The design and physical characteristics of a small animal positron emission tomograph

Abstract

A small diameter positron emission tomography, designed specifically for small animal studies, was constructed from existing, commercially available, bismuth germanate (BGO) detectors and electronics. The scanner consists of 16 BGO detector blocks arranged to give a tomograph with a diameter of 115 mm and an axial field of view (FOV) of 50 mm. Each block is cut to produce eight (axial) by seven (radial) individual detector elements. The absence of interplane septa enables the acquisition of 3D data sets consisting of 64 sinograms. A 2D data set of 15 sinograms, consisting of eight direct and seven adjacent cross planes, can be extracted from the 3D data set. Images are reconstructed from the 2D sinograms using a conventional filtered backprojection algorithm. Two methods of normalization were investigated, based on either a rotating 68Ge rod source, or a uniform 68Ge plane source, with a uniform cylindrical 18F phantom. Attenuation of the emitted photons was estimated using a rotating 68Ge rod source. The transaxial resolution of the tomograph was measured as 2.3 mm full width at half maximum (FWHM) and 5.6 mm full width at tenth maximum (FWTM) at the centre of the FOV, degrading to 6.6 mm (radial) and 4.4 mm (tangential) FWHM and 10.4 mm (radial) and 14.4 mm (tangential) FWTM at 40.0 mm from the centre of the FOV. The axial slice width was 4.3 mm FWHM, 10.3 mm FWTM at the centre of the transaxial field of view and 4.4 mm FWHM, 10.6 mm FWTM at 20.0 mm from the centre of the FOV. A scatter fraction of 31.0% was measured at 250-850 keV, for an 18F line source centred in a 60 mm diameter, water-filled phantom, reducing to 20.4% and 13.8% as the lower energy discrimination was increased to 380 keV and 450 keV, respectively. The count rate performance was measured using a noise equivalent count rate method, and the linearity of the dead time correction was confirmed over the count rates encountered during routine scanning. In 2D mode, the absolute sensitivity of the tomograph was measured as 9948 counts s-1 MBq-1 at 250-850 keV, 8284 counts s-1 MBq-1 at 380-850 keV and 6280 counts s-1 MBq-1 at 450-850 keV.

Preclinical positron emission tomography scanner based on a monolithic annulus of scintillator: initial design study

“…Application of this paradigm has been reduced over the last two decades with the introduction of high-resolution scanners designed for imaging of small animals. [1][2][3][4][5][6][7][8] It is now possible to perform longitudinal studies on relatively small cohorts of animals. The application of radiopharmaceutical-based molecular imaging techniques is of particular interest to investigators due to the ability to track and quantify physiologic processes.…”

Performance Evaluation of the FLEX Triumph X-PET Scanner Using the National Electrical Manufacturers Association NU-4 Standards

“…Molecular imaging using dedicated small-animal PET scanners is now well established in the field of drug development and experimental studies using animal models of various diseases (2). After the development of the first dedicated rodent PET scanner at Hammersmith Hospital in collaboration with CTI PET Systems, Inc., various design concepts of preclinical PET scanners are continually being investigated, developed, and, in some cases, made commercially available through spin-off companies from university research (3)(4)(5)(6)(7). With the commercial introduction and widespread availability of preclinical PET systems, small-animal imaging is becoming readily accessible and increasingly popular (8).…”

Resolution properties of a prototype continuous miniature crystal element (cMiCE) scanner

“…The likelihood function for making any single observation m i from distribution M i given x is: (1) Mathematically the maximum likelihood estimator of the event position x is given by: (2) The SBP method requires that statistics (e.g., mean and variance) of the detector response be characterized as a function of interaction location. The detector response at a given location is measured using a coincidence timing collimated point source with a spot size of ~0.6 mm full width at half maximum (FWHM).…”