of handheld US devices was investigated in an in vivo setup with 20 healthy volunteers. Inter-observer variability was classified as excellent for Telemed (0.901), good for Lumify (0.827) and moderate for Butterfly (0.684) with a difference of, respectively, 0.005 ± 0.031 cm, 0.020 ± 0.050 cm and -0.003 ± 0.033 cm. In conclusion, handheld US devices demonstrated an excellent construct validity and intra-observer variability. Additionally, excellent-to-good inter-observer variability for Telemed and Lumify was observed, and Butterfly demonstrated a moderate inter-observer agreement. These results indicate that handheld US devices are effective for measuring carotid arterial diameter.

Accuracy of Optic Nerve Sheath Diameter Measurements in Pocket-Sized Ultrasound Devices in a Simulation Model

Introduction

Transorbital sonographic measurement of optic nerve sheath diameter (ONSD) is an emerging non-invasive technique for the identification and monitoring of intracranial hypertension. In recent years, new pocket ultrasound devices have become available, and it is uncertain if they have the resolution to measure such small structures appropriately as compared to their predecessors. In this study, we measure the performance of three ultrasound units on a simulation model to establish their precision and accuracy.

Methods

ONSD was measured by three expert point-of-care sonographers using ultrasound machines three times on each of seven discrete ONS model sizes ranging from 3.5 to 7.9 mm. Two pocket ultrasounds (IVIZ, Sonosite, and Lumify, Philips) and one standard-sized portable ultrasound (M-Turbo, Sonosite) were used. Measurements were analyzed for mean error and variance and tested for significance using blocked covariance matrix regression analyses.

Results

The devices differed in their variances (Lumify: 0.19 mm², M-Turbo: 0.26 mm², IVIZ: 0.34 mm²) and their mean error (Lumify: -0.05 mm, M-Turbo: 0.10 mm, IVIZ: -0.10 mm). The difference in mean error between users is not significant (p = 0.45), but there is a significant difference in mean error between devices (p = 0.02).

Conclusions

Accurate ONSD measurement is possible utilizing pocket-sized ultrasound, and in some cases, may be more accurate than larger portable ultrasound units. While the differences in these devices were statistically significant, all three were highly accurate, with one pocket device (Lumify) outperforming the rest. Further study in human subjects should be conducted prior to using pocket ultrasound devices for in vivo diagnosis of intracranial hypertension.

Interrater reliability of emergency medicine residents in measurement of optic nerve sheath diameter with computed tomography

OBJECTIVES:

Many studies have recently been conducted on measuring optic nerve sheath diameter (ONSD) with computed tomography (CT). However, no studies focused on the interrater reliability in ONSD measurements with CT yet. Our first aim was to investigate the interrater reliability of the emergency medicine residents in the measurement of the ONSD with CT. Our secondary aim was to evaluate the interrater reliability and agreement of the emergency medicine residents and neuroradiologist measurements, which is the gold standard.

METHODS:

Twelve residents (six seniors and six juniors) and a neuroradiologist measured ONSD in twenty different CTs in axial and sagittal planes. The interrater reliability was calculated by the intraclass correlation coefficient (ICC), and the level of agreement in categorical variables was calculated by kappa (ĸ) analysis.

RESULTS:

We found that the interrater reliability level of all residents was “good” (ICC: 0.824), for seniors was “good” (ICC: 0.824), and for juniors was “moderate” (ICC: 0.748) in the measurement of ONSD. ICC was 0.812 for axial, and 0.783 for sagittal plane measurements. The interrater reliability between residents and the neuroradiologist measurements was “good” (ICC 0.891), and the agreement was found to be “good” (ĸ: 0.688; P < 0.001). The sensitivity of residents in detecting increased ONSD was 78%, and specificity was 90.8%.

CONCLUSION:

The ONSD measurements with CT performed by the residents are reliable in themselves, and they are compatible with the gold standard measurements.

A New Inexpensive Simulation Model for Ultrasound Assessment of Optic Nerve Sheath Diameter

BACKGROUND

Sonographic measurement of optic nerve sheath diameter (ONSD) is becoming increasingly accepted as a diagnostic modality to detect elevations in intracranial pressure. As this technique becomes more widespread, methods to address the inherent operator-dependent nature of this modality will need to be developed. We propose a novel low-cost model to accurately simulate sonographic ONSD measurement for purposes of training and assessment.

METHODS

We designed models composed of medical tubing of various diameters readily available from typical hospital supplies and suspended them in gelatin. The models were evaluated by ultrasound by three expert point-of-care sonographers using a standard linear array probe and technique proposed in the literature.

RESULTS

This model generates faithful simulation of the ONS that closely approximates in vivo images and can be used to produce accurate, reproducible measurements. Materials are low cost and easy to acquire and assemble.

CONCLUSIONS

Our model provides realistic simulated images of the ONS. Through comparison of sonographic measurements to the known tube diameters, this model serves as a promising inexpensive tool to teach the method of ultrasound assessment of ONSD or as a way to determine accuracy of this novel ultrasound technology.

ESR statement on portable ultrasound devices

The use of portable ultrasound (US) devices has increased in recent years and the market has been flourishing. Portable US devices can be subdivided into three groups: laptop-associated devices, hand-carried US, and handheld US devices. Almost all companies we investigated offer at least one portable US device. Portable US can also be associated with the use of different US techniques such as colour Doppler US and pulse wave (PW)-Doppler. Laptop systems will also be available with contrast-enhanced US and high-end cardiac functionality.

Portable US devices are effective in the hands of experienced examiners. Imaging quality is predictably inferior to so-called high-end devices.

