Study of Freezing and Defrosting Effects on Complex Permittivity of Biological Tissues

Abstract

We study the effect of freezing and defrosting on the dielectric properties of biological tissues. The electromagnetic characterization of tissues at microwave frequencies is crucial for the development of microwave-based biomedical devices. These measurements are often not practical, as tissue degradation restricts the time available between tissue excision and dielectric measurements. For this reason, measurement of tissues that underwent freezing and defrosting may provide researchers with more flexibility in setting measurement campaigns, thus speeding up the development of microwave-based biomedical devices. To this end, this paper presents dielectric measurement on frozen and defrosted tissue, which translates into the following objectives: (i) investigate if the dielectric properties of defrosted tissues depend on frozen storage time; (ii) determine if defrosted tissue dielectric properties differ from those of fresh tissues. As a result, we measure the dielectric properties of 10 samples of chicken muscle, bovine liver, and bovine fat, each before and after freezing (up to 14 days) and defrosting. The measurements are performed with the open-ended coaxial-probe method at the frequency band of 0.5 -8.5 GHz. We observe a slight increase -less than 10% -in complex permittivity of high-water-content tissues (muscle and liver) after defrosting, and negligible effect on fat tissues.

Analysis of the Mechanical Characteristics of Human Pancreas through Indentation: Preliminary In Vitro Results on Surgical Samples

“…Freezing, unlike cryopreservation, not only preserves cell vitality but also maintains the mechanical properties of the analyzed tissues. Previous studies on soft materials have demonstrated that viscoelastic features remain unchanged after freezing at −80 • C for 14 days, showing no statistically significant differences [21][22][23]. Nevertheless, due to the lack of similar tests involving pancreatic tissue, we chose to compare fresh samples with those post-freezing, analyzing the same sample at identical points before and after freezing.…”

“…Nevertheless, due to the lack of similar tests involving pancreatic tissue, we chose to compare fresh samples with those post-freezing, analyzing the same sample at identical points before and after freezing. Building on previous studies conducted on various biological tissues [23], we adopted a gradual defrosting protocol. All the samples were kept at −20 • C for 12 h and subsequently at 5 • C for the next 5 h. Following this, they were hydrated with saline solution for 1 h and subjected to indentation once they reached a stable temperature of 18-20 • C.…”

Controlled Measurement Setup for Ultra-Wideband Dielectric Modeling of Muscle Tissue in 20–45 °C Temperature Range

“…Afterwards, they were stored in a fridge at 7 • C to prevent tissue degradation. Recent studies demonstrate the negligible influence of storage on dielectric measurements at frequencies above 1 kHz [24,34,35]. Experiments were performed at eight different temperatures from room temperature up to hyperthermia temperatures with special attention for body temperature (20,25,30,35,37,40,43, and 45 • C).…”

“…Recent studies demonstrate the negligible influence of storage on dielectric measurements at frequencies above 1 kHz [24,34,35]. Experiments were performed at eight different temperatures from room temperature up to hyperthermia temperatures with special attention for body temperature (20,25,30,35,37,40,43, and 45 • C). Before every round of measurements at a single temperature, three samples of 2 cm × 2 cm × 2 cm were freshly cut off.…”

Dielectric Characterization of Healthy Human Teeth from 0.5 to 18 GHz with an Open-Ended Coaxial Probe

“…Microwave imaging has been used in medical applications, including the imaging of breast cancer [ 19 ], axillary lymph nodes [ 20 , 21 , 22 ], brain strokes [ 23 , 24 ] and bones [ 25 ]. These medical applications have justified the study of dielectric properties of many biological tissues, including liver [ 26 ], breast [ 27 , 28 ] among many others [ 29 , 30 ], and have triggered classification based studies [ 31 , 32 , 33 , 34 , 35 , 36 ]. Experimental work carried out in the field of dentistry has shown that frequencies in the microwave/millimetre-wave range are able to discriminate between healthy teeth and teeth with visible caries [ 37 , 38 ], which motivates further investigation of microwave diagnostics applicability in detecting healthy teeth and teeth affected by caries.…”