· · · Repository hosted by TU Delft Library

Digital breast tomosynthesis (DBT) aims for improving the diagnosis of breast cancer and reducing the false positive rates by going from 2D projection mammography to 3D volume information. With the acquisition of a series of projection images, taken over a limited angular range, DBT allows for tomographic reconstruction with high in-plane but reduced depth resolution. Therefore, anatomical structures get blurred along the depth direction and produce out-of-plane artifacts. Prominent streak artifacts can be observed for high-contrast objects such as calcifications, which degrade the image quality, see for example Figure 8(a) - (f) in [4]. In this work, a second pass method for correcting these streak-like artifacts is introduced. For evaluation of this method, a software based breast phantom has been developed from segmented MRI breast data.

The contrast of iodine to soft tissue (water) decreases with higher tube voltage in reconstructed 3D X-ray images. Improved acquisition protocols with a tube voltage of about 80 kV for imaging iodine have been proposed earlier for diagnostic CT imaging. We investigate the contrast-to-noise ratio (CNR) and the CNR-to-dose ratio (CDR) for different concentrations of iodinated contrast agent inserts in water background. The tube voltage of the protocol is lowered from 123 kV to 83 kV in 10 kV steps. A series of measurements with 16 different settings of tube voltage, current and filter settings are investigated. The weighted computed tomography dose index CTDIW for the new protocol settings is measured. Four protocols with tube voltages between 83 kV and 103 kV and similar X-ray dose are compared to the original protocol. A low contrast phantom, containing a water filled cylinder with 5 tubes of different mixtures of iodine contrast inside a 32 cm PMMA ring, is imaged with each protocol. Increased contrast of the iodine filled tubes to the water background is clearly visible in the reconstructed volumes for lower tube voltage and less copper filtering. The best results are obtained with the (83 kV, 561 mA, 0.4 Cu) – protocol. This protocol may improve iodine contrast agent visibility in various 3D imaging applications. For large patients a higher tube voltage, e.g. the (103 kV, 325 mA, 0.4 Cu) – protocol, may be used to avoid tube power limitations at 83 kV. This protocol still has improved iodine imaging compared to the 123 kV protocol and a larger tube power reserve.

Circular scanning with an off-center planar detector is an acquisi-tion scheme that allows to save detector area while keeping a largefield of view (FOV). Several filtered back-projection (FBP) algorithmshave been proposed earlier. The purpose of this work is to present twonewly developed back-projection filtration (BPF) variants and evaluatethe image quality of these methods compared to the existing state-of-the-art FBP methods.

Filtered back-projection (FBP) has been commonly used as an efficient and robust reconstruction technique in tomographic X-ray imagingduring the last decades. For limited angle tomography acquisitions such as digital breast tomosynthesis, however, standard FBP reconstruction algorithms provide poor results and give rise to image artifacts due to the limited angular range and the coarse angular sampling.Therefore, iterative algorithms are often used in digital breast tomosynthesis since they potentially yield a reconstructed image thatis in better accordance with the measured data. In this work, a generalized FBP algorithm is presented, which uses the filtered projection data of all acquired views for back-projection along one direction in order to compute an image that is similar to an iteratively calculated one. The proposed method yields a computationally efficientgeneralized FBP algorithm for digital breast tomosynthesis, which provides similar image quality as iterative reconstruction techniqueswhile preserving the ability for region of interest reconstructions. Both a small number of views and a limited angular range can be handled with the generalized FBP while common FBP reconstruction yields a severe loss of the average value, which will be demonstrated onsimulated breast tomosynthesis data. Moreover, due to the filter computation as the pseudo-inverse operator, the reconstructed image provides an optimal solution in the least-squares sense, which minimizes the error between the measured data and the reprojections of thereconstructed image.

Large area detector computed tomography systems with fastrotating gantries enable volumetric dynamic cardiac perfusion studies. Prospectively ECG-triggered acquisitions limit the data acquisition to a predefined cardiac phase and thereby reduce X-ray dose andlimit motion artifacts. Even in the case of highly accurate prospective triggering and stable heart rate, spatial misalignment of the cardiac volumes acquired and reconstructed per cardiac cycle may occurdue to small motion pattern variations from cycle to cycle. These misalignments reduce the accuracy of the quantitative analysis of myocardial perfusion parameters on a per voxel basis. An image based solution to this problem is elastic 3D image registration of dynamic volume sequences with variable contrast, as it is introduced in thiscontribution. After circular cone-beam CT reconstruction of cardiacvolumes covering large areas of the myocardial tissue, the completeseries is aligned with respect to a chosen reference volume. The results of the quantitative perfusion analysis are compared on pig datausing the non-registered versus the registered data set. The reduced spatial misalignment leads to an improved characterization of myocardial perfusion confirming the potential of this method. Conclusions - In conclusion, an elastic image registration-based method was proposed to improve the characterization of CT-based estimates of myocardial perfusion. The technique’s performance, that was visually and quantitatively assessed on three pig data sets, confirmed its potential. The proposed method may also be applied to other perfusion studies being limited by inconsistent motion states.

C-arm based tomographic 3D imaging is applied in an increasing number of minimal invasive procedures. Due to the limited acquisition speed for a complete projection data set required for tomographic reconstruction, breathing motion is a potential source of artifacts. Intra-scan motion estimation and compensation is required. Here, a scheme for projection based local breathing motion estimation is combined with an anatomy adapted interpolation strategy and subsequent motion compensated filtered back projection. This approach is applied in animal experiments on a flat panel C-arm system delivering improved image quality in 3D liver tumor imaging.