Ziele: Da zunehmend 80kV- und 100kV-Protokolle für die pädiatrische Mehrdetektorcomputertomographie (MDCT) publiziert werden, sollte bei konstantem CTDIvol der Einfluss einer Röhrenspannungsreduktion auf die Strahlendosis und die Bildqualität an einem anthropomorphen Kinderphantom untersucht werden. Methode: Die Studie erfolgte mit einem anthropomorphen Kinderphantom (ATOM 705-C, CIRS, USA), einem 5-jährigen Jungen entsprechend, an einem 64-Schicht-MDCT (SOMATOM Sensation 64, Siemens, Forchheim) mit 64×0,6mm Kollimation und 500ms Rotationszeit. Die rekonstruierte Schichtdicke betrug 5mm. Die Scanlänge betrug thorakal 175mm und abdominell 109mm. Ausgehend von einem Standardprotokoll für den Thorax von 120kV und 20mAs mit einem CTDIvol von 1,52mGy und für das Abdomen von 120kV und 50mAseff mit einem CTDIvol von 3,82mGy erfolgten die 100kV und 80kV Scans unter Beibehaltung des CTDIvol. Das Phantom wurde an 47 Stellen mit je drei TLDs bestückt. Jede Messung wurde zehnmal wiederholt. Die Messergebnisse wurden gemittelt. Die Berechnung der effektiven Dosis (ED) erfolgte gemäß ICRP 60 für Jungen(m) und Mädchen(w) getrennt. Zur Beurteilung der objektiven Bildqualität wurden 2 zufällig ausgewählte Serien voneinander subtrahiert. Anhand der Subtraktionsbilder erfolgte mittels ROI-Messung die Bestimmung des Bildrauschens als Maß für die objektive Bildqualität. Ergebnis: Bei konstantem CTDIvol und Absenkung der Röhrenspannung steigt die ED an. Beim Thorax-CT betrug dies bei 100kV 8,05% (m) bzw. 8,95% (w) und bei 80kV 14,64% (m) bzw. 15,06% (w). Bei der abdominellen Untersuchung erhöhte sich die ED auf 4,23% (m) bzw. 5,71% (w) bei 100kV und 9,55% (m) bzw. 9,20% (w) bei 80kV. Die Rauschmessung ergab folgende Werte: thorakal 12,7HE bei 120kV, 13,0HE bei 100kV und 13,7HE bei 80kV sowie abdominell 12,7HE bei 120kV, 12,9HE bei 100kV und 14,5HE bei 80kV. Schlussfolgerung: Eine Reduktion der Röhrenspannung unter Beibehaltung des CTDIvol führt bei einem anthropomorphen Kinderphantom zu einer Erhöhung der Strahlendosis bei gleichzeitiger Verschlechterung der objektiven Bildqualität.

In dual source CT (DSCT) with two X-ray sources and two data measurement systems mounted on a CT gantry with a mechanical offset of 90 deg, cross scatter radiation, (essentially 90 deg Compton scatter) is added to the detector signals. In current DSCT scanners the cross scatter correction is model based: the idea is to describe the scattering surface in terms of its tangents. The positions of these tangent lines are used to characterize the shape of the scattering object. For future DSCT scanners with larger axial X-ray beams, the model based correction will not perfectly remove the scatter signal in certain clinical situations: for obese patients scatter artifacts in cardiac dual source scan modes might occur. These shortcomings can be circumvented by utilizing the non-diagnostic time windows in cardiac scan modes to detect cross scatter online. The X-ray generators of both systems have to be switched on and off alternating. If one X-ray source is switched off, cross scatter deposited in the respective other detector can be recorded and processed, to be used for efficient cross scatter correction. The procedure will be demonstrated for cardiac step&shoot as well as for spiral acquisitions. Full rotation reconstructions are less sensitive to cross scatter radiation; hence in non-cardiac case the model-based approach is sufficient. Based on measurements of physical and anthropomorphic phantoms we present image data for DSCT systems with various collimator openings demonstrating the efficacy of the proposed method. In addition, a thorough analysis of contrast-to-noise ratio (CNR) shows, that even for a X-ray beam corresponding to a 64x0.6 mm collimation, the maximum loss of CNR due to cross scatter is only about 7% in case of obese patients.

