PHOTO ACOUSTIC DETERMINATION OF MELANOMA THICKNESS
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Introduction
Over the years there has been a huge increase in the reports of cancer cases globally. The occurrence of skin cancer has gradually and steadily increased over the years and the related deaths have also been on the rise (McCormack, et al., 2009). It has therefore become prudent that a prognosis and treatment of cancer become a priority as this poses a threat to public health and has in a great ways affected the life expectancy of individuals, both men and women. Melanoma is a form of skin disease which is considered one of the most potentially serious types of skin cancer. It involves the uncontrolled multiplication of pigment cells or as they are sometimes known, the melanocytes. Melanin, the content that makes the skin color darker occurs in both the white and black people. The melanin is produced by these melanocytes. The melanocytes are found in equal in all people regardless of their skin color. The only difference is that the melanocytes produce more melanin in black people than in white people. This melanin protects the skin from ultra violet rays. Due to the higher concentration of melanin in people with dark skin, their exposure to UV rays is minimal. The uncontrolled growth of non-cancerous melanocytes is what produces moles, while the multiplication of melanocytes that are cancerous results to melanoma. Melanoma is described according to the extent of its spread, whether it is in the epidermis, has spread to the dermis or has spread to other parts of the body (Stoffels, et al., 2015). The tumor still in the epidermis is insitu, dermis, invasive and after spreading to the other parts of the body it is known as metastatic. The occurrence of melanoma is mostly in adults and very few cases have been reported that related to children (Weight, et al., 2006). After prostate, breast and colectoral cancer in both men and women, melanoma is reported as the fourth most occurring type of cancer. The people in their mid 40s and 50s are mostly prone to the cancer. This age group contributes to more than 50% of the total melanoma cancer cases. The major risk factors that are associated with melanoma include, advancement in age, the occurrence of may moles or freckles due to the uncontrolled growth of melanocytes, exposure to certain environmental factors, a change in genes that is, melanoma related, a weak immune system, a history of melanoma occurrences in the lineage and white skin that lacks enough melanin to protect itself from UV rays (Kim, et al., 2010). Signs of melanoma include moles that are ulcerated, asymmetric in size and shape, which has different pigmentations, a change in the skin color and what we call satellite moles. These are moles that grow near already existing moles. . This discussion will critically review the developments that have been made in fighting cancer and specifically the melanoma skin cancer. The newest development in the prognosis of melanoma being the photo acoustic microscopic imaging that is a non invasive technique used in detection of the melanoma (Galanzha, et al., 2009).
Melanoma is considered a malignant tumor and is actually number five on the list of most occurring forms of cancer currently in the USA. In 2013 more than 70,000 individuals, both men and women were diagnosed with the disease and an estimated 9,000 deaths were as a result of the same by the year 2015. Of all the very many types of skin cancer, melanoma accounts for only 5% but it is quite deadly as it has caused over 75% of deaths that are as a result of skin cancer. By 2015, the values had rapidly increased to an estimated value of over 8,000 reported cases in a span of only two years (Zhou, et al., 2014). Currently due to the increased incidence of the skin cancer, it is crucial that methods of accurately conducting diagnosis and prognosis are developed. The prognosis, prediction of the outcome that is more likely to occur is directly related to the time that the cancer is actually detected and treatment is conducted. This is dependent on what stage of cancer progression at which it is diagnosed and treatment commences. The survival rate and complete treatment of the disease is quite high in cases where the tumor is recognized way before it metastasizes, spreads to other parts through the lymphatic system. The survival rate is currently at 98% for any early diagnosis (Oh, et al., 2006). The chances of the spreading of a tumor from its original point of occurrence to other parts of the body are increased by the invasive nature of the cancer cells. By invading the dermis, the cells then gain access to the body fluids, blood and use the lymphatic vessels to spread to other parts of the body. Measuring the thickness of the melanoma is key to determining treatment and also predicting the probable future outcome of the disease. In determining the stage of the cancer and the spread within the body, the thickness of the melanoma is key. We can use nano molecules in measuring the different stages of melanoma ranging from T1 all the way to T4. This is done through the process of tumor node metastasis and hence the T. for T1, the size of melanoma is less than or equal to 1.0 nanomolecules, for T2, the size of the thickness lies between 1 and 2 nanomolecules. Is it is ranged as T3, it is because the thickness ranges between 1 and 4 nanomolecules, for the stage to be T4, the thickness of melanoma needs to be anything higher than 4 nanomolecules. The increase of the thickness of melanoma is directly and positively related to the spread of the tumor and thus it is correct to say that, with a bigger. Larger thickness melanoma is considered more deadly and there are high chances of melanoma caused mortality.
