Time‐varying reconstruction in single photon emission computed tomography

We propose a new method for reconstruction of images in single photon emission computed tomography (SPECT), when the activity distribution of the object is time‐varying. The activity evolution is modeled with the first‐order Markov model, and linear observation model is used to characterize the measurement system. The state‐space representation of the measurement sequence reduces to an ill‐conditioned state estimation problem, which is solved recursively using the Kalman filter and smoother algorithms. Two special models, the compartmental model and the diffusion model, for the time variation are discussed. The method is evaluated using simulations. © 2005 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 14, 186–197, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20023     

X‐ray computed tomography quantification of damage in concrete under compression considering irreversible mode‐II microcracks

A method for X‐ray computed tomography quantification of damage in concrete under compression considering irreversible mode‐II microcracks is developed. To understand damage behaviour in concrete, a micromechanical analysis of damage under biaxial compression is conducted focusing on random micro‐defects in micro‐cells isolated from the representative volume element. Furthermore, for stress–strain response prediction, a quantification is developed concerning the behaviours of the dominant macrocracks in multiaxial compression. Specifically, two crack types are taken into account: mode‐I cracks and irreversible deformation cracks (including mode‐II microcracks). Furthermore, mode‐I cracks generate compression‐induced tensile load (transverse) area reduction and further stiffness degradation, whereas the latter contribute to the development of irreversible strains. Additionally, by investigating the development of gradually converging dominant cracks, the procedure for quantifying damage is competently executed. In addition, distinguished from other approaches, the quantified damage can be applied directly to constitutive models to produce stress–strain response highly agrees with experimental results.     

Attenuating noise from computed tomography medical images using a coefficients‐driven total variation denoising algorithm

The aim of image denoising is to recover a visually accepted image from its noisy observation with as much detail as possible. The noise exists in computed tomography images due to hardware errors, software faults and/or low radiation dose. Because of noise, the analysis and extraction of accurate medical information is a challenging task for specialists. Therefore, a novel modification on the total variational denoising algorithm is proposed in this article to attenuate the noise from CT images and provide a better visual quality. The newly developed algorithm can properly detect noise from the other image components using four new noise distinguishing coefficients and reduce it using a novel minimization function. Moreover, the proposed algorithm has a fast computation speed, a simple structure, a relatively low computational cost and preserves the small image details while reducing the noise efficiently. Evaluating the performance of the proposed algorithm is achieved through the use of synthetic and real noisy images. Likewise, the synthetic images are appraised by three advanced accuracy methods –Gradient Magnitude Similarity Deviation (GMSD), Structural Similarity (SSIM) and Weighted Signal‐to‐Noise Ratio (WSNR). The empirical results exhibited significant improvement not only in noise reduction but also in preserving the minor image details. Finally, the proposed algorithm provided satisfying results that outperformed all the comparative methods.     

Image reconstruction with a shift‐variant filtration in circular cone‐beam CT

It is well known that cone‐beam data acquired with a circular orbit are insufficient for exact image reconstruction. Despite this, because a cone‐beam scanning configuration with a circular orbit is easy to implement in practice, it has been widely employed for data acquisition in, e.g., micro‐CT and CT imaging in radiation therapy. The algorithm developed by Feldkamp, Davis, and Kress (FDK) and its modifications, such as the Tent–FDK (T‐FDK) algorithm, have been used for image reconstruction from circular cone‐beam data. In this work, we present an algorithm with spatially shift‐variant filtration for image reconstruction in circular cone‐beam CT. We performed computer‐simulation studies to compare the proposed and existing algorithms. Numerical results in these studies demonstrated that the proposed algorithm has resolution properties comparable to, and noise properties better than, the FDK algorithm. As compared to the T‐FDK algorithm, our proposed algorithm reconstructs images with an improved in‐plane spatial resolution. © 2005 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 14, 213–221, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20026     

Both pelvic radiography and lateral abdominal radiography correlate well with coronary artery calcification measured by computed tomography in hemodialysis patients: A cross‐sectional study

