Statistical iterative reconstruction for streak artefact reduction when using multidetector CT to image the dento-alveolar structures

OBJECTIVES

When metallic prosthetic appliances and dental fillings exist in the oral cavity, the appearance of metal-induced streak artefacts is not avoidable in CT images. The aim of this study was to develop a method for artefact reduction using the statistical reconstruction on multidetector row CT images.

METHODS

Adjacent CT images often depict similar anatomical structures. Therefore, reconstructed images with weak artefacts were attempted using projection data of an artefact-free image in a neighbouring thin slice. Images with moderate and strong artefacts were continuously processed in sequence by successive iterative restoration where the projection data was generated from the adjacent reconstructed slice. First, the basic maximum likelihood-expectation maximization algorithm was applied. Next, the ordered subset-expectation maximization algorithm was examined. Alternatively, a small region of interest setting was designated. Finally, the general purpose graphic processing unit machine was applied in both situations.

RESULTS

The algorithms reduced the metal-induced streak artefacts on multidetector row CT images when the sequential processing method was applied. The ordered subset-expectation maximization and small region of interest reduced the processing duration without apparent detriments. A general-purpose graphic processing unit realized the high performance.

CONCLUSIONS

A statistical reconstruction method was applied for the streak artefact reduction. The alternative algorithms applied were effective. Both software and hardware tools, such as ordered subset-expectation maximization, small region of interest and general-purpose graphic processing unit achieved fast artefact correction.

Non-uptake of highly active antiretroviral therapy among patients with a CD4 count < 350 cells/μL in the UK

OBJECTIVES

Current British HIV Association (BHIVA) guidelines recommend that all patients with a CD4 count <350 cells/μL are offered highly active antiretroviral therapy (HAART). We identified risk factors for delayed initiation of HAART following a CD4 count <350 cells/μL.

METHODS

All adults under follow-up in 2008 who had a first confirmed CD4 count <350 cells/μL from 2004 to 2008, who had not initiated treatment and who had >6 months of follow-up were included in the study. Characteristics at the time of the low CD4 cell count and over follow-up were compared to identify factors associated with delayed HAART uptake. Analyses used proportional hazards regression with fixed (sex/risk group, age, ethnicity, AIDS, baseline CD4 cell count and calendar year) and time-updated (frequency of CD4 cell count measurement, proportion of CD4 counts <350 cells/μL, latest CD4 cell count, CD4 percentage and viral load) covariates.

RESULTS

Of 4871 patients with a confirmed low CD4 cell count, 436 (8.9%) remained untreated. In multivariable analyses, those starting HAART were older [adjusted relative hazard (aRH)/10  years 1.15], were more likely to be female heterosexual (aRH 1.13), were more likely to have had AIDS (aRH 1.14), had a greater number of CD4 measurements < 350 cells/μL (aRH/additional count 1.18), had a lower CD4 count over follow-up (aRH/50 cells/μL higher 0.57), had a lower CD4 percentage (aRH/5% higher 0.90) and had a higher viral load (aRH/log(10) HIV-1 RNA copies/ml higher 1.06). Injecting drug users (aRH 0.53), women infected with HIV via nonsexual or injecting drug use routes (aRH 0.75) and those of unknown ethnicity (aRH 0.69) were less likely to commence HAART.

CONCLUSION

A substantial minority of patients with a CD4 count < 350 cells/μL remain untreated despite its indication.

Do we need real-time MRI for diagnosis of temporomandibular joint disorders?

INTRODUCTION

Magnetic resonance imaging (MRI) has been approved as an appropriate radiological modality for temporomandibular joint (TMJ) diagnosis, whereas the results of international multicenter studies impressively show the limitations of static three-dimensional MRI. The state of the art for dynamic imaging of the TMJ in real-time are TrueFISP sequences in one sagittal plane. In order to support the diagnostics, a computer-assisted visualization procedure has been developed by the authors for both the static and dynamic MRI.

