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HIFU is one of the most important representative technologies in minimally invasive medicine. By delivering ultrasound energy externally and precisely focusing it on internal lesions, HIFU directly ablates pathological tissue through thermal or cavitation effects. This technique offers true non-invasiveness, high precision, and a favorable safety profile. In 1942, American scientist Frank Fry proposed the theoretical foundation for HIFU (; ; ). However, technological breakthroughs remained elusive. In the 1990s, Professor Zhibiao Wang of Chongqing Medical University developed, in China, the world's first HIFU system for tumor treatment; its successful use in treating patients with bone tumors marked a major breakthrough in HIFU technology (, ). Subsequently, major global economies accelerated the development and application of HIFU, and related publications increased substantially. To objectively present the global distribution of HIFU research, this study analyzes HIFU-related publications using bibliometric methods.

The Web of Science Core Collection database (WoS) indexes high-quality international scientific literature and provides not only numerous HIFU-related journal articles but also complete bibliographic and citation information for journals and articles (). For bibliometric analysis, the WoS database can automatically generate files in BibTeX format that can be readily recognized by bibliometric software. Therefore, WoS was selected as the data source for this study ().

As shown in , First, HIFU-related subject terms were selected as search terms and then combined using the Boolean operators “AND” and “OR.” The combined search strategy was as follows: TS = (“HIFU” OR “high-intensity focused ultrasound”) AND PY = (1994–2024). The search was conducted on August 10, 2025, and covered publications from 1994 to 2024. Through this process, 5,899 records were obtained. Second, the literature screening process was performed in accordance with the PRISMA 2020 statement. Initially, 5,899 records were retrieved from the Web of Science Core Collection. After 300 duplicates were removed, 5,599 unique records were screened based on their titles and abstracts. Among these records, 750 were excluded because they addressed irrelevant topics, were classified as non-research documents, or lacked key information. The remaining 4,849 records were assessed for eligibility through full-text review, and no further records were excluded at this stage. Finally, 4,849 studies were included in the bibliometric analysis. Third, the filtered data were imported into bibliometric software for analysis. Finally, the analytical results were summarized, and the current shortcomings, challenges faced by HIFU, and future research directions were presented.

The Category Normalized Citation Impact (CNCI) is a normalized metric that measures the citation impact of a paper or research entity; it accounts for differences in discipline, publication date, and document type. The CNCI is scaled such that 1 serves as the baseline. A CNCI greater than 1 indicates that the citation performance of a paper or research entity exceeds the global average, the higher the value, the greater the citation impact. A CNCI equal to 1 indicates that the citation performance is on par with the global average. A CNCI less than 1 indicates that the citation performance falls below the global average, suggesting relatively limited academic impact ().

The Collaboration Category Normalized Citation Impact (Collab-CNCI) is an extended bibliometric indicator introduced by Clarivate's Institute for Scientific Information (ISI) in 2020. It builds on the standard CNCI by adding a fourth normalization layer for collaboration type, including domestic single-country collaboration, domestic multi-institutional collaboration, and international bilateral, trilateral, and quadrilateral-or-higher collaboration, eliminating the bias of varying collaboration patterns on citation performance. A Collab-CNCI value of 1 represents the global average citation impact for publications in the same subject category, publication year, document type, and collaboration type. Values greater than 1 indicate above-average citation impact within the same collaboration type, whereas values less than 1 indicate below-average citation impact.

This study uses patent citations as an indicator of technological influence. This metric counts the total number of times publications associated with a given entity are cited in patents, effectively measuring the technological impact, industry recognition, and commercialization value of research outcomes. It thereby addresses the limitations of evaluating research output solely based on the number of published papers (). All relevant raw data were sourced from the InCites database, with the search period, strategy, and field-specific paper data kept consistent throughout the study. Regarding sample selection, at the national and institutional levels, the top ten entities worldwide in terms of HIFU-related paper output were selected as the research subjects. As these entities also rank among the top in the field in terms of patent citation counts, this approach ensures both sample representativeness and analytical consistency. However, at the author level, given the weak correlation between publication output and patent citation counts, as well as the asynchronous development patterns of these two metrics, this study did not adopt a ranking based on publication volume. Instead, patent citation counts were directly calculated for core authors in the field to objectively reflect differences in research orientation among scholars.

, the publication trend chart, illustrates the evolution of global research output in the field of HIFU from 1994 to 2024, clearly revealing the developmental trajectory and dynamic trends of this research domain. From 1994 to 2002, HIFU research output increased slowly, with an average of 21 publications per year. In 1994, only three papers were published. Although there was a slight increase in the following years, the annual number of publications reached only 29 in 2002. From 2003 onward, the publication volume showed a more pronounced upward trend. In 2003, 49 papers were published, and the annual publication count continued to increase, reaching 159 in 2007 and marking the first peak. In 2008, the number of publications declined slightly to 137, compared with 159 in 2007. However, from 2008 to 2012, the number of publications increased rapidly, reaching 263 articles in 2012 and forming a second peak. From 2013 to 2024, the annual publication volume remained generally high and rose steadily, despite some fluctuations, reaching 304 articles in 2024.

