Accurate molecular imaging of small animals taking into account animal models, handling, anaesthesia, quality control and imaging system performance

Small-animal imaging has become an important technique for the development of new radiotracers, drugs and therapies. Many laboratories have now a combination of different small-animal imaging systems, which are being used by biologists, pharmacists, medical doctors and physicists. The aim of this paper is to give an overview of the important factors in the design of a small animal, nuclear medicine and imaging experiment. Different experts summarize one specific aspect important for a good design of a small-animal experiment

Co-planar PET/CT for small animal imaging

Proceeding of: 2005 IEEE Nuclear Science Symposium Conference Record, Puerto Rico, October 23 - 29, 2005A small animal PET/CT system based on a common rotating gantry is proposed. The PET detection subsystem is composed of two detector modules based on MLS arrays and four flat panel type PS PMT. The CT subsystem consists in a micro focus X ray tube and a semiconductor X ray detector. Space for opposed PET detectors and the CT scanner have been allocated on the same plane in such a way that the trans axial and axial centers are common for both systems. Shielding elements have been placed around the detectors to avoid cross modality contamination. The gantry can rotate 370 degrees to provide complete data sets for the CT image reconstruction algorithm that is based on the cone beam geometry. PET image reconstruction is implemented using FBP (2D and 3D) and OSEM. Sequential acquisition protocols minimize the scan duration, and CT information can be used to implement PET imaging corrections. The coplanar configuration of this system provides intrinsically co registered data sets, and it is not necessary to reposition the animal to perform any modality imaging, avoiding undesired animal or additional accessories movements. An additional advantage is the compactness of the system that saves space and allows a direct visual monitoring of the animal during the scanPart of this work is founded by the IM3 network (G03/185 Ministerio de Sanidad), with grants from the Ministerio de Educación y Ciencia, project TEC2004-07052-C02-01, and Ministerio de Industria, Turismo y Comercio project FIT-330101-2004-3. J.J. Vaquero has support from the “Ramón y Cajal” Program, Ministerio de Educación y Cienci

Curved array photoacoustic tomographic system for small animal imaging

We present systematic characterization of a photoacoustic imaging system optimized for rapid, high-resolution tomographic imaging of small animals. The system is based on a 128-element ultrasonic transducer array with a 5-MHz center frequency and 80% bandwidth shaped to a quarter circle of 25mm radius. A 16-channel data-acquisition module and dedicated channel detection electronics enable capture of a 90-deg field-of-view image in less than 1s and a complete 360-deg scan using sample rotation within 15s. Measurements on cylindrical phantom targets demonstrate a resolution of better than 200μm and high-sensitivity detection of 580-μm blood tubing to depths greater than 3cm in a turbid medium with reduced scattering coefficient μ′s =7.8cm^(−1). The system is used to systematically investigate the effects of target size, orientation, and geometry on tomographic imaging. As a demonstration of these effects and the system imaging capabilities, we present tomographic photoacoustic images of the brain vasculature of an ex vivo mouse with varying measurement aperture. For the first time, according to our knowledge, resolution of sub-200-μm vessels with an overlying turbid medium of greater than 2cm depth is demonstrated using only intrinsic biological contrast

A fast 512-element ring array photoacoustic imaging system for small animals

A 512-element photoacoustic tomography system for small animal imaging using a ring ultrasound array has been developed. The system features a 5 MHz piezocomposite transducer array formed into a complete circular aperture. Custom receiver electronics consisting of dedicated preamplifiers, 8:1 multiplexed post-amplifiers, and a 64-channel data acquisition module provide full tomographic imaging at up to 8 frames/second. We present details of the system design along with characterization results of the resolution, imaging volume, and sensitivity. Small animal imaging performance is demonstrated through images of mice brain vasculature at different depths and real-time spectroscopic scans. This system enables real-time tomographic imaging for functional photoacoustic studies for the first time

