Distribution of Treatment Time in Physiotherapeutic Application of Ultrasound

Abstract

Background and Purpose In physiotherapy, the ultrasound transducer is moved across the treated area. Because of the movement, some points in the tissue are exposed to soundwaves for less than the total treatment time. In the literature, some authors use the total treatment time, while others use an average local exposure time to describe the temporal part of the exposure. It is unknown to what degree the total treatment time and the planned average local exposure time actually represent the local exposure. The reproducibility and sources of variation in spatial and temporal distribution of local exposure time across the tissue were investigated in this work. Method Ideal scanning patterns were constructed mathematically, and manual application patterns from 22 therapists were sampled using a digitiser. One transducer model and various sizes of tissue models were used. From these application patterns the distributions of local exposure were calculated. The calculation model consisted of a circle, representing the cross-section of the beam, moving across a plane surface, the tissue. By relating the beam position to tissue co-ordinates, the local exposure periods were found. Results Constructed applications showed an excellent match between planned and resulting average exposure. The therapists produced median local exposure times that were 0.3-0.9 times the planned average local exposure time. Considerable variation was found, where the calculated maxima were 0.4-3.8 times the planned average values. Conclusion Part of the variation is inherent in the nature of scanning application. Careful planning, concentration and guidelines drawn around the lesion increased the reproducibility of manual application. While the total treatment time alone was inadequate as a time parameter, the planned average local exposure time predicted the central tendency of the exposure, when the application was confined to the designated area. The investigation indicated that clinical testing of different application strategies with equal average exposure is necessary. In physiotherapy, the ultrasound transducer is moved across the treated area. Because of the movement, some points in the tissue are exposed to soundwaves for less than the total treatment time. In the literature, some authors use the total treatment time, while others use an average local exposure time to describe the temporal part of the exposure. It is unknown to what degree the total treatment time and the planned average local exposure time actually represent the local exposure. The reproducibility and sources of variation in spatial and temporal distribution of local exposure time across the tissue were investigated in this work. Ideal scanning patterns were constructed mathematically, and manual application patterns from 22 therapists were sampled using a digitiser. One transducer model and various sizes of tissue models were used. From these application patterns the distributions of local exposure were calculated. The calculation model consisted of a circle, representing the cross-section of the beam, moving across a plane surface, the tissue. By relating the beam position to tissue co-ordinates, the local exposure periods were found. Constructed applications showed an excellent match between planned and resulting average exposure. The therapists produced median local exposure times that were 0.3-0.9 times the planned average local exposure time. Considerable variation was found, where the calculated maxima were 0.4-3.8 times the planned average values. Part of the variation is inherent in the nature of scanning application. Careful planning, concentration and guidelines drawn around the lesion increased the reproducibility of manual application. While the total treatment time alone was inadequate as a time parameter, the planned average local exposure time predicted the central tendency of the exposure, when the application was confined to the designated area. The investigation indicated that clinical testing of different application strategies with equal average exposure is necessary.