FieldBrite™ Xi - Excellent Sensitivity
All aspects of the Pearl Impulse are designed and optimized for animal imaging. Exceptional sensitivity is achieved through detection at near-infrared wavelengths and laser excitation.
The Pearl Impulse is optimized to detect two industry leading IRDye® Near-Infrared Dyes, including IRDye 800CW, which has ideal absorption/emission wavelengths for in vivo imaging.
Excitation at near-infrared wavelengths is essential to achieve high target-to-background ratios with deeper tissue penetration. Detection systems utilizing visible fluorophores typically have low target-to-background ratios and shallow tissue penetration due to high tissue autofluorescence and light scattering at visible wavelengths.
Efficient Laser Excitation
FieldBrite™ Xi incorporates two separate lasers (685 and 785 nm) for excitation, each closely matching the absorption wavelength of an IRDye for best excitation efficiency. Near-infrared laser illumination also permits much deeper tissue penetration than white light. Smaller targets can be visualized at greater depths, allowing earlier detection of orthotopic tumors.
[Above] There are three types of light sources typically used for in vivo imaging: White light, LED, and laser. (A) White light sources have a wide spectral range that is filtered to a narrow band matching the absorption spectra of the dye. Most of the optical power is lost when the white light source is filtered, as illustrated by the wide arrow transitioning to a very thin arrow. Due to filtering limitations, the spectrum of the excitation light (red curve) is not all that efficient at exciting a dye. Additionally, the excitation light spills into the emission spectra of the dye, which increases the noise in the resulting image. This is shown in the yellow overlapping area between the dyes emission spectra and the light spectra. (B) LED sources have a much narrower spectral range, but the source still must be filtered. Although the spectrum of this light is narrower than from a white light source, optical power is still lost and it still is not the most efficient at exciting the dye. Once again, due to filtering limitations, there is still some spillover into the emission spectra due to the spectral width of the light. (C) For laser sources, by contrast, the filtered light is very narrow, most of the optical power is conserved and the laser very efficiently excites the dye. With a laser source, there is also little to no spillover of the excitation light into the emission spectra of the dye. The result is higher absorption efficiency and more signal from the dye, as well as lower background noise for better overall signal-to-noise ratio.
Advanced Near-Infrared Detection
The Pearl Impulse uses a proprietary CCD-based optical system specifically designed for in vivo imaging in the spectral region. Patented FieldBrite™ Xi filtering design dramatically reduces noise.
[Above]To illustrate the wide dynamic range of the detection system, a series of tubes containing increasing concentration of IRDye 800 CW(0-10 μM) was imaged. Signal represents the total fluorescence for a region of interest minus background fluorescence for the region.
Six logs (22 bits) of dynamic range are available for each image: Up to 4 logs of usable dynamic range when imaging mice in the 800 nm channel, or up to 6 logs of dynamic range when imaging excised tumors or organs, allowing strong and weak signals to be detected without saturation.
Advanced imaging methods in Pearl Impulse Software use the 22-bit dynamic range to assure proper exposure on the first attempt with no user adjustments. Saturated or underexposed images are eliminated, producing a perfect image every time.
[Above] Variations in inherent autofluorescence as a function of illumination wavelength in pre-injected mice was demonstrated when mice were illuminated with 785 nm light (Image A) and 660 nm light (Image B). Image A has a reference vial containing 10 pmol of IRDye 800CW EGF. Image B has a reference vial containing 10 pmol of Cy® 5.5 EGF. The NIR Image (Image A) shows a significantly lower level of autofluorescence from the mouse when compared to the red fluorescent image (Image B). Chlorophyll in animal's diet causes the bright signal in Image B.1
[Above] Orthotopic Imaging: NOD/SCID mouse were orthotopically implanted with prostate tumor cells and monitored over a 6 week period. IRDye 800CW EGF was injected weekly and animals were imaged 96 hours post injection. The orange rectangles pinpoint the region of the tumor.
[Above] Dorsal view of a nude mouse injected with MDA-231 Luc breast cancer cells (IC injection 3 weeks prior to imaging) which demonstrated metastasis to the lungs (dorsal view). IRDye® 680 BoneTag was injected 7 days prior to imaging (Red). IRDye® 800CW EGF was injected 4h prior to imaging (Green).2
[Above] Each laser module contains a 685nm laser, a 785nm laser, and an LED source that produces white light. Matched pairs of sources are sequentially turned on and off, and the CCD detector captures all three images in less than 30 seconds.
1Data Source: K. Adams, S. Ke, Z. Fan, K. Hirschi, M. Mawad, M. Barry, E. Sevick-Muraca, Comparison of visible and near-infrared wavelength excitable fluorescent dyes for molecular imaging of cancer, Journal of Biomedical Optics, 12(2), 024017 (March/April 2007).
Data courtesy of Dr. E.M. Sevick-Muraca, Baylor College of Medicine, Houston, TX. Comparison of visible and near-infrared wavelength excitable dyes for molecular imaging of cancer. Journal of Biomedical Optics 12 024017 (2007).
2Data courtesy of Ivo Que, Leiden University Medical Center.
