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Focused ultrasound and metrics of diffusion of disruptive medical innovation
1. I Jonathan Pomeraniec1,2,
2. Robert Spekman2,
3. Neal Kassell1,2
1. 1Department of Neurological Surgery, University of Virginia Health System, University of Virginia, Charlottesville, Virginia, USA
2. 2Focused Ultrasound Foundation, Charlottesville, Virginia, USA
1. Correspondence to Dr Neal Kassell, Focused Ultrasound Foundation, University of Virginia Health System, 1230 Cedars Ct, Charlottesville 22903, VA, USA;nkassell{at}fusfoundation.org

## Abstract

Innovation, as a concept in healthcare, has broad implications ranging from diagnosis to treatment of disease. The advent of new surgical modalities and medical devices continues to refine and reshape the provision of care for millions of patients across the world. Despite the tangible promise of such innovation, there remains a dearth of frameworks to understand how and how much progress has been made, particularly with regard to early-stage, non-invasive therapeutic technologies that have the potential to transform the treatment of medical disorders. A chief example of this is provided by MR-guided Focused Ultrasound. To the best of our knowledge, there are no prior reviews of the factors affecting adoption and diffusion of MR-guided Focused Ultrasound as a proxy for disruptive medical technologies. The purpose of this review is to provide a comprehensive set of metrics to measure the factors affecting the rate of adoption and diffusion of these medical technologies with special focus on MR-guided Focused Ultrasound, Gamma Knife radiosurgery, and the da Vinci system. The authors review background information and literature regarding innovation in medical technology, and what constitutes disruptive innovation in the medical field. Metrics of adoption and diffusion are evaluated and applied to MR-guided Focused Ultrasound. Gamma Knife radiosurgery and the da Vinci system provide reasonable proxy technologies to understand the factors affecting the adoption and diffusion of MR-guided Focused Ultrasound. With a more comprehensive set of metrics to measure the rate of uptake and use of disruptive technology, we might move towards a better understanding of the limitations of new and potentially beneficial therapeutic modalities.

• Focused ultrasound
• Disruptive innovation
• Delivery
• Economics
• Metrics
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## Objective

To the best of our knowledge, there are no prior reviews of the factors affecting adoption and diffusion of MR-guided Focused Ultrasound as a proxy for disruptive medical technologies. The purpose of this review is to provide a comprehensive set of metrics to measure the factors affecting the rate of adoption and diffusion of these medical technologies with special focus on MR-guided Focused Ultrasound (FUS), Gamma Knife radiosurgery, and the da Vinci system.

## Design

The authors review background information and literature regarding innovation in medical technology, and what constitutes disruptive innovation in healthcare. Metrics of adoption and diffusion of proxy innovative medical technologies are evaluated. The growth of MR-guided FUS is discussed with a new set of metrics to understand the rate of uptake and use of disruptive technology.

## Introduction

Innovation as a concept in healthcare has broad implications ranging from diagnosis to treatment of disease. The advent of new surgical modalities and medical devices continues to refine and reshape the provision of care for millions of patients across the world. Despite the tangible promise of such innovation, there remains a dearth of frameworks to understand how and how much progress has been made, particularly with regard to early-stage, non-invasive therapeutic technologies that have the potential to transform the treatment of medical disorders.

It is common sense that disruptive innovations disrupt existing markets, and alter the value proposition relative to incumbent technologies in treating diseases.1 For example, MR-guided FUS technology can target tissue deep in the body without incisions or radiation. Since the 1940s, and particularly over the past decade, this technology has enjoyed significant growth, including advancements in technical, preclinical and clinical research, regulatory approval and reimbursement, manufacturer growth, and other commercial and public sector investments, within an environment of multiple stakeholders.2 As a disruptive innovation, FUS has helped evolve the non-invasive treatment of various disease states that previously required incisions and prolonged recovery, including neurological and neurofunctional disorders such as essential tremor and Parkinson's disease.

