This invention relates to apparatus for diagnosing pathological disorders such as cancer of the breast.
About 7% of women contract cancer of the breast. Of the cases nowadays detected, 50% lead to the patient's death within ten years of establishment of cancer. The prognosis is decisively dependent on how early the diagnosis can be made.
For diagnosing cancer of the breast are employed: X-ray examination, thermography, and manual palpation. Most efficient among these is X-ray examination, but owing to the high depth of penetration of X-rays in soft tissue, diagnosis of cancer in its initial stage is difficult by X-rays. A further detriment of X-rays is the radiation dose received by the patient, whereby X-ray examination is hardly applicable in mass screening.
Thermography is based on recording the infrared radiation emitted by the human body. This procedure is completely free of risk to the patient, but its reliability is poor (only 50% of cases diagnosed with X-ray apparatus are detected). Thermography is therefore only appropriate as a procedure supplementing X-ray examinations. The unreliability of thermography is due to the fact that it records only changes in the surface temperature of the skin, and such changes ensue as a consequence of cancer only when the neoplasm is large or located quite close to the skin surface.
Making a successful diagnosis by manual palpation implies that the neoplasm has already sufficient size, and it requires a certain experience on the side of the person making the diagnosis.
Also appearing on the scene nowadays are ultrasonic examinations, which are completely risk-free to the patient but are capable of diagnosis only if the neoplastic tissue is clearly encapsulated (that is, acoustically clearly differing from other tissues).
Summarizing the above, the observation may be made that nowadays no reliable procedure or apparatus is available which would be proper for earliest possible diagnosis of cancer of the breast, for instance with the aid of mass screening studies.
In the developing of the apparatus, that information served as starting point: that the breast tissue is comparatively homogeneous tissue resembling fat tissue, while cancerous tissue resembles muscle tissue in its electrical properties. On the basis hereof, microwaves are used for diagnosis in the apparatus of the invention.
In the following table (I) are presented the characteristics of tissues at the frequency of 10 GHz.
TABLE I ______________________________________ Wave- Depth of length, Conductivity Dielectric penetration, cm s constant Er cm ______________________________________ Fat tissue 1.4 0.3-0.5 4.5 3.4 Muscle tissue 0.5 10 40 0.5 ______________________________________
In the following table (Table II) are given the coefficients of reflection of the tissue interfaces at frequency 10 GHz.
TABLE II ______________________________________ .phi. r (Coefficient of reflection) (Phase Shift) ______________________________________ Fat/muscle interface 0.5 +175 Muscle/fat interface 0.5 -6 ______________________________________
As can be estimated from the values in the table, about 65% of the microwave radiation at 10 GHz frequency striking the cancerous tissue is reflected. As Table II reveals, reflection of microwaves takes place in the front and rear parts of the cancer growth, and each such reflection is also accompanied by a phase shift, of which the magnitude at different interfaces can be read in the table.
It is obvious on this basis that since the cancerous tissue is clearly different from normal breast tissue in its electric properties, microwaves can be used in diagnostics of cancer of the breast.
On the other hand, microwaves have been used in materials testing in various fields of industry. For instance, microwaves are used as aid in examinations of various coating layers for their thickness, materials for variations of porosity, for internal cracks, boards for knottiness, etc. But these types of apparatus of prior art are of such design that the idea of possibly constructing an apparatus, based on microwaves, for diagnosis of cancer of the breast is not at all suggested or obvious on their basis.