Stefan Ulzheimer

Cardiovascular Center Bethanien, Frankfurt, Hesse, Germany

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Publications (39)120.07 Total impact

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    ABSTRACT: To evaluate the image quality and diagnostic accuracy of very low-dose computed tomography (CT) angiography (CTA) for the evaluation of coronary artery stenosis.
    European Heart Journal – Cardiovascular Imaging 06/2014; 15(11). DOI:10.1093/ehjci/jeu113 · 2.65 Impact Factor
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    C Ozdoba · J Slotboom · G Schroth · S Ulzheimer · R Kottke · H Watzal · C Weisstanner ·
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    ABSTRACT: Computed tomography (CT) accounts for more than half of the total radiation exposure from medical procedures, which makes dose reduction in CT an effective means of reducing radiation exposure. We analysed the dose reduction that can be achieved with a new CT scanner [Somatom Edge (E)] that incorporates new developments in hardware (detector) and software (iterative reconstruction). We compared weighted volume CT dose index (CTDIvol) and dose length product (DLP) values of 25 consecutive patients studied with non-enhanced standard brain CT with the new scanner and with two previous models each, a 64-slice 64-row multi-detector CT (MDCT) scanner with 64 rows (S64) and a 16-slice 16-row MDCT scanner with 16 rows (S16). We analysed signal-to-noise and contrast-to-noise ratios in images from the three scanners and performed a quality rating by three neuroradiologists to analyse whether dose reduction techniques still yield sufficient diagnostic quality. CTDIVol of scanner E was 41.5 and 36.4 % less than the values of scanners S16 and S64, respectively; the DLP values were 40 and 38.3 % less. All differences were statistically significant (p < 0.0001). Signal-to-noise and contrast-to-noise ratios were best in S64; these differences also reached statistical significance. Image analysis, however, showed "non-inferiority" of scanner E regarding image quality. The first experience with the new scanner shows that new dose reduction techniques allow for up to 40 % dose reduction while still maintaining image quality at a diagnostically usable level.
    01/2014; 24(1). DOI:10.1007/s00062-013-0263-5
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    ABSTRACT: To compare the computed tomography (CT) dose and image quality with the filtered back projection against the iterative reconstruction and CT with a minimal electronic noise detector. A lung phantom (Chest Phantom N1 by Kyoto Kagaku) was scanned with 3 different CT scanners: the Somatom Sensation, the Definition Flash and the Definition Edge (all from Siemens, Erlangen, Germany). The scan parameters were identical to the Siemens presetting for THORAX ROUTINE (scan length 35 cm and FOV 33 cm). Nine different exposition levels were examined (reference mAs/peek voltage): 100/120, 100/100, 100/80, 50/120, 50/100, 50/80, 25/120, 25/100 and 25 mAs/80 kVp. Images from the SOMATOM Sensation were reconstructed using classic filtered back projection. Iterative reconstruction (SAFIRE, level 3) was performed for the two other scanners. A Stellar detector was used with the Somatom Definition Edge. The CT doses were represented by the dose length products (DLPs) (mGycm) provided by the scanners. Signal, contrast, noise and subjective image quality were recorded by two different radiologists with 10 and 3 years of experience in chest CT radiology. To determine the average dose reduction between two scanners, the integral of the dose difference was calculated from the lowest to the highest noise level. When using iterative reconstruction (IR) instead of filtered back projection (FBP), the average dose reduction was 30%, 52% and 80% for bone, soft tissue and air, respectively, for the same image quality (P < 0.0001). The recently introduced Stellar detector (Sd) lowered the radiation dose by an additional 27%, 54% and 70% for bone, soft tissue and air, respectively (P < 0.0001). The benefit of dose reduction was larger at lower dose levels. With the same radiation dose, an average of 34% (22%-37%) and 25% (13%-46%) more contrast to noise was achieved by changing from FBP to IR and from IR to Sd, respectively. For the same contrast to noise level, an average of 59% (46%-71%) and 51% (38%-68%) dose reduction was produced for IR and Sd, respectively. For the same subjective image quality, the dose could be reduced by 25% (2%-42%) and 44% (33%-54%) using IR and Sd, respectively. This study showed an average dose reduction between 27% and 70% for the new Stellar detector, which is equivalent to using IR instead of FBP.
