Computed Tomography Imaging Techniques Research Articles

Playing wind instruments as a potential aetiologic cofactor in external cervical resorption: two case reports

To present two cases of external cervical resorption (ECR) on maxillary incisors, in which the primary aetiologic factor is suggested to be pressure trauma by frequently playing wind instruments. The exact aetiological spectrum of ECR is still poorly understood. For resorption to occur, a defect in the cementum layer (trigger) is a likely prerequisite. Whilst the mechanism for continuation (stimulus) is still unclear, knowledge of potential predisposing factors is important in assessing patients at risk. Pressure generated by playing wind instruments could present an aetiological factor in ECR because it affects the cervical region of the root surface. The cases that are presented may confirm this hypothesis and the extent of resorption defects is shown by cone-beam computer tomography (CT) and micro-focus CT imaging techniques.

Three-Dimensional Morphology and Kinematics of the Craniovertebral Junction in Rheumatoid Arthritis

A case-series study. To measure the 3-dimensional (3D) morphology and kinematics of the craniovertebral junction (CVJ) using a 3D computed tomography (CT) model; to reveal abnormal patterns and the relationships between pathology and kinematics. Evaluations using radiography, 2-dimensional (2D) CT and magnetic resonance imaging have limitations because of the complex 3D structure of the CVJ. Twenty-four rheumatoid arthritis patients (21 females, 3 males) with cervical involvement underwent CT scanning of the cervical spine from the basilar process of the occipital bone to the first thoracic vertebra in neutral and flexed positions. The 3D morphology of the occipital condyle, atlas, and axis were classified based on the type of deformity observed. Periodontoid lesions (continuous bony lesions between the atlas and the odontoid process) were also noted. The 3D kinematics in the atlanto-occipital and atlantoaxial joints were evaluated using the volume merge method. Deformities in the atlanto-occipital joints appeared more frequently than those in the atlantoaxial joints. The most common instability pattern was flexural rotation during flexion at the CVJ. The direction of translational motions during flexion was posterior in the atlanto-occipital joint and anterior and caudal in the atlantoaxial joint. The results suggest that bilateral occipital condyle deformation, unilateral and bilateral mass collapse, and periodontoid lesions may affect flexion/extension rotational instability in the atlantoaxial joint. In addition, unilateral occipital condyle deformation and atlantoaxial joint stability may affect sagittal translational instability to the posterior side in the atlanto-occipital joint. The noninvasive 3D CT imaging technique employed here would be useful for predicting the prognosis of patients with rheumatoid deformities at the CVJ.

A changing understanding in the presentation of patients with hepatoportal venous gas: a case report

Often believed to be a poor prognostic sign, hepatoportal venous gas (HPVG) has been associated with massive intra-abdominal sepsis. It is more frequently detected as computed tomography imaging techniques improve. A patient presenting with radiological evidence of HPVG is discussed and the literature reviewed. This study aims to highlight the increasing understanding that HPVG may sometimes follow a more indolent course than previously believed. Patient assessment is the key in selecting those who need urgent laparotomy.

Circuit-Level Design of Human Voice Source

Communication is heavily dependent on ideas expressed through speech. The ideas and tonal qualities during vocal expression give voice an idea about person characteristics and personality. The problem of representing speech events with robust and compact signals that describe the salient features of speech is an important area of speech communication. The Glottal Source is an important component of voice as it can be considered as the excitation signal to the voice apparatus. Nowadays, new techniques of speech processing such as speech recognition and speech synthesis use the glottal closure and opening instants. The pitch synchronous analysis that is used in several area of speech processing often requires robust detection of the instants of glottal closure and opening. Current models of the glottal waves derive their shape from approximate information rather than from exactly measured data. General method concentrate on assessment of the glottis opening using optical, acoustical methods, or on visualization of the larynx position using ultrasound, computer tomography or magnetic resonance imaging techniques. In this work, an experimental integrated circuit of human glottis using MOS is presented by exploiting fluid volume velocity to current, fluid pressure to voltage, and linear and nonlinear mechanical impedances to linear and nonlinear electrical impedances. The glottis modeled as current source includes linear, non-linear impedances to represent laminar and turbulent flow respectively, in vocal tract. The MOS modeling and simulation of glottis were carried out on TSMC 0.18 micrometer technology.

