Siemens Somatom Plus Research Articles

Comparison of computed tomography dose reporting software

Computed tomography (CT) dose reporting software facilitates the estimation of doses to patients undergoing CT examinations. In this study, comparison of three software packages, i.e. CT-Expo (version 1.5, Medizinische Hochschule, Hannover, Germany), ImPACT CT Patients Dosimetry Calculator (version 0.99×, Imaging Performance Assessment on Computed Tomography, www.impactscan.org) and WinDose (version 2.1a, Wellhofer Dosimetry, Schwarzenbruck, Germany), has been made in terms of their calculation algorithm and the results of calculated doses. Estimations were performed for head, chest, abdominal and pelvic examinations based on the protocols recommended by European guidelines using single-slice CT (SSCT) (Siemens Somatom Plus 4, Erlangen, Germany) and multi-slice CT (MSCT) (Siemens Sensation 16, Erlangen, Germany) for software-based female and male phantoms. The results showed that there are some differences in final dose reporting provided by these software packages. There are deviations of effective doses produced by these software packages. Percentages of coefficient of variance range from 3.3 to 23.4 % in SSCT and from 10.6 to 43.8 % in MSCT. It is important that researchers state the name of the software that is used to estimate the various CT dose quantities. Users must also understand the equivalent terminologies between the information obtained from the CT console and the software packages in order to use the software correctly.

Minimum slicing interval and frequency for CT-based prediction of pig’s body composition

The aims of our study were to test the effect of CT scanning protocol on the fattening performance of pigs, and the necessary scanning interval to accurately estimate tissue volumes in the body of pigs. A total of 16 Large White type pigs were used in this study. Pigs were kept individually and in concrete floor pen and fed at the level of 3.0 times of the maintenance energy requirements. Eight pigs were scanned at 30, 40, 50, 60, 75, 90 and 105kg live weight, while another eight pigs were not scanned during the fattening period. The scanning was performed with Siemens Somatom Plus spiral computer tomograph from head to tail with 10mm slice thickness and 10mm distances between the images. In conclusion restrictedly fed pigs can be examined with CT several times without negative effect on growing performance, but in the fattening phase some reduction in feed conversion can be expected. For the accurate determination of tissue volumes scanning of every 5th cm is sufficient in the 30-105 kg live weight range.

Radiation doses in examination of lower third molars with computed tomography and conventional radiography

To measure organ doses and calculate effective doses for pre-operative radiographic examination of lower third molars with CT and conventional radiography (CR). Measurements of organ doses were made on an anthropomorphic head phantom with lithium fluoride thermoluminescent dosemeters. The dosemeters were placed in regions corresponding to parotid and submandibular glands, mandibular bone, thyroid gland, skin, eye lenses and brain. The organ doses were used for the calculation of effective doses according to proposed International Commission on Radiological Protection 2005 guidelines. For the CT examination, a Siemens Somatom Plus 4 Volume Zoom was used and exposure factors were set to 120 kV and 100 mAs. For conventional radiographs, a Scanora unit was used and panoramic, posteroanterior, stereographic (scanogram) and conventional spiral tomographic views were exposed. The effective doses were 0.25 mSv, 0.060 mSv and 0.093 mSv for CT, CR without conventional tomography and CR with conventional spiral tomography, respectively. The effective dose is low when CT examination with exposure factors optimized for the examination of bone structures is performed. However, the dose is still about four times as high as for CR without tomography. CT should therefore not be a standard method for the examination of lower third molars. In cases where there is a close relationship between the tooth and the inferior alveolar nerve the advantages of true sectional imaging, such as CT, outweighs the higher effective dose and is recommended. Further reduction in the dose is feasible with further optimization of examination protocols and the development of newer techniques.

TU-FF-A4-02: Impact of Sinogram Modeling Inaccuracies On Image Quality in X-Ray CT Imaging Using the Alternating Minimization Algorithm

