Ronald Nutt

Image analysis in patients with cancer studied with a Combined PET and CT scanner

Purpose To compare combined whole-body PET and CT images of different cancers with PET images alone. Materials and Methods Thirty-two patients with known or possible cancers were examined using a combined positron emission tomographic (PET) and computed tomographic (CT) scanner. All data were acquired using this same combined scanner. After an injection of F-18 fluorodeoxyglucose (FDG), noncontrast helical CT imaging of the neck, chest, abdomen, or pelvis was performed. The spiral CT was followed by a PET scan covering the same axial extent as the CT. Results Coregistered PET–CT images identified and localized 55 lesions. In 10 patients (31%), areas with variable amounts of normal physiologic FDG uptake were distinguished from potential uptake of FDG in a nearby neoplastic lesion. Improved localization was achieved in 9 patients (for a total of 13 lesions, or 24%). Conclusion Combined PET–CT images appear more effective than PET images alone to localize precisely neoplastic lesions and to distinguish normal variants from juxtaposed neoplastic lesions.

The SMART scanner: a combined PET/CT tomograph for clinical oncology

A combined PET/CT tomograph with the unique capability to acquire accurately aligned functional and anatomical images for any part of the human body has been designed and built. The PET/CT, or SMART scanner, was developed by combining a Siemens Somatom AR.SP spiral CT scanner with a partial ring rotating ECAT ART PET tomograph. All components are mounted on a common rotational support within a single gantry that has an axial depth of 110 cm. The PET and CT components can be operated either separately or in combined mode. In combined mode, the CT images are used to correct the PET data for scatter and attenuation. Fully quantitative whole-body images can be obtained for an axial extent of up to 100 cm in an imaging time of less than one hour. When operated in PET mode alone, transmission scans are acquired with two 15 mCi cesium sources. We report the first performance measurements from the scanner, and present some illustrative clinical studies.

A Custom CMOS Integrated Circuit For PET Tomograph Front-end Applications

A custom CMOS integrated circuit has been designed, prototyped, and evaluated for PET tomograph front-end applications. The integrated circuit reduces the size. cost, and power consumption of existing PET frontend circuits by Over a factor of two. The integrated circuit, fabricated in a standard digital, 2 p, double-metal, double-poly, n-well CMOS process, has a die size of 6.6mmx6.4mm and power consumption of under 600 mW. The PET front-end CMOS integrated circuit processes energy, position, and timing information from a BGO block detector containing four photomultiplier tubes. Photomultiplier preamplifiers and variable gain amplifiers are co~ected to summing circuits and gated integrators to provide energy and position (x and y) signals. A constantfraction discriminator, requiring no external delay line, provides a timing output derived from the sum of the four photomultiplier signals. Eight 7- and 8-bit digital-to-analog converters. connected to a readwrite serial data interface, provide gain-control and threshold levels. The measured position, energy, and timing performance (3.05ns FWHM) of the integrated circuit is comparable to existing discrete PET frontend circuits.

A rotating PET camera using BGO block detectors

A positron emission tomography (PET) scanner with a reduced number of detectors per ring subtending two opposing arcs of 60 degrees and mounted on a circular support was developed. Projection data at all angles are acquired by rotating the detector assembly. The scanner has no septa, and data from the equivalent of 16 full rings of detectors are collected and sorted into 256 sinograms. The number of rotational positions at which data must be acquired depends on the size of the field of view (FOV) required. Reconstruction is performed using a fully 3-D reconstruction algorithm. The scanner has an absolute efficiency of 0.5% at the center of the FOV, which is the same as that of a full ring scanner with septa extended. The sensitivity measured with a 20-cm uniform cylinder is 175000 cps/ mu Ci/ml, and the transaxial and axial spatial resolution is the same as for a full ring scanner ( approximately 6 mm). The scatter fraction is 39% with a lower energy threshold at 250 keV. The maximum noise equivalent count rate estimated for a 15-cm-diameter cylinder is 42000 cps at a concentration of 0.5 mu Ci/ml. The camera was used for a number of /sup 18/FDG applications in neurology, cardiology, and oncology.<<ETX>>

The NEC dependence of different scintillators for positron emission tomography

In positron emission tomography (PET), the concept of noise equivalent count rate (NEC) is a measure of image quality. It has been shown that the local signal-to-noise ratio in the images reflects the global signal-to-noise ratio, which, in turn, can be related to the NEC. Factors that affect the NEC include the scanner geometry and scintillator material. The peak NEC has long been considered an indicator of PET scanner performance, whereas the sensitivity, represented by the slope of the NEC curve at the origin is equally important. This initial slope is proportional to the true coincidence sensitivity times the factor (1-SF), where SF is the scatter fraction. The peak NEC value is a strong function of scanner geometry and scintillator material, scatter fraction, system dead time and random coincidence fraction. The scatter fraction depends mainly on the low level discriminator setting of the system. Access to time-of-flight information may have a strong impact on the signal-to-noise properties and hence on the NEC performance. However, this work will focus specifically on the effect of the scintillator properties on the NEC, in particular the stopping power, light output, decay time and the interaction with the electronics. Three scintillators have been compared, the standard BGO, the fast high density LSO and a new fast, high light yield scintillator LaBr/sub 3/. The scintillators have been compared for the fixed scanner geometry of the ECAT EXACT.