Computed tomography (CT) virtual autopsy and classical autopsy discrepancies: Radiologist's error or a demonstration of post-mortem multi-detector computed tomography (MDCT) limitation?

Modern imaging technologies, such as computed tomography (CT) techniques, represent a great challenge in forensic pathology. The field of forensics has experienced a rapid increase in the use of these new techniques to support investigations on critical cases, as indicated by the implementation of CT scanning by different forensic institutions worldwide. Advances in CT imaging techniques over the past few decades have finally led some authors to propose that virtual autopsy, a radiological method applied to post-mortem analysis, is a reliable alternative to traditional autopsy, at least in certain cases. The authors investigate the occurrence and the causes of errors and mistakes in diagnostic imaging applied to virtual autopsy. A case of suicide by a gunshot wound was submitted to full-body CT scanning before autopsy. We compared the first examination of sectional images with the autopsy findings and found a preliminary misdiagnosis in detecting a peritoneal lesion by gunshot wound that was due to radiologist's error. Then we discuss a new emerging issue related to the risk of diagnostic failure in virtual autopsy due to radiologist's error that is similar to what occurs in clinical radiology practice.

A system for parallel measurement of glottis opening and larynx position

The simultaneous assessment of glottal dynamics and larynx position can be beneficial for the diagnosis of disordered voice or speech production and swallowing. Up to now, methods either concentrate on assessment of the glottis opening using optical, acoustical or electrical (electroglottography, EGG) methods, or on visualisation of the larynx position using ultrasound, computer tomography or magnetic resonance imaging techniques. The method presented here makes use of a time-multiplex measurement approach of space-resolved transfer impedances through the larynx. The fast sequence of measurements allows a quasi simultaneous assessment of both larynx position and EGG signal using up to 32 transmit–receive signal paths. The system assesses the dynamic opening status of the glottis as well as the vertical and back/forward motion of the larynx. Two electrode-arrays are used for the measurement of the electrical transfer impedance through the neck in different directions. From the acquired data the global and individual conductivity is calculated as well as a 2D point spatial representation of the minimum impedance. The position information is shown together with classical EGG signals allowing a synchronous visual assessment of glottal area and larynx position. A first application to singing voice analysis is presented that indicate a high potential of the method for use as a non-invasive tool in the diagnosis of voice, speech, and swallowing disorders.

A three-dimensional medical imaging model for quantitative assessment of proximal tibia vs. anterior iliac crest cancellous bone

The proximal tibia metaphysis is a potential alternative donor site for a sufficient amount of cancellous bone, associated with low morbidity and complication rate. We performed an observational computed tomography imaging study to determine the volume of cancellous bone that can be harvested from the proximal tibia compared to the anterior iliac crest, based on an advanced three-dimensional medical imaging model. Results of this study support the findings that a sufficient amount of cancellous bone can be harvested from the proximal tibia compared to the anterior iliac crest. By using a computed tomography imaging technique, the volume of cancellous bone can be precisely determined. However, this study does not show how much bone is safe to remove before increasing the tibial fracture risk.

CT-measured regional specific volume change reflects regional ventilation in supine sheep

Computer tomography (CT) imaging techniques permit the noninvasive measurement of regional lung function. Regional specific volume change (sVol), determined from the change in lung density over a tidal breath, should correlate with regional ventilation and regional lung expansion measured with other techniques. sVol was validated against xenon (Xe)-CT-specific ventilation (sV) in four anesthetized, intubated, mechanically ventilated sheep. Xe-CT used expiratory gated axial scanning during the washin and washout of 55% Xe. sVol was measured from the tidal changes in tissue density (H, houndsfield units) of lung regions using the relationship sVol = [1,000(Hi - He)]/[He(1,000 + Hi)], where He and Hi are expiratory and inspiratory regional density. Distinct anatomical markings were used to define corresponding lung regions of interest between inspiratory, expiratory, and Xe-CT images, with an average region of interest size of 1.6 +/- 0.7 ml. In addition, sVol was compared with regional volume changes measured directly from the positions of implanted metal markers in an additional animal. A linear relationship between sVol and sV was demonstrated over a wide range of regional sV found in the normal supine lung, with an overall correlation coefficient (R(2)) of 0.66. There was a tight correlation (R(2) = 0.97) between marker-measured volume changes and sVol. Regional sVol, which involves significantly reduced exposure to radiation and Xe gas compared with the Xe-CT method, represents a safe and efficient surrogate for measuring regional ventilation in experimental studies and patients.

