PubMed Health⌕ Search

Biomedical subjects

Stefan Schaller

Publications and source records attributed to Stefan Schaller.

15 recordsLinked to original sources
PubMed2006

Augmented reality visualization for CT-guided interventions: system description, feasibility, and initial evaluation in an abdominal phantom.

UNLABELLED: The purpose of this study was to evaluate the feasibility and performance of an augmented reality (AR) visualization prototype for virtual computed tomography (CT)-guided interventional procedures in a multimodality abdominal phantom. With the aid of AR guidance, three radiologists performed 30 attempts at targeting simulated liver lesions of different sizes (range, 5-15 mm) with a biopsy needle. The position of the needle tip relative to the lesion was verified by using ultrasonography and CT. With AR guidance, lesions were successfully targeted with the first needle pass in all cases. On the basis of these results, AR visualization for CT-guided intervention appears feasible and allows intuitive and accurate lesion targeting in a phantom. SUPPLEMENTAL MATERIAL: radiology.rsnajnls.org/cgi/content/full/2401040018/DC1

Abdomen↗
PubMed2005

Peripheral artery stent visualization and in-stent stenosis analysis in 16-row computed tomography: an in-vitro evaluation.

The accuracy of 16-row multidetector CT in the visualization of different peripheral artery stents and in the appraisal of in-stent stenosis was assessed. Nine different stent types (nitinol and stainless steel) with three diameters (6, 8 and 10 mm) were used; altogether 27 stents were analyzed in a barrel-shaped vascular model. Low-grade (<40%) and high-grade (>60%) in-stent stenoses were simulated by polyurethane sticks (70 HU) of differing diameters (2-6 mm). Imaging was performed with 16x0.75-mm detector collimation, 130 mAs, 120 kV, 12-mm table feed/rotation, 1.0-mm slice thickness and 0.5-mm increment. The stent diameter, strut thickness, in-stent attenuation values, degree and degree of in-stent stenosis were evaluated. Nitinol stents showed significantly (P<10-6) less stent lumen narrowing, artificial strut thickening and overestimation of the degree of in-stent stenoses than stainless steel stents. In-stent attenuation values and artificial strut thickening were significantly (P<10-6) lower in 10- and 8-mm stents than in 6-mm stents. Stent lumen narrowing was significantly less in 10-mm stents than in 8-mm (P<10-4) or 6-mm (P<10-6) stents. In-stent stenoses were significantly overestimated, irrespective of the stent diameter. In 6-mm stents overestimation was significantly higher than in 8-mm (P<0.01) or 10-mm stents (P<10-6). Under in-vitro conditions 16-row MDCT allowed an accurate identification of in-stent stenosis, but significantly overestimated the effective degree of the stenosis.

Constriction, Pathologic↗
PubMed2005

Multi-detector row CT systems and image-reconstruction techniques.

The introduction in 1998 of multi-detector row computed tomography (CT) by the major CT vendors was a milestone with regard to increased scan speed, improved z-axis spatial resolution, and better utilization of the available x-ray power. In this review, the general technical principles of multi-detector row CT are reviewed as they apply to the established four- and eight-section systems, the most recent 16-section scanners, and future generations of multi-detector row CT systems. Clinical examples are used to demonstrate both the potential and the limitations of the different scanner types. When necessary, standard single-section CT is referred to as a common basis and starting point for further developments. Another focus is the increasingly important topic of patient radiation exposure, successful dose management, and strategies for dose reduction. Finally, the evolutionary steps from traditional single-section spiral image-reconstruction algorithms to the most recent approaches toward multisection spiral reconstruction are traced.

Electrocardiography↗
PubMed2005

Assessment of coronary artery stents using 16-slice MDCT angiography: evaluation of a dedicated reconstruction kernel and a noise reduction filter.

