Udo van Stevendaal

A Study on Mastectomy Samples to Evaluate Breast Imaging Quality and Potential Clinical Relevance of Differential Phase Contrast Mammography

ObjectivesDifferential phase contrast and scattering-based x-ray mammography has the potential to provide additional and complementary clinically relevant information compared with absorption-based mammography. The purpose of our study was to provide a first statistical evaluation of the imaging capabilities of the new technique compared with digital absorption mammography. Materials and MethodsWe investigated non-fixed mastectomy samples of 33 patients with invasive breast cancer, using grating-based differential phase contrast mammography (mammoDPC) with a conventional, low-brilliance x-ray tube. We simultaneously recorded absorption, differential phase contrast, and small-angle scattering signals that were combined into novel high-frequency-enhanced images with a dedicated image fusion algorithm. Six international, expert breast radiologists evaluated clinical digital and experimental mammograms in a 2-part blinded, prospective independent reader study. The results were statistically analyzed in terms of image quality and clinical relevance. ResultsThe results of the comparison of mammoDPC with clinical digital mammography revealed the general quality of the images to be significantly superior (P < 0.001); sharpness, lesion delineation, as well as the general visibility of calcifications to be significantly more assessable (P < 0.001); and delineation of anatomic components of the specimens (surface structures) to be significantly sharper (P < 0.001). Spiculations were significantly better identified, and the overall clinically relevant information provided by mammoDPC was judged to be superior (P < 0.001). ConclusionsOur results demonstrate that complementary information provided by phase and scattering enhanced mammograms obtained with the mammoDPC approach deliver images of generally superior quality. This technique has the potential to improve radiological breast diagnostics.

Slit-scanning differential x-ray phase-contrast mammography: Proof-of-concept experimental studies

PURPOSE The purpose of this work is to investigate the feasibility of grating-based, differential phase-contrast, full-field digital mammography (FFDM) in terms of the requirements for field-of-view (FOV), mechanical stability, and scan time. METHODS A rigid, actuator-free Talbot interferometric unit was designed and integrated into a state-of-the-art x-ray slit-scanning mammography system, namely, the Philips MicroDose L30 FFDM system. A dedicated phase-acquisition and phase retrieval method was developed and implemented that exploits the redundancy of the data acquisition inherent to the slit-scanning approach to image generation of the system. No modifications to the scan arm motion control were implemented. RESULTS The authors achieve a FOV of 160 × 196 mm consisting of two disjoint areas measuring 77 × 196 mm with a gap of 6 mm between them. Typical scanning times vary between 10 and 15 s and dose levels are lower than typical FFDM doses for conventional scans with identical acquisition parameters due to the presence of the source-grating G0. Only minor to moderate artifacts are observed in the three reconstructed images, indicating that mechanical vibrations induced by other system components do not prevent the use of the platform for phase contrast imaging. CONCLUSIONS To the best of our knowledge, this is the first attempt to integrate x-ray gratings hardware into a clinical mammography unit. The results demonstrate that a scanning differential phase contrast FFDM system that meets the requirements of FOV, stability, scan time, and dose can be build.

Coherent scatter computed tomography: a novel medical imaging technique

Fan-beam coherent scatter computed tomography (CSCT) is a novel X-ray based imaging method revealing structural information of tissue under investigation. The source of contrast is the angular-dependent coherent scatter cross-section, which is determined by the molecular structure. In this work a phantom consisting of water, tricalcium phosphate, collagen and fat was used to investigate the contrast resolution of these four tissue constituents. Scatter projections were measured in fan-beam 3rd generation CT-geometry using an experimental demonstrator set-up equipped with a 4.5 kW DC power X-ray tube and photon-counting detectors. Reconstruction was performed using two algorithms, one based on algebraic reconstruction technique (ART) and the other based on filtered back-projection (FBP). The reconstruction results of the two techniques are compared. Furthermore, scatter functions of the four components were extracted from the 3D data sets and compared to previous measurements. The applicability of this technique for medical diagnosis is discussed.

Clinical boundary conditions for grating-based differential phase-contrast mammography

Research in grating-based differential phase-contrast imaging (DPCI) has gained increasing momentum in the past couple of years. The first results on the potential clinical benefits of the technique for X-ray mammography are becoming available and indicate improvements in terms of general image quality, the delineation of lesions versus the background tissue and the visibility of microcalcifications. In this paper, we investigate some aspects related to the technical feasibility of DPCI for human X-ray mammography. After a short introduction to state-of-the-art full-field digital mammography in terms of technical aspects as well as clinical aspects, we put together boundary conditions for DPCI. We then discuss the implications for system design in a comparative manner for systems with two-dimensional detectors versus slit-scanning systems, stating advantages and disadvantages of the two designs. Finally, focusing on a slit-scanning system, we outline a possible concept for phase acquisition.