Adaptive mean filtering for noise reduction in CT polymer gel dosimetry

X-ray computed tomography (CT) as a method of extracting 3D dose information from irradiated polymer gel dosimeters is showing potential as a practical means to implement gel dosimetry in a radiation therapy clinic. However, the response of CT contrast to dose is weak and noise reduction is critical in order to achieve adequate dose resolutions with this method. Phantom design and CT imaging technique have both been shown to decrease image noise. In addition, image postprocessing using noise reduction filtering techniques have been proposed. This work evaluates in detail the use of the adaptive mean filter for reducing noise in CT gel dosimetry. Filter performance is systematically tested using both synthetic patterns mimicking a range of clinical dose distribution features as well as actual clinical dose distributions. Both low and high signal-to-noise ratio (SNR) situations are examined. For all cases, the effects of filter kernel size and the number of iterations are investigated. Results indicate that adaptive mean filtering is a highly effective tool for noise reduction CT gel dosimetry. The optimum filtering strategy depends on characteristics of the dose distributions and image noise level. For low noise images (SNR approximately 20), the filtered results are excellent and use of adaptive mean filtering is recommended as a standard processing tool. For high noise images (SNR approximately 5) adaptive mean filtering can also produce excellent results, but filtering must be approached with more caution as spatial and dose distortions of the original dose distribution can occur.

Modified lipoproteins as contrast agents for imaging of atherosclerosis

The ability to detect and characterize atherosclerosis with targeted contrast agents may enable initiation of therapy for atherosclerotic lesions prior to becoming symptomatic. Since lipoproteins such as high-density lipoprotein (HDL) and low-density lipoprotein (LDL) play a critical role in the regulation of plaque biology through the transport of lipids into and out of atherosclerotic lesions, modifying HDL and LDL with radioisotopes for nuclear imaging, chelates for magnetic resonance imaging (MRI) or other possible contrast agents for computed tomography imaging techniques may aid in the detection and characterization of atherosclerosis. This review focuses on the literature employing lipoproteins as contrast agents for imaging atherosclerosis and the feasibility of this approach.

Evaluating the aggregate structure in hot-mix asphalt using three-dimensional computer modeling and particle packing simulations

In a hot-mix asphalt (HMA) pavement, the aggregate structure serves as a backbone and is primarily responsible for resisting pavement distresses. A sound aggregate structure implies optimal packing of aggregates providing both particle–particle contact and sufficient void space to fill in asphalt. In this paper, three-dimensional particle packing concepts are applied to the study of aggregate structure in HMA. A sequential deposition packing algorithm was used for packing typical aggregate gradations. The packing fraction and the distribution of particle–particle contacts in the simulated compact were studied. The packing simulation gave satisfactory results when aggregates above a certain minimum size were considered. Regression models were established to estimate the coordination number of any size aggregate in the compact. Such studies, in conjunction with the recent advances in X-ray computed tomography imaging techniques and discrete element modeling (DEM) simulations, have tremendous potential to help develop a deeper understanding of the HMA aggregate structure, develop and optimize the various parameters that describe the aggregate structure, and relate these parameters to the performance of pavements in a scientific way.Key words: packing, aggregate structure, computer simulation, aggregate–aggregate contact, pavement performance.