    11/2013; 5(11):421-429. DOI:10.4329/wjr.v5.i11.421
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    ABSTRACT: OBJECTIVES: To evaluate the image quality and diagnostic accuracy of very low-dose, dual-source computed tomography (DSCT) angiography for the evaluation of coronary stents. BACKGROUND: Iterative reconstruction (IR) leads to substantial reduction of image noise and hence permits the use of very low-dose data acquisition protocols in coronary computed tomography angiography. METHODS: Fifty symptomatic patients with 87 coronary stents (mean ± SD diameter 3.0 ± 0.4 mm) underwent coronary DSCT angiography (heart rate, 60 ± 6 beats/min; prospectively electrocardiography-triggered axial acquisition; 80 kV, 165 mA, 2 × 128 × 0.6-mm collimation; 60 ml of contrast at 6 ml/s) before invasive coronary angiography. DSCT images were reconstructed using both standard filtered back projection and a raw data-based IR algorithm (SAFIRE, Siemens Healthcare, Forchheim, Germany). Subjective image quality (4-point scale from 0 [nondiagnostic] to 3 [excellent image quality]), image noise, contrast-to-noise ratio as well as the presence of in-stent stenosis >50% were independently determined by 2 observers. RESULTS: The median dose-length product was 23.0 (22.0; 23.0) mGy·cm (median estimated effective dose of 0.32 [0.31; 0.32] mSv). IR led to significantly improved image quality compared with filtered back projection (image quality score, 1.8 ± 0.6 vs. 1.5 ± 0.5, p < 0.05; image noise, 70 Hounsfield units [62; 80 Hounsfield units] vs. 96 Hounsfield units [82; 113 Hounsfield units], p < 0.001; contrast-to-noise ratio, 11.0 [9.6; 12.4] vs. 8.0 [6.2; 9.3], p < 0.001). To detect significant coronary stenosis in filtered back projection reconstructions, the sensitivity, specificity, positive predictive value, and negative predictive value were 97% (32/33), 53% (9/17), 80% (32/40), and 90% (9/10) per patient, respectively; 89% (43/48), 79% (120/152), 57% (42/74), and 96% (121/126) per vessel, respectively; and 85% (12/14), 69% (51/73), 32% (11/34), and 96% (51/53) per stent, respectively. In reconstructions obtained by IR, the corresponding values were 100% (33/33), 65% (11/17), 85% (33/39), and 100% (11/11) per patient, respectively; 96% (46/48), 84% (129/152), 66% (47/71), and 98% (127/129) per vessel, respectively; and 100% (14/14), 75% (55/73), 44% (14/32), and 100% (55/55) per stent, respectively. These differences were not significant. CONCLUSIONS: In selected patients, prospectively electrocardiography-triggered image acquisition with 80-kV tube voltage and low current in combination with IR permits the evaluation of patients with implanted coronary artery stents with reasonable diagnostic accuracy at very low radiation exposure.
    JACC. Cardiovascular imaging 03/2013; 6(4). DOI:10.1016/j.jcmg.2012.10.023 · 7.19 Impact Factor
  • Stefan Ulzheimer · Heidrun Endt · Thomas Flohr ·

    Health physics 03/2011; 100(3):325-8. DOI:10.1097/HP.0b013e318209635e · 1.27 Impact Factor
  • Stefan Ulzheimer · Thomas Flohr ·
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    ABSTRACT: Since its introduction in the early 1970s, computed tomography (CT) has undergone tremendous improvements in terms of technology, performance and clinical applications. Based on the historic evolution of CT and basic CT physics, this chapter describes the status quo of the technology and tries to anticipate future developments. Besides the description of key components of CT systems, a special focus is placed on breakthrough developments, such as multi-slice CT and dedicated scan modes for cardiac imaging.
    12/2008: pages 3-23;
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    ABSTRACT: This work assesses the temporal resolution of dual-source computed tomography (CT) in a visually intuitive manner. Exploiting the principles of ring artifact creation, a phantom containing a highly attenuating delta function signal (a wire) was rotated at the same speed as the gantry, creating a partial ring artifact where the angular extent of the artifact provides a direct indication of the temporal resolution. A demonstration of the effect of the evaluated 165 and 83 ms nominal temporal resolutions on motion artifacts in cardiac CT is provided using patient data.
