MONICA: a compact, portable dual gamma camera system for mouse whole-body imaging

Abstract

Introduction: We describe a compact, portable dual-gamma camera system (named "MONICA" for MObile Nuclear Imaging CAmeras) for visualizing and analyzing the whole-body biodistribution of putative diagnostic and therapeutic single photon emitting radiotracers in animals the size of mice.

Methods: Two identical, miniature pixelated NaI(Tl) gamma cameras were fabricated and installed "looking up" through the tabletop of a compact portable cart. Mice are placed directly on the tabletop for imaging. Camera imaging performance was evaluated with phantoms and field performance was evaluated in a weeklong In-111 imaging study performed in a mouse tumor xenograft model.

Results: Tc-99m performance measurements, using a photopeak energy window of 140 keV+/-10%, yielded the following results: spatial resolution (FWHM at 1 cm), 2.2 mm; sensitivity, 149 cps (counts per seconds)/MBq (5.5 cps/microCi); energy resolution (FWHM, full width at half maximum), 10.8%; count rate linearity (count rate vs. activity), r(2)=0.99 for 0-185 MBq (0-5 mCi) in the field of view (FOV); spatial uniformity, <3% count rate variation across the FOV. Tumor and whole-body distributions of the In-111 agent were well visualized in all animals in 5-min images acquired throughout the 168-h study period.

Conclusion: Performance measurements indicate that MONICA is well suited to whole-body single photon mouse imaging. The field study suggests that inter-device communications and user-oriented interfaces included in the MONICA design facilitate use of the system in practice. We believe that MONICA may be particularly useful early in the (cancer) drug development cycle where basic whole-body biodistribution data can direct future development of the agent under study and where logistical factors, e.g., limited imaging space, portability and, potentially, cost are important.

Figure 1

MONICA cart. Yellow arrows (left panel) point to the two upward-looking gamma cameras. Router (white box, left panel) enables wireless communication between user Macintosh laptop computer and interior system computers. Tabletop is 62-cm wide × 55-cm deep and 97-cm above the floor.

Figure 2

(A): collimator and matching scintillator array for one of MONICA’s gamma cameras; (B): partially assembled detector module to be mechanically attached to the rear of the collimator such that holes and crystals are exactly aligned; PSPMT = position-sensitive photomultiplier tube.

Figure 3

Interior view of the MONICA cart. Camera 1/Camera 2 arrows point to tungsten boxes surrounding each gamma camera on five sides; HV/LV Supplies: high and low voltage supplies powering PSPMTs and support electronics in each gamma camera; DAQ1/2: data acquisition modules for cameras 1 and 2; DAC: digital-to-analog converter; PC: personal (laptop) computer for camera signal processing; UPS: uninterruptible power supply; Mac Tower: Macintosh tower-type computer (not visible) running NucLear Mac® software for data acquisition and processing.

Figure 4

MONICA system diagram. Components are described in the text.

Figure 5

(A): User interface for Gain Calibration with the onboard Co-57 field flood source. (B): Camera Setup for selection of cameras to be used in the study and their associated energy windows. (C): Progress window for monitoring count rates in each energy window during a study. (D): NucLear Mac® interface for entering data acquisition parameters, for analyzing acquired data and for viewing persistence images of the fields-of-view (FOV) of both cameras during data collection. All of these interfaces are continuously visible to the user on the Macintosh laptop computer.

Figure 6

Anterior projection images of the time variation of tumor (arrows) and body distribution of In-111 Panitumumab in two mice imaged with MONICA. Animals were injected with less than 3.7 MBq (100 μCi) of In-111 at time zero and were imaged in pairs (top and bottom) for 5 minutes at each time point during isoflurane inhalation. Images have been decay corrected to time zero. Mouse 1 had the smallest tumor mass and Mouse 2 the largest tumor mass of all animals studied.