AngioVis Toolbox

AngioVis Publications

Original Papers - Clinical

Schernthaner RE, Wolf F, Mistelbauer G, Weber M, Sramek M, Gröller E, Loewe C.
New hybrid reformations of peripheral CT angiography: do we still need axial images?

Clinical Imaging. 2015 Jul-Aug;39(4):603-7. DOI: 10.1016/j.clinimag.2015.03.005

Purpose To quantify the detectability of peripheral artery stenosis on hybrid CT angiography (CTA) reformations.
Methods Hybrid reformations were developed by combining multipath curved planar reformations (mpCPR) and maximum intensity projections (MIP). Fifty peripheral CTAs were evaluated twice: either with MIP, mpCPR and axial images or with hybrid reformations only. Digital subtraction angiography served as gold standard.
Results Using hybrid reformations, two independent readers detected 88.0% and 81.3% of significant stenosis, respectively. However, CTA including axial images detected statistically significant more lesions (98%).
Conclusion Peripheral CTA reading including axial images is still recommended. Further improvement of these hybrid reformations is necessary. More...

M.M. Schreiner, C. Loewe, S. Unterhumer, M. Weber, G. Mistelbauer, M. Šrámek , E. Gröller, and R.E. Schernthaner.
Accuracy and time-efficiency of multi-path curved planar reformations in the evaluation of low-dose CT angiography of the peripheral arteries.

In ECR 2015 Book of Abstracts - B - Scientific Sessions and Late-Breaking Clinical Trials, pages B–0632, March 2015.

Tran DN, Straka M, Roos JE, Napel S, Fleischmann D
Dual-energy CT discrimination of iodine and calcium: experimental results and implications for lower extremity CT angiography.
Acad Radiol. 2009 Feb;16(2):160-71.

RATIONALE AND OBJECTIVES: The purpose of this work was to measure the accuracy of dual-energy computed tomography for identifying iodine and calcium and to determine the effects of calcium suppression in phantoms and lower-extremity computed tomographic (CT) angiographic data sets. MATERIALS AND METHODS: Using a three-material basis decomposition method for 80- and 140-kVp data, the accuracy of correctly identified contrast medium and calcium voxels and the mean attenuation before and after calcium suppression were computed. Experiments were first performed on a phantom of homogenous contrast medium and hydroxyapatite samples with mean attenuation of 57.2, 126, and 274 Hounsfield units (HU) and 50.0, 122, and 265 HU, respectively. Experiments were repeated in corresponding attenuation groups of voxels from manually segmented bones and contrast medium-enhanced arteries in a lower-extremity CT angiographic data set with mean attenuation of 293 and 434 HU, respectively. Calcium suppression in atherosclerotic plaques of a cadaveric specimen was also studied, using micro-computed tomography as a reference, and in a lower-extremity CT angiographic data set with substantial below-knee calcified plaques. RESULTS: Higher concentrations showed increased accuracy of iodine and hydroxyapatite identification of 87.4%, 99.7%, and 99.9% and 88.0%, 95.0%, and 99.9%, respectively. Calcium suppression was also more accurate with higher concentrations of iodine and hydroxyapatite, with mean attenuation after suppression of 47.1, 122, and 263 HU and 7.14, 11.6, and 12.6 HU, respectively. Similar patterns were seen in the corresponding attenuation groups of the contrast medium-enhanced arteries and bone in the clinical data set, which had overall accuracy of 81.3% and 78.9%, respectively, and mean attenuation after calcium suppression of 254 and 73.7 HU, respectively. The suppression of calcified atherosclerotic plaque was accurate compared with the micro-CT reference; however, the suppression in the clinical data set showed probable inappropriate suppression of the small vessels. CONCLUSION: Dual-energy computed tomography can detect and differentiate between contrast medium and calcified tissues, but its accuracy is dependent on the CT density of tissues and limited when CT attenuation is low.

Schernthaner R, Stadler A, Lomoschitz F, Weber M, Fleischmann D, Lammer J, Loewe C
Multidetector CT angiography in the assessment of peripheral arterial occlusive disease: accuracy in detecting the severity, number, and length of stenoses.
Eur Radiol. 2008 Apr;18(4):665-71. Epub 2007 Dec 19.

