Artifact Patterns Research Articles

A practical MRI-based reconstruction method for a new endocavitary and interstitial gynaecological template.

PurposeThere are perineal templates for interstitial implants such as MUPIT and Syed applicators. Their limitations are the intracavitary component deficit and the necessity to use computed tomography (CT) for treatment planning since both applicators are non-magnetic resonance imaging (MRI) compatibles. To overcome these problems, a new template named Template Benidorm (TB) has been recently developed. Titanium needles are usually reconstructed based on their own artifacts, mainly in T1-weighted sequence, using the void on the tip as the needle tip position. Nevertheless, patient tissues surrounding the needles present heterogeneities that complicate the accurate identification of these artifact patterns. The purpose of this work is to improve the titanium needle reconstruction uncertainty for the TB case using a simple method based on the free needle lengths and typical MRI pellets markers.Material and methodsThe proposed procedure consists on the inclusion of three small A-vitamin pellets (hyperintense on MRI images) compressed by both applicator plates defining the central plane of the plate's arrangement. The needles used are typically 20 cm in length. For each needle, two points are selected defining the straight line. From such line and the plane equations, the intersection can be obtained, and using the free length (knowing the offset distance), the coordinates of the needle tip can be obtained. The method is applied in both T1W and T2W acquisition sequences. To evaluate the inter-observer variation of the method, three implants of T1W and another three of T2W have been reconstructed by two different medical physicists with experience on these reconstructions.Results and conclusionsThe differences observed in the positioning were significantly smaller than 1 mm in all cases. The presented algorithm also allows the use of only T2W sequence either for contouring or reconstruction purposes. The proposed method is robust and independent of the visibility of the artifact at the tip of the needle.

Artefact expression associated with several cone-beam computed tomographic machines whenimaging root filled teeth.

To evaluate the characteristic artefact patterns associated with teeth root filled with Gutta-percha when scanned with four cone-beam CT devices. Whilst using soft tissue simulation, ten root filled human premolars were placed in empty sockets in a dry human skull. Subsequently, the skull was scanned using 3D Accuitomo 170(®) , WhiteFox(®) , Cranex 3D(®) and Scanora 3D(®) following clinical protocols with the highest resolution and artefact reduction. After proper image registration in OnDemand3D(®) software (Cybermed, Seoul, Korea), each image slice was evaluated by three trained and calibrated dentomaxillofacial radiologists, which scored absence (0) and presence (1) of cupping artefact, hypodense halos and streak artefacts. Kappa test was performed for intra- and interobserver agreement. A moderate to perfect agreement for each observer (intra-observer κ = 0.5-1.0) was found. Agreement between the different observers was moderate to almost perfect for the different artefact patterns (interobserver κ = 0.55-0.9). Cupping artefact was the most prevalent (70%), followed by a hypodense halo (35%) and streak artefacts (16%). The Chi-squared test revealed significantly more streaks in axial slices (P < 0.0001), with some CBCT systems yielding significantly inferior results to others (P < 0.05). The dedicated EndoMode and artefact reduction did not improve the result significantly. The variation of artefact expression was significantly different amongst CBCT machines for root filled teeth. Continuous efforts are needed to improve CBCT reconstruction algorithms, with a specific focus on reducing artefacts induced by dense dental materials, whilst striving for enhanced image quality at low-radiation doses.

Detection of motion artifact patterns in photoplethysmographic signals based on time and period domain analysis

The presence of motion artifacts in photoplethysmographic (PPG) signals is one of the major obstacles in the extraction of reliable cardiovascular parameters in continuous monitoring applications. In the current paper we present an algorithm for motion artifact detection based on the analysis of the variations in the time and the period domain characteristics of the PPG signal. The extracted features are ranked using a normalized mutual information feature selection algorithm and the best features are used in a support vector machine classification model to distinguish between clean and corrupted sections of the PPG signal. The proposed method has been tested in healthy and cardiovascular diseased volunteers, considering 11 different motion artifact sources. The results achieved by the current algorithm (sensitivity—SE: 84.3%, specificity—SP: 91.5% and accuracy—ACC: 88.5%) show that the current methodology is able to identify both corrupted and clean PPG sections with high accuracy in both healthy (ACC: 87.5%) and cardiovascular diseases (ACC: 89.5%) context.

