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A quantitative comparison of four injectable contrast agents…
Abstracts of the AMI Annual Meeting 2004 83
In this contribution we present an imaging system comprised of a tripleheaded gamma camera and three multi-pinhole collimators. Each collimators can be equipped with different apertures having one to 10 pinholes. The tomographic field of view can be easily tailored to different imaging tasks (e.g. brain SPECT or whole-body imaging) by switching the multipinhole aperture. Image reconstruction is performed using a dedicated ordered subset expectation maximization (OSEM) algorithm. Our multi-pinhole imager provides a reconstructed resolution of 1.2 to 1.5mm and a mean system sensitivity of up to 1500cps/MBq. We will present the results of numerous phantom and animal studies to display the imaging capabilities of our system. We will also discuss the system performance with respect to resolution, sensitivity, and overall image quality. Furthermore, we will investigate the imaging capabilities of varying pinhole arrangements using the signal-to-noise ratio (SNR) as a figure of merit.
Methods: A 99mTc-labeled MMP targeted compound (RP805, 1.3±0.3mCi) was injected in control mice (n=4) or mice (n=16) one week, two weeks or three weeks following surgical-induced MI, and in vivo pinhole planar imaging was performed 75 minutes later. Thallium-201 (TL, 0.24±0.05mCi) was injected for assessment of myocardial perfusion. 20 minutes later, hearts were excised and sectioned for gamma well counting. Myocardial RP805 and TL activity within MI area was expressed as %nonischemic. RP805 uptake was compared with ex vivo measures of MMP activity, using zymography. Results: Myocardial RP805 activity was seen on in vivo pinhole images in areas of decreased TL perfusion in post-MI mice. A three to four-fold increase in RP805 activity and reduced TL perfusion were seen in infarcted regions of post-MI groups, but not in control group. Conclusion: We demonstrated increased myocardial RP805 activity in an intact murine model of post-MI remodeling. Thus, MMP radiotracer imag-
No. 52 EVALUATING THE CORRELATION BETWEEN TUMOR 2DEOXY-2-[18F]FLUORO-D-GLUCOSE UPTAKE AND BLOOD FLOW IN AN EXPERIMENTAL LIVER TUMOR MODEL USING HYBRID POSITRON EMISSION TOMOGRAPHY /COMPUTED TOMOGRAPHY E. E. Stewart, X. Chen, J. Hadway, T. Y. Lee Robarts Research Institute, London, ON, CANADA.
ing may provide a novel non-invasive approach for evaluation of MMP mediated post-MI remodeling. No. 54
By serial measurements of hepatic blood flow (HBF) and glucose uptake we seek to characterize growing tumors in a rabbit model. Six healthy male New Zealand White rabbits were implanted with 0.25 ml of VX2 carcinoma cells. Computed tomography (CT) liver perfusion studies were performed on all animals prior to and every four days after tumor implantation. Each perfusion study started with a continuous (cine) scan for 30 seconds with breath-hold after a bolus injection of 5 mL non-ionic contrast, followed by bursts of four seconds cine scans without breath-hold every 10 seconds for two minutes. These latter images were registered with the breath-hold images to eliminate breathing motion. The weighted summation of the aortic and portal venous time-density curves was deconvolved against that from the liver parenchyma to derive HBF. Three out of six animals had 2-deoxy-2-[18F]fluoro-D-glucose (FDG) with positron emission tomography (PET) scans performed on 0, 8, 16 and 24 days after tumor implantation. FDG uptake was measured as whole body standardized uptake value (SUV) in g mL-1. In the hypovascular core of animals scanned with FDG-PET: (i) HBF decreased from 257 + 13 at Day 0 to 74 + 15 mL min-1 (100g)-1 at Day 24 (p < 0.05); and, (ii) SUV increased from 2.08 + 0.04 to 5.1 + 0.19 g mL-1 (p < 0.05) during the same period. The disparity between HBF and SUV in tumors suggests tumor hypoxia. This suggests that functional CT in combination with FDG-PET can characterize growing tumors and non-invasively image tumor hypoxia. No. 53 NON-INVASIVE TARGETED IMAGING OF MATRIX METALLOPROTEINASE ACTIVATION IN MURINE MODEL OF POSTINFARCT REMODELING H. Su1, F. G. Spinale2, J. Hua1, C. Chow1, S. Sweterlitsch2, B. N. Bourke1, P. Cavaliere1, X. Hu1, L. W. Dobrucki1, M. Azure3, D. S. Edwards3, A. J. Sinusas1 1Yale University, New Haven, CT, 2Medical University of South Carolina, Charleston, SC, 3Bristol-Myers Squibb Medical Imaging, North Billerica, MA. Background: A cause-effect relationship between myocardial matrix metalloproteinase (MMP) activity and adverse post infarction (MI) left ventricular remodeling has been established. Imaging with a radiolabeled tracer targeted at MMPs could provide a novel approach for serial in vivo evaluation of MMP activation during remodeling.
