OPTO-ACOUSTIC BREAST IMAGING
Opto acoustic breast imaging is a new generation diagnostic tool currently in the clinical trial stage for diagnosis of malignant or benign breast lumps. According to a European journal of breast cancer around 4 million new cases of breast cancer are detected every year with almost 80 percent of them turning out to be benign on laboratory testing. It is difficult for radiologists to rule out malignancy at the imaging stage. The cost of conducting surgical or core needle biopsy for every suspicious lump outweighs the results especially in women coming from struggling economies. A low cost diagnostic tool such as opto acoustic imaging can help in the timely detection of breast cancer in the early stages and also help prevent and control the increasing mortality due to this disease in developing as well as developed countries.
About Opto Acoustic Breast Imaging
Opto-acoustic breast imaging, also known as photo-acoustic imaging, is an innovative diagnostic tool that is rapidly gaining attention for its potential to overcome many limitations of conventional ultrasound imaging. Traditional ultrasound relies on the mechanical and elastic properties of tissues to create contrast in the images, which can sometimes lead to ambiguous results. In contrast, opto-acoustic imaging leverages the light absorption characteristics of different tissues, offering a fundamentally different approach to imaging that enhances specificity.
This technique utilizes laser-induced ultrasound waves, generated when tissues absorb specific wavelengths of light. As these tissues absorb light, they emit sound waves that are captured to create detailed images. Opto-acoustic imaging is particularly effective at identifying various chromophores, such as hemoglobin, lipids, and water. These substances have distinct absorption spectra, which allows the imaging to differentiate between different tissue types more effectively than traditional ultrasound.
One of the significant advantages of opto-acoustic imaging is its ability to achieve greater penetration depths compared to purely optical imaging modalities, which rely on ballistic photons. Ballistic photons can only penetrate tissues to a limited extent before scattering, whereas opto-acoustic imaging can visualize structures several centimeters below the surface. This capability is especially beneficial for breast imaging, where it is crucial to detect abnormalities deep within the tissue.
Furthermore, opto-acoustic imaging can provide real-time data on tissue temperature, blood flow, and oxygenation levels. This functionality is due to the sensitive detection of changes in the optical properties of tissues, which can indicate physiological and pathological changes. For instance, it can map the distribution of oxygenated and deoxygenated blood, providing insights into the vascularization and metabolic state of tumors.
The integration of opto-acoustic imaging into clinical practice could revolutionize breast cancer diagnostics. It offers the potential to reduce the number of unnecessary biopsies by providing more accurate and non-invasive assessments of suspicious breast lesions. While opto-acoustic imaging is still in the clinical trial phase, its promising results suggest that it could become a valuable tool in the early detection and management of breast cancer, ultimately improving patient outcomes and reducing healthcare costs.
One of the key advantages of opto-acoustic imaging is its ability to provide real-time information on tissue temperature, blood flow, and oxygen content, alongside detailed anatomical images of smaller arteries and capillaries. These structures can be visualized with high resolution, and the images can be scaled from micrometers to centimeters, offering versatile spatial resolution. This capability is particularly valuable for thorough and precise breast imaging.
In opto-acoustic imaging, laser wavelengths in the visible and near-infrared (NIR) part of the spectrum, typically between 550 and 900 nm, are employed. The near-infrared spectral range of 600-900 nm is particularly effective as it allows for the greatest depth of penetration, reaching several centimeters into the tissue. This significant penetration depth is crucial for effective imaging of breast tissue, enabling the visualization of deeper structures that are often challenging to assess with other modalities.
Opto-acoustic imaging represents a cost-effective technology developed as a potential alternative to biopsies. While it is not designed to be a first-line screening tool, it has the potential to substantially reduce the number of unnecessary biopsies, which are both costly and time-consuming. This minimally invasive technique offers high accuracy in determining whether a breast lump is benign or malignant, thus providing critical information that can guide clinical decision-making.
Although opto-acoustic breast imaging is still in the clinical trial phase, it holds significant promise for reducing breast cancer-related mortality worldwide. By providing detailed and specific imaging, this technology enhances the ability to diagnose and treat breast cancer early, potentially improving patient outcomes and reducing the need for invasive procedures. Its ability to deliver comprehensive real-time data on tissue physiology and anatomy makes it a powerful tool in the fight against breast cancer.