## Background

Advancement in the surgical treatment of disease has been largely tied to technological innovation, and has helped shift the access of care for patients and the way in which that care is provided.3 Over the past 20 years, the theory of disruptive innovation and the characteristics of new technologies that displace existing competitors has been popularised in academic business literature.4–10 Utterback and Christensen both developed models that outline innovative product lifecycles that tend to be ‘simpler, cheaper and lower performing’, ‘first commercialised in emerging or insignificant markets’, and promise ‘lower margins, not higher profits’.6 ,10

In healthcare models, disruptive innovations alter the metrics of performance on which these products compete.7–9 A counter example of this definition is the case of angioplasty. As the most popularised example of disruptive innovation within the surgical device industry, angioplasty offered an entirely new value proposition relative to coronary bypass surgery for patients with coronary artery disease. However, angioplasty did not disrupt other competing products but rather indicated the need for more invasive cardiothoracic surgical techniques and skill; it did not create a new market, but introduced a new method in a previously well-defined market with fixed patient indications. Finally, it did not spawn an initially small market with low profitability, but instead offered early profitable growth and attracted significant investment.1

Unlike other academic schemas, the theory of disruptive innovation in healthcare remains nebulous. Complex and evolving economic and regulatory frameworks chiefly provided by the Food and Drug Administration (FDA) not only limit market entry, but also restrict product marketing to clearly defined end users. The Christensen model holds that lower cost and lower margin disruptive technologies must be commercialised through independent organisational structures since incumbent organisations would be effectively disincentivised to invest in innovations of lower profitability in ill-defined markets.1 Furthermore, Christensen predicted that consumers would eventually shift to lower cost options when traditional technologies outperform their needs. However, in the field of medical devices, physicians act as intermediate agents between developers (manufacturers) and end users (patients); so technologies that are significantly more expensive could be used so far as they improved patient outcomes. Medical devices deviate from established models of innovation as further evidenced by the trajectory of the automatic external defibrillators (AED) market. As a Class III FDA regulated device, the AED required premarket approval prior to market introduction. Traditional models of innovation propose that inferior products enter the market and eventually capture market share through positive technological trajectories. In contrast, the AED market exhibited an inverse technological course from high-end hospital model defibrillators down to adequate general use devices.11

As an early-stage, non-invasive therapeutic alternative to surgery and radiation, FUS technology largely models disruptive innovation by altering the course of preferred treatment regimens and upsetting the status quo. In this sense, disruption provides potential benefit for patients and businesses as effective, non-invasive treatments can be cheaper and safer. FUS technology is also an example of compounded disruption as it drives further innovation. For example, while manufacturers are currently seeking ways to improve this technology, MRI is becoming faster to better support FUS, and hospitals are supplementing their surgical armamentarium for disorders of many kinds.12

## Adoption and diffusion of technological innovation

Theories of how new innovation is adopted by and diffuses through markets are drawn from multiple disciplines.13 Diffusion, the process by which innovation spreads after the initial adoption, stems from Rogers’ roadmap of communication through specific channels over time: (1) knowledge (awareness), (2) persuasion (interest), (3) decision (evaluation), (4) implementation (trial), and (5) confirmation (adoption).13 While this sketch does not rest on any empirical foundation, Rogers’ diffusion theory remains paramount in academic fields.14 ,15 Different channels and channel characteristics have since evolved, but all capture a similar underlying staged process. In the medical field, various stakeholders affected by innovation (eg, researchers, academic medical centres, government agencies, and venture philanthropists) have been mapped according to function and influence within a three-stage model: discovery, development and delivery.16

The concept of disruptive technology popularised by Christensen in 1995 primarily described technologies that transformed existing markets and consumer expectations towards new dimensions of performance.17 Disruptive innovation was subsequently expanded to include technological, product, process and business model innovations.7 ,8 Christensen claimed that when faced with the threat of disruptive change, almost all incumbent firms would be displaced by organisational and managerial inertia towards adopting of new ways for doing things.7 ,8 ,10 ,18 More often than not, however, consumers and end users of these new products had little incentive to change preference from existing products or services. Christensen, hence, proposed innovation as either ‘sustaining’—reaffirming current paradigms of competition and technological progression—or as ‘disruptive’—transforming existing paradigms and shifting them towards new dimension of innovative performance.19–21 Disruptive innovations, thereby, create new markets and stimulate new growth by changing the underlying value proposition expected by mainstream customers.