Ireland is currently number 14 on the countries with the highest skin cancer incidents. Out of all the cases that are diagnosed 16% lead to death of the patients (Marton, et al., 2014). Studies carried out in Ireland that there is a high incidence rate of skin cancer with roughly over 850 new cases each year. This high occurrence of skin cancer can be attributed to the fact that the individuals are exposed to high ultra violet rays and the effects of their skin color.
The physics behind photo acoustic imaging:-
Research underlying the physics of photo acoustic methodology is quite long and dates back to the late eighteenth century. Alexander graham discovered this photo acoustic effect while he was observing the generation of sound as an effect of absorbed sunlight. Though there was not much research on the same then later on in the 1990s scientists started conducting research of the use of this effect in biotechnology imaging. In photo acoustic imaging, optical wavelengths of roughly 550 to 900 nm are normally used (Wang, 2009). This range produces the greatest penetration of up to a few centimeters this results in emission of broad bands that are propagated to the surface. These are detected by an ultra sound receiver obtaining A lines. Taking into account the speed of sound and measuring the time taken by the waves, an image can therefore be constructed.
There have been several methodologies and tools that have been used over the years to measure the thickness of melanoma. Most of these methods are highly invasive and in most cases leave huge scars and also destroy surrounding tissues (Wang, & Hu, 2012). The diagnosis of melanoma is currently based and dependent on clinical suspicions that later lead to biopsy excision of the damaged or abnormal body tissue. Biopsy excision is the process by which a damaged or abnormal part of an infected tissue or region is cut out for examination purposes in order to determine the cause of the abnormality and work on treating the infected tissues. After the biopsy excision, histological examinations are carried out. Histology involves the microscopic examination of abnormal or infected tissues for proper and accurate diagnosis (Gutierrez-Juarez, 2010). This process is however quite invasive and may actually lead to the destruction of other adjacent tissues that are healthy. The excision process is also characterized by a lot of pain and leaves scars behind that are unsightly and that take long to heal. Most of the tests and procedures involving biopsy excision result in the tissues being characterized as cancer free while this may not be the case. This clinical examination alone is considered not adequately thorough as it may lead to the non-detection of existing cancerous cells. This has therefore created the need for better imaging methods that are non-invasive in character.
Over the years there have been several non invasive methodologies that have been adopted all in the effort of diagnosing melanoma in its early stages and beginning on treatments. Early diagnosis of any cancer is key to its being fully treated. The following are some of the non invasive techniques that have been developed over the years. One of these non invasive methods is dermascopy (dematoscopy). Most clinicians use dematoscopy that aids in the prognosis and diagnosis of melanoma (Li, & Wang, 2009). A dermatoscopy is a handheld device that uses skin surface microscopy device to carry out examinations on the skin. The dermatoscopy uses magnifying lens and allows examination on skin structure characteristics of both pigmented and non-pigmented abnormalities on the skin. When connected to the appropriate devices, the dermatoscopy provides a visual image or a video for analysis. Dermascopy uses the pattern, structure and the color of pigmentations to evaluate what specific ailment is affecting a tissue. The figure below shows an image of how pigmentation due to melanoma would look like.
Figure 1:An image of a dermoscopy, view of an infected tissue
The dermoscopy does not however aid in the determination of the thickness of the tumor, which is a very important parameter that would aid in the accurate diagnosis and treatment of melanoma. Most surgeons have to deal with the issues that are raised by the inadequate diagnosis of melanoma. Evaluation on only a part of the affected lension area gives inadequate information of the extent of penetration of the tumor and the characteristics. If this information were to be used to conduct surgery, the surgery may not be successful and would thus require a second or even third surgery to treat the tumor. This therefore raises the need for an in vivo imaging method that would facilitate a successful single surgery and avoid consequent surgeries in an effort to provide treatment.
