Interactive monitoring system for visual respiratory ...

Current Directions in Biomedical Engineering 2016; 2(1): 723–726

Open Access Robert Odenbach*, Axel Boese and Michael Friebe

Interactive monitoring system for visual respiratory biofeedback Assessment of an air bellows belt DOI 10.1515/cdbme-2016-0157

Abstract: In almost any medical procedure respiratory motion is an issue and may result in image degradation. Most currently available devices and systems, which are intended to reduce respiratory influences do not come into operation however in clinics due to their high cost and complex operation. In our paper we evaluated an interactive breath hold control system that helps flat breathing to subsequently reduce respiratory motion during signal acquisitions or procedure treatments. With that the human subjects are enabled to regulate their own breath by following visual feedback via a specially designed display. That display shows biofeedback information about the respiratory excursion through air pressure deviations measured inside an air bellows belt. The system was assessed quantitatively in a laboratory setup and qualitatively by applications in real clinical procedures. The obtained results are very promising and can be further improved with additional developments to provide an easy to use and relatively inexpensive solution for respiratory motion related imaging problems. Keywords: air belt; breath hold; flat breathing; respiratory motion; visual biofeedback.

1 Introduction There are imaging methods such as computed tomography (CT), ultrasound (US) or magnetic resonance imaging (MRI) and interventional (biopsy, radiation therapy) procedures in which respiratory motion of organs (e.g. liver,

*Corresponding author: Robert Odenbach, Department of Medical Engineering, Otto-von-Guericke-University of Magdeburg, Germany, E-mail: [email protected] Axel Boese and Michael Friebe: Department of Medical Engineering, Otto-von-Guericke-University of Magdeburg, Germany, E-mail: [email protected] (A. Boese); [email protected] (M. Friebe)

pancreas, lung) may have a negative influence on procedure time or the obtained image quality. Especially in case of radiation therapy, healthy tissue can be excessively harmed due to the application of high radiation dose rates [1–3]. In order to reduce these problems and to minimise the delivered dose we evaluated the application of an interactive monitoring system for visual respiratory biofeedback (interactive breath hold control system – IBC, Medspira LLC, MN, USA) [1, 4], see Figure 1. That system is intended to help the patients to interactively control and regulate their own respiration during procedure time. For that, it transforms the respiratory dilatation, related to a reference point set before, to light signals. These light signals give information about the respiratory amplitude via a display which is visible for the patient. There are multiple respiratory motion measuring systems available e.g. based on optical tracking or image reconstruction. But those are generally quite expensive and are limited in operation due to the bounded space in a CT-gantry or radiation therapy system. Furthermore e.g. the present optical systems are relatively complex to apply and operate and additional expert staff may be required [5–10]. Hence, current procedures in clinics are mostly performed under free and steady breathing, without giving any kind of feedback to the patient. As the IBC is appropriate for application in CT-gantries, we wanted to evaluate the qualitative benefit of the system tested under realistic conditions in clinical applications. For that purpose, an assessment of the clinicians was obtained. In addition, the extra time for setting up the system and for instructing the human subjects should be measured quantitatively in the clinical workflow. Finally, the complete implementability of the IBC to the clinical workflow should be studied qualitatively. We initially performed laboratory tests to analyse the difference between the respiratory motion without and with the visual biofeedback control display. These tests were made under ideal conditions to determine the

© 2016 Robert Odenbach et al., licensee De Gruyter. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 License.

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right side in relation to the centre light. With that biofeedback signal on the display, the patient should be able to hold his breath in better quality or should be enabled to breathe with a lower respiratory excursion compared to free breathing.

2.1 Lab tests

Figure 1: The complete IBC-system with base unit, air bellows belt and multiple wireless displays [image source: Medspira LLC, MN, USA].

maximum effect of the IBC for respiratory motion compensation. Subsequently we tested the system in clinical applications during CT-imaging and radiation therapy procedures, respectively. Our hypothesis for the benefit of the IBC primarily was that the patient would be enabled to interactively and significantly decrease the amplitude of respiration. With that, e.g. radiation of structures outside a specific target volume could be decreased because of a more controlled and adjusted organ motion during radiation therapy. With that the quality of the CT-images should be enhanced, which might have a positive influence on shortening the duration of these procedures and minimising the delivered dose.

2 Material and methods The IBC consists of a base unit, the air bellows belt and multiple wireless displays. The air bellows belt is positioned around the thorax or abdomen exactly on the location of the maximal excursion during breathing. While the patient is breathing, the length of the belt alters and the air pressure inside of it changes. The main function of the base unit is to measure these air pressure variations and to transfer the signal to the wireless display according to an adjustable sensitivity. After calibration of the system on a predetermined and individual breathing position, only the centre light of the display lights up. The higher the alternation of the beltlength becomes with inhalation and exhalation, the more led-lights are lighted to the left and, respectively to the

The comparison test was performed on four healthy subjects (four male, age: 24–28 years). The IBC sensitivity was set on the middle level 3 (one led-light = 1 mm variation of belt length). Then the subjects were told to hold their breath at a comfortable respiratory position for 5 s in order to calibrate the reference point. For the first run, each subject was instructed to breathe freely and steady without any kind of feedback signal which represents the usual clinical procedure. The respiration was measured with the IBC and recorded with appropriate software. After a break of 5 min, the wireless display was mounted in the field of vision of the subjects. A training period of 3 min allowed the subjects to breathe according to the active principle of the IBC. For the second run the subjects were instructed to breathe with the help of the visual biofeedback signal from the wireless display with the lowest possible respiratory excursion. Each of these two runs was operated in a total time of 3 min.