The theory proposed by Christensen suggests that disruptive innovations emerge from specific processes22 that initially under-perform in established technologies with respect to the prevailing performance measures in mainstream markets.8 ,9 This is precisely where the medical field and Christensen part ways: innovation that disrupts healthcare is often more expensive than and outperforms the incumbent technology it serves to replace. Nascent mainstream commercial markets (eg, mobile vs cell phone, digital vs film camera) offer disruptive innovation as often more expensive and technologically more advanced than existing innovations.23–25

Diffusion of innovations theory helps establish the social and economic benefits attributed to innovation as well as the myriad dynamics that affect how well, how far and how fast new innovation can spread.13 ,26–29 Consequently, the diffusion processes of new products and services have become increasingly complex and multifaceted in recent years.30 Originally, Rogers provided a conceptual model of diffusion as the outcome of a communication process dependent on the inherent variables of innovation: relative advantage (innovation perceived as being superior than precursor; compatibility (innovation perceived as being consistent with existing values, needs and past experiences of potential adopters); complexity (innovation perceived as being difficult to use; trialability (results of innovation are observable to others); and observability (innovation may be experimented with before adoption).13 ,28

Recent literature has investigated factors that influence the process of disruption, which include catalysts that affect the rate at which disruption occurs.22 ,29 ,31 ,32 Other research streams examine the relationship between disruptive innovation and methods available for incumbent firms to respond to potentially disruptive threats.10 ,18 ,33 ,34 By expounding on the prospect that technologies with inferior performance can displace established incumbents, Adner established a demand-based perspective of competition with three competitive outcomes: convergence (technologies evolve to compete head-on for same consumer groups), isolation (technologies do not interact throughout the course of their evolution) and disruption (one technology cedes dominance of home market to its rival).29 Still, research on diffusion of disruptive technologies and underlying driving mechanisms remains sparse.17 ,23

Diffusion modelling research examines the spread of innovation through product and consumer lifecycles. These forecasting methods attempt to predict the market share of new innovations, and evaluate the influence of various externalities and environmental factors. Traditional management models follow the distinctive S-shaped curve that depicts the cumulative number of adopters plotted over time.13 Rogers used the normal distribution to differentiate among adopter categories and their respective rates of adoption: innovators, early adopters, early majority, late majority and laggards (figure 1).13 This traditional view endorsed disruption as an outcome of market structure (size, distribution and segmentation of consumers into different adopter categories).17 However, measuring and predicting rates of adoption and diffusion of disruptive innovation poses a more sensitive and complex challenge.

Figure 1

Composite of value chain stages and diffusion of innovation.

By creating new markets and industries, the performance attributes offered by disruptive innovation can differ drastically from the performance expected by mainstream markets.19 ,30 This includes drivers and barriers that might affect the staging of development, launch and diffusion of innovative medical technologies (figure 2). The set of drivers and barriers are grouped by potential to advance diffusion of new technology (low, medium and high). Drivers refer to circumstances that promote adoption and diffusion. Barriers refer to circumstance that hinder adoption or diffusion. Staging refers to the progression from development to deployment, approval, and acceptance in the commercial market. Some of these factors are more practical than others in targeting adoption and diffusion strategies. For example, technology breakthroughs, target conditions, convergence of technologies, competing and substituting technologies, and liability are less plausible as public interventions to accelerate adoption and diffusion of innovations. Other drivers above might significantly impact diffusion through public, private and joint public–private initiatives.35

Figure 2

Drivers and barriers affecting diffusion of technology.

