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S Schaller

Publications and source records attributed to S Schaller.

At least 19 recordsLinked to original sources
PubMed2002

A retrospectively ECG-gated multislice spiral CT scan and reconstruction technique with suppression of heart pulsation artifacts for cardio-thoracic imaging with extended volume coverage.

A method for cardio-thoracic multislice spiral CT imaging with ECG gating for suppression of heart pulsation artifacts is introduced. The proposed technique offers extended volume coverage compared with standard ECG-gated spiral scan and reconstruction approaches for cardiac applications: Thin-slice data of the entire thorax can be acquired within one breath-hold period using a four-slice CT system. The extended volume coverage is enabled by a modified approach for ECG-gated image reconstruction. For a CT system with 0.5-s gantry rotation time, images are reconstructed with 250-ms image temporal resolution. Instead of selecting scan data acquired in exactly the same phase of the cardiac cycle for each image as in standard ECG-gated reconstruction techniques, the patient's ECG signal is used to omit scan data acquired during the systolic phase of highest cardiac motion. With this approach cardiac pulsation artifacts in CT studies of the aorta, of paracardiac lung segments, and of coronary bypass grafts can be effectively reduced.

Aortic Diseases↗
PubMed2002

Strategies for cardiac CT imaging.

We review the scanning techniques for cardiac CT imaging with single slice and multislice scanners. Combined with prospective triggering for transaxial scanning and retrospective gating for helical scanning the potential advantages and the basic limitations are discussed. Based on those theoretical considerations, the major conclusion is that high resolution data sets with isotropic spatial resolution can be acquired with quadslice, spiral scanning, only. First clinical results support this conclusion.

Heart↗
PubMed2002

Defining the optimum upper heart rate limit during exercise: a study in pacemaker patients with heart failure.

AIMS: There is no non-invasive method to determine the individual optimum of maximum exercise heart rate. Knowledge of this value is of particular interest in patients with structural heart disease who are prone to tachycardia intolerance. The purpose of this study was to define the optimal maximum heart rate using cardiopulmonary exercise testing and exercise Doppler echocardiography and to compare the results of both approaches. METHODS AND RESULTS: In 49 pacemaker patients with chronotropic incompetence, the optimum upper heart rate limit was determined using cardiopulmonary exercise testing and exercise Doppler echocardiography. The optimum upper rate limit was given by the highest pacing rate which still produced an increase in oxygen consumption, or by that pacing rate which was linked to the lowest value for the Doppler-derived myocardial performance index. In patients with normal left ventricular ejection fraction (>or=55%) the optimum upper rate limit was 86% of age-predicted maximum heart rate, in patients with left ventriuclar dysfunction (ejection fraction <or=45%) it was 75% of the age-predicted maximum rate (P=0.004). The optimum upper rate limit, as defined by cardiopulmonary exercise testing and exercise Doppler echocardiography, were closely correlated (P<0.0001) with a mean deviation of 6+/-6 beats x min(-1). CONCLUSION: Cardiopulmonary exercise testing and exercise Doppler echocardiography are valuable tools which help to determine the optimum upper rate limit in order to avoid excess heart rates in heart failure patients. The application of these methods is not limited to pacemaker patients but may be helpful in therapeutic interventions with chronotropic drugs.

Adult↗
PubMed2002

[A differentiated approach to the diagnosis of pulmonary embolism and deep venous thrombosis using multi-slice CT].

