Tapani Lahtinen

Measurement of dielectric properties of subcutaneous fat with open-ended coaxial sensors

A three-layer model of stratum corneum, epidermis/dermis and subcutaneous fat has been developed for the capacitance of an open-ended coaxial line in contact with human skin. Applying the model, the electrical properties of subcutaneous fat can be calculated from skin dielectric measurements with three probes of different sizes. The three-layer model is based on a variational formula for the capacitance of the coaxial probe. An accurate approximation for the dielectric constant of the multilayer cutaneous structure is presented for the inverse problem of solving the dielectric constants of various layers. The method was tested at 300 MHz with breast cancer patients who often have radiotherapy-induced late alterations in the structure of subcutaneous fat due to the development of subcutaneous fibrosis. Measurements from 206 sites yielded a good agreement between the dielectric constant of subcutaneous fat and the clinical score for subcutaneous fibrosis.

A closed unventilated chamber for the measurement of transepidermal water loss

Background/aims Open chamber systems for measuring transepidermal water loss (TEWL) have limitations related to ambient and body‐induced airflows near the probe, probe size, measurement sites and angles, and measurement range. The aim of the present investigation was to develop a closed chamber system for the TEWL measurement without significant blocking of normal evaporation through the skin. Additionally, in order to use the evaporimeter to measure evaporation rates through other biological and non‐biological specimens and in the field applications, a small portable, battery‐operated device was a design criteria.

A dielectric method for measuring early and late reactions in irradiated human skin

BACKGROUND AND PURPOSE To measure the dielectric constant of irradiated human skin in order to test the feasibility of the dielectric measurements in the quantitation of acute and late radiation reactions. MATERIALS AND METHODS The dielectric constant of irradiated breast skin was measured at an electromagnetic frequency of 300 MHz in 21 patients during postmastectomy radiotherapy. The measurements were performed with an open-ended coaxial line reflection method. The irradiation technique consisted of an anterior photon field to the lymph nodes and a matched electron field to the chest wall using conventional fractionation of five fractions/week to 50 Gy. Fourteen out of the 21 patients were remeasured 2 years later and the skin was palpated for subcutaneous fibrosis. RESULTS At 5 weeks the dielectric constant had decreased by 31 and 39% for the investigated skin sites of the photon and electron fields, respectively. There was a statistically significant inverse correlation between the mean dielectric constant and the clinical score of erythema. An unexpected finding was a decrease of the dielectric constant of the contralateral healthy skin during radiotherapy. Two years later a statistically significant positive correlation was found between the dielectric constant at the irradiated skin sites and the clinical score of subcutaneous fibrosis. CONCLUSIONS Dielectric measurements non-invasively yield quantitative information concerning radiation-induced skin reactions.

Variational formulation of open-ended coaxial line in contact with layered biological medium

An open-ended coaxial probe designed to measure layered biological media is analyzed with a new method. The probe is considered as an electrostatic circuit element whose capacitance is solved using a stationary functional. The fundamental transverse electric and magnetic field (TEM)-mode and the series of evanescent wavemodes in the coaxial cable are used as basis functions. The field outside the probe is solved using a Hankel transform. The capacitance is calculated for homogeneous materials and two-layer structures and the results are compared with values measured with a phantom model. The method can be easily extended for structures with an arbitrary number of layers. A practical approximation for two-layer cases, originally developed to take into account the effect of subcutaneous fat in skin measurements, is presented and its validity for different combinations of dielectric constants and the thickness of the first layer is demonstrated. The static approximation limits the frequency range, but it covers biological measurements up to 500 MHz. The developed method is accurate and easy to adopt in practice.

Measurement of hydration in the stratum corneum with the MoistureMeter and comparison with the Corneometer

Background/purpose: MoistureMeter is a novel capacitive device for measuring the hydration of stratum corneum (SC). The capacitor ‘plates’ are formed by the probe material and the well‐conducting epidermal–dermal skin layers, while the dry layer of SC acts as an ‘insulator’ of the capacitor. Due to this measurement principle, the measurement depth is not constant, but equal to the thickness of the dry layer of SC. The present study was undertaken to test the MoistureMeter SC‐2 in an experimental setup simulating the uppermost skin structure. The sensitivity of the MoistureMeter was compared with a conventional device Corneometer CM 820 in eight healthy volunteers.