To compare the effect of different reconstruction kernels and a noise-reducing postprocessing filter on the delineation of coronary artery stents in 16-slice CT-angiography. Ten patients with coronary stents (seven LAD, five RCX and three RCA) were examined with a 16-slice MDCT using standard acquisition parameters. Images were reconstructed using a medium soft (B30f) and a dedicated, edge-enhancing kernel (B46f). Additional postprocessing with an edge-preserving filter was performed on B46f images to reduce the image noise. In multiplanar reformations (MPRs) along and perpendicular to the stent axis, intraluminal attenuation values and the visible lumen diameter were measured. Image noise was measured in the subcutaneous fat using a region of interest (ROI) technique. Arterial enhancement in the aorta was 275.1 HU. Attenuation in the stent lumen was 390.4, 340.0 and 346.8 HU in MPRs derived from B30f, original B46 and postprocessed B46f images. The mean noise level was 20.4, 35.0 and 24.9 HU respectively. The visible lumen diameter was significantly greater in B46f and postprocessed B46f images (2.17 and 2.16 mm), compared to 1.93 mm in B30f images (p<0.01). Edge-enhancing reconstruction kernels increase the visible stent lumen, but also increase image noise. Dedicated postprocessing filters can reduce the introduced noise without a loss of spatial resolution.

Artifacts↗
PubMed2005

Approaches to CT perfusion imaging in pulmonary embolism.

Computed tomography (CT) has become an increasingly accepted technique and is the method of choice for direct visualization of pulmonary emboli (PE). The quantitative assessment of tissue perfusion may yield more important information for patient management than the direct visualization of emboli by CT alone. Several attempts have been made to measure pulmonary blood flow by administration of intravenous contrast material. In this article, various experimental CT approaches for visualization and quantification of pulmonary perfusion are discussed. Ideally, CT will be able to provide both structural and functional information. Simple measurement of lung density before and after intravenous contrast delivery has been performed with single-slice CT technology using region-of-interest methodology. For electron-beam CT, a repeated data acquisition on a 7.6-cm lung volume has proven to be technically feasible. Using such dynamic scanning, reduced blood flow was observed in occluded lung segments. Color-encoded parenchymal density distribution in the axial, coronal, and sagittal planes was derived from thin collimation data sets using four-row multi-slice spiral CT (MSCT). Initial animal data from 16-slice MSCT offer a real CT-subtraction technique of the entire chest for the first time.

Color↗
PubMed2004

Weighted FBP--a simple approximate 3D FBP algorithm for multislice spiral CT with good dose usage for arbitrary pitch.

A new 3D reconstruction scheme, weighted filtered backprojection (WFBP) for multirow spiral CT based on an extension of the two-dimensional SMPR algorithm is described and results are presented. In contrast to other 3D algorithms available, the algorithm makes use of all available data for all pitch values. The algorithm is a FBP algorithm: linear convolution of the parallel data along the row direction followed by a 3D backprojection. Data usage for arbitrary pitch values is maintained through a weighting scheme which takes into account redundant data. If proper row weighting is applied, the image quality is superior to the image quality of the SMPR algorithm.

Algorithms↗
PubMed2003

Multidetector-row cardiac CT: diagnostic value of calcium scoring and CT coronary angiography in patients with symptomatic, but atypical, chest pain.

The aim of this study was to investigate the accuracy of multidetector-row cardiac CT (MDCT), calcium scoring (Ca-Sc), and MDCT coronary angiography (MD CTA) in the assessment of coronary atherosclerosis. Thirty-eight patients underwent invasive coronary angiography (CA) and MDCT (collimation 4x1 mm, pitch 1.5 mm, TI 500 ms, 120 kV, 300 mAs, and retrospective ECG-gating). Calcium scoring was calculated for the total coronary artery territory and for RCA, LCA, and LCX separately. The MD CTA served to assess the degree and the localization of stenoses. All findings were compared to invasive coronary angiography. Approximately 68.4% (390 of 570) of all coronary segments could be visualized by MDCT. Correlation coefficient for MD CTA and CA amounted to r=0.58, showing distinct differences for the individual segments. Proximal segments generally showed better correlation (range 0.81-0.77) than medial segments (range 0.91-0.20), distal segments (range 0.55-0.04), or side branches (range 0.76-0.00). Patients with hemodynamically relevant (>75%) stenoses were detected by MD CTA with 72.2% sensitivity (13 of 18) and 100% specificity (20 of 20). For Ca-Sc sensitivity ranged between 94.7% (17 of 18) and 66.7% (12 of 18), specificity between 20% (4 of 20) and 80% (16 of 20) respectively, depending on the prevailing cutoff value. Combination of both methods led to 83.3% sensitivity (15 of 18) and 100% specificity (20 of 20), reaching no level of significance as compared with Ca-Sc (p=0.73) or MD CTA (p=0.23) alone. Calcium scoring as a single method showed highest sensitivity in the detection of coronary atherosclerosis but at the expense of low specificity. In patients with no or moderate calcifications, combination with MD CTA helped to distinctly increase specificity and NPV.