## Proxies for disruptive medical innovation

Where literature falls short of describing the adoption and diffusion of disruptive innovations in healthcare, proxies can help to illuminate trajectories of similar technologies. The more similar the proxy to the new technology in consideration, the more accurate will be the prospective trajectory of adoption and diffusion in clinical practice. Innovation of medical devices can manifest as development of previously undefined technology or the redesign of prior technologies in novel ways. Predicting the rate and course of diffusion can be speculative at best. However, defining and measuring specific dynamics and trends can help raise awareness of the potential benefits of new innovation.

Underlying dynamics and metrics of diffusion of disruptive medical technologies remain relatively undetermined. In order to ascertain the potential rate of diffusion for new technologies, such as FUS, a logical approach might hinge on identifying existing, analogous innovations. Like FUS, Gamma Knife and da Vinci represent clinical and scientific innovations that offer state-of-the-art minimally invasive options for major surgery. Both of these non-invasive surgical modalities overcame risks, competition, and barriers to providing an emerging technology to patients in need. In a similar vein, the benefits of a foundation in supporting the development and adoption of new technology have been well recognised: Gamma Knife existed for decades before becoming the standard of care, and gained traction much more efficiently after the establishment of the Leksell Gamma Knife Society.

Gamma Knife radiosurgery is a proxy example of a disruptive innovation that has diffused widely in clinical indications and surgical use. Over 884 000 patients have been treated for various indications through 2014, ; an increase from 740 200 and 809 000 through to 2012 and 2013, respectively. This includes 293 treatments per centre worldwide, on average, with a global case mix of malignant tumours (44%), benign tumours (40%), vascular disorders (10%) and functional disorders (7%). From 1991 to 2014, indications treated included 386 895 malignant tumours, 325 009 benign tumours, 103 991 vascular disorders, 64 992 functional disorders and 3317 ocular disorders.36

Cumulative patients with functional disorders treated by Gamma Knife have burgeoned from a mere 175 in 1991 to slightly less than 65 000 in 2014. The treatment of these disorders represents a 9% annual increase over the past 5 years. In 2014, approximately 5000 patients were treated for trigeminal neuralgia (4468), essential tremor (195), Parkinson's disease (162), epilepsy (38), intractable pain (34) and other behavioural disorders (34). Trigeminal neuralgia comprises the vast majority of cumulative patients treated for functional disorders (87.1%), followed by epilepsy (4.3%) and Parkinson's disease (3.2%).36

The diffusion of Gamma Knife can perhaps best be understood from the lens of an organisation with a mission similar to the FUS foundation. The Leksell Gamma Knife Society was founded in 1989 as a forum for Gamma Knife clinicians, physicists and researchers to exchange information, experiences, and clinical techniques as well as clinical data on the use of Leksell Gamma Knife. The mission of the society is to further define and expand the role of Gamma Knife Surgery in the treatment of intracranial disorders, and the development of best practices in order to improve patient outcomes.36 Like the FUS foundation, this society acts as a forum for information sharing and partnerships, and has succeeded in developing and communicating progress and best practices in radiosurgery. At the most recent meeting in 2014, almost 600 delegates presented the current and growing scientific status of Leksell Gamma Knife through the presentation of more than 100 new scientific reports.37 A list of relevant Gamma Knife metrics have been summarised and displayed in table 1; table 2 provides a comprehensive list of neurological conditions treatable with Leksell Gamma Knife.

Table 1

Gamma Knife metrics

Table 2

Summary of neurological conditions treatable with Leksell Gamma Knife65

## Da Vinci system

The da Vinci Surgical System, manufactured by Intuitive Surgical, was first approved for clinical use by the FDA in 2000. The da Vinci modality was designed foremost to facilitate complex surgical procedures through a minimally invasive approach and named for Leonardo da Vinci's use of anatomical accuracy and three-dimensional details in his work.38 A list of metrics employed by Intuitive to understand the development and distribution of the da Vinci system have been summarised in table 3.