The purpose was to evaluate the accuracy of multidetector CT angiography (MD-CTA) in the morphologic assessment of peripheral arterial occlusive disease (PAOD) compared to digital subtraction angiography (DSA). Fifty consecutive patients referred for DSA of the peripheral arteries due to PAOD were prospectively included in this study and underwent 16-row MD-CTA prior to DSA. Maximum intensity projections and multipath curved planar reformations were created with a semi-automated toolbox. Twenty-one vascular segments were defined in each leg and compared to DSA findings with regard to gradation, length, and number of lesions. Mean sensitivity and specificity in the detection of significant stenoses (over 70%) were 100% and 99.5% in the iliac arteries, 97.4% and 99.0% in the femoro-popliteal arteries, and 98.3% and 99.8% in the infrapopliteal arteries, respectively. High kappa values for exact stenoses gradation (0.74-1), lesion length (0.74-1), and number of lesions (0.71-1) were reached by MD-CTA, indicating high agreement with DSA. Non-invasive MD-CTA is an accurate tool for the assessment of all treatment-relevant morphologic information of PAOD (gradation, length, and number of stenoses) compared to DSA.

Schernthaner R, Fleischmann D, Lomoschitz F, Stadler A, Lammer J, Loewe C
Effect of MDCT angiographic findings on the management of intermittent claudication
AJR Am J Roentgenol. 2007 Nov;189(5):1215-22.

OBJECTIVE: The purpose of this study was to assess the reliability of treatment decisions based on MDCT angiographic findings of stage IIb peripheral arterial occlusive disease (PAOD). MATERIALS AND METHODS: Fifty-eight patients with stage IIb PAOD underwent CT angiography of the abdominal aorta and runoff vessels for further treatment planning. Treatment reports, discharge summaries, and follow-up examinations were reviewed to determine the number of treatments correctly planned on the basis of CT angiographic findings. RESULTS: On the basis of CT angiographic findings, endovascular treatment was indicated for 18 patients, surgical revascularization for nine patients, and a combined endovascular and surgical approach for two patients. Conservative treatment was indicated for 29 patients. On the basis of successful revascularization, the correctness of the treatment decision was confirmed in all but one patient (n = 28). The treatment plan was modified for one patient referred for surgical revascularization. In that patient, stenosis of the common femoral artery had been overlooked on CT angiography. Patients for whom conservative management was indicated on the basis of CT angiographic findings (n = 29) had a mean follow-up period of 501 days without needing revascularization treatment. This result was defined as indirect confirmation of the accuracy of the decision made with CT angiography. CONCLUSION: The findings on MDCT angiography led to correct treatment recommendations for patients with claudication. Thus, CT angiography should be used in the management of PAOD.

Roos JE, Fleischmann D, Köchl A, Rakshe T, Straka M, Napoli A, Kanitsar A, Sramek M, Gröller E
Multipath curved planar reformation of the peripheral arterial tree in CT angiography.
Radiology. 2007 Jul;244(1):281-90. Epub 2007 May 10.

The study was approved by the institutional review board and informed consent was obtained. The purpose of our study was to prospectively quantify the angular visibility range, determine the existence of orthogonal viewing pairs, and characterize the conditions which cause artifacts in multi-path curved planar reformations (mpCPR) of the peripheral arterial tree in ten patients (8 men and 2 women; mean age 69 years, range 54–80 years) with peripheral arterial occlusive disease. Percentage of segments with the maximal possible visibility score of 1 was significantly greater (odds ratio 1.42, P<.001) for mpCPR than for maximum intensity projection (MIP). One or more orthogonal viewing pairs were identified for all above-knee arterial segments and artifactual vessel-distortion was observed when the vessel axis approached a horizontal course in mpCPR.

Fleischmann D, Lammer J
Peripheral CT angiography for interventional treatment planning

Europ Radiology 2006; 16, S7, M58-64

Lower extremity CT angiography (CTA) has evolved into a very effective, widely available and robust imaging modality for patients with peripheral arterial occlusive disease (PAOD). In this article we briefly review the acquisition and contrast administration techniques for 4- through 64-channel peripheral CTA. Visualization of atherosclerotic disease with CTA in general requires ‘angiography-like’ 3D images (such as volume rendered or maximum intensity projection images), but-notably in the presence of vessel wall calcifications and stentscross- sectional views (such as curved planar reformations, CPR) are also required to accurately assess the flow lumen of the aorta down to the pedal arteries. Adequate visualization and mapping of atherosclerotic lesions in patients with PAOD is not only a prerequisite for generating a dictated report, but more importantly, standardized postprocessed images are the key to communicating the findings to the treating physician, and they also serve as a treatment planning tool. Treatment decisions (surgical versus transluminal revascularization, or conservative treatment), and percutaneous treatment planning (access site, antegrade versus retrograde puncture) can be made in the majority of patients with PAOD based on lower extremity CT angiograms.