    Medical Physics 03/2008; 35(2):764-8. DOI:10.1118/1.2826559 · 2.64 Impact Factor
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    ABSTRACT: Stent implantation is the predominant therapy for non-surgical myocardial revascularization in patients with coronary artery disease. However, despite substantial advances in multidetector computed tomography (MDCT) coronary imaging, a reliable detection of coronary in-stent restenosis is currently not possible. To examine the ability of 64-detector-row CT to detect and to grade in-stent stenosis in coronary stents using a newly developed ex-vivo vessel phantom with a realistic CT density pattern, artificial stenosis, and a thorax phantom. Four different stents (Liberté and Lunar ROX, Boston Scientific; Driver, Medtronic; Multi-Link Vision, Guidant) were examined. The stents were placed on a polymer tube with a diameter of 2.5, 3.0, 3.5, or 4.0 mm. Different degrees of stenosis (0%, 30%, 50%, 70-80%) were created inside the tube. For quantitative analysis, attenuation values were measured in the non-stenotic vessel outside the stent, in the non-stenotic vessel inside the stent, and in the stenotic area inside the stent. The grade of stenosis was visually assessed by two observers. All stents led to artificial reduction of attenuation, the least degree of which was found in the Liberté stent (11.3+/-10.2 HU) and the Multi-Link Vision stent (17.6+/-17.9 HU; P = 0.25). Overall, the non-stenotic vessel was correctly diagnosed in 55.5%, the low-grade stenosis in 58.3%, the intermediate stenosis in 63.8%, and the high-grade stenosis in 80.5%. In the 3.0-, 3.5-, and 4.0-mm vessels, in none of the cases was a non-stenotic or low-grade stenotic vessel misdiagnosed as intermediate or high-grade stenosis. The average deviation from the real grade of stenosis was 0.40 for the Liberté stent, 0.46 for the Lunar ROX stent, 0.45 for the Driver stent, and 0.58 for the Multi-Link Vision stent. Our ex-vivo data show that non-stenotic stents and low-grade in-stent stenosis can be reliably differentiated from intermediate and high-grade in-stent stenosis in vessels with a diameter of 3 to 4 mm. With regard to artifacts and the grading of stenoses, the Liberté stent was best suited for CT coronary angiography.
    Acta Radiologica 03/2008; 49(1):56-64. DOI:10.1080/02841850701678804 · 1.60 Impact Factor
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    ABSTRACT: The aim of the study was to examine the ability of a 64-slice MDCT to detect in-stent stenoses in an ex vivo model of coronary stents. Five different stents (Liberté, Boston Scientific; Driver, Medtronic; Multi-Link Vision, Guidant; Taxus Express, Boston Scientific; Cypher, Cordis) were examined using a dynamic cardiac phantom. The stents were pulled over a vessel model that consists of a polymer tube with diameters of 3.0, 3.5, and 4.0 mm and four different degrees of stenoses (0%; 30%; 50%; 70-80%). This model was moved with a rate of 60 bpm to mimic cardiac motion. To assess the degree of artificial signal reduction (artificial reduction of attenuation (ARA)) by the different stents, attenuation values were measured in the vessel outside the stent, and in the non-stenotic vessel inside the stent. Furthermore the grade of stenosis was assessed by two clinical observers. Highest ARA was found for the Cypher Stent (35 HU), whereas the Liberté Stent presented the lowest ARA (16 HU). Depending on the stent and the vessel diameter, up to 87.5% of the stenoses were correctly diagnosed. In the 3.0 and 3.5 mm vessels, a nonstenotic or low-grade stenotic vessel was diagnosed as intermediate or high-grade stenosis in 22.5%, whereas in the 4.0 mm vessels, this kind of overestimation did not occur. A 50% stenosis was diagnosed as a 30% stenosis in 30%. On the other hand, high-grade stenoses were underestimated in only 10%. On a four-point scale, the average deviation from the real grade of stenosis was 0.21 for the Liberté stent, 0.54 for the Taxus Express stent, 0.29 for Driver stent, 0.62 for the Multi-Link Vision stent, and 0.37 for the Cypher stent. In a dynamic cardiac phantom model, high grade stenoses in vessels with a diameter of 4 mm could be reliably detected irrespective of the stent type used in this study. Vice versa, high grade stenoses (> or = 50%) could only be ruled out with certainty in vessels with a diameter of 4 mm. In smaller vessels, the ability to correctly diagnose high-grade stenoses was dependent on the type of stent and the imaging artifacts associated with it.