Short Background
Opto-acoustic imaging is an innovative fusion of light and sound, integrating the principles of optical imaging and ultrasound. This functional imaging device emits pulses of short wavelength infrared light, which is safe for the human body. The infrared light penetrates the breast tissue and generates sound waves within it. These sound waves are then captured by a transducer placed over the breast being examined. The intensity and density of the sound waves are analyzed to provide detailed images.
Different tissues absorb infrared light in varying degrees, and the resultant sound waves differ based on the tissue’s density and health. This differential absorption and sound wave production form the basis of opto-acoustic breast imaging. By leveraging these properties, opto-acoustic imaging offers a highly specific and informative view of breast tissue, enhancing the ability to detect abnormalities and assess tissue health more accurately than traditional methods.
The metabolic rates, oxygen uptake, and hemoglobin concentration in blood vessels differ significantly between healthy and diseased tissues. Studies have shown that tumor tissues exhibit higher metabolic rates compared to healthy tissues. This difference in metabolic activity forms the basis for diagnostic tools that use contrast agents. The uptake pattern of these agents helps distinguish healthy tissue from diseased tissue.
Cancerous tissues are known to deplete blood oxygen more rapidly than healthy tissues. This creates areas of deoxygenated blood that appear as brightly colored regions in contrast to their surroundings, aiding in the localization of cancerous masses. The variation in light absorption and sound wave generation is utilized to create detailed maps of oxygenated and deoxygenated blood, as well as hemoglobin concentration. These maps help differentiate between malignant and benign tissues.
The choice of laser light wavelengths or colors in opto-acoustic imaging is based on their differential absorption by oxygenated and deoxygenated blood. This selective absorption allows for precise imaging, enabling healthcare providers to identify and assess the extent of cancerous tissues more accurately.
Opto-acoustic imaging is an advanced functional imaging technique capable of differentiating tissue types by measuring the levels of oxygenated and deoxygenated blood utilized by the tissue without needing a contrast agent. This innovative technology combines new photo imaging methods with conventional ultrasound to produce both functional and anatomical images of the breast.
This dual-modality approach enhances diagnostic accuracy. By assessing angiogenesis (the formation of new blood vessels) and the deoxygenation of circulating blood, opto-acoustic imaging provides critical insights. Tumor tissues typically exhibit increased angiogenesis and higher rates of deoxygenated blood compared to healthy tissues. Identifying these factors can help radiologists confirm or rule out malignancy with greater precision.
About the Procedure
The procedure for opto-acoustic imaging involves directing near-infrared light of two different wavelengths, typically between 550 nm and 900 nm, at the site of suspected malignancy. The breast is exposed to laser light. If the lump is cancerous, it will absorb more light than the surrounding healthy tissue and consequently heat up. This heating causes a momentary expansion of the tissues, generating broadband low amplitude sound waves.
These sound waves are captured by a single sensor or an array of sensors arranged in the transducer head placed on the breast. The ultrasound transducer head then relays the sound waves to a computer, which processes the data to generate two-dimensional images of the area of interest. This advanced imaging technique allows for precise differentiation between malignant and benign tissues, enhancing diagnostic accuracy and aiding in the effective detection and treatment of breast cancer.
By measuring the time of arrival of the acoustic waves and knowing the speed of sound, an image can be reconstructed similarly to a conventional pulse-echo ultrasound image. A key difference between conventional ultrasound (US) and photo-acoustic imaging is in the beam focusing process. In conventional ultrasound, both the transmit and receive beams can be focused to achieve localization. However, in photo-acoustic imaging, the transmit beams can scatter due to varying tissue densities beyond 1 millimeter, allowing only the receive beam to be focused. The collected signals are then analyzed and reconstructed to develop brightly colored, high-resolution images.
Although photo acoustic and ultrasound image formation and resolution are essentially the same, the bases of image contrast are fundamentally different. An ultrasound image represents differential acoustic impedance mismatch between target tissues. Ultrasound image contrast therefore, depends on the mechanical and elastic properties of tissue. An opto or photo acoustic image represents the initial pressure distribution produced by the absorption of the light energy. This image can be taken to be proportional to the absorbed optical energy distribution, which depends on the optical absorption and scattering properties of the tissue. In fact, the property of optical absorption dominates and thus opto- acoustic image contrast is often said to be ‘absorption-based’.
