Andrea Crespi

Performance measurements for the PET/CT Discovery-600 using NEMA NU 2-2007 standards.

PURPOSE The aim of this study was to assess the performance measurements of the new PET/CT system Discovery-600 (D-600, GEMS, Milwaukee, WI). METHODS Performance measures were obtained with the National Electrical Manufacturers Association (NEMA) NU 2-2007 procedures. RESULTS The transverse (axial) spatial resolution FWHMs were 4.9 (5.6) mm and 5.6 (6.4) mm at 1 and 10 cm off axis, respectively. The sensitivity (average at 0 and 10 cm) was 9.6 cps/kBq. The scatter fraction was 36.6% (low energy threshold: 425 keV). The NEC peak rate (k=1) was 75.2 kcps at 12.9 kBq/cc. The hot contrasts for 10, 13, 17, and 22 mm spheres were 41%, 51%, 62%, and 73% and the cold contrasts for 28 and 37 mm spheres were 68% and 72%. CONCLUSIONS The Discovery-600 has good performance for the NEMA NU 2-2007 parameters, particularly in improved sensitivity compared to the scanners of the same Discovery family, D-ST and D-STE.

Motion Management in PET/CT: Technological Solutions

BACKGROUND AND OBJECTIVE Motion due to patients breathing can introduce heavy bias in PET/CT, both in image quality and quantitation. This paper is a review of the main technical solutions available to manage movement in PET/CT studies: a) Respiratory Gated (RG), b) Motion Free (MF), c) End Expiration (EE), d) Banana Artefact Management (BAM) and e) Data Driven Gating (DDG). METHODS The most diffused solutions (RG, MF and EE) are based on LIST mode acquisition of a PET Field of View (4D FOV), centered on the anatomical region of interest; to link PET data not only to time and to spatial position but also to the corresponding breathing phase, the synchronized acquisition of the patients breathing curve is performed by an external tracking device. Different commercial tools to track and to record patient breathing cycle are available to associate the internal organ motion with a measurable external parameter; for example these systems can measure the pressure on a chest elastic belt, the air flow trough patient nose, the breath-in and breath-out air temperature or the markers movement on the thorax/ abdominal region. Recently DDG techniques are developed to correct respiratory motion without the help of external motion tracking devices and to obtain a comparable result to that based on standard RG protocols. RESULTS The final result of an RG or DDG protocol is a sequence of 3D images showing organs and lesions movement; using the other motion management options a single 3D motion-free image is obtained without motion artefacts and degradation. Compared to the previously described options the BAM solution is not a real motion management protocol but just a Banana Artefact correction technique obtained using an Attenuation Correction Map calculated merging the Whole Body Helical CT with a Cine CT on the diaphragm area. CONCLUSION The motion management in PET/CT imaging shows benefits in terms of image quality, quantification and lesion detectability and it is useful both in diagnostic and radiotherapy planning.

A Statistical Method for Low Contrast Detectability Assessment in Digital Mammography

This study proposes a method to estimate low contrast detectability LCD applying a statistical method, based on the analysis of a uniform region. A dedicated test object was designed, made up of an acetate sheet equipped with a central uniform insert and an aluminium step wedge, allowing linear conversion from pixel values to millimeters of aluminium. A Matlab program for automated image analysis was developed. Phantom images were acquired on two different digital mammography systems. Reproducibility and sensitivity to exposure variations of the proposed method were investigated for different dose levels. Further the impact of scattering and attenuation on LCD was studied adding PMMA layers of variable thickness 2 to 7i¾?cm upon the acetate sheet during exposure in automatic exposure control modality. The statistical method turned out to be a reliable and rapid method for LCD evaluation. Applications include routine assessment of equipment performance for digital mammography systems.