- Case study
- Open Access
Wedged gel pad for bowel manipulation during MR-guided high-intensity focused ultrasound therapy to treat uterine fibroids: a case report
© The Author(s) 2018
- Received: 27 July 2018
- Accepted: 23 October 2018
- Published: 28 November 2018
Magnetic resonance guided high-intensity focused ultrasound (MR-HIFU) therapy is not feasible in all patients with uterine fibroids because of limiting anatomical factors such as scar tissue, bowel loops or other obstacles in the sonication path. These may prevent the treatment or limit the treatment window, and therefore, also the volume where HIFU therapy can be delivered. Bowel loops present a particular problem because of bowel gas bubbles and hard particles which may cause reflection or absorption of ultrasound energy, potentially leading to thermal damage and even bowel perforation. Most commonly used techniques for bowel repositioning are bladder and/or rectum filling but these are not always sufficient to reposition the bowel loops. With more efficient bowel repositioning technique, the number of eligible patients for MR-HIFU treatment could be increased, and therapy efficacy be improved in cases where bowel loops limit the treatment window.
A wedged exterior gel pad was used in two patients presented with in total of four symptomatic fibroids undergoing MR-HIFU treatment when bladder and/or rectum filling was not sufficient to reposition the bowel loops. No severe adverse effects were observed in these cases. The non-perfused volume ratios (NPVs) immediately after treatment were 86% and 39% for the first patient, and 3% for the second patient.
Our preliminary experience suggests that the use of a wedged gel pad during MR-HIFU treatment could be an effective tool to manipulate the bowels in cases where the bladder and/or rectum filling is not sufficient to reposition the bowel loops. A wedged gel pad could also be used in other situations to achieve better treatment coverage to the uterine fibroid.
- Gel pad
- Uterine fibroid
- Bowel repositioning
- MR-guided high-intensity focused ultrasound
Uterine fibroids, also known as leiomyomas or myomas, are the most frequent benign tumors affecting women in premenopausal age [1, 2]. Uterine fibroids can cause symptoms including severe menorrhea, urinary incontinence, dysmenorrhea, and infertility which can have a huge impact to women’s quality of life [3–6]. Current, conventional treatment options for symptomatic uterine fibroids are medical, surgical, and uterine arterial embolization (UAE) which can have major side effects or are invasive .
Magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) therapy is a promising noninvasive treatment method for uterine fibroids with good adverse event profile . In MR-HIFU uterine fibroid therapy the ultrasound waves are focused into the body targeting fibroid tissue, to form a localized area of high-intensity ultrasound (HIU), inducing rapid temperature elevation. Heat generation is due to absorption of the ultrasound waves in tissue, therefore acoustic energy is transformed to heat. Heating the tissue above 57∘C induces, e.g., coagulative necrosis and irreversible tissue damage in seconds, while surrounding tissue remains viable [8, 9]. At the moment, uterine fibroids are one of the most commonly MR-HIFU -treated tumors. In addition, HIFU’s clinical efficacy in the treatment of uterine fibroids has been widely shown [10–15].
However, not all patients are suitable for MR-HIFU therapy. For reasons such as excessively thick subcutaneous fat layer (> 4 cm), large fibroid (> 10 cm), location of fibroid (fibroid is too deep, > 10 cm from the skin) or fibroid tissue type is not favorable (Funaki classification). Funaki et al.  showed that the efficacy of MR-HIFU treatment correlates with the signal intensity of T2-weighted magnetic resonance images and classified fibroids into 3 types based on the signal intensity of T2-weighted magnetic resonance images as follows: type 1, low intensity; type 2, intermediate intensity; type 3, high intensity. Funaki type 1 and type 2 fibroids are suitable candidates for MR-HIFU treatment, whereas type 3 fibroids are not.
One major factor negatively affecting HIFU treatment feasibility is bowel loops between the abdominal wall and the uterine fibroid. Since, the ultrasound beam focusing is implemented by a concave ultrasound transducer that consists of multiple transducer elements. The ultrasound beam shape is a conical being wider at the base. This conical shape of the beam may present a limitation in the uterine fibroid treatment delivery due to overlying bowel gas bubbles and hard particles within the lumen which may reflect or absorb the ultrasound energy in unpredictable ways. This may potentially lead to unintended thermal damage, and at worst, bowel perforation that requires surgical intervention [17–21]. A safe acoustic window can be established in some cases with beam shaping and/or tilting, or by manipulating bowel loops with bladder and/or rectum filling .
Previous studies [17, 18, 23] have reported that 14-74% of patients requesting MR-HIFU are good candidates for the treatment, and in 7-13% of cases bowels were partially or completely obstructing the acoustic window. Usually, the bowel loops can be repositioned with bladder and/or rectum filling but these are not always sufficient to reposition the bowel loops [22, 24]. Kim et al.  reported that bladder and/or rectum filling technique is not effective in repositioning bowels in 5% of bowel obstruction cases. With an alternative or adjuvant bowel repositioning technique, the number of patients suitable for MR-HIFU treatment could be increased, and better treatment results could be achieved in cases where the bowel loops limit the treatment window.
Hesley et al.  reported that in some cases, a convex gel pad was helpful in displacing the bowel loops away from the treatment window during HIFU therapy. However, a disadvantage of the method was that the use of a convex gel pad resulted in a considerably longer distance between the transducer and targeted tissue, limiting the reach of HIFU. The study did not assess the safety and feasibility of convex gel pad for bowel displacement during HIFU therapy.
