Design and performance of a compact and stationary microSPECT system

Purpose: Over the last ten years, there has been an extensive growth in the development of microSPECT imagers. Most of the systems are based on the combination of conventional, relatively large gamma cameras with poor intrinsic spatial resolution and multipinhole collimators working in large magnification mode. Spatial resolutions range from 0.58 to 0.76 mm while peak sensitivities vary from 0.06% to 0.4%. While pushing the limits of performance is of major importance, the authors believe that there is a need for smaller and less complex systems that bring along a reduced cost. While low footprint and low-cost systems can make microSPECT available to more researchers, the ease of operation and calibration and low maintenance cost are additional factors that can facilitate the use of microSPECT in molecular imaging. In this paper, the authors simulate the performance of a microSPECT imager that combines high space-bandwidth detectors and pinholes with truncated projection, resulting in a small and stationary system. Methods: A system optimization algorithm is used to determine the optimal SPECT systems, given our high resolutions detectors and a fixed field-of-view. These optimal system geometries are then used to simulate a Defrise disk phantom and a hot rod phantom. Finally, a MOBY mouse phantom, with realistic concentrations of Tc99m-tetrofosmin is simulated. Results: Results show that the authors can successfully reconstruct a Defrise disk phantom of 24 mm in diameter without any rotating system components or translation of the object. Reconstructed spatial resolution is approximately 800 mu m while the peak sensitivity is 0.23%. Finally, the simulation of the MOBY mouse phantom shows that the authors can accurately reconstruct mouse images. Conclusions: These results show that pinholes with truncated projections can be used in small magnification or minification mode to obtain a compact and stationary microSPECT system. The authors showed that they can reach state-of-the-art system performance and can successfully reconstruct images with realistic noise levels in a preclinical context. Such a system can be useful for dynamic SPECT imaging. 2013 American Association of Physicists in Medicine

The clinical utilities of multi-pinhole single photon emission computed tomography

Single photon emission computed tomography (SPECT) is an important imaging modality for various applications in nuclear medicine. The use of multi-pinhole (MPH) collimators can provide superior resolution-sensitivity trade-off when imaging small field-of-view compared to conventional parallel-hole and fan-beam collimators. Besides the very successful application in small animal imaging, there has been a resurgence of the use of MPH collimators for clinical cardiac and brain studies, as well as other small field-of-view applications. This article reviews the basic principles of MPH collimators and introduces currently available and proposed clinical MPH SPECT systems

A versatile imaging system for in vivo small animal research

In vivo small animal imaging has become an essential technique for molecular biology studies. However, requirements of spatial resolution, sensitivity and image quality are quite challenging for the development of small-animal imaging systems. The capabilities of the system are also significant for carrying out small animal imaging in a wide range of biological studies. The goal of this dissertation is to develop a high-performance imaging system that can readily meet a wide range of requirements for a variety of small animal imaging applications. Several achievements have been made in order to fulfill this goal.;To supplement our system for parallel-hole single photon emission computed tomography (SPECT) based upon a 110 mm diameter circular detector, we have developed novel compact gamma cameras suitable for imaging an entire mouse. These gamma cameras facilitate multi-head (\u3e2) parallel-hole SPECT with the mouse in close proximity to the detector face in order to preserve spatial resolution. Each compact gamma cameras incorporates pixellated Nal(Tl) scintillators and a pair of Hamamatsu H8500 position sensitive photomultiplier tubes (PSPMTs). Two types of copper-beryllium parallel-hole collimators have been designed. These provide high-sensitivity imaging of I-125 or excellent spatial resolution over a range of object-detector distances. Both phantom and animal studies have demonstrated that these gamma cameras perform well for planar scintigraphy and parallel-hole SPECT of mice.;To further address the resolution limitations in parallel-hole SPECT and the sensitivity and limited field of view of single-pinhole SPECT, we have developed novel multipinhole helical SPECT based upon a 110 mm diameter circular detector equipped with a pixellated Nal(Tl) scintillator array. A brass collimator has been designed and produced containing five 1 mm diameter pinholes. Results obtained in SPECT studies of various phantoms show an enlarged field of view, very good resolution and improved sensitivity using this new imaging technique.;These studies in small-animal imaging have been applied to in vivo biological studies related to human health issues including studies of the thyroid and breast cancer. A re-evaluation study of potassium iodide blocking efficiency in radioiodine uptake in mice suggests that the FDA-recommended human dose of stable potassium iodide may not be sufficient to effectively protect the thyroid from radioiodine contamination. Another recent study has demonstrated that multipinhole helical SPECT can resolve the fine structure of the mouse thyroid using a relatively low dose (200 muCi). Another preclinical study has focused on breast tumor imaging using a compact gamma camera and an endogenous reporter gene. In that ongoing study, mammary tumors are imaged at different stages. Preliminary results indicate different functional patterns in the uptake of radiotracers and their potential relationship with other tumor parameters such as tumor size.;In summary, we have developed a versatile imaging system suitable for in vivo small animal research as evidenced by a variety of applications. The modular construction of this system will allow expansion and further development as new needs and new opportunities arise

