Trends in Ultrasound Use in Low and Middle Income Countries: A Systematic Review

1. Introduction

Ultrasonography is a clinically accepted imaging modality that enables a low-powered, mobile diagnostic pathway that can be readily learned by a variety of medical personnel to enable rapid assessment and treatment in a variety of settings. Ultrasonography devices are able to be used by a single-operator, handheld, and can provide diagnostic capabilities at a much lower cost than other imaging tools such as Computed Tomography (CT) or Magnetic Resonance Imaging (MRI). These characteristics make ultrasonography (otherwise referred to as ultrasound (US)) an attractive option for clinical use in low and middle income countries (LMICs) for both in-patient and out-patient use.

In 1997, the World Health Organization (WHO) estimated that 50% of the developing world did not have access to ultrasound imaging, and where it was available, equipment was outdated or broken.1 Technically trained maintenance for machine repair and the circulation of unregulated ultrasound equipment presented barriers to imaging access in metropolitan areas, in addition to the substantial lack of access to healthcare and imaging resources in rural areas. However, recognition of the potential advantages of ultrasound imaging in low resource settings has spurred the growth of ultrasound machine availability, diagnostic capability, trained technologists, educational and training programs, research and overall ultrasound utilization in LMICs.2

Despite this progress, there has been little recent literature on the applications of ultrasound in LMICs, including new uses for diagnosis and treatment adapted for medical challenges in low resource settings. We conducted a systematic review to determine recent trends in the utility and applicability of ultrasound use in LMICs. We aim to characterize and evaluate trends in (1) the geographic and specialty specific use of ultrasound in LMICs, (2) the novel applications of ultrasound imaging in low-resource settings and the accompanying research findings, and (3) the development of educational and training programs adapted for ultrasound use in LMICs.

2. Methods

We performed a systematic review of the literature with search strategy development assistance by a trained medical librarian (LO) at Baylor College of Medicine. Medline OVID, EMBASE, and Cochrane Clinical Trials were searched with the developed strategy for English, Spanish and French articles from 2010 to 2018. Low and middle income countries were selected by the World Bank definition and categorization in the year 2018; countries with low income economies and lower-middle economies were chosen for inclusion. Commentaries, opinion articles, reviews and book chapters were excluded. The last search was completed on April 4^th, 2019.

Two categories for study selection were created; (1) ‘applications of ultrasound,’ or all studies using ultrasound imaging technology in a medical context, and a sub-category, (2) ‘novel ultrasound research.’ Novel ultrasound research studies were selected from articles included in the first category, and were defined as involving novel application of ultrasound technology in a low resource setting, involving the use of a hand-held ultrasound probe, or including educational and training curriculum on ultrasound imaging in a low resource setting. For example, “Simplified rheumatic heart disease screening criteria for handheld echocardiography” was included as a novel study, but “Prevalence of rheumatic heart disease in Zambian school children” was not included as a novel study. Both were included in the systematic review of all ultrasound studies in LMICs.

Study selection was performed independently by three researchers (SN, GT and SK), discrepancies between reviewers were resolved by KS. Data extraction was performed using a standardized template by five researchers (SN, SL, GT, SK and RP) and reviewed by KS.

Data collected on all ultrasound studies include the year of publication, journal title, article title, country, and geographical region. Data collected on novel ultrasound studies include (in addition to the above) the hospital type (public vs. private), institution type (tertiary, district or primary care health center), study design, name of first and last author, institution of first and last author, and country of first and last author, application of ultrasound, medical specialty, type of ultrasound machine, skill level of provider, title of provider, descriptive findings of the study, and study outcomes (depending on study design). Novel ultrasound research articles that were randomized controlled trials were reviewed and graded according to the Cochrane Risk of Bias Tool.3 Data was aggregated and analyzed in Excel (Microsoft, Redmond, WA, USA). Statistical analysis was performed in SPSS (V. 21, IBM, Armonk, NY, USA).

This study was exempt from institutional review board approval. The review protocol has not been previously published or registered. We completed our review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

3. Results

Initial database search (after deduplication) yielded 6,276 articles (Figure 1). Abstracts were reviewed for inclusion, after which 1,713 studies were excluded for not reporting ultrasound use, describing non-clinical applications, or for studies not performed in an LMIC. An additional 287 articles were included in the novel research sub-category as defined above. Nine articles that met novel research criteria were excluded after the full-text was not available for review, with an additional 5 articles excluded for being research studies conducted in a military setting.