Fleischmann D, Hallett RL, Rubin GD
CT Angiography of Peripheral Arterial Disease
J Vasc Interv Radiol. 2006 Jan;17(1):3-26.

Lower-extremity computed tomographic (CT) angiography (ie, peripheral CT angiography) is increasingly used to evaluate patients with peripheral arterial disease. It is therefore increasingly important for all vascular specialists to become familiar with the strengths and limitations of this new technique. The aims of this review are to explain the principles of scanning and injection technique for a wide range of CT scanners, to explain and illustrate the properties of current image postprocessing tools for effective visualization and treatment planning, and to provide an overview of current clinical applications of peripheral CT angiography.

Fleischmann D, Rubin GD
Quantification of intravenously administered contrast medium transit through the peripheral arteries: implications for CT angiography
Radiology. 2005 Sep;236(3):1076-82. Epub 2005 Jul 6.

PURPOSE: To prospectively determine the range of aortopopliteal bolus transit times in patients with moderate-to-severe peripheral arterial occlusive disease (PAOD) as a guideline for developing injection strategies for computed tomographic (CT) angiography of peripheral arteries. MATERIALS AND METHODS: The study protocol was approved by the local ethics board, and informed consent was obtained. Twenty patients with PAOD referred for CT angiography of the lower extremities were categorized into two groups, Fontaine stage IIb (group 1) and stage III or IV (group 2), and demographic information was collected. In all patients, a 16-mL test bolus was injected intravenously, and single-level dynamic acquisitions were obtained at the level of the abdominal aorta. After injection of a second 16-mL test bolus, dynamic acquisitions were obtained at the level of the knee (popliteal arteries). Aortopopliteal bolus transit times were calculated by subtracting the time to peak enhancement in the popliteal arteries from that in the aorta. Aortopopliteal transit speeds also were derived. Transit times and speeds were compared graphically between clinical stage groups. The time required for the contrast medium to enhance the entire peripheral arterial tree in patients with PAOD was estimated by using linear extrapolation. RESULTS: Sixteen men and four women with a mean age of 69 years (range, 49-86 years) were included. Twelve patients were included in group 1, and eight patients, in group 2. Aortopopliteal bolus transit times ranged from 4 to 24 seconds (median, 8 seconds) in all subjects, which corresponded to bolus transit speeds of 177 and 29 mm/sec, respectively. Wide overlap of transit times and transit speeds was observed between clinical stage groups. The estimated time needed for the bolus to enhance the entire peripheral arterial tree was 6-39 seconds. CONCLUSION: Aortopopliteal bolus transit times differ widely among patients and may be substantially delayed in all patients with PAOD. Empirical injection protocols should include an injection duration of 35 seconds or more, as well as an increased scanning delay, with table speeds of more than 30 mm/sec.

Original Papers - Technical

Alexey Karimov, Gabriel Mistelbauer, Thomas Auzinger, Stefan Bruckner.
Guided Volume Editing based on Histogram Dissimilarity.

Computer Graphics Forum, 34(3):91-100, May 2015. DOI = 10.1111/cgf.12621

Segmentation of volumetric data is an important part of many analysis pipelines, but frequently requires manual inspection and correction. While plenty of volume editing techniques exist, it remains cumbersome and error-prone for the user to find and select appropriate regions for editing. We propose an approach to improve volume editing by detecting potential segmentation defects while considering the underlying structure of the object of interest. Our method is based on a novel histogram dissimilarity measure between individual regions, derived from structural information extracted from the initial segmentation. Based on this information, our interactive system guides the user towards potential defects, provides integrated tools for their inspection, and automatically generates suggestions for their resolution. We demonstrate that our approach can reduce interaction effort and supports the user in a comprehensive investigation for high-quality segmentations. More...

Haichao Miao, Gabriel Mistelbauer, Christian Nasel, and Eduard Gröller.
Cowradar: Visual quantification of the circle of Willis in stroke patients.