Purpose: To provide a scientific basis for setting sinogram modeling accuracy targets based on impact of such errors on image quality. Modeling inaccuracies in photon spectrum and scatter distribution assumed by statistical image reconstruction (SIR) algorithms lead to systematic image artifacts. Methods and Materials: A synthetic two-dimensional phantom (25×35 cm) was used to generate both noiseless and noisy sinogram data, based upon a 120 kVp spectrum filtered by 12 mm Al (66.6 keV mean energy)and variable scatter levels (4%, 20%, and 100% of the minimum primary transmission through the phantom). A third generation Siemens Somatom Plus 4 scanner geometry was assumed. The SIR algorithm was the alternating minimization (AM) algorithm [IEEE TMI 26:283]. 500 AM iterations using 22 ordered subsets were applied to the data. Various mismatches between the assumptions in the algorithm and the truth were studied, including erroneous spectra (110kVp to 130kVp, filtration from 6 mm to 18 mm Al, or 62.2 to 69.7 keV mean energy) and erroneous scatter levels (0.25 to 4.0 times the actual sinogram scatter). Result: AM image quality was evaluated in terms of bias, noise, contrast ratio, etc. To assure +/−2% accuracy in the reconstructed attenuation image, photon spectrum uncertainties corresponding to 2 keV shifts in mean energy can be tolerated. For a 30 cm thick subject, this corresponds to errors in primary transmission of 6%–8%. For 20% scatter levels, the maximum tolerated discrepancy in scatter-to-primary ratio (SPR) is about 5% to 8%and 30%–50% for typical MSCT scatter levels. Conclusions: This work indicates AM and other SIR algorithm image estimates are sensitive to errors in the detector response models assumed by the algorithms. For thick patients, a sinogram modeling accuracy of 6% is needed to support reconstructed images of 2% accuracy. Supported in part by NIH grant R01 CA 075371.

CT calibration for two-dimensional scaling of proton pencil beams

For proton dose calculations in heterogeneous media, it was shown in a previous work that the conventional pencil beam approach based on pathlength scaling does not properly account for scattering effects in nonwater media (Szymanowski and Oelfke 2002 Phys. Med. Biol. 47 3313–30). A two-dimensional scaling method was therefore introduced, which is able to predict with high accuracy the propagation of proton pencil beams both along the depth and the lateral directions in inhomogeneous media. In order to integrate this improved pencil beam algorithm in a CT based treatment planning system, two CT calibration curves are needed. The first one relates the Hounsfield numbers to the relative stopping powers, as for the conventional pencil beam approach. The second curve is to relate the Hounsfield numbers to the material-specific lateral scaling factors. The purpose of this work is to provide the CT calibration curves needed for the integration of the pencil beam algorithm featuring the two-dimensional scaling method. Similarly to as suggested by Schneider et al (1996 Phys. Med. Biol. 41 111–24) for the calibration curve in terms of stopping powers, we follow a stoichiometric procedure to get the calibration curve in terms of material-specific lateral scaling factors. The calibration curves for a CT scanner of the type Siemens Somatom Plus 4 are obtained from the analytical calculation of the CT Hounsfield numbers, relative stopping powers and material-specific lateral scaling factors for human biological tissues.

Die stereoskopische Simulation ohrchirurgischer Eingriffe an einem neuartigen 3D-Computermodell1

The presentation of the surgical anatomy of the temporal bone by standard anatomical figures is not suitable for otosurgical training. For the comprehension of its complex morphology temporal bone drilling is inalienable. Aim of the present cooperation was to gain an interactive real-3D program for the simulation of specific laterobasal surgical approaches. The program was derived from a standard horizontal section of a human temporal bone using a Siemens Somatom Plus 4 Tomograph. The slice thickness was 1 mm, the image matrix was 512. The Voxel-Man-system was used to built up the application for unix workstations. Each step of a surgical approach to the temporal bone can be performed by the present computer model. Calculation in a stereo mode even allows spatial 3D-perception when using red/green glasses. This program is a novel tool to simulate critical aspects of otosurgical procedures on a computer. Up to now the lack of tactile and kinesthetic information does not allow to renounce individual temporal bone drilling.

A three-dimensional finite element model from computed tomography data: a semi-automated method.

Three-dimensional finite element analysis is one of the best ways to assess stress and strain distributions in complex bone structures. However, accuracy in the results may be achieved only when accurate input information is given. A semi-automated method to generate a finite element (FE) model using data retrieved from computed tomography (CT) was developed. Due to its complex and irregular shape, the glenoid part of a left embalmed scapula bone was chosen as working material. CT data were retrieved using a standard clinical CT scanner (Siemens Somatom Plus 2, Siemens AG, Germany). This was done to produce a method that could later be utilized to generate a patient-specific FE model. Different methods of converting Hounsfield unit (HU) values to apparent densities and subsequently to Young's moduli were tested. All the models obtained were loaded using three-dimensional loading conditions taken from literature, corresponding to an arm abduction of 90 degrees. Additional models with different amounts of elements were generated to verify convergence. Direct comparison between the models showed that the best method to convert HU values directly to apparent densities was to use different equations for cancellous and cortical bone. In this study, a reliable method of determining both geometrical data and bone properties from patient CT scans for the semi-automated generation of an FE model is presented.