    Clinical Research in Cardiology 12/2007; 96(12):883-90. DOI:10.1007/s00392-007-0564-2 · 4.56 Impact Factor
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    ABSTRACT: To develop a consensus standard for quantification of coronary artery calcium (CAC). A standard for CAC quantification was developed by a multi-institutional, multimanufacturer international consortium of cardiac radiologists, medical physicists, and industry representatives. This report specifically describes the standardization of scan acquisition and reconstruction parameters, the use of patient size-specific tube current values to achieve a prescribed image noise, and the use of the calcium mass score to eliminate scanner- and patient size-based variations. An anthropomorphic phantom containing calibration inserts and additional phantom rings were used to simulate small, medium-size, and large patients. The three phantoms were scanned by using the recommended protocols for various computed tomography (CT) systems to determine the calibration factors that relate measured CT numbers to calcium hydroxyapatite density and to determine the tube current values that yield comparable noise values. Calculation of the calcium mass score was standardized, and the variance in Agatston, volume, and mass scores was compared among CT systems. Use of the recommended scanning parameters resulted in similar noise for small, medium-size, and large phantoms with all multi-detector row CT scanners. Volume scores had greater interscanner variance than did Agatston and calcium mass scores. Use of a fixed calcium hydroxyapatite density threshold (100 mg/cm(3)), as compared with use of a fixed CT number threshold (130 HU), reduced interscanner variability in Agatston and calcium mass scores. With use of a density segmentation threshold, the calcium mass score had the smallest variance as a function of patient size. Standardized quantification of CAC yielded comparable image noise, spatial resolution, and mass scores among different patient sizes and different CT systems and facilitated reduced radiation dose for small and medium-size patients.
    Radiology 06/2007; 243(2):527-38. DOI:10.1148/radiol.2432050808 · 6.87 Impact Factor

  • Journal of Biomechanics 12/2006; 39. DOI:10.1016/S0021-9290(06)83994-1 · 2.75 Impact Factor

  • Herz 06/2006; 31(3):269. · 0.69 Impact Factor
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    ABSTRACT: Ohne Zusammenfassung
    Herz 05/2006; 31(3):269-269. DOI:10.1007/s00059-006-2789-7 · 0.69 Impact Factor
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    ABSTRACT: PURPOSE To improve the spatial resolution and contrast characteristics of a scanned projection radiograph (SPR), e.g. Topogram®, obtained with a multi-slice CT system (Siemens Medical Solutions, Forchheim, Germany), and to evaluate the image quality for potential replacement of conventional radiographic examinations (e.g. trauma or intravenous pyelograms). METHOD AND MATERIALS A modified scan and reconstruction technique was implemented for SPRs acquired with a 40- or 64-slice CT system (Siemens, Forchheim, Germany). A periodic motion of the X-ray tube focal spot was used to double the in-plane (x,y) sampling density, resulting in a sampling distance of 0.38 mm at isocenter. A weighted summation was created to adjust the image contrast characteristics and spatial resolution, using the original scan data and the data after high-pass filtration. The resulting SPR was displayed with 0.25 mm x 0.25 mm pixel-size using non-linear look-up tables. A bar pattern phantom was scanned to measure spatial resolution. Patient SPR acquisitions were processed with the new algorithm to evaluate image quality and diagnostic utility. RESULTS The spatial resolution obtained with the modified SPR was about 0.4 mm x 0.4 mm. Image characteristics closely resembled diagnostic radiographs with respect to image contrast, brightness and latitude. Initial patient studies confirm the diagnostic appearance of the modified SPR. Anticipated clinical applications include examinations of cervical and lumbar spine in trauma patients and CT urography. CONCLUSION An algorithm to produce high spatial resolution SPR (Topogram®) images was successfully implemented, resulting in SPR images with the qualitative appearance of traditional radiographs in preliminary patient studies. These high spatial resolution SPR images may provide a convenient method by which to acquire digital radiograph at the time of CT, perhaps obviating the need for additional radiographic studies. DISCLOSURE T.G.F.,S.U.,B.S.: Employee of Siemens Medical Solutions
    Radiological Society of North America 2005 Scientific Assembly and Annual Meeting; 12/2005