Approaching quantitative Zernike phase contrast in full-field transmission hard X-ray microscopy: Origin and reduction of artifacts

Zernike phase contrast in hard X-ray transmission microscopy provides in-line observation of phase enhanced imaging of weak-absorbing objects. However, the inherent artifacts are the major hurdle to acquire quantitative structural analysis, and may even present misleading information. We explore the origin of these artifacts by frequency analysis in Fourier domain. Subsequently, a simple and flexible method for artifacts reduction well-suited for full-field transmission hard X-ray microscopy based on combination of spectra is proposed. It is demonstrated to yield quantitative local phase maps, with the characteristic artifact patterns reduced.

Early Holocene soil cryoturbation in northeastern USA: Implications for archaeological site formation

The study of buried soil archives in alluvial settings can be used to characterize floodplain and terrace habitats and complement other paleoenvironmental and archaeological archives. This study examines the early Holocene alluvial paleopedology along the Delaware River Valley in the northeastern USA. Chronological and alluvial stratigraphic data show that a widespread loam alluvial paleosol formed from 10.7 to 9.3 ka, herein referred to as the Jennings Lane Pedocomplex (JLP). The JLP at the Jennings Lane locality along the Delaware River, NJ, is a loam to silt loam soil that formed on mixed alluvium and windblown and/or reworked dust, likely sourced from nearby periglacial fines. This finding supports previous interpretations of late Quaternary dust deposition and reworking in the region. Fragic properties (e.g., firm peds with brittle manner of failure and rapid slaking in water) and cryogenic micromorphological features (lenticular pores, stone jacking and shattered grains) present within the JLP suggest cryoturbation. Soil mass-balance modeling suggests that the strain (ɛ) in immobile elements Ti and Zr show a dilation–collapse profile. These data indicate that organic matter and/or dust addition, and freeze-thaw created soil dilation at the JLP paleosurface. Mass-balance additions in Fe, K, and Mg are consistent with illuviated Fe-rich clay coatings present in thin section. The X-ray diffraction results show that these clays are illite, vermiculite, and kaolinite. Paleosol data presented here suggest that the JLP was overprinted by later pedogenic processes during the middle Holocene. τTi,Na shows minimal loss throughout much of the profile. Although rapid thaws may have promoted downward translocation of fines, the cold environment impeded base loss through either minimal release of cations from primary minerals or negligible water flux, as suggested by τTi,Na profiles and gains in τTi,K and τTi,Mg. This silt-rich JLP pedofacies experienced minimal chemical depletion over the course of ∼1200–3500 years. This cold-climate weathering coincides with rapid temperature fluctuations (10.5, 9.3, 8.2 ka) during the early Holocene in northeastern USA. This soil cryoturbation evidence has archaeological implications as well. The cryoturbation in this early Holocene pedocomplex suggests that vertical and lateral artifact redistribution is possible. Archaeologists should use caution when interpreting archaeological stratigraphy and intrasite artifact patterns at mid- to high-latitude archaeological sites.

HIGH-SPEED OPTICAL COHERENCE TOMOGRAPHY AS A RELIABLE ADJUVANT TOOL TO GRADE OCULAR ANTERIOR CHAMBER INFLAMMATION

To evaluate the high-speed anterior segment optical coherence tomography (AS-OCT) grading of the AS inflammation in patients with ocular inflammation. A retrospective consecutive case series study. Patients with clinically visible AS inflammation in at least one eye underwent AS-OCT (Visante; Zeiss Meditec) with three to eight line scans per eye, performed by a trained masked examiner. The images were reviewed for hyperreflective spots, noise, and artifact, and these were correlated to clinical examination. Seventy-eight eyes of 41 patients were imaged. Forty-seven eyes had anterior chamber cells on clinical examination, and 68 had hyperreflective spots visible on AS-OCT. There was a significant correlation (Spearman r = 0.7274) between clinical examination and Visante OCT images. Several patterns of inflammation and artifacts were apparent. The AS-OCT is a promising technique for grading anterior chamber cells. There was a significant correlation between clinical examination and Visante grading.