PURPOSE: To establish a differentiated protocol for multi-slice CT (MSCT) examinations in cases of clinically suspected pulmonary embolism (PE) using pulmonary CT-angiography (CTA) and indirect CT-phlebography (CTP). MATERIALS AND METHODS: 161 patients with suspected PE were examined using an MSCT (SOMATOM Volume Zoom; Siemens, Forchheim, Germany). After intravenous administration of 120 ml of contrast material, a thin collimation chest-CT scan was performed (120 kV, 100 mAs, collimation: 4 x 1 mm). If PE was present, or previous examinations and clinical signs suggested deep venous thrombosis (DVT), a CTP was subsequently completed. CTPs were performed using a 4 x 5 mm protocol (120 kV, 170 mAs). Venous phase scanning, starting from the pelvic crest, was completed in the popliteal fossa three minutes after contrast material injection. In 73 extremities, CTP were compared to the results of ultrasound, phlebography and autopsy. Scan ranges were documented in all patients. Cumulative doses were calculated for male and female subgroups. RESULTS: 62 patients in our series suffered from PE and in 47 of these patients deep venous thrombosis was seen additionally. Of the 99 patients without PE, 47 also received indirect CTP. CTP confirmed the suspicion and extent of DVT in 8 patients. Only in 2 of 39 patients (5.1 %) was previously unknown DVT found, despite the exclusion of PE. Regarding DVT, sensitivity was 94.3 % and specificity was 92.1 % for indirect CTP. Cumulative chest CT doses averaged 3.3 mSv for males and 4.2 mSv for females, the calculated CTP dosage was 9.3 mSv (according to ICRP 60). CONCLUSIONS: The examination protocol presented is suitable for clinical usage in patients with suspected PE. If PE is confirmed, indirect CTP is justified, so that detailed information of the venous system can be obtained. However, the relatively high radiation dosage of an additional CTP requires a strict indication regiment in patients with a negative CTA.

Adult↗
PubMed2002

[Visualization of coronary arteries in CT as assessed by a new 16 slice technology and reduced gantry rotation time: first experiences].

PURPOSE: First evaluation of image quality of a new 16-slice multidetector-row computed tomography (MDCT) for the assessment of coronary artery disease and lesion detection of the coronary arteries. MATERIALS AND METHODS: On a newly developed 16-slice CT scanner (SOMATOM Sensation 16, Siemens, Forchheim, Germany) a calcium score as well as a contrast-enhanced CT angiography (CTA) were performed on 4 patients with retrospective ECG-gating and a gantry rotation time of 420 ms to exclude or follow-up coronary heart disease. CTA was performed after injecting 120 ml contrast media intravenously. After medication with a ss-Blocker, the heart rate was between 55 and 67 bpm. RESULTS: The scan time for calcium score was 12 s, for CTA 18 s (scan range 15 and 12 cm, respectively). Volume score was between 0 and 256.4. In the CT angiography the entire coronary tree could be visualized in all patients up to the very distal subsegmental branches. In two patients a complete occlusion of the RCA and the LAD were depicted, respectively. In one of these patients, a large aneurysm of the left anterior ventricular wall was also delineated. CONCLUSION: Considering our first experiences with the new 16-slice technology, an excellent visualization of the entire coronary tree including the very distal and side branches due to substantially increased spatial resolution seems to be achievable. In these patients the acquired image quality raises the hope for improved, non-invasive cardiac diagnostics. In larger studies, the clinical impact of this new technology needs to be further investigated.

Aged↗
PubMed2002

New technical developments in multislice CT--Part 1: Approaching isotropic resolution with sub-millimeter 16-slice scanning.

The introduction of multislice CT was a breakthrough with regard to increased scan speed, improved axial resolution and better utilization of the tube output. The new generation of multislice CT scanners offering simultaneous acquisition of up to 16 sub-millimeter slices represents an important leap on the way towards true isotropic scanning. We present an evaluation of a state-of-the-art 16-slice CT system (SOMATOM Sensation 16, Siemens AG, Forchheim, Germany). After an introduction to the detector design we discuss dose utilization and finally elaborate on multislice spiral scanning with 16 slices. Due to the increased number of slices dose utilization is improved compared to current 4-slice CT scanners, and sub-millimeter collimation needs no longer be restricted to special applications. For CT systems with 8 or more slices, the cone-beam geometry causes severe artifacts if not corrected for by a so-called cone-correction, which thus becomes mandatory in this case. With the Adaptive Multiple Plane Reconstruction AMPR, cone beam artifacts are effectively suppressed, while the benefits of Adaptive Axial Interpolation are maintained: free selection of the spiral pitch according to the clinical needs of an examination, slice width independent of the pitch, full dose utilization at all pitch values. Clinical practice will have to demonstrate the application spectrum that is opened with the new generation of multislice CT systems.

