The principle of OCT imaging is similar to that of ultrasound, which uses reflected near-infrared rays as an imaging medium to form an image instead of using reflected sound waves. Near-infrared (typically 800-1300 nm) sources are divided into two pathways, one for tissue sampling and the other for reference mirrors. When the sampling arm is scanned through the tissue, an interferometer can be used to continuously block the reflection from the back end of the sampled tissue with the light from the reference arm. For light that is permanently blocked, a digital signal processing algorithm is executed to achieve a depth-resolved axial scan. These scans are stacked on each other to form a 2D or 3D tissue image.
OCT application in biomedicine
Today's OCT medical systems are mostly used in ophthalmology, but there have been several emerging applications in the past few years. For example, otolaryngologists and pediatricians also use OCT technology as a diagnostic tool. In general, physicians use otoscopes to detect redness in the ear, external auditory canal, and tympanic membrane due to bacterial infection. OCT can be used to image the epidermis and subcutaneous membrane to determine whether it is infected with pathogenic bacteria and improve the diagnostic accuracy. After taking several antibiotics, the OCT system can be used to analyze whether the antibiotics are effective. If the infected biofilm has been removed, the patient can stop taking antibiotics.
Other emerging OCT medical applications include dental diagnostic systems and the use of interdisciplinary surgical techniques. For example, dentists can use OCT imaging to determine X-rays and early caries and certain gum diseases that cannot be detected by visual inspection in order to take more effective precautions.
In terms of interdisciplinary surgery, OCT can analyze the presence or absence of cancer cells during the surgical procedure to remove the tumor. In general, when a surgeon removes tissue surrounding a tumor, it is always desirable to remove all cancer cells. The cleared tumor and surrounding tissues are sent to the pathology laboratory for a week of analysis to make a written report after the operation. Because OCT images have the same resolution in histology/pathology applications, the OCT system in the operating room allows the surgeon to accurately know how much tissue needs to be removed during the procedure, while leaving a number of safety margins. Such an approach would not mistakenly remove tissue that is not infected with cancer, thus eliminating the cost and pain of subsequent surgery. OCT technology allows doctors to see images in real-time at a level of histological resolution to make better decisions when performing a first tumor removal procedure.
There will be more medical applications using OCT technology in the future. For example, OCT can be used with small tumors in the early stages of puncture slice removal. For patients with breast cancer, OCT can be combined with visual and "smart" signal processing techniques to guide fine needle insertion into precise tumor locations to identify suspected infected tissue and minimize surgical invasiveness. For patients with cardiovascular disease, OCT can be used with very small catheter stents to more accurately identify intravascular stents or to detect plaque deposits. In these types of applications, advanced digital signal processing technology not only achieves excellent image quality, but also enables tissue classification.
Improved signal processing performance
When OCT was first introduced as a medical imaging application, the system used was a personal computer (PC) platform, the second generation system has been modified, and the third generation system currently under development will also be changed. Some OCT system manufacturers have or will soon adopt embedded processing platforms with single or multi-core digital signal processors (DSPs) rather than general purpose processors (GPPs) used in personal computers.
Compared to traditional computing methods, DSP can achieve more signal processing per milliwatt of power consumption, which means that programmable algorithms can be used to obtain accurate results without the need for costly power supplies and heat sinks. . DSPSoC enables powerful signal processors to coexist with system application processors with appropriate interfaces for data processing, memory and storage, enabling designers to reduce system size and power consumption.
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