In EG Workshop on Visual Computing for Biology and Medicine, pages VCBM 2015, Honorable Mention. DOI: 10.2312/vcbm.20151203

This paper presents a method for the visual quantification of cerebral arteries, known as the Circle of Willis (CoW). The CoW is an arterial structure that is responsible for the brain’s blood supply. Dysfunctions of this arterial circle can lead to strokes. The diagnosis relies on the radiologist’s expertise and the software tools used. These tools consist of very basic display methods of the volumetric data without support of advanced technologies in medical image processing and visualization. The goal of this paper is to create an automated method for the standardized description of cerebral arteries in stroke patients in order to provide an overview of the CoW’s configuration. This novel display provides visual indications of problematic areas as well as straightforward comparisons between multiple patients. Additionally, we offer a pipeline for extracting the CoW from Time-of-Flight Magnetic Resonance Angiography (TOF-MRA) data sets. An enumeration technique for the labeling of the arterial segments is therefore suggested. We also propose a method for detecting the CoW’s main supplying arteries by analyzing the coronal, sagittal and transverse image planes of the data sets. We evaluated the feasibility of our visual quantification approach in a study of 63 TOF-MRA data sets and compared our findings to those of three radiologists. The obtained results demonstrate that our proposed techniques are effective in detecting the arteries of the CoW. More...

Florian Mistelbauer, Gabriel Mistelbauer, Eduard Gröller.
ActiveDICOM - Enhancing Static Medical Images with Interaction.

In Posters at Eurographics Workshop on Visual Computing for Biology and Medicine. September 2014.

Digital Imaging and Communications in Medicine (DICOM) is a well-establish standard in medical imaging, consisting not only of image data, but sensitive data such as patient and examination information. Nowadays, although having a large variety of advanced rendering techniques available, DICOM images are still generated and sent to the Picture Archiving and Communication System (PACS). These images are then fetched by the medical doctor from a workstation and used for medical reporting. The user has no other possibilities than being able to change the windowing function for displaying the DICOM images. If a certain region is of special interest, either images of the whole data set are generated or have to be specifically requested. Both approaches consume a considerable amount of time. Secondly, the image generation on demand remains pending until done by the responsible assistant. Despite supporting a broad range of features and being widely applied, DICOM images remain static. We propose a visualization mapping language, Active DICOM Script (ADICT), which enhances conventional DICOM with interactive elements by combining heterogeneous data, interaction and visualization. Such DICOM images are then called Active Digital Imaging and Communications in Medicine (ActiveDICOM). More...

Gabriel Mistelbauer, Anca Morar, Andrej Varchola, Rüdiger Schernthaner, Ivan Baclija, Arnold Köchl, Armin Kanitsar, Stefan Bruckner, and Eduard Gröller.
Vessel visualization using curvicircular feature aggregation.

Computer Graphics Forum, 32(3):231–240, June 2013. DOI: 10.1111/cgf.12110

Radiological investigations are common medical practice for the diagnosis of peripheral vascular diseases. Existing visualization methods such as Curved Planar Reformation (CPR) depict calcifications on vessel walls to determine if blood is still able to flow. While it is possible with conventional CPR methods to examine the whole vessel lumen by rotating around the centerline of a vessel, we propose Curvicircular Feature Aggregation (CFA), which aggregates these rotated images into a single view. By eliminating the need for rotation, vessels can be investigated by inspecting only one image. This method can be used as a guidance and visual analysis tool for treatment planning. We present applications of this technique in the medical domain and give feedback from radiologists. More...

Alexey Karimov, Gabriel Mistelbauer, Johanna Schmidt, Peter Mindek, Elisabeth Schmidt, Timur Sharipov, Stefan Bruckner, and Eduard Gröller.
Vivisection: Skeleton-based volume editing.

Computer Graphics Forum, 32(3):461–470, June 2013. DOI: 10.1111/cgf.12133

Volume segmentation is important in many applications, particularly in the medical domain. Most segmentation techniques, however, work fully automatically only in very restricted scenarios and cumbersome manual editing of the results is a common task. In this paper, we introduce a novel approach for the editing of segmentation results. Our method exploits structural features of the segmented object to enable intuitive and robust correction and verification. We demonstrate that our new approach can significantly increase the segmentation quality even in difficult cases such as in the presence of severe pathologies. More...

Thomas Auzinger, Gabriel Mistelbauer, Ivan Baclija, Rüdiger Schernthaner, Arnold Köchl, Michael Wimmer, Eduard Gröller, and Stefan Bruckner.
Vessel visualization using curved surface reformation.

IEEE Transactions on Visualization and Computer Graphics (Proceedings of IEEE Scientific Visualization 2013), 19(12):2858–2867, December 2013. DOI: 10.1109/TVCG.2013.215.