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Figure 1

PRISMA flow diagram

Novel: designates novel ultrasound research studies (n=287); Application: designates all applications of ultrasound studies included in review (n=3,888)

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Trends by year and geographical region of ultrasound use in LMICs for all studies and novel ultrasound studies are shown in Figures 2 and 3. The number of countries with reported ultrasound use has increased 24% since 2010 from 50 to 62 countries. The countries with the highest number of ultrasound studies included India (20%), Egypt (9.8%), Nigeria (8.8%), and Pakistan (7.3%). The specialties represented in all ultrasound studies included cardiology (25%), obstetrics and gynecology (14%). Other key specialties included gastroenterology (7.3%), pediatrics (5.8%), infectious disease (5.7%), internal medicine (6.2%), endocrinology (2.9%), and general surgery (3.5%). The most common journals of publication were the Indian Heart Journal (n=103), the Pan African Medical Journal (n=77), the Journal of Medical Case Reports (n=57), Mymensingh Medical Journal (n=53), Pakistan Journal of Medical Sciences (n=50), PLoS ONE (n=48), and BMC Research (n=44).

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Figure 2

Ultrasound studies in LMIC over time

Novel: designates novel ultrasound research studies; Application: designates all applications of ultrasound studies included in review

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Figure 3

Ultrasound studies in LMIC by geographical region

Novel: designates novel usage of ultrasound studies; Application: designates all non-novel application of ultrasound studies included in review

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Of the 287 novel ultrasound application studies, 48% were prospective studies, 13% qualitative, 12% retrospective, 11% cross-sectional studies, 8% case reports, 5% randomized controlled trials, and 1.0% case-controls. Studies were largely performed at public hospitals (86%), of which 59% were conducted at tertiary hospitals and 41% were carried out in a primary care or rural setting. Novel research studies in the form of RCTs are shown in Table 1.

The novel applications of ultrasound technology in novel studies was primarily for screening (26%) and obstetrical use (34%), however, key applications also included infectious disease (10%), cardiology (9%), abdominal conditions (8%), trauma (8%), and gynecologic conditions (3%). Ultrasound imaging providers in novel studies included physicians (85%), midwives (7%), residents (3%), community health workers (2%), and ultrasound technicians (2%). Hand-held ultrasound devices were used in 28% (n=47) of novel studies. The most common journals of publication for novel ultrasound research include the Journal of Ultrasound in Medicine (n=12), BMC Pregnancy and Childbirth (n=7), Critical Ultrasound Research (n=7), PLoS ONE (n=6), Egyptian Journal of Radiology and Nuclear Medicine (n=5), the Egyptian Journal of Chest Diseases and Tuberculosis (n=5), and the American Journal of Tropical Medicine and Hygiene (n=5).

Global collaboration, defined as the inclusion of at least one author whose listed publication affiliation was within the country in which the novel ultrasound study was conducted, was present in 70% of studies. The majority of studies that involved global collaboration occurred in India (n=22), Uganda (n=22), Nigeria (n=15) and Tanzania (n=15). Of first authors, 67% were from the country of ultrasound study, of last authors, 60% were from the country of ultrasound study. A total of 75 papers (26%) included both a first and last author from the country of ultrasound study, including 18 from India and 14 from Nigeria. Thirty one percent of novel ultrasound research was funded (n=91), including by NIH grants, the Bill and Melinda Gates Foundation, the General Electric (GE) Foundation, and European foundation grant funding. The countries with the most number of studies with funding were Uganda (n=13), Tanzania (n=10), and Rwanda (n=6). Using the Cochrane risk of bias tool, 70% of the studies reviewed were characterized of having more than one categorized medium and high risk of bias for at least one ‘Risk of Bias’ category.

Sixty eight percent of novel research studies (n=196) contained an educational or training component on ultrasound imaging. Of those educational studies, 91 (46.4%) occurred in the sub-Saharan geographical region, including a majority in Uganda (n=20), Nigeria (17), and Tanzania (n=9). Details of educational studies with funding and known ultrasound, including a description of the training program or curriculum, are shown in Table 2. The number of annual educational ultrasound studies has increased to nearly 2.9 times the amount from 2010 to 2018 (from 14 to 40 per year).

4. Discussion

5. Conclusion and Global Health Implications

In conclusion, this literature review focused on ultrasound trends and usage in LMICs. With the decreasing cost of ultrasound equipment and increasing availability of handheld ultrasound devices, it is important to continue assessment of the adoption and effective novel application of ultrasound technology in LMICs. Furthermore, there is a pressing need to address the potential capabilities and delineate limitations of ultrasound within resource limited settings. We found evidence of the role of educational training programs increasing screening and diagnostic clinical decision making. We also found the increasing adoption of ultrasound technology globally.