Robert M. Allman M.D. Katherine P.Andriole Ph.D. Don Baune Daniel Bednarek Ph.D. Geoffrey Bookman Kenneth Burgess Eugene Chien Allan G. Farman M.D. Rao P.Gullapalli, Ph.D. Geoffrey S. Hastings M.D. Cynthia E. Keen ElizabethA. Krupkinski Ph.D. Nicola Montanari M.D. Sunita Munjal Bruce Reiner M.D. Ronald Schilling Ph.D. Eliot Siegel M.D. Douglas M. Tucker Ph.D. Paul WeissM.D. Gary J. Whitman M.D. Bym Williamson M.D.

ESPITE 2 DECADES of optimistic and confident predictions that filmless radiology was imminent, the centennial commemoration of Wilhelm Roentgen's discovery of the x-ray will come and go this year with only a small number of radiology departments interpreting more than a small fraction of imaging studies using a computer workstation. The reasons for this undoubtedly representa combination of economic constraints, concerns about image quality and time required for image interpretation, and the inertia that must be overcome with any paradigm shift as great as is required to abandon film for the largely uncharted waters of digital imaging. The combination of construction Ÿ associated with the Veterans Administration's (VA's) new high-tech showcase, exhaustive investigation into quality and productivity issues associated with digital imaging, a great deal of energy and enthusiasm, and perhaps a bit of naivet› resulted in the decision to pursue filmless operation at the Baltimore VA Medical

Bone density measurement by quantitative computed tomography (QCT) commonly uses an external reference phantom to decrease scan-to-scan and scanner-to-scanner variability. However, the peripheral location of these phantoms and other phantom variables is also responsible for a measurable degradation in accuracy and precision. Due to non-uniform artifacts such as beam hardening, scatter, and volume averaging, the ideal reference phantom should be as close to the target tissue as possible. This investigation developed and tested a computer program that uses paraspinal muscle and fat tissue as internal reference standards in an effort to eliminate the need for an external phantom. Because of their proximity, these internal reference tissues can be assumed to reflect more accurately the local changes in the x-ray spectra and scatter distribution at the target tissue. A user interactive computerized histogram plotting technique enabled the derivation of reproducible CT numbers for muscle, fat, and trabecular bone. Preliminary results indicate that the use of internal reference tissues with the histogram technique may improve reproducibility of scan-to-scan measurements as well as inter-scanner precision. Reproducibility studies on 165 images with intentional region-of-interest (ROI) mispositioning of 1.5, 2.5, or 3.5 mm yielded a precision of better than 1% for normals and 1% to 2% for osteoporotic patients--a twofold improvement over the precision from similar tests using the standard technique with an external reference phantom. Such improvements in precision are essential for QCT to be clinically useful as a noninvasive modality for measurement of the very small annual changes in bone mineral density.

The radiology practice is going through rapid changes due to the introduction of state-of-the-art computed based technologies. For the last twenty years we have witnessed the introduction of many new medical diagnostic imaging systems such as x-ray computed tomo-graphy, digital subtraction angiography (DSA), computerized nuclear medicine, single pho-ton emission computed tomography (SPECT), positron emission tomography (PET) and more re-cently, computerized digital radiography and nuclear magnetic resonance imaging (MRI). Other than the imaging systems, there has been a steady introduction of computed based information systems for radiology departments and hospitals.

We applied dendrochronology techniques to develop a 103-year growth increment chronology using geoduck clams (Panopea abrupta) collected from the Tree Nob region of northern British Columbia, Canada. Using acetate peels of the chondrophore region of fifteen geoduck clams, growth increments were photographed under a dissecting microscope and imported into image analysis software. All samples were visually crossdated and growth increment widths measured. A crossdating check in COFECHA calculated an interseries correlation of 0.716 and mean sensitivity of 0.29. We then used negative exponential functions to detrend all measurement time series before averaging them into a final master chronology that spanned 1901-2003. The resulting geoduck chronology showed strong interannual and interdecadal variability and closely tracked the Pacific Decadal Oscillation, including the regime shifts of 1945 and 1976. Geoduck growth is most strongly limited by cold winters, as indicated by strongly positive (r > 0.6) correlations with Jan-March sea surface temperatures. Ultimately, geoduck growth chronologies could be used for i) crossdating as a means of age validation, ii) establishing climate-growth relationships, and iii) climate reconstructions for periods prior to instrumental records.