Image fusion algorithm for differential phase contrast imaging

Differential phase-contrast imaging in the x-ray domain provides three physically complementary signals:1, 2 the attenuation, the differential phase-contrast, related to the refractive index, and the dark-field signal, strongly influenced by the total amount of radiation scattered into very small angles. In medical applications, it is of the utmost importance to present to the radiologist all clinically relevant information in as compact a way as possible. Hence, the need arises for a method to combine two or more of the above mentioned signals into one image containing all information relevant for diagnosis. We present an image composition algorithm that fuses the attenuation image and the differential phase contrast image into a composite, final image based on the assumption that the real and imaginary part of the complex refractive index of the sample can be related by a constant scaling factor. The merging is performed in such a way that the composite image is characterized by minimal noise-power at each frequency component.

Improvement of cardiac CT reconstruction using local motion vector fields

The motion of the heart is a major challenge for cardiac imaging using CT. A novel approach to decrease motion blur and to improve the signal to noise ratio is motion compensated reconstruction which takes motion vector fields into account in order to correct motion. The presented work deals with the determination of local motion vector fields from high contrast objects and their utilization within motion compensated filtered back projection reconstruction. Image registration is applied during the quiescent cardiac phases. Temporal interpolation in parameter space is used in order to estimate motion during strong motion phases. The resulting motion vector fields are during image reconstruction. The method is assessed using a software phantom and several clinical cases for calcium scoring. As a criterion for reconstruction quality, calcium volume scores were derived from both, gated cardiac reconstruction and motion compensated reconstruction throughout the cardiac phases using low pitch helical cone beam CT acquisitions. The presented technique is a robust method to determine and utilize local motion vector fields. Motion compensated reconstruction using the derived motion vector fields leads to superior image quality compared to gated reconstruction. As a result, the gating window can be enlarged significantly, resulting in increased SNR, while reliable Hounsfield units are achieved due to the reduced level of motion artefacts. The enlargement of the gating window can be translated into reduced dose requirements.

Experimental feasibility study of energy-resolved fan-beam coherent scatter computed tomography

Energy-resolved fan beam coherent scatter computed tomography (CSCT) is a novel X-ray based imaging method revealing structural information on the molecular level of tissue or other material under investigation with high resolution of the momentum-transfer dependent coherent scatter cross-section. Since the molecular structure is the source of contrast a very good material discrimination and possibly also medical diagnosis of structural changes of tissue can be achieved with this technique. Poor spectral resolution as found in previous work due to the application of a polychromatic X-ray source can be overcome when energy-resolved detection is used. In this paper experimental results on phantoms using an energy-resolving CdTe-detector are shown. With the present setup the spatial resolution was found to be 4.5 mm (FWHM) and a spectral resolution of 6% was achieved. Applications of this technique can be found in medical imaging, material analysis and baggage inspection.

Accelerating image acquisition in 64-MDCT: the influence of scan parameters on image resolution and quality in a phantom study.

Computed tomographic (CT) image resolution and quality were evaluated utilizing varying scan protocols with accelerated image acquisition. A resolution phantom with hole diameters from 0.2 to 1.0 mm was scanned in axial, coronal, and sagittal plane using a 64-slice multidetector CT with varying scan parameters. No relevant differences in image resolution and quality were detected between the fastest scan protocol, with the shortest rotation time and highest pitch, and the slowest protocol. Accelerated CT protocols resulted in diagnostic images with adequate resolution and quality.

Vector field interpolation for cardiac motion compensated reconstruction

Cardiac CT image reconstruction suffers from motion artifacts due to heart motion during acquisition. In order to mitigate these effects, it is common practice to acquire with fast gantry rotation and do gated reconstruction. In addition, it is possible to estimate heart motion retrospectively and to incorporate that information in a motion compensated reconstruction (MCR). However, if shape tracking algorithms are used for generation of a heart motion vector field (MVF), the number and positions of the resulting motion vectors will not coincide with the number and positions of the voxels in the reconstruction grid. For MCR algorithms that require one motion vector at each voxel location, the MVF must be interpolated. This work examines different interpolation approaches for the MVF interpolation problem and their effects on the MCR results.

Sensitivity-based optimization for the design of a grating interferometer for clinical X-ray phase contrast mammography

An X-ray grating interferometer (GI) suitable for clinical mammography must comply with quite strict dose, scanning time and geometry limitations, while being able to detect tumors, microcalcifications and other abnormalities. Such a design task is not straightforward, since obtaining optimal phase-contrast and dark-field signals with clinically compatible doses and geometrical constraints is remarkably challenging. In this work, we present a wave propagation based optimization that uses the phase and dark-field sensitivities as figures of merit. This method was used to calculate the optimal interferometer designs for a commercial mammography setup. Its accuracy was validated by measuring the visibility of polycarbonate samples of different thicknesses on a Talbot-Lau interferometer installed on this device and considering some of the most common grating imperfections to be able to reproduce the experimental values. The optimization method outcomes indicate that small grating pitches are required to boost sensitivity in such a constrained setup and that there is a different optimal scenario for each signal type.