Table 3

da Vinci metrics38

Approximately 523 000 da Vinci procedures were performed in 2013, an increase of 16% from 2012, with Q3 2014 procedures up by approximately 9%. There were 3174 da Vinci systems installed base as 2014: 2185 in the USA, 516 in Europe and 473 in the rest of the world.38 This technology has gained numerous FDA and international regulatory clearances with primary markets, including urology, gynaecology, general surgery and cardiothoracic surgery.

Even with substantial fixed costs, with prices ranging from approximately $1–2.5 million per installed unit, the adoption of robotic technology has spread broadly and rapidly worldwide. The number of da Vinci systems in hospitals grew by 75% in the USA, and by 100% in other countries between 2007 and 2009. The number of robot-assisted procedures tripled during that same period.39 These da Vinci systems served to displace not only open surgeries but also some being performed laparoscopically, with notable consequences to costs and volumes of these procedures. In 2010, Barbash and colleagues considered the net per procedure costs of robot assistance and estimated that these procedures added$1600, or 6%, of variable costs on to the average costs across all types of procedures. The authors determined that replacing conventional surgeries with robot-assistance across all procedures would generate an additional $1.5 billion in annual healthcare costs.39 Despite a fragmented and decentralised purchasing process—for example, decisions are made by competing hospitals—robotic technology seemingly also led to the substitution of surgical for non-surgical treatment of disease. Prostatectomy discharges increased by more than 60% despite a decrease in underlying incidence, according to the Nationwide Inpatient Sample.39–41 Interestingly, the advent of da Vinci procedures simultaneously increased the cost and volume of these surgical procedures primarily due to the short-term benefits of reduced postoperative recovery and more patients opting for surgical intervention.39 ## Focused ultrasound FUS is an early stage, non-invasive therapeutic technology with the potential to transform the treatment of many medical disorders by using ultrasonic energy to target tissue deep in the body without incisions or radiation. FUS resulted from the amalgamation of two innovative technologies: ultrasound (provides energy to treat tissue precisely and non-invasively) and MR or ultrasound imaging (identifies and targets tissue to be treated, guides and controls the treatment in real time, and confirms the effectiveness of treatment).42 The use of FUS blossomed from a seminal publication demonstrating potential therapeutic use in 194243. The first FDA approval for a FUS device came in 1988.44 ,45 MRI-guided FUS device introduction in the 1990s46–49 helped in treating more than 80 000 patients, including those with symptomatic uterine fibroids,50 ,51 brain tumours,52 ,53 painful bone metastases,54 ,55 cancer of the prostate,56–59 pancreas60 and breast61 as well as abdominal tumours.60 ,62 As a novel reconstruction of prior technology, FUS can be considered a disruptive technology with the potential to transform standard or care treatment for a variety of serious medical conditions. The growth in this field of technology, and its requisite level of development and adoption in clinical practice has historically been assessed via financial support and general awareness by tracking the amount of research funding provided to projects, number of publications in peer-reviewed journals and general awareness metrics such as visits to specific FUS websites, including its Wikipedia page. The impact of FUS on the health of the global community can be gleaned through examination of the number of clinical indications reaching first-in-human stage and the number of successfully treated patients.2 The Focused Ultrasound Foundation (FUSF) has endorsed the mission of advancing the development and clinical adoption of image-guided FUS as a technology platform for the treatment of a variety of clinical conditions. The foundation has actively identified and addressed many of the barriersi to innovation, and emphasised activities meant to catalyse the adoption and diffusion of this new technology. These activities include fostering collaborations, funding translational research, and influencing the direction of the field. In both basic science and clinical medicine, FUSF identifies and eliminates rate-limiting steps such as technology shortfalls, gaps in the current funding landscape, lack of evidence, regulatory approval hurdles and acceptance from patients, physicians and insurers.2 ## Growth of FUS FUS remains in the early stages of technological development and clinical use. The pace of research and development has increased rapidly over the past few years along with the growing number of publications, patient treatments, and number of device manufacturers. The technology has been approved for commercial use for some applications, including oncological (bone mestases, prostate cancer), women's health (uterine fibroids) and urological (prostate cancer, benign prostatic hyperplasia) disorders. Other uses, particularly for neurological disorders, are undergoing research and are either in preclinical, pilot or pivotal trials, with Essential tremor, neuropathic pain and Parkinson's disease already receiving approval outside the USA (figure 3).42 Figure 3 State of research and regulatory approval of Focused Ultrasound. More than 89 000 patients have been treated with FUS to date, and more than 8000 patients were treated commercially or in clinical trials worldwide in 2014. The vast majority of these patients were treated for prostate cancer (45 000), followed by uterine fibroids (20 000) and liver cancer (15 000). In order to better understand growth of adoption in clinical practice, the number of treated diseases and clinical indications have been tracked for over 25 years. The clinical indications of FUS have increased more than 15-fold, from just 2 before 1990 to over 30 in 2014 (figure 4).42 The total number of research sites has increased by 11% and NIH funding for this research has increased 48%, from$21 million in 2013 to \$31 million in 2014.2 ,42

