Our group pioneered the use of 4D (spatio-temporal) image processing algorithms, and continues to study their use in improving image quality in cardiac SPECT, a standard imaging procedure to assess coronary artery disease. In 4D techniques, image sequences are treated as fully four-dimensional signals, consisting of three spatial dimensions plus time. In new 5D methods, the time axis is split into a dynamic dimension (for large-scale time evolution) and a gated dimension (which captures a single cardiac cycle). The 5D approach may pave the way for alternative imaging protocols in which cardiac patients are evaluated in a single imaging session that provides information about cardiac perfusion, wall motion, and tracer kinetics simultaneously. This research is sponsored by NIH/NHLBI.
Diffraction tomography (DT) is an imaging technique for reconstructing the complex-valued refractive index distribution of an object. An undesirable characteristic of DT is that it requires measurement of the amplitude and phase of the transmitted wavefield. Phase measurements generally present considerable difficulities in optical and X-ray applications. Recently, a new theory of intensity DT (I-DT) has been proposed that circumvents the need to make explicit wavefield phase measurements. We are analytically and numerically investigating the I-DT reconstruction theory and generalizing it to accommodate scanning geometries that are of practical importance. Applications of I-DT to optical microscopy and coherent X-ray imaging are being explored actively.
Thermoacoustic tomography (TAT) is an emerging imaging technique with great potential for a wide range of biomedical imaging applications. In TAT, a short electromagnetic pulse is used to irradiate a biological tissue. When the electromagnetic pulse is absorbed by the tissue, a thermoacoustic effect results in the emission of acoustic signals that are measured subsequently. The objective of TAT is to produce an image that represents a map of the spatially variant electromagnetic absorption properties of the tissue. We are currently developing and evaluating tomographic reconstruction algorithms for TAT. These algorithms produce images that have greatly improved accuracy and statistical properties, which will facilitate diagnostic tasks.