Lung ultrasound artifacts in a case of P. Jirovecii pneumonia : Coexistence of A and B lines

This article presents lung ultrasound findings in a proven case of P. Jirovecii pneumonia. Ultrasound-based diagnoses of lung pathology are largely based on the patterns of artifacts encountered. The expected finding in an interstitial pneumonia is a B profile (multiple B lines). The original description of B lines stated that they should erase A lines, thus A and B lines where tought as being mutually exclusive. This case is a clear example of interstitial syndrome presenting with both A and B lines on lung ultrasound. It suggests that the absence of A lines should not be a formal criterion for the identification of B-lines.

FREQUENCY AND NUMBER OF ULTRASOUND LUNG ROCKETS (B‐LINES) USING A REGIONALLY BASED LUNG ULTRASOUND EXAMINATION NAMED VET BLUE (VETERINARY BEDSIDE LUNG ULTRASOUND EXAM) IN DOGS WITH RADIOGRAPHICALLY NORMAL LUNG FINDINGS

Lung ultrasound is superior to lung auscultation and supine chest radiography for many respiratory conditions in human patients. Ultrasound diagnoses are based on easily learned patterns of sonographic findings and artifacts in standardized images. By applying the wet lung (ultrasound lung rockets or B-lines, representing interstitial edema) versus dry lung (A-lines with a glide sign) concept many respiratory conditions can be diagnosed or excluded. The ultrasound probe can be used as a visual stethoscope for the evaluation of human lungs because dry artifacts (A-lines with a glide sign) predominate over wet artifacts (ultrasound lung rockets or B-lines). However, the frequency and number of wet lung ultrasound artifacts in dogs with radiographically normal lungs is unknown. Thus, the primary objective was to determine the baseline frequency and number of ultrasound lung rockets in dogs without clinical signs of respiratory disease and with radiographically normal lung findings using an 8-view novel regionally based lung ultrasound examination called Vet BLUE. Frequency of ultrasound lung rockets were statistically compared based on signalment, body condition score, investigator, and reasons for radiography. Ten left-sided heart failure dogs were similarly enrolled. Overall frequency of ultrasound lung rockets was 11% (95% confidence interval, 6-19%) in dogs without respiratory disease versus 100% (95% confidence interval, 74-100%) in those with left-sided heart failure. The low frequency and number of ultrasound lung rockets observed in dogs without respiratory disease and with radiographically normal lungs suggests that Vet BLUE will be clinically useful for the identification of canine respiratory conditions.

The Role of Ultrasonography (US), Doppler US Artifacts and Elastography in the Detection of Foreign Bodies

Purpose: The aim of the study is to characterize the ultrasound and Doppler ultrasound artifact patterns of foreign bodies and to define the role of elastography in their detection. Material and method: Two in-vitro environments including a lamb leg and a lamb stomach coated with ultrasound gel, were prepared. Twenty-seven foreign bodies grouped as metallic, organic and inorganic were evaluated using the US, Doppler US and elastography imaging modalities. The B-mode US, Doppler US and spectral Doppler US images including their composed artifacts and the elastography findings were recorded. Results: US had detected all the foreign bodies located in both in-vitro environments. Clear and dirty shadowing was observed posteriorly to the foreign bodies and varying degrees of reverberation artifacts were present with 24 of the foreign bodies. Among the foreign bodies, 7 had twinkling artifacts, 23 had edge artifacts and 20 had spectral noise. Using power Doppler US, signals were received from the posterior aspect or the edge of 20 foreign bodies. The reverberation artifacts of the foreign bodies became more apparent in the elastography images. Conclusion: Knowledge of sonographic results along with ultrasound and Doppler ultrasound artifacts plays a key role in the detection and visualization of foreign bodies. Elastography further facilitates the diagnosis of the foreign bodies

Ultrasound image enhancement using structure-based filtering.