Another non invasive technique adopted is the Total Body Photography, TBP. This is an optical technique that involves the use of high technology visual aid items. Images are taken, stored and then retrieved for examination (Viator, et al., 2010). This method is used in scanning individuals that are at a high risk of getting melanoma. This is due to its specific property of noticing or determining changes in the structure of lensions. Another invasive technique to discuss is the optical coherence tomography, OCT. This involves taking a picture of the body tissues. It uses light and takes cross sectional images. Using this technique, the technician can measure the thickness of each layer and thus any irregularities on the thickness would be easy to detect.
All these discussed non invasive methodologies have a common limitation which is that they do not have adequate penetration capabilities to determine the exact thickness of melanoma (Amouroux, & Blondel, 2011).
Using of high ultra sound is also insufficient in melanoma diagnosis as mostly melanoma is deeply imbedded in the tissue and as such the imaging provided is very poor and thus not substantially helpful. The ultra sound just like the photo acoustic imaging uses high frequency sound waves and their echoes. This is similar to the echolocation that is used by whales and dolphins in movement. These waves, unlike those of the photo acoustic imaging go through the tumor and thus the image produced is not clear since we already established above that the melanocytes are good absorbers and will absorb some of the sound waves. The ultra sound will also not provide a clear measure of the thickness of the tumor. Other techniques that have been used in melanoma diagnosis are MRI. Magnetic Resonance imaging and the Positron Emission Tomography, PET. These two have not only provided poor tissue resolutions but are also quite expensive. The PET in particular can only detect melanoma that has a thickness close to a centimeter T4. This then implies that it cannot detect melanoma in its early stages, T1 all the way to T3. We have already seen that the key to successful treatment is dependent on early diagnosis and as such all these techniques are considered inadequate in the diagnosis of melanoma.
Most recently there has been the adoption of photo acoustic microscopy in the diagnosis of melanoma (Yao, Xia, & Wang, 2016). This technique has exhibited strong detection skills of skin abnormalities and provides deep penetrative abilities. Laser pulses are used to illuminate the object and following absorption of photons, waves that are considered ultrasonic re induced through the photo acoustic device. Due to the high absorption properties of skin that is melanoma infected. The image of the high contrast between the infected and non infected tissue can be detected. With deep penetration, high resolution images are produced. The device is highly efficient as it allows light to penetrate to the deepest part of the melanoma and it can detect even the slightest trace of melanoma, as little as T1. The device also comes in handy as it is hand held. Photo acoustic imaging is a very good example of a non-invasive method of melanoma diagnosis. The photo acoustic imaging device is based on the principle of passing electromagnetic photons and how the pulses are actually converted into ultra sounds. Photo acoustic imaging provides deeper penetration than all other previously used non invasive techniques. The contrast is due to the abilities it has of mapping the distribution of melanin and blood vessels in a small biological window of roughly 500-1000 nano molecules. Photo acoustic imaging has proved useful over time in determining the thickness and exact measurements of any lensions on the skin and thus is considered crucial in the diagnosis of melanoma.
The schematics and working of a photo acoustic hand held device
The diagram below shows the schematics of the hand held photo acoustic device.
Figure 2:schematics of the hand held photo acoustic device
The pulsed laser generates light as input for the dye cell. Blood and water have low absorption levels whereas; the melanoma is characterized by quite high absorption levels. The lens then concentrates the light to the optic fiber around the ultrasonic transducer. The light is then delivered into the body tissue. The light instead of going through the melanoma, finds its way around it. The surrounding tissue, note, is affected by the optical light but is quite low in absorption as it only consists of blood and water which both aid in enabling the light get to the bottom part of the melanoma, which is the extent of the thickness of the melanoma. The beam is characterized by an inner diameter of 8 mm and an outer diameter of roughly 20 mm. the transducer is characterized by 100% nominal width and a frequency of 25Mhsz which detects the photo acoustic signals. The length of the detector is roughly 12.5 mm while its diameter is 6.4mm thus producing an aperture of about 0.25. The figure 2 b above shows how the fibers and transducers are connected and fixed on a translation stage that is motorized a cross sectional image is therefore obtained.
