Dynamic Spectral Imaging
Dynamic spectral imaging is an imaging method capable of performing time-resolved spectroscopy, which is used to measure and model the absorption kinetics of biomarkers in vivo.[1]
Background[edit]
The concept of dynamic spectral imaging was first investigated as a multi-spectral imaging system by quantitatively evaluating the dynamics of the interaction between acetic acid and tissue in clinical diagnosis in 1999.[2]
Traditional spectral imaging method has the unique feature of combining the advantages of both imaging and spectroscopy (high spatial and spectral resolution) in a single instrument. In spectral imaging, the light intensity is recorded as a function of both wavelength and location. Spectral imaging contains information about imaging and spectroscopy. The results contain a full image at each individual wavelength in the image domain and a fully resolved spectrum at each individual pixel recorded in the spectroscopy domain, respectively. However, spectral imaging has no temporal information, the deficiency of which leads to the development of dynamic spectral imaging.
Smear test is the primary screening method of cell-level microscopic examination. Smear tests are usually used to investigate diseases involving a wide range of body sites but limited in accuracy, often to aid in the diagnosis of cancer. For example, a famous kind of smear test called pap smear is a screening method to detect cervical cancer. Cytopathology The technique is simple and its accuracy is limited by both sampling and reading errors in cervical cancer detection.[3]
Methodology[edit]
Biomarker-Tissue Interaction[edit]
The dilute solution of acetic acid can be used as a biomarker to help visualize abnormal uterine cervix sites. The abnormal part will become reversibly whitened by the application of the acetic acid solution (3%–5%). The detection of neoplasm can be achieved by measuring the biomarker’s uptake kinetics by generating dynamic optical power.
Light-Tissue Interaction[edit]
Refractive index differences will encourage reflections of light, especially at the boundaries of overlapping layers. Normal and abnormal epithelia are almost transparent originally before acetic acid application and the appearance of tissue is largely determined by the spectral characteristics of the non-absorbed and backscattered photons from the vascular network. Spectral analysis of tissue areas with acetic acid affected and unaffected epithelium is required. For the purpose of spectrometry, the maximum difference in which to their light scattering characteristics is recorded. Abnormal epithelium becomes opaque after acetic acid application and scatters equally all the incident wavelengths, and gradually changes the intensity and spectral characteristics of the backscattered light from the tissue and evenly disperses all wavelengths.[4]
Spectral characteristics can be obtained by measuring the intensity of the backscattered light as a function of both time and wavelength, in any spatial point of the area of interest.
System Setup[edit]
A charge-coupled device (CCD) video camera is interfaced with a computer-controlled liquid crystal tunable filter (LCTF) by means of a relay lens. A zoom lens is attached to the other side of the filter, the lens is used for the optical imaging of the cervix instead of common colposcopes. A ring fiberoptic bundle, which surrounds the front part of the lens, transmits light onto the tissue surface. The polarization plane of the incident light is selected by means of a ring-shaped linear polarizer, which in turn is attached to the fiberoptic ring.
Using the displayed image of pre-selected bands as a reference, the optimal settings are obtained. When completed the calibration procedure, the successive spectral imaging in vivo is repeated every 10 seconds for a total duration of 10 minutes in an experiment. In each imaging cycle, the image capturing and storing procedure is synchronized with the filter tuning according to the retrieved calibration dataset.
Pros and Cons[edit]
The basic configuration for DSI is concise and easy to implement, which allowed for low-cost and widely usage. However, DSI modality can only visualize the superficial images in low-resolution and thus it has limited applications.
References[edit]
- ↑ Balas, Costas. "Review of biomedical optical imaging—a powerful, non-invasive, non-ionizing technology for improving in vivo diagnosis." Measurement Science and Technology 20.10 (2009): 104020.
- ↑ Balas, Constantin J., et al. "In-vivo assessment of acetic acid-cervical tissue interaction using quantitative imaging of backscattered light: its potential use for in-vivo cervical cancer detection grading and mapping." Optical Biopsies and Microscopic Techniques III. Vol. 3568. International Society for Optics and Photonics, 1999.
- ↑ Kurman, Robert J., et al. "Interim guidelines for management of abnormal cervical cytology." Jama 271.23 (1994): 1866-1869.
- ↑ Balas, Costas. "A novel optical imaging method for the early detection, quantitative grading, and mapping of cancerous and precancerous lesions of cervix." IEEE Transactions on biomedical engineering 48.1 (2001): 96-104.
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