Visualizations of vascular structures are frequently used in radiological investigations to detect and analyze vascular diseases. Obstructions of the blood flow through a vessel are one of the main interests of physicians, and several methods have been proposed to aid the visual assessment of calcifications on vessel walls. Curved Planar Reformation (CPR) is a wide-spread method that is designed for peripheral arteries which exhibit one dominant direction. To analyze the lumen of arbitrarily oriented vessels, Centerline Reformation (CR) has been proposed. Both methods project the vascular structures into 2D image space in order to reconstruct the vessel lumen. In this paper, we propose Curved Surface Reformation (CSR), a technique that computes the vessel lumen fully in 3D. This offers high-quality interactive visualizations of vessel lumina and does not suffer from problems of earlier methods such as ambiguous visibility cues or premature discretization of centerline data. Our method maintains exact visibility information until the final query of the 3D lumina data. We also present feedback from several domain experts. More...

Gabriel Mistelbauer, Andrej Varchola, Hamed Bouzari, Juraj Starinsky, Arnold Köchl, Rüdiger Schernthaner, Dominik Fleischmann, Eduard Gröller, and Miloš Šrámek.
Centerline reformations of complex vascular structures.

In Pacific Visualization Symposium (PacificVis), 2012 IEEE, pages 233–240, 2012. DOI: 10.1109/PacificVis.2012.6183596

Visualization of vascular structures is a common and frequently performed task in the field of medical imaging. There exist well established and applicable methods such as Maximum Intensity Projection (MIP) and Curved Planar Reformation (CPR). However, when calcified vessel walls are investigated, occlusion hinders exploration of the vessel interior with MIP. In contrast, CPR offers the possibility to visualize the vessel lumen by cutting a single vessel along its centerline. Extending the idea of CPR, we propose a novel technique, called Centerline Reformation (CR), which is capable of visualizing the lumen of spatially arbitrarily oriented vessels not necessarily connected in a tree structure. In order to visually emphasize depth, overlap and occlusion, halos can optionally envelope the vessel lumen. The required vessel centerlines are obtained from volumetric data by performing a scale-space based feature extraction. We present the application of the proposed technique in a focus and context setup. Further, we demonstrate how it facilitates the investigation of dense vascular structures, particularly cervical vessels or vessel data featuring peripheral arterial occlusive diseases or pulmonary embolisms. Finally, feedback from domain experts is given. More...

Gabriel Mistelbauer, Hamed Bouzari, Rüdiger Schernthaner, Ivan Baclija, Arnold Köchl, Stefan Bruckner, Miloš Šrámek, and Eduard Gröller.
Smart super views - a knowledge-assisted interface for medical visualization.

In IEEE Conference on Visual Analytics Science and Technology (IEEE VAST) 2012, pages 163–172. IEEE Computer Society, 10 2012. DOI: 10.1109/VAST.2012.6400555,

Due to the ever growing volume of acquired data and information, users have to be constantly aware of the methods for their exploration and for interaction. Of these, not each might be applicable to the data at hand or might reveal the desired result. Owing to this, innovations may be used inappropriately and users may become skeptical. In this paper we propose a knowledge-assisted interface for medical visualization, which reduces the necessary effort to use new visualization methods, by providing only the most relevant ones in a smart way. Consequently, we are able to expand such a system with innovations without the users to worry about when, where, and especially how they may or should use them. We present an application of our system in the medical domain and give qualitative feedback from domain experts. More...

Accurate arterial centerline extraction is essential for comprehensive visualization in CT Angiography. Time consuming manual tracking is needed when automated methods fail to track centerlines through severely diseased and occluded vessels. A previously described algorithm, Partial Vector Space Projection (PVSP), which uses vessel shape information from a database to bridge occlusions of the femoropopliteal artery, has a limited accuracy in long (>100 mm) occlusions. In this article we introduce a new algorithm, Intermediate Point Detection (IPD), which uses calcifications in the occluded artery to provide additional information about the location of the centerline to facilitate improvement in PVSP performance. It identifies calcified plaque in image space to find the most useful point within the occlusion to improve the estimate from PVSP. In this algorithm candidates for calcified plaque are automatically identified on axial CT slices in a restricted region around the estimate obtained from PVSP. A modified Canny edge detector identifies the edge of the calcified plaque and a convex polygon fit is used to find the edge of the calcification bordering the wall of the vessel. The Hough transform for circles estimates the center of the vessel on the slice, which serves as a candidate intermediate point. Each candidate is characterized by two scores based on radius and relative position within the occluded segment, and a polynomial function is constructed to define a net score representing the potential benefit of using this candidate for improving the centerline. We tested our approach in 44 femoropopliteal artery occlusions of lengths up to 398 mm in 30 patients with peripheral arterial occlusive disease. Centerlines were tracked manually by four-experts, twice each, with their mean serving as the reference standard. All occlusions were first interpolated with PVSP using a database of femoropopliteal arterial shapes obtained from a total of 60 subjects. Occlusions longer than 80 mm (N = 20) were then processed with the IPD algorithm, provided calcifications were found (N = 14). We used the maximum point-wise distance of an interpolated curve from the reference standard as our error metric. The IPD algorithm significantly reduced the average error of the initial PVSP from 2.76 to 1.86 mm (p < 0.01). The error was less than the clinically desirable 3 mm (smallest radius of the femoropopliteal artery) in 13 of 14 occlusions. The IPD algorithm achieved results within the range of the human readers in 11 of 14 cases. We conclude that the additional use of sparse but specific image space information, such as calcified atherosclerotic plaque, can be used to substantially improve the performance of a previously described knowledge-based method to restore the centerlines of femoropopliteal arterial occlusions.

