Coded-aperture imaging in nuclear medicine

Coded-aperture imaging is a technique for imaging sources that emit high-energy radiation. This type of imaging involves shadow casting and not reflection or refraction. High-energy sources exist in x ray and gamma-ray astronomy, nuclear reactor fuel-rod imaging, and nuclear medicine. Of these three areas nuclear medicine is perhaps the most challenging because of the limited amount of radiation available and because a three-dimensional source distribution is to be determined. In nuclear medicine a radioactive pharmaceutical is administered to a patient. The pharmaceutical is designed to be taken up by a particular organ of interest, and its distribution provides clinical information about the function of the organ, or the presence of lesions within the organ. This distribution is determined from spatial measurements of the radiation emitted by the radiopharmaceutical. The principles of imaging radiopharmaceutical distributions with coded apertures are reviewed. Included is a discussion of linear shift-variant projection operators and the associated inverse problem. A system developed at the University of Arizona in Tucson consisting of small modular gamma-ray cameras fitted with coded apertures is described

Tc-99m pyrophosphate imaging of poloxamer-treated electroporated skeletal muscle in an in vivo rat model

Objective: This study investigates whether 99mTc pyrophosphate (PYP) imaging provides a quantitative non-invasive assessment of the extent of electroporation injury, and of the effect of poloxamer in vivo on electroporated skeletal muscle. Methods: High-voltage electrical shock was used to produce electroporation injury in an anesthetized rat\u27s hind limb. In each experiment, the injured limb was treated intravenously by either poloxamer-188, dextran, or saline, and subsequently imaged with 99mTc PYP. The radiotracer\u27s temporal behavior among the experimental groups was compared using curve fitting of time-activity curves from the dynamic image data. Results: The washout kinetics of 99mTc PYP changed in proportion to the electric current magnitude that produced electroporation. Also, 99mTc PYP washout from electroporated muscle differed between poloxamer-188 treatment and saline treatment. Finally, 10-kDa dextran treatment of electroporated muscle altered 99mTc PYP washout less than poloxamer-188 treatment. Conclusions: Behavior of 99mTc PYP in electroporated muscle appears to be an indicator of the amount of electroporation injury. Compared to saline, intravenous polaxamer-188 treatment reduced the amount of 99mTc PYP uptake. Coupled to results showing poloxamer-188 seals ruptured cellular membranes, lessens the extent of electroporation injury and improves cell viability, 99mTc PYP imaging appears to be a useful in vivo monitoring tool for the extent of electroporation injury. © 2006 Elsevier Ltd and ISBI

Arebinning technique for 3D reconstruction of Compton camera data

ABSTRACT: Anewlydeveloped 3D image reconstruction technique for Compton camera data is described in this paper. For Compton cameras, the energies and positions of gamma-ray interactions in at least two detectors from a single incident photon are recorded using coincidence techniques. Based on this information, the Compton scattering formula establishes a cone surface from which the incident photon must have originated. Through an extension of the previously developed rebinning technique, instead of tracing the entire cone surface into the image space, a number of lines on the cone surface are sampled. All the lines start from the apex of the cone and are evenly distributed over the cone surface. The number of lines on each cone is determined by the desired spatial resolution. Each line is then projected to a perpendicular imaginary detector plane. The 2D Fourier transform of the line-projection data on this plane is shown to be one rotated plane of the 3D Fourier transform of the source distribution in the frequency domain. By projecting all of the sampled lines, performing Fourier transforms on all of the projected data, and summing up all the transformed data in the frequency domain, the 3D Fourier transform of the source distribution can be obtained. Interpolation and geometry normalization of data points in the 3D frequency domain will subsequently be applied. An image can then be reconstructed by a 3D inverse Fourier transform. The development of this technique will be discussed in detail. I

Modular detector systems for nuclear medicine imaging

Modular detectors provide system design flexibility that makes possible the development of many imaging systems not possible through the use of more traditional approaches such as employing fixed ring configurations or large FOV (field-of-view) detectors. We have developed two such modular detector systems. The first is a small FOV modular gamma camera based on a position-sensitive photomultiplier tube (PSPMT) and single contiguous NaI(Tl) scintillation crystal. This detector can be used, for example, in the development of systems for planar single-photon emission imaging and for single-photon emission computed tomography (SPECT). The second is a modular panel based on an array of small FOV photomultiplier tubes (PMTs) and a pixilated array of LSO crystals. This detector can be used in development of systems for positron emission tomography (PET). For each modular detector, special signal -processing and computer- interface electronics have been designed and implemented in conjunction with its own radiation shielding, crystal or crystal array, PSPMT or PMTs, and computing processors. Such modular detectors can be employed as components of general-purpose or application-specific emission imaging systems for human (clinical or research) imaging or for laboratory animal imaging. Applications for which systems with modular detectors may be relevant include diagnostic imaging of humans in specialized clinical procedures and research imaging of animals for drug discovery and development, and for biotechnology development. © 2004 IEEE

Physiological imaging of electrical trauma and therapeutic responses

In victims of electrical trauma, electroporation of cell membrane, in which lipid bilayer is permeabilized by thermal and electrical forces, is thought to be a substantial cause of tissue damage. It has been suggested that certain mild surfactant in low concentration could induce sealing of permeabilized lipid bilayers, thus repairing cell membranes that had not been extensively damaged. With an animal model of electrically injured hind limb of rats, we have demonstrated and validated the use of radiotracer imaging technique to assess the physiology of the damaged tissues after electrical shock and of their repairs after applying surfactant as a therapeutic strategy. For example, using Tc-99 m labeled pyrophosphate (PYP), which follows calcium in cellular function and is known to accumulate in damaged tissues, we have established a physiological imaging approach for assessment of the extent of tissue injury for diagnosis and surgical planning, as well as for evaluation of responses to therapy. With the use of a small, hand-held, miniature gamma camera, this physiological imaging method can be employed at patient\u27s bedside and even in the field, for example, at accident site or during transfer for emergency care, rapid diagnosis, and prompt treatment in order to maximize the chance for tissue survival