**4. Biological explanation**

Thermography is a method of cancer screening that has been known to detect early‐stage cancer [3]. However, there is a lot of variation in the results of clinical studies based on ther‐ mography and many show low specificity. A medical scientist and deep expert in thermogra‐ phy, Dr. Gautherie, observed that the lack of technical skill and expertise to interpret thermal images leads to this low diagnostic accuracy [3]. Recent developments on high‐resolution thermal cameras and computer algorithms for thermal analysis are making the interpretation process more factual. With increased computation power, automated diagnostics is also able to decrease the false‐positive rates. Hence, thermal imaging along with computer‐aided diag‐ nostics is showing a promise of upgrading breast thermography to main stream usage. In this chapter, we study these recent trends in advanced thermal imaging as well as the advances

Infrared thermography is the recording of temperature distribution of a body using the infra‐ red radiation emitted by the surface of that body at wavelengths between 7 and 14 μm. With this information, it is possible to create a visual map or thermogram of the distribution of temperatures on the surface of the object imaged. The sensitivity of modern infrared cameras

Thermography can be used for breast cancer screening based on the fact that the tempera‐ ture of the tumor is about 2°C higher than the neighboring tissues and blood vessel activ‐ ity surrounding a developing cancer is almost always higher than in normal breast tissue. Since breast tissue is part of the skin, vascular alterations due to cancer result in tempera‐ ture changes on the surface of the breast which can be captured with infrared thermography. Thermal abnormalities identified with thermal imaging are among the earliest signs of a pre‐

Thermal imaging is a noncontact, noninvasive and extremely privacy aware. Since thermal cameras are small, they are very portable and can be used for screening in rural camps.

There are many certified thermographers and thermologists who continue to practice using

Most common methods used for cancer screening today is clinical examination, mammog‐ raphy and ultrasound. Among them, mammography is considered as a gold standard for breast cancer screening. It uses X‐rays to screen the breast region and digitizes the density difference in image format. Typically, cancerous tumor has high density compared to sur‐ rounding region and can be easily distinguished from other regions. Studies [5–7] show that it gives a sensitivity of 68% to 88% (or as low as 48% for extremely dense breasts) and specifici‐

ties ranging from 82% to 98%. In addition, it has the following disadvantages:

in imaging algorithms.

92 New Perspectives in Breast Imaging

**2. Introduction to thermography**

cancerous or cancerous lesion of the breast.

thermal analysis for breast cancer diagnosis [4].

**3. Comparison with mammography**

is such that temperature differences to 0.025°C can be detected.

Cancer cells release nitric oxide [12, 13] into the blood and lead to alteration in microcircula‐ tion. This nitric oxide coupled with aggressiveness of cancer to grow increases the blood cir‐ culation by dilating the vessels and leads to creation of new blood vessels (neo‐angiogenesis) and dormant vessel recruiting. Experimentally, Folkman [14, 15] observed this dependency of tumor growth with angiogenesis by implanting tumour cells in mice. Large volume of blood flow in these vessels connected to tumor makes them hotter when compared to normal blood vessels. This large flow distorts the vessel structure, and vessels become dilated as well as elongated, causing the increase in the dimension of vessel caliber and length [16, 17]. This elongation combined with the large flow deviates the vessel structure from normal vessels by making them more tortuous due to formation of bends [18–20]. In fact, it is experimentally evident that this high tortuosity is observed much before angiogenesis [18].

In addition, it has been empirically observed that tumor temperature is higher than the neighboring temperatures with the help of contact temperature measurements. In Ref. [21], Gautherie claimed that this high heat is due to high metabolic activity at tumor location. Hence, this region appears brighter and hotter in thermographic images when compared to surroundings. It is also observed that tumor temperature is warmer compared to the blood vessels feeding the tumor region [21]. Aggressiveness of cancer cells makes the boundary of tumor irregular as they break the boundary formed by basal laminas to invade the neighbor‐ ing tissues [19, 20]. This is not seen in case of benign tumors whose cells behave similar to normal cells. This makes the benign tumor boundaries regular.

The size of tumor indicates the stage of cancer and largely affects the survival rate. A survey conducted by Narod [2] observed drastic decrease in survival rate with increase in tumor size. Early detection of cancer increases the chances of survival. Thermography outperforms other modalities when it comes to early detection. Changes such as vasodilation, neo‐angiogenesis and high tortuosity of blood vessels which are found in initial stages of cancer result in ther‐ mal impressions and hence can be detected in thermography [15–19]. These might not be observed in other modalities which depend upon detecting architectural distortions that appear only when tumor is sufficiently grown. A study by Gautherie and Gros [3] over 58,000 patients for 12 years showed that thermography detected breast cancer five years earlier in around 400 patients than mammography and ultrasonography.

Abnormality in thermogram is not the sole criterion for malignancy. Increase in heat pattern might even be observed due to hormonal response, lactation and presence of benign tumors such as fibrocystic and fibroadenoma. However, these non‐malignant conditions have different projections in the thermographic image when compared to malignant tumors. Unlike in malignant breasts where there is asymmetrical heat map, heat response is mostly symmetrical across the two breasts with high hormonal response. Estrogen released during hormonal activity produces nitric oxide that causes increase in heat and vessel dilation [12]. Similar activity happens in the case of lactating mothers except that a little asymmetry in heat map is seen due to uneven lactation in both breasts. There is an increase in heat signature even in benign cases such as fibro‐ cystic and fibroadenoma [21, 22]. In contrast to malignant tumors, these cells are not aggressive and behave similar to normal cells [19, 23]. Other than these cases, abnormal heat pattern leading to vasodilation and angiogenesis can also occur during inflam‐ mation caused by infection or wound healing [12, 14]. Though these abnormalities are formed, they have distinct features compared to malignancy that can be distinguished.

Some recent explorations have shown that thermography can even help in prognosis. Since the increase of temperature in malignant tumors is primarily due to the release of nitric oxide, which is caused due to hormonal activity, the temperature distribution on the breasts also pro‐ vides signals on the hormonal receptor status of malignant tumors. Zore et al. [9] have studied the effect of hormone receptor status of malignant tumors on thermograph through a quanti‐ tative analysis of average or maximum temperatures of the tumor, the mirror tumor site and the breasts. While no statistically significant difference was found in the overall temperature distribution in breasts with hormone receptors being positive or negative, they report a signif‐ icant difference in average and maximum tumor temperature measurements. Another com‐ puter‐aided study [24] reported an accuracy of more than 80% for automated estimation of hormonal receptor status of malignant tumors. This shows the potential of a non‐invasive way of predicting the hormone receptor status of malignancies through thermal imaging, before going through Immuno‐Histo‐Chemistry (IHC) analysis on the tumor samples after surgery.
