W Stiller

Reduction of radiation exposure and improvement of image quality with BMI-adapted prospective cardiac computed tomography and iterative reconstruction

PURPOSEnTo assess the impact of body mass index (BMI)-adapted protocols and iterative reconstruction algorithms (iDose) on patient radiation exposure and image quality in patients undergoing prospective ECG-triggered 256-slice coronary computed tomography angiography (CCTA).nnnMETHODSnImage quality and radiation exposure were systematically analyzed in 100 patients. 60 Patients underwent prospective ECG-triggered CCTA using a non-tailored protocol and served as a control group (Group 1: 120 kV, 200 mAs). 40 Consecutive patients with suspected coronary artery disease (CAD) underwent prospective CCTA, using BMI-adapted tube voltage and standard (Group 2: 100/120 kV, 100-200 mAs) versus reduced tube current (Group 3: 100/120 kV, 75-150 mAs). Iterative reconstructions were provided with different iDose levels and were compared to filtered back projection (FBP) reconstructions. Image quality was assessed in consensus of 2 experienced observers and using a 5-grade scale (1=best to 5=worse), and signal- and contrast-to-noise ratios (SNR and CNR) were quantified.nnnRESULTSnCCTA was performed without adverse events in all patients (n=100, heart rate of 47-87 bpm and BMI of 19-38 kg/m2). Patients examined using the non-tailored protocol in Group 1 had the highest radiation exposure (3.2±0.4 mSv), followed by Group 2 (1.7±0.7 mSv) and Group 3 (1.2±0.6 mSv) (radiation savings of 47% and 63%, respectively, p<0.001). Iterative reconstructions provided increased SNR and CNR, particularly when higher iDose level 5 was applied with Multi-Frequency reconstruction (iDose5 MFR) (14.1±4.6 versus 21.2±7.3 for SNR and 12.0±4.2 versus 18.1±6.6 for CNR, for FBP versus iDose5 MFR, respectively, p<0.001). The combination of BMI adaptation with iterative reconstruction reduced radiation exposure and simultaneously improved image quality (subjective image quality of 1.4±0.4 versus 1.9±0.5 for Group 2 reconstructed using iDose5 MFR versus Group 1 reconstructed using FBP, p<0.05).nnnCONCLUSIONSnProspective ECG-triggered 256-slice CCTA allows for visualization of the coronary artery tree with high image quality within a wide range of heart rates and BMIs. The combination of BMI-adapted protocols with iterative reconstruction algorithms can reduce radiation exposure for the patients and simultaneously improve image quality.

Dual-energy perfusion-CT of pancreatic adenocarcinoma

PURPOSEnTo evaluate the feasibility of dual-energy CT (DECT)-perfusion of pancreatic carcinomas for assessing the differences in perfusion, permeability and blood volume of healthy pancreatic tissue and histopathologically confirmed solid pancreatic carcinoma.nnnMATERIALS AND METHODSn24 patients with histologically proven pancreatic carcinoma were examined prospectively with a 64-slice dual source CT using a dynamic sequence of 34 dual-energy (DE) acquisitions every 1.5s (80 ml of iodinated contrast material, 370 mg/ml, flow rate 5 ml/s). 80 kV(p), 140 kV(p), and weighted average (linearly blended M0.3) 120 kV(p)-equivalent dual-energy perfusion image data sets were evaluated with a body-perfusion CT tool (Body-PCT, Siemens Medical Solutions, Erlangen, Germany) for estimating perfusion, permeability, and blood volume values. Color-coded parameter maps were generated.nnnRESULTSnIn all 24 patients dual-energy CT-perfusion was. All carcinomas could be identified in the color-coded perfusion maps. Calculated perfusion, permeability and blood volume values were significantly lower in pancreatic carcinomas compared to healthy pancreatic tissue. Weighted average 120 kV(p)-equivalent perfusion-, permeability- and blood volume-values determined from DE image data were 0.27 ± 0.04 min(-1) vs. 0.91 ± 0.04 min(-1) (p<0.0001), 0.5 ± 0.07 *0.5 min(-1) vs. 0.67 ± 0.05 *0.5 min(-1) (p=0.06) and 0.49 ± 0.07 min(-1) vs. 1.28 ± 0.11 min(-1) (p<0.0001). Compared with 80 and 140 kV(p) the standard deviations of the kV(p)120 kV(p)-equivalent values were manifestly smaller.nnnCONCLUSIONnDual-energy CT-perfusion of the pancreas is feasible. The use of DECT improves the accuracy of CT-perfusion of the pancreas by fully exploiting the advantages of enhanced iodine contrast at 80 kV(p) in combination with the noise reduction at 140 kV(p). Therefore using dual-energy perfusion data could improve the delineation of pancreatic carcinomas.

Heidelberg-mCT-Analyzer: a novel method for standardized microcomputed-tomography-guided evaluation of scaffold properties in bone and tissue research.