As a consequence, photo acoustic imaging can provide greater tissue differentiation and specificity than ultrasound because differences in optical absorption between different tissue types are much larger than those in acoustic impedance. For example the strong preferential optical absorption of haemoglobin makes photo acoustic imaging particularly well suited for visualising the microvasculature, which can be difficult to visualize with traditional ultrasound owing to the weak echogenicity of micro blood vessels.
Pro’s and Con’s compared to other diagnostic tools
There are many other methods used to screen and diagnose breast cancer, with each one having one or more major drawbacks. Few common diagnostic tests include blood marker test, breast MRI, CT scan, PET, Chest X-ray, mammogram and ultrasound. Mammogram and ultrasound are the more commonly used tests.
Let us understand the merits and demerits of these tools. During a mammogram, the breast to be examined is compressed between two plates that are attached to a camera. The camera takes two pictures from two different directions. The procedure is repeated on the other breast too. The test is time consuming as it requires 20 minutes for each breast. Also the test can give false positive test in young women who have dense breast, active milk glands and a lot of glandular tissue. Sometimes the tumor may get missed because of dense breast tissue leading to false negative test. It is more accurate in older women. The procedure is uncomfortable and painful at times. During an ultrasound examination, high frequency sound waves are targeted at the breast. The reflected waves are converted into meaningful images. Though the test doesn’t involve any ionization radiation, it can only detect whether the mass is solid or fibroadenoma or a cyst. It cannot determine whether the lump is malignant or not. [5]
Advantages of Opto acoustic breast imaging technique
All the above demerits are absent in the opto acoustic imaging technique. It is a non-invasive, cost effective and easy to administer functional imaging test. It does not require appointing highly trained personnel. Radiology technicians can be trained in a very short time. The diagnostic tool is safe for the patient as well as the technician as no ionizing radiations are emitted. There is no need to use a contrast agent or dye. The procedure does not cause any discomfort to the patient and is not time consuming too.
Another benefit of using functional imaging like opto acoustic imaging is that the results are accurate and precise. Since the laser light travels deep, it can help the technician to analyze the location and size of the lesion, which can be added to the results from ultrasound, to get a clear picture. The ultrasound imaging helps to identify the shape of the lesion. The opto acoustic imaging can help to analyze the mass and the area under concern. In addition opto-acoustic imaging is highly specific and sensitive which helps in providing accurate diagnosis. It uses the specificity of light imaging and sensitivity of ultrasound testing. The images obtained are also high resolution ones which make the diagnosis easy. The tool is sensitive enough to pick up very small tumors also. Ongoing trials have also showed that opto acoustic imaging has a very high detection rate and can detect tumors as small as 2 mm. In fact it can detect tumors smaller than this which means highly malignant tumors can be detected very early. [3]
The test can be performed in younger as well as older women with almost no chance of false positive or false negative test. The breast tissue density, presence of milk glands and glandular tissue does not affect the accuracy of the test. It can not only detect a lump with precision but can also differentiate a malignant growth from a benign one. [3] The investigation procedure is comfortable for the patients as they can lie down during the procedure. The array of sensors can be arranged over the area of interest in fixed position. There is no unnecessary compression and discomfort felt by the patient.
The current clinical trials conducted for this technology reveal that opto acoustic breast imaging can help separate a group of people having a breast lump but not requiring biopsy from another group having breast lump and requiring biopsy. If these trials are successful and consistent it can help to eliminate the need for unnecessary biopsies thus saving big on diagnostic costs of breast cancer. [5] Researchers are also trying to establish positive correlation between the images obtained and stage of the cancer identified on laboratory analysis. [6]
References
- http://www.medgadget.com/2014/04/seno-imagio-opto-acoustic-breast-cancer-imaging-system-cleared-in-europe.html
- http://consultqd.clevelandclinic.org/2014/06/opto-acoustic-breast-imaging-can-it-reduce-the-need-for-breast-biopsy/
- http://www.medscape.com/viewarticle/780708_6
- senomedical.com
- http://www.breastcancer.org/symptoms/testing/types/ultrasound
- http://medicalphysicsweb.org/cws/article/newsfeed/55693
- http://rsfs.royalsocietypublishing.org/content/royfocus/1/4/602.full.pdf
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