Artifacts↗
PubMed2002

New technical developments in multislice CT, part 2: sub-millimeter 16-slice scanning and increased gantry rotation speed for cardiac imaging.

Despite all promising advances, some challenges remain for ECG-gated multislice CT examinations of the heart and the coronary arteries with current 4-slice detectors: adequate visualization of stents and severely calcified coronary arteries, examination of patients with higher heart rates and patients, who cannot adequately hold their breath for at least 30 sec. The new generation of multislice CT systems offering simultaneous acquisition of up to 16 sub-millimeter slices and gantry rotation times shorter than 0.5 sec has the potential to overcome these limitations. We describe the technical principles of cardiac scanning with a state-of-the-art 16-slice CT equipment (SOMATOM Sensation 16, Siemens AG, Forchheim, Germany). We discuss an extension of the Adaptive Cardio Volume (ACV) reconstruction approach for ECG-gated multislice spiral CT. We show the impact of reduced gantry rotation time (0.42 sec) on temporal resolution, and we demonstrate the influence of slice width on the visualization of stents and plaques. Deviating from general purpose applications a cone-correction is not required for cardiac scanning with 16-slice CT systems. In addition to the absolute improvement, the temporal resolution shows a different dependence on the patient's heart rate for 0.42 sec rotation time, reaching its optimum (105 msec) at 81 BPM. This has the potential to expand the range of heart rates accessible to routine clinical examinations. Owing to sub-millimeter slice width and optimized in-plane resolution characteristics, visualization of stents and severe calcifications in coronary arteries is significantly improved. Clinical experience will be needed to fully evaluate the potential of 16-slice technology for cardiac imaging.

Artifacts↗
PubMed2001

A human RNA polymerase II subunit is encoded by a recently generated multigene family.

BACKGROUND: The sequences encoding the yeast RNA polymerase II (RPB) subunits are single copy genes. RESULTS: While those characterized so far for the human (h) RPB are also unique, we show that hRPB subunit 11 (hRPB11) is encoded by a multigene family, mapping on chromosome 7 at loci p12, q11.23 and q22. We focused on two members of this family, hRPB11a and hRPB11b: the first encodes subunit hRPB11a, which represents the major RPB11 component of the mammalian RPB complex; the second generates polypeptides hRPB11balpha and hRPB11bbeta through differential splicing of its transcript and shares homologies with components of the hPMS2L multigene family related to genes involved in mismatch-repair functions (MMR). Both hRPB11a and b genes are transcribed in all human tissues tested. Using an inter-species complementation assay, we show that only hRPB11balpha is functional in yeast. In marked contrast, we found that the unique murine homolog of RPB11 gene maps on chromosome 5 (band G), and encodes a single polypeptide which is identical to subunit hRPB11a. CONCLUSIONS: The type hRPB11b gene appears to result from recent genomic recombination events in the evolution of primates, involving sequence elements related to the MMR apparatus.

Journal Article↗
PubMed2001

[Diagnosis of lung embolism with multislice spiral CT].

In recent years CT has been established as the method of choice for the diagnosis of central pulmonary embolism to the level of the segmental arteries. The key advantage of CT over competing modalities is the reliable detection of relevant alternative or additional disease causing the patient's symptoms. Although the clinical relevance of isolated peripheral emboli remains unclear, the alleged poor sensitivity of CT for the detection of such small clots has to date prevented the acceptance of CT as the gold standard for diagnosing pulmonary embolism. With the advent of multislice CT we can now cover the entire chest of a patient with 1-mm slices within one breath-hold. In comparison with thicker sections the detection rate of subsegmental emboli can be significantly increased with 1-mm sections. In addition the interobserver correlation which can be achieved with 1-mm sections by far exceeds the reproducibility of competing modalities. Meanwhile use of multislice CT for a combined diagnosis of pulmonary embolism and deep venous thrombosis with the same modality appears to be clinically accepted. In the vast majority of patients who receive a combined thoracic and venous multislice CT examination the scan either confirms the suspected diagnosis or reveals relevant alternative or additional disease. The therapeutic regimen is usually chosen based on the functional effect of embolic vascular occlusion. With the advent of fast CT scanning techniques, also functional parameters of lung perfusion can be non-invasively assessed by CT imaging. These advantages let multislice CT appear as an attractive modality for a non-invasive, fast, accurate and comprehensive diagnosis of pulmonary embolism, its causes, effects and differential diagnoses.