Purpose Assessment of calcium scoring (Ca-scoring) on a 64-slice multi-detector computed tomography (MDCT) scanner, a dual-source computed tomography (DSCT) scanner and an electron beam tomography (EBT) scanner with a moving cardiac phantom as a function of heart rate, slice thickness and calcium density. Methods and materials Three artificial arteries with inserted calcifications of different sizes and densities were scanned at rest (0 beats per minute) and at 50-110 beats per minute (bpm) with an interval of 10 bpm using 64-slice MDCT, DSCT and EBT. Images were reconstructed with a slice thickness of 0.6 and 3.0 mm. Agatston score, volume score and equivalent mass score were determined for each artery. A cardiac motion susceptibility (CMS) index was introduced to assess the susceptibility of Ca-scoring to heart rate. In addition, a difference (Delta) index was introduced to assess the difference of absolute Ca-scoring on MDCT and DSCT with EBT. Results Ca-score is relatively constant up to 60 bpm and starts to decrease or increase above 70 bpm, depending on scoring method, calcification density and slice thickness. EBT showed the least susceptibility to cardiac motion with the smallest average CMS-index (2.5). The average CMS-index of 64-slice MDCT (9.0) is approximately 2.5 times the average CMS-index of DSCT (3.6). The use of a smaller slice thickness decreases the CMS-index for both CT-modalities. The Delta-index for DSCT at 0.6 mm (53.2) is approximately 30% lower than the Delta-index for 64-slice MDCT at 0.6 mm (72.0). The Delta-indexes at 3.0 mm are approximately equal for both modalities (96.9 and 102.0 for 64-slice MDCT and DSCT respectively). Conclusion Ca-scoring is influenced by heart rate, slice thickness and modality used. Ca-scoring on DSCT is approximately 50% less susceptible to cardiac motion as 64-slice MDCT. DSCT offers a better approximation of absolute calcium score on EBT than 64-slice MDCT when using a smaller slice thickness. A smaller slice thickness reduces the susceptibility to cardiac motion and reduces the difference between CT-data and EBT-data. The best approximation of EBT on CT is found for DSCT with a slice thickness of 0.6 mm.

Truncation of CT projection data is always coupled with incomplete angular sampling and can lead to severe image artifacts in clinical CT. Extrapolation of projection data is needed to restore CT values inside and outside the scan field of view (SFOV). We present three types of extrapolation schemes. The first type (M1) is characterized by extrapolation of projection data using a virtual object of constant attenuation. For multi-slice helical CT this extrapolation scheme is applied in a row-wise manner. The second type (M2) utilizes consistency conditions of parallel projection data. The conservation of mth order moments of non-truncated projections can be utilized for the extrapolation of truncated projection data by fitting extrapolation functions of variable length. The third method (M3) extrapolates truncated data by sinogram decomposition and completion. For each voxel in image space the corresponding trace in the 3D-sinogram is computed. The minimum signal within each trace is extrapolated to the extended sinogram parts, which represent the extended FOV. Based on the evaluation of both simulation data of an anthropomorphic thorax phantom and clinical data, we evaluate the three reconstruction techniques. Sinogram decomposition proofs to be better than the other techniques, but is computationally very demanding.

We present and evaluate a special ultrahigh resolution mode providing considerably enhanced spatial resolution both in the scan plane and in the ‐axis direction for a routine medical multi‐detector row computed tomography (CT) system. Data acquisition is performed by using a flying focal spot both in the scan plane and in the ‐axis direction in combination with tantalum grids that are inserted in front of the multi‐row detector to reduce the aperture of the detector elements both in‐plane and in the ‐axis direction. The dose utilization of the system for standard applications is not affected, since the grids are moved into place only when needed and are removed for standard scanning. By means of this technique, image slices with a nominal section width of (measured full width at half maximum=) can be reconstructed in spiral mode on a CT system with a detector configuration of . The measured 2% value of the in‐plane modulation transfer function (MTF) is , the measured 2% value of the longitudinal ( axis) MTF is . In a resolution phantom with metal line pair test patterns, spatial resolution of can be demonstrated both in the scan plane and along the axis. This corresponds to an object size of that can be resolved. The new mode is intended for ultrahigh resolution bone imaging, in particular for wrists, joints, and inner ear studies, where a higher level of image noise due to the reduced aperture is an acceptable trade‐off for the clinical benefit brought about by the improved spatial resolution.