To show how the new photo acoustic device differs from the previous ones and its superiority over them we can use several experiments.
This is where we compare the images and results of previous non invasive techniques and the images obtained from a photo acoustic examination of an affected tissue.
Figure 3:Monte Carlo simulations of the old and new Photo acoustic microscopic systems, in melanoma imaging.
Figure 3 a shows the image from an invasive technique while figure 3 b will shows the results of imaging of a photo acoustic device. The two were exposed to similar conditions, and the amount of energy used in each was the same. The length and thickness of melanoma was the same in both cases. From the diagrams we can deduce the following, optical absorption in the first simulation was a bit higher than was witnessed in the second part where photo acoustic device was used. This is evident in the subsequent figures 3c and 3 d respectively. A small black area was used in the calculations to make an analysis between the two. The photo acoustic image and resolution is 1660 times better than in the one without. This is due to the system that is used in the delivery of the light in the two cases is very different (Akers, et al., 2010). The results indicate that the new photo caustic system is better and the results are more accurate as it is now easier to determine the bottom part of the melanoma accurately and the measurement of the thickness of the melanoma is easier to find.
In order to demonstrate the ability of the device to measure thickness by penetration, phantom experiment can be carried out. Figure 4 below shows the results of such an experiment that was carried out. Different samples of melanoma each with a distinct diameter were used. The phantoms were made of a mixture of ink and gelatin that is considered to have a similar absorption coefficient like melanoma. The diameters in these specific experiments were, 7, 9.5 and 14 mm, respectively. The use of a photo acoustic device to measure the thickness of the mixture gave values ranging between 0.7mm and 4.1mm. These figures cover the entire melanoma stages all the way from T1 through to T4. We can therefore conclude that the photo acoustic will measure the thickness of the melanoma accurately.We developed handheld photo acoustic microscopy (PAM) to detect melanoma and determine tumor depth in nude mice in vivo. Compared to our previous PAM system for melanoma imaging, a new light delivery mechanism is introduced to improve light penetration. We show that melanomas with 4.1 mm and 3.7 mm thicknesses can be successfully detected in phantom and in in vivo experiments, respectively. With its deep melanoma imaging ability and handheld design, this system can be tested for clinical melanoma diagnosis, prognosis, and surgical planning for patients at the bedside.
The figure below shows the results of the phantom experiments in an effort to determine the accuracy of photo acoustic imaging. The graph below it also shows how we can relate the thickness measured by the photo acoustic imaging device to the pre determined measures of melanoma.
Figure 4:Photos of photo acoustic measurements of melanoma with different diameters and a graphical representation of the comparison of results obtained with the already pre determined sizes of melanoma.
To show the in vivo ability of the photo acoustic device, we can look at the images of laboratory mice infected with the melanoma. A laboratory mouse was injected with the melanoma virus such that the melanoma would grow on the skin. Using anesthesia, the rat was induced to a motionless state enabling the taking of the photo acoustic image. This is image 5 a in the figure five below. On measurements, the thickness of the melanoma was found to be 3.6mm and from the image we can see a clear distinction all the way from the top of the skin to the bottom of the melanoma infected area (Grootendorst, et al., 2011). We then used biopsy excision on the same tissue and found the thickness of the melanoma to be 3.75, which is very close to the results of our non invasive photo acoustic image. This goes to show the in vivo detecting abilities of the photo acoustic imaging are accurate and reliable. Figure 5 c below shows how the photo acoustic microscopic imaging goes a long way in detecting melanoma that is deeply metastasized.
