In this work, a newly developed reconstruction algorithm, Synchronized MultiArtifact Reduction with Tomographic RECONstruction (SMART-RECON), was applied to C-arm cone beam CT perfusion (CBCTP) imaging. This algorithm contains a special rank regularizer, designed to reduce limited-view artifacts associated with super- short scan reconstructions. As a result, high temporal sampling and temporal resolution image reconstructions were achieved using an interventional C-arm x-ray system. The algorithm was evaluated in terms of the fidelity of the dynamic contrast update curves and the accuracy of perfusion parameters through numerical simulation
studies. Results shows that, not only were the dynamic curves accurately recovered (relative root mean square error ∈ [3%, 5%] compared with [13%, 22%] for FBP), but also the noise in the final perfusion maps was dramatically reduced. Compared with filtered backprojection, SMART-RECON generated CBCTP maps with much improved capability in differentiating lesions with perfusion deficits from the surrounding healthy brain tissues.
KEYWORDS: Spatial resolution, 3D image processing, Modulation transfer functions, Angiography, Spatial frequencies, Temporal resolution, 3D image reconstruction, Point spread functions, 3D acquisition, Medical imaging
C-Arm CT three-dimensional (3-D) digital subtraction angiography (DSA) reconstructions cannot provide temporal information to radiologists. Four-dimensional (4-D) DSA provides a time series of 3-D volumes utilizing temporal dynamics in the two-dimensional (2-D) projections using a constraining image reconstruction approach. Volumetric limiting spatial resolution (VLSR) of 4-D DSA is quantified and compared to a 3-D DSA. The effects of varying 4-D DSA parameters of 2-D projection blurring kernel size and threshold of the 3-D DSA (constraining image) of an in silico phantom (ISPH) and physical phantom (PPH) were investigated. The PPH consisted of a 76-micron tungsten wire. An 8-s/248-frame/198-deg scan protocol acquired the projection data. VLSR was determined from MTF curves generated from each 2-D transverse slice of every (248) 4-D temporal frame. 4-D DSA results for PPH and ISPH were compared to the 3-D DSA. 3-D DSA analysis resulted in a VLSR of 2.28 and 1.69 lp/mm for ISPH and PPH, respectively. Kernel sizes of either 10×10 or 20×20 pixels with a 3-D DSA constraining image threshold of 10% provided 4-D DSA VLSR nearest to the 3-D DSA. 4-D DSA yielded 2.21 and 1.67 lp/mm with a percent error of 3.1 and 1.2% for ISPH and PPH, respectively, as compared to 3-D DSA. This research indicates 4-D DSA is capable of retaining the resolution of 3-D DSA.
Purpose: The purpose of this work is to improve the segmentation of interventional devices (e.g. guidewires) in fluoroscopic images. This is required for the real time 3D reconstruction from two angiographic views where noise can cause severe reconstruction artifacts and incomplete reconstruction. The proposed method reduces the noise while enhancing the thin line structures of the device in images with subtracted background.
Methods: A two-step approach is presented here. The first step estimates, for each pixel and a given number of directions, a measure for the probability that the point is part of a line segment in the corresponding direction. This can be done efficiently using binary masks. In the second step, a directional filter kernel is applied for pixel that are assumed to be part of a line. For all other pixels a mean filter is used.
Results: The proposed algorithm was able to achieve an average contrast to noise ratio (CNR) of 6.3 compared to the bilateral filter with 5.8. For the device segmentation using global thresholding the number of missing or wrong pixels is reduced to 25 % compared to 40 % using the bilateral approach.
Conclusion: The proposed algorithm is a simple and efficient approach, which can easily be parallelized for the use on modern graphics processing units. It improves the segmentation results of the device compared to other denoising methods, and therefore reduces artifacts and increases the quality of the reconstruction without increasing the delay in real time applications notably.