Introduction Lateral abdominal radiograph is suggested as an alternative to coronary artery computed tomography (CT) in evaluating vascular calcification. Simple scoring systems including pelvic radiograph scoring and abdominal scoring system were utilized to study their correlation with coronary artery calcification. Methods In 106 MHD patients, coronary artery CT, lateral abdominal, and pelvic radiograph were taken. The Agatston scoring system was applied to evaluate the degree of coronary artery calcification which was categorized according to Agatston coronary artery calcification score (CACS) ≥ 30, ≥100, ≥400, and ≥1000. Abdominal aortic calcification was scored by 4‐scored and 24‐scored systems. Pelvic artery calcification was scored by a 4‐scored system. Sensitivities and specificities of abdominal aortic calcification scores and pelvic artery calcification scores to predict different categories of coronary artery calcification were analyzed. We studied the diagnostic capability of abdominal aorta calcification and pelvic artery calcification to predict different CACS categories by calculating likelihood ratios. Receiver operator characteristic curves were used to determine the area under the curve for each of these testing procedures. Findings The prevalence was 48(45.3%), 15 (14.2%), 11 (10.4%), 11 (10.4%), and 11 (10.4%) for CACs > 0, ≥30, ≥100, ≥400, and ≥1000, respectively. The degree of CACs was positively correlated with patient age, prevalence of diabetes, abdominal aorta scores, and pelvic calcification scores. The areas under the curves for different CACS by all X‐ray scoring systems were above 0.70 except pelvic 4‐scored system for diagnosing CACS ≥30, without significant difference (P > 0.05). Discussion Both lateral abdominal and pelvic plain radiographs were demonstrated as acceptable alternatives to CT in evaluating vascular calcification.     

A rare case of Actinomyces skin and soft tissue infection in an end‐stage kidney disease patient with a review of the literature

End‐stage kidney disease (ESKD) patients are a commonly overlooked immunocompromised population that places them at risk for rare infections. We describe the case of a 78‐year‐old man with a history of ESKD managed with thrice weekly in‐center hemodialysis who had a prolonged episode of left elbow pain and drainage and was eventually found to have a skin and soft tissue infection from Actinomyces radingae. We review the bacteriology of Actinomyces spp. and the experiences of other providers who have treated actinomycosis in individuals with ESKD. The anatomic sites and demographics of these individuals are heterogeneous, but they all generally require a long antibiotic course with a beta‐lactam and portend to a good prognosis. High index of suspicion is needed to identify rare and atypical infections in the ESKD population.     

Clearance of myoglobin by high cutoff continuous veno‐venous hemodialysis in a patient with rhabdomyolysis: A case report

Continuous veno‐venous hemodialysis using high cutoff filters (HCO‐CVVHD) is a promising technique, which may be effective to decrease the extremely high level of circulating myoglobin in patients with rhabdomyolysis (RM). Here, we report a patient with RM caused by heat stroke who was successfully treated by HCO‐CVVHD. A male patient received HCO‐CVVHD with 4 L/h dialysate for 5 days and then pre‐dilution continuous veno‐venous hemofiltration (CVVH) at a dose of 4 L/h until recovery of renal function. The clearance of myoglobin and albumin at 5 minutes, and at 4, 12, and 24 hours were calculated. The serum myoglobin level decreased from a peak of 25,400 ng/mL on admission to 133 ng/mL at discharge. During HCO‐CVVHD, the mean clearances of serum myoglobin at four timepoints were 61.3 (range, 61.0–61.6), 52.3 (38.9–65.8), 47.3 (46.8–47.9), and 43.7 (39.5–48.0) mL/min, respectively, and the mean clearances of albumin were 12.4 (range, 11.8–13.1), 3.1 (2.5–3.8), 1.2 (1.0–1.4), and 0.8 (0.6–1.0) mL/min, respectively. During CVVH, the clearance rates of myoglobin at 5 minutes and 24 hours were 17.0 and 3.8 mL/min, respectively, with a negligible clearance of albumin. HCO‐CVVHD can effectively decrease serum myoglobin in patients with RM because of much higher clearance of myoglobin than CVVH. However, attention should be paid to albumin loss during HCO‐CVVHD.     

An unusual cause of subacute airway obstruction in a hemodialysis patient with brachio‐cephalic arteriovenous fistula: A rare presentation of central venous occlusion

A young lady with an arteriovenous (AV) fistula on hemodialysis was referred for surgical management following a failed endovascular approach to relieve central venous occlusion. She had an obstructed left brachiocephalic vein with a history of numerous central vein catheter placements. Alternative routes for new arteriovenous fistula creation had been exhausted due to previous contralateral upper limb fistula rupture and ligation. To the best of our knowledge, no similar cases of airway obstruction in central venous occlusion occurring in hemodialysis patients with AV fistula have been reported. The importance of identifying the possible emergency red flags in hemodialysis patients with central venous occlusion is important to prevent unwanted consequences.