Figure 4

Clinical indications of Focused Ultrasound. OCD, obsessive compulsive disorder.

The industry around this innovation has also risen, with 28 manufacturers in 2014, up from being only 5 in 2000. The types of manufacturers include 16 US guidance, 5 MR guidance, 4 MR+US guidance, 2 transducer and 1 camera guidance. The majority of companies reside in Europe (11), followed by North America (9) and Asia (8).42

## Diffusion metrics for FUS

In 2014, Tyshlek et al presented a snapshot of the field of FUS and described progression over the past several decades. The authors assessed the iterative clinical adoption of this non-invasive therapeutic modality using metrics, including quantity and breadth of academic work, funding trends, manufacturers’ presence, number of treated patients, number of indications reaching first-in-human status and quantity and breadth of clinical indications.2 The data showed evidence of progress demonstrated by the increased number of clinical indications explored from 1 to 21 since 1950, or by the increase in the amount of research indicated by a steady increase in the annual number of publications. Additionally, a rising number of abstracts at FUS events and symposia indicates higher levels of activity. Publications and citations for FUS have also been increasing annually and by a greater percentage than the total number of medical publications overall (a similar trend can be seen in NIH funding awards proportional to other research). The group employed several metrics and data sources, which have been summarised in table 4. Moving beyond these metrics, several additional measures might provide a more comprehensive view of how, when and where such technology has been diffused in the marketplace: number of new adoptions; number of cumulative adopters; number of products made prior to product launch; potential market size; number of markets.

Table 4

Focused ultrasound metrics2

Using as foundation the previous set of metrics employed by Tyshlek et al, and incorporating the proxy metrics of Gamma Knife and da Vinci, a comprehensive set of metrics to understand diffusion of FUS has been summarised in figure 5. These key metrics have been segmented along the stages of a communications theory network with corresponding stages of the value chain. Diffusion of innovations in communications theory was originally popularised by Everett Rogers, and describes a process by which innovation manifests through certain channels over time. Innovation must be widely adopted before becoming a self-sustaining system and this relies heavily on human capital: innovators, early adopters, early majority, late majority and laggards.64 The five-step process through which diffusion progress can be linked to a corresponding stage in the value chain as well as the metrics within each stage are:

Figure 5

Comprehensive set of metrics to understand rate of diffusion for Focused Ultrasound. FDA, Food and Drug Administration;NIH, National Institutes of Health.