Varchola A, Vaško A, Solčány V, Dimitrov LI, Šrámek M
Processing of volumetric data by slice- and process-based streaming
In Proceedings of the 5th international Conference on Computer Graphics, Virtual Reality, Visualisation and interaction in Africa (Grahamstown, South Africa, October 29 - 31, 2007). S. N. Spencer, Ed. AFRIGRAPH '07. ACM, New York, NY, 101-110

Although the main memory capacity of modern computers is constantly growing, the developers and users of data manipulation and visualization tools fight all over again with the problem of its shortage. In this paper, we advocate slice-based streaming as a possible solution for the memory shortage problem in the case of preprocessing and analysis of volumetric data defined over Cartesian, regular and other types of structured grids. In our version of streaming, data flows through independent processing units---filters---represented by individual system processes, which store each just a minimal fraction of the whole data set, with a slice as a basic data entity. Such filters can be easily interconnected in complex networks by means of standard interprocess communication using named pipes and are executed concurrently on a parallel system without a requirement of specific modification or explicit parallelization.
In our technique, the amount of stored data by a filter is defined by the algorithm implemented therein, and is in most cases as small as one data slice or only several slices. Thus, the upper bound on the processed data volume is not any more defined by the main memory size but is shifted to the disc capacity, which is usually orders of magnitude larger. We propose implementations of this technique for various point, local and even global data processing operations, which may require multiple runs over the input data or eventually temporary data buffering. Further, we give a detailed performance analysis and show how well this approach fits to the current trend of employing cheap multicore processors and multiprocessor computers.

Tran DN, Fleischmann D, Rakshe T, Roos JE, Rosenberg J, Straka M, Napel S
Femoropopliteal artery centerline interpolation using contralateral shape.
Med Phys. 2007 Sep;34(9):3428-35.

Curved planar reformation allows comprehensive visualization of arterial flow channels, providing information about calcified and noncalcified plaques and degrees of stenoses. Existing semiautomated centerline-extraction algorithms for curved planar reformation generation fail in severely diseased and occluded arteries. We explored whether contralateral shape information could be used to reconstruct centerlines through femoropopliteal occlusions. We obtained CT angiography data sets of 29 subjects (16m/13f, 19-86yo) without peripheral arterial occlusive disease and five consecutive subjects (1m/4f, 54-85yo) with unilateral femoropopliteal arterial occlusions. A gradient-based method was used to extract the femoropopliteal centerlines in nondiseased segments. Centerlines of the five occluded segments were manually determined by four experts, two times each. We interpolated missing centerlines in 2475 simulated occlusions of various occlusion lengths in nondiseased subjects. We used different curve registration methods (reflection, similarity, affine, and global polynomial) to align the nonoccluded segments, matched the end points of the occluded segments to the corresponding patent end points, and recorded maximum Euclidean distances to the known centerlines. We also compared our algorithm to an existing knowledge-based PCA interpolation algorithm using the nondiseased subjects. In the five subjects with real femoropopliteal occlusions, we measured the maximum Euclidean distance and the percentage of the interpolation that remained within a typical 3 mm radius vessel. In the nondiseased subjects, we found that the rigid registration methods were not significantly (p<0.750) different among themselves but were more accurate than the nonrigid methods (p<0.001). In simulations using nondiseased subjects, our method produced centerlines that stayed within 3 mm of a semiautomatically tracked centerline in occlusions up to 100 mm in length; however, the PCA method was significantly more accurate for all occlusions lengths. In the actual clinical cases, we found the following [occlusion length (mm):error (mm)]: 16.5:0.775, 42.0:1.54, 79.9:1.82, 145:3.23, and 292:6.13, which were almost always more accurate than the PCA algorithm. We conclude that the use of contralateral shape information, when available, is a promising method for the interpolation of centerlines through arterial occlusions.

