Biomedical subjects

C Hoeschen

Publications and source records attributed to C Hoeschen.

8 recordsLinked to original sources

PubMed2005

[Comparison of four digital and one conventional radiographic image systems for the chest in a patient study with subsequent system optimization].

PURPOSE: Using a patient study to prove the clinical relevance of a comparison of five different radiographic systems for the chest conducted with an anthropomorphic chest phantom. Depending on the results, it was tested whether the performance of a modern digital system with a transparent imaging plate can be improved by changing the post-processing of the image. METHOD: Chest radiographs of patients were taken with a CsI/aSi-flat panel detector (FDR), transparent imaging plate (tDLR), selenium drum detector (DSR), conventional storage phosphor plate (DLR) and asymmetrical screen-film-system (aFFS), and compared using image criteria scoring (ICS) and visual grading analysis (VGA) for anatomical structures (modified criterions of the EUR 16 260 EN guidelines). After optimizing the post processing, the images of the tDLR-system were evaluated once more in a phantom ROC study and patient VGA study. RESULTS: The flat panel detector-system proved to meet best the anatomical image quality criteria, followed by DSR, tDLR, aFFS and DLR. The modified post processing of the tDLR-images resulted in a significantly better detection of simulated pathological lung-structures, but improved the perceptibility of anatomical structures only slightly. CONCLUSIONS: The results of the patient VGA study and the phantom ROC study are similar and considered valid. The new digital imaging systems with flat panel detector and transparent imaging plate provide the best image quality of the tested radiographic devices for chest imaging, assuming that all system components are attuned and optimized for the type of structure to be detected. Image processing is of primary importance for system optimization.

Humans↗

PubMed2005

Average glandular dose conversion coefficients for segmented breast voxel models.

For 8 voxel models of a compressed breast (4-7 cm thickness and two orientations for each thickness) and 14 radiation qualities commonly used in mammography (HVL 0.28-0.50 mm Al), tissue dose conversion coefficients were calculated for a focus-to-film distance of 60 cm using Monte Carlo methods. The voxel models were segmented from a high-resolution (slice thickness of 1 mm) computed tomography data set of an ablated breast specimen fixated while being compressed. The contents of glandular tissues amounted to 2.6%, and were asymmetrically distributed with regard to the midplane of the model. The calculated tissue dose conversion coefficients were compared with the recent literature values. These earlier tissue dose conversion coefficients were also calculated using Monte Carlo methods and breast models of various thickness, but these consist of homogeneous mixtures of glandular and adipose tissues embedded in 5 mm pure adipose tissue both at the entrance and exit sides. The results show that the new glandular tissue dose conversion coefficients agree well with the literature values for those cases where the glandular tissue is predominantly concentrated in the upper part of the model. In the opposite case, they were lower by up to 40%. These findings reveal a basic problem in patient dosimetry for mammography: glandular dose is not only governed by the average breast composition, which could be derived from the breast thickness, but also by the local distribution of glandular tissue within the breast, which is not known.

Air↗

PubMed2005

RADIUS--closing the circle on the assessment of imaging performance.

The RADIUS (Radiological Imaging Unification Strategy) project addresses the assessment of image quality in terms of both physical and clinically relevant measures. The aim is to unify our understanding of both types of measure as well as the numerous underlying factors that play a key role in the assessments of imaging performance. In this way it is expected to provide a solid basis for the improvement in radiological safety management, where not only radiation risks are considered but also diagnostic risks of incorrect clinical outcomes (i.e. false positive/false negative). The project has applied a variety of relevant experimental and theoretical methods to this problem, which is generic to medical imaging as a whole. Digital radiography of the chest and the breast has been employed as the clinical imaging domain vehicles for the study. The project addressed the problem from the following directions: role and relevance of pathology, human observer studies including receiver operating characteristics, image quality criteria analysis, structural noise analysis, physical measurements on clinical images, physical measurements on imaging system, modelling of imaging system, modelling of visual processes, modelling of doses delivered and IT-based scientific support strategies. This paper presents an overview of the main outcomes from this project and highlights how the research outcomes actually apply to the real world. In particular, attention will be focused on new and original findings and methods and techniques that have been developed within the framework of the project. The relevance of the project's outcomes to future European research will also be presented.

Algorithms↗

PubMed2005

Assessment and optimisation of the image quality of chest-radiography systems.

A complete evaluation strategy had been developed for thoracic X-ray imaging. It has been validated by investigating five chest-radiography systems, two of these systems after optimising image processing. The systems were a screen-film combination, a selenium drum, a conventional and a transparent imaging plate and a Cs/I-based flat panel detector (the two latter ones have been optimised using different post processing). At first all detectors have been characterised using physical parameters like DQE and MTF. After that all systems have been evaluated by human observer studies using anatomy in clinical images (VGA, ICS) and added pathological structures in thoracic phantom images (ROC). The ranking of the image quality of the systems was nearly the same in all studies. There was a similar assessment of main image quality parameters like spatial resolution, dynamic range and MTF. The modification of image post processing changed the visibility of pathological structures more than the visualisation of the anatomical criteria. The assessment of the clinical image quality has to be done for anatomical structures, and the recognition of pathological structures has to be evaluated.