A QUANTITATIVE COMPARISON OF FOUR INJECTABLE CONTRAST AGENTS FOR VASCULAR IMAGING WITH SMALL ANIMAL X-RAY MICRO-CT IMAGING SYSTEMS M. Thornton1, N. Ford2, B. Durkee1, D. Holdsworth2 1GE medical systems, London, ON, CANADA, 2The Robarts Research Institute, London, ON, CANADA. X-ray computed tomography (CT) is an established diagnostic imaging modality for vascular imaging. The lack of inherent X-ray contrast between blood and the surrounding tissues is overcome by the use of injectable contrast agents. These contrast agents contain a high atomic number material, which increases the attenuation of the vascular space into which they are injected. Several dilutions of two commercially available contrast agents: Omnipaque and Magnivist, and two novel contrast agents: one an iodine based blood pool agent and the other a gadolinium based blood pool agent, were imaged with a dedicated small animal micro-CT scanner. Sample dilutions ranging from 10% to 100% were placed in 1 ml tubes around a water phantom, 25mm in diameter, to simulate the attenuation of a mouse. CT scans were acquired at three X-ray tube voltages, ranging from 50-80 kVp, in order to determine the optimal tube settings for each material. The tube current-exposure time product (mA*s) was adjusted for each scan protocol to normalize the X-ray exposure in each scan. The contrast-to-noise ratio per unit dose was used as the figure of merit to quantify the attenuation effectiveness of each material. The iodinated contrast agents produced higher contrast-to-noise values than the gadolinium agents when normalized for injection volume or mass of active material. The scanning system was limited to a tube voltage of 80kVp (41 keV) and therefore produced a spectrum that was better suited to the k-edge of iodine (33 keV) when compared to gadolinium (50 keV). No. 55 RESPIRATORY GATING PROTOCOLS FOR COMPUTED TOMOGRAPHY AND POSITRON EMISSION TOMOGRAPHY WITH A 16-SLICE LSO PET/CT SCANNER D. W. Townsend1, J. T. Yap1, J. P. Carney1, M. J. Long1, N. C. Hall1, T. Bruckbauer2, C. Howe2, K. Lohman2, B. Smith2, C. Thierfelder3 1University of Tennessee, Knoxville, TN, 2CPS Innovations, Knoxville, TN, 3Siemens Medical Solutions, Forchheim, GERMANY.
In this contribution we present an imaging system comprised of a tripleheaded gamma camera and three multi-pinhole collimators. Each collimators can be equipped with different apertures having one to 10 pinholes. The tomographic field of view can be easily tailored to different imaging tasks (e.g. brain SPECT or whole-body imaging) by switching the multipinhole aperture. Image reconstruction is performed using a dedicated ordered subset expectation maximization (OSEM) algorithm. Our multi-pinhole imager provides a reconstructed resolution of 1.2 to 1.5mm and a mean system sensitivity of up to 1500cps/MBq. We will present the results of numerous phantom and animal studies to display the imaging capabilities of our system. We will also discuss the system performance with respect to resolution, sensitivity, and overall image quality. Furthermore, we will investigate the imaging capabilities of varying pinhole arrangements using the signal-to-noise ratio (SNR) as a figure of merit.
Methods: A 99mTc-labeled MMP targeted compound (RP805, 1.3±0.3mCi) was injected in control mice (n=4) or mice (n=16) one week, two weeks or three weeks following surgical-induced MI, and in vivo pinhole planar imaging was performed 75 minutes later. Thallium-201 (TL, 0.24±0.05mCi) was injected for assessment of myocardial perfusion. 20 minutes later, hearts were excised and sectioned for gamma well counting. Myocardial RP805 and TL activity within MI area was expressed as %nonischemic. RP805 uptake was compared with ex vivo measures of MMP activity, using zymography. Results: Myocardial RP805 activity was seen on in vivo pinhole images in areas of decreased TL perfusion in post-MI mice. A three to four-fold increase in RP805 activity and reduced TL perfusion were seen in infarcted regions of post-MI groups, but not in control group. Conclusion: We demonstrated increased myocardial RP805 activity in an intact murine model of post-MI remodeling. Thus, MMP radiotracer imag-
No. 52 EVALUATING THE CORRELATION BETWEEN TUMOR 2DEOXY-2-[18F]FLUORO-D-GLUCOSE UPTAKE AND BLOOD FLOW IN AN EXPERIMENTAL LIVER TUMOR MODEL USING HYBRID POSITRON EMISSION TOMOGRAPHY /COMPUTED TOMOGRAPHY E. E. Stewart, X. Chen, J. Hadway, T. Y. Lee Robarts Research Institute, London, ON, CANADA.