Ziele: Evaluation des Einflusses von Herzfrequenz und zeitlicher Auflösung auf die Quantifizierung der globalen Herzfunktion in der Dual-Source Computertomographie (DSCT). Methode: Ein dynamische Herzphantom wurde wiederholt mit einem DSCT Scanner (SOMATOM Definition, Siemens, Forchheim, D) unter Verwendung eines standardisierten Untersuchungsprotokolls mit retrospektivem EKG-Gating gescannt (2×2x32×0.6mm; 120kV; 320 mAsrot, Pitch 0,2). Es wurden verschiedene Herzfrequenzen im Bereich von 40 bis 140 Schlägen/Minute simuliert. Die Bildrekonstruktion erfolgte mit mono- und bi-segmentalen Rekonstruktionsalgorithmen unter Verwendung von Daten einer und beider Röhren-Detektorsysteme. Die ventrikulären Volumina und die die Ejektionsfraktion (EF) wurden mittels semi-automatischer Auswertealgorithmen ermittelt und mit den echten Volumina des Phantoms verglichen. Außerdem wurden die Interscan- and Intraobservervariabilität berechnet. Ergebnis: Die zeitliche Auflösung der Single-Source Datenrekonstruktion betrug 165ms, während die Dual-Source Bildrekonstruktion eine zeitliche Auflösung von 83ms (mono-segmental) bzw. 67,7±14,2ms (bi-segmental) lieferte. Die Abweichung der gemessenen Volumina von den echten Volumina des Phantoms war mit der Dual-Source Datenrekonstruktion geringer als mit der Single-Source Datenrekonstruktion. Für die EF betrug die prozentuale Abweichung von den wahren Volumina des Phantoms im Vergleich der Dual-Source Rekonstruktion mit der Single-Source Rekonstruktion 0,7% (mono-segmental), 0,7% (bi-segmental) bzw. 4,3% (Single-Source). Mit der Dual-Source Datenrekonstruktion bestand keine Korrelation zwischen Herzfrequenz und EF (r=-0,168;r=-0,157), während für die Single-Source Rekonstruktion eine relevante Korrelation (r=-0.844) zu beobachten war. Die Interscan- und Intraobservervariabilität für die EF betrugen 1,4% bzw. 0,9%. Schlussfolgerung: Die DSCT ermöglicht eine herzfrequenzunabhängige Quantifizierung der globalen Herzfunktion. Mit der DSCT kann auf eine multi-segmentale Bildrekonstruktion für die Bestimmung der ventrikulären Funktion verzichtet werden.

Neurogenesis in the adult brain occurs within the two principle neurogenic regions, the hippocampus and the SVZ of the lateral ventricles. The occurrence of adult neurogenesis in non-neurogenic regions including the midbrain remains controversial, but isolation of neural stem cells (NSCs) from several parts of the adult brain including the substantia nigra has been reported. Nevertheless it is unclear whether adult NSCs do have the capacity to produce functional dopaminergic neurons, the cell type lost in Parkinson's disease. We describe here the existence and characterization of NSC in the adult tegmentum (midbrain and hindbrain) in vivo. We developed a model of neurogenesis in the tegmetum according to Doetsch and colleagues for the SVZ of the lateral ventricle, showing the existence of type B and A cells with nearly no C cells at the fourth ventricle. Furthermore, we show here the isolation, expansion and in vitro characterization of adult mouse tegmental neural stem cells (tNSCs) and their differentiation into functional nerve cells including dopaminergic neurons. These tNSCs showed neurosphere formation, expressed high levels of early neuroectodermal markers, such as the proneural genes NeuroD1, Neurog2 and Olig2, the NSC markers Nestin and Musashi1 and the proliferation markers Ki67 and BrdU. The cells showed typical PI-FACS analysis of slowly dividing cells. In the presence of selected growth factors, tNSCs differentiated into astroglia, oligodendroglia and neurons expressing markers for cholinergic, GABAergic and glutamatergic cells. Electrophysiological analyses revealed functional properties of mature nerve cells, such as TTX-sensitive sodium channels, action potentials as well as GABA-, glutamate and NMDA-induced currents. Clonal analysis demonstrated that individual NSCs retain the capacity to generate both glia and neurons. After a multiple-step differentiation protocol using co-culture conditions with PA6 stromal cells, a small number of cells acquired morphological and functional properties of dopaminergic neurons in culture. Here we demonstrate the existence of adult tNSCs with functional neurogenic and dopaminergic potential, a prerequisite for future endogenous cell replacement strategies in Parkinson's disease.