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    ABSTRACT: DISCLOSURE B.S.,C.S.,S.U.,M.G.,T.G.F.: Employee of Siemens Medical Solutions, GermanyM.K.K.: Received a research grant from Siemens Medical Solutions, Germany ABSTRACT Purpose: CT scanning of large patients is a significant clinical problem due to weight limitations for gantry tables (350- 400 lbs), and inability to generate adequate x-ray beam with single x-ray source (80 kW) for obtaining optimum image quality. Thus, the purpose of our study was to compare single-source 64-channel MDCT and dual source MDCT scanners for evaluation of large patients with a phantom study. Material and Methods: A new MDCT system (Siemens Medical Solutions), with two x-ray tubes (both 80 kW), dual detector arrays (both with 32*0.6 mm, double z-sampling, 0.4 mm z-axis resolution) and wide bore gantry (78 cm) was developed. This system allows scanning of patients weighing up to 615 lbs with simultaneous exposure from two x-ray tubes (80+80=160 kW). Two PMA phantoms, measuring 32 cm (standard adult abdomen phantom) and 50 cm (simulating large patient�s abdomen) in diameter, were scanned on both single-source MDCT (Siemens Sensation 64) and dual source MDCTat 290 mAs (both phantoms, maximum of 580 mA at 0.5s rotation time) and at 500 mAs (only 50 cm phantom, maximum of 500 mA at 1s rotation time). Remaining parameters were held constant for both systems and included 120 kVp, 500 mm field of view, and soft/standard body kernels. Image noise was measured with a constant size and shape ROI in all image datasets. Results: Image noise in standard size phantom was 12.2 (290 mAs) with single source MDCT, and 6.2 (290 mAs) with dual source MDCT. Image noise in large phantom was 92.6 (290 mAs) and 68.0 (500 mAs) with single source MDCT, and 71.6 (290 mAs) and 49.2 (500 mAs) with dual source MDCT. Regardless of mAs, there was improvement in image noise for large phantom scanned with dual source MDCT compared to the single source MDCT (p< .01). Conclusions: Compared to single source 64-slice MDCT, the dual source MDCT resulted in substantial improvement in image quality of the large phantom. Dual source MDCT scanners can help in obtaining optimum image quality in large patients due to their greater weight tolerance (up to 615 lbs), higher x-ray tube power (160 kW), and data over-sampling (from two detector arrays).
    Radiological Society of North America 2005 Scientific Assembly and Annual Meeting; 11/2005
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    ABSTRACT: PURPOSE The attenuation of x-rays in the human body is subjected to a huge variation, depending on the body size and region. This leads to a strong variance of noise levels in the reconstructed images if CT scans are performed with a constant exposure level. In order to guarantee a consistent diagnostic image quality with lowest possible dose an adaptive x-ray tube current modulation with respect to the projection angle and the patient’s long axis (z) is necessary. METHOD AND MATERIALS We present a new automatic exposure control (AEC) concept which is based on the evaluation of a single projection radiogram. The proper modulation is performed on-line by measuring the actual attenuation distribution. Within the scope of a first clinical study, we have determined an empirical transfer function between measured local attenuation and the optimal tube current. The applied model uses an organ specific reference attenuation, given by the analysis of a collective of 100 patients, and a power law to adapt to smaller or larger signal attenuation. Exponents were adapted by assessing clinical images where noise had been added synthetically in order to simulate different levels of image quality. With the fixed set of parameters, 200 patients were scanned with the AEC. Dose reduction was estimated by comparison with non-modulated scans typically used for a specific patient and examination. RESULTS Evaluation of different transfer functions showed clearly that constant image noise for all sizes of patients is not desirable from a clinical point few. In fact, a square (third) root function between signal attenuation and tube current for adaptation to high (small) attenuation values turns out to meet the clinical image quality requirements. For typical clinical examinations of neck, thorax, thorax-abdomen, abdomen we found an average dose reduction of 38%, 13%, 37%, 39% respectively with the AEC yielding the same or better diagnostic image quality compared to standard scans with constant current. The local dose reduction was up to 67% even for standard size patients. CONCLUSION The presented concept of an AEC for CT scanners reduces the radiation dose for CT examinations up to 67% without compromising image quality. DISCLOSURE C.S.,R.R.,H.W.,A.S.: Employee of Siemens AG Medical SolutionsS.U.: Employee of Siemens Medical Solutions, GermanyU.B.: Employee of University of Erlangen, Germany
    Radiological Society of North America 2005 Scientific Assembly and Annual Meeting; 11/2005
