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Letter to the Editor: Differentiating Ultrasound Technologies

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Letter to the Editor: Differentiating Ultrasound Technologies

Index: Ostomy Wound Manage. 2014;60(5):8-9.


As a wound care practitioner who has specialized in the use of therapeutic technologies for more than 30 years, I have first-hand experience with the confusion regarding the different types of ultrasound used to treat wounds. I am concerned the content in the article (Maher SF, Halverson J, Misiewicz R, Reckling T, Smart O, Benton C, Schoenherr D. Low-frequency ultrasound for patients with lower leg ulcers due to chronic venous insufficiency: a report of two cases. Ostomy Wound Manage. 2014;60[2]:52–61) will add to the existing confusion.   This article focuses specifically on the effectiveness of contact ultrasound debridement (Qoustic Wound Therapy System, Arobella Medical, LLC, Minnetonka, MN) in wound healing and draws improper clinical conclusions on the use of ultrasound generally based on a range of both contact and noncontact ultrasound devices.

The authors report on a variety of low-frequency ultrasound (LFU) devices (25 kHz – 40 kHz) delivered through a number of different of mediums (direct contact, water-bath, and noncontact saline mist). As presented, the results are intertwined, making it difficult to distinguish between technologies, so the uninformed reader could easily assume they are all the same. Contact ultrasound debridement devices are used to remove fibrin and slough early in the healing process. Noncontact, low-frequency ultrasound delivered through a saline mist (MIST® Therapy System, Celleration, Inc, Eden Prairie, MN) is used to promote wound healing throughout the healing process. The clinical results discussed in this article demonstrate the markedly different uses and clinical outcomes of these technologies, yet the authors report, “a number of studies utilizing LFU have been published; the results are mixed.” The mixed results are caused by combining study results from different ultrasound devices intended to be used for clearly different purposes.

As clinicians, we are looking for the most efficacious and cost-effective products to heal our patients. The longer we allow data from different ultrasound technologies (LFU contact debriders, LFU water bath, LFU wound healing through saline mist, high frequency) to be inappropriately commingled in our reporting and publications, the more difficult it will be for us to understand which therapy should be applied to a particular patient. On a broader scale, the practice of mixing of data has resulted in a number of inconclusive reports on LFU products, which has caused certain payors to restrict or deny coverage and ultimately limit patient access.

As the manufacturer of MIST® Ultrasound Healing Therapy, Celleration has invested substantial resources to develop a body of evidence that allows clinicians to make evidence-based decisions for their patients. Today, there are 18 peer-reviewed publications (Evidence Level I-III) citing the healing benefits of this product. We have a vested interest in ensuring these clinical data are presented accurately. At the same time, as a member of the wound care community, I believe our responsibility as clinicians is to ensure clinical publications are not only accurate, but also not misleading, whether intentional or not. It is time we recognize the distinctions between ultrasound technologies and no longer allow the reporting of inappropriately grouped therapeutic technologies.

Pamela G. Unger, PT, CWS VP Medical Affairs, Celleration


We appreciate Ms. Unger’s concerns. As a vice-president for the manufacturer of MIST® Therapy, she has an interest in positive representation of this form of low-frequency ultrasound.

The articles we cited —Uhlemann et al’s literature review, Voight et al’s meta-analysis, and Cullum et al’s Cochrane review — present mixed results. Uhlemann et al reviewed both high- and low-frequency ultrasound. Low-frequency ultrasound was differentiated according to the frequency of the sound wave and ranged from 30 kHz to 3-MHz in the study. The mode of ultrasound transmission was not identified consistently in the cited article. According to the authors, “The quality of the studies done so far and of the evidence of the usefulness of ultrasound is poor. Nevertheless, high-frequency and low-frequency ultrasound may be reasonable options in the management of chronic wounds.”

In Voight et al’s meta-analysis, the intensity of low-frequency ultrasound ranged from 20 to 30 kHz and the sound wave delivery media included water (saline), saline mist, and saline wash. When discussing the quality of evidence, these authors stated, “Although it appears from the meta-analysis performed that low-frequency, low-intensity ultrasound is more effective at complete healing than standard care, the quality of the evidence as it relates to biases was poor.” The authors concluded that despite the evidence quality being generally lower, “the evidence does demonstrate a short-term clinically beneficial effect of low-frequency ultrasound used as an adjunctive therapy on the clinical end points of complete healing and reduction in wound area size for patients presenting with venous stasis and diabetic foot ulcers.”

The Cochrane review included two trials that examined low-frequency ultrasound delivered via a water footbath. “Both trials reported no evidence of a difference in the proportion of ulcers healed with ultrasound compared to no ultrasound: both were significantly underpowered.” The reviewers concluded, “There is no evidence of benefit associated with low-frequency ultrasound.”

Our use of the word “mixed,” therefore, resulted from review articles that arrived at three different conclusions that ranged from low-frequency ultrasound has “no evidence of benefit” to “may be reasonable” to “short-term clinically beneficial effects.”

Because we concur with Ms. Unger that data from different ultrasound technologies can be confusing, we then identified specific articles from three different forms of low-frequency ultrasound, including noncontact ultrasound delivered in either water or a saline mist (MIST® Therapy System, Celleration), contact ultrasound in the form of a probe (Sonica 180, Soring Gmbh, Soring, Inc, Germany), and contact ultrasound delivered through a curette (Qoustic, Arobella). We were surprised to learn of Ms. Unger’s concern with regard to noncontact low-frequency ultrasound, because our reviewed articles presented this form of treatment in a positive light — ie, we stated “the application of noncontact, low-frequency ultrasound has been shown to be effective in decreasing wound size and in some cases shortening healing times.” The specific outcomes of four different studies were clearly articulated, with close attention paid to describing the wound etiologies of the participants, method of ultrasound delivery (when known), and study designs. We noted that low-frequency ultrasound delivered through a curette (Qoustic, Arobella) had no clinical trials at the time of our literature review, limiting us to in vitro studies.

My co-authors and I firmly believe a difference exists in ultrasound delivery methods and tried to articulate this by clearly identifying specific information about each study described. Because we are not biased toward any particular form of low-frequency ultrasound, we tried to provide a comprehensive view of the literature. Meanwhile, we are grateful to Ms. Unger for helping raise awareness relevant to the distinctions among low-frequency ultrasound technologies. We hope continued research will allow clinicians to make evidence-based decisions for their patients.

Sara F. Maher, PT, DScPT, OMPT Associate Professor, Physical Therapy Department Oakland University



This article was not subject to the Ostomy Wound Management peer-review process.