OBJECTIVE:The purpose of our study was to evaluate the dose reduction potential of combined online (x- and y-axes) and topogram-based (l) X-ray tube current modulation in CT colonography in a screening population.MATERIALS AND METHODS:Eighty asymptomatic individuals underwent CT colonography screening for colon polyps. A 16-MDCT scanner (Somatom Sensation 16) was used. Forty patients were examined at 120 kVp and 120 effective mAs (supine) and 40 effective mAs (prone) using online x- and y-axis tube current modulation. Another 40 patients were scanned using combined x-, y-, and z-axis tube current modulation. Individual patient radiation exposure was determined using the dose-length product. Image noise was determined by Hounsfield unit measurements in the colonic lumen at four anatomic levels. Image quality was rated on a 5-point confidence scale by two independent reviewers. The unpaired Student's t test (for radiation dose, image noise) and Wilcoxon's test (for image quality) were used to test for statistically significant differences between these values.RESULTS:Radiation dose was significantly lower in the patient group scanned with x-, y-, and z-axis tube current modulation than in the group scanned with x- and y-axis tube current modulation (supine: 4.24 vs 6.50 mSv, p < 0.0001; prone: 1.61 vs 2.38 mSv, p < 0.0001). Radiation dose was reduced by 35% (supine) and 33% (prone). No statistically significant difference was seen in overall image noise (supine: 15.9 vs 16.3 H, p = 0.13; prone: 23.5 vs 24.8 H, p = 0.44) or image quality (supine: 4.6 vs 4.5, p = 0.62; prone: 3.5 vs 3.6, p = 0.54).CONCLUSION:Combined x-, y-, and z-axis tube current modulation leads to a significant reduction of radiation exposure in CT colonography without loss of image quality.

In cardiac CT temporal resolution is directly related to the gantry rotation time of P generation CT scanners. This time cannot be substantially reduced below current standards of 0.33 s - 0.35 s due to mechanical limitations. As an alternative we present a dual source CT (DSCT) system. The system is equipped with two X-ray tubes and two corresponding detectors that are mounted onto the rotating gantry with an angular offset of 90 degrees. Due to the simultaneous data acquisition and the angular offset, complementary quarter-scan data are measured at the same phase in the cardiac cycle. Hence, the exposure time of any image slice is reduced by a factor of two and the temporal resolution is improved by the same factor. In contrast to single source cardiac CT with multi-segment image reconstruction, the temporal resolution does not depend on the heart rate.Since multi-seament reconstruction techniques applied in single source cardiac CT, which limit the table speed, are no longer needed, faster volume coverage in cardiac spiral imaging can be achieved. As a consequence of these concepts, patient dose in cardiac CT can be significantly reduced.ECG correlated image reconstruction is based on 3D backprojection of the Feldkamp type. Data truncation coming from the fact that one detector (A) covers the entire scan field of view (50 cm in diameter), while the other detector (B) is restricted to a smaller, central field of view (26 cm in diameter), has to be treated. We evaluate temporal resolution and dose efficiency by means of phantom scans and computer simulations. We present first patient scans to illustrate the performance of DSCT for ECG correlated cardiac imaging.

