Sensing volume of tissue dielectric property measurement with open-ended coaxial probe / 浙江大学学报·医学版

OBJECTIVE@#To investigate the sensing volume of open-ended coaxial probe technique for measurement of dielectric characteristics.@*METHODS@#A measurement model combining macro- measurement device with a layer model of dielectric properties parameters was established for evaluating the sensing volume of open-ended coaxial probe technique. We defined sensing depth and sensing diameter to describe the distance that could be detected in vertical and horizontal direction. Using a variety of materials with different dielectric properties (Teflon, deionized water, ethanol, and gradient concentration sodium chloride solution), a layered model of dielectric properties differentiation was established. The total combined uncertainties (TCU) were calculated for different output power, and the output power was controlled to increase from -50 dBm to 15 dBm to calibrate the error range of the dielectric properties measurement system. The optimal output power range was determined based on the results of TCU test. In sensing volume measurement experiment, we set the control groups based on measurement parameters that potentially affect the sensing volume including output power (-10, -5, 0, 3, 6, and 9 dBm), frequency (1-500 MHz), Teflon, deionized water, and ethanol to form a dielectric constant difference between high and low contrast groups. Different concentrations of sodium chloride solution and Teflon were used to generate a conductivity difference between high and low contrast groups. These groups were tested in the sensing depth and sensing diameter measurement experiments.@*RESULTS@#The result of TCU test indicated that accurate and stable measurement results could be obtained when the output power was greater or equal to-10 dBm (TCU < 2%). Sensing volume measurement experiment revealed a positive correlation between the sensing depth and output power ( < 0.05). As the measured power increased, the sensing depth gradually increased in deionized water and ethanol, and the difference reached 70 μm. The sensing depth was negatively correlated frequency ( < 0.05). As the concentration of sodium chloride solution increased, the corresponding sensing depth gradually decreased, with a difference reaching 270 μm. The sensing depth of high dielectric materials was greater than that pf low dielectric materials. The results of sensing diameter measurement were not obviously affected by the measurement parameters, and the sensing diameter was stable in a fixed range (1.0 to 1.8 mm) between the diameter of the inner conductor and the diameter of the insulation layer, and was less than the diameter of the probe.@*CONCLUSIONS@#The sensing volume of open-ended coaxial probe technique is affected by measurement parameters and dielectric properties of materials, which significantly affect the sensing depth.

Sensing volume of tissue dielectric property measurement with open-ended coaxial probe / 南方医科大学学报

OBJECTIVE@#To investigate the sensing volume of open-ended coaxial probe technique for measurement of dielectric characteristics.@*METHODS@#A measurement model combining macro- measurement device with a layer model of dielectric properties parameters was established for evaluating the sensing volume of open-ended coaxial probe technique. We defined sensing depth and sensing diameter to describe the distance that could be detected in vertical and horizontal direction. Using a variety of materials with different dielectric properties (Teflon, deionized water, ethanol, and gradient concentration sodium chloride solution), a layered model of dielectric properties differentiation was established. The total combined uncertainties (TCU) were calculated for different output power, and the output power was controlled to increase from -50 dBm to 15 dBm to calibrate the error range of the dielectric properties measurement system. The optimal output power range was determined based on the results of TCU test. In sensing volume measurement experiment, we set the control groups based on measurement parameters that potentially affect the sensing volume including output power (-10, -5, 0, 3, 6, and 9 dBm), frequency (1-500 MHz), Teflon, deionized water, and ethanol to form a dielectric constant difference between high and low contrast groups. Different concentrations of sodium chloride solution and Teflon were used to generate a conductivity difference between high and low contrast groups. These groups were tested in the sensing depth and sensing diameter measurement experiments.@*RESULTS@#The result of TCU test indicated that accurate and stable measurement results could be obtained when the output power was greater or equal to-10 dBm (TCU < 2%). Sensing volume measurement experiment revealed a positive correlation between the sensing depth and output power ( < 0.05). As the measured power increased, the sensing depth gradually increased in deionized water and ethanol, and the difference reached 70 μm. The sensing depth was negatively correlated frequency ( < 0.05). As the concentration of sodium chloride solution increased, the corresponding sensing depth gradually decreased, with a difference reaching 270 μm. The sensing depth of high dielectric materials was greater than that pf low dielectric materials. The results of sensing diameter measurement were not obviously affected by the measurement parameters, and the sensing diameter was stable in a fixed range (1.0 to 1.8 mm) between the diameter of the inner conductor and the diameter of the insulation layer, and was less than the diameter of the probe.@*CONCLUSIONS@#The sensing volume of open-ended coaxial probe technique is affected by measurement parameters and dielectric properties of materials, which significantly affect the sensing depth.