Imaging of Interstitial Cryotherapy—Anin VitroComparison of Ultrasound, Computed Tomography, and Magnetic Resonance Imaging

Rationale and objectives.To evaluate the imaging capabilities of ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) in monitoring interstitial cryotherapy and to compare them with visual control.Methods.An experimental MR-compatible, vacuum-insulated and liquid nitrogen-cooled cryoprobe was inserted underin vitroconditions into a porcine liver, which was kept at a temperature of 37 ± 1°C, in a water bath with continuous stirring. The freezing procedure was controlled macroscopically, by US (Toshiba Sonolayer, 7.5-MHz linear array transducer), by CT (Siemens Somatom Plus, slice thickness 2–8 mm, 165–210 mA at 120 kV), and by MRI (Philips Gyroscan ACS-NT, FFE TR/TE/FA = 15/5.4/25°, T1-SE 550/20, T2-TSE 1800/100) after the iceball reached its maximum size.Results.The maximum iceball diameter around the probe tip was 12.0 mm by visual control, 12.4 mm by US, 12.7 mm by CT, and within 12.8 mm by spin echo sequences and 11 mm by gradient echo sequence. Due to the nearly signal-free appearance of the frozen tissue on MR images, the ice/tissue contrast on T1-weighted and gradient echo images was superior to T2-weighted images and CT images. Sonographically, the ice formation appeared as a hyperechoic sickle with nearly complete acoustic shadowing.Conclusion.Due to the better ice/tissue contrast, T1-weighted or gradient echo MR images were superior to CT and US in monitoring interstitial cryotherapy. Gradient echo sequences generally underestimated the ice diameter by 15%.

Optimizing dose reduction in CT scanning of the paranasal sinuses: A randomized control trial of recommended versus lowest achievable dose protocols

<h3>Aim</h3> To determine optimum CT scan protocols for patients undergoing prefunctional endoscopic sinus surgery (FESS) imaging. <h3>Methods</h3> Following head phantom dosimetry experiments for a variety of mAs values on each of two CT scanners (Siemens Somatom DRH and GE Pace), a randomized control trial was performed on 60 consecutive patients referred for pre-FESS imaging. Each was assigned to either ‘the current' protocol or a ‘lowest achievable' dose protocol and to either the prone or supine position, on one of two CT scanners in a single department. Entrance skin doses were measured at pre-determined positions for each patient. Hard copy images were scored by two radiologists for image quality. These radiologists were blinded to scan protocol and patient position when scoring images. Subsequent to the Department acquiring a Siemens Somatom Plus 4 Helical scanner, similar head phantom dosimetry measurements at various mAs values were obtained, and image quality similarly scored. <h3>Results</h3> Dose reductions of 28% (Siemens Somatom DRH), 79% (GE Pace) and 80% (Siemens Somatom Plus 4) were obtained using the ‘lowest achievable' dose protocol. Images were of diagnostic quality as scored by two radiologists, with either protocol. Patient position was not a significant variable in either dose received or patient acceptability. <h3>Conclusion</h3> Scans of diagnostic quality can be achieved in patients requiring pre-FESS imaging, at considerable dose reduction, by using mAs values lower than those recommended by the manufacturers.

A new MR-(and CT-) compatible bone biopsy system: first clinical results

To describe the development and clinical evaluation of a new, hand-powered or alternatively motor-driven, MRI and CT compatible percutaneous bone biopsy system. A new coaxial drill system (Cook Europe A/S) was designed for percutaneous, MR-guided bone biopsies and powered either by hand or an optional motor (10-250 rotations/minute using 6 bar [88.2 PSI] compressed air). The system has been used in 23 patients. Fourteen procedures were performed in a 1.5 T MR scanner (Philips-Gyroscan ACS-NT) which has an attached C-arm (Philips-BV 212-Angio) in case fluoroscopy is required, and 9 procedures in a CT scanner (Siemens-Somatom Plus). Driven by hand or by the pneumatic motor unit, the system achieved safe and accurate MR-guided access to all of the lesions and was even able to penetrate osteosclerotic lesions. MR- or CT-guided percutaneous biopsy yielded a correct diagnosis in all but 5 cases. No procedural complications occurred. MR-guided percutaneous bone biopsy performed with the new coaxial drill system was found to be safe and reliable, and suitable for obtaining histological specimens from skeletal lesions even when covered with thick cortical or sclerotic bone.

Optimising imaging parameters in experimental spiral CT.