Ultrasound images are prone to speckle noises. Speckles blur features which are essential for diagnosis and assessment. Thus despeckling is a necessity in ultrasound image processing. Linear filters can suppress speckles, but they smooth out features. Median filter based despeckling algorithms produce better results. However, they may produce artifact patterns in the resulted images and oversmooth nonuniform regions. This paper presents an innovative despeckle procedure for ultrasound images. In the proposed method, the diffusion tensor of intensity is computed at each pixel at first. Then the eigensystem of the diffusion tensor is calculated and employed to detect and classify the underlying structure. Based on the classification result, a feasible filter is selected to suppress speckles and enhance features. Test results show that the proposed despeckle method reduces speckles in uniform areas and enhances tissue boundaries and spots.

Using network expectations to identify multiple exchange systems: A case study from Postclassic Sauce and its hinterland in Veracruz, Mexico

Exchanges of material objects often play a pivotal role in the trajectories of political, social, and economic development for ancient societies, but the study can be challenging because of the complexity of exchange. Multiple forms of exchange co-exist in ancient societies including market exchange and social exchange such as gift-giving. A further complicating factor is that different exchange systems such as redistribution and central place market exchange can result in the same regional spatial patterning of artifacts. Recent innovations in identifying exchange systems use network expectations for spatial, contextual, and distributional information to help distinguish between social exchanges such as gift-giving versus market exchange using household inventories. I introduce a Monte Carlo computer simulation to evaluate network expectations for alternative exchange mechanisms, using a case study of decorated ceramics from 65 residential inventories from the center of Sauce and its hinterland during the Middle Postclassic period (1200–1350 A.D.) in southcentral Veracruz, Mexico. Using these new tools, I identify the coexistence of several exchange systems operating simultaneously. The methods developed here demonstrate the potential of using network expectations to refine existing methods to identify different exchange systems that can be applied to other complex ancient economies.

Detection of artifacts from high energy bursts in neonatal EEG

Detection of non-cerebral activities or artifacts, intermixed within the background EEG, is essential to discard them from subsequent pattern analysis. The problem is much harder in neonatal EEG, where the background EEG contains spikes, waves, and rapid fluctuations in amplitude and frequency. Existing artifact detection methods are mostly limited to detect only a subset of artifacts such as ocular, muscle or power line artifacts. Few methods integrate different modules, each for detection of one specific category of artifact. Furthermore, most of the reference approaches are implemented and tested on adult EEG recordings. Direct application of those methods on neonatal EEG causes performance deterioration, due to greater pattern variation and inherent complexity. A method for detection of a wide range of artifact categories in neonatal EEG is thus required. At the same time, the method should be specific enough to preserve the background EEG information. The current study describes a feature based classification approach to detect both repetitive (generated from ECG, EMG, pulse, respiration, etc.) and transient (generated from eye blinking, eye movement, patient movement, etc.) artifacts. It focuses on artifact detection within high energy burst patterns, instead of detecting artifacts within the complete background EEG with wide pattern variation. The objective is to find true burst patterns, which can later be used to identify the Burst-Suppression (BS) pattern, which is commonly observed during newborn seizure. Such selective artifact detection is proven to be more sensitive to artifacts and specific to bursts, compared to the existing artifact detection approaches applied on the complete background EEG. Several time domain, frequency domain, statistical features, and features generated by wavelet decomposition are analyzed to model the proposed bi-classification between burst and artifact segments. A feature selection method is also applied to select the feature subset producing highest classification accuracy. The suggested feature based classification method is executed using our recorded neonatal EEG dataset, consisting of burst and artifact segments. We obtain 78% sensitivity and 72% specificity as the accuracy measures. The accuracy obtained using the proposed method is found to be about 20% higher than that of the reference approaches. Joint use of the proposed method with our previous work on burst detection outperforms reference methods on simultaneous burst and artifact detection. As the proposed method supports detection of a wide range of artifact patterns, it can be improved to incorporate the detection of artifacts within other seizure patterns and background EEG information as well.