Bone tissue engineering and bone scaffold development represent two challenging fields in orthopaedic research. Micro-computed tomography (mCT) allows non-invasive measurement of these scaffolds’ properties in vivo. However, the lack of standardized mCT analysis protocols and, therefore, the protocols’ user-dependency make interpretation of the reported results difficult. To overcome these issues in scaffold research, we introduce the Heidelberg-mCT-Analyzer. For evaluation of our technique, we built 10 bone-inducing scaffolds, which underwent mCT acquisition before ectopic implantation (T0) in mice, and at explantation eight weeks thereafter (T1). The scaffolds’ three-dimensional reconstructions were automatically segmented using fuzzy clustering with fully automatic level-setting. The scaffold itself and its pores were then evaluated for T0 and T1. Analysing the scaffolds’ characteristic parameter set with our quantification method showed bone formation over time. We were able to demonstrate that our algorithm obtained the same results for basic scaffold parameters (e.g. scaffold volume, pore number and pore volume) as other established analysis methods. Furthermore, our algorithm was able to analyse more complex parameters, such as pore size range, tissue mineral density and scaffold surface. Our imaging and post-processing strategy enables standardized and user-independent analysis of scaffold properties, and therefore is able to improve the quantitative evaluations of scaffold-associated bone tissue-engineering projects.

Dual-Energy Perfusion-CT in Recurrent Pancreatic Cancer - Preliminary Results.

PURPOSEnTo evaluate the diagnostic performance of dual energy (DE) perfusion-CT for the differentiation between postoperative soft-tissue formation and tumor recurrence in patients after potentially curative pancreatic cancer resection.nnnMATERIAL AND METHODSn24 patients with postoperative soft-tissue formation in the conventional regular follow-up CT acquisition after pancreatic cancer resection with curative intent were included prospectively. They were examined with a 64-row dual-source CT using a dynamic sequence of 34 DE acquisitions every 1.5u200as (80u200aml of iodinated contrast material, 370u200amg/ml, flow rate 5u200aml/s). Weighted average (linearly blended M0.5) 120kVp-equivalent dual-energy perfusion image data sets were evaluated with a body-perfusion CT tool (see above) for estimating blood flow, permeability, and blood volume. Diagnosis was confirmed by histological study (nu200a=u200a4) and by regular follow-up.nnnRESULTSnFinal diagnosis was local recurrence of pancreatic cancer in 15 patients and unspecific postoperative tissue formation in 9 patients. The blood-flow values for recurrence tissue trended to be lower compared to postoperative tissue formation with 16.6u200aml/100u200aml/min and 24.7u200aml/100u200aml/min, respectively for weighted average 120kVp-equivalent image data, which was not significant (n.s.) (pu200a=u200a0.06, significance level 0.05). Permeability- and blood-volume values were only slightly lower in recurrence tissue (n.s.).nnnCONCLUSIONnDE perfusion-CT is feasible in patients after pancreatic cancer resection and a promising functional imaging technique. As only a trend for lower perfusion values in local recurrence compared to unspecific postoperative alterations was found, the perfusion differences are not yet sufficient to differentiate between malignancy and unspecific postoperative alterations for this new technique. Further studies and technical improvements are needed to generate reliable data for this clinically highly relevant differentiation.nnnKEY POINTSn•u2007DE Perfusion CT is feasible in patients after pancreatic cancer resection.•u2007While reliable differentiation of unspecific postoperative tissue formation from recurrent malignancy cannot be achieved yet, it is within reach.•u2007DE Perfusion CT has the potential to overcome todays limitations of pure morphological diagnosis of recurrent pancreatic cancer. Citation Format: •u2007Fritz F, Skornitzke S, Hackert T etu200aal. Dual-Energy Perfusion-CT in Recurrent Pancreatic Cancer - Preliminary RESULTS. Fortschr Röntgenstr 2016; 188: 559u200a-u200a565.

Improved image quality with simultaneously reduced radiation exposure: Knowledge-based iterative model reconstruction algorithms for coronary CT angiography in a clinical setting

BACKGROUNDnThe aim of this study was to assess the potential for radiation dose reduction using knowledge-based iterative model reconstruction (K-IMR) algorithms in combination with ultra-low dose body mass index (BMI)-adapted protocols in coronary CT angiography (coronary CTA).nnnMETHODSnForty patients undergoing clinically indicated coronary CTA were randomly assigned to two groups with BMI-adapted (I: <25.0xa0kg/m2, II: <28.0xa0kg/m2, III: <30.0xa0kg/m2, IV: ≥30.0xa0kg/m2) low dose (LD, I: 100kVp/75xa0mAs, II: 100kVp/100xa0mAs, III: 100kVp/150xa0mAs, IV: 120kVp/150xa0mAs, nxa0=xa020) or ultra-low dose (ULD, I: 100kVp/50xa0mAs, II: 100kVp/75xa0mAs, III: 100kVp/100xa0mAs, IV: 120kVp/100xa0mAs, nxa0=xa020) protocols. Prospectively-triggered coronary CTA was performed using a 256-MDCT with the lowest reasonable scan length. Images were generated with filtered back projection (FBP), a noise-reducing hybrid iterative algorithm (iD, levels 2/5) and K-IMR using cardiac routine (CR) and cardiac sharp settings, levels 1-3.nnnRESULTSnGroups were comparable regarding anthropometric parameters, heart rate, and scan length. The use of ULD protocols resulted in a significant reduction of radiation exposure (0.7 (0.6-0.9) mSv vs. 1.1 (0.9-1.7) mSv; pxa0<xa00.02). Image quality was significantly better in the ULD group using K-IMR CR 1 compared to FBP, iD 2 and iD 5 in the LD group, resulting in fewer non-diagnostic coronary segments (2.4% vs. 11.6%, 9.2% and 6.1%; pxa0<xa00.05).nnnCONCLUSIONSnThe combination of K-IMR with BMI-adapted ULD protocols results in significant radiation dose savings while simultaneously improving image quality compared to LD protocols with FBP or hybrid iterative algorithms. Therefore, K-IMR allows for coronary CTA examinations with high diagnostic value and very low radiation exposure in clinical routine.

