Southwestern In Vivo Cellular and Molecular Imaging Program

Core 2
Nuclear Imaging
(Director: Orhan Kemal Öz, M.D., Ph.D.)

Clinical Nuclear Imaging | Small Animal  PET/SPECT

Dr. Öz, a board-certified radiologist and biophysicist will direct the Nuclear Imaging Core. His on-going projects include development and/or testing tumor targeting radiopharmaceuticals and the application of multiple imaging modalities in the characterization of small animal models of human disease. He has experience in constructing synthetic genes that encode targeting agents, labeling peptides and proteins for biodistribution and imaging studies, and in the use of plain film radiography, magnetic resonance imaging, planar, and SPECT imaging in mice.

Dr. Dana Mathews (Director Clinical PET Center and Director of Nuclear Medicine at Zale Lipshy University Hospital (ZLUH)) is both a neurologist and a board certified Nuclear Medicine physician with a special interest in application of nuclear imaging in the nervous system and cerebral blood flow. Dr. Erdman (Director Nuclear Medicine, PMH) will serve as an advisor for thoracic imaging. Dr. Anderson (PET/SPECT board certified medical physicist) will provide QA, implement studies and perform data analysis for small animal experiments on clinical nuclear medicine devices. The Pre-ICMIC will have access to the nuclear medicine imaging facilities at Parkland Memorial Hospital and Zale Lipshy University Hospital. Both facilities have extensive experience in functional imaging of tumor localization and recurrence as well as functional assessment of cerebral blood flow and metabolism using single photon emitters. In addition, Drs. Mathews and Öz, in collaboration with Dr. McColl (Informatics Core) frequently employ coregistration of CT and SPECT studies for tumor localization. The PET Facility opened the summer of 2001 with a state of the art Siemens/CTI Exact HR plus PET scanner (Figure). This scanner has an axial resolution of 3.9 mm and is capable of rapid dynamic imaging.  A combined CT/PET scanner will be available before 2002.

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Dr. Antich’s Group has built small animal imaging devices, which are immediately available to perform 3D tomography by PET or SPECT (Figs. 1, 2, 3). This core facility will not only provide a resource for the Pre-ICMIC, but continue to develop advanced imaging instrumentation (laboratory and clinical) through industrially supported research. Currently, a three-man development team led by Dr. Edward Tsyganov operates the small animal imaging devices and is engaged in active research (materials science, mechanics, electronics, analysis algorithms) to enhance the equipment. Image coregistration with MR, if necessary for the study, will be done in collaboration with Dr. McColl (Core 7). 

• Small animal PET device (Figure)

• Images of phantom obtained using small animal PET device (Figure)

• Quantitative validation of small animal PET device (Figure)

Small animal SPECT will be feasible on clinical systems, which are optimized for high energy ^99mTc. Dr. Antich's small animal instrument incorporates novel technology providing enhanced sensitivity at low energy. Traditional SPECT is associated with high energy isotopes (e.g., ^99mTc, 0.14 MeV; ¹³¹I, 0.35 MeV) making collimation and spatial definition difficult due to Compton scattering and thick shielding requirements. Iodine-125 has been largely neglected since the electron capture decay produces low energy emissions, which are heavily attenuated by tissue. This actually provides a unique opportunity to achieve extremely high resolution by using a multiple pin-hole collimation device requiring little shielding.

Advantages of ¹²⁵I include:

1) Long half-life (t_1/2 ~60 days, vs. 6 h ^99mTc, 8 days ¹³¹I). This places less stringent requirements on speed of synthesis of tagged molecules, increases shelf-life of products, increases feasible imaging time and allows agents to be followed for long-term biodistribution studies.

2) Low-energy (35 keV vs. 350 keV for ¹³¹I) Less stringent shielding requirements for collimation and safety. Photoelectrons are generated at specific location by single photoelectric absorption rather than multiple Compton scatters.

3) Range of labeling. Iodination of proteins is well established and straightforward. There is extensive literature describing labeling procedures for antibodies, blood volume markers etc.

While less satisfactory in large animals, low energy photon emission is well suited for imaging mice, as their low mass and size do not produce excessive attenuation. Given the abundant availability of gene-knock-out mice (models of disease pathology) and SCID mice (implanted with human tumors), this provides a rich array of models for biomedical investigations. Moreover, ready iodination of antibodies, drugs, hormones, and metabolites ensures many significant applications (e.g., tumor detection and antibody delivery). Investigations will be closely integrated with Core 3. All nuclear medicine investigations related to animals will be conducted by Dr. Anca Constantinescu, an expert in radiolabeling, isolation, quality control and animal handling.

For Further Information Contact: RALPH  P. MASON, Ph.D.
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