Rakshe T, Fleischmann D, Rosenberg J, Roos JE, Napel S.
Knowledge-based interpolation of curves: Application to femoropopliteal arterial centerline restoration.

Med Image Anal. 2007 Apr;11(2):157-68. Epub 2007 Jan 10.

We present a novel algorithm, Partial Vector Space Projection (PVSP), for estimation of missing data given a database of similar datasets, and demonstrate its use in restoring the centerlines through simulated occlusions of femoropopliteal arteries, derived from CT angiography data. The algorithm performs Principal Component Analysis (PCA) on a database of centerlines to obtain a set of orthonormal basis functions defined in a scaled and oriented frame of reference, and assumes that any curve not in the database can be represented as a linear combination of these basis functions. Using a database of centerlines derived from 30 normal femoropopliteal arteries, we evaluated the algorithm, and compared it to a correlation-based linear Minimum Mean Squared Error (MMSE) method, by deleting portions of a centerline for several occlusion lengths (OL: 10mm, 25mm, 50mm, 75mm, 100mm, 125mm, 150mm, 175mm and 200mm). For each simulated occlusion, we projected the partially known dataset on the set of basis functions derived from the remaining 29 curves to restore the missing segment. We calculated the maximum point-wise distance (Maximum Departure or MD) between the actual and estimated centerline as the error metric. Mean (standard deviation) of MD increased from 0.18 (0.14) to 4.35 (2.23) as OL increased. The results were fairly accurate even for large occlusion lengths and are clinically useful. The results were consistently better than those using the MMSE method. Multivariate regression analysis found that OL and the root-mean-square error in the 2cm proximal and distal to the occlusion accounted for most of the error.

Straka M, Cervenanský M, La Cruz A, Köchl A, Srámek M, Gröller E, Fleischmann D
: Focus & Context Visualization in CT-Angiography
IEEE Visualization 2004 2004; 385-392.

Accurate and reliable visualization of blood vessels is still a challenging problem, notably in the presence of morphologic changes resulting from atherosclerotic diseases. In this paper we take advantage of partially segmented data with approximately identified vessel centerlines to comprehensively visualize the diseased peripheral arterial tree. We introduce the VesselGlyph as an abstract notation for novel focus & context visualization techniques of tubular structures such as contrast-medium enhanced arteries in CT-Angiography (CTA). The proposed techniques combine direct volume rendering (DVR) and curved planar reformation (CPR) within a single image. The VesselGlyph consists of several regions where different rendering methods are used. The region type, the used visualization method and the region parameters depend on the distance from the vessel centerline and on viewing parameters as well. By selecting proper rendering techniques for different regions, vessels are depicted in a naturally looking and undistorted anatomic context. This may facilitate the diagnosis and treatment planning of patients with peripheral arterial occlusive disease. In this paper we furthermore present a way how to implement the proposed techniques in software and by means of modern 3D graphics accelerators.

La Cruz A, Straka M, Köchl A, Srámek M, Gröller E, Fleischmann D
Non-Linear Model Fitting to Parameterize Diseased Blood Vessels
IEEE Visualization 2004 2004; 393-400.

Accurate estimation of vessel parameters is a prerequisite for automated visualization and analysis of healthy and diseased blood vessels. The objective of this research is to estimate the dimensions of lower extremity arteries, imaged by computed tomography (CT). These parameters are required to get a good quality visualization of healthy as well as diseased arteries using a visualization technique such as curved planar reformation (CPR). The vessel is modeled using an elliptical or cylindrical structure with specific dimensions, orientation and blood vessel mean density. The model separates two homogeneous regions: Its inner side represents a region of density for vessels, and its outer side a region for background. Taking into account the point spread function (PSF) of a CT scanner, a function is modeled with a Gaussian kernel, in order to smooth the vessel boundary in the model. A new strategy for vessel parameter estimation is presented. It stems from vessel model and model parameter optimization by a nonlinear optimization procedure, i.e., the Levenberg-Marquardt technique. The method provides center location, diameter and orientation of the vessel as well as blood and background mean density values. The method is tested on synthetic data and real patient data with encouraging results.

Straka M, La Cruz A, Köchl A, Dimitrov LI, Srámek M, Fleischmann D, Gröller E
Bone Segmentation in CT Angiography Data Using a Probabilistic Atlas
Vision, Modeling, and Visualization VMV 2003 2003; 505-512.