PURPOSE:We sought to investigate the influence of heart rate and temporal resolution on the assessment of left-ventricular (LV) function with multislice spiral computed tomography (CT). MATERIAL AND METHODS:A dynamic cardiac phantom was repeatedly scanned with a 64-slice CT scanner using a standardized scan protocol (64 x 0.6 mm, 120kV, 770mAs(eff), 330 milliseconds rotation time) at different simulated heart rates, ranging from 40 to 140 beats per minute. Images were reconstructed with an algorithm utilizing data from 1 to 4 cardiac cycles (RR intervals). Ejection fraction (EF), end-systolic, end-diastolic, and stroke volume as well as cardiac output were calculated. Results of the measurements were compared with the real volumes of the phantom. Interscan and intraobserver variability were calculated. RESULTS:Using a monosegmental reconstruction algorithm, the temporal resolution was fixed to 165 milliseconds. With bi-, tri-, and quad-segmental image reconstruction, mean temporal resolution was 128.3 +/- 33.2 milliseconds, 103.3 +/- 49.2 milliseconds, and 87.8 +/- 81.5 milliseconds, respectively. Multisegmental image reconstruction resulted in a lower deviation when comparing measured and real volumes. Using mono-, bi-, tri-, and quad-segmental image reconstruction, the percent deviation between measured and real values for EF was 8.2%, 4.5%, 3.3%, and 3.4%, respectively. Applying multisegmental image reconstruction with improved temporal resolution the deviation decreased with increasing heart rate when compared with mono-segmental image reconstruction. Interscan and intraobserver variability for EF were 1.1% and 1.9%, respectively. CONCLUSION:Enhanced temporal resolution improves the quantification of LV volumes in cardiac multislice spiral CT, enabling reliable assessment of LV volumes even at increased heart rates.

OBJECTIVE The objective of our study was to compare image quality and radiation dose associated with abdominopelvic CT using combined modulation, angular modulation, and constant tube current. CONCLUSION Compared with using a constant tube current to scan the abdomen and pelvis, the use of a combined modulation technique results in a substantial reduction (42-44%) in radiation dose with acceptable image noise and diagnostic acceptability.

OBJECTIVE:Evaluation of the attenuation-based on-line modulation of tube current on multislice computed tomography (CT) to explore the potential of this dose-saving technique.METHODS:Fifty-five patients with follow-up CT examinations were scanned without and with a CARE Dose (Siemens Medical Solutions, Erlangen, Germany). The applied dose, image noise, and subjective image quality were evaluated. The reduction in patient exposure was determined by obtaining the effective milliamperes per second for each reconstructed scan and the absolute dosage requirement for the whole scan.RESULTS:The dose reduction achieved by applying the attenuation-based on-line modulation of tube current was 29.4% +/- 3.1% (P=0.002) for all scans, 30.5% +/- 3.2% (P=0.002) for the thorax scans, 29.7% +/- 2.9% (P=0.002) for the abdomen scans, and 28.7% +/- 2.7% (P=0.003) for the thorax and abdomen scans together. No significant restrictions in image quality were observed.CONCLUSIONS:Remarkable dose reduction can be obtained using the attenuation-based on-line modulation of tube current on multislice CT without compromising image quality.

Ziele: Eine neue Generation der Mehrzeilen-Computertomographie (MSCT) mit 64-Schichten (Sensation 64) steht seit kurzem klinisch zur Verfügung. Zur Beurteilung des Dosisoutputs (gemessener CT-Dosisindex=CTDI pro eingestellter mAs-Zahl) wurde diese Studie im Vergleich zum 16-Zeilen-Spiral-CT-Gerät (Sensation 16) durchgeführt. Methode: Der CTDI wurde am zylindrischen 32-cm-Body-Plexiglas-Phantom mittels Ionisationskammer (Wellhöfer Dosimetrie) und Capintec-Digital-Dosimeter (WK 92 Schwarzenbruck) gemessen. Das Röhrenstromzeitprodukt beider Geräte wurde systematisch variiert. Die einstellbaren Kollimationen 0,6mm und 1,2mm (64-MSCT), bzw. 0,75mm und 1,5mm (16-MSCT) wurden verglichen. Die Übereinstimmung der gemessenen Daten mit den am CT-Monitor ablesbaren CTDI-Angaben wurde geprüft. Ergebnis: Die gemessenen CTDI-Werte unterschieden sich von den Monitordaten um maximal 8% (z.B. 16-MSCT, Kollimation 0.75mm: CTDIgemessen 9,2 mGy/100 mAs, CTDIMonitor 8,5 mGy/100 mAs). Um die gleiche Dosis zu erzielen, muss das einzustellende mAs-Produkt am 64-MSCT um ca. 24% höher eingestellt werden (z.B. CTDI 12,0 mGy bei 64-MSCT Kollimation 1,2mm: 190 mAs; bei 16-MSCT, Kollimation 1,5mm, 158 mAs). Sowohl beim 64-MSCT als auch beim 16-MSCT steigt beim Übergang von der größeren zur kleineren Kollimation die Dosis um ca. 11% (Overbeaming-Effekt). Schlussfolgerung: Die CTDI-Angaben der Scanner stimmten mit den Dosismessungen mittels Ionisationskammer praktisch überein. Um dieselbe Dosis zu erzielen, ist beim neuen 64-MSCT ein höheres Röhrenstromzeitprodukt als beim 16-MSCT notwendig. Bei der Wahl einer kleineren Kollimation erhöht sich die Dosis um ca. 11% bei beiden CT-Geräten. Bei der Wahl optimaler Scanparameter für neue Standardprotokolle sollte dies berücksichtigt werden.

