Towards a full-reference, information-theoretic quality assessment method for X-ray images

This work aims at defining an information-theoretic quality assessment technique for cardiovascular X-ray images, using a full-reference scheme (relying on averaging a sequence to obtain a noiseless reference). With the growth of advanced signal processing in medical imaging, such an approach will enable objective comparisons of the quality of processed images. A concept for describing the quality of an image is to express it in terms of its information capacity. Shannon has derived this capacity for noisy channel coding. However, for X-ray images, the noise is signal-dependent and non-additive, so that Shannon's theorem is not directly applicable. To overcome this complication, we exploit the fact that any invertible mapping on a signal does not change its information content. We show that it is possible to transform the images in such a way that the Shannon theorem can be applied. A general method for calculating such a transformation is used, given a known relation between signal mean and noise standard deviation. After making the noise signal-independent, it is possible to assess the information content of an image and to calculate an overall quality metric (e.g. information capacity) which includes the effects of sharpness, contrast and noise. We have applied this method on phantom images under different acquisition conditions and computed the information capacity for those images. We aim to show that the results of this assessment are consistent with variations in noise, contrast and sharpness, introduced by system settings and image processing

Image quality analysis of vibration effects In C-arm-flat panel X-ray imaging

The motion of C-arm scanning X-ray systems may result in vibrations of the imaging sub-system. In this paper, we connect C-arm system vibrations to Image Quality (IQ) deterioration for 2D angiography and 3D cone beam X-ray imaging, using large Flat Panel detectors. Vibrations will affect the projected image sharpness and the projected image position. The former will appear as blur and the latter as image shift for the 2D projection radiography process. If this phenomenon is not corrected in the post processing (pixel shift), it will manifest as subtraction registration artifacts. We will model and verify the effect of vibrations in 2D subtracted and non-subtracted flat panel imaging. Two effects on 3D IQ are modeled: (1) vibrations during an actual acquisition run inducing movement blur and (2) C-arm movement calibration errors in the iso-center giving remnant blur. The model establishes a relation between vibration amplitudes and image quality for dominant system Eigen-frequencies. The validity and accuracy of the model for 2D and 3D imaging modes is supported and demonstrated by experiments and even provides sufficient quality for defining image quality requirements

Innovations in 3D interventional X-ray imaging

Minimal invasive interventions allow the treatment of lesions without the strain of full open surgery. Such image guided interventions and therapies fully rely on the guidance and navigation based on real-time peri-interventional imaging equipment, such as interventional X-ray and ultrasound. Since these imaging modalities are the ‘eyes’ of the treating physician, the associated image quality and imaging features are essential. The addition and further development of 3D imaging capabilities in recent years has broadened the possibilities and capabilities of such procedures, and enabled minimal invasive treatment that could only be performed by open surgery in the past. In this chapter we describe several recent innovations in the area of 3D interventional X-ray imaging in the areas of image quality, 3D model-based catheter reconstruction, multi-modal image fusion, and stereoscopic visualizations

New insights on the formation of colloidal whey protein particles

This paper describes the formation and properties of whey protein particle suspensions having different particle sizes and different abilities to form S–S bridges. Simple shear flow was used to control the protein particles size. The ability to form S–S bridges was steered by blocking the reactive thiol groups of the whey proteins with N-ethylmaleimide. Microscopy and light scattering showed that simple shear flow applied during the formation of whey protein particles give irregularly shaped particles. Especially small particles aggregated into particle clusters. Microscopy and rheological measurements (strain and shear rate sweeps) showed that the protein particle clustering was favoured by the ability of the protein to form S–S bridges and to a lesser extend by a smaller particle size. From the study, it can be concluded that the formation of S–S bridges has no effect on the formation process of protein particles, but S–S bridges are important for the ability of the whey protein particles to form particle cluster

An information-theoretic quality assessment approach for X-ray images

In this work, Shannon's formulation of the information capacity of a communication channel is considered as a framework for the quantification of image quality. We describe a method to apply Shannon's noisy channel coding theorem on radiographic images, which exhibit signal-dependent noise. Results of a number of experiments on real X-ray images are presented, showing the correlation of the proposed method with classical image quality metrics from Linear Systems Theory

