High resolution and sensitivity gamma camera with active septa. A first Monte Carlo study

Abstract

Gamma cameras are of great interest due to their high potential in the field of Nuclear Medicine Imaging. They allow for an early diagnosis of reduced size tumors, and also for a wide variety of preclinical studies with the aim of designing more effective treatments against cancer. In this work we propose a significantly improved multi-pinhole collimator gamma camera and perform a first Monte Carlo analysis of its characteristics. Maintaining the configuration of a multi-pinhole collimator with a high degree of overlapping (thus with a high sensitivity), we add a new element, an active septa, that besides acting as a collimator, is able to measure the impact coordinates of the incident photon. This way one is able to unambiguously identify through which pinhole any gamma ray passes before being detected. The result is a high sensitivity and resolution multi-pinhole gamma camera with an arbitrarily large field of view. As a consequence, the final reconstructed image does not suffer from the undesired artifacts or truncation associated to the multiplexing phenomenon. In this study we focus on the development of a system able to visualize in 3D tumors, nodes and metastasis in real time in the operating room with very low dose. We also briefly analyse and propose a novel design for a Single Photon Emission Computed Tomography system.

Gamma Camera Imaging with Rotating Multi-Pinhole Collimator. A Monte Carlo Feasibility Study

“…The image reconstruction method that we use is the list-mode ordered-subsets expectation maximization (LM-OSEM) algorithm [ 29 , 30 , 31 , 32 , 33 , 34 , 35 ], based on ordered sets of events (and non-indexed lines of response (LORs), as previously described in [ 24 ]). In our case, a LOR corresponds to the straight line passing through the gamma ray impact point (in the detector) and the center of the corresponding pinhole collimator.…”

“…If we divide the whole set of LORs into subsets and call the l th subset, the image estimate (at voxel j, m th iteration and l th subset) is given by where is the set of all LORs, is the LOR corresponding to the k th event, J is the set of voxels traversed by the LOR and is the probability of an emission from voxel j being detected along the LOR i . Again, as mentioned in our previous work [ 24 ], we use an effective Monte Carlo approach to estimate the matrix elements (sensitivity matrix) by simulating a high activity radioactive source that fills the whole FOV. In our case, the FOV is a cm cube with mm voxels.…”

“…The foregoing proposals are highly object-dependent and a generic solution without additional technical challenges [ 24 ], or with a large FOV [ 25 ], has not been found yet. In this paper.…”

“…we propose and analyze a simple, efficient and elegant generic solution to the overlapping/mutiplexing problem inherent to multi-pinhole gamma camera imaging. As in our previous study [ 24 ], we are particularly interested in obtaining a detector with unprecedented sensitivity and a spatial resolution suitable for this particular imaging application (i.e., in vivo surgical interventions), which requires a spatial resolution of the order of 0.5–1.5 cm. The solution consists of using a mobile collimator capable of either linear or rotational motion relative to the gamma-ray detector [ 26 ].…”