Fluorescence-enhanced optical imaging of large phantoms using single and simultaneous dual point illumination geometries A. Godavarty Photon Migration Laboratory, Texas A&M University, College Station, Texas77843-3573 C. Zhang and M. J. Eppstein a) Department of Computer Science, University of Vermont, Burlington, Vermont05405 E. M. Sevick-Muraca b) Photon Migration Laboratory, Texas A&M University, College Station, Texas77843-3573 Received 2 July 2003; revised 4 November 2003; accepted for publication 18 November 2003; published 8 January 2004 Fluorescence-enhanced optical tomography is typically performed using single point illumination and multiple point collection measurement geometry. Single point illumination is often insufficient to illuminate greater volumes of large phantoms and results in an inadequate fluorescent signal to noise ratio SNR for the majority of measurements. In this work, the use of simultaneous multiple point illumination geometry is proposed for acquiring a large number of fluorescent measurements with a sufficiently high SNR. As a feasibility study, dual point excitation sources, which are in-phase, were used in order to acquire surface measurements and perform three-dimensional re- constructions on phantoms of large volume and/or significant penetration depth. Measurements were acquired in the frequency–domain using a modulated intensified CCD imaging system under different experimental conditions of target depth 1.4 –2.8 cm deep with a perfect uptake optical contrast. Three-dimensional reconstructions of the fluorescence absorption from the dual point illumination geometry compare well with the reconstructions from the single point illumination geometry. Targets located up to 2 cm deep were located successfully, establishing the feasibility of reconstructions from simultaneous multiple point excitation sources. With improved excitation light rejection, multiple point illumination geometry may prove useful in reconstructing more challeng- ing domains containing deeply embedded targets. Image quality assessment tools are required to determine the optimal measurement geometry for the largest set off imaging tasks. © 2004 Ameri- can Association of Physicists in Medicine. DOI: 10.1118/1.1639321 I. INTRODUCTION Fluorescence-enhanced optical imaging has been rapidly de- veloping toward three-dimensional 3-D tomographic stud- ies in phantoms as well as in in-vivo animal studies. 1 To date, tomographic studies have been performed using sequential point illumination and sequential point collection schemes as the measurement geometries. More recently, rapid tomogra- phic fluorescence measurements are acquired using a charge- coupled device CCD camera for simultaneous area collec- tion of light received from multiple boundary points in both continuous wave cw 2,3 and time-dependent 4 measurement approaches. For small rodent studies or for phantom studies, which are either small in volume or offer limited penetration depths, sufficient fluorescence generation, and collection across the depth of the entire phantom is possible with sequential illu- mination at single boundary points. Consequently, three- dimensional reconstruction of the target location and size is feasible with the single point illumination measurement geometry. 5–7 However, in studies involving large phantoms of greater volumes and penetration depths, a single point illumination of the phantom surface may be insufficient to generate a fluorescent signal that arises throughout the entire phantom with a sufficient SNR. Weak fluorescent signals are usually dominated by noise, thus impacting the measurement precision and accuracy, and eventually hindering the accurate reconstruction of the target location and size. In this work, we explore the feasibility of using simulta- neous multiple point illumination measurement geometry in order to increase the volume of illumination, and the total number of fluorescent measurements with robust SNR. As a preliminary study toward applying the multiple point illumi- nation geometry, initial studies are performed using dual point illumination geometry for different experimental con- ditions. In the past, researchers employed dual excitation sources that were 180° out-of-phase destructive interfering photon density waves for 2-D spatial localization of an ab- sorbing or fluorescing target located in a 3-D phantom, 8–12 without actually reconstructing the target in three dimen- sions. However, in the current work, surface fluorescence measurements obtained from dual excitation sources, which are in-phase, are used to reconstruct the target location and size in three dimensions. The current work represents the first time that fluorescence measurements acquired using more than a single point of excitation illumination have been used to reconstruct 3-D targets in large tissue phantoms for comparison to single points of excitation illumination. Herein, time-dependent fluorescence measurements are acquired on large breast phantoms using a frequency– domain imaging system employing a gain-modulated inten- sified CCD ICCD camera for rapid data acquisitions. Image 183 183 Med. Phys. 31 „2…, February 2004 0094-2405Õ2004Õ31„2…Õ183Õ8Õ$22.00 © 2004 Am. Assoc. Phys. Med.