Resolution Properties of a Prototype Continuous Miniature Crystal Element (cMiCE) Scanner

2013

IEEE Trans. Nucl. Sci.

We used simulations to investigate the relationship between sensitivity and spatial resolution as a function of crystal thickness in a rectangular PET scanner intended for quantitative assessment of breast cancers. The system had two 20 × 15-cm2 and two 10 × 15-cm2 flat detectors forming a box, with the larger detectors separated by 4 or 8 cm. Depth-of-interaction (DOI) resolution was modeled as a function of crystal thickness based on prior measurements. Spatial resolution was evaluated independent of image reconstruction by deriving and validating a surrogate metric from list-mode data (dFWHM). When increasing crystal thickness from 5 to 40 mm, and without using DOI information, the dFWHM for a centered point source increased from 0.72 to 1.6 mm. Including DOI information improved dFWHM by 12% and 27% for 5- and 40-mm-thick crystals, respectively. For a point source in the corner of the FOV, use of DOI information improved dFWHM by 20% (5-mm crystal) and 44% (40-mm crystal). Sensitivity was 7.7% for 10-mm-thick crystals (8-cm object). Increasing crystal thickness on the smaller side detectors from 10 to 20 mm (keeping 10-mm crystals on the larger detectors) boosted sensitivity by 24% (relative) and degraded dFWHM by only ~3%/8% with/without DOI information. The benefits of measuring DOI must be evaluated in terms of the intended clinical task of assessing tracer uptake in small lesions. Increasing crystal thickness on the smaller side detectors provides substantial sensitivity increase with minimal accompanying loss in resolution.

Section: Discussionmentioning

confidence: 84%

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Effects of Detector Thickness on Geometric Sensitivity and Event Positioning Errors in the Rectangular PET/X Scanner

MacDonald

Kinahan

2013

IEEE Trans. Nucl. Sci.

“…Our group has previously reported on high resolution, monolithic crystal small animal PET detector designs, which have a number of advantages over discrete crystal detector designs [1,2]. Relatively large crystals are preferred for a monolithic crystal detector because of the challenges of positioning events near the edges of a crystal.…”

Section: Introductionmentioning

confidence: 99%

Design of a trapezoidal slat crystal (TSC) PET detector for small animal PET/MR imaging

Lewellen

IEEE Nuclear Science Symposuim &Amp; Medical Imaging Conference

2010

The aim of this work is to develop a high spatial resolution, high sensitivity, compact PET detector for small animal PET/MR imaging. The key design features are the use of trapezoidal slat crystals (TSC), the use of silicon photomultiplier (SiPM) arrays, and the use of a 3D statistics based positioning (SBP) algorithm. Through simulation, the performance of a detector module consisting of 8 trapezoidal 0.92 mm (0.63 mm) by 47.52 mm by 12 mm crystals readout by a 2x12 SiPM array was evaluated. A PET detector ring with a 57 mm inner ring diameter could be built using 32 of these detector modules. The average intrinsic spatial resolution in Y and X were 0.84 mm and 0.72 mm FHWM, respectively. There was a 28% miscoding error in X, mainly from Compton scatter in the crystal array. The Z or depth of interaction (DOI) resolution is 1.74 mm. The intrinsic spatial resolution is reasonably uniform across the whole detector module.

“…[1,2] A key component of the design is the use of a 3D statistics based positioning (SBP) algorithm for event positioning. [3,4] The Cramer-Rao lower bound (CRLB) expresses a lower bound on the variance of estimators for a deterministic parameter.…”

Section: Introductionmentioning

confidence: 99%

Spatial resolution performance evaluation of a monolithic crystal PET detector with Cramer-Rao lower bound (CRLB)

Lewellen

IEEE Nuclear Science Symposuim &Amp; Medical Imaging Conference

2010

We have previously reported on continuous miniature crystal element (cMiCE) PET detectors that provide depth of interaction (DOI) positioning capability.A key component of the design is the use of a statistics based positioning (SBP) method for 3D event positioning. The Cramer-Rao lower bound (CRLB) expresses a lower bound on the variance of estimators for a deterministic parameter. Therefore, the CRLB could be used to evaluate whether our SBP algorithm is efficient and to quickly determine the best possible spatial resolution when investigating new detector designs.In this work, the CRLB is first reported based upon experimental results from a PET detector using a 50 mm by 50 mm by 15 mm LYSO crystal readout by a 64-channel PMT on the exit surface of the crystal. The X/Y spatial resolution is very close to the CRLB, while the depth of interaction (DOI) resolution is more than double the CRLB even after correcting for beam size and finite X resolution of the detector.A simulation study was conducted to investigate what causes the difference between measured DOI resolution and the CRLB for DOI. The PET detector was modeled as a 50 mm by 50 mm by 15 mm LYSO crystal readout by a 64-channel SiPM array placed on the entrance surface of the crystal. The results show that Compton scatter in the crystal degrades the DOI resolution. A second interesting result was that the DOI CRLB could not be achieved even when tested using only photoelectric events. This is because of the limitations of the DOI decoding algorithm.