Initial results from a PET/planar small animal imaging system

A pair of stationary, opposed scintillation detectors in time coincidence is being used to create planar projection or tomographic images of small animals injected with positronemitting radiotracers. The detectors are comprised of arrays of individual crystals of bismuth germanate coupled to position-sensitive photomultiplier tubes. The system uses FERA (LeCroy Research Systems) charge-sensitive ADCs and a low cost digital YO board as a E R A bus-to-host bridge. In projection mode, the animal is placed within the 55 mm x 45 mm useful field-of-view of the detectors and images are formed from coincidence lines that fall close to the normals of both detectors. In tomographic mode, the animal is placed on a rotation stage between the detectors and rotated around a vertical axis to acquire all possible lines-of-response. Tomographic images are then reconstructed from those lines falling within a user-specified angle of each detector normal. In mice, the system is capable of high-speed, whole-body dynamic projection imaging, and whole body tomographic imaging of slowly varying tracer distributions. An ECG gating capability is also available for evaluating cardiac function. This system is currently being used to study tracer transport in normal and genetically engineered mice.Publicad

GePEToS : A Geant4 Monte Carlo simulation package for Positron Emission Tomography

GePEToS is a simulation framework developed over the last few years for assessing the instrumental performance of future PET scanners. It is based on Geant4, written in Object-Oriented C++ and runs on Linux platforms. The validity of GePEToS has been tested on the well-known Siemens ECAT EXACT HR+ camera. The results of two application examples are presented : the design optimization of a liquid Xe micro-PET camera dedicated to small animal imaging as well as the evaluation of the effect of a strong axial magnetic field on the image resolution of a Concorde P4 micro-PET camera.Comment: 5 pages, 12 figures, submitted to IEEE Transactions on Nuclear Scienc

Small animal imaging using a curved array photoacoustic tomography system

We report experimental imaging results with mice using an array-based photoacoustic tomography system designed for small animal imaging. The system features a 128-element curved transducer array with stage rotation to enable complete two-dimensional tomographic imaging in less than 15 seconds. High fidelity imaging of ex vivo mouse brain vasculature was achieved with resolution of vessels less than 200 microns in diameter in the cortex as well as the cerebellum. Images obtained using varying measurement surface angular spans clearly illustrate the impact on feature definition with orientation. The high sensitivity of the system was demonstrated by images of the brain vasculature with an overlying turbid medium (μ_a = 0.03 cm^(-1) and μ_s' ~ 7 cm^(-1) at 780 nm) of over 2 cm depth. In phantom experiments, high-quality images of blood tubing in a turbid medium were achieved at depths greater than 3 cm for incident fluences of less than 15 mJ/cm^2. These results illustrate the suitability for near real-time small animal imaging of deep tissue with high definition

A liquid Xenon Positron Emission Tomograph for small animal imaging : first experimental results of a prototype cell

A detector using liquid Xenon (LXe) in the scintillation mode is studied for Positron Emission Tomography (PET) of small animals. Its specific design aims at taking full advantage of the Liquid Xenon scintillation properties. This paper reports on energy, time and spatial resolution capabilities of the first LXe prototype module equipped with a Position Sensitive Photo- Multiplier tube (PSPMT) operating in the VUV range (178 nm) and at 165 K. The experimental results show that such a LXe PET configuration might be a promising solution insensitive to any parallax effect.Comment: 34 pages, 18 pages, to appear in NIM

A curved array photoacoustic tomography system for small animal imaging

We have developed and tested a photoacoustic imaging system based on a 128 element curved-phased ultrasonic array, which spans a quarter of a complete circle with a radius of curvature equal to 25mm. The center frequency of the array is 5 MHz with 60% bandwidth. The physical dimensions of the elements are 10x0.3mm (elevation x azimuth) with an elevation focus of 19mm. Earlier we reported acoustic measurements of the axial and lateral resolutions of the system that were limited by the impulse response of the narrowband source used in the test. In this paper we discuss photoacoustic characterization of the system including resolution and sensitivity. The array forms the building block for a 512-element ring designed for complete tomographic imaging of small animals. Imaging results of phantoms will be compared with simulations