Meaney Paul M, Gregory Andrew P, Epstein Neil R, Paulsen Keith D
Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH 03755, USA.
National Physical Laboratory, Teddington, Middlesex, UK.
BMC Med Phys. 2014 Jun 17;14:3. doi: 10.1186/1756-6649-14-3. eCollection 2014.
Tissue dielectric properties are specific to physiological changes and consequently have been pursued as imaging biomarkers of cancer and other pathological disorders. However, a recent study (Phys Med Biol 52:2637-2656, 2007; Phys Med Biol 52:6093-6115, 2007), which utilized open-ended dielectric probing techniques and a previously established sensing volume, reported that the dielectric property contrast may only be 10% or less between breast cancer and normal fibroglandular tissue whereas earlier data suggested ratios of 4:1 and higher may exist. Questions about the sensing volume of this probe relative to the amount of tissue interrogated raise the distinct possibility that the conclusions drawn from that study may have been over interpreted.
We performed open-ended dielectric probe measurements in two-layer compositions consisting of a background liquid and a planar piece of Teflon that was translated to predetermined distances away from the probe tip to assess the degree to which the probe produced property estimates representative of the compositional averages of the dielectric properties of the two materials resident within a small sensing volume around the tip of the probe.
When Teflon was in contact with the probe, the measured properties were essentially those of pure Teflon whereas the properties were nearly identical to those of the intervening liquid when the Teflon was located more than 2 mm from the probe tip. However, when the Teflon was moved closer to the probe tip, the dielectric property measurements were not linearly related to the compositional fraction of the two materials, but reflected nearly 50% of those of the intervening liquid at separation distances as small as 0.2 mm, and approximately 90% of the liquid when the Teflon was located 0.5 mm from the probe tip.
These results suggest that the measurement methods reported in the most recent breast tissue dielectric property study are not likely to return the compositional averages of the breast tissue specimens evaluated, and thus, the conclusions reached about the expected dielectric property contrast in breast cancer from this specimen study may not be correct.
组织介电特性具有生理变化特异性，因此一直被视作癌症及其他病理疾病的成像生物标志物。然而，最近一项研究（《物理医学与生物学》52:2637 - 2656, 2007；《物理医学与生物学》52:6093 - 6115, 2007）利用开放式介电探测技术和先前确定的传感体积，报告称乳腺癌与正常纤维腺组织之间的介电特性对比度可能仅为10%或更低，而早期数据表明可能存在4:1及更高的比率。关于该探头的传感体积相对于所探测组织量的问题，引发了一种明显的可能性，即该研究得出的结论可能被过度解读了。
我们在由背景液体和一块平面特氟龙组成的两层组合物中进行开放式介电探头测量，将特氟龙平移至距探头尖端的预定距离，以评估探头产生的特性估计值代表探头尖端周围小传感体积内两种材料介电特性组成平均值的程度。
当特氟龙与探头接触时，测量到的特性基本上是纯特氟龙的特性；而当特氟龙距离探头尖端超过2毫米时，其特性与中间液体的特性几乎相同。然而，当特氟龙移近探头尖端时，介电特性测量值与两种材料的组成比例并非线性相关，而是在分离距离小至0.2毫米时反映了近50%的中间液体特性，当特氟龙距离探头尖端0.5毫米时反映了约90%的液体特性。
这些结果表明，最近乳腺组织介电特性研究中报告的测量方法不太可能得出所评估乳腺组织标本的组成平均值，因此，基于该标本研究得出的关于乳腺癌预期介电特性对比度的结论可能不正确。