The removal of melanoma and the skin layers is done by a specialized dermatologist or in some cases a surgeon. A mohs surgery is conducted to remove the tumor. After the surgery, there is need for follow up tests, procedures and examinations that help in determining how successful the initial surgery was. It is also important to carry out follow ups in order to detect early recurrences of melanoma and ensure that it is treated before it spreads. Research has shown that recurrences are much worse than the initial diagnosis. Out of all melanoma patients, recurrences occur in between 5% to 20%. Some of the follow up procedures include a regular skin examination, whether by self or by a specialist, regular monthly or weekly checks in health institutions and post education and counseling to the patients to help them adjust and also create awareness in the society. For in situ melanoma patients, the chances of a full recovery are quite high, but this is not the case for patients of invasive melanoma and mestases. For invasive, the success of the surgery is all dependent on how far into the dermis the tumor had spread. This is then followed up by physical regular checks and examinations. If a melanoma tumor were to be left on the skin, it would actually mestasize and through the lymphatic vessels and blood vessels spread to the whole body (Samson, et al., 2012). This is detrimental to health, the spread of the cancerous to vital organs like the liver and heart actually cause death.
Spectral Unmixing
Spectral unmixing refers to the separation of signals from different optical absorbers in a PA image using spectroscopic methods to determine their concentration accurately in tissues such as accurate measures of blood oxygenation saturation and nanoparticle deposits (Luke, Nam & Emelianov 2013: 36). According to Luke, Nam & Emelianov (2013: 36), tissue components and highly absorbing contrast agents such as plasmonic nanoparticles have different optical absorption spectra that vary with optical wavelengths. The contrast between the tissues and contrast agents occurs along different excitation wavelengths, which facilitates differential imaging of biodistribution of vascular, blood oxygen saturation and biomarkers (Morscher et al. 2011: 1). Blood has a particularly high optical absorption scale thus produces a large photoacoustic signal in PA imaging while biomarkers have low concentration of absorbing molecules thus create weak photoacoustic signals that can easily be mistaken for background (Morscher et al. 2011: 1). In fact, blood occupies a large proportion of the image generated because of its high optical density (Morscher et al. 2011: 1). As such, separating them within the resultant PA image is necessary for clear image interpretation for further prognosis. This technique is referred to as spectroscopic PA (sPA) (Luke, Nam & Emelianov 2013: 36).
There are various different methods to spectral unmixing. For the most part, the simplest sPA focus on optical wavelengths to distinguish between contrasting agents and tissue components. One method involves acquiring the ratio of PA signals at two optical wavelengths then using the ratio to compare either blood oxygenation saturation or an activatable contrast agent (Luke, Nam & Emelianov 2013: 36). Unfortunately, due to its use of the broad optical wavelengths to interpret the data provided in the PA image, this method can only distinguish between a maximum of two absorbers (Luke, Nam & Emelianov 2013: 36). As such, its application is relatively limited. On the other hand, the intraclass correlation (ICC) method adequately distinguishes between multiple absorbers by measuring the PA spectrum at each pixel in the image and correlating the measure to the anticipated absorbers known absorption spectra thereby assigning each pixel to a specific absorber. However, the assumption that each pixel only correlates to one chromophore is incorrect such as in the case of oxygenated and deoxygenated blood in a single tissue (Luke, Nam & Emelianov 2013: 36). Hence, methods that rely on optical wavelength identification or analysis run the risk of providing inaccurate spectral unmixing when developing PA images for complex systems.
In their study, Morscher et al. (2011) analyzed three methods of spectral unmixing using multispectral optoacoustic/photoacoustic tomography (MSOT). The first method analyzed was spectral fitting. This refers to the inversion of spectral profiles of absorbers suspected to be in the sample analyzed using the Moore-Penrose pseudo-inverse multiplied with the matrix of the measured images in the PA image generated (Morscher et al. 2011: 2). The second method was principal component analysis (PCA), which decomposes data into statistically uncorrelated basis vectors that maximize variance by a singular value or eigenvalue decomposition of the covariance matrix of the image data (Morscher et al. 2011: 2). By separating basis vectors by variance, this method provides the most important components first. The last method is independent component analysis, which also uses statistically unrelated directions in the data by finding maximum non-gaussianity that presumably represents maximum information from the image data. As such, the most maximum non-gaussianity components represent the most important information in terms of absorber concentration within the tissue or section under observation.
