Millimeter wave silicon micromachined waveguide probe as an aid for skin diagnosis--results of measurements on phantom material with varied water content.

BACKGROUND: More than 2 million cases of skin cancer are diagnosed annually in the United States, which makes it the most common form of cancer in that country. Early detection of cancer usually results in less extensive treatment and better outcome for the patient. Millimeter wave silicon micromachined waveguide probe is foreseen as an aid for skin diagnosis, which is currently based on visual inspection followed by biopsy, in cases where the macroscopical picture raises suspicion of malignancy. AIMS: Demonstration of the discrimination potential of tissues of different water content using a novel micromachined silicon waveguide probe. Secondarily, the silicon probe miniaturization till an inspection area of 600 × 200 µm2, representing a drastic reduction by 96.3% of the probing area, in comparison with a conventional WR-10 waveguide. The high planar resolution is required for histology and early-state skin-cancer detection. MATERIAL AND METHODS: To evaluate the probe three phantoms with different water contents, i.e. 50%, 75% and 95%, mimicking dielectric properties of human skin were characterized in the frequency range of 95-105 GHz. The complex permittivity values of the skin are obtained from the variation in frequency and amplitude of the reflection coefficient (S11), measured with a Vector Network Analyzer (VNA), by comparison with finite elements simulations of the measurement set-up, using the commercially available software, HFSS. The expected frequency variation is calculated with HFSS and is based on extrapolated complex permittivities, using one relaxation Debye model from permittivity measurements obtained using the Agilent probe. RESULTS: Millimeter wave reflection measurements were performed using the probe in the frequency range of 95-105 GHz with three phantoms materials and air. Intermediate measurement results are in good agreement with HFSS simulations, based on the extrapolated complex permittivity. The resonance frequency lowers, from the idle situation when it is probing air, respectively by 0.7, 1.2 and 4.26 GHz when a phantom material of 50%, 75% and 95% water content is measured. DISCUSSION: The results of the measurements in our laboratory set-up with three different phantoms indicate that the probe may be able to discriminate between normal and pathological skin tissue, improving the spatial resolution in histology and on skin measurements, due to the highly reduced area of probing. CONCLUSION: The probe has the potential to discriminate between normal and pathological skin tissue. Further, improved information, compared to the optical histological inspection can be obtained, i.e. the complex permittivity characterization is obtained with a high resolution, due to the highly reduced measurement area of the probe tip.

Initial experiences with a miniaturized pressure transducer during coronary angioplasty.

A newly constructed pressure sensor with a diameter of 0.45 mm was evaluated in 15 patients undergoing balloon coronary angioplasty (PTCA). The sensor and an optic fiber were mounted on a 0.018" guide wire, which was used in the balloon catheter. Pressure gradients were recorded before and after PTCA, respectively. The pressure tracings were of satisfactory quality in all cases. The mean systolic and diastolic gradients before PTCA were 32 +/- 20mm Hg and 44 +/- 26mm Hg, respectively. Pressure gradients were also obtained with the balloon placed in the lesion in order to simulate the conventional way of pressure measurement through the balloon catheter. In this setting, the systolic and diastolic gradients were 77 +/- 32mm Hg and 59 +/- 25mm Hg, respectively. Following balloon dilatation, the systolic pressure gradient decreased to 14 +/- 12mm Hg, and the diastolic gradient to 13 +/- 11mm Hg. In conclusion, this new pressure sensor delivers recordings of good quality and may be especially of interest during angioplasty due to its small diameter.