Richard A. Robb

Population‐Based Study of Age and Sex Differences in Bone Volumetric Density, Size, Geometry, and Structure at Different Skeletal Sites

In a population‐based, cross‐sectional study, we assessed age‐ and sex‐specific changes in bone structure by QCT. Over life, the cross‐sectional area of the vertebrae and proximal femur increased by ∼15% in both sexes, whereas vBMD at these sites decreased by 39–55% and 34–46%, respectively, with greater decreases in women than in men.

A Population-Based Assessment of Rates of Bone Loss at Multiple Skeletal Sites : Evidence for Substantial Trabecular Bone Loss in Young Adult Women and Men

Using QCT, we made a longitudinal, population‐based assessment of rates of bone loss over life at the distal radius, distal tibia, and lumbar spine. Cortical bone loss began in perimenopause in women and later in life in men. In contrast, trabecular bone loss began in young adulthood in both sexes.

Interactive display and analysis of 3-D medical images

The ANALYZE software system, which permits detailed investigation and evaluation of 3-D biomedical images, is discussed. ANALYZE can be used with 3-D imaging modalities based on X-ray computed tomography, radionuclide emission tomography, ultrasound tomography, and magnetic resonance imaging. The package is unique in its synergistic integration of fully interactive modules for direct display, manipulation, and measurement of multidimensional image data. One of the most versatile and powerful capabilities in ANALYZE is image volume rendering for 3-D display. An important advantage of this technique is that it can be used to display 3-D images directly from the original data set and to provide on-the-fly combinations of selected image transformations, such as surface segmentation, cutting planes, transparency, and/or volume set operations (union, intersection, difference, etc.). The module has been optimized to be fast (interactive) without compromising image quality. The software is written entirely in C and runs on standard UNIX workstations.

Visualization in biomedical computing

Abstract Visualizable objects in biology and medicine extend across a vast range of scale, from individual molecules and cells, to the varieties of tissue and interstitial interfaces, to complete organs, organ systems and body parts, and include functional attributes of these systems, such as biophysical, biomechanical and physiological properties. Medical applications include accurate anatomy and function mapping, enhanced diagnosis, accurate treatment planning and rehearsal, and education/training. However, the greatest potential for revolutionary innovation in the practice of medicine lies in direct, fully immersive, real-time multisensory fusion of real and virtual information data streams into online, real-time visualizations available during an actual clinical procedure. Current high-performance computers and advanced image processing capabilities have facilitated major progress toward realization of this goal. With these advances in hand, there are several important applications possible to be delivered soon that will have a significant impact on the practice of medicine and on biological research.

Method for producing high resolution real-time images, of structure and function during medical procedures

Images of a heart are acquired with a high resolution medical imaging system used to construct a dynamic high resolution 4D model. During a medical procedure such as endocardial physiology mapping and ablation, real-time images are produced by an ultrasonic transducer inserted into the heart. The high resolution heart model is registered with the acquired real-time images and used to produce dynamic, high resolution images for display during the medical procedure. An electrical activation map which depicts the spatial distribution of heart wall electrical activation is merged with the anatomic images to facilitate cardiac ablation therapy.

New approach to 3-D registration of multimodality medical images by surface matching

Multimodality images obtained from medical imaging systems such as computed tomography (CT), magnetic resonance (MR) imaging, positron emission tomography (PET), and single photon emission computed tomography (SPECT), generally provide complementary characteristic and diagnostic information. Synthesis of these image data sets into a single composite image containing these complementary attributes in accurate registration and congruence would provide truly synergistic information about the object(s) under examination. We have developed a new method which produces such correlation using parametric Chamfer matching. The method is fast, accurate, and reproducible. Surfaces ar initially extracted from two different images to be matched using semi-automatic segmentation techniques. These surfaces are represented as contours with common features to be matched. A distance transformation is performed for one surface image, and a cost function for the matching process is developed using the distance image. The geometric transformation includes three- dimensional translation, rotation, and scaling to accommodate images of different position, orientation, and size. The matching process involves searching this multi-parameter space to find the best fit which minimizes the cost function. The local minima problem is addressed by using a large number of starting points. A pyramid multi-resolution approach is employed to speed up both the distance transformation and the multi-parameter minimization processes. Robustness in noise handling is accomplished using multiple thresholds embedded in the multi- resolution search. The algorithm can register both partially overlapped and fragmented surfaces. Manual intervention is generally not necessary. Preliminary results suggest registration accuracy on the order of the voxel size used in the registration process. Computational time scales with the number of matching elements used, with about five minutes typical for 2563 images using a modern desktop workstation.

Structural Determinants of Vertebral Fracture Risk

Vertebral fractures are more strongly associated with specific bone density, structure, and strength parameters than with areal BMD, but all of these variables are correlated.

The biomedical imaging resource at Mayo Clinic

This editorial reviews the history and summarizes achievements, describes current activities, indicates future directions, and finally suggests some keys to success of the Biomedical Imaging Resource (BTR) at Mayo Clinic/Foundation. The origin and history section provides a chronological description, with associated references, emphasizing progress and milestones over the past three decades. Several figures are included to illustrate and highlight some particularly unique achievements.

Age- and sex-specific differences in the factor of risk for vertebral fracture: a population-based study using QCT.

We used QCT scans obtained in 687 men and women, 21–97 years of age, to estimate the factor of risk for vertebral fracture, Φvert, defined as the ratio of spinal loading to vertebral strength. With age, vertebral strength declined and Φvert increased significantly more in women than men. Age‐ and sex‐specific differences in Φvert closely resembled previously reported vertebral fracture incidence.

Relationship of Volumetric BMD and Structural Parameters at Different Skeletal Sites to Sex Steroid Levels in Men

In a population‐based, cross‐sectional study, we related age‐associated changes in vBMD and in bone structural parameters to circulating bioavailable estradiol and testosterone levels in men. Associations between these bone mass/structural parameters and sex steroid levels were progressively stronger with age. Our previously postulated “threshold” for skeletal estrogen deficiency was most evident at cortical sites.