Penetration of electromagnetic fields of an open-ended coaxial probe between 1 MHz and 1 GHz in dielectric skin measurements.

An open-ended coaxial probe is often used for investigating the dielectric properties of biological tissues. The present study indicates that in addition to the probe size, the penetration of the electromagnetic (EM) fields of an open-ended coaxial probe in contact with the skin is dependent on the applied frequency between 1 MHz and 1 GHz. At high frequencies, above 100 MHz, the measured dielectric parameters are functions of the dielectric properties of different cutaneous layers and subcutaneous fat. At lower frequencies, less than 10 MHz, the measurement is mainly dependent on the dielectric properties of superficial structures of the skin. The reason for this is that the probe, the surface of the skin, mainly stratum corneum, and underlying skin form a capacitance where the stratum corneum with low water content lies between the well-conducting dermis and the probe. The situation is equivalent to the frequency-dependent Maxwell-Wagner interfacial polarization. This result is verified by experimental dielectric measurements and with human skin in vivo.

Dielectric constant of skin and subcutaneous fat to assess fluid changes after cardiac surgery

The ability to objectively determine the degree of tissue edema and to monitor on-line fluid balance in critically ill patients would be a clinical benefit. In this prospective descriptive trial, we evaluated a new noninvasive method--dielectric constant of skin and subcutaneous fat (SSF)--in assessing fluid balance during cardiac surgery. The dielectric constant at the applied high radiofrequency is a direct measure of tissue water content. Twenty-nine patients with elective cardiac surgery participated in the study. Dielectric constants on forearm, thigh and abdomen were measured before surgery, within 1 h after surgery and in the first, second, third and fourth postoperative morning. At the same time the patients were weighed, except immediately after the operation and the first postoperative day when fluid balances were calculated. A statistically significant correlation (r = 0.60, p < 0.01) was found between the increase of the dielectric constant of SSF and weight gain of the patients from the baseline to the second postoperative morning. From the second to the fourth postoperative day when the patients were losing the weight, a statistical significant correlation between the dielectric constant and weight loss was not found. The results suggest that the measurement of the dielectric constant is a promising new method in assessing the fluid status of operated patients during the time the patients cannot be weighed.

Dielectric properties of the skin

Department of Oncology, Kuopio University Hospital, FIN-70210 Kuopio, Finland Received 1 April 1997

Eight years experience of local prostate cancer treatment with permanent I125 seed brachytherapy--morbidity and outcome results.

BACKGROUND AND PURPOSE There are only a limited number of reports of treatment of prostate cancer with permanent prostate seed I(125) brachytherapy (PPB) in Europe. We describe results from one Finnish institution having treated 444 patients with a follow-up of eight years. MATERIAL AND METHODS Morbidity was evaluated by International Prostate Symptom Score and International Index of Erectile Function questionnaires. Urine flow, residual urine volume and the PSA values were measured pre-treatment and during follow-up. Any additional treatments were recorded. RESULTS PPB was well tolerated. Median IPSS increased from 8 at baseline to 18 at three months post-therapy and returned to baseline score within 12 months. Median urine flow decreased from 15.2 ml/s at baseline to 10.2 ml/s at three months and returned to baseline value within two years. Acute urinary retention, potency preservation and severe proctitis were observed in 11%, 86% and 2% of patients, respectively. The PSA bounce was observed in 13% and PSA nadir < or =0.5 microg/l was reached by 81% of patients. Disease-free survival (DFS) was 90.2%. In the Cox regression analysis, the independent predictors of DFS were risk group and PSA nadir < or =0.5 microg/l (p<0.0001 for both). PC-specific survival was 98.5% and overall survival was 94.6%. CONCLUSIONS Our results are in concordance and comparable with other reports on PPB.

Measurement of oedema in irritant-exposed skin by a dielectric technique.

Background: Easily applicable water‐specific instruments measuring local oedema in skin are not available. The aim of this study is to demonstrate quantitative assessment of skin oedema with the dielectric technique by measuring increase of skin water content related to sodium lauryl sulphate (SLS)‐induced irritant contact dermatitis.