METHODS

A number of validated sequences are available for the static 3D-MRI within the clinical routine. For dynamic MRI in real-time, True-FISP sequences in one sagittal plane with a slice thickness of 5-10 mm and 1.3 mm x 1.3 mm spatial resolution were applied. Both the dynamic and static MRI datasets are animated and visualized using the computer-assisted procedure.

RESULTS

The computer-assisted procedure reliably supported the clinical diagnosis, especially the visibility of the articular disc was enhanced. On the basis of the static MRI, a 60-year-old patient was diagnosed with anterior disc displacement without reduction. In contrast, by the dynamic MRI, it was recognized how the articular disc was firstly somehow stretched and flattened before the mandibular condyle again glided under the disc, thus resulting in an anterior disc displacement with reduction.

CONCLUSION

These results endorse the relevance of real-time diagnosis for the TMJ. The computer-assisted visualization has been approved as a reliable help for clinical diagnosis.

Acute seronegative polyarthritis associated with lymphogranuloma venereum infection in a patient with prevalent HIV infection

A 44-year-old man who has sex with men presented with a three-month asymmetrical polyarthropathy. He had a positive HIV-1 antibody test consistent with infection acquired more than six months previously. Lymphogranuloma venereum (LGV)-associated DNA was detected from a rectal swab. Following successful treatment for LGV his arthritis resolved completely. Infection with HIV-1 has been hypothesized to cause reactive arthritis but this has been disputed. The most likely diagnosis in this patient was sexually acquired reactive arthritis secondary to LGV infection. As LGV can be asymptomatic and treatment differs from that of the other serovars, screening should be considered in all men who have sex with men (MSM) presenting with acute arthritis, particularly if they are HIV infected.

Computer-assisted pre- and postoperative evaluation of surgically assisted rapid maxillary expansion

OBJECTIVE

Computer-assisted methods were used to evaluate different variants of surgically assisted rapid maxillary expansion (SARME) in terms of bone repositioning, new bone formation in the osteotomy gap, and bone quality before and after surgery.

MATERIALS AND METHODS

Twenty-nine patients (18 male, 11 female) with a mean age of 29 years (16 to 44 years) were included in the study. Surgically assisted rapid maxillary expansion with Le Fort I osteotomy was performed in all patients studied. High-resolution computed tomography (CT) was carried out directly before and 6 to 8 weeks after surgery. After registration of the preoperative CT data on the postoperative data, 3D models were constructed and superimposed. New bone formation in the osteotomy gap was visualized by means of a visualization procedure developed specifically for this purpose. Bone quality was analyzed by dividing the models into different anatomical segments. A qualitative comparison of the data was accomplished using a direct volume rendering procedure with a special transfer function. A quantitative comparison was carried out based on the pre- and postoperative histograms of each region.

RESULTS

Maxillary widening was confirmed in all patients by computer-assisted analysis. Four patients exhibited significant maxillary asymmetry after surgery. New bone formation within the osteotomy gap was irregular along the osteotomy lines but often symmetrical on both sides. The more symmetrical the osteotomy, the more symmetrical the new bone formation proved to be. In all but two cases, the postoperative qualitative and quantitative analyses showed a significant decrease in Hounsfield units, particularly in the vestibular bone.

CONCLUSION

The differences in new bone formation in the osteotomy gap suggest that the type of surgical technique and distractor used influence the outcome. Our results indicate that SAME results in a decrease in bone quality, particularly in the vestibular bone. Computer-assisted analysis clearly results in an information gain.

It's not all swine flu...are we missing opportunities to diagnose primary HIV infection in patients with flu symptoms?

The advantages of diagnosis of primary HIV infection (PHI) for the individual and public health are well documented. However, symptoms of HIV seroconversion are often not recognized by health-care professionals. Also, symptomatic patients themselves often do not present to health-care services. With the emergence of H1N1 infection, many patients with flu-like symptoms are seeking medical advice. Currently in the UK, the management of H1N1 is in the treatment phase, that is, patients are diagnosed and treated for H1N1 influenza based on clinical observation rather than laboratory testing. Symptoms of H1N1 infection are often similar to those of PHI. We present two cases of men who have sex with men from Brighton, UK presenting to general practice and accident and emergency with flu-like symptoms. Both were initially diagnosed on clinical grounds with H1N1 infection and treated empirically with antivirals but were later confirmed to, in fact, have symptomatic PHI. It is important in high-risk patients with flu symptoms attributed to swine flu infection, that PHI is also considered and excluded.

