PURPOSE: Rheumatiod arthritis (RA) of the hand is a widespread and debilitating disease with a large social and economic impact. RA damages the inter articular cartilage, causing narrowing of the joint space width (JSW.) In this study a template-based approach for measuring the 3D JSW is presented, which uses multiple projections of the joint and a comparison to 3D templates from anatomical specimens. METHODS: This study examined 20 proximal interphalangeal (PIP), and 20 metacarpophalangeal (MCP) joints. Realistic simulated radiographs with a pitch of 0.1 mm were produced from 3D data sets obtained by imaging skeletal specimens with a 0.066 mm pitch μCT. The technique attempted to match each bone to an anatomical template after the template had undergone transformations in virtual imaging space.For each native joint projection, the two opposing margins were delineated using a technique developed to segment bone margins on hand radiographs. The projected margins of each joint surface at each acquisition were then compared to a set of margins created by projecting rays through the surfaces of the anatomical templates, and the best-matched template was chosen. The performance was evaluated by calculating dJSW = |Native joint JSW- Template JSW|.
RESULTS: The average dJSW ranged from 0.10 mm to 0.30 mm for approximately half of the average joint radius.CONCLUSIONS: A new technique for 3D imaging based on anatomical templates has been demonstrated. The work is specific to hand imaging but may be applied to other anatomical objects with regularity of shape. It may also complement previous work in digital tomosynthesis.
PURPOSE: Rheumatoid arthritis (RA) of the hand is a significant healthcare problem. Techniques to accurately quantity the structural changes from RA are crucial for the development and prescription of therapies. Analysis of radiographic joint space width (JSW) is widely used and has demonstrated promise. However, radiography presents a 2D view of the joint. In this study we performed tomosynthesis reconstructions of proximal interphalangeal (PIP), and metacarpophalangeal (MCP) joints to measure the 3D joint structure.
METHODS: We performed a reader study using simulated radiographs of 12 MCP and 12 PIP joints from skeletal specimens imaged with micro-CT. The tomosynthesis technique provided images of reconstructed planes with 0.75 mm spacing, which were presented to 2 readers with a computer tool. The readers were instructed to delineate the joint surfaces on tomosynthetic slices where they could visualize the margins. We performed a quantitative analysis of 5 slices surrounding the central portion of each joint. Reader-determined JSW was compared to a gold standard. As a figure of merit we calculated the average root-mean square deviation (RMSD).
RESULTS: RMSD was 0.22 mm for both joints. For the individual joints, RMSD was 0.18 mm (MCP), and 0.26 mm (PIP). The reduced performance for the smaller PIP joints suggests that a slice spacing less than 0.75 mm may be more appropriate.
CONCLUSIONS: We have demonstrated the capability of limited 3D rendering of joint surfaces using digital tomosynthesis. This technique promises to provide an improved method to visualize the structural changes of RA.
Arthritis is a painful condition with enormous societal impact. Arthritis damages the articular cartilage between adjacent bones in a joint, which is seen radiographically as narrowing of the joint space width (JSW). JSW is an important arthritis outcome measure however a single radiographic image is a 2D projection of a 3D structure and diseased areas can be obscured. To quantify the JSW in three dimensions we have applied digital tomosynthesis imaging to hand radiography. A tomosynthesis algorithm, developed for use in chest radiography, was modified to provide reconstructed slices through the bones that formed joints of the hand. The methodology was tested using simulated radiographs of dry-bone specimens from 3 hand skeletons. Estimates to the JSW in 3D were made from the reconstructed slices. The algorithm produced tomographic slices through the bones of the joint with minimal loss of spatial resolution. We discovered that hand radiography is ideally suited for tomosynthesis imaging due to the small amount of scatter and lack of truncation artifacts. We have demonstrated the utility of digital tomosynthesis for use in quantifying JSW for arthritis assessment. The method shows promise for improving the assessment of disease progression.
This investigation tests the hypothesis that volume anisotropy intrinsic to tomosynthetic reconstructions can be minimized through integration of contiguously sampled orthogonal projections. The basic idea involves the acquisition of data from two orthogonal projection geometries using total disparity angles of 90 degree(s) for each projection series. This allows projections at the angular extremes of one series to correspond to projections produced at opposite angular extremes of the series orthogonal to the first.
Rheumatoid arthritis of the hand can be characterized and assessed by the narrowing of the phalangeal joint spaces. These are ordinarily scored semi-quantitatively by a radiologist using radiographs of the hand. Software which delineates and measures the joint spaces would be a useful tool for diagnosis. The first part of such an algorithm has been developed which segments and identifies eight individual bones on digitized hand radiographs: the middle and proximal phalanges of the 2nd to 5th digits. The software also determines the locations of the distal interphalangeal, proximal interphalangeal, and metacarpophalangeal joint spaces for each digit.
The resolution of a fiberoptical boule was determined experimentally. A boule is a matrix of scintillating glass fibers arranged parallel to each other and compressed into a thick plate. A 51 mm X 51 mm by 3 mm thick terbium-activated boule was optically coupled to a 1 k X 1 k X 16 bit CCD camera. The image of an edge was used to compute the line spread function, and the modulation transfer function was calculated. After correcting for the MTF of the CCD and optics, the MTF of the fiberoptical plate demonstrated 20% modulation at a spatial resolution of 15 line pairs per millimeter. The x-ray absorption of the 3 mm thick plate was 98% at 70 kV (3.3. mm half value layer). It is shown using simple trigonometry that for a very high resolution detector, x-ray beam divergence (angled photons striking the receptor) at the periphery of the field of view may cause substantial resolution losses. The role that fiberoptical plate technology may play in diagnostic medical imaging is discussed.
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