Department of Biomedical Engineering, Kyung Hee University, Yongin-si, Gyeonggi-do 446-701, Korea.
Biomed Eng Online. 2012 Sep 25;11:75. doi: 10.1186/1475-925X-11-75.
Malignant breast tumor tissue has a significantly different electrical impedance spectrum than surrounding normal tissues. This has led to the development of impedance imaging as a supplementary or alternative method to X-ray mammography for screening and assessment of breast cancers. However low spatial resolution and poor signal to noise ratio has limited the clinical application.
In order to improve spatial resolution we developed a trans-admittance mammography (TAM) system including an array of 60×60 current sensing electrodes. We adopted a similar setup to X-ray mammography where the breast is situated between two holding plates. The top plate is a large solid metal electrode for applying a sinusoidal voltage over a range of frequencies from 50 Hz to 500 kHz. The bottom plate has 3600 current sensing electrodes that are kept at the ground potential. Currents are generated from the top voltage-applying electrode and spread throughout the breast, entering the TAM system through the array of current sensing electrodes on the bottom plate. The TAM system measures the exit currents through 6 switching modules connected to 600 electrodes each. Each switching module is connected to 12 ammeter channels which are switched sequentially to 50 of the 600 electrodes each measurement time. Each ammeter channel is comprised of a current-to-voltage converter, a gain amplifier, filters, an analog to digital converter, and a digital phase sensitive demodulator.
We found an average noise level of 38 nA, amplitude stability of less than 0.2%, crosstalk of better than -60 dB and 70 dB signal to noise ratio over all channels and operating frequencies. Images were obtained in time difference and frequency difference modes in a saline phantom.
We describe the design, construction, and calibration of a high density TAM system in detail. Successful high resolution time and frequency difference images showed regions of interest with the expected admittivity changes in the frequency spectrum.
恶性乳腺肿瘤组织的电阻抗频谱与周围正常组织有显著差异。这导致了阻抗成像作为 X 射线乳腺摄影的补充或替代方法的发展，用于筛查和评估乳腺癌。然而，低空间分辨率和较差的信噪比限制了其临床应用。
为了提高空间分辨率，我们开发了一种 Trans-admittance 乳腺摄影（TAM）系统，该系统包括 60×60 个电流感应电极阵列。我们采用了类似于 X 射线乳腺摄影的设置，将乳房置于两个固定板之间。上极板是一个大的固体金属电极，用于在 50 Hz 至 500 kHz 的频率范围内施加正弦电压。下极板有 3600 个电流感应电极，保持在接地电位。电流从上极板的施加电压产生，并在乳房中传播，通过下极板上的电流感应电极阵列进入 TAM 系统。TAM 系统通过连接到每个测量时间的 600 个电极中的 6 个开关模块来测量出口电流。每个开关模块连接到 12 个电流表通道，这些通道顺序切换到每个测量时间的 50 个 600 个电极中的 12 个。每个电流表通道由电流到电压转换器、增益放大器、滤波器、模数转换器和数字相敏解调器组成。
我们发现平均噪声水平为 38 nA，幅度稳定性小于 0.2%，串扰优于-60 dB，所有通道和工作频率的信噪比为 70 dB。在盐溶液体模中，以时差和频差模式获得了图像。
我们详细描述了高密度 TAM 系统的设计、构建和校准。成功的高分辨率时差和频差图像显示了在频谱中具有预期介电常数变化的感兴趣区域。