Cesium↗

PubMed2003

[Chest radiography: ROC phantom study of four different digital systems and one conventional radiographic system].

PURPOSE: To compare the diagnostic quality of five different radiographic systems used in chest radiography for visualization of differently configured, clinically relevant pathologic pulmonary structures. MATERIALS AND METHODS: Four digital detector systems using as detection unit a CsI/aSi-based flat panel detector, a transparent imaging plate, a selenium detector and a conventional storage phosphor plate were analyzed for this study, as well as an asymmetrical film-screen system. The analyzed imaging material consisted of radiographs of an anthropomorphic chest-phantom with superimposed simulated pulmonary structures. The images were evaluated for different pathologic structures by a newly developed multiple structure ROC (ms-ROC). RESULTS: The performance of each system was found to have a strong structure-related variability. The flat panel detector system had the best overall performance. The theoretical advantage of the 4k-matrix of the transparent imaging plate over the 3k-matrix of the flat panel detector was only confirmed for reticular structures. CONCLUSIONS: In addition to comparing the image quality of the different systems, this study shows that the performance of a radiographic system depends on the structure to be analyzed. The modified ROC (ms-ROC) provides valid results with less effort.

Humans↗

PubMed2002

[First clinical experience with a full-size, flat-panel detector for imaging the peripheral skeleton - Part II: Post-processing with a newly developed adaptive autowindow algorithm].

PURPOSE: of the second part of the investigation was the evaluation of a newly developed adaptive autowindow algorithm in comparison to the system processing radiographs of the wrist and ankle to further optimize the image quality with softcopy reading. MATERIAL AND METHODS: All 120 radiographs of the wrist and all 100 radiographs of the ankle used in the 1st part of this paper were processed with the adaptive autowindow algorithm. The evaluation was again performed by 5 radiologists with softcopy reading. For the data analysis a variation of the Visual Grading Analysis (VGA) was used. RESULTS: Up to 19 % of the wrist radiographs and 2 % of the ankle radiographs processed with the system software had to be processed manually afterwards to get acceptable results. By the application of the adaptive autowindow algorithm a manual post-processing was no longer necessary. Highly significant (p less-than-or-equal 0.001) differences for all criteria to be evaluated were found for the wrist radiographs and in the case of the ankle radiographs for the bone contrast, the contrast in soft-tissue regions, the fine details in the bone and the artifacts, the adaptive autowindow algorithm performed always better than the system software. CONCLUSION: Using half of the exposition dose on a flat-panel detector, an optimized post-processing leads to comparable or better results compared to the conventional film-screen-system concerning the image quality.

Algorithms↗

PubMed2002

[Optimized image processing with modified preprocessing of image data sets of a transparent imaging plate by way of the lateral view of the cervical spine].

PURPOSE: To improve the diagnostic quality of lateral radiographs of the cervical spine by pre-processing the image data sets produced by a transparent imaging plate with both-side reading and to evaluate any possible impact on minimizing the number of additional radiographs and supplementary investigations. MATERIAL AND METHODS: One hundred lateral digital radiographs of the cervical spine were processed with two different methods: processing of each data set using the system-imminent parameters and using the manual mode. The difference between the two types of processing is the level of the latitude value. Hard copies of the processed images were judged by five radiologists and three neurosurgeons. The evaluation applied the image criteria score (ICS) without conventional reference images. RESULTS: In 99 % of the lateral radiographs of the cervical spine, all vertebral bodies could be completed delineated using the manual mode, but only 76 % oft the images processed by the system-imminent parameters showed all vertebral bodies. Thus, the manual mode enabled the evaluation of up to two additional more caudal vertebral bodies. The manual mode processing was significantly better concerning object size and processing artifacts. This optimized image processing and the resultant minimization of supplementary investigations was calculated to correspond to a theoretical dose reduction of about 50 %. CONCLUSION: The introduction of optimized organ programs for the upper and lower cervical spine based on the 12-bit data of the images should improve the evaluation of the lateral radiograph of the cervical spine without reducing the latitude value.

Cervical Vertebrae↗

PubMed2001

[First clinical experience with a full-size, flat-panel detector for imaging the peripheral skeletal system].

PURPOSE: This investigation was intended to show that exposures of the peripheral skeleton system can be done with half of the dose used for conventional screen-film systems with a full-size CsI/a-Si flat panel detector. MATERIAL AN METHODS: 120 exposures of the wrist and 100 exposures of the ankle have been made on a full-size flat panel detector system (43 x 43 cm). The patient dose has been reduced by a factor of two compared to conventional images. Five radiologists evaluated every image as a softcopy and a hardcopy image. For the evaluation, a variation of the Visual Grading Analysis (VGA) without reference images was used. For the determination of the patient entrance dose, measurement of a phantom were performed. RESULTS: A dose reduction of about 50 % is possible with the same or even better image quality in routine diagnostics. Only 3 % of the ankle and approx. 21 % of the wrist exposures required a postprocessing. Exposures with implants did not show any artifacts and some of the those achieved better evaluation results compared with exposures without implants. CONCLUSION: A halving of the patient dose is possible with acceptable results for the image quality. The effect of an improved image processing remains to be evaluated. The patient entrance dose is suitable for an evaluation of a radiographic detector and especially for a dose-referred comparison of digital X-ray units.

Ankle Joint↗