This in vitro study was conducted to analyse lesion detection and relative radiation exposure in different CT techniques. We used a plastic phantom (12 x 8 x 2 cm) containing holes filled with air or fluid of varying densities to simulate lesions. This was imaged with Siemens Somatom Plus S and GE High Speed Advantage units. We varied table feeds (3 and 6 mm/s in Siemens and 3 and 4.5 mm/s in GE) and increments (2 mm and 4 mm) while keeping collimation at 3 mm. The SmartScan program of GE and the reformatting algorithm of Siemens were also analysed. To evaluate the different methods, the phantom lesions were counted by 3 observers. Radiation exposures associated with each technique were also measured. The images reformatted to a coronal direction were significantly inferior (p < 0.01) to those in other techniques. The use of SmartScan did not influence lesion detection, nor did changes in pitch or increment. Spiral and non-spiral techniques proved to be equal. Radiation exposure was lowest when a greater pitch or the SmartScan program was used. Radiation exposure in CT can be limited without significantly impairing the image quality by using low-dose techniques. Reformatting to a coronal direction should be used with care as it debases the image quality.

A method of computer-assisted, 3-dimensional subtraction angiography using spiral roentgen computerized tomography

The objective of this study was to develop a method for 3D subtraction CT angiography and to optimize the visualization after semi-automatic segmentation. Ten patients with aneurysms of the abdominal aorta were examined using spiral CT. To reconstruct the vessels, as well as adjacent organs such as the liver and kidneys, one image data volume was acquired before and after injection of the contrast agent. The CT scans were obtained with a Siemens Somatom Plus 4. To improve the results of automatic segmentation, as well as visualization by maximum intensity projection (i.e. removal of bony structures), subtraction of both image volumes is necessary. However, small translation shifts disturb the subtraction process and produce artificial contours. To calculate the disparities along the three coordinate axes of two corresponding image volumes, a cepstrum filter is applied to a pair of image volumes. After detection of the disparities, which manifest as bright spots, the real shift of the two subsignals can be calculated. Translation of the corresponding image volume pairs to their correct positions improves the subtraction process. In all cases the size of the aneurysm and the abdominal organs could be better segmented and visualized. Application of the cepstrum filter and subtraction of the image volumes before and after contrast medium injection completely removes the bony structures in the image data and results in superior visualization results.

Aortic Motion

Artefacts complicate the diagnosis of thoracic aortic dissection by CT. Aortic compliance and cardiac motion may be responsible but the precise cause of these artefacts remains unclear. Fifty consecutive clinical thoracic CT examinations performed on a Siemens Somatom Plus scanner (8 mm slice thickness, 1 s scan time) were reviewed (mean patient age 56 years). For each examination, the presence, position, and displacement of motion artefact from the aortic wall were noted at three ascending aortic levels. Cine ultrafast CT on 10 volunteers (mean age 49 years) was used to assess aortic motion for the same three levels (8 mm slice thickness, 50 ms scan time). Digital subtraction of consecutive cine CT allowed the position of the aortic wall throughout the cardiac cycle to be tracked. Curvilinear motion artefacts were seen in the ascending aorta in 17 conventional CT scans, occurring left anterior and right posterior in all but one and maximally at the aortic root (mean amplitude 3.5 mm). Ultrafast CT, however, showed no motion artefact and no significant change in aortic area with systole. Aortic motion in the sagittal-oblique plane at the ascending aorta was confirmed. Motion artefacts simulating ascending aortic dissection occur frequently on conventional CT. Their position is predictable and is related to systolic aortic motion from the left anterior to the right posterior position.

Is Asthma a Vascular Disorder?

Is Asthma a Vascular Disorder?

スパイラルCTを用いた三次元管腔表示の形状再現性に影響する諸因子について

We have evaluated the accuracy of three-dimensional endoscopic images which were reconstructed with a double threshold shaded surface display. The factors examined are as follows: thickness of three-dimensional endoscopic images, specific artifacts of spiral CTs. We used a spiral CT(SIEMENS SOMATOM PLUS). In this study, we used a Full Scatter Water phantom which is used in radiation therapy, SPECT QA Test phantoms with an empty acrylic cylinder and a Funnel phantom. The thickness of the wall on three-dimensional endoscopic image was influenced by the function of reconstruction, the threshold and the partial volume effect. When the phantom with an empty acrylic cylinder was obliquely laid on the Z-axis, a regular spiral artifact could always be observed. This was the same as the artifact which appeared in clinical three-dimensional endoscopy. This artifact was changed by collimation and table speed. If we take these three factors into consideration which influence the thickness of the wall on a three-dimensional endoscopic image and choose the least possible collimation and table feed, it is possible to improve the accuracy of three-dimensional endoscopic imaging.