Reduction of motion artefacts in non-gated dual-energy radiography.

The objective of this work was to reduce motion artefacts in non-gated dual-energy subtraction radiography whilst preserving the contrast-to-noise ratio (CNR) in regions with low motion. Dual-energy radiography provides material-selective information (soft-tissue and bone images) that may be used for improved detection of calcifications in lung nodules. The weighted logarithmic dual-energy subtraction of thoracic images performed without electrocardiogram gating results in motion-induced artefacts. The low-energy image was acquired at the usual dose setting at 60 kV. To obtain the high-energy (120 kV) information, a series of consecutive images at a time interval of 30 ms were made. The series integral dose was equivalent to the dose of a single conventional high-energy image. A motion-free merging technique was introduced that combines standard images yielding low image noise with phase-selective images yielding motion artefact-free image regions which are used for dual-energy subtraction. Evaluations of the method were performed with simulations and measurements using a C-arm system (Axiom Artis; Siemens AG, Germany) equipped with a flat detector of 40 x 30 cm(2). The merging approach conserved standard image noise levels and the CNR in areas without cardiac motion, whereas image noise in pericardial lung regions and in the heart was increased compared with standard images. Motion artefacts in the heart and in the lung areas close to the heart are significantly reduced in the material-selective images when compared with a standard non-gated subtraction.

Simultaneous misalignment correction for approximate circular cone-beam computed tomography.

Currently, CT scanning is often performed using flat detectors which are mounted on C-arm units or dedicated gantries as in radiation therapy or micro CT. For perspective cone-beam backprojection of the Feldkamp type (FDK) the geometry of an approximately circular scan trajectory has to be available for reconstruction. If the system or the scan geometry is afflicted with geometrical instabilities, referred to as misalignment, a non-perfect approximate circular scan is the case. Reconstructing a misaligned scan without knowledge of the true trajectory results in severe artefacts in the CT images. Unlike current methods which use a pre-scan calibration of the geometry for defined scan protocols and calibration phantoms, we propose a real-time iterative restoration of reconstruction geometry by means of entropy minimization. Entropy minimization is performed combining a simplex algorithm for multi-parameter optimization and iterative graphics card (GPU)-based FDK-reconstructions. Images reconstructed with the misaligned geometry were used as an input for the entropy minimization algorithm. A simplex algorithm changes the geometrical parameters of the source and detector with respect to the reduction of entropy. In order to reduce the size of the high-dimensional space required for minimization, the trajectory was described by only eight fix points. A virtual trajectory is generated for each iteration using a least-mean-squares algorithm to calculate an approximately circular path including these points. Entropy was minimal for the ideal dataset, whereas strong misalignment resulted in a higher entropy value. For the datasets used in this study, the simplex algorithm required 64-200 iterations to achieve an entropy value equivalent to the ideal dataset, depending on the grade of misalignment using random initialization conditions. The use of the GPU reduced the time per iteration as compared to a quad core CPU-based backprojection by a factor of 10 resulting in a total of 15-20 ms per iteration, and thus providing an online geometry restoration after a total computation time of approximately 1-3 s, depending on the number of iterations. The proposed method provides accurate geometry restoration for approximately circular scans and eliminates the need for an elaborate off-line calibration for each scan. If a priori information about the trajectory is used to initialize the simplex algorithm, it is expected that the entropy minimization will converge significantly faster.

Image file interoperability for data protection, communication and trans-system connectivity.

DICOM (Digital Imaging and Communication in Medicine) is a set of international imaging standards developed for medicine and extended to incorporate other professions. These standards encompass primary digital and secondary capture images made for dental diagnostic procedures. The standards provide a basis of interoperability for digital system outputs, providing portability and reducing the danger of obsolescence that would render valuable diagnostic information impossible to display. The American Dental Association, through the activities of its Working Group 12.1, is promoting interoperability within DICOM as the industry standard for digital imaging in dentistry.