Safety for Patient and Workers
The three fundamental principles of PA imaging underscore patient safety concerns. They include the use of a laser to excite and lighten up the imaged material, laser energy absorption by the imaged material resulting in heat generation, transient thermoelastic expansion and ultrasonic image production as well as use of the detected ultrasonic for anatomical PA and functional analysis (Liu & Zhang 2016:14). In principle, the electromagnetic (EM) energy used is nonionizing with limited radiation exposure (Xu & Wang 2006: 2). Nonetheless, exposure to EM radiation should never exceed the recommended levels of maximum permissible exposure (MPE). MPE It is a function of EM wavelength, exposure time and pulse repetition where the longer the wavelength, the higher the MPE and the longer the exposure time, the lower the MPE (Xu & Wang 2006:3). IEEE’s recommended MPE levels are 3KHz-300GHz (Xu & Wang 2006:3). Hence, both the patient and staff must limit their exposure time and use in the process. For staff, this implies wearing radiation protective clothing including gloves and goggles when operating the machinery. Moreover, they must place warning signs outside the room to war people of the ongoing process and danger of radiation to prevent accidental exposure. In terms of laser energy absorption and use of detected ultrasonic, endogenous chromophore agents provide two advantages for the patient: they are biologically safe and they differentiate pathological and normal tissue through the metabolic and physiological changes that occur such as oxygen saturation (Mehrmohammadi et al. 2013: 91). Energy absorption is a particular safety concern when dealing with sensitive organs such as the eyes where overexposure and illumination intensity can lead to thermal damage, thermal acoustic damage and photochemical damage (Liu & Zhang 2016: 15). Nonetheless, the core similarities between photoacoustic imaging and ultrasound imaging make it safe for staff.
Compared to all previous non invasive techniques and methodologies of diagnosing melanoma, we can conclude that photo acoustic microscopic imaging is the best. From the experiments carried out above, we have shown the accuracy of the device in measuring the thickness of melanoma which is crucial in the prognosis and treatment process. Thickness ranging from 0.7 mm to 4.2 mm can be measured and in the in vivo experiment, the thickness of 3.75 was imaged. This invasive technique of the prognosis of melanoma could be key to successful surgery treatment of the deadly skin cancer (Valluru, et al., 2016).
METHODOLOGY
Introduction
In this chapter we are going to discuss how to identify accurately the thickness of melanomas before operating based on data or reading by of a photo acoustic system, the materials that comprise the photoacoustic imaging system, the technical aspect and the functional aspect of the system.
Design
Commercially available high resolution 3D optical imaging modalities which includes confocal microscopy, two photon microscopies andoptical coherence tomography. These were used then and proven not to be effective when it comes to skin penetration (not deeper than approx. 1 mm). Photoacoustic tomography, a combination of strong optical contrast in a single modality and a high ultrasonic resolution, has proven to be effective in going through this set – depth and has manage to achieve a significant deeper depth combined with a high – resolution optical imaging. We shall use the description of the photoacoustic system called Vevo 2100.
MATERIALS
Photoacoustic Imaging system (Vevo® 2100 Imaging System)
This machine houses the electronics, manual controls, software and monitor which controls the transducer functions and help in image data processing at the time when image acquisition sessions are happening.
The cart is produced in two configurations (A and B) that feature small variances based on components requirements. We shall identify the differences where they appear.
Vevo 2100 is believed to support the imaging modes mentioned below:
- B – mode
- M – mode
- AM – mode
- PW (Pulsed Wave) Doppler Mode
- PW Tissue Doppler Mode
- 3D – Mode
- Power Doppler
- Linear Contrast Mode
- Nonlinear Contrast Mode
- EKV™ Mode
Figure 1:Images of the Vevo 2100 photoacoustic Imaging device
The composite safety warning label is located at the back of the cart, below the rear panel.
Figure 2:Composite safety warning label and the explanations of the symbols
The cart is produced in two configurations:
Configuration A has a retractable air filter trays located at the bottom of the cart chassis, both back and front.
Configuration B has an integrated power components assembly on the rear panel that has a power switch, a fuse box and AC In.