Finite element simulation of the human mandible: the role of (natural) teeth

INTRODUCTION

Individual bone quality depends on genetic, biological, and mechanical influencing factors, where the latter is accessible via Finite Element Simulation. This work is part of an interdisciplinary research project with the purpose of stepwise refinement towards anatomical reality. This approach opened the door for many interrelated applications such as atrophy of the jaw bone, periodontology, implantology, or TMJ disorders. This lecture is dedicated to the influence of dental anatomy on mandibular biomechanics.

MATERIALS AND METHODS

In general, biomechanical simulation requires reconstruction of the individual anatomy, implementation of the inhomogeneous and anisotropic material law of bone, and realization of the load case due to tooth, muscle and joint forces. The simulation chain ranges from image processing of CT data up to specifically adapted post-processing of the simulation results. In spite of ongoing research, there is still a fundamental difference of dental implants compared to natural teeth: the periodontal ligament (PDL) present at the interface between teeth and mandibular corpus. Due to its thickness of about 0.2 mm, the PDL was introduced to the simulation model by a special semiautomatic procedure.

RESULTS

Simulations "with and without PDL" proved remarkable force absorption due to the PDL, as well as qualitative changes of the stress/strain profiles of the alveolar ridge. Concerning the simulation without PDL, the observed high compressive strains at the adjacent bone were in agreement with regions of frequent implant failure.

CONCLUSION

The PDL is essential for the structural behavior of the human mandible. Based on the mechanical adaptation of bone, the comparison of the simulation with and without PDL provided special insight to the changes due to dental implants, in particular implant loss and bone resorption. Finally, the simulation will serve as a virtual platform for further evaluation (a) of implant design (b) of implant placement.

Mandibular finite element simulation as a tool for trauma surgery

PURPOSE

Despite remarkable progress within the last decade, the treatment of mandibular fractures is still a highly discussed topic in oral and cranio-maxillofacial surgery. The possible traumatologic scenarios are characterized by high variability. A current project is focused on "resimulation" of traumatologic cases given by clinical radiographs by means of finite element method.

METHODS

The applied finite element model of the mandible is very refined, providing detailed dental anatomy especially of the periodontal ligament. The mandible was modelled as inhomogeneous and anisotropic. The temporomandibular joints were realized as simplified joint capsules, wherein the mandibular condyles are freely mobile with certain limitations. The user has the choice of 5 regions on the mandibular surface where the virtual injury can be inflicted. Power and direction of the impact force vector can be set at will. The masticatoy system including the digastrics and the mylohyoid muscles can be activated.

RESULTS

The situations given by radiographs could be "reproduced" by a simulation scenario characterized by high compressive strain at the location of fractures. If masticatory muscles were activated and teeth clenched, the stress/strain profiles were qualitatively changed.

DISCUSSION

The approach may be of benefit for optimized behavior with regard to certain sports or vocations. For forensic analysis, the method will contribute by elimination of scenarios not matching the given fracture locations. Nevertheless, the immediate purpose of our approach is a better understanding of the injured organ's condition. Fractures of bone as an adaptive biological tissue differ fundamentally from mechanical failure in engineering. Many of our trauma simulations showed elevated stress/strain around the fracture, leading to the suggestion of weakened bone there. This finding was confirmed by surgical observation.

An approach for three-dimensional visualization using high-resolution MRI of the temporomandibular joint

OBJECTIVES

To visualize the temporomandibular joint (TMJ) and the surrounding tissues in detail utilizing high-resolution MR images for the diagnosis of soft- and hard-tissue abnormalities. Clinically routine MR slices are processed by tissue segmentation and three-dimensional (3D) reconstruction and viewed with visualization software.