Based on regional publication data from InCites, this study analyzes key metrics in the HIFU field, including Web of Science publication volume, citation counts, and CNCI values, to examine the global distribution of HIFU research. As shown in , larger nodes in the VOSviewer diagram indicate higher publication volumes, with the United States, China, and France representing the main contributing countries in HIFU research. As shown in , the United States ranks first with 1,325 publications, followed by mainland China with 1,150 and France with 504. In terms of citations, the United States ranks first with 36,220 citations (27.34 citations per paper, 88.60% of total citations). Mainland China ranks second with 21,724 citations (18.89 citations per paper, 85.48%), while the United Kingdom ranks third with 16,505 citations (40.16 citations per paper, 90.27%). The CNCI value based on a single paper or a very small number of papers is insufficient to assess research impact; therefore, this study focuses on the top ten countries ranked by publication volume to evaluate their field-normalized citation impact. England has the highest CNCI value (1.45), followed by the Netherlands (1.40) and the United Kingdom (1.39). As for Collab-CNCI, England has the highest Collab-CNCI value (1.25), followed by the United Kingdom (1.19) and the Netherlands (1.13).

Using the number of patent citations as a measurement indicator, as shown in , among the top 10 countries by publication volume, the United States ranks first in patent citations in the HIFU field, with a total of 1,731 citations, followed by France with 405 citations. The United Kingdom ranks third, with 239 citations. These results suggest that the United States, France, and the United Kingdom place greater emphasis on technological innovation and the translational application of HIFU research outcomes.

In the field of HIFU, a total of 1,604 institutions contributed to publications between 1994 and 2024. The institutional distribution is illustrated in , in which larger nodes represent institutions with higher publication volumes, including Chongqing Medical University in China, Inserm in France, and the University of Washington in the United States.

The collaboration network diagram reveals that Chongqing Medical University's partnerships are predominantly domestic, encompassing institutions such as Chongqing Haifu Hospital, the Chinese Academy of Sciences, Shanghai Jiao Tong University, and Zhejiang University. Internationally, it maintains close collaborative relationships with the University of Washington and Stanford University in the United States, as well as with the University of Oxford in the United Kingdom. The University of Washington has an even more extensive international collaboration network, encompassing Chongqing Medical University, the University of Tokyo in Japan, Inserm in France, Lomonosov Moscow State University, Cancer Research UK, and Philips in the Netherlands. In contrast, Inserm in France maintains a more limited network of international collaborations, partnering with Shanghai Jiao Tong University in China, the University of Washington, the University of Michigan, Lomonosov Moscow State University, and Cancer Research UK. The University of London's partner institutions are primarily based in the United Kingdom and include Imperial College London, Cancer Research UK, and the National Physical Laboratory. Its international partners include the University Medical Center Utrecht in the Netherlands and the University of Michigan in the United States.

As shown in , in terms of publication volume, Chongqing Medical University ranked first with 328 publications, followed by the Institut National de la Santé et de la Recherche Médicale (Inserm) with 249 publications. The University of Washington Seattle and the University of Washington tied for third place, with 203 publications each. In terms of citation count, Chongqing Medical University also ranked first, with a total of 10,732 citations, followed closely by the University of London with 8,571 citations. The University of Washington Seattle and the University of Washington tied for third place, with 7,716 citations each. Regarding the H-index, Chongqing Medical University ranked first with an H-index of 54, followed by the University of Washington Seattle and the University of Washington, both with an H-index of 49. The University of London ranked third, with an H-index of 47. Measured by patent citation count, the University of Washington leads by a wide margin, with 556 citations. INSERM ranks second with 241 citations, followed by Philips Corporation in third place with 147 patent citations. Another French research institution, CNRS, ranks fourth with 138 citations.