The frontal panel of the photoacoustic vevo imaging system is believed to have three transducer ports and transducer cable holder as depicted in the figure below
Figure 3:The frontal panel of the Vevo Imaging System
It’s important that we show the rear panel connections of the Vevo photoacoustic imaging system. This part provides the power controls and connections to external devices. This too is designed in two configurations, based on the ones that were shown in Fig. 1. The rear panel connections are shown in the Fig. 4 below:
Figure 4:The rear panel connections of Vevo 2100 imaging system
Vevo® LAZR Photoacoustic Imaging System
It’s a multiple component system that usually integrate laser light delivery with ultrasound image acquisition and result in producing a photoacoustic (PA – Mode) image data.
Figure 5:Vevo® LAZR Photoacoustic Imaging System
It has four components
- Vevo LAZR cart: the enclosure that houses the laser optical system that usually generate the laser beam delivered through the LZ series Micro – Scan laser transducer for PA – Mode (photoacoustic mode) imaging sessions.
- Vevo® LAZRTight™: this is a dedicated steel cabinet that give users a protected environment where they can perform photoacoustic imaging (PA – Mode) sessions without exposing themselves to laser beam/light.
- LZ series Microscan Transducer: this is a probe that delivers the laser light and receives the ultrasound signals that gives the images during PA – Mode imaging sessions.
- Vevo 2100 ultrasound cart: it’s a standing workstation that houses the electronics, manual controls, software and monitor that controls the transducer functions and processes the image data during at the time of image acquisition sessions.
Vevo LAZR cart
Figure 6:Vevo LAZR cart houses the optical, cooling and power generation components in the laser generation system and the frontal part of it.
These are the parts/areas on the frontal part of the Vevo LAZR cart
| Area | Description |
| 1 | Laser cart power on/off. Light indicates whether the system is powered or not by AC. On= system is powered |
| 2 | Laser light status. Solid light indicates that the light is firing, while blinking light indicates that the laser is firing single shots. |
| 3 | Interlock status light. Showswhether or notthe interlock system is activated. On=interlock is activated and at least one of the interlock is activated at least one of the interlocks is not completely closed. The laser cannot fire in this state. |
| 4 | Laser fiber port with interlock. Accepts the laser fiber bundle optic cable that connects the laser system to deliver the laser light from the cart to the transducer. If the cable pulls from the cart, the interlock will instantly stop the laser from firing. |
| 5 | Water quality status indicator light. This indicates whether the ionization level in the distilled water is within the required range. After 20 or so minutes, the light will turn green if the ionization level is within range. But if the light turns red after the warm up period, the ionization level in the distilled water is out of range. The distilled water and the water filter must now be changed only by Visual – Sonics service personnel. |
| 6 | Fiber interlock connector. This connects with fiber interlock box inside Vevo LAZRTight. The laser safety fiber bundle interlock cable tether, prevents any user from operating the transducer outside of the fully interlocked Vevo LAZRTight. |
Vevo LAZR Transducers
These transducers are a solid-state device that requires real – time images of the target in any Photoacoustic Mode (PA – Mode) by integrating laser light delivery with ultrasound signal acquisition. These transducers also obtain data in all other modes supported by the system.
Figure 8:VisualSonics Vevo® Imaging Systems
It has the following features
- 256 – element linear array detector
- 3 cables
- Connects either to the ball joint on the Vevo Imaging Station or to the 3D motor connected which, in turn, is connected to the ball joint on the Vevo Imaging Station.
METHODS
Photoacoustic mode acquisition
The Vevo imaging system integrates four core systems, in order to generate useful image data
- Image acquisition modes –the Vevo imaging system gives a range of imaging modes to achieve different imaging objectives, like the frame based modes and the time-based modes. Several Vevo imaging system features apply to multiple imaging modes, there are frequent references here to frame – based and time – based modes.
- Frame – based imaging modes
Images are measured in frames, based on two-dimensional B – Mode data, which includes the following modes. B – Mode, PA – Mode, Color Doppler Mode, Power Doppler Mode, Linear Contrast Mode, Nonlinear Contrast Mode and EKV – Mode.