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    ABSTRACT: PURPOSE We developed a prototype flat-panel detector based Volume CT (VCT) scanner and evaluated image quality. Additional to the standard scanning modes we implemented a Fluoroscopy scan mode. The novel functionality combines the advantages of a high resolution Volume CT scanner with the ability to acquire projection images with a reasonable field of view. Image quality is improved by using different detector settings and reducing x-ray scatter intensities. METHOD AND MATERIALS We mounted a Varian 4030CB a-Si flat-panel detector in a multi slice CT-gantry (Siemens Medical Solutions) which provides a 25 cm field of view with 18 cm z-coverage at isocenter. To extend the dynamic range of the detector we implemented an automatic gain-switching read out method. We evaluated the improvement of image quality by the use of a shaped filter. To reduce the impact of scatter we tested anti-scatter grids and signal correction algorithms. Scanning without rotation is equivalent to a conventional fluoroscopic examination. Additional to the projection data a volume CT scan provides tomographic images with 3D isotropic resolution of the same section. We measured the dose in a 32 cm long CTDI phantom and defined a new metric for a ‘Volume CT dose index’ (VCTDI). VCTDI for our scanner is in the range of 15 mGy to 40 mGy for a high quality VCT scan. RESULTS Depending on the shape and on the material composition of the scanned object, the shaped filter remarkably reduces scatter intensities. The anti-scatter grid reduces the scatter intensities and provides an increased low contrast resolution (4 mm, 5 HU @ 40 mGy) as well as improved image uniformity (+/- 10HU). Software based algorithms are efficient to reduce scatter intensities in the projected data, but a careful adjustment of the parameter is needed to avoid artefacts caused by the algorithm. CONCLUSION Up to now the scanner was used for phantom and specimen studies. At the current level of image quality, several clinical applications are in reach. The integration of a flat panel detector in a CT gantry opens the possibility to combine conventional fluoroscopy and CT functionality with a large field of view and very high spatial resolution. DISCLOSURE M.G.,C.S.,K.S.,S.P.,T.G.F.: All authors are employees of Siemens Medical Solutions, Forchheim Germany
    Radiological Society of North America 2005 Scientific Assembly and Annual Meeting; 11/2005
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    ABSTRACT: We present a theoretical overview and a performance evaluation of a novel z-sampling technique for multidetector row CT (MDCT), relying on a periodic motion of the focal spot in the longitudinal direction (z-flying focal spot) to double the number of simultaneously acquired slices. The z-flying focal spot technique has been implemented in a recently introduced MDCT scanner. Using 32 x 0.6 mm collimation, this scanner acquires 64 overlapping 0.6 mm slices per rotation in its spiral (helical) mode of operation, with the goal of improved longitudinal resolution and reduction of spiral artifacts. The longitudinal sampling distance at isocenter is 0.3 mm. We discuss in detail the impact of the z-flying focal spot technique on image reconstruction. We present measurements of spiral slice sensitivity profiles (SSPs) and of longitudinal resolution, both in the isocenter and off-center. We evaluate the pitch dependence of the image noise measured in a centered 20 cm water phantom. To investigate spiral image quality we present images of an anthropomorphic thorax phantom and patient scans. The full width at half maximum (FWHM) of the spiral SSPs shows only minor variations as a function of the pitch, measured values differ by less than 0.15 mm from the nominal values 0.6, 0.75, 1, 1.5, and 2 mm. The measured FWHM of the smallest slice ranges between 0.66 and 0.68 mm at isocenter, except for pitch 0.55 (0.72 mm). In a centered z-resolution phantom, bar patterns up to 15 lp/cm can be visualized independent of the pitch, corresponding to 0.33 mm longitudinal resolution. 100 mm off-center, bar patterns up to 14 lp/cm are visible, corresponding to an object size of 0.36 mm that can be resolved in the z direction. Image noise for constant effective mAs is almost independent of the pitch. Measured values show a variation of less than 7% as a function of the pitch, which demonstrates correct utilization of the applied radiation dose at any pitch. The product of image noise and square root of the slice width (FWHM of the respective SSP) is the same constant for all slices except 0.6 mm. For the thinnest slice, relative image noise is increased by 17%. Spiral windmill-type artifacts are effectively suppressed with the z-flying focal spot technique, which has the potential to maintain a low artifact level up to pitch 1.5, in this way increasing the maximum volume coverage speed that can be clinically used.
