Count-Rate Performance of the Discovery STE PET Scanner Using Partial Collimation

Abstract

We investigated the use of partial collimation on a clinical PET scanner by removing septa from conventional 2D collimators. The goal is to improve noise equivalent count-rates (NEC) compared to 2D and 3D scans for clinically relevant activity concentrations. We evaluated two cases: removing half of the septa (2.5D); and removing two-thirds of the septa (2.7D). System performance was first modeled using the SimSET simulation package, and then measured with the NEMA NU2-2001 count-rate cylinder (20 cm dia., 70 cm long), and 27 cm and 35 cm diameter cylinders of the same length. An image quality phantom was also imaged with the 2.7D collimator. SimSET predicted the relative NEC curves very well, as confirmed by measurements, with 2.5D and 2.7D NEC greater than 2D and 3D NEC in the range of ~5-20 mCi in the phantom. We successfully reconstructed images of the image quality phantom from measured 2.7D data using custom 2.7D normalization. Partial collimation shows promise for optimized clinical imaging in a fixed-collimator system.

Estimating live-time for new PET scanner configurations

“…The encouraging results from that work motivated building and testing a 2.7D collimator for the DSTE [6]. From the measured 2.7D data we determined the corresponding system livetime and compared it to what our model predicted.…”

“…The intent of the model is to predict live-time fractions for new, untested scanner configurations when clinically relevant activity concentrations are on the patient bed. In a separate report [6] we used the model to investigate the count-rate capabilities of a Discovery STE PET scanner equipped with partial collimation. In this work we presented the derivation of the live-time model.…”

“…In this paper we focus on the case of septa between every third detector ring (2.7D mode) because we have measured data in 2.7D mode that can be used to verify our predictive live-time model. The results of applying the live-time model to partial collimation has been reported elsewhere [6].…”

“…We have used computer models to investigate performance parameters of new PET scanner configurations, namely intermediate degrees of collimation between 2D and 3D acquisition modes [6]. To estimate count-rate dependent parameters, such as the noise equivalent counts (NEC), it is necessary to know how the singles and coincidence count rates are affected by scanner live-time.…”

Image Reconstruction for a Partially Collimated Whole Body PET Scanner

“…MacDonald et al in a follow-up study presented measured results that show roughly 30% NEC gains over 2-D and 3-D in an actual system with two out of every three septa removed [ 7 ]. Likewise, Qi et al simulated multiple sparse collimation schemes for a prostate scanner and showed NEC and signal-to-noise improvements [ 12 ] over 2-D and 3-D mode for several schemes.…”