Adult↗
PubMed2003

Performance evaluation of a multi-slice CT system with 16-slice detector and increased gantry rotation speed for isotropic submillimeter imaging of the heart.

BACKGROUND: 4-slice CT scanners have shown limitations in clinical application for noninvasive coronary CT angiography (CTA). We evaluate advances in ECG-gated scanning of the heart and the coronary arteries with recently introduced 16-slice CT equipment (SOMATOM Sensation 16, Siemens, Forchheim, Germany). MATERIALS AND METHODS: The technical principles of ECG-gated cardiac scanning, scan parameters, and detector design of the new scanner are presented. ECG-gated scan and image reconstruction techniques and ECG-controlled dose modulation ("ECG pulsing") for a reduction of the patient dose are described, key parameters for image quality and simulation results presented, and phantom studies and initial patient experience discussed. The impact of reduced gantry rotation time (0.42 s) on temporal resolution and initial estimations of the patient dose are presented. RESULTS: Extensions of ECG-gated reconstruction algorithms used for 4-slice CT provide adequate image quality for up to 16 slices. For each detector collimation different slice widths are available for retrospective reconstruction with well-defined slice sensitivity profiles (SSPs). For coronary CTA the heart can be covered with 0.75 mm collimation within a 20-s breathhold. The best possible spatial resolution is 0.5 x 0.5 x 0.6 mm. For 0.42 s gantry rotation time, temporal resolution reaches its optimum (105 ms) at a heart rate of 81 bpm. Effective patient dose for coronary CTA is 4-5 mSv using ECG-pulsed acquisition. CONCLUSION: The clinical performance of coronary CTA by means of spatial resolution, temporal resolution and scan time is substantially improved with the evaluated 16-slice CT scanner. Also, display of smaller coronary segments and instent visualization are substantially improved.

Algorithms↗
PubMed2003

Advances in cardiac imaging with 16-section CT systems.

RATIONALE AND OBJECTIVES: The authors present advances in electrocardiographically (ECG) gated cardiac spiral scanning with recently introduced 16-section computed tomographic (CT) equipment. MATERIALS AND METHODS: The authors discuss the technical principles of ECG-gated cardiac scanning. They give an overview on system properties and on the detector design. They describe ECG-gated scan- and image-reconstruction techniques and ECG-controlled dose modulation ("ECG pulsing") for a reduction of the patient dose. They discuss key parameters for image quality and present simulation and phantom studies and they give preliminary values for the patient dose. RESULTS: An extension of the adaptive cardiac volume reconstruction for ECG-gated spiral CT provides adequate image quality for up to 16 sections. With the smallest reconstructed section width (about 0.83 mm) and overlapping image reconstruction, cylindrical holes 0.6-0.7 mm in diameter can be resolved in a transverse resolution phantom independent of the heart rate. For coronary CT angiography, the influence of transverse resolution is most pronounced for coronary segments that are only slightly tilted relative to the scan plane. In this case, visualization of stents and plaques is considerably improved with 1.0-mm or smaller section width. For 0.42-second gantry rotation time, temporal resolution reaches its optimum (105 msec) at a heart rate of 81 beats per minute. Effective patient dose for the standard protocols recommended by the manufacturer ranges from 0.45 mSv (male) for ECG-triggered calcium scoring to 7.1 mSv (male) for high-resolution ECG-gated coronary CT angiography. With ECG pulsing, the dose is reduced by 30%-50% depending on the patient's heart rate. CONCLUSION: Clinical experience will be needed to evaluate fully the potential of 16-section technology for cardiac imaging.

Artifacts↗
PubMed2003

Low-dose multislice spiral computed tomography in acute lung injury: animal experience.

