浅岡 善雄¹, 伊東 紘一², 森 博昭², 金澤 暁太郎¹

Yoshio ASAOKA¹, Kouichi ITOH², Hiroaki MORI², Kyoutarou KANAZAWA¹

¹自治医科大学　消化器・一般外科, ²自治医科大学　臨床病理

¹Departmant of Surgery, Jichi Medical School, ²Clinical Pathology, Jichi Medical School

キーワード : Breast tumor, Internal echoes, Histogram, Maximum frequency

It has been reported that the increment in gain to some extent causes the shift of maximum frequency of echo level on histograms derived from tumor tissue toward the more echogenic side. Furthermore, the shift rate varies between fibroadenoma and carcinoma of the breast.
After performing a series of meticulous histogram examinations using probes of different emission frequencies (3.5 MHz and 7.5 MHz) on breast tumor tissue which had been isolated from 23 fibroadenoma and 30 carcinoma patients, we were not able to agree the reports mentioned above.
Our results showed that the maximum echo level frequency on the histograms did not shift proportionally toward the intensive side with the gain increment. This tendency was more conspicuous with the higher emission frequency probe. To verify the causes of the phenomena we found, we performed a series of basic studies using 3 probes of different emission frequencies (3.5 MHz, 5.0 MHz and 7.5 MHz) and using a phantom model. We emphasized the significance of the depth of the region of interest from the phantom model. The more the region of interest was located in the superficial part of the phantom, the more conspicuous the increase of the maximum frequency of echo level on the histogram. However, because of the more extensive absorption of energy and the higher emission frequency, the maximum frequency of the echo level was divided.
At 3 cm away from the surface of the phantom, it is difficult to detect the same findings.
On the other hand, it is dangerous to reach the conclusions descrived before examining numerous lesions located at various depth in the mammary gland.
Although there is a trend toward introducing higher emission probes into clinical practice, we should be very careful to differentiate these lesions keeping in mind this proportional shift of maximum frequency of echo level with gain intensity.