Knowledge (discovery; preclinical proof of concept) refers to first exposure of innovation, but lacks formal information about that innovation. Discovery and preclinical proof of concept of FUS technology form the foundation of awareness as a critical first step. Metrics in this stage should help illustrate the value of FUS as a therapeutic modality and promote further investigation for its adoption. These metrics act as surrogates for learning about the capabilities of FUS technology and provide information about potential clinical uses. These measures are meant to provide insight into level of patient, physician, researcher and administrator awareness; this still is a critical first step in the spreading of valuable knowledge about the new non-invasive therapeutics modalities.

In the persuasion (preclinical proof of concept; clinical testing) stage, decisionmakers are more interested in the innovation and actively seek related information. Transitioning from proof of concept to clinical testing relies on early adopters and thought leaders. Collaboration in research can likely be a leverage for leading physicians at the university and teaching hospital levels. The concept of change is subsequently balanced against advantages/disadvantages of innovation and culminates ultimately in a decision of adoption or rejection. According to Rogers, this presents the most difficult stage in which to acquire empirical evidence.13 ,28 The key delineation between knowledge and persuasion rests on individuals more proactively searching and adopting new technology. Metrics in this stage are focused on collaboration and partnerships by those who will lead the adoption of the use of FUS by more clearly establishing its efficacy and safety across a wider clinical array.

Decision (regulatory approval) refers to FDA approval across a range of clinical indications. Approval from the FDA across a spectrum of clinical indications (patient populations, diseases and conditions) provides the key metric in this category. There are other metrics that fall short of regulatory approval such as number of meetings with FDA and NIH personnel, and the number of jointly sponsored research endeavours and conferences. Clinical work in this stage should be used as further evidence of FUS viability and serve to reinforce academic and commercial partnerships, including trade groups, medical societies and equipment manufacturers. These partnerships should attempt to increase the overall acceptance of FUS as a standard of care.

Following the decision to adopt, the implementation (insurance coverage; reimbursement) stage includes deployment of innovation at varying degrees and contexts, and gauging the utility of such innovation. In order to measure the viability of FUS as a new therapeutic modality, one might consider how insurance coverage and structure, and amount of reimbursements evolve over time. Payer coverage presents a major barrier to widespread adoption and diffusion as there is as yet no standard coverage for FUS intervention.

In the last stage of confirmation (commercialisation), the decision to continue using the innovation is finalised. Metrics should provide insight into free market dynamics—how, when, and to what extent FUS has been deployed in the clinical setting. These measures are meant to more closely resemble statistics employed by foundations of proxy disruptive medical innovations (eg, Gamma Knife and da Vinci). In large part, these metrics serve to map FUS growth as a therapeutic modality over time.

## Conclusion

Gamma Knife radiosurgery and the da Vinci system continue to grow rapidly in clinical and research indications. They provide reasonable proxy technologies to understand the factors affecting the adoption and diffusion of MR-guided FUS. FUS represents an early-stage technology with the potential for disruptive change to more invasive surgical procedures. With a more comprehensive set of metrics to measure the rate of uptake and use of such technology, we might move towards a better understanding of the limitations of new and potentially beneficial therapeutic modalities.

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## Footnotes

• Contributors IJP, RS and NK provided substantial contributions to conception and design of the work. IJP provided acquisition, analysis and interpretation of data for the work. IJP, RS and NK revised this work critically for important intellectual content and gave final approval of the version to be published. IJP, RS and NK are in agreement to be accountable for all aspects of the work.

• Competing interests None declared.

• Provenance and peer review Not commissioned; externally peer reviewed.

• i Barriers to innovation in medical devices include: supplier-driven, linguistic barriers (eg, literature not translated), maintenance contracts, insufficient staff and training, limited access to technical information, poor maintenance and repair facilities, lack of training culture, costs, unrecognised standards for quality control and maintenance, inadequate guidelines, lack of coordination, procurement issues, shortage of technical expertise, indirect link between producer/vendor and end user, lack of funding.63

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