KEYWORDS: Image processing, Denoising, Data acquisition, Angiography, Medical imaging, Arteries, Algorithm development, In vivo imaging, Optimization (mathematics), Image quality
In this work we developed a novel denoising algorithm for DSA image series. This algorithm takes advantage of the low rank nature of the DSA image sequences to enable a dramatic reduction in radiation and/or contrast doses in DSA imaging. Both spatial and temporal regularizers were introduced in the optimization algorithm to further reduce noise. To validate the method, in vivo animal studies were conducted with a Siemens Artis Zee biplane system using different radiation dose levels and contrast concentrations. Both conventionally processed DSA images and the DSA images generated using the novel denoising method were compared using absolute noise standard deviation and the contrast to noise ratio (CNR). With the application of the novel denoising algorithm for DSA, image quality can be maintained with a radiation dose reduction by a factor of 20 and/or a factor of 2 reduction in contrast dose. Image processing is completed on a GPU within a second for a 10s DSA data acquisition.
Static C-Arm CT 3D FDK baseline reconstructions (3D-DSA) are unable to provide temporal information to radiologists. 4D-DSA provides a time series of 3D volumes implementing a constrained image, thresholded 3D-DSA, reconstruction utilizing temporal dynamics in the 2D projections. Volumetric limiting spatial resolution (VLSR) of 4DDSA is quantified and compared to a 3D-DSA reconstruction using the same 3D-DSA parameters. Investigated were the effects of varying over significant ranges the 4D-DSA parameters of 2D blurring kernel size applied to the projection and threshold applied to the 3D-DSA when generating the constraining image of a scanned phantom (SPH) and an electronic phantom (EPH). The SPH consisted of a 76 micron tungsten wire encased in a 47 mm O.D. plastic radially concentric thin walled support structure. An 8-second/248-frame/198° scan protocol acquired the raw projection data. VLSR was determined from averaged MTF curves generated from each 2D transverse slice of every (248) 4D temporal frame (3D). 4D results for SPH and EPH were compared to the 3D-DSA. Analysis of the 3D-DSA resulted in a VLSR of 2.28 and 1.69 lp/mm for the EPH and SPH respectively. Kernel (2D) sizes of either 10x10 or 20x20 pixels with a threshold of 10% of the 3D-DSA as a constraining image provided 4D-DSA VLSR nearest to the 3D-DSA. 4D-DSA algorithms yielded 2.21 and 1.67 lp/mm with a percent error of 3.1% and 1.2% for the EPH and SPH respectively as compared to the 3D-DSA. This research indicates 4D-DSA is capable of retaining the resolution of the 3D-DSA.
This paper provides a fast and patient-specific scatter artifact correction method for cone-beam computed tomography (CBCT) used in image-guided interventional procedures. Due to increased irradiated volume of interest in CBCT imaging, scatter radiation has increased dramatically compared to 2D imaging, leading to a degradation of image quality. In this study, we propose a scatter artifact correction strategy using an analytical convolution-based model whose free parameters are estimated using a rough estimation of scatter profiles from the acquired cone-beam projections. It was evaluated using Monte Carlo simulations with both monochromatic and polychromatic X-ray sources. The results demonstrated that the proposed method significantly reduced the scatter-induced shading artifacts and recovered CT numbers.
In this work we applied dose reduction using the prior image constrained compress sensing (DR-PICCS) method
on a C-arm cone beam CT system. DR-PICCS uses a smoothed image as the prior image. After applying DRPICCS,
the final image will have noise variance inherited from the prior image and spatial resolution from the
projection data. In order to investigate the dose reduction of DR-PICCS, three different dose levels were used in
C-arm scans of animal subjects using a Siemens Zeego C-arm system under an IACUC protocol. Image volumes
were reconstructed using the standard FBP and DR-PICCS algorithms(total of 160 images). These images were
randomly mixed and presented to three experienced interventional radiologists(each having more than twenty
years reading experience) to review and score using a five-point scale. After statistical significance testing, the
results show that DR-PICCS can achieve more than 60% dose reduction while keeping the same image quality.