The purpose of this case report is 1) to introduce a novel way of repositioning the bowel loops positioned between the abdominal wall and the uterine fibroid by using a wedge shaped gel pad, and 2) to discuss the potential benefits and drawbacks of this technique from the aspect of safety and feasibility.
Materials and methods
MRI imaging protocols for screening, HIFU therapy and 3-month follow-up
Section thickness (mm)
Air bubble assessment
Uterine fibroid volume
Uterine fibroid volume
HIFU therapy was performed using an extracorporeal, clinical tabletop MR-HIFU system (Sonalleve V2 MR-HIFU system, Profound Medical Inc., Mississauga, Canada) in combination with a 3.0 T clinical MR scanner (Ingenia, Philips Healthcare, Best, The Netherlands). Immediately prior to the therapy, lower abdomen was depilated and a Foley catheter was inserted. Premedication (1 g paracetamol, 800 mg ibuprofen and 5 mg diazepam) was administered to reduce possible pain and discomfort during the treatment. The patient was positioned on the Sonalleve table in prone position and acoustic coupling between skin and the device was achieved with degassed and deionized water. The Sonalleve table was then advanced into the magnet bore and 3D T2-weighted TSE images were acquired and transferred to therapy delivery console for treatment planning. Based on these images, a safe sonication path was ensured by excluding any interleaving bowel loops or, if necessary, by repositioning them.
In case of bowel obstruction our protocol is 1) bladder filling (till discomfort) 2) rectum filling if necessary 3) bladder emptying. At each point we try to establish sufficient coverage (> 50% of the fibroid) to the fibroid with beam shaping or tilting. Due to natural limitations of these techniques, we are sometimes forced to apply the herein described wedged gel pad and in some cases also vaginal pessary in order to improve the position of the uterine cervix. We have used wedged gel pad in total of three cases and have achieved a satisfactory reposition of the bowel loops in all three cases.
In MR-HIFU treatments, unfavorable bowel loop position can prevent or limit the treatment window, and therefore, also the volume where HIFU therapy can be delivered to. Manipulation of the bowel loops with bladder and/or rectum filling can be attempted but these are not always sufficient to reposition the bowel loops. Hesley et al.  reported that a convex gel pad was helpful in displacing the bowel loops from the treatment window during HIFU therapy.
In this report, we assess MR-HIFU therapy of two patients with a total of four symptomatic uterine fibroids where bladder and/or rectum filling was not sufficient to reposition the bowel loops. Temperature images were closely monitored to detect any unwanted heating on the gel pad surface. Longer cooling times were used during the gel pad assisted treatments to account for cumulative heating on the skin, due to gel pad preventing the cooling effect to the skin from the direct skin cooling device. The basic principle was that the more power was used the longer cooling time was applied. The minor adverse effects in the second patient with Funaki type II fibroid could suggest that the use of wedged gel pad is not preferable in treating Funaki type III fibroids and that care should be taken when treating Funaki type II fibroids. However, there were no thermal injuries in the abdominal muscle or subcutaneous fat layer.
Poor treatment result in case two demonstrates that Funaki classification alone may not be sufficient to predict treatment outcome. Particularly in Funaki type II fibroids. In these cases perfusion and diffusion imaging might offer additional, sometimes crucial, information.
Both MR-HIFU therapies were technically successful. The wedged gel pad in the sonication beam did not seem to reduce the efficacy of the energy delivery to the target, which was expected as the gel pad mostly consists of water. Due to the asymmetric shape of the gel pad in the ultrasound beam path, a slight deformation in the ultrasound focal point might be induced. However, the patient-specific ultrasound simulations were conducted and they showed that the use of the wedged gel pad does not cause a reduction in the ultrasound peak pressure nor focal point deformation, and therefore, no therapeutic efficacy is lost.
The wedged gel pad seems to be able to create a force in anteroposterior direction which increases the pressure in the lower abdomen displacing bowel loops in cranial direction allowing a safe sonication path to the fibroid. Wedged gel pad can therefore be used as an alternative or adjuvant bowel repositioning technique. Using this technique the number of patients suitable for MR-HIFU treatment could be increased, and better treatment results could be achieved in cases where bowel loops limit the treatment window. On the other hand there are also drawbacks related to this technique, for example increased cumulative heating which can result in skin irritations. It might also be more time consuming than bladder and/or rectum filling techniques.
Among the limitations of this study have to be mentioned the small number of patients and the lack of Funaki type III fibroids, although these type of lesions are typically not well suitable for HIFU therapy .
In conclusion, our experience presented here, suggests that the use of wedged gel pad during MR-HIFU treatment could be a simple and effective tool to manipulate the bowels in cases where filling of the bladder is not sufficient to create a suitable treatment window. Wedged gel pad could also be beneficial in other situations to achieve better treatment coverage to the uterine fibroid.
Finnish Cultural Foundation.
Availability of data and materials
The datasets used and/ analysed during the current study are available from the corresponding author on reasonable request.
TS, GK, JS, KJ, AP, VS and RBS have made substantial contributions to the conception and design of the study, acquisition of data, and analysis and interpretation of data; have been involved in drafting the article; and have approved the final version to be published. VS and AV have been involved in revising it critically for important intellectual content. All authors have approved the final version to be published
Ethics approval and consent to participate
This case study was part of Treatment of Benign Uterine Disorders Using High Intensity Focused Ultrasound (MR-HIFU) trial (clinicaltrials.gov identifier NCT02914704). Local ethics committee approval was obtained from Ethics Committee, Hospital District of Southwest Finland for the protocol prior to study initiation.
Consent for publication
Consents for publication were obtained from all participants.
The authors declare that they have no competing interests.
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