The present paper is focused on portable US devices and clinical applications describing their possible use in different organs and clinical settings, keeping in mind that patient safety must never be compromised. Hence, portable devices must undergo the same decontamination assessment and protocols as the standard equipment, especially smartphones and tablets.

Assessment of peripheral muscle thickness and architecture in healthy volunteers using hand-held ultrasound devices; a comparison study with standard ultrasound

BACKGROUND

Pocket-sized ultrasound devices are increasingly used in a variety of clinical situations, and perform well against standard ultrasound machines. We sought to investigate if a pocket-sized ultrasound device can assess muscle thickness and architecture in healthy volunteers.

METHODS

Healthy male volunteers (n = 21) across a range of ages were recruited to the study. Laying supine, ultrasound images were taken from the right anterior and lateral thigh. Thickness of the rectus femoris (RFMT), vastus intermedius (VIMT), and the two combined (anterior thigh, AMT) were measured, along with thickness of vastus lateralis (VLMT), pennation angle (VLPA) and derived fascicle length (VLFL). These scans were performed initially using a pocket-sized ultrasound (VScan) and then using a standard device (Telemed Echoblaster 128).

RESULTS

In all six variables, there was no significant difference between the two sets of measurements. Intra-class correlation co-efficients (ICC) for VLMT, VLPA, and AMT were all excellent (0.93, 0.89, 0.90 respectively) with the derived value of VLFL having an ICC of 0.84. All ICC values were statistically significant. Regression analysis demonstrated no evidence of proportional bias in any of the measured or derived variables.

CONCLUSION

A pocket-sized ultrasound device gives similar measurements of lower limb muscle thickness and architecture as a standard device in healthy volunteers.

Validity and reliability of pocket-sized ultrasound devices in measurement of optic nerve sheath diameter in ICU patients

The measurement of the optic nerve sheath diameter (ONSD) by ultrasonography (USG) is particularly important for intracranial pressure (ICP) monitoring when invasive measurements are not possible or are contraindicated. Standard USG (SUDs) devices can be bulky and may break down the workflow. The validity and reliability of pocket-sized USG devices (PSUDs) compared to SUDs for ONSD measurement has not been investigated, yet. We compared the reliability and validity of PSUDs with SUDs for ONSD measurement. 35 patients were included in the study. ONSD measurements with PSUDs and SUDs were performed by two clinicians as three different measurements in both sagittal and transverse axis of the eye. There was agreement between mean transverse ONSD (mtONSD), mean sagittal ONSD (msONSD), and mean ONSD(mONSD) values measured with each device according to Bland-Altman test (p = 0.166, p = 0.135, p = 0.066, respectively) with no proportional bias (p = 0.544, p = 0.868, p = 0.929, respectively). Intraclass correlation coefficients (ICC) were found to be greater than 0.7 for mtONSD, msONSD, and mONSD values measured by SUD (ICC = 0.790, ICC = 0.817, and ICC = 0.844, respectively). Similarly, for mtONSD, msONSD, and mONSD values measured by PSUD, ICC were found greater than 0.7 (ICC = 0.763, ICC = 0.814, and ICC = 0.843, respectively). There was no statistically significant difference between mtONSD and msONSD (p = 0.441 for SUD and p = 0.893 for PSUD). There was a good correlation between mtONSD and msONSD (r = 0.767 for SUD and r = 0.816 for PSUD). The total variance between three different measurements in the transverse and sagittal axis was ± 0.6 mm. PSUDs can be used with similar validity and reliability as SUDs for ONSD measurement.

Automatic Estimation of the Optic Nerve Sheath Diameter from Ultrasound Images

We present an algorithm to automatically estimate the diameter of the optic nerve sheath from ocular ultrasound images. The optic nerve sheath diameter provides a proxy for measuring intracranial pressure, a life threating condition frequently associated with head trauma. Early treatment of elevated intracranial pressures greatly improves outcomes and drastically reduces the mortality rate. We demonstrate that the proposed algorithm combined with a portable ultrasound device presents a viable path for early detection of elevated intracranial pressure in remote locations and without access to trained medical imaging experts.

New Optic Nerve Sonography Quality Criteria in the Diagnostic Evaluation of Traumatic Brain Injury

Background

New sonographic quality criteria to optimize optic nerve sheath diameter (ONSD) measurements were suggested. The latter were correlated to elevated intracranial pressure (ICP) in traumatic brain injury (TBI).

Aim

We investigated whether ONSD measurements were correlated to simultaneous ICP measurements in severe TBI.

Methods

Forty patients with severe TBI (Marshall Scale ≥II and GCS ≤8) participated in the study. All patients had an intraparenchymal ICP catheter inserted, while ONSD was measured bilaterally, upon admission and over the next 48 hours, based on the new sonographic criteria. A total of 400 ONSD measurements were performed, while mean ONSD values of both eyes were used in the analysis.

Results

ONSD measurements were strongly correlated to ICP values (r=0.74, p < 0.0001). Receiver operator curve (ROC) analysis revealed that the ONSD cutoff value for predicting elevated ICP was 6.4 mm when using the mean of both eyes (AUC = 0.88, 95% CI = 0.80 to 0.95; sensitivity = 85.3%, specificity = 82.6%). Linear regression analysis nested models revealed that sex (p=0.006) and height (p=0.04) were significant predictors of ONSD values.

Conclusion

When applying the new sonographic quality criteria, ONSD is strongly correlated to ICP in severe TBI. Whether to use such criteria to monitor ONSD as a proxy for ICP trend in TBI remains to be further explored.