RATIONALE AND OBJECTIVES: To compare low-dose multislice spiral CT (MSCT) with a standard protocol for the evaluation of acute lung injury (ALI) in an animal model. MATERIALS AND METHODS: Eleven healthy intubated pigs (weight: 32.4 kg +/- 1.9 kg) underwent lung lavage to induce experimental lung injury before CT examinations. Scanning was performed using a MSCT-technique. The entire chest was scanned using a thin-collimated protocol (140 kV; 100 mAs). The examinations were performed in inspiratory breath-hold in supine and in prone positions. Scanning was repeated after reduction of the tube current time product down to 20 mAs. All other parameters were kept constant. Subjective image quality was rated using a six-point scale by three experienced radiologists. In addition, objective criteria, based on signal to noise measurements, were assessed. Finally, the extent, localization, and distribution of lung opacities was analyzed using dedicated postprocessing software. RESULTS: Subjective image quality was rated inferior in the low-dose MSCT-examinations (prone position: 2.1 vs. 3.0; supine position: 1.5 vs. 2.5). Hence, pixel noise was nearly doubled. However, exact information about the extent, localization and distribution of lung opacities was provided. There were no statistically significant differences between standard and low-dose MSCT in this respect. CONCLUSIONS: In the animal experiments, low-dose MSCT-scanning did not impair the diagnostic accuracy in ALI, offering an advantageous reduction of radiation exposure.

Animals↗
PubMed2003

A new algorithm for metal artifact reduction in computed tomography: in vitro and in vivo evaluation after total hip replacement.

RATIONALE AND OBJECTIVES: To evaluate a newly developed algorithm for metal artifact reduction (MAR) in Computed Tomography (CT). METHODS: A projection interpolation algorithm for MAR with threshold-based metal segmentation was developed. First, the algorithm was tested with a simulated hip phantom. On demand, the presence of metallic inserts was simulated, representing total hip endoprostheses. Second, CT data of 20 patient with total hip endoprosthesis were reconstructed with and without application of the MAR algorithm. Image quality was independently assessed by 2 experienced radiologists using a qualitative score. The results of the in vitro study were evaluated with the Student's t test. Results of the in vivo study were analyzed using a repeated-measure analysis of variance. RESULTS: Applying the MAR algorithm the phantom study showed no significant difference between images with and without simulated metal contributions. The patient study revealed improved image quality using the MAR algorithm. Results were statistically significant for fat (P=0.0097), vessels (P=0.0091), and bone (P=0.0005). Improvement of the image quality for muscle was not statistically significant (P=0.0287). CONCLUSIONS: A new algorithm for metal artifact reduction was successfully introduced into clinical routine. The algorithm led to a robust reduction of metal artifacts. The MAR algorithm may serve for an improvement in image quality in patients with metallic implants.

Aged↗
PubMed2003

Spatial domain filtering for fast modification of the tradeoff between image sharpness and pixel noise in computed tomography.

In computed tomography (CT), selection of a convolution kernel determines the tradeoff between image sharpness and pixel noise. For certain clinical applications it is desirable to have two or more sets of images with different settings. So far, this typically requires reconstruction of several sets of images. We present an alternative approach using default reconstruction of sharp images and online filtering in the spatial domain allowing modification of the sharpness-noise tradeoff in real time. A suitable smoothing filter function in the frequency domain is the ratio of smooth and original (sharp) kernel. Efficient implementation can be achieved by a Fourier transform of this ratio to the spatial domain. Separating the two-dimensional spatial filtering into two subsequent one-dimensional filtering stages in the x and y directions using a Gaussian approximation for the convolution kernel further reduces computational complexity. Due to efficient implementation, interactive modification of the filter settings becomes possible, which can completely replace the variety of different reconstruction kernels.

Algorithms↗
PubMed2003

Multi-detector row CT versus coronary angiography: preoperative evaluation before totally endoscopic coronary artery bypass grafting.