In the field of HIFU, 14,408 researchers worldwide have published studies related to this topic. As shown in , the larger nodes within each cluster represent highly productive authors, including Jean-Yves Chapelon from Inserm in France, Zhibiao Wang from Chongqing Medical University in China, and Vera A. Khokhlova from the University of Washington in the United States. The clustered network diagram indicates that the collaboration networks of highly productive authors primarily involve domestic researchers, whereas international collaborations are predominantly indirect. As shown in , the top ten authors by publication volume are summarized. Jean-Yves Chapelon ranks first with 121 papers, accounting for 26.71% of the total, with an average of 31.20 citations per paper, a citation rate of 76.86%, and an H-index of 35. Zhibiao Wang ranks second with 88 papers, accounting for 19.43% of the total, with an average of 32.50 citations per paper, a citation rate of 93.18%, and an H-index of 30. Shin Yoshizawa ranks third with 84 papers, accounting for 18.54% of the total, with an average of 14.58 citations per paper, a citation rate of 82.14%, and an H-index of 22.

presents the ranking of authors based on patent citation count. Lawrence Crum from the University of Washington ranks first with 373 citations, followed by S. Vaezy from the same institution with 324 citations, E. S. Ebbini from the University of Minnesota Twin Cities with 220 citations, Jean-Yves Chapelon from INSERM with 166 citations, and J. Ophir from Tel Aviv University in Israel with 140 citations. When comparing the patent citation counts of the top 10 most prolific researchers, it is evident that although E. S. Ebbini and J. Ophir did not rank among the top 10 in terms of publication output, their patent citation counts placed them among the top 5 globally. This indicates that authors with high patent citation counts do not necessarily belong to the group of high-output researchers in their fields, and that there is no clear correlation between the volume of academic publications and the impact of patent technologies.

Keyword co-occurrence analysis reveals research hotspots in the field of HIFU. Using CiteSpace 6.1.R6, a keyword co-occurrence map was generated, and the results were filtered according to betweenness centrality, as shown in . Nodes with higher betweenness centrality are shown with thicker purple borders. The keyword with the highest betweenness centrality is “benign prostatic hyperplasia” at 0.22, followed by “therapy” at 0.21, “tissue ablation” at 0.19, “prostate cancer” at 0.18, and “enhancement” at 0.15. Other important keywords, including “lesion” at 0.12 and “cancer” at 0.11, function as mediators linking basic research to clinical applications, as shown in .

Keyword bursts reflect rapidly evolving research hotspots in the field of HIFU from 1994 to 2024 and suggest potential future research trends. As shown in , 25 burst keywords were identified, with red bars indicating their burst periods. Chronologically, the earliest burst keyword was “carcinoma,” which had a burst period from 1995 to 2008 and a burst strength of 16.59. The second earliest was “benign prostatic hyperplasia” with a burst strength of 13.93 and a burst period from 1995 to 2004. The third earliest burst keyword was “hyperthermia,” with a burst strength of 12.35 and a burst period from 1995 to 2009. At the end of the timeline, keywords such as “management”, “safety”, “efficacy”, “uterine fibroid”, “outcome” and “focal therapy” showed the most recent bursts in prominence, with their periods of prominence concentrated between 2017 and 2024. Among them, “efficacy” (45.52), “management” (42.70), and “safety” (36.47) had the highest burst strengths. The relatively high burst strengths of “uterine fibroid” (31.30) and “outcome” (23.65). Notably, although “focal therapy” (12.65) had a relatively low burst strength, it emerged most recently, suggesting that this topic represents a frontier area in HIFU research and may become an important growth direction for future studies.

Overall, HIFU research has progressed through three distinct phases. From 1994 to 2002, publication output was low and increased slowly, with an average of approximately 21 papers per year, indicating the initial stage of HIFU research. From 2003 to 2012, publications increased rapidly, with an average of approximately 150 papers per year, reflecting a period of accelerated growth. From 2013 to 2024, publication output continued to rise steadily despite fluctuations, with an average of approximately 264 papers per year, indicating a transition to a stable, high-output phase. Currently, however, publication growth has plateaued, likely because HIFU technology has matured within existing fields, increasing research complexity and creating a need to explore new research domains.

In its early stages, HIFU research consisted primarily of single-center studies and had not yet developed into a large-scale multicenter collaborative framework. Studies during this period focused mainly on animal models to explore the fundamental principles and technical feasibility of HIFU (). Since 1994, the advantages of HIFU in minimally invasive and even non-invasive tumor treatment have continued to attract attention. Beginning in 1994, researchers in the United States published several papers exploring the feasibility of using HIFU to ablate hyperplastic prostatic tissue in animal models, thereby laying a foundation for understanding the technology's technical principles and establishing its experimental methodology (). During the rapid growth phase of HIFU research, Zhibiao Wang's team at Chongqing Medical University in China developed the world's first HIFU-based tumor ablation system. This marked a major technological breakthrough in HIFU research, propelling the technology from laboratory research to clinical application, as evidenced by the surge in HIFU-related publications and the expansion of its clinical indications. During the maturation and standardization phase, publication output stabilized at a high level, and the HIFU technical system and its clinical applications became increasingly mature and standardized.

In the field of HIFU, the United States has the largest publication volume, followed by China, and both countries far exceed all others in citation counts and overall output. France is also an active contributor. Although the United Kingdom produces fewer publications than these countries, its citation count, CNCI, and Collab-CNCI values rank among the top three globally, underscoring the high quality and disciplinary influence of its research.