Mass profile monitoring in trace analysis by gas chromatography/mass spectrometry.

The advantages of gas chromatography/mass spectrometry (GC/MS) selected-ion monitoring (SIM) in the mass profile (MP) mode at medium mass resolving power were investigated for analyses requiring detection of low-picogram quantities of analytes in complex mixtures. The mass profile monitoring provides a certainty at least 10 times greater than that achieved by conventional GC/MS-SIM in the peak-top monitoring mode, and it can be operated at lower mass resolving power to compensate for the loss of sensitivity in the MP mode. The examination of mass profile peak shape, central mass shift, and sequential changes during GC elution not only reveals the presence of interfering compounds but also results in accurate mass measurement for those interferences. The latter feature takes the MP mode beyond the target mass analysis that GC/MS-SIM was originally designed for. This additional dimension of information is particularly useful for those complex and incompletely characterized matrices that are frequently encountered in environmental and biological sample analyses.

Recurrent posttraumatic dislocation of the hip. A report of two cases and review of the literature.

Posttraumatic recurrent posterior hip dislocations were observed in two adult patients. In neither case was there evidence of acetabular dysplasia, paralysis, or infection. In both cases the only significant abnormality discovered was a marked posterior capsular redundancy. In the second case this was clearly shown by a computed tomography (CT) arthrogram. In both instances plication of the posterior capsule prevented further dislocations; however, the second patient developed massive heterotopic ossification around the involved joint and osteonecrosis of the femoral head. Investigation with CT arthrography of patients sustaining one or more dislocations in response to minimal trauma aids in evaluation of capsular abnormalities that may be surgically correctable.

One-year follow-up of cardiac and coronary artery disease in infants and children with Kawasaki disease.

Of 75 patients meeting clinical criteria for Kawasaki disease, 67 patients were followed with serial ECG and echocardiograms (echo) for at least 1 year. Sixteen patients had coronary artery aneurysms and three had dilated coronary arteries as assessed by initial two-dimensional (2D) echo and/or angiocardiographic studies. ECG findings of first and second-degree heart block and ST-T wave changes (36%) as well as M-mode echo abnormalities (45%) including pericardial effusion, decreased ventricular septal motion, and decreased left ventricular function were all normalized by 6 months, except in two infants who continued to have decreased function and flat ventricular septal motion. In four patients with single proximal coronary aneurysm and two with dilated coronary artery, resolution of lesions occurred by 1 year. Among 11 patients with multiple coronary aneurysms discovered by initial studies, the 2D echo became normal in seven and showed aneurysms in four as corroborated by angiogram. One patient with an isolated distal coronary aneurysm, not seen by initial or serial echo, had a normal follow-up angiogram. Our study suggests that in Kawasaki disease careful, serial, 2D echo is sufficient to monitor the course of coronary artery disease that tends to regress and follow a benign course. However, the long-term effects of this disease on cardiac and coronary arteries remain to be elucidated.

Wagner resurfacing total hip arthroplasty: early results.

This preliminary report deals with the early results obtained from a new conservative hip arthroplasty--the Wagner resurfacing total hip arthroplasty in which the acetabulum is replaced with a high-density polyethylene cup and the femoral head resurfaced with a metallic cup. Between February 1977 and September 1978, 51 patients, ranging in age from 12 to 70 years, underwent this operation. They had a variety of hip diseases. All patients were assessed prospectively by the Harris hip rating method. The results of operation were excellent. All patients but one had complete or marked relief of pain. To date there have only been two failures. With this procedure the considerable problem associated with the conventional hip arthroplasty, that of stem loosening, is avoided. It is possible to salvage a failed Wagner resurfacing operation by hip arthrodesis or by conventional total hip arthroplasty. While it is still too early to advocate its universal acceptance, the Wagner resurfacing total hip arthroplasty is expected to be widely adopted and used with success.