A near-infrared (NIR) tomography system with spectral-encoded sources at two wavelength bands was built to quantify
the temporal contrast at 20 Hz bandwidth, while imaging breast tissue. The NIR system was integrated with a magnetic
resonance (MR) machine through a custom breast coil interface, and both NIR data and MR images were acquired
simultaneously. MR images provided breast tissue structural information for NIR reconstruction. Acquisition of finger
pulse oximeter (PO) plethysmogram was synchronized with the NIR system in the experiment to offer a frequency-locked
reference. The recovered absorption coefficients of the breast at two wavelengths showed identical temporal
frequency as the PO output, proving this multi-modality design can recover the small pulsatile variation of absorption
property in breast tissue related to the heartbeat. And it also showed the system's ability on novel contrast imaging of
fast flow signals in deep tissue.
A near-infrared (NIR) tomography system has been built to allow for imaging thick tissue at high frame rate. This
tomography system uses a spectrally encoded source arrangement consisting of eight fibers coupled from temperature
controlled single mode laser diode sources with about 1 nm spacing in their lasing wavelengths, having an overall
spectrum confined to within 10 nm in the NIR region. Eight
fiber-coupled, high-resolution, CCD based spectrometers
were used to detect the intensities and decode their source origin locations. All detection CCDs were frame-synchronized
using a computer controlled external TTL trigger circuit in order to preserve the temporal kinetics of the detected signals.
A set of static heterogeneous phantom imaging was performed on a 64 mm thick resin phantom to verify the linearity
and accuracy of the system and algorithm. Furthermore, to test the performance of this system at high frame rate, a
dynamically varying absorption contrast study was realized by letting India ink diffuse into the phantom inclusion while
continuously imaging it at 20 frames per second. The algorithm and the results from these phantom studies are presented.
The 20 frames/second exposure rate and ability to image tissue beyond 60 mm thick makes this system perfect for
potential clinical imaging of pulsatile hemodynamics in breast tumors.
Video rate diffuse tomography can be implemented within the magnetic resonance breast exam. The following paper outlines the basics of a spectrally encoded source set up, being designed and tested for use in breast imaging within a specialized breast surface coil. The system design maximizes input power to the breast, while confining the spectrum to a 10 nm bandwidth of near-infrared light. The center spectral band can be varied, since it is supplied by a tunable Ti:Sapphire laser. The encoding of each source is achieved by splitting the signal into individual nanometer bands through a high resolution grating, and focusing the output of this into each source fiber. This source configuration then requires spectral detection at the output, and so each detection fiber is delivered to a high resolution spectrometer to resolve the detected intensities. Breast imaging with this system has some subtle dynamic range issues, which means that light from sources farthest from the detector pickup are likely not providing useful data, but the closest 4-6 fibers near each source can provide useful data. The implementation of this is being carried out within a magnetic resonance breast array, and initial testing of the signals is shown, along with diagrams and photographs of the system configuration.