New insights on the formation of colloidal whey protein particles

This paper describes the formation and properties of whey protein particle suspensions having different particle sizes and different abilities to form S–S bridges. Simple shear flow was used to control the protein particles size. The ability to form S–S bridges was steered by blocking the reactive thiol groups of the whey proteins with N-ethylmaleimide. Microscopy and light scattering showed that simple shear flow applied during the formation of whey protein particles give irregularly shaped particles. Especially small particles aggregated into particle clusters. Microscopy and rheological measurements (strain and shear rate sweeps) showed that the protein particle clustering was favoured by the ability of the protein to form S–S bridges and to a lesser extend by a smaller particle size. From the study, it can be concluded that the formation of S–S bridges has no effect on the formation process of protein particles, but S–S bridges are important for the ability of the whey protein particles to form particle cluster

Particle size effects in colloidal gelatin particle suspensions

This paper describes the effects of simple shear flow on the formation and properties of colloidal gelatin particle suspensions. Microscopy and light scattering show that simple shear flow of a phase-separating gelatin–dextran mixture gave smaller particles with a narrower size distribution. Upon gelation due to a temperature decrease, the viscosity of the gelatin increased, which altered the coalescence and break-up behaviour of the particles formed. The small particles obtained by a high shear during processing aggregated into larger particle clusters, once particle solidified upon gelation. The particle size can be predicted using correlation with droplet break-up and coalescence considering the properties before gelation. The sizes of the clusters can be predicted with the coalescence behaviour using the properties after gelation. Clusters originating from small particles resist more deformation, resulting in pronounced rheological effects (e.g. increase viscosity, increased strain softening point)

Toward a full-reference information-theoretic quality assessment method for x-ray images

This work aims at de¯ning an information-theoretic quality assessment technique for cardiovascular X-ray images, using a full-reference scheme (relying on averaging a sequence to obtain a noiseless reference). With the growth of advanced signal processing in medical imaging, such an approach will enable objective comparisons of the quality of processed images. A concept for describing the quality of an image is to express it in terms of its information capacity. Shannon has derived this capacity for noisy channel coding. However, for X-ray images, the noise is signal-dependent and non-additive, so that Shannon's theorem is not directly applicable. To overcome this complication, we exploit the fact that any invertible mapping on a signal does not change its information content. We show that it is possible to transform the images in such a way that the Shannon theorem can be applied. A general method for calculating such a transformation is used, given a known relation between signal mean and noise standard deviation. After making the noise signal-independent, it is possible to assess the information content of an image and to calculate an overall quality metric (e.g. information capacity) which includes the e®ects of sharpness, contrast and noise. We have applied this method on phantom images under di®erent acquisition conditions and computed the information capacity for those images. We aim to show that the results of this assessment are consistent with variations in noise, contrast and sharpness, introduced by system settings and image processing

Flat detector ghost image reduction by UV irradiation

We study flat detectors for X-ray imaging performance degradation. In cone beam C-arm-CT, memory effects have a detrimental effect on image quality. Depending on the magnitude and history of irradiance differences, detector sensitivity variations may persist for a long period of time (days) and are visible as rings upon 3D reconstruction. A new method is proposed for reducing memory effects produced in CsI:Tl based Flat Detector X-ray imaging, which is based upon trap-filling by UV-light. For experiments, a commercial detector has been modified such that UV back-lighting is accomplished. A regular LED refresh light array for reducing photodiode temporal effects is interleaved with UV LED sub-arrays of different wavelengths in the near UV range. The array irradiates the scintillator through translucent parts of the detector substrate. In order to assess the efficacy of the method, ghost images are imprinted by well-defined transitions between direct radiation and attenuated or shuttered radiation. As an advantage, the new method accomplishes ghost-prevention, either by (1) continuous trap-filling at image-synchronous UV light pulsing, or (2) by applying a single dose of UV light. As a result, ring artefacts in reconstructed 3D-images are reduced to low levels. An effective wavelength has been found and an equilibrium UV dosage could be set for effective trap-filling. The overall sensitivity of the detector increases at saturated trap-filling. It was found that with optimised detector settings, i.e. optimum saturated trap-filling, the dependence on X-ray irradiation levels is low, so that the usage of the detector and its performance is robust

Innovations in 3D interventional X-ray imaging

Minimal invasive interventions allow the treatment of lesions without the strain of full open surgery. Such image guided interventions and therapies fully rely on the guidance and navigation based on real-time peri-interventional imaging equipment, such as interventional X-ray and ultrasound. Since these imaging modalities are the ‘eyes’ of the treating physician, the associated image quality and imaging features are essential. The addition and further development of 3D imaging capabilities in recent years has broadened the possibilities and capabilities of such procedures, and enabled minimal invasive treatment that could only be performed by open surgery in the past. In this chapter we describe several recent innovations in the area of 3D interventional X-ray imaging in the areas of image quality, 3D model-based catheter reconstruction, multi-modal image fusion, and stereoscopic visualizations