The 2006 Henry N. Wagner Lecture: Of mice and men (and positrons)--advances in PET imaging technology.

There have been major advances in PET technology that cumulatively have helped improve image quality, increased the range of applications for PET, and contributed to the more widespread use of PET. Examples of these technologic advances include whole-body imaging, 3-dimensional imaging, new scintillator materials, iterative reconstruction algorithms, combined PET/CT, and preclinical PET. New advances on the immediate horizon include the reintroduction of time-of-flight PET, which takes advantage of the favorable timing properties of newer scintillators; the integration of PET and MRI scanners into a dual-modality imaging system; and the possibility of further significant improvements in spatial resolution in preclinical PET systems. Sensitivity remains a limiting factor in many PET studies. Although, conceptually, huge gains in sensitivity are still possible, realizing these gains is thwarted largely by economic rather than scientific concerns. Predicting the future is fraught with difficulty; nonetheless, it is apparent that ample opportunities remain for new development and innovation in PET technology that will be driven by the demands of molecular medicine, notably sensitive and specific molecular diagnostic tools and the ability to quantitatively monitor therapeutic entities that include small molecules, peptides, antibodies, nanoparticles, DNA/RNA, and cells.     

3D PET using a conventional multislice tomograph without septa

A conventional multislice positron emission tomography scanner was modified to operate without interplane septa to evaluate its performance in collecting and reconstructing data in a three-dimensional (3D) format, thereby significantly increasing system sensitivity. A 3D filtered backprojection algorithm was implemented and tested, using both computer simulations and phantom measurements. No artifacts were apparent in the test images, although the algorithm was shown to lead to a 11% degradation in transaxial resolution in the outer planes. Following septa removal, sensitivity was found to increase by a factor of 7 with an increase in scatter fraction from 16 to 41%. Axial resolution degraded from 6.9 to 7.7 mm full width at half maximum at the center of the field of view. The maximum count rate without septa was 2.4 x 10(5) cps, at a concentration of 0.4 microCi/ml, compared with 1.3 x 10(5) cps at 1.5 microCi/ml with septa. Brain studies were performed with volunteers using 18F-fluorodeoxyglucose, 18F-fluorodopa, and H2 15O to compare noise-equivalent count rates and qualitatively assess image quality over a wide range of imaging conditions.     

Radiographic analysis of selective ligament sectioning at the carpal scaphoid: a cadaver study

Although scapholunate diastasis with rotatory subluxation of the scaphoid (stage I perilunar instability determined by Mayfield's classification) has been studied by several investigators, the exact contribution of the supporting ligaments is still being defined. We designed and executed an experimental study using six fresh-frozen cadaver specimens to demonstrate the radiographic changes seen on standard and stress wrist radiographs that correlate with the sequential sectioning of the scapholunate stabilizing ligaments. The radioscapho-lunate ligament, the palmar scapholunate interosseous ligament, the dorsal scapholunate interosseous ligament, and the radiocapitate ligament were sectioned sequentially to simulate a progressive wrist injury caused by an extension, intercarpal supination and ulnar deviation force. The results showed significant ligamentous injury must occur before commonly used radiographic limits are exceeded. The lateral scapholunate angle most closely reflected the progressive nature of this injury.