ing may provide a novel non-invasive approach for evaluation of MMP mediated post-MI remodeling. No. 54
By serial measurements of hepatic blood flow (HBF) and glucose uptake we seek to characterize growing tumors in a rabbit model. Six healthy male New Zealand White rabbits were implanted with 0.25 ml of VX2 carcinoma cells. Computed tomography (CT) liver perfusion studies were performed on all animals prior to and every four days after tumor implantation. Each perfusion study started with a continuous (cine) scan for 30 seconds with breath-hold after a bolus injection of 5 mL non-ionic contrast, followed by bursts of four seconds cine scans without breath-hold every 10 seconds for two minutes. These latter images were registered with the breath-hold images to eliminate breathing motion. The weighted summation of the aortic and portal venous time-density curves was deconvolved against that from the liver parenchyma to derive HBF. Three out of six animals had 2-deoxy-2-[18F]fluoro-D-glucose (FDG) with positron emission tomography (PET) scans performed on 0, 8, 16 and 24 days after tumor implantation. FDG uptake was measured as whole body standardized uptake value (SUV) in g mL-1. In the hypovascular core of animals scanned with FDG-PET: (i) HBF decreased from 257 + 13 at Day 0 to 74 + 15 mL min-1 (100g)-1 at Day 24 (p < 0.05); and, (ii) SUV increased from 2.08 + 0.04 to 5.1 + 0.19 g mL-1 (p < 0.05) during the same period. The disparity between HBF and SUV in tumors suggests tumor hypoxia. This suggests that functional CT in combination with FDG-PET can characterize growing tumors and non-invasively image tumor hypoxia. No. 53 NON-INVASIVE TARGETED IMAGING OF MATRIX METALLOPROTEINASE ACTIVATION IN MURINE MODEL OF POSTINFARCT REMODELING H. Su1, F. G. Spinale2, J. Hua1, C. Chow1, S. Sweterlitsch2, B. N. Bourke1, P. Cavaliere1, X. Hu1, L. W. Dobrucki1, M. Azure3, D. S. Edwards3, A. J. Sinusas1 1Yale University, New Haven, CT, 2Medical University of South Carolina, Charleston, SC, 3Bristol-Myers Squibb Medical Imaging, North Billerica, MA. Background: A cause-effect relationship between myocardial matrix metalloproteinase (MMP) activity and adverse post infarction (MI) left ventricular remodeling has been established. Imaging with a radiolabeled tracer targeted at MMPs could provide a novel approach for serial in vivo evaluation of MMP activation during remodeling.
A QUANTITATIVE COMPARISON OF FOUR INJECTABLE CONTRAST AGENTS FOR VASCULAR IMAGING WITH SMALL ANIMAL X-RAY MICRO-CT IMAGING SYSTEMS M. Thornton1, N. Ford2, B. Durkee1, D. Holdsworth2 1GE medical systems, London, ON, CANADA, 2The Robarts Research Institute, London, ON, CANADA. X-ray computed tomography (CT) is an established diagnostic imaging modality for vascular imaging. The lack of inherent X-ray contrast between blood and the surrounding tissues is overcome by the use of injectable contrast agents. These contrast agents contain a high atomic number material, which increases the attenuation of the vascular space into which they are injected. Several dilutions of two commercially available contrast agents: Omnipaque and Magnivist, and two novel contrast agents: one an iodine based blood pool agent and the other a gadolinium based blood pool agent, were imaged with a dedicated small animal micro-CT scanner. Sample dilutions ranging from 10% to 100% were placed in 1 ml tubes around a water phantom, 25mm in diameter, to simulate the attenuation of a mouse. CT scans were acquired at three X-ray tube voltages, ranging from 50-80 kVp, in order to determine the optimal tube settings for each material. The tube current-exposure time product (mA*s) was adjusted for each scan protocol to normalize the X-ray exposure in each scan. The contrast-to-noise ratio per unit dose was used as the figure of merit to quantify the attenuation effectiveness of each material. The iodinated contrast agents produced higher contrast-to-noise values than the gadolinium agents when normalized for injection volume or mass of active material. The scanning system was limited to a tube voltage of 80kVp (41 keV) and therefore produced a spectrum that was better suited to the k-edge of iodine (33 keV) when compared to gadolinium (50 keV). No. 55 RESPIRATORY GATING PROTOCOLS FOR COMPUTED TOMOGRAPHY AND POSITRON EMISSION TOMOGRAPHY WITH A 16-SLICE LSO PET/CT SCANNER D. W. Townsend1, J. T. Yap1, J. P. Carney1, M. J. Long1, N. C. Hall1, T. Bruckbauer2, C. Howe2, K. Lohman2, B. Smith2, C. Thierfelder3 1University of Tennessee, Knoxville, TN, 2CPS Innovations, Knoxville, TN, 3Siemens Medical Solutions, Forchheim, GERMANY.