Adjusting the Low Energy Threshold for Large Bodies in PET

The performance of a PET scanner on three different phantom sizes was studied as a function of low energy threshold (LET). Phantom cross sections ranged from 20 cm diameter circular to 28 cm x 43 cm oval and LET\u27\u27s ranged from 350 keV to 475 keV, in 25 keV increments. System sensitivity, scatter fraction, and NEC were measured over a wide range of radioactivity levels. Increasing the low energy threshold lowered both sensitivity and scatter fraction. The statistical quality of the raw data was maximized for the 425 keV setting for all three phantoms. System stability and uniformity of response was also studied for 375 keV to 450 keV thresholds, and indicated acceptable performance for this system through 425 keV

Image Quality vs. NEC in 2D and 3D PET

To investigate the relationship between NEC and image quality to 2D and 3D PET, while simultaneously optimizing 3D low energy threshold (LET), we have performed a series of phantom measurements. The phantom consisted of 46 1 cm fillable hollow spheres on a random grid inside a water-filled oval cylinder, 21 cm tall, 36 cm wide, and 40 cm long. The phantom was imaged on a Discovery ST PET/CT system (GE Healthcare, Milwaukee, WI) in a series of 3 min scans as it decayed from an activity of 7.2 mCi. The scans included LET settings of 375,400, and 425 keV in 3D, and 375 keV in 2D. Image signal-to-noise (SNR) was calculated and compared wash NEC. While both NEC and image quality in 3D improved for LETs above the default of 375 keV, we found that there were significant differences between NEC and image quality for 2D and 3D. Most importantly, 3D image-quality was strongly dependent on the reconstruction algorithm and its associated parameters. In conclusion, a direct measure of image quality as necessary for comparing 2D vs. 3D performance

Optimizing Sequential Dual Tracer P.E.T. Studies using a Combined 2D/3D Imaging Protocol

We have investigated a combined 2D/3D protocol for minimizing contamination in dual tracer P.E.T. studies in which the tracers are administered on a timescale that is short compared to the half-lives. We have performed a series of phantom studies on an Advance and a Discovery ST (GE Healthcare Technologies), using a torso phantom with cardiac insert (Data Spectrum Corporation) to simulate a combined FDG and NH3 scan protocol for a patient with ischemia. The phantom was imaged in a series of alternating 2D/3D acquisitions as it decayed over 6 half-lives. By comparing 2D and 3D images, we have verified that 3D images are of comparable accuracy to 2D images, even with realistic out-of-field activity challenging the 3D scans. Based on scan and image statistical quality, we have recommended optimal doses for maximizing the image quality of both scans

Performance of a BGO PET/CT with Higher Resolution PET Detectors

A new PET detector block has been designed to replace the standard detector of the Discovery ST PET/CT system. The new detector block is the same size as the original, but consists of an 8/spl times/6 (tangential× axial) matrix of crystals rather than the original 6/spl times/6. The new crystal dimensions are 4.7× 6.3× 30 mm/sup 3/ (tangential× axial× radial). Full PET/CT systems have been built with these detectors (Discovery STE). Most other aspects of the system are identical to the standard Discovery ST, with differences including the low energy threshold for 3D imaging (now 425 keV) and front-end electronics. Initial performance evaluation has been done, including NEMA NU2-2001 tests and imaging of the 3D Hoffman brain phantom and a neck phantom with small lesions. The system sensitivity was 1.90 counts/s/kBq in 2D, and 9.35 counts/s/kBq in 3D. Scatter fractions measured for 2D and 3D, respectively, were 18.6% and 34.5%. In 2D, the peak NEC of 89.9 kcps occurred at 47.0 kBq/cc. In 3D, the peak NEC of 74.3 kcps occurred at 8.5 kBq/cc. Spatial resolution (all expressed in mm FWHM) measured in 2D for 1 cm off-axis source 5.06 transaxial, 5.14 axial and for 10 cm source 5.45 radial, 5.86 tangential, and 6.23 axial. In 3D for 1 cm off-axis source 5.13 transaxial, 5.74 axial, and for 10 cm source 5.92 radial, 5.54 tangential, and 6.16 axial. Images of the brain and neck phantom demonstrate some improvement, compared to measurements on a standard Discovery ST

Patient-specific radiation dose and cancer risk estimation in CT: Part II. Application to patients: Patient-specific CT dose and risk: Application to patients

Purpose: Current methods for estimating and reporting radiation dose from CT examinations are largely patient-generic; the body size and hence dose variation from patient to patient is not reflected. Furthermore, the current protocol designs rely on dose as a surrogate for the risk of cancer incidence, neglecting the strong dependence of risk on age and gender. The purpose of this study was to develop a method for estimating patient-specific radiation dose and cancer risk from CT examinations

Patient-specific radiation dose and cancer risk estimation in CT: Part I. Development and validation of a Monte Carlo program: Patient-specific CT dose and risk: Monte Carlo program

Purpose: Radiation-dose awareness and optimization in CT can greatly benefit from a dose-reporting system that provides dose and risk estimates specific to each patient and each CT examination. As the first step toward patient-specific dose and risk estimation, this article aimed to develop a method for accurately assessing radiation dose from CT examinations

Patient-specific Radiation Dose and Cancer Risk for Pediatric Chest CT

At pediatric chest CT, radiation dose and cancer risk, when normalized by tube current–time product, volume-weighted CT dose index, or dose–length product (DLP), decreased exponentially with increasing patient chest diameter; when normalized by DLP, effective dose and cancer risk were independent of beam collimation, helical pitch, and tube potential

Patient-specific radiation dose and cancer risk estimation in CT: Part II. Application to patients

Purpose: Current methods for estimating and reporting radiation dose from CT examinations are largely patient-generic; the body size and hence dose variation from patient to patient is not reflected. Furthermore, the current protocol designs rely on dose as a surrogate for the risk of cancer incidence, neglecting the strong dependence of risk on age and gender. The purpose of this study was to develop a method for estimating patient-specific radiation dose and cancer risk from CT examinations

Patient-specific radiation dose and cancer risk estimation in CT: Part I. Development and validation of a Monte Carlo program

Purpose: Radiation-dose awareness and optimization in CT can greatly benefit from a dose-reporting system that provides dose and risk estimates specific to each patient and each CT examination. As the first step toward patient-specific dose and risk estimation, this article aimed to develop a method for accurately assessing radiation dose from CT examinations