Household and community behavior at Bronze Age Politiko-Troullia, Cyprus

We investigate intrasite patterns of artifacts and floral and faunal data to interpret household and community behavior at the Middle Cypriot (Bronze Age) village of Politiko-Troullia in the foothills of the Troodos Mountains, Cyprus. Floral evidence indicates cultivation of orchard crops (e.g., olive and grape), as well as the persistence of woodlands that provided wood for fuel. Animal management combined herding of domesticated sheep, goat, pig, and cattle with the hunting of Mesopotamian fallow deer. Metallurgical evidence points to the production of utilitarian copper tools in household workshops. Group activities are reflected by the deposition of anthropomorphic figurines, spinning and weaving equipment, and deer bones in an open courtyard setting. In sum, Politiko-Troullia exemplifies a diversified agrarian economy on a distinctly anthropogenic landscape that fostered the development of household and supra-household social differentiation in pre-urban Bronze Age Cyprus.

Investigating absence: Assessing the cumulative effects of casual collecting at a 19th century Bahamian plantation

Recent archaeological work at Prospect Hill, a 19th century plantation in the Bahamas, revealed artifact patterns that are inconsistent with expectations for a plantation site. The quantity and quality of artifacts in residential areas associated with the planter family and the enslaved population were inverted and suggest significant post abandonment changes. The site of Prospect Hill has been a destination for tourists and student groups since the mid-20th century, and the areas of the site most accessible to these visitors are also those with surprisingly low artifact counts. I investigated the possibility that regular visitation involved casual collecting using historical data as well as artifact assemblages from archaeological work at Prospect Hill. My analysis suggests that the archaeological record has been altered significantly through casual, opportunistic collecting, and it offers insights for identifying casual collecting elsewhere.

Beyond Belief

Beyond Belief

Limitations of using micro‐computed tomography to predict bone–implant contact and mechanical fixation

Fixation of metallic implants to bone through osseointegration is important in orthopaedics and dentistry. Model systems for studying this phenomenon would benefit from a non-destructive imaging modality so that mechanical and morphological endpoints can more readily be examined in the same specimens. The purpose of this study was to assess the utility of an automated microcomputed tomography (μCT) program for predicting bone-implant contact (BIC) and mechanical fixation strength in a rat model. Femurs in which 1.5-mm-diameter titanium implants had been in place for 4 weeks were either embedded in polymethylmethacrylate (PMMA) for preparation of 1-mm-thick cross-sectional slabs (16 femurs: 32 slabs) or were used for mechanical implant pull-out testing (n= 18 femurs). All samples were scanned by μCT at 70 kVp with 16 μm voxels and assessed by the manufacturer's software for assessing 'osseointegration volume per total volume' (OV/TV). OV/TV measures bone volume per total volume (BV/TV) in a 3-voxel-thick ring that by default excludes the 3 voxels immediately adjacent to the implant to avoid metal-induced artefacts. The plastic-embedded samples were also analysed by backscatter scanning electron microscopy (bSEM) to provide a direct comparison of OV/TV with a well-accepted technique for BIC. In μCT images in which the implant was directly embedded within PMMA, there was a zone of elevated attenuation (>50% of the attenuation value used to segment bone from marrow) which extended 48 μm away from the implant surface. Comparison of the bSEM and μCT images showed high correlations for BV/TV measurements in areas not affected by metal-induced artefacts. In addition for bSEM images, we found that there were high correlations between peri-implant BV/TV within 12 μm of the implant surface and BIC (correlation coefficients ≥0.8, p < 0.05). OV/TV as measured on μCT images was not significantly correlated with BIC as measured on the corresponding bSEM images. However, OV/TV was significantly, but weakly, correlated with implant pull-out strength (r= 0.401, p= 0.049) and energy to failure (r= 0.435, p= 0.035). Thus, the need for the 48-μm-thick exclusion zone in the OV/TV program to avoid metal-induced artefacts with the scanner used in this study means that it is not possible to make bone measurements sufficiently close to the implant surface to obtain an accurate assessment of BIC. Current generation laboratory-based μCT scanners typically have voxel sizes of 6-8 μm or larger which will still not overcome this limitation. Thus, peri-implant bone measurements at these resolutions should only be used as a guide to predict implant fixation and should not be over-interpreted as a measurement of BIC. Newer generation laboratory-based μCT scanners have several improvements including better spatial resolution and X-ray sources and appear to have less severe metal-induced artefacts, but will need appropriate validation as they become available to researchers. Regardless of the μCT scanner being used, we recommend that detailed validation studies be performed for any study using metal implants because variation in the composition and geometry of the particular implants used may lead to different artefact patterns.