Untersuchung von Dual-energy (DE) Mischverhältnissen in Abhängigkeit der Strahlenexposition und des DE-Aufnahmemodus zur Erzeugung optimaler linearer DE-Mischbilder

Zielsetzung: Inhalt der Studie war die systematische Untersuchung der DE-Mischverhaltnisse α in Abhangigkeit der Strahlenexposition und des DE-Aufnahmemodus mit dem Ziel der Berechnung von DE-Mischbildern mit gleicher oder besserer Bildqualitat im Vergleich zu dosisaquivalenten Single-energy (SE) Aufnahmen. Material und Methodik: Neun Patienten mit Leberlasionen wurden mindestens einmal mittels CT, die aus drei unabhangigen Serien mit gleicher Dosis bestand (SE 120kVp, DE 80/Sn140kVp, DE 100/Sn140kVp, insgesamt 17 Untersuchungen), untersucht. Die CT-Untersuchungen unterteilen sich in drei Gruppen unterschiedlicher Dosisstufen mit CTDIvol = 10mGy; 7mGy; 5mGy. Zu jeder aufgenommen SE-Bildschicht wurden 100 dosisequivalente lineare DE-Mischbilder der gleichen Schicht mit α zwischen 0,0 und 1,0 berechnet. In Abhangigkeit vom DE-Aufnahmemodus und der Dosisstufe wurden fur jedes DE-Mischbild quantitative Bildqualitatsparameter (CT-Wert, Rauschen, Kontrast-zu-Rauschen (CNR) und Signal-zu-Rauschen (SNR)) ermittelt und mit denen der entsprechenden SE-Bildschicht verglichen. Ergebnisse: Der optimale Wert fur α ist unabhangig von der Dosisstufe. Bestmogliche α unterscheiden sich signifikant (p < 0,05) je nach untersuchtem Bildqualitatsparameter und DE-Aufnahmemodus: Optimales α_CNR/SNR (α_CNR≈0,7/α_SNR≈0,6) liefert nicht nur ein signifikant hoheres CNR/SNR (bis zu 40%; p < 0,05) als die entsprechende SE-Bildschicht fur beide DE-Modi, sondern unterscheidet sich auch signifikant von den DE-Standard Mischverhaltnissen (α_80/Sn140kVp = 0,3; α_100/Sn140kVp = 0,5). Der DE80/Sn140kVp Modus liefert ein hoheres CNR/SNR als der DE100/Sn140kVp Modus. Das kleinste Bildrauschen wurde bei α≈0,3 in beiden DE-Modi gemessen. Aquivalente CT-Werte und CNR-Verhaltnisse werden mit dem DE-Standardwert im DE80/Sn140kVp Modus erreicht. Schlussfolgerungen: DE-Mischbilder, die mit bestmoglichem DE-Mischverhaltnis berechnet wurden, erreichen eine hohere Bildqualitat als entsprechende dosisequivalente SE-Bildschichten und bieten Potenzial fur Dosiseinsparungen.

Compton scattering spectroscopy for determining filtration of a clinical Computed Tomography system

Purpose: Compton spectroscopy is a widely accepted tool for measuring the primary X-ray spectra of a diagnostic computed tomography (CT) system. The aim of this work is to spectroscopically detect CT X-ray photons subjected to 90-degree Compton scattering for accurate modelling of CT beam-shaping filtration, which necessary for computation of radiation exposure and for other research applications in medical physics. Methods: For a tube potential of 120 kVp X-ray spectra have been measured under fan angles of 0° to 20° in steps of 2° and at 21° from the central ray. At each fan angle the value of the X-ray path length determining the relative filter transmission was iteratively varied in order to estimate the thickness of the aluminium filter and the filter geometry was implemented in a Monte Carlo (MC) simulation of the CT scanner. Results: Direct comparison of measured and simulated filtered X-ray spectra indicates that the spectra match very well, with a correlation of 1 for small fan angles (below 4°) and an average correlation of 0.996 for the whole field-of-view (FOV). Conclusion: The agreement between the simulated X-ray spectra and the measured spectra suggest that spectral measurements using Compton spectroscopy across the fan beam of a CT system are suitable for modelling the beam-shaping filtration currently used in commercially available CT systems.