And if we compare FBP and DR-PICCS at the same dose level the results show that DR-PICCS will generate
higher quality images.
It is highly desirable to obtain perfusion information with the C-arm CBCT system in the interventional room. However,
due to hardware limitations, it is still elusive to achieve cone-beam CT perfusion measurements. In this study, we
performed a systematic study to investigate what the main limiting factors are that need to be addressed for future C-arm
cone beam CT perfusion imaging. To do so, we performed systematic numerical simulation studies using a diagnostic
CT perfusion data set. Specifically, a forward projection was performed to simulate cone-beam CT perfusion experiment
with C-arm CBCT geometry and temporal behavior. Different x-ray delays after contrast injection have been simulated
with this method. The view angle undersampling artifacts, shading artifacts from dynamic objects, and the importance of
arterial input function (AIF) for perfusion study were investigated in this study with different x-ray delay times. From the
simulation results, it was found that the view angle undersampling artifacts do not have much impact on perfusion maps.
The shading artifacts from dynamic object were shown to have a negligible effect on the NRMSE in perfusion maps. The
accuracy of AIF is an important but not a dominating factor for perfusion studies. C-arm CBCT cannot accurately
recover the slowly changing contrast in brain tissues due to the low temporal resolution. Therefore, to enable cone beam
C-arm CT perfusion measurement, it is critical to improve the temporal behavior of CBCT by either employing new
hardware upgrades or introducing new software methods.
In the current workflow of ischemic stroke management, it is highly desirable to obtain perfusion information with the
C-arm CBCT system in the interventional room. Due to hardware limitations, the data acquisition speed of the current Carm
CBCT systems is relatively slow and only 7 time frames are available for a 45 s perfusion study. In this study, a
novel temporal recovery method was proposed to recover contrast enhancement curves in C-arm CBCT perfusion
studies. The proposed temporal recovery problem is a constrained optimization problem. Two numerical methods were
used to solve the proposed problem. The feasibility of proposed temporal recovery method was validated with numerical
experiments. Both solvers can achieve a satisfactory solution for the temporal recovery problem, while the result of the
Bregman algorithm is more accurate than that from the CG. In vivo animal studies were used to demonstrated the
improvement of the proposed method in C-arm CBCT perfusion. A stoked canine model was scanned with both C-arm
CBCT and diagnostic CT. Perfusion defects can be clearly indentified from the cerebral blood flow (CBF) map of
diagnostic CT perfusion. Without the temporal recovery technique, these defects can hardly be identified from the CBCT CBF map. After applying the proposed temporal recovery method, the CBCT CBF map well correlates with the CBF
map from diagnostic CT.
While perfusion imaging is a well established diagnostic imaging technique, until now, it could not be performed
using angiographic equipment. The ability to assess information about tissue perfusion in the angiographic suite
should help to optimize management of patients with neurovascular diseases. We present a technique to measure
cerebral blood volume (CBV) for the entire brain using an angiographic C-arm system. Combining a rotational
acquisition protocol similar to that used for standard three-dimensional rotational angiography (3D DSA) in
conjunction with a modified injection protocol providing a steady state of tissue contrast during the acquisition
the data necessary to calculate CBV is acquired. The three-dimensional (3D) CBV maps are generated using a
special reconstruction scheme which includes the automated detection of an arterial input function and several
correction steps. For evaluation we compared this technique with standard perfusion CT (PCT) measurements
in five healthy canines. Qualitative comparison of the CBV maps as well as quantitative comparison using 12
ROIs for each map showed a good correlation between the new technique and traditional PCT. In addition we
evaluated the technique in a stroke model in canines. The presented technique provides the first step toward
providing information about tissue perfusion available during the treatment of neurovascular diseases in the
angiographic suite.
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