Positron emission tomography (PET) is a sensitive research tool that utilizes radiolabeled tracers for viewing molecular targets and biochemical pathways in vivo. The ability to image tissue perfusion, glucose metabolism, drug/receptor interactions, and gene expression have made it a particularly effective tool in oncology, cardiology and neuroscience research. The functional imaging achieved with PET can be combined with anatomical information obtained from the same animal using microCT or MRI to refine the identification of sites of PET radiotracer uptake.

The nuclear imaging suite is equipped with 2 microPET scanners, an F120 (Siemens) and an Inveon DPET (Siemens), as well as an Inveon CT/SPECT scanner (Siemens).  Three separate injection stations for each scanner are designed for simultaneous induction and/or maintenance anesthesia (isoflurane).  Other support equipment include a dose calibrator (CRC 15R; Capintec), a commercial mouse tail illuminator/injection platform (Braintree Scientific), a warming light and both electric and circulating water heating pads.  A second-generation prototype microPET scanner, MicroPET II (described below), designed and constructed in Dr. Cherry’s laboratory, is also available for PET imaging studies.  A fourth microPET scanner (P4; formerly Concorde Microsystems) is located at a satellite facility and is used exclusively for non-human primate studies (described below).

DPET

Inveon DPET This third generation small animal scanner uses LSO crystal elements for detection of gamma radiation produced from radioactive decay by positron emission.  It features both high sensitivity (~ 10%) and high spatial resolution (1.4 mm FWHM with filtered back projection reconstruction).  In addition, it is particularly well suited to whole body imaging of mice and rats:  the bore is 12 cm, with an active transaxial FOV of 10 cm and an axial FOV of 12.7 cm.  Continuous bed motion can extend the axial FOV to 30 cm, providing a larger whole body single frame FOV for rats.  Transmission scans with 57Co can be performed to apply attenuation correction during image reconstruction.  The animal bed can be rapidly interchanged with the adjacent Inveon CT/SPECT bed to acquire CT scans of the same animal, thereby allowing reconstruction of a multimodality image that melds the functional information attained by PET within the anatomical framework rendered by CT.

Focus120

Focus 120 (F120) The F120 is a third generation small animal PET scanner produced by Siemens Medical Solutions, Inc (formerly CTI Concorde Microsystems). Compared to the previous generation R4 model, which has the same ring diameter and axial length, the sensitivity and volumetric resolution are improved by more than 50% and 250%, respectively (5). The longer axial length of the F120 compared to microPET II makes it more suitable for whole body mouse imaging, which requires 2 bed positions with microPET II. The animal bed from the F120 can be easily removed and attached to our Inveon scanner to acquire CT anatomical images for coregistration with a PET image. Fiducial markers visible on both PET and CT are placed on or near the animal for precise co-registration of the images.

MicroPET II

MicroPET II This custom-built PET scanner is a second-generation tomograph developed and fabricated in the laboratory of Simon Cherry (1,2). It succeeds the original microPET scanner that was designed and constructed at UCLA in the late 1990’s by a group of collaborators headed by Dr. Cherry (3). That prototype was the design concept for the first commercial small animal PET scanners produced in 2000 by Concorde Microsystems, Inc. (acquired by Siemens, 2005). MicroPET II has approximately 4-fold greater resolution and sensitivity than the prototype scanner.

MicroPET P4

MicroPET P4 The P4 PET scanner has slightly lower spatial resolution than the other three microPET scanners, but has a larger bore to accommodate larger animals (6). It has been in routine use at UC Davis since 2002 and has been used for studies in mice, rats and non-human primates. It is located in a satellite facility at the California National Primate Research Center (CNPRC) and is maintained and operated by our staff. The animals imaged at this facility are handled and cared for by the CNPRC veterinary staff during PET imaging.

microPET Specifications Comparison

microPET	DPET	P4	F120	MP2
Animal Port Diameter	12 cm	22 cm	12 cm	15 cm
Axial Field of View	12.7 cm	8 cm	7.6 cm	4.9 cm
Timing Window	2.808, 3.432, 4.056, or 4.680 nsec	2, 6, 10, 14, or 18 nsec	2, 6, 10, or 14 nsec	2, 6, 10, or 14 nsec
Energy Window	Variable: 0 – 814 keV	Variable: 0 – 810 keV	Variable: 0 – 814 keV	Variable: 0 – 814 keV
Absolute System Sensitivity	~10%	2.25%	7%	2.26%
Reconstructed Spatial Resolution	~ 1.5 mm	~ 2.0 mm	~ 1.5 mm	~ 1 mm
Reconstructed Volumetric Resolution	~ 5 µL (FBP)	~ 6.4 µL	~ 2 µL	~ 1.4 µL

MODALITY	MODEL	MANUFACTURER	RESOLUTION
PET	Inveon DPET	Siemens	~ 1.5 mm
PET	Focus 120	Siemens	~ 1.5 mm
PET	Primate 4	Siemens	~ 2.0 mm
PET	microPET II	Custom-built	~ 1 mm
SPECT	Inveon	Siemens	~ 0.5 – 3 mm
CT	Inveon	Siemens	~ 50 – 150 µm
MRI	Biospec 7T	Bruker	~ 100 – 250 µm
Ultrasound	Sequoia	Siemens	~ 100 – 500 µm
Optical	Maestro 2	CRi (Caliper)	~ 1 – 5 mm
Optical	IVIS 100	Xenogen (Caliper)	~ 1 – 5 mm
Autoradiography	Storm 860	Amersham Biosciences	~ 50 – 100 µm

References

1. Tai YC, Chatziioannou A, Yang YF, Silverman RW, Meadors K, Siegel S, Newport D, Stickel JR, Cherry SR. MicroPET II: design, development, and initial performance of an improved microPET scanner for small-animal imaging. Phys Med Biol; 48:1515-37, 2003.

2. Yang Y, Tai Y-C, Siegel S, Newport DF, Bai B, Li Q, Leahy RM, Cherry SR. Optimization and performance evaluation of the microPET II scanner for in vivo small-animal imaging. Phys Med Biol; 49:2527-45, 2004.

3. Cherry SR, Shao Y, Siegel S et al. MicroPET: a high resolution PET scanner for imaging small animals. IEEE Trans Nucl Sci ; 44:1161-6, 1997.

4. Liang H, Yang Y, Yang K, Wu Y, Boone JM, Cherry SR. A microPET/CT system for in vivo small animal imaging. Phys Med Biol; 52:3881-94, 2007.

5. Kim JS, Lee JS, Im KC, Kim SJ, Kim S-Y, Lee DS, Moon DH. Performance measurement of the microPET Focus 120 scanner. J Nucl Med; 48:1527-35, 2007.

6. Tai YC, Chatziioannou A, Siegel S, Young J, Newport, D, Goble RN, Nutt RE, Cherry SR. Performance evaluation of the microPET P4: a PET system dedicated to animal imaging. Phys Med Biol; 46:1845-62, 2001.

For additional Information:

* Phelps ME. Positron emission tomography provides molecular imaging of biological processes. Proc Natl Acad Sci; 97:9226-33, 2000.

* Cherry SR. In vivo molecular and genomic imaging: new challenges for imaging physics. Phys Med Biol; 49:R13-48, 2004.

* Cherry SR. The 2006 Henry N. Wagner Lecture: Of mice and men (and positrons) – advances in PET imaging technology. J Nucl Med; 47:1735-45, 2006.

* Cherry SR. Multimodality in vivo imaging systems: twice the power or double the trouble? Annu Rev Biomed Eng; 8:35-62, 2006.