We developed and evaluated a prototype flat-panel detector based Volume CT (VCT) scanner. We focussed on improving the image quality using different detector settings and reducing x-ray scatter intensities. For the presented results we used a Varian 4030CB flat-panel detector mounted in a multislice CT-gantry (Siemens Medical Systems). The scatter intensities may severely impair image quality in flat-panel detector CT systems. To reduce the impact of scatter we tested bowtie shaped filters, anti-scatter grids and post-processing correction algorithms. We evaluated the improvement of image quality by each method and also by a combination of the several methods.To achieve an extended dynamic range in the projection data, we implemented a novel dynamic gain-switching mode. The read out charge amplifier feedback capacitance is changing dynamically in this mode, depending on the signal level. For this scan mode dedicated corrections in the offset and gain calibration are required. We compared image quality in terms of low contrast for both, the dynamic mode and the standard fixed gain mode.VCT scanners require different types of dose parameters. We measured the dose in a 16 cm CTDI phantom and free air in the scanners iso-center and defined a new metric for a VCT dose index (VCTDI). The dose for a high quality VCT scan of this prototype scanner varied between 15 and 40 mGy.

The aim of the study was to implement an abdominal CT angiography protocol using 100 kVp and to compare SNR and CNR, as well as subjective image quality, to a standard CT angiography protocol using 120 kVp on a 16 detector-row CT scanner. Forty-eight patients were referred for routine abdominal CT angiography on a 16 detector-row CT scanner. Patients were scanned using either 120 or 100 kVp at constant mAs settings. Vessel opacification was provided by automated contrast injection using similar injection protocols. Density measurements were performed along the aorto-iliac axis with SNR and CNR calculation. In addition, the estimated effective patient radiation dose was calculated. Results of both protocols were compared. The 100-kVp protocol (432±80 HU) showed a significantly higher vessel density than the 120-kVp (333±90 HU; P<0.001) protocol, corresponding to an average increase in signal intensity of 30.7%. SNR (36.0 vs 37.0) and CNR (31.1 vs 31.7) for the 100-kV protocol were not significantly lower that those for the standard protocol (P=0.79 and P=0.87), whilst the average estimated dose was significantly lower using the 100-kVp protocol (6.7±0.4 vs 10.1±1.2 mSv; P<0.0001). Tube kVp reduction from 120 to 100 kVp allows for significant reduction of patient dose in abdominal CT angiography, without significant change in SNR,CNR and image quality.

We designed, assembled and evaluated a prototype volume CT scanner (VCT) for the purpose of investigating various calibration methods and cone beam reconstruction algorithms as well as the potential clinical benefits of a high-resolution volume CT scanner. The new VCT is based on SIEMENS Sensation4 CT scanner. To achieve larger volume coverage and higher spatial resolution we replaced the prior 4-slices detector with a flat-panel detector. We also modified the prior x-ray tube to achieve a very small focus size by a smaller emitter and wider axial coverage by a larger anode angle. In addition the high-voltage generator was enhanced to support pulsed operation. Special measurement methods were elaborated and applied to measure the focus size, shape and position as well as the uniformity of the flat field x-ray exposure. The accuracy and stability of gantry rotation speed has been evaluated to decide for the most appropriate exposure trigger. New methods are applied to measure and calibrate the resulted x-ray geometry. One prototype VCT scanner is installed at a pre-clinical site to evaluate the application potential of the new VCT technology. The new volume scanner achieves unprecedented spatial resolution, slice sensitivity and spatial coverage. In a complementary paper we present the image quality, contrast resolution and dose issues associated with this scanner.