Millimeter wave exposure induces apoptosis in human melanoma A375 cells / 南方医科大学学报

OBJECTIVE@#To investigate the effects of millimeter wave (MMW) exposure on apoptosis of human melanoma A375 cells and explore the mechanisms.@*METHODS@#Through electromagnetic field calculation we simulated MMW exposure in cells and calculated the specific absorption rate (SAR). The optimal irradiation parameters were determined according to the uniformity and intensity of the SAR. A375 cells were then exposed to MMV for 15, 30, 60, or 90 min, with or without pretreatment with the caspase-3 inhibitor AC-DEVD-fmk (10 μmol/L) for 1 h at 90 min before the exposure. CCK-8 assay was used to assess the changes in the viability and Annexin-V/ PI staining was used to detect the apoptosis of the cells following the exposures; Western blotting was used to detect the expression of caspase-3 in the cells.@*RESULTS@#The results of electromagnetic field calculation showed that for optimal MMV exposure, the incident field needed to be perpendicular to the bottom of the plastic Petri dish with the antenna placed below the dish. CCk-8 assay showed that MMW exposure significantly inhibited the cell viability in a time-dependent manner ( < 0.05); exposures for 15, 30, 60, and 90 min all resulted in significantly increased apoptosis of the cells ( < 0.05). The cells with MMW exposure showed significantly increased expression of caspase-3. The inhibitory effect of MMW on the cell viability was antagonized significantly by pretreatment of the cells with AC-DEVD-fmk ( < 0.05), which increased the cell viability rate from (36.7±0.09)% to (59.8±0.06)% ( < 0.05).@*CONCLUSIONS@#35.2 GHz millimeter wave irradiation induces apoptosis in A375 cells by activating the caspase-3 protein.

Dynamic imaging of melanoma development in nude mice using high-frequency ultrasound and optical coherence tomography / 南方医科大学学报

OBJECTIVE@#To investigate the application of high-frequency ultrasound (HFUS) and optical coherence tomography (OCT) for monitoring the progression of cutaneous melanoma (CM) in nude mice.@*METHODS@#Twenty 4-week-old nude mice were randomly divided into CM group (=16) and control group (=4). In CM group, A375 cell suspension were injected subcutaneously on the back of the nude mice, and only culture medium was injected in the control group. The tumor growth was monitored by gross observation and with HFUS and OCT on a daily basis. The tumor formation rate, time, and size were recorded and melanoma visibility was assessed quantitatively using the contrast- to-background-noise ratio (CNR). Twentyfour days after cell implantation, the tumors were dissected for pathological examination.@*RESULTS@#The tumor formation rate was 87.5% in CM group. OCT detected tumor formation at an earlier time than HFUS. With the growth of the tumor, HFUS detected spots or bands of strong echoes, and flattening of the upper dermis could be observed in OCT; the of HFUS and OCT were obviously enhanced over time ( < 0.05). The tumor growth curve showed that OCT was more sensitive for measurement of the tumor thickness than HFUS. The length, depth and volume of the tumors measured by HFUS were significantly greater than those measured by OCT ( < 0.05).@*CONCLUSIONS@#HFUS and OCT can monitor the dynamic development of cutaneous melanoma in nude mice, and their imaging performance differs in different stages of tumor development.