MATERIALS AND METHODS

A 1.5 T MRI system was used. The double-echo procedure for taking oblique sagittal images was applied to obtain both proton density-weighted (PDW) and T2 weighted (T2W) images simultaneously, with separate examinations in both open and closed mouth positions. Diagnosis of the abnormality in the placement and morphology of articular discs and the joint effusion status is usually performed using multiple MRI slices. Clinically routine continuous MR slices were processed by segmentation, reconstruction and visualization algorithms, and the mandibular condyle, fossa, articular disc and other intra-articular tissues were visualized on the 3D and two-dimensional (2D)-3D fusion images.

RESULTS

In a clinical case, the anterior disc displacement without reduction, with mouth open and closed, was clearly depicted in the 3D images. Also 2D-3D superposed images with changeable tissue transparency successfully depicted the stereoscopic TMJ morphology in three dimensions.

DISCUSSION AND CONCLUSION

High-resolution PDW- and T2W MR images could be processed by tissue segmentation and 3D-reconstruction procedures, and the resultant images showed the anatomical details in an easily recognizable way. By the simultaneous visualization of both bony surfaces and soft tissues, disc displacement and deformity can be recognized in a 3D context. The additional superposition of the 3D visualization with the original 2D MR slices allows for a combination with conventional diagnostics.

Consideration of anisotropic elasticity minimizes volumetric rather than shear deformation in human mandible

This article is focused on the role of anisotropic elasticity in the simulation of the load distribution in a human mandible, due to a lateral bite on the leftmost premolar. Based on experimental evidence, orthotropy of the elastic properties of the bone tissue has been adopted. The trajectories of anisotropic elasticity are reconstructed from (i) the organ's geometry and (ii) from coherent structures which can be recognized from the spatial distribution of the grey values coming from computer tomography (CT). A sensitivity analysis comprising various three-dimensional (3D) finite element (FE) simulations reveals the relevance of elastic anisotropy for the load carrying behavior of a human mandible: comparison of the load distributions in isotropic and anisotropic simulations indicates that anisotropy seems to "spare" the mandible from loading. Moreover, a maximum degree of anisotropy leads to kind of load minimization of the mandible, expressed by a minimum of different norms of local volumetric strain, evaluated throughout the organ. The observed optimization with respect to volumetric rather than shear strain seems to confirm the frequently emphazised role of volumetric-strain-induced fluid flow for the stimulation of cellular activity.

[Stress analysis of the human mandible in standard trauma situations with numerical simulation]

For the stress analysis of the human mandible a flexible simulation concept basing on finite element-method has been developed. One of the main issues is the prediction of fractures as a consequence of known forces as well as the forensic reconstruction of the traumatologic situation. At first, the individual geometry was reconstructed by 3D-CT-Scans. To reduce the simulation efforts, for the time being the anisotropic structural mechanics of the jaw bone was neglected in favour of an homogeneous and isotropic material law. Assuming the Von-Mises-Stress as a failure indicator the results of the simulations were in good agreement with typical traumatologic situations. For further validation of the model, a real failure case, shown on a radiograph of a injured human mandible with three fractures, was simulated and, by this, the real incident was reconstructed. Reasonable planned extensions of the actual simulation concept have the regard on the nerve channel, the temporomandibular joint's function, the paradontal apparatus and the individual mechanical properties of the bone.

[Numerical simulation (FEM) of the human mandible: validation of the function of the masticatory muscles]

The article describes part of a research project aiming to develop a new modular software tool for the individual dynamic numerical simulation of the human mandible using the finite element method (FEM). Its planned use in the clinical setting makes it very important to validate the results of the simulations. Here, the function of the masticatory muscles is to be tested. On the basis of biomechanical data from the literature, standard movements, such as closing the mouth, forward movement, lateral movement or backward movement, were dynamically simulated. Apart from muscle activity, the movements of the mandible are defined by the temporomandibular joint. At present, translating the condylar dynamics to the simulation still poses problems. For this reason, therefore, simulations of the two extreme cases "fixed" and "force-free" condyles are compared. While in the case of fixed condyles, some of the movements could be reproduced either not at all or only weakly, in the case of force-free condyles, all standard movements were reproduced qualitatively, albeit without the guiding effect of the joint capsule or the articular disc.

