Opto-Acoustic Imaging

Opto-acoustic imaging, also known as photoacoustic imaging (PAI), uses ultrashort laser pulses whose frequencies range from sub-MHz to hundreds of MHz. This technique has been used for in vivo disease diagnosis and therapy monitoring. Opto-acoustic imaging uses mechanical waves due to light absorption by chromophores within the tissue. It is a light-induced sound phenomenon that occurs when the excitation light is usually within the visible and near-infrared section of the electromagnetic spectrum.

If the excitation energy is definitely within the radio-frequency or microwave region, the image resolution technique can be instead referred to as thermoacoustic Image resolution. The opto-acoustic imaging procedure involves illuminating the area of cells using a short pulse of light. Specific tissue parts, such as haemoglobin or lipids, mainly absorb this light.  The interaction of the short pulse of light generates a mechanical wave in the ultrasound frequency range.

These signals can be detected by an ultrasound sensor or an array of ultrasound sensors. The indicators can be used to form an image with various picture reconstruction algorithms currently available in the literature. The resulting contrast of the image is generally based upon the distribution of absorbed optical energy within the tissue, which is related to the wavelength of light utilised and the optical properties of the cells under study.

Photoacoustic Imaging is usually investigated in brain image resolution. This is credited to strong optical scattering by the skull and mind tissues, which severely limits the optical fluence. Currently, photoacoustic imaging for human brain image resolution is still preclinical, as experiments on rodents are less challenging due to their thin heads. Thyroid cancer can be overdiagnosed and overtreated.

Ultrasonography, in combination with fine-needle aspiration cytology (FNAC) followed by histology, is certainly the primary diagnostic tool for thyroid malignancy.  However, FNAC does not differentiate between aggressive lesions and subclinical cancers. Other clinical imaging techniques such as hybrid PET/CT, MRI, CT and scintigraphy lack the specificity to distinguish between benign and malignant follicular nodules that would benefit from surgical treatment.

Such image resolution limitations lead to many nodule biopsies, overdiagnosis, and over-treatment. Since the thyroid gland is normally 2-3 cm deep and allows sufficient light penetration, PAI is an attractive imaging technique to facilitate ultrasound and fine-needle aspiration cytology to investigate thyroid nodules.

The breast image resolution is usually a promising region for PAI. Breast cancer is the most common female malignancy and a leading cause of worldwide cancer-related death. The screening methods include ultrasound imaging and X-ray mammography (XRM).  However, XRM suffers from a low positive predictive value, exposure to ionising radiation, and reduced sensitivity in ladies with dense breast tissue as well as causing extreme discomfort. Ultrasonography results depend on the radiographer’s interpretation and, therefore, could result in a high false-positive rate.

However, an MRI of the breasts offers a high level of sensitivity but low specificity and high cost. As a result, there can be a strong need for improved breast tumour image resolution methods that can reduce false-positive rates and improve awareness. Invasive biopsy, combined with a histopathologic analysis, is still the technique of choice for accurately diagnosing many skin diseases since it is normally the most accessible and shallow organ in the human body. However, dermatological illnesses are highly amenable to non-invasive optical analysis.

Typical dermatologic applications of PAI include the detection of pores and skin malignancies, burn depth estimation, a medical diagnosis of psoriasis, and various cosmetic forms. Early recognition of melanoma, an intense cutaneous tumour, is essential since it is usually challenging to diagnose yet is responsible for most epidermis cancer deaths. Existing imaging techniques for skin image resolution in the clinic, such as optical coherence tomography (OCT) or high-frequency ultrasonography, are either fundamentally limited in their imaging depth (1-2 mm) or absent functional and molecular image resolution capabilities.

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