M. D. A NDERSON Cancer Center Nuclear Imaging (M.Cam) Richard E. Wendt III, Ph.D. and William D. Erwin, M.S. Small Animal Cancer Imaging Research Facility A Overview of Modality The Siemens Medical Solutions, USA m.CAM ™ gamma camera is designed for imaging pharmaceuticals labeled with gamma emitting radionuclides, in a range of laboratory animals, from mice to small primates or dogs. It is an ideal instrument for biomedical research laboratories to quantitatively measure the biodistribution of radiolabeled diagnostic and therapeutic compounds in vivo, in either 2-D or 3-D (SPECT) mode. Instrument Description The Siemens m.CAM consists of a single High Definition Digital Detector (HD 3 ) mounted onto a portable stand. The HD 3 head may be rotated over 90 degrees, for imaging at any angle between horizontal (face up) to vertical (face out). The HD 3 technology provides improved spatial and energy resolution, uniformity and count rate performance, in an energy independent fashion, compared to conventional detector head designs. This is especially important when imaging small objects such as mice. Performance and Capabilities The maximum imaging field-of-view (FOV) is 53.3 cm (21”) x 38.7 cm (15.25”) with an intrinsic resolution of 3.2 mm. The m.CAM is equipped with a Low Energy High Resolution (LEHR) collimator for imaging radionuclides such as Tc-99m (140 keV), and a Medium Energy Low Penetration (MELP) collimator for radionuclides such as In-111 (172, 247 keV). The system resolution is 4-20 mm (6.3 mm at 10 cm, LEHR with Tc- 99m) depending upon gamma ray energy, subject size and collimator. Achievable image pixel sizes range from mm (32x32 image matrix, zoom factor = 1) down to mm (1024x1024 image matrix, zoom factor = 3.2). Inherent system deadtime is 5.74  sec, resulting in a count rate data loss of 20% at 38,400 counts per second (cps). C B A Gamma Imaging with DigiRad: 111 In-DTPA-PEG-Annexin V Mice with MDA-MB-468 tumors without treatment (A), treated with PG-TXL 4 d earlier (B), or C225 4 d earlier (C). Mice were then injected with 111 In-DTPA- PEG-Annexin V. Images were acquired 48 h after radiotracer injection. Arrow: Tumor. Gamma Imaging with m.CAM: 111 In-DTPA-Annexin V vs. 111 In-DTPA-PEG-Annexin V Mice with MDA-MB-468 tumors without treatment (A), treated with PG-TXL 4 d earlier (B), or PG-TXL + C225 1 d earlier (C). Mice were then injected with 111 In-DTPA-Annexin V (A&B) or with 111 In-DTPA-PEG-Annexin V (C). B A C System sensitivity (Tc-99m, 15% energy window) is 172 cpm/  Ci for the LEHR collimator, and 237 cpm/  Ci for the MELP collimator. Up to six independent energy windows (50 keV – 600 keV) can be selected. The system is capable of acquiring conventional 2-D (planar) static images and dynamic images (for cardiac imaging or perfusion imaging). A Tomographic Accessory for 3-D SPECT imaging of mice and rats is currently under evaluation. Data output formats are Siemens ICON, Interfile 3.3, and DICOM 3.0. Images can be converted to several standard formats as well (TIFF, JPEG, etc.) Data can be provided to investigators via ftp or on Zip (100 Mb), Jaz (1Gbyte), CD-R, and CD-RW physical media. Potential Applications Single animal imaging: mouse through small primate or dog Simultaneous imaging of several animals: Up to 12 mice have been imaged at once, yielding higher throughput, consistent deadtime characteristics across a cohort, and synchronized dynamic data across a cohort Gamma Imaging with m.CAM: Example Image First 2-D image acquired with the m.CAM. Twelve nude mice containing an 111 In radiolabeled compound were imaged simultaneously at 48 hr post-injection. Image acquisition parameters were: 5 min static, 1024x1024 matrix, zoom = 1 (pixel size = 0.6 mm), and three simultaneous energy window settings (top to bottom: 172 keV/15%, 247 keV/15% and combined).