RESEARCH DEVELOPMENT

Kurt Grey

Physiotherapist

Seven Methods for Measuring the Treated Area

Grey, K: ”Surface Areas in Ultrasound Therapy. Evaluation of Seven Measurements for Measuring the Treated Skin Area in Physiotherapeutic Application of Ultrasound.” Scand J Rehab Med, 25: 11-15, 1993. (Original paper, peer-reviewed).

ABSTRACT. Recent articles on ultrasound (US) do not contain information about precise dosage, thus risking a nonvalid conclusion of possible effects. To ensure safer standards in treatment time, the present study compared 7 methods for the calculation of areas. Measurement by eye had a median relative difference (MRD) from the true reading of 22% (lower quartile(l.q.)=-14%, upper quartile(u.q)=+46%), with large intraindividual varia­tion, the span of MRD being ‑46% to +53%. Measuring with the transducer showed a systematic error: MRD was ‑48% (l.q.=-55%, u.q.=-35%), which is unacceptable. Areas were measured with satisfactory accuracy with 5 methods that re­quire little training and use accessories, some of which are inexpensive. Plates with ellipses of known size had a MRD of 0.1%, (l.q.=-3%, u.q.=+2%), while rulers showed MRD of ‑2%, (l.q.=‑0.6%, u.q.=+5%) both on selected mate­rial. The most accurate and versatile instruments were a plani­meter (MRD=-0.1%; l.q.=‑0.6%; u.q.=+0.5%), a Mettler weighing apparatus (MRD=3%; l.q.=2%; u.q.=6%), and a digitizer (MRD=-0.1%; l.q=‑0.4%; u.q=+0.3%).

Fig 1. Measuring a rectangular lesion by the ultrasound transducer head (turquoise) tends to underestimate the area of the lesion. In the study above the underestimate was 48%.

The transducer rarely fits the lesion exactly. The exceeding area is shown by dark blue covered with the numbers "1". The Beam area (ERA) (covered by the numbers "3") is usually smaller than the transducer housing ("2" and "3").

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