Field study on requirements engineering: Investigation of artefacts, project parameters, and execution strategies

Context Requirements Engineering (RE) is a critical discipline mostly driven by uncertainty, since it is influenced by the customer domain or by the development process model used. Volatile project environments restrict the choice of methods and the decision about which artefacts to produce in RE. Objective We aim to investigate RE processes in successful project environments to discover characteristics and strategies that allow us to elaborate RE tailoring approaches in the future. Method We perform a field study on a set of projects at one company. First, we investigate by content analysis which RE artefacts were produced in each project and to what extent they were produced. Second, we perform qualitative analysis of semi-structured interviews to discover project parameters that relate to the produced artefacts. Third, we use cluster analysis to infer artefact patterns and probable RE execution strategies, which are the responses to specific project parameters. Fourth, we investigate by statistical tests the effort spent in each strategy in relation to the effort spent in change requests to evaluate the efficiency of execution strategies. Results We identified three artefact patterns and corresponding execution strategies. Each strategy covers different project parameters that impact the creation of certain artefacts. The effort analysis shows that the strategies have no significant differences in their effort and efficiency. Conclusions In contrast to our initial assumption that an increased effort in requirements engineering lowers the probability of change requests or project failures in general, our results show no statistically significant difference between the efficiency of the strategies. In addition, it turned out that many parameters considered as the main causes for project failures can be successfully handled. Hence, practitioners can apply the artefact patterns and related project parameters to tailor the RE process according to individual project characteristics.

Comparison of ring artifact removal methods using flat panel detector based CT images

BackgroundRing artifacts are the concentric rings superimposed on the tomographic images often caused by the defective and insufficient calibrated detector elements as well as by the damaged scintillator crystals of the flat panel detector. It may be also generated by objects attenuating X-rays very differently in different projection direction. Ring artifact reduction techniques so far reported in the literature can be broadly classified into two groups. One category of the approaches is based on the sinogram processing also known as the pre-processing techniques and the other category of techniques perform processing on the 2-D reconstructed images, recognized as the post-processing techniques in the literature. The strength and weakness of these categories of approaches are yet to be explored from a common platform.MethodIn this paper, a comparative study of the two categories of ring artifact reduction techniques basically designed for the multi-slice CT instruments is presented from a common platform. For comparison, two representative algorithms from each of the two categories are selected from the published literature. A very recently reported state-of-the-art sinogram domain ring artifact correction method that classifies the ring artifacts according to their strength and then corrects the artifacts using class adaptive correction schemes is also included in this comparative study. The first sinogram domain correction method uses a wavelet based technique to detect the corrupted pixels and then using a simple linear interpolation technique estimates the responses of the bad pixels. The second sinogram based correction method performs all the filtering operations in the transform domain, i.e., in the wavelet and Fourier domain. On the other hand, the two post-processing based correction techniques actually operate on the polar transform domain of the reconstructed CT images. The first method extracts the ring artifact template vector using a homogeneity test and then corrects the CT images by subtracting the artifact template vector from the uncorrected images. The second post-processing based correction technique performs median and mean filtering on the reconstructed images to produce the corrected images.ResultsThe performances of the comparing algorithms have been tested by using both quantitative and perceptual measures. For quantitative analysis, two different numerical performance indices are chosen. On the other hand, different types of artifact patterns, e.g., single/band ring, artifacts from defective and mis-calibrated detector elements, rings in highly structural object and also in hard object, rings from different flat-panel detectors are analyzed to perceptually investigate the strength and weakness of the five methods. An investigation has been also carried out to compare the efficacy of these algorithms in correcting the volume images from a cone beam CT with the parameters determined from one particular slice. Finally, the capability of each correction technique in retaining the image information (e.g., small object at the iso-center) accurately in the corrected CT image has been also tested.ConclusionsThe results show that the performances of the algorithms are limited and none is fully suitable for correcting different types of ring artifacts without introducing processing distortion to the image structure. To achieve the diagnostic quality of the corrected slices a combination of the two approaches (sinogram- and post-processing) can be used. Also the comparing methods are not suitable for correcting the volume images from a cone beam flat-panel detector based CT.

