Biomedical subjects

Margaret E Daube-Witherspoon

Publications and source records attributed to Margaret E Daube-Witherspoon.

6 recordsLinked to original sources

PubMed2006

Fast reconstruction of 3D time-of-flight PET data by axial rebinning and transverse mashing.

Faster scintillators like LaBr(3) and LSO have sparked renewed interest in PET scanners with time-of-flight (TOF) information. The TOF information adds another dimension to the data set compared to conventional three-dimensional (3D) PET with the size of the projection data being multiplied by the number of TOF bins. Here we show by simulations and analytical reconstruction that angular sampling for two-dimensional (2D) TOF PET can be reduced significantly compared to what is required for conventional 2D PET. Fully 3D TOF PET data, however, have a wide range of oblique and transverse angles. To make use of the smaller necessary angular sampling we reduce the 3D data to a set of 2D histoprojections. This is done by rebinning the 3D data to 2D data and by mashing these 2D data into a limited number of angles. Both methods are based on the most likely point given by the TOF measurement. It is shown that the axial resolution loss associated with rebinning reduces with improved timing resolution and becomes less than 1 mm for a TOF resolution below 300 ps. The amount of angular mashing that can be applied without tangential resolution loss increases with improved TOF resolution. Even quite coarse angular mashing (18 angles out of 324 measured angles for 424 ps) does not significantly reduce image quality in terms of the contrast or noise. The advantages of the proposed methods are threefold. Data storage is reduced to a limited number of 2D histoprojections with TOF information. Compared to listmode format we have the advantage of a predetermined storage space and faster reconstruction. The method does not require the normalization of projections prior to rebinning and can be applied directly to measured listmode data.

Algorithms↗

PubMed2006

Investigation of time-of-flight benefit for fully 3-D PET.

The purpose of this paper is to determine the benefit that can be achieved in image quality for a time-of-flight (TOF) fully three-dimensional (3-D) whole-body positron emission tomography (PET) scanner. We simulate a 3-D whole-body time-of-flight PET scanner with a complete modeling of spatial and energy resolutions. The scanner is based on LaBr3 Anger-logic detectors with which 300ps timing resolution has been achieved. Multiple simulations were performed for 70-cm long uniform cylinders with 27-cm and 35-cm diameters, containing hot spheres (22, 17, 13, and 10-mm diameter) in a central slice and 10-mm diameter hot spheres in a slice at 1/4 axial FOV. Image reconstruction was performed with a list-mode iterative TOF algorithm and data were analyzed after attenuation and scatter corrections for timing resolutions of 300, 600, 1000 ps and non-TOF for varying count levels. The results show that contrast recovery improves slightly with TOF (NEMA NU2-2001 analysis), and improved timing resolution leads to a faster convergence to the maximum contrast value. Detectability for 10-mm diameter hot spheres estimated using a nonprewhitening matched filter (NPW SNR) also improves nonlinearly with TOF. The gain in image quality using contrast and noise measures is proportional to the object diameter and inversely proportional to the timing resolution of the scanner. The gains in NPW SNR are smaller, but they also increase with increasing object diameter and improved timing resolution. The results show that scan times can be reduced in a TOF scanner to achieve images similar to those from a non-TOF scanner, or improved image quality achieved for same scan times.

Algorithms↗

PubMed2005

Imaging performance of A-PET: a small animal PET camera.

The evolution of positron emission tomography (PET) imaging for small animals has led to the development of dedicated PET scanner designs with high resolution and sensitivity. The animal PET scanner achieves these goals for imaging small animals such as mice and rats. The scanner uses a pixelated Anger-logic detector for discriminating 2 x 2 x 10 mm3 crystals with 19-mm-diameter photomultiplier tubes. With a 19.7-cm ring diameter, the scanner has an axial length of 11.9 cm and operates exclusively in three-dimensional imaging mode, leading to very high sensitivity. Measurements show that the scanner design achieves a spatial resolution of 1.9 mm at the center of the field-of-view. Initially designed with gadolinium orthosilicate but changed to lutetium- yttrium orthosilicate, the scanner now achieves a sensitivity of 3.6% for a point source at the center of the field-of-view with an energy window of 250-665 keV. Iterative image reconstruction, together with accurate data corrections for scatter, random, and attenuation, are incorporated to achieve high-quality images and quantitative data. These results are demonstrated through our contrast recovery measurements as well as sample animal studies.