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

Design of a low-dose, stationary, tomographic Molecular Breast Imaging system using 3D position sensitive CZT detectors

Molecular Breast Imaging (MBI) has been shown to have high sensitivity for lesion detection, particularly in patients with dense breasts where conventional mammography is limited. However, relatively high radiation dose and long imaging time are limiting factors. Most current MBI systems are based on planar imaging. Improved performance can be achieved using tomographic techniques, which normally involve detector motion. Our goal is to develop a low-dose stationary tomographic MBI system with similar or better performance in terms of lesion detection compared to planar MBI. The proposed system utilizes two opposing CZT detectors with high intrinsic resolution and depth of interaction (DOI) capability, combined with densely packed multi-pinhole collimators. This leads to improved efficiency and adequate angular sampling, but also to significant multiplexing (MX), which can result in artefacts. We have developed de-MX algorithms that take advantage of the DOI information. We have performed both analytic and Monte Carlo simulations to demonstrate the feasibility, optimize the design and investigate the expected performance of the proposed system. Lesion detectability was preserved with reduction of acquisition time (or radiation dose) by a factor of 2 compared to planar images at the lowest reported dose. The first prototype is under evaluation at Kromek

Design of a static full-ring multi-pinhole collimator for brain SPECT

In clinical practice, brain SPECT is mostly performed using a dual-head SPECT scanner with fan-beam or parallel-beam collimators rotating around the patient's head. The resolution of such a system is typically about 6-8 mm, which is rather poor to image the complex structures of the human brain. We developed a non-rotating multi-pinhole collimator for brain SPECT imaging with a resolution of 4 mm. A full-ring geometry allows for complete transaxial sampling. This enables the use of a stationary collimator. The collimator is a tungsten ring with two rows of pinholes. Each pinhole can individually be opened or closed with shutters. A sequence of shutter movements is performed to obtain an acquisition setup that simulates a rotational movement. The collimator is designed for the LaPET system (a PET detector ring made of 24 LaBr 3 detectors) and is optimized to maximize the system performance, resulting in a collimator radius of 145 mm and a pinhole diameter of 2 mm. This system has a sensitivity that is 4 times lower than a dual-head system with LEHR parallel-beam collimators. However, the resolution is 2 times better, a trade-off that is supported by Muehllehner [1]. Monte-Carlo simulated projections of a resolution phantom are successfully reconstructed and the resulting image shows that a resolution of 4 mm is indeed achieved

Investigation of Axial and Angular Sampling in Multi-Detector Pinhole-SPECT Brain Imaging

We designed a dedicated multi-detector multi-pinhole brain SPECT scanner to generate images of higher quality compared to general-purpose systems. The system, AdaptiSPECT-C, is intended to adapt its sensitivity-resolution trade-off by varying its aperture configurations allowing both high-sensitivity dynamic and high-spatial-resolution static imaging. The current system design consists of 23 detector heads arranged in a truncated spherical geometry. In this work, we investigated the axial and angular sampling capability of the current stationary system design. Two data acquisition schemes using limited rotation of the gantry and two others using axial translation of the imaging bed were also evaluated concerning their impact on image quality through improved sampling. Increasing both angular and axial sampling in the current prototype system resulted in quantitative improvements in image quality metrics and qualitative appearance of the images as determined in studies with specifically selected phantoms. Visual improvements for the brain phantoms with clinical distributions were less pronounced but presented quantitative improvements in the fidelity (normalized root-mean-square error (NRMSE)) and striatal specific binding ratio (SBR) for a dopamine transporter (DAT) distribution, and in NRMSE and activity recovery for a brain perfusion distribution. More pronounced improvements with increased sampling were seen in contrast recovery coefficient, bias, and coefficient of variation for a lesion in the brain perfusion distribution. The negligible impact of the most cranial ring of detectors on axial sampling, but its significant impact on sensitivity and angular sampling in the cranial portion of the imaging volume-of-interest were also determined