The open-ended coaxial line method for colorectal cancer detection and depth evaluation of tumor invasion / 实用医学杂志

Objective To confirm whether the open-ended coaxial line is effective in detection of the differences in dielectric properties between colorectal cancer tissues and surrounding normal tissues and evaluation of the depth of tumor invasion. Methods The open-ended coaxial line system at frequencies ranging from 50 to 500 MHz in 98 freshly excised colorectal cancerous specimens obtained from the operating theatre of Zhujiang Hospital, was used to detect both the relative permittivity and conductivity on the serosal surface of the carcinoma nidus, the mucosa of the carcinoma nidus, and the mucosa of the surgical resection margin. Pathological examinations were conducted on each specimen after surgery. Results The values for relative permittivity and conductivity of the colorectal cancerous mucosa were significantly higher than those of the normal mucosa (P < 0.01). For the tumor which had invaded or penetrated the serosa (stage ≥ T3), the dielectric properties of both the cancerous serosa and mucosa were higher than the one restricted to muscularis propria or less intestine wall (stage < T3) over the measured frequency range, and there existed statistical differences at the common frequencies of 213 MHz and 426 MHz. Conclusion The open-ended coaxial line system may result in fast and effective diagnostic differentiation between cancerous and normal colorectal tissues as well as reasonable assessment of the tumor infiltration depth.

B(1) field homogeneity and specific absorption rate in ultra-high field magnetic resonance imaging for guiding high-intensity focused ultrasound / 南方医科大学学报

<p><b>OBJECTIVE</b>To study the efficacy of B1 field shimming technique and evaluate the specific absorption rate (SAR) in ultra-high field magnetic resonance imaging (MRI) for MRI-guided high-intensity focused ultrasound (HIFU).</p><p><b>METHODS</b>An electromagnetic model of the female pelvis with a temperature gradient was established. B1 field homogeneity and local SAR were simulated and calculated using regular and optimized B1 shimming coefficients.</p><p><b>RESULTS</b>The maximum local SAR reached 10.24 W/kg, which exceeded the safe threshold of 10 W/kg, as calculated using regular B1 shimming coefficients in the normal model. Using the optimized B1 shimming coefficients, the maximum local SAR of the tissue was 9.65 W/kg, which was below the safe threshold.</p><p><b>CONCLUSION</b>The temperature distributions in the body generated by ultrasound energy need to be considered in ultra-high field MRI-guided HIFU surgery. The proposed optimized B1 shimming strategy based on the temperature gradient can be used to control the local SAR levels.</p>

Research of the influences on the electromagnetic fields by the pelvic tissues in the design of the radio frequency coils / 生物医学工程学杂志

In the present study, the effect of the electromagnetic field, induced by radio frequency (RF) coils and coupled with the pelvic tissues, was calculated with the method of finite difference time domain (FDTD). Using the established electromagnetic model of human pelvis region, the simulation was implemented. The imaging uniformity was quantitatively calculated and scaled with the values of the percentage image uniformity (PIU). The electromagnetic model was derived from the anatomical data of human pelvic region and loaded into the simulation. The results showed that the homogeneity of the magnetic fields was severely damaged due to the coupling between the RF coil and the human tissues when loaded with the human pelvis in the Birdcage RF coils at 3T. The research results set a basis meaningful for the design of RF coils.

Decoupling of multi-channel RF coil and its application in the intraoperative MRI / 生物医学工程学杂志

The coupling from different elements of the multi-channel coil leads to the splitting of the resonance frequency and deviation from the Lamor frequency. Decoupling between different elements is the key technology in the design of the radiofrequency (RF) coil. The electrical decoupling circuits should vary with different arrangements of the elements. A novel method of decoupling for the RF coil used in the intraoperative MR-guided focused ultrasound system is reported in the paper. The prototype RF coil was made according to the proposed decoupling method. The bench test of the prototype showed that the performance of the decoupling of the coil was excellent. The images in vivo were acquired with the designed prototype RF coil.