The University of Washington is a leading institution in HIFU research and ranks second worldwide in H-index for HIFU-related publications, reflecting substantial institutional investment in the field. The University of Washington has demonstrated exceptional performance in international collaboration, indicating the strong international influence of its HIFU research. This facilitates the integration of resources, such as funding, data, and equipment, from different countries, enabling complementary strengths to be fully leveraged. The University of Washington's close collaboration with Philips in the Netherlands and Cancer Research UK demonstrates its strong emphasis on translating research findings into practical applications with real-world value. Its first-place ranking in patent citations further indicates a clear focus on research translation and applications with significant market potential. Research in the United States focuses on MRgFUS-based neurostimulation and functional brain disorders, localized cancer treatment and palliative pain management, focal therapy for prostate cancer, and blood–brain barrier opening and drug delivery to the brain (; ; ).

Chongqing Medical University is among the world's leading contributors to HIFU research and is the top institution in China in this field. The university was the birthplace of the world's first HIFU device, the “HIFU Knife,” which was developed in 1997 by Professor Zhibiao Wang's team. The team also pioneered the theory of the “biological focal zone” (). Its research findings have been published in leading journals such as Ultrasonics Sonochemistry, forming the basis for the university's high-impact contributions. The collaborative network for HIFU research at Chongqing Medical University primarily involves partnerships with domestic universities, research institutes, and leading scientific institutions in Europe and the United States. In the future, the university can expand the scope of its international cooperation, strengthen exchanges with partners in Asia, Africa, and Latin America, and enhance collaboration with multinational medical companies to further increase its global influence. Among Western countries, France and the United Kingdom are the primary contributors to HIFU research. In particular, France's leading medical research institutions play a central role in advancing HIFU studies.

Research in France primarily focuses on prostate cancer treatment (; ) pericardial disease (), and varicose vein treatment (). Publications from the United Kingdom are of high quality and are widely recognized internationally. HIFU research in the United Kingdom centers on focal therapy for prostate cancer, using HIFU's precise ablation capabilities to provide a function-preserving alternative to radical prostatectomy ().

The top ten global HIFU researchers display clear patterns of national distribution and institutional collaboration: four are from the United States, two are from France, and one each is from China, Japan, the United Kingdom, and Russia. The United States is represented by Vera A. Khokhlova's team, France by Jean-Yves Chapelon's team, and China by Zhibiao Wang's team. Chapelon's institution integrates the full research continuum from basic science to clinical application, and his leading H-index reflects the prominent position of French researchers in HIFU research. Through collaborations with the Chinese Academy of Sciences and the University of Vermont, Wang's team has established an innovation network spanning original technological development, clinical validation, and international dissemination. Although Shin Yoshizawa's team at the University of Tokyo publishes extensively, its global citation impact remains modest, highlighting the tension between locally oriented technological applications and international outreach.

At the University of Washington, Vera A. Khokhlova, Lawrence Crum, Shahram Vaezy, and Arnaud Gelet form a major author cluster, demonstrating strong intra-institutional collaboration. Khokhlova's multinational publication record exemplifies transnational research activity, while Crum's global leadership in patent citations underscores the market-oriented value of the institution's HIFU research. In the United Kingdom, the HAAR and GT departments at University College London produce relatively fewer papers but achieve high H-index and CNCI values, reflecting a national tendency toward “fewer but higher-quality” publications. It is worth noting that authors with a high number of patent citations, such as E. S. Ebbini and J. Ophir, are not necessarily high-output authors; this discrepancy may be due to differences in research focus and output objectives. Basic research emphasizes theoretical exploration and academic exchange, whereas patents focus on practical technological innovation and industrial application (). Furthermore, researchers may choose different forms of output based on their research orientation, leading to inconsistencies between the number of published papers and the impact of patents.

Keywords with high betweenness centrality appeared relatively early, indicating that HIFU technology for solid tumor ablation gained broad recognition during its early stage of development. The timeline of keyword emergence further shows that HIFU research has evolved through three distinct phases. First, the period from 1994 to 2004 represents the stage of foundational research and technological groundwork. Prominent keywords include carcinoma (16.59; 1995–2008), benign prostatic hyperplasia (13.93; 1995–2004), hyperthermia (12.35; 1995–2009), lesion (10.00; 1995–2005), tissue (12.45; 2001–2006), and radiation therapy (2003–2010). Early American studies confirmed the efficacy of HIFU in animal models and later expanded its application to tumors of the kidney, liver, breast, and brain (; ; ). Concurrently, researchers investigated the physical mechanisms underlying HIFU-induced tissue damage. Although HIFU is designed for precise ablation, heat may be conducted to surrounding tissues, causing damage to non-target areas. Therefore, HIFU treatment typically requires real-time monitoring using MRI (; ).