Animals↗

PubMed2003

Developments in instrumentation for emission computed tomography.

Instrumentation for emission computed tomography continues to evolve, taking advantage of developments in detector technology, data processing and correction methods, and reconstruction algorithms. This article reviews the basic principles and latest developments in emission computed tomography instrumentation, for both positron emission tomography and single-photon emission computed tomography applications.

Equipment Design↗

PubMed2003

Performance of a brain PET camera based on anger-logic gadolinium oxyorthosilicate detectors.

UNLABELLED: A high-sensitivity, high-resolution brain PET scanner ("G-PET") has been developed. This scanner is similar in geometry to a previous brain scanner developed at the University of Pennsylvania, the HEAD Penn-PET, but the detector technology and electronics have been improved to achieve enhanced performance. METHODS: This scanner has a detector ring diameter of 42.0 cm with a patient aperture of 30.0 cm and an axial field of view of 25.6 cm. It comprises a continuous light-guide that couples 18,560 (320 x 58 array) 4 x 4 x 10 mm(3) gadolinium oxyorthosilicate (GSO) crystals to 288 (36 x 8 array) 39-mm photomultiplier tubes in a hexagonal arrangement. The scanner operates only in 3-dimensional (3D) mode because there are no interplane septa. Performance measurements on the G-PET scanner were made following National Electrical Manufacturers Association NU 2-2001 procedures for most measurements, although NU 2-1994 procedures were used when these were considered more appropriate for a brain scanner (e.g., scatter fraction and counting-rate performance measurements). RESULTS: The transverse and axial resolutions near the center are 4.0 and 5.0 mm, respectively. At a radial offset of 10 cm, these numbers deteriorate by approximately 0.5 mm. The absolute sensitivity of this scanner measured with a 70-cm long line source is 4.79 counts per second (cps)/kBq. The scatter fraction measured with a line source in a 20-cm-diameter x 19-cm-long cylinder is 39% (for a lower energy threshold of 410 keV). For the same cylinder, the peak noise equivalent counting rate is 60 kcps at an activity concentration of 7.4 kBq/mL (0.20 micro Ci/mL), whereas the peak true coincidence rate is 132 kcps at an activity concentration of 14 kBq/mL (0.38 micro Ci/mL). Images from the Hoffman brain phantom as well as (18)F-FDG patient scans illustrate the high quality of images acquired on the G-PET scanner. CONCLUSION: The G-PET scanner attains the goal of high performance for brain imaging through the use of an Anger-logic GSO detector design with continuous optical coupling. This detector design leads to good energy resolution, which is needed in 3D imaging to minimize scatter and random coincidences.

Brain↗

PubMed2002

PET performance measurements using the NEMA NU 2-2001 standard.

UNLABELLED: The NU 2-1994 standard document for PET performance measurements has recently been updated. The updated document, NU 2-2001, includes revised measurements for spatial resolution, intrinsic scatter fraction, sensitivity, counting rate performance, and accuracy of count loss and randoms corrections. The revised measurements are designed to allow testing of dedicated PET systems in both 2-dimensional and 3-dimensional modes as well as coincidence gamma cameras, conditions not considered in the original NU 2-1994 standard. In addition, the updated measurements strive toward being more representative of clinical studies, in particular, whole-body imaging. METHODS: Performance measurements following the NU 2-1994 and NU 2-2001 standards were performed on several different PET scanners. Differences between the procedures and resulting performance characteristics, as well as the rationale for these changes, were noted. RESULTS: Spatial resolution is measured with a point source in all 3 directions, rather than a line source, as specified previously. For the measurements of intrinsic scatter fraction, sensitivity, and counting rate performance, a 70-cm line source is now specified, instead of a 19-cm-long cylindric phantom. The longer configuration permits measurement of these performance characteristics over the entire axial field of view of all current PET scanners and incorporates the effects of activity outside the scanner. A measurement of image quality has been added in an effort to measure overall image quality under clinically realistic conditions. This measurement replaces the individual measurements of uniformity and of the accuracy of corrections for attenuation and scatter. CONCLUSION: The changes from the NU 2-1994 standard to the NU 2-2001 standard strive toward establishing relevance with clinical studies. The tests in the updated standard also are, in general, simpler and less time-consuming to perform than those in the NU 2-1994 standard.

Gamma Cameras↗