Development and validation of a hybrid simulation technique for cone beam CT: application to an oral imaging system

This paper proposes a hybrid technique to simulate the complete chain of an oral cone beam computed tomography (CBCT) system for the study of both radiation dose and image quality. The model was developed around a 3D Accuitomo 170 unit (J Morita, Japan) with a tube potential range of 60–90 kV. The Monte Carlo technique was adopted to simulate the x-ray generation, filtration and collimation. Exact dimensions of the bow-tie filter were estimated iteratively using experimentally acquired flood images. Non-flat radiation fields for different exposure settings were mediated via ‘phase spaces’. Primary projection images were obtained by ray tracing at discrete energies and were fused according to the two-dimensional energy modulation templates derived from the phase space. Coarse Monte Carlo simulations were performed for scatter projections and the resulting noisy images were smoothed by Richardson–Lucy fitting. Resolution and noise characteristics of the flat panel detector were included using the measured modulation transfer function (MTF) and the noise power spectrum (NPS), respectively. The Monte Carlo dose calculation was calibrated in terms of kerma free-in-air about the isocenter, using an ionization chamber, and was subsequently validated by comparison against the measured air kerma in water at various positions of a cylindrical water phantom. The resulting dose discrepancies were found <10% for most cases. Intensity profiles of the experimentally acquired and simulated projection images of the water phantom showed comparable fractional increase over the common area as changing from a small to a large field of view, suggesting that the scatter was accurately accounted. Image validation was conducted using two small phantoms and the built-in quality assurance protocol of the system. The reconstructed simulated images showed high resemblance on contrast resolution, noise appearance and artifact pattern in comparison to experimentally acquired images, with <5% difference for voxel values of the aluminum and air insert regions and <3% difference for voxel uniformity across the homogeneous PMMA region. The detector simulation by use of the MTF and NPS data exhibited a big influence on noise and the sharpness of the resulting images. The hybrid simulation technique is flexible and has wide applicability to CBCT systems.

Whole lung lavage: a unique model for ultrasound assessment of lung aeration changes

Whole lung lavage (WLL) pathophysiologically represents a human model of controlled lung de-aeration, resembling various pathological conditions encountered in the critically ill. Through one-lung ventilation and progressive alveolar flooding, it mimics, respectively, re-absorption atelectasis formation and lung consolidation. With re-ventilation of the treated lung, PEEP application and diuretics administration, it then creates a model of pulmonary edema and its progressive resolution. No studies have so far described lung aeration changes during WLL with ultrasound: objectives of the study were to describe ultrasound findings during WLL with validated semiotics in the critically ill and to investigate their relation with the lung's state of relative aeration. In seven patients, 12 lung areas/patient were prospectively studied with ultrasound during six procedural steps of WLL. A three-tiered pattern classification was assigned (1, normal/nearly normal; 2, alveolar-interstitial syndrome; 3, alveolar consolidation) consistently with their previously described meaning in terms of relative air content. The distribution was compared throughout different WLL maneuvers as it was for arterial oxygen measurement distribution. During one-lung ventilation and saline flooding, ultrasound findings shifted from artifact patterns (normal/nearly normal and alveolar-interstitial syndrome) to alveolar consolidation. Saline removal, re-ventilation and negative water balance were associated with a gradual return to alveolar-interstitial syndrome, then to a normal/nearly normal pattern. Arterial oxygen tension variations were not always consistent with these changes. In a controlled human model of lung air content variation, the different states of aeration determined by WLL procedure were reliably described with lung ultrasound.