Humans↗
PubMed2001

Multi-slice computed tomography as a screening tool for colon cancer, lung cancer and coronary artery disease.

Recent promising trials that use low-dose CT for the early detection of lung cancer have reinvigorated the interest in screening approaches. At the same time the development of fast image acquisition techniques, such as multislice CT, have sparked renewed interest in cardiac imaging within the radiological community. In addition to special cardiac capabilities, multislice CT has several other features such as high acquisition speed and low-dose requirements that may make this modality a universal radiological screening tool. Non-invasive disease detection is the radiologist's domain. In this paper we identify criteria for effective screening and apply these criteria to screening approaches with multislice CT when used for detection of three disease entities: colon cancer; lung cancer; and cardiovascular disease.

Colonic Neoplasms↗
PubMed2001

Multi-slice CT for visualization of pulmonary embolism using perfusion weighted color maps.

PURPOSE: The purpose of our preliminary study was to evaluate the feasibility of a new technique for the perfusion weighted color display of the density of lung parenchyma derived from multi-slice CT (MSCT) data sets of clinical routine examinations for visualization of pulmonary embolism (PE). MATERIALS AND METHODS: Imaging of patients with suspected PE was performed on a commercially available MSCT (Somatom Volume Zoom; Siemens, Forchheim, Germany) after intravenous application of 120 cc of contrast-medium using a power injector. Scan parameters were 140 kV and 100 mAs, using a thin collimation of 4 x 1 mm and a table speed of 7 mm (pitch: 1.75). Derived from thin collimation axial slices (slice thicknesseff. 1.25 mm, reconstruction increment 0.8 mm), a new image processing technique was deployed. Based on these source images, an automated 3D-segmentation of the lungs was performed followed by threshold based extraction of major airways and vascular structures. The filtered volume data were color encoded and finally overlayed onto the original CT images. This color encoded display of parenchymal density distribution of the lungs was shown in axial, coronal and sagittal plane orientation. In four patients with excluded PE as well as in two patients with proven PE this new technique was performed. RESULTS: In the four patients that were considered negative regarding PE on MSCT, lung densitometry showed a homogeneous distribution of color encoded densities without circumscribed decreased or increased areas, beside the usually present gravity-dependent gradient in ventro-dorsal direction. In the two patients with proven PE, low density values on perfusion weighted color maps were found distally to the occluded pulmonary arteries. CONCLUSIONS: Our initial experience indicates that lung densitometry with an optimized display of the density distribution within the lung parenchyma may provide additional information in patients with suspected or proven PE. However, a comparison with ventilation/perfusion scintigraphy and a larger number of patients are necessary for the full clinical evaluation of this new functional imaging methodology.

Aged↗
PubMed2001

[Multi-slice spiral CT of the abdomen in oncological patients: influence of table support and detector configuration on image quality and radiation exposure].

PURPOSE: To evaluate the image quality and radiation exposure of different spiral CT scanning parameters for routine staging examination of the abdomen in oncologic patients using a multi-slice CT scanner. METHODS/MATERIALS: Examination of 40 patients in 4 groups on a multi-slice CT scanner (Somatom VolumeZoom, Siemens AG, Forchheim). Functional detector width (4 x 2.5, 4 x 5 mm) and pitch (table feed in relation to collimated slice width) were varied (3 and 5). Tube voltage (120 kV), effective tube current (160 mAs), slice-thickness (6 mm), increment (4 mm), kernel (B 30), and contrast injection parameters were kept constant. Axial images were assessed by three radiologists regarding delineation of anatomic structures, artifacts, and overall image quality. RESULTS: Significantly reduced image quality especially due to artifacts was observed using a 5 mm detector configuration with a pitch of 5 (scan time 9 sec). Image quality was rated best for a 2.5 mm detector configuration with a pitch of 3 and a scan time of 28 sec. The effective dose was independent of the pitch. However, the mean effective dose was 9% higher using the smaller detector configuration (9.9 mSv vs 10.9 mSv). CONCLUSIONS: For routine staging CT of the abdomen use of a 4 x 2.5 mm detector configuration with a pitch between 3 and 5 is recommended. A 4 x 5 mm detector configuration using overlapping data acquisition can also be recommended, but additional thin slice reformations are not possible.