    Medical Physics 09/2005; 32(8):2536-47. DOI:10.1118/1.1949787 · 2.64 Impact Factor
  • T Flohr · K Stierstorfer · R Raupach · S Ulzheimer · H Bruder ·
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    ABSTRACT: The meanwhile established generation of 16-slice CT systems enables routine sub-millimeter imaging at short breath-hold times. Clinical progress in the development of multidetector row CT (MDCT) technology beyond 16 slices can more likely be expected from further improvement in spatial and temporal resolution rather than from a mere increase in the speed of volume coverage. We present an evaluation of a recently introduced 64-slice CT system (SOMATOM Sensation 64, Siemens AG, Forchheim, Germany), which uses a periodic motion of the focal spot in longitudinal direction (z-flying focal spot) to double the number of simultaneously acquired slices. This technique acquires 64 overlapping 0.6 mm slices per rotation. The sampling scheme corresponds to that of a 64 x 0.3 mm detector, with the goal of improved longitudinal resolution and reduced spiral artifacts. After an introduction to the detector design, we discuss the basics of z-flying focal spot technology (z-Sharp). We present phantom and specimen scans for performance evaluation. The measured full width at half maximum (FWHM) of the thinnest spiral slice is 0.65 mm. All spiral slice widths are almost independent of the pitch, with deviations of less than 0.1 mm from the nominal value. Using a high-resolution bar pattern phantom (CATPHAN, Phantom Laboratories, Salem, NY), the longitudinal resolution can be demonstrated to be up to 15 lp/cm at the isocenter independent of the pitch, corresponding to a bar diameter of 0.33 mm. Longitudinal resolution is only slightly degraded for off-center locations. At a distance of 100 mm from the isocenter, 14 lp/cm can be resolved in the z-direction, corresponding to a bar diameter of 0.36 mm. Spiral "windmill" artifacts presenting as hyper- and hypodense structures around osseous edges are effectively reduced by the z-flying focal spot technique. Cardiac scanning benefits from the short gantry rotation time of 0.33 s, providing up to 83 ms temporal resolution with 2-segment ECG-gated reconstruction.
    RöFo - Fortschritte auf dem Gebiet der R 01/2005; 176(12):1803-10. DOI:10.1055/s-2004-813717 · 1.40 Impact Factor
  • Stefan Ulzheimer · Kaiss Shanneik · Willi A. Kalender ·
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    ABSTRACT: Calcium in the form of hydroxyapatite (HA) is regarded as a known marker for the presence of atherosclerotic lesions of the coronary arteries. Several studies have demonstrated that the risk for coronary events is associated and strongly correlated with the amount of coronary calcium (1,2). The absence of coronary calcium does almost certainly imply the absence of coronary artery disease (CAD) (3), which, according to a World Health Report by the World Health Organization (WHO), is the leading cause of mortality in the world, amounting to 13.7%.
    12/2004: pages 129-141;

Publication Stats

3k Citations
120.07 Total Impact Points


  • 2008
    • Cardiovascular Center Bethanien
      Frankfurt, Hesse, Germany
    • Mayo Clinic - Rochester
      • Department of Radiology
      Rochester, Minnesota, United States
  • 2006
    • Siemens
      München, Bavaria, Germany
    • University Hospital Essen
      • Institut für Diagnostische und Interventionelle Radiologie und Neuroradiologie
      Essen, North Rhine-Westphalia, Germany
  • 2000-2003
    • Friedrich-Alexander Universität Erlangen-Nürnberg
      • Institute of Physics
      Erlangen, Bavaria, Germany