Automatic segmentation of bony structures in CT angiography datasets is an essentioal pre-processing step necessary for most visualization and analysis tasks. Since traditional density and gradient operators fail in non-trivial cases (or at least require extensive operator work), we propose a new method for segmentation of CTA data based on a probabilistic atlas. Storing densities and masks of previously manually segmented tissues in the atlas can constitute a statistical information base for later accurate segmentation. In order to eliminate dimensional and anatomic variability of the atlas input datasets, these have to be spatially normalized (registered) first by aplying a non-rigid transformation. After this transformation, densities and tissue masks are statistically processed (e.g. averaged) within the atlas. Records in the atlas can be later evaluated for estimating the probability of bone tissue in a voxel of unsegmented dataset.

Kanitsar A, Wegenkittl R, Fleischmann D, Gröller E
Advanced Curved Planar Reformation: Flattening of Vascular Structures
IEEE Visualization 2003 2003; 43-50.

Traditional volume visualization techniques may provide incomplete clinical information needed for applications in medical visualization. In the area of vascular visualization important features such as the lumen of a diseased vessel segment may not be visible. Curved Planar Reformation (CPR) has proven to be an acceptable practical solution. Existing CPR techniques, however, still have diagnostically relevant limitations. In this paper we introduce two advanced methods for efficient vessel visualization, based on the concept of CPR. Both methods benefit from relaxation of spatial coherence in favor of improved feature perception. We present a new technique to visualize the interior of a vessel in a single image. A vessel is re-sampled along a spiral around its central axis. The helical spiral depicts the vessel volume. Furthermore, a method to display an entire vascular tree without mutually occluding vessels is presented. Minimal rotations at the bifurcations avoid occlusions. For each viewing direction the entire vessel structure is visible.

Kanitsar A, Fleischmann D, Wegenkittl R, Felkel P, Gröller E
CPR - Curved Planar Reformation

IEEE Visualization 2002 2002; 37-44.

Visualization of tubular structures such as blood vessels is an importanttopic in medical imaging. One way to display tubularstructures for diagnostic purposes is to generate longitudinal cross-sectionsin order to show their lumen, wall, and surrounding tissuein a curved plane. This process is called Curved Planar Reformation(CPR). We present three different methods to generate CPRimages. A tube-phantom was scanned with Computed Tomography(CT) to illustrate the properties of the different CPR methods. Furthermorewe introduce enhancements to these methods: thick-CPR,rotating-CPR and multi-path-CPR.

Kanitsar A, Wegenkittl R, Felkel P, Fleischmann D, Sandner D, Gröller E
Computed Tomography Angiography: A Case Study of Peripheral Vessel Investigation
IEEE Visualization 2001 2001; 477-480.

This paper deals with vessel exploration based on computed tomography angiography. Large image sequences of the lower extremities are investigated in a clinical environment. Two different approaches for peripheral vessel diagnosis dealing with stenosis and calcification detection are introduced. The paper presents an automated vessel-tracking tool for curved planar reformation. An interactive segmentation tool for bone removal is proposed.

Diploma and Doctoral Theses

Thomas Auzinger.
Sampled and Prefiltered Anti-Aliasing on Parallel Hardware

PhD Thesis, Vienna University of Technology, 2015

Haichao Miao.
Visual Quantification of the Circle of Willis in Stroke Patients

Diploma Thesis, Vienna University of Technology, 2015

Markus Schreiner.
Accuracy of Low-Dose CT Angiography of the Peripheral Arteries in Patients with Symptomatic Peripheral Arterial Occlusive Disease: Comparison to DSA.

Diploma Thesis, Medical University of Vienna, 2014

Christian Hirsch.
Automatic Breast Lesion Examination of DCE-MRI Data Based on Fourier Analysis

Diploma Thesis, Vienna University of Technology, 2015

Gabriel Mistelbauer.
Smart Interactive Vessel Visualization in Radiology.

PhD Thesis, Vienna University of Technology, 2013

Andrea Harant
Towards Automatic Processing of Peripheral CT-A Datasets

Diploma Thesis, Vienna University of Technology, 2006

Matthias Michael Bernhard
Efficient CPU-based Direct Volume Rendering For CT-Angiography Diploma
Diploma Thesis, Vienna University of Technology, 2006

Matúš Straka
Processing and Visualization of Peripheral CT-Angiography Datasets
PhD Thesis, Vienna University of Technology, 2006

Alexandra La Cruz
Modelling and Reconstruction of Peripheral Vascular Structures

PhD Thesis,
Vienna University of Technology, 2006

Armin Kanitsar
Curved Planar Reformation for Vessel Visualization

PhD Thesis,
Vienna University of Technology, 2004

Armin Kanitsar
Advanced Visualization Techniques for Vessel Investigation

Diploma Thesis, Vienna University of Technology, 2001