2.2 Clinical tests The clinical application tests were performed during CTimaging and radiation therapy procedures. The IBC was set up in the respective suites without any operational interconnection to other systems. For safety reasons (e.g. risk of falling) it was operated without the power cable in battery mode. Once the subjects arrived and were positioned on the patient table, the location of the individual maximal respiratory excursion was identified and the bellows belt was put as close as possible to it with regard to other attached systems (e.g. ECG electrodes). These tests were all done with the subjects having a direct view on the biofeedback display as shown in Figure 2. Comparison tests without the wireless display were not executed because of a high variation of the given test parameters in the clinic (in particular: procedure time, subject repetitions, availability of clinicians). During the complete procedure time and the operation of the IBC, the subjects were not given any further specific commands.


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The other excursion lights illuminate all in green: the higher the excursion is the more green lights are illuminated. Confusion appeared as the “good zone” lighted up in red lights and the “bad zone” in green. In addition, the duration of 3 min of flat breathing with the biofeedback display was described to require a certain amount of concentration, although the sensitivity of the base unit was set in the middle level.

3.2 Clinical tests

Figure 2: Application of the IBC during one radiation therapy procedure. Subject with air bellows belt around its abdomen and the wireless display in his field of view.

3 Results 3.1 Lab tests The recorded respiration curves of both sessions are shown in Figure 3. Comparing the measurements with and without the visual feedback shows that large differences of respiratory motion are observable. With the help of the biofeedback the subjects were able to reduce their respiratory excursion between 32.8% and 59.7% (average: 50.35%). Following the measurement, we also interviewed the subjects on their experience with the IBC. Primarily the arrangement of the color scale on the biofeedback display was perceived as irritating. The reference light in the center of the display is coloured in red.

In the clinical tests it took 10 min on average to install the system in the suite and on the subjects. Additional 5 min were needed for instructing the subjects. Apart from these installation and instruction times, the use of the IBC did not have a further negative influence on the duration (10–20 min) of the respective clinical procedures. At the end the belt could rapidly be removed from the subjects, but a distinct skin impression, caused by the edges of the holding plate, was visible on their backs. The system was well accepted by the subjects and was described as very helpful for respiratory orientation. In combination with the concentration on the IBC signal and the associated regulation of the own respiration to low excursion, the comfort of the procedure was described as physically and mentally stressful all the way up to exhausting. The clinicians remarked that the system is simple to install and provides valuable feedback for the subjects. Even though no comparative values could be gained, they assessed from experience that the respiratory motion of the subjects was more regular compared to free breathing. Giving the subjects a visual biofeedback on their respiration was considered as very useful to reduce

Figure 3: Excerpt from the recordings of the respiratory motion measuring with the IBC and comparison of the respiratory excursion from subject 1–4 without (red curve) and with (blue curve) the visual biofeedback signal.


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any negative influence caused by respiratory motion. All clinical test procedures were performed without any complications.

4 Conclusion We have successfully performed our tests with the Medspira Breath Hold Control System in the clinic during procedures with a CT-Scanner and a tomotherapy system, as well as for objective reference measurements in our lab. Our tests have shown that the IBC contributes to a reduction of respiratory motion to an average of 50%. It is simple and fast to install and the operation is easily explained and understood by the patients. The system operated stable and free from any errors. The conversion of the air pressure variations in the air bellows belt to the lights from the wireless display was precise enough to indicate respiratory motion. For future technical improvement we consider that the array of the colour scale should be inverted together with the addition of a “medium”, yellow lighted zone in between the green and red zone. With that the wireless display should provide more intuitive feedback to the patient. Furthermore, an external interface can be added to allow transmission of the respiratory motion for MRI/CT/LINAC triggering purposes. Theoretically the data could also be used for retrospective correction of images and for a warning to the radiographer. Regarding the workflow in the clinic we think it would be reasonable to give the patient some extra training sessions on the IBC in advance to the actual procedure and in the meantime to test and adjust the optimal sensitivity of the system. With that the patient would have better experience working with the system and the application of the system in the clinical workflow would be even faster, which might lead to higher acceptance by the clinicians. We also think that the implementation of specific breathing commands can also help to reduce physical and mental stress to patients by limiting the respiratory regulation to the actual duration that is needed for the respective procedures (e.g. tomotherapy sequences).

Author’s Statement Research funding: This research was funded by the German BMBF (grant 03IPT7100X). Conflict of interest: Authors state no conflict of interest. Material and Methods: Informed consent: Informed consent has been obtained from all individuals included in this study. Ethical approval: The research related to human use complies with all the relevant national regulations, institutional policies and was performed in accordance with the tenets of the Helsinki Declaration, and has been approved by the authors’ institutional review board or equivalent committee.

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