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As part of the development of dedicated scintillation cameras for breast imaging, we compared the performances of two dedicated cameras with a standard clinical camera (Siemens Orbiter). One dedicated camera was based on a single position-sensitive photomultiplier tube (PSPMT) coupled to a 6 cm by 6 cm by 6 mm NaI(TI) crystal. The other (LumaGem) was based on multiple-PSPMTs coupled to a 2 mm x 2 mm by 6 mm matrix of NaI(TI) crystals. Spatial resolution was measured with all cameras as a function of depth. The ability of the cameras to image small superficial tumors was tested with a phantom consisting of six hot cylindrical tumors of height 3 mm and varying diameters against a warm background. The tumors were imaged at various depths within the background using tumor-to-background activity concentration ratios of 10:1 and 5:1. Tumor contrast and signal-to-noise ratio were measured in all cases for all cameras. The dedicated cameras show improved shallow depth of field spatial resolution, contrast, and signal-to-noise ratio relative to the clinical camera when imaging the breast tumor phantom. This, with the additional advantage of being able to position the cameras close to the region of interest, suggests that dedicated cameras will play a strong role in scintimammography and other shallow depth of field applications. Index Terms--Biomedical nuclear imaging, cancer, image region analysis, object detection, position-sensitive photomultiplier tube (PSPMT), scintillation detectors, scintimammography. more...

We are developing an accelerated Monte Carlo simulation of positron emission tomography (PET) that can be used for scatter correction of three-dimensional (3-D) PET data. Our Monte Carlo technique accurately accounts for single, multiple, and dual Compton scatter events, attenuation through the patient bed, and activity from outside the field of view. We have incorporated innovative sampling techniques that are compatible with our simulation approach, increasing computational efficiency by a factor of seven while improving accuracy through more sophisticated stratification and by incorporating the true energy response of the scanner. The required execution time to acquire 10 million scatter coincidence events for a 3-D thorax PET scan is only 4 min on a 300-MHz Sun dual-processor workstation. We demonstrate that for a low-noise thorax phantom study, image data corrected using the Monte Carlo 3-D PET scatter correction demonstrate no statistically significant deviation from the true activity concentration provided corresponding input data are accurate. The speed and accuracy of our simulation makes it an efficient research tool for studying scatter effects in PET and a practical scatter correction for 3-D PET clinical imaging. Index Terms--Compton scatter, Monte Carlo simulation, photon tracking, positron emission tomography (PET), sampling techniques, scatter correction, three-dimensional (3-D) PET, variance reduction. more...

We are developing a 1-2 [cm.sup.2] area camera for imaging the distribution of beta-emitting radiopharmaceuticals at the surface of tissue exposed during surgery. The front end consists of a very thin continuous or segmented scintillator sensitive to betas (positrons or electrons) of a few hundred keV, yet insensitive to gamma rays. The light from the scintillator is piped through clear fibers to the photon detector (PD). This approach requires that a sufficient number of scintillation photons be transported from the scintillator, through the fibers to the PD. The scintillator, reflector, surface treatments, geometry, fiber light guides, and optical couplings must be optimized. We report here on efforts made to optimize the light collection from more...

We are developing a hand-held imaging probe intended for intra-operative use. This probe is to be used after the bulk of a tumor has been removed. It will locate residual malignant tissue labeled by a pre-operative injection of a tumor-seeking radiopharmaceutical. The device presented here is a prototype system that consists of a 4 x 8 array of 925 [[micro]meter] diameter plastic scintillating fibers. The imaging array is coupled to Visible Light Photon Counters (VLPCs) via 2 meters of optical fiber. We have obtained an intrinsic spatial resolution of < 1.0 mm with a highly collimated beta source, and a 2.0 mm resolution with a 1 mm, uncollimated source. Standard deviations of the relative gain and sensitivity over the 32 imaging elements were found to be 9.6% and 11.7% of the mean, respectively. more...

A Monte Carlo simulation has been developed to simulate and correct for the effect of Compton scatter in 3-D acquired PET brain scans. The method utilizes the 3-D reconstructed image volume as the source intensity distribution for a photon-tracking Monte Carlo simulation. It is assumed that the number of events in each pixel of the image represents the isotope concentration at that location in the brain. The history of each annihilation photon's interactions in the scattering medium is followed, and the sinograms for the scattered and unscattered photon pairs are generated in a simulated 3-D PET acquisition. The calculated scatter contribution is used to correct the original data set. The method is general and can be applied to any scanner configuration or geometry. In its current form the simulation requires 25 hours on a single Sparc10 CPU when every pixel in a 15-plane, 128x128 pixel image volume is sampled, and less than 2 hours when 16 pixels (4x4) are grouped as a single pixel. Results of the correction applied to 3-D human and phantom studies are presented. more...

We have been developing Monte Carlo Techniques for calculating primary and scatter photon distributions in PET. Our first goal has been to accelerate the Monte Carlo Code for fast PET simulation. Our second goal has been to use the simulation to analyze scatter effects in PET and explore the potential for use in scatter correction of clinical 3D PET studies. We have reduced the execution time to about 30 minutes or ~1 million coincidences per minute on a dual 300MHz processor UltraSparcII workstation. The short execution time makes it feasible to use this technique for 3D PET scatter correction in the clinic. Fast simulation also allows us rapid feedback for the close examination of the accuracy of the method. We present techniques used to improve computational efficiency of Monte Carlo PET simulations. We use the simulation to analyze how scatter from within the body, outside the FOV, and from scanner shielding as well as the chosen energy threshold affect 3D PET sinograms. more...