Abdominal Neoplasms↗
PubMed2001

Individually adapted examination protocols for reduction of radiation exposure in chest CT.

RATIONALE AND OBJECTIVES: To develop a simple directive for the reduction of radiation exposure without loss of diagnostic information in routine chest CT examinations. METHODS: Two hundred fifty adult patients (164 male, 86 female) were entered into a prospective trial. All examinations were performed with a multislice CT technique (Somatom Volume Zoom, Siemens). Four groups of 50 patients each were scanned with patient-related specific parameters: individual mA-s values were derived from the estimated body weight: kilograms + 10, +/- 0, - 10, and - 20 mAs. The results were compared with those of 50 patients who were examined by a standard chest protocol by using the parameters 120 mAs and 140 kV. All other parameters including the tube voltage were kept constant. Subjective image quality was rated on a three-point scale: 1 = excellent, 2 = fair, 3 = nondiagnostic. In addition, objective criteria based on signal-to-noise measurements were assessed by using a region-of-interest methodology. RESULTS: Image quality was sufficient in all cases. Mean subjective gradings of image quality, based on soft-tissue window settings, were 1.1 for the 120-mAs protocol, 1.1 for the (body weight [kg] + 10) mAs protocol, 1.1 for the (body weight [kg] +/- 0) mAs protocol, 1.3 for the (body weight [kg] - 10) mAs protocol, and 1.2 for the (body weight [kg] - 20) mAs protocol. Objective criteria based on noise measurements showed mean +/- standard deviation values of 5.7 +/- 0.8 Hounsfield units (HU) for the 120-mAs protocol. For the reduced-dose protocols, values were calculated as 7.6 +/- 1.2 HU (group + 10), 7.9 +/- 1.3 HU (group +/- 0), 8.7 +/- 1.2 HU (group - 10), and finally 9.1 +/- 1.3 HU (group - 20). The best correlation for an entire subgroup was achieved with the - 10 protocol (body weight [kg] - 10) mAs, with nearly constant noise related to body weight in all patients. CONCLUSIONS: By deriving mAs values from body weight estimation, an individually adapted protocol for chest CT can be recommended and easily employed in a clinical setting. With an adaptation of the tube current-time product based on the estimated body weight of the patient - 10 (body weight [kg] - 10 mAs), a well-balanced examination without significant loss of information, even in soft-tissue window settings, can be performed with this particular scanner. For this adapted mAs protocol, a mean reduction of radiation exposure of 45% was achievable, compared with the standard protocol. A maximum decrease per case down to 31 mAs was obtained, without relevant loss of image quality. Therefore, for other types of CT scanners, analogous protocols may be adapted.

Adult↗
PubMed2001

Advanced single-slice rebinning for tilted spiral cone-beam CT.

Future medical CT scanners and today's micro CT scanners demand cone-beam reconstruction algorithms that are capable of reconstructing data acquired from a tilted spiral trajectory where the vector of rotation is not necessarily parallel to the vector of table increment. For the medical CT scanner this case of nonparallel object motion is met for nonzero gantry tilt: the table moves into a direction that is not perpendicular to the plane of rotation. Since this is not a special application of medical CT but rather a daily routine in head exams, there is a strong need for corresponding reconstruction algorithms. In contrast to medical CT, where the special case of nonperpendicular motion is used on purpose, micro CT scanners cannot avoid aberrations of the rotational axis and the table increment vector due to alignment problems. Especially for those micro CT scanners that have the lifting stage mounted on the rotation table (in contrast to setups where the lifting stage holds the rotation table), this kind of misalignment is equivalent to a gantry tilt. We therefore generalize the advanced single-slice rebinning algorithm (ASSR), which is considered a very promising approach for medical cone-beam reconstruction due to its high image quality and its high reconstruction speed [Med. Phys. 27, 754-772 (2000)], to the case of tilted gantries. We evaluate this extended ASSR approach (which we will denote as ASSR+, for convenience) in comparison to the original ASSR algorithm using simulated phantom data for reconstruction. For the case of nonparallel object motion ASSR+ shows significant improvements over ASSR, however, its computational complexity is slightly increased due to the broken symmetry of the spiral trajectory.