PURPOSE: To assess multi-detector row spiral computed tomography (CT) for preoperative evaluation of patients undergoing totally endoscopic coronary artery bypass grafting and to correlate the data with coronary angiographic and intraoperative findings. MATERIALS AND METHODS: Thirty-six patients preoperatively underwent multi-detector row CT (4 x 1-mm collimation, pitch of 1.5, 500-msec rotation time, retrospective electrocardiographic gating, 1.25-mm effective section thickness) and coronary angiography. Assessment criteria for both techniques were visibility and cardiac course of coronary arteries, localization and degree of stenoses, composition of atherosclerotic plaques, and vascular diameter at anastomosis site. Site for distal bypass anastomosis was recommended. Results at multi-detector row CT were calculated relative to results at coronary angiography and surgery. RESULTS: Multi-detector row CT properly displayed 79.4% (154 of 194) of all surgical relevant coronary segments and 80.4% (434 of 540) of all coronary segments. For coronary angiography, ratios of 88.7% (172 of 194) and 94.6% (511 of 540), respectively, were observed. For detection of calcified plaques, multi-detector row CT results exceeded those at coronary angiography by a difference of 17% (18 of 18 [100%] compared with 15 of 18 [83%]). Hemodynamically relevant stenoses were identified with multi-detector row CT in 76% (42 of 55) of cases. Bridging of coronary segments through either myocardium (four of five) or epicardial fat (two of three) was better identified at multi-detector row CT than it was at coronary angiography (one of five compared with zero of three, respectively). At multi-detector row CT, 76% (28 of 37) of all distal bypass touchdown segments were identified, but at coronary angiography, only 70% (26 of 37) were identified. CONCLUSION: Multi-detector row CT provides extended information about coronary target site and therefore should be regarded as an ideal additive planning tool for complex minimally invasive procedures such as totally endoscopic coronary artery bypass grafting or minimally invasive direct coronary artery bypass grafting.

Adult↗
PubMed2002

Spatial domain image filtering in computed tomography: feasibility study in pulmonary embolism.

Our objective was to evaluate the clinical feasibility of spatial domain filtering as an alternative to additional image reconstruction using different kernels in chest CT. Spatial domain filtering generates smooth images from sharp images and thus avoids the need for additional reconstructions when two sets of images are desired. Forty adult patients with clinical suspicion of pulmonary embolism were examined utilizing multi-slice CT (Somatom Volume Zoom, Siemens, Germany). Derived from thin collimated source images (100 mAs, collimation 4x1 mm, rotation time 0.5 s, table speed 7 mm/rotation), two sets of images [effective slice thickness (S(eff)) 5 mm, reconstruction increment (RI) 5 mm) were generated using lung (Siemens B50) and soft tissue (Siemens B30) kernels. Additionally, B50 images were filtered in the spatial domain, producing images largely equivalent to B30 images. Firstly, diagnostic accuracy was assessed on spatial domain filtered images regarding central, segmental, and subsegmental pulmonary embolism. In a second step, diagnostic accuracy was assessed for the initially reconstructed B30 images. The results were compared with thin axial slices from the same data set, which were considered as the gold standard in this respect (S(eff )1.25 mm, RI 0.8 mm; B30). Initially reconstructed B30 slices and secondary filtered images were rated for subjective image quality, using a five-point scale (1=excellent, 2=good, 3=moderate, 4=poor, 5=non-diagnostic). Finally, quantitative measurements were assessed using the region of interest (ROI) methodology. In 20 patients pulmonary embolism was proven. Five-millimeter images revealed 10 of 10 central emboli, 18 of 19 segmental thrombi, and 18 of 20 emboli on the subsegmental level. Pulmonary embolism was excluded in 18 of 20 subjects, and in 2 patients a false-positive result was obtained in subsegmental arteries. These findings were concordant for reconstructed and filtered images. Quantitative density measurements provided comparable Hounsfield units in this respect. Subjective gradings of image quality, based on soft tissue settings, were 1.30 (+/-0.61) for reconstructed slices vs 1.35 (+/-0.62) for filtered images (weighted kappa coefficient 0.6117; 95% confidence intervals 0.3298-0.8935). Spatial domain filtering has proved to be feasible. Compared with conventional soft tissue reconstructions for central, segmental, and subsegmental pulmonary embolism, no significant difference in the diagnostic value of spatial domain filtered images was found. Online modifications of image sharpness and pixel noise in real time leads to a considerable reduction of processing time and cost saving for storage of CT images. Despite different data processing methods, thin effective slice thicknesses and overlapping reconstruction increments are mandatory for detailed CT analysis of pulmonary embolism on the segmental and subsegmental level.

Feasibility Studies↗