Differences in the time course of proximal and distal airway response to inhaled histamine studied by synchrotron radiation CT

We studied the kinetics of proximal and distal bronchial response to histamine aerosol in healthy anesthetized and mechanically ventilated rabbits up to 60 min after histamine administration using a novel xenon-enhanced synchrotron radiation computed tomography imaging technique. Individual proximal airway constriction was assessed by measuring the luminal cross-sectional area. Distal airway obstruction was estimated by measuring the ventilated alveolar area after inhaled xenon administration. Respiratory system conductance was assessed continuously. Proximal airway cross-sectional area decreased by 57% of the baseline value by 20 min and recovered gradually but incompletely within 60 min. The ventilated alveolar area decreased immediately after histamine inhalation by 55% of baseline value and recovered rapidly thereafter. The results indicate that the airway reaction to inhaled histamine and the subsequent recovery are significantly slower in proximal than in distal bronchi in healthy rabbit. The findings suggest that physiological reaction mechanisms to inhaled histamine in the airway walls of large and small bronchi are not similar.

Anterior Skull Base Fractures

Anterior skull base trauma evaluation and management has historically been difficult to systematically study secondary to the relative rarity of its occurrence, associated major morbidity and high mortality, and poor radiographic techniques. It has only been recently that improved care has allowed for decreased morbidity and mortality. The advent of computed tomography imaging techniques has led to anatomic characterization and detailed study of injury patterns. This article reviews current techniques for evaluation and management of the associated sinonasal, orbital, and neurologic sequelae of anterior skull base injuries.

Pancreatic and Peripancreatic Diseases Mimicking Primary Pancreatic Neoplasia

A variety of anatomic variants and pathologic conditions in and around the pancreas may simulate primary pancreatic neoplasia at routine abdominal cross-sectional imaging. An ambiguous lesion whose appearance suggests a pancreatic origin requires a broad differential diagnosis that can subsequently be narrowed on the basis of both clinical history and features at optimal computed tomography (CT) and magnetic resonance (MR) imaging. Pancreas-specific multidetector CT and MR imaging techniques with thin collimation, multiplanar and multiphasic scans, and newly introduced curved planar reformation may help avoid potential diagnostic pitfalls. These techniques can help identify and characterize a mass in multiple viewing planes, thereby helping distinguish a true pancreatic neoplasm from peripancreatic adenopathy or from a tumor of the adjacent duodenum or small bowel. They can also help determine the cause of a tumor. It is important that the radiologist be familiar with the wide spectrum of anatomic variants and disease entities that can mimic primary pancreatic neoplasia in order to initiate the appropriate lesion-specific work-up and treatment and avoid unnecessary tests or procedures, including surgery.

Computed tomography for the diagnosis of congenital heart disease in pediatric and adult patients

The development of multi-slice spiral computed tomography (CT) has increased the clinical use of cardiac CT imaging in patients with congenital heart disease. Multi-slice CT has the advantages of fast scan speed; high spatial resolution, enabling the acquisition of isotropic volume data; and simultaneous evaluation of airways and lung parenchyma, thus increasing the ability to answer most clinical questions about structural abnormalities in patients with congenital heart disease. When coupled with electrocardiography-gating, multi-slice spiral CT can be used in functional evaluations, including ventricular wall motion, ventricular ejection fraction, and motion of cardiac valves, as well as enabling the performance of high-quality coronary CT angiography. In this article, we review imaging techniques of multi-slice spiral CT and imaging findings in pediatric and adult patients with various congenital heart diseases.

Strain-induced anisotropy in fabric and hydraulic parameters of oil sand in triaxial compression

Dense locked Athabasca oil sand specimens were tested in drained triaxial compression with lubricated ends at confining pressures of 5–750 kPa. Computer tomography and scanning electron microscopy imaging techniques were used to examine the microstructural features (interlocked structure, grain fabric, and rearrangement inside and outside shear bands) of the intact and sheared specimens. The average hydraulic radii and tortuosity along three principal directions were also measured using thin section imaging and electrical resistivity measurement methods. It was found that changes in fabric and hydraulic parameters of oil sand in triaxial compression are highly inter-related. Intrinsic and induced anisotropies in permeability were observed.Key words: oil sand, fabric, strain induced anisotropy, permeability, tortuosity, dilatancy.

Imaging of acute ischemic brain injury

Purpose of reviewClassical and modern computed tomography imaging techniques, including conventional computed tomography, perfusion-computed tomography and computed tomography-angiography for acute stroke are reviewed.Recent findingsThrombolysis has become an approved therapy for acute stroke. Howev

Imaging of acute ischemic brain injury: the return of computed tomography.