Algorithms↗
PubMed2001

Implementation of a cone-beam reconstruction algorithm for the single-circle source orbit with embedded misalignment correction using homogeneous coordinates.

We present an efficient implementation of an approximate cone-beam image reconstruction algorithm for application in tomography, which accounts for scanner mechanical misalignment. The implementation is based on the algorithm proposed by Feldkamp et al. and is directed at circular scan paths. The algorithm has been developed for the purpose of reconstructing volume data from projections acquired in an experimental x-ray micro-tomography (microCT) scanner. To mathematically model misalignment we use matrix notation with homogeneous coordinates to describe the scanner geometry, its misalignment, and the acquisition process. For convenience analysis is carried out for x-ray CT scanners, but it is applicable to any tomographic modality, where two-dimensional projection acquisition in cone beam geometry takes place, e.g., single photon emission computerized tomography. We derive an algorithm assuming misalignment errors to be small enough to weight and filter original projections and to embed compensation for misalignment in the backprojection. We verify the algorithm on simulations of virtual phantoms and scans of a physical multidisk (Defrise) phantom.

Algorithms↗
PubMed2000

Exact radon rebinning algorithm for the long object problem in helical cone-beam CT.

This paper addresses the long object problem in helical cone-beam computed tomography. We present the PHI-method, a new algorithm for the exact reconstruction of a region-of-interest (ROI) of a long object from axially truncated data extending only slightly beyond the ROI. The PHI-method is an extension of the Radon-method, published by Kudo, Noo, and Defrise in issue 43 of journal Physics in Medicine and Biology. The key novelty of the PHI-method is the introduction of a virtual object fpsi(x) for each value of the azimuthal angle psi in the image space, with each virtual object having the property of being equal to the true object f(x) in some ROI omegam. We show that, for each psi, one can calculate exact Radon data corresponding to the two-dimensional (2-D) parallel-beam projection of fpsi(x) onto the meridian plane of angle psi. Given an angular range of length pi of such parallel-beam projections, the ROI omegam can be exactly reconstructed because f(x) is identical to fpsi(x) in Omegam. Simulation results are given for both the Radon-method and the PHI-method indicating that 1) for the case of short objects, the Radon- and PHI-methods produce comparable image quality, 2) for the case of long objects, the PHI-method delivers the same image quality as in the short object case, while the Radon-method fails, and 3) the image quality produced by the PHI-method is similar for a large range of pitch values.

Algorithms↗
PubMed2000

Spiral interpolation algorithm for multislice spiral CT--part I: theory.

This paper presents the adaptive axial interpolator (AAI), a novel spiral interpolation approach for multislice spiral computed tomography (CT) implemented in a clinical multislice CT scanner, the SOMATOM Volume Zoom (Siemens Medical Systems, Forchheim, Germany). The method works on parallel-beam data generated from the acquired fan-beam data by azimuthal rebinning. Spiral interpolation is performed by distance-dependent weighting; i.e., for each ray, its distance to the image plane is evaluated and serves as an argument to a freely selectable weighting function, resulting in a weight factor. A normalization step is applied to the weight factors to ensure that the sum of all corresponding weights (i.e., the weights applied to rays that contribute to the same ray in the interpolated sinogram) is 1. By selection of appropriate weighting functions and suitable adjustment of the tube current, it is possible to keep the slice sensitivity profiles (SSP) as well as the pixel noise constant for all pitch values in the relevant range. Also, a large range of slice-thickness can be reconstructed from a given collimation. The method is, thus, very versatile. Further advantages are that it uses the entire applied dose for imaging and allows for efficient implementation using a table lookup approach.

Algorithms↗