Abstract
Over the last two decades there have been a growing number of designs for positron emission tomography (PET) cameras optimized to image the breast. These devices, commonly known as positron emission mammography (PEM) cameras allow much more spatial resolution by putting the photon detectors directly on the breast. PEM cameras have a compact geometry with a restricted field of view (FOV)thus exhibiting higher performance and lower cost than large whole body PET scanners. Typical PEM designs are based on scintillators such as bismuth germanate (BGO), lutetium oxorthosilicate (LSO) orlutetium yttrium orthosicilate (LYSO), and characterized by large parallax error due to deficiency of thedepth of interaction (DOI) information from crystals. In the case of parallel geometry PEM,large parallax error results in poor image resolution along the vertical axis.In the framework of the Voxel Imaging PET (VIP) pathfinder project,we propose a high resolution PEM scanner based on pixelated solid-state CdTe detectors. The pixel PEM device with a millimeter-size pixel pitch provides an excellent spatial resolution inall directions 8 times better than standard commercial devices with a point spread function (PSF) of 1 mm full width at halfmaximum (FWHM) and excellent energy resolution of down to 1.6% FWHM at 511 keV photons at room temperature. The system is capable to detect down to 1 mm diameter hot spheres in warm background.
Highlights
Breast cancer is the most common cause of cancer death among women [1]
Designs based on scintillator crystals have many intrinsic limitations including a relatively poor energy resolution (5–10% for commonly used crystals [6]), the incompatibility with strong magnetic fields when coupled with photo-multipliers (PMT), and relatively large parallax error due to the uncertainty of the depth of interaction information (DOI) (> 5 mm full width at half maximum (FWHM)) [7]
In the framework of the Voxel Imaging PET (VIP) pathfinder project [8], we propose a high resolution positron emission mammography (PEM) design [9] based on finely segmented room temperature CdTe detectors to overcome the intrinsic limitations of state-of-the-art commercial PEMs based on scintillating crystals
Summary
Breast cancer is the most common cause of cancer death among women [1]. PEM is an organ dedicated PET scanner for breast screening [2]. Designs based on scintillator crystals have many intrinsic limitations including a relatively poor energy resolution (5–10% for commonly used crystals [6]), the incompatibility with strong magnetic fields when coupled with photo-multipliers (PMT), and relatively large parallax error due to the uncertainty of the depth of interaction information (DOI) (> 5 mm FWHM) [7]. All these intrinsic limitations affect the detector sensitivity, and the image quality, and limit the minimum detectable tumor size and the correct assessment of the malignancy of small lesions [7]. The high resolution VIP-PEM design is simulated and evaluated in terms of detector performance, and imaging performance according to the NEMA NU-4 2008 protocol [10] and by using the LM-OSEM algorithm [11] for image reconstruction
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