Classical and modern computed tomography imaging techniques, including conventional computed tomography, perfusion-computed tomography and computed tomography-angiography for acute stroke are reviewed. Thrombolysis has become an approved therapy for acute stroke. However, many stroke patients do not benefit from such treatment, since the presently used criteria are very restrictive, notably with respect to the accepted time-window. Even so, a significant rate of intracranial hemorrhage still occurs. Conventional cerebral computed tomography has been proposed as a selection tool for acute stroke patients. Recently, more modern computed tomography techniques, referred to as functional computed tomography or perfusion-computed tomography, have been introduced. Such perfusion-computed tomography techniques are competing favorably with diffusion-weighted/perfusion-weighted magnetic resonance imaging in the delineation of the penumbra. They are more easy to perform, because they are readily available and accessible in emergency settings, and less time-consuming. Furthermore, perfusion-computed tomography combined with computed tomography-angiography affords a comprehensive non-invasive survey of acute stroke patients as early as at the time of their emergency admission, with accurate demonstration of the site of arterial occlusion and its hemodynamic and pathophysiological repercussions for the brain parenchyma. A renewal of computed tomography in the field of stroke has been afforded by the introduction of functional techniques such as perfusion-computed tomography, which provides promising insights into cerebral tissue viability and can be used as a guidance tool for therapy when combined with computed tomography-angiography.

Imaging of acute ischemic brain injury: the return of computed tomography

Purpose of review Classical and modern computed tomography imaging techniques, including conventional computed tomography, perfusion-computed tomography and computed tomography-angiography for acute stroke are reviewed. Recent findings Thrombolysis has become an approved therapy for acute stroke. However, many stroke patients do not benefit from such treatment, since the presently used criteria are very restrictive, notably with respect to the accepted time-window. Even so, a significant rate of intracranial hemorrhage still occurs. Conventional cerebral computed tomography has been proposed as a selection tool for acute stroke patients. Recently, more modern computed tomography techniques, referred to as functional computed tomography or perfusion-computed tomography, have been introduced. Such perfusion-computed tomography techniques are competing favorably with diffusion-weighted/perfusion-weighted magnetic resonance imaging in the delineation of the penumbra. They are more easy to perform, because they are readily available and accessible in emergency settings, and less time-consuming. Furthermore, perfusion-computed tomography combined with computed tomography-angiography affords a comprehensive non-invasive survey of acute stroke patients as early as at the time of their emergency admission, with accurate demonstration of the site of arterial occlusion and its hemodynamic and pathophysiological repercussions for the brain parenchyma. Summary A renewal of computed tomography in the field of stroke has been afforded by the introduction of functional techniques such as perfusion-computed tomography, which provides promising insights into cerebral tissue viability and can be used as a guidance tool for therapy when combined with computed tomography-angiography.

Periodontal probing in comparison to diagnosis by CT-Scan

To compare clinical periodontal probing and the corresponding CT-evaluation of the loss of bone. 639 measurement sites were studied on 95 periodontal sites. The measured length was the distance between the cemento-enamel junction (CEJ) and the pocket base on probing and the bone base of the pocket on the CT-analysis. Additionally, a comparison of the diagnostic potential of both methods regarding the furcation involvement was made. Clinical probing depths showed a mean value of 2.6+/-2.0 mm, while the CT-measurements exhibited a figure of 4.2+/-2.3 mm. In 49.5% of the measured sites, the difference between clinical and CT-measurement was 2mm or higher. The greatest differences between the measured values were found on the buccal and lingual sites (P=0.0004). The narrower the vertical bone defects in the CT (angle in coronal direction), the greater were the differences between the clinical probing depths and the measurements carried out on the CT (P=0.02). Clinically, in 31% of the cases the furcation involvement was underestimated or not identified at all. Computed tomography imaging techniques could be beneficial in the field of periodontal diagnosis. The results underscore the higher accuracy of the CT-technique, compared with clinical probing, while assessing periodontal breakdown and its marked superiority in the diagnosis of furcation areas, compared to the clinical examinations performed.