- Time – based imaging modes
Images are measured in seconds, based on unique source data. It is characterized by the following: M – Mode, AM – Mode, PW Tissue and Doppler Mode.
- Application packages
This package entails a group of predefined image acquisition settings that are used to ensure that an optimal image is obtained to work with it and be able to take the necessary measurements. Through the application packages you can be able to quickly cycle through the pre ordered measurements protocol for your application. The system has general imaging and cardiology as the two default application packages.
- Studies, series and images
- Users
PA – Mode
PA – Mode (photoacoustic mode), this method gets optical contrast from the biological tissues and detecting it with ultrasound. This takes place when illumination happens on the tissue with pulsed laser light, what follows, thermoelastic expansion occurs and this expansion produces an ultrasound wave which is then detected by an ultrasound transducer. The PA – Mode window is the workspace that is used whenever a view of an image data in PA – Mode (described above). The following are the features in the PA – Mode window.
Figure 10:Features in the PA – Mode window
B – Mode
B – Mode is the imaging mode more often used because of its effectiveness in locating anatomical structures. B – Mode is more or less the same as a conventional ultrasound image. B – Mode can also be used in:
- Other imaging modes as a background orientation image over which the active data is applied (Visual Sonic, Vevo 2100).
- In real – time orientation window in other imaging mode windows so one can visually guide the transducer to the right location to obtain the most useful data in an imaging mode.
B – Mode window is the workspace whenever one views an image data in B – mode. The image below describes the B – Mode window.
Figure 11:The features in B – Mode window
The 3D Mode
The 3D Mode is known for providing a three dimensional view of the area of interest under observation, in this case the melanoma affected area from the frame based imaging modes and excluding the photo acoustic mode, that is spectro and the EKV mode. The system obtains a 3D data by
- Creation of B-Mode slices quick series.Creating a quick series of B – Mode slices
- Combination of the slices into a whole image.
We can then view the structures we are interested in by the use of the analysis and measurement tools.
Figure 16:The features in 3D Mode window
FINDING BASELINE VALUES OF PATIENT
Any study that involves obtaining some results or investigating the past or the present records of patients, often needs to be permitted by the hospital. The role is to ensure that the dignity, rights well – being and safety of the research participants are preserved. The study of my research got the approval from Galway University Hospital and based on the Breast Cancer center at Galway University Hospital.
After all these are taken into considerations, we must make sure that both the patient and the stuff get limited exposure time to the radiations emitted in the process. The staff should therefore ensure that they wear protective clothing that includes gloves and goggles when operating the machinery. For patients should ensure that they wear goggles to protect their eyes from the laser.
The Photoacoustic is used to obtain the scan for the 26 patients sampled in my research. There are 6 patients had Melanoma, 20 were Nevi. Most melanomas show symptoms of abnormal area on the skin, unusual moles, lumps, blemishes, markings or changes that are suspicious on the skin. If a doctor experiences these, then they will examine them and test may commence if it is melanoma or another skin disease. If they find that is melanoma, then they may begin to examine the extent or the spread in other areas of the body. The size shape, color and texture is examined by the doctor and whether it is bleeding. The doctor may also feel the lymph nodes (small, bean – sized collections of the immune cells) under the skin in the neck, underarm, or the groin area near the abnormal areas. When taken to a histologist, he uses a technique called histology to see it is melanoma or not.
In a photoacoustic mode, PA Mode, an optical contrast is obtained from the biological tissues and it is detected with ultrasound. By illuminating tissues, a thermoelastic expansion creates an ultrasound wave which can be detected with an ultrasound transducer. This way we can determine the baseline for patients.
Conclusion
In photoacoustic mode or PA Mode, as an integrated feature built in the Vevo LAZR system, we find preference in scanning patients with melanoma. It is enhanced with a high-resolution ultrasound that derives images with its enabled high sensitive optical imaging. What results after a scan of PA Mode is gotten, is a visually stunning anatomical image overlapped with functional molecular and hemodynamic data. The way histologists, cancer biologist, neurologists and other people conducting research in a quest to obtain accurate data has just been made easy, thanks to photoacoustic. For melanomas, this technique is key to a successfully conducted surgery.
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