[A modular software concept for individual numerical simulation (FEM) of the human mandible]

A new modular software concept for individual numerical simulation of the human mandible using the finite element method (FEM) is presented. The main task is an individual analysis of regional stress and stress-compatibility on the basis of computed tomographic data in individual patients. Simulation should, however, also be possible in parallel with biomechanical experiments, or for further research projects. For this purpose, rapid and uncomplicated generation of the FEM model, easy modification of input data, and short computation times are required. Practical use in the clinical setting makes appreciable additional demands on the individual software components.

HIV roundtable. Strategies to enhance professional awareness and involvement. Part II

Despite extensive public attention to the social and medical problems associated with HIV infection and AIDS, many clinicians remain largely uninvolved in public health and patient counseling programs aimed at preventing infection and getting patients into treatment. Suggestions to enhance professional involvement include improved schooling and continuing medical education; increased liaison and exchange of information among the various groups working with AIDS patients and at-risk populations; and programs to help clinicians confront their own feelings and concerns relating to AIDS.

HIV roundtable. Strategies to enhance professional awareness and involvement, Part I

Despite extensive public attention to the social and medical problems associated with HIV infection and AIDS, many clinicians remain largely uninvolved in public health and patient counseling programs aimed at preventing infection and getting patients into treatment. Suggestions to enhance professional involvement include improved schooling and continuing medical education; increased liaison and exchange of information among the various groups working with AIDS patients and at-risk populations; and programs to help clinicians confront their own feelings and concerns relating to AIDS.

Urinary retention in the course of neuroleptic therapy with haloperidol

A case history was presented of a 49-year-old female patient, who had developed paranoid-hallucinatory schizophrenia for the first time and suffered from an acute functional bladder obstruction while receiving haloperidol. Thorough urological examination showed no pathologic findings except for a medium-grade urinary tract infection. No beneficial effects were obtained after application of parasympathicomimetic substances (carbachol, distigminebromide). After discontinuation of haloperidol therapy normal bladder function returned. The question as to the basic causative pharmacologic mechanism remains unanswered but the hypothesis that bladder dysfunction is due solely to the anticholinergic side-effects of haloperidol merits further critical elucidation and research.

Local recurrences in patients with breast cancer at the North Carolina Memorial Hospital (1970-1982)

A study of predictive factors for locoregional recurrences after curative surgery for breast cancer was undertaken. Specifically, the authors wished to determine whether such recurrences correlated with either hormonal receptor status or a delay between the initial biopsy and the definitive surgery. A retrospective chart review was done on all women with breast cancer who had surgery for cure between 1970 and 1982. Factors analyzed included, among others, size of the tumor, clinical and pathologic status of the axilla, estrogen and progesterone receptors status, and delay between biopsy and definitive surgery. There were 404 patients studied. Pathologic axillary nodal status was the most important predictor of locoregional recurrence, with failures in 36 of 188 (19%) node-positive but only 9 of 216 (4%) node-negative patients (P = 0.0001). In node-positive patients, tumor size was a predictor of local recurrence, with failure in only 4 of 51 (8%) of tumors less than 2 cm, but in 14 of 44 (32%) of tumors greater than 6 cm (P = 0.004). Progesterone receptor (PR) status correlated with locoregional recurrence, but estrogen receptor status did not. In node-positive women, there were 4 of 14 PR-negative but 0 of 15 PR-positive local failures (P = 0.017); this result has not been previously reported. The presence of palpable axillary disease was also found to be a predictor of local recurrence. Finally, no increase in locoregional recurrence could be attributed to the delay between biopsy and definitive surgery. Two new predictors for locoregional recurrence in breast cancer, not previously emphasized, are PR and clinical axillary status. Should these findings be substantiated, patients at high risk for locoregional recurrence could then be more readily identified.