Exploring the Intersection of Sex and Race Within Transcranial Doppler Sonography: Implications for Future Neuroergonomic Research and Application

Abstract

Transcranial Doppler Sonography (TCD) employs ultrasound to measure cerebral blood flow velocity for medical diagnostics and research. Unfortunately, certain groups experience disproportionately higher TCD failure rates than others, impacting their representation in healthcare and research. To delve into the factors influencing successful TCD application, particularly across different sexes and racial populations, a literature review was conducted. It emerged that factors such as bone density and headset design contribute to these disparities. For example, minority women, on average had comparatively denser temporal windows, consequently facing elevated failure rates in comparison to other groups. Moreover, TCD headset designs often overlook accommodating diverse hairstyles, especially those prevalent in Black communities. While addressing bone density of the transtemporal window is a deeper biomedical engineering issue of the TCD, designers should build upon the insights highlighted in this paper to create a more inclusive TCD that can safely adapt to varying bone density.

Objectives

Transcranial Doppler Sonography ultrasound (TCD) is a non-invasive tool that uses ultrasound signals to measure cerebral blood flow velocity (CBFV) in the major arteries of the brain (Aaslid et al., 1982; Tripp et al., 2006). For human factors research, CBFV is used as a real-time, objective measure of workload and fatigue associated with a task. In medical settings, TCD is a diagnostic tool for the identification of afflictions such as stenosis and cerebral hemorrhages (Brunser et al., 2012; Pan et al., 2022). Given the value of TCD for human factors research and medical applications, it is vital that TCD be accessible and applicable to any population.

Unfortunately, some groups are more likely to be excluded from the benefits of TCD than others. TCD requires a technician to locate and insonate a target artery using an ultrasound probe (Aaslid et al., 1982). This calibration procedure is not always successful, meaning that measurement of CBFV is sometimes impossible or of poor quality—even when performed by a well-trained TCD technician. Research suggests that the likelihood of these calibration failures may be governed, in part, by the race and sex of the individual on whom TCD is applied (Marinoni et al., 1997).

To start, TCD failures occur for about 13% of the Caucasian male population. Caucasian women experience comparatively higher failure rates at approximately 18%. However, within Black and Asian populations, successful applications of the TCD fall further. In a study examining the success rates of middle cerebral artery insonation among Japanese patients, a failure rate of approximately 12.9% was observed for Japanese men (Itoh et al., 1993). Black American men experience a failure rate of approximately 23% (Halsey, 1990). Women in both of those racial groups experienced far higher rates of failure than their male counterparts; approximately 39.3% in Japanese women and 50% of Black American women experienced insonation failure. These are far larger numbers that unfortunately limit the representation of these populations within research studies.

In this vein, neuroergonomics research relying on the TCD may not accurately translate findings and recommendations that benefit these racial and sex groups.

In addition, given that many of these studies already take place within universities, overrepresentation of Caucasian populations is expected to a degree (Ellsworth et al., 2022). Lack of accurate representation within research is a disservice to the populations with which these studies hope to aid. This in tandem with failure rates of artery insonation, further alienates certain groups from benefiting from the recommendations and discoveries these studies provide.

Given the risks these overlooked populations face because of comparatively higher failure rates in insonating cerebral arteries, it is important to understand why these populations experience such high rates of application failure. By understanding why, possible future steps can be taken to improve the overall representation within TCD literature. This paper aims to describe potential reasons why certain populations experience high rates of application failure in comparison to other groups. Lastly, this critique aims to provide a detailed discussion on race/ethnicity and sex in relation to the Transcranial Doppler Sonography, as well as present potential recommendations toward improving upon the design of the TCD to widen applicability.

Approach

A literature review was conducted to investigate the factors influencing successful transcranial Doppler (TCD) insonation, particularly focusing on different racial populations and considering the intersection of sex. This review aimed to gain insights into the determinants of successful TCD insonation and to identify any research gaps in the existing literature. The primary objective was to identify common factors influencing successful insonation rates and discuss recommendations based on the findings. Additionally, insights from researchers experienced in using TCD were also explored to uncover any information not currently addressed in TCD-related literature.

Findings

Existing research on bone density within the transtemporal window was explored to pinpoint potential factors affecting the success rates of insonation in specific populations. The transtemporal window is an acoustic window in the skull characterized by thinner bone density compared to other regions of the skull. Its proximity to the middle cerebral artery (MCA) facilitates easier access for ultrasound imaging (Tripp et al., 2006). As a result, a narrow transtemporal window or relatively high bone density in this area leads to lower insonation success. Variations in bone density within the transtemporal window can be influenced by sex and race (Baumgartner, 2006; Marinoni et al., 1997). Given their comparatively high rates of insonation failure, it is unsurprising that Black women display the highest average bone density in this region while Caucasian men exhibit the lowest.

Focusing on the realm of research, most neuroergonomics studies using TCD require the use of a TCD headset so participants can attend to their tasks relatively unobstructed. While there are different types of TCD headsets, most headset designs do not allow for thicker hair types or styles. For example, the rear of many TCD headsets must rest near the occipital bone. If a participant arrives with thick hair or large hairstyles that block this kind of placement, TCD setup may be impossible. Certain populations, such as Black communities, may be more likely to wear hairstyles that can be deemed challenging for headset placement (Joseph et. al., 2024). Examples of such hairstyles include box braids, dreadlocks, crochet braids/twists, etc. Consequently, headset design is another potential cause of demographic disparity in the likelihood of TCD failure.

Takeaways

Short-term approaches to addressing transtemporal window challenges involve boosting ultrasound signal strength to enhance MCA insonation success. However, while this may offer a temporary solution, it can lead to adverse effects on participants, including persistent discomfort after use (Halsey, 1990). Unfortunately, accounting for the bone density of the transtemporal window is a deeper biomedical engineering issue of the TCD, but designers should build upon the insights highlighted in this paper to create a more inclusive TCD that can safely adapt to varying bone density.

In terms of headset design, there is little information available on redesigning TCD hardware to fit the hair types and styles of wider populations. However, efforts have already been made to enhance TCD headset designs for use in infants and individuals with head sizes outside the acceptable range (Watt, 2012). As such, creating headsets that cater to a wider variety of participants’ hair types/styles is well within the realm of possibility.

In conclusion, this paper emphasizes the importance of integrating intersectionality into the design of the TCD. Acknowledging the necessity for a nuanced and inclusive methodological approach, we suggest that future studies examining this subject embrace participatory design. This approach aligns the interests of designers, stakeholders, and marginalized groups in the design process, offering a promising avenue for the success of marginalized populations in utilizing future TCD designs.