Siemens Somatom Definition Flash Research Articles

Analysis of experience in the clinical use of dual-energy computed tomography in patients with undifferentiated arthritis

Dual-energy computed tomography (DECT) is a radiation diagnostic method that is used in rheumatology to verify microcrystalline arthritis, but in Russia this method is little known and the experience of its use is rather scarce.Objective of the research. To analyze the experience of using DECT in patients with undifferentiated arthritis and lesions of the axial skeleton in clinical practice.Material and Methods. The retrospective study included 20 patients (14 men and 6 women) observed at the V. A. Nasonova Research Institute of Rheumatology, who underwent DECT for diagnostic purposes. 13 patients with undifferentiated arthritis underwent DECT of peripheral joints to diagnose gout; 7 patients with an established diagnosis of gout (based on the 2015 ACR/EULAR classification criteria for gout) – to clarify the genesis of lesions to the axial joints and spine. The study was performed on a Siemens SOMATOM Definition Flash computed tomograph.Results. Using DECT in patients with undifferentiated arthritis, deposits of monosodium urate crystals (MSUc) were detected in 7 out of 13 (54 %), which made it possible to verify the diagnosis of gout. In the second sample, 6 out of 7 patients (85 %) showed signs of MSUc deposition on DECT, which explained the genesis of the existing complaints. Among these 6 patients, in 1 person, DECT revealed the presence of MSUc and calcium pyrophosphate crystals in the shoulder joint, which made it possible to make two diagnoses at once – gout and calcium pyrophosphate deposition disease.Conclusion. DECT in patients with undifferentiated arthritis makes it possible to verify the diagnosis of gout in more than half of the cases (54 %). In 85 % of patients with gout and pain in the back and axial joints of unknown origin, urate deposits are detected according to DECT. This method may be a useful tool for identifying microcrystalline arthritis of the axial joints, but further research is needed to implement the method in routine practice.

Effect of arm position on image quality and radiation dose during thorax and abdomen computed tomography scans

IntroductionDuring Computed Tomography (CT) scans of the Thorax-Abdomen-Pelvis (TAP) the patient's arms should be positioned above the head to obtain optimal image quality and expose the patient to the lowest possible radiation dose. This may be impossible with patients with shoulder problems leading to arms being positioned in other ways. This study aimed to investigate differences in objective image quality and estimated effective dose (E), when positioning the arms below shoulder level in CT-TAP. MethodsAn anthropomorphic phantom with cadaver arms was used. Four arm positions were tested: Along the torso (A), on the pelvis (B), on a pillow on the pelvis (C), and one arm on pillow on the pelvis and the other arm on the pelvis (D). A Siemens SOMATOM Definition Flash CT-scanner with CareDose 4D was used. The dose length product was read to estimate E. Image quality was assessed objectively by measuring noise within the region of interest in the liver and urinary bladder. ResultsSignificant differences in E between all arm positions were seen (p = 0.005). The lowest E was obtained in position C, reducing E by 8.42%. Position A provided the best image quality but the highest E. ConclusionThis study showed no unequivocal optimal positioning of arms in CT-TAP. Position A provided the best object image quality, while position C yielded the lowest E. These results may impact the planning of diagnostic CT where positioning of arms may influence optimal image quality and radiation dose. Implication for practiceThis study illustrates tendencies for objective image quality and E when arms are positioned below shoulder level. Further research is needed to assess the clinical relevance with the diagnostic potential.

Presentation of Organ Dose and Effective Dose Conversion Factors in Dual-Energy Computed Tomography: A Monte Carlo Simulation Study.

The same conversion factors (k-factors) of Single CT (SECT) are applied to estimate the Effective Dose (ED) in Dual Energy Computed Tomography (DECT). However, k-factors for different organs need independently validating for DECT, due to the different conditions in DECT. This study aimed to calculate organ dose and k-factors in different imaging protocols (liver, chest, cardiac, and abdomen) for male and female phantoms. This Monte Carlo Simulation study used Monte Carlo N-Particle (MCNP) code for modeling a Siemens Somatom Definition Flash dual-source CT scanner. The organ dose, dose length product, and k-factors were calculated for the Medical Internal Radiation Dose (MIRD) of male and female phantoms. For the male phantom, the k-factors for the liver, chest, cardiac, and abdomen-pelvis imaging protocols are equal to 0.020, 0.012, 0.016, and 0.014 mSv.mGy-1cm-1, respectively. For the female phantom, the corresponding values are equal to 0.026, 0.023, 0.036, and 0.018, respectively. These values for DECT are different from those corresponding values for SECT, especially for the female phantom. The calculated k-factors for DECT can be used as reference values for the estimation of ED in DECT.

Sex-based differences of the impact of aortic valve calcium score on mortality and post-procedural outcomes after trans-catheter aortic valve replacement

Abstract Introduction Sex based differences exist in the presentation, outcomes, and management of cardiovascular diseases. Although aortic valve calcium (AVC) score has been postulated to be associated with post-procedural outcomes after transcatheter aortic valve replacement (TAVR), data on the impact of AVC score on procedural outcomes after TAVR based on sex have been scarce. Objective The aim of the present study was to elucidate sex related differences in the prognostic impact of AVC score as a predictor of post-procedural outcomes and mortality in patients with severe aortic stenosis (AS) who underwent TAVR. Methods We retrospectively abstracted the records of 497 patients with severe AS who underwent TAVR between January 2016 and July 2019 at our institution. All patients underwent a non-contrast cardiac CT scan on a Siemens Somatom Definition Flash 128 slice scanner. AVC score using the Agatston method was calculated retrospectively. Primary outcome was 1-year mortality. Patients were divided into two groups: 1) Non-severe AVC score group [women <1200 Agatston unit (AU) and men <2000 AU]; 2) Severe AVC Score group [women >1200 AU and men >2000 AU]. Cox-regression model was used to predict effect of variables on 1-year mortality in male and female patients. Results Among 466 patients included, 268 patients were male and 198 were female (57.5% vs 42.5%). When compared with males, female patients had significantly lower AVC score (p<0.001), aortic valve area (AVA) (p<0.001), obstructive CAD (p<0.001), and history of previous PCI (p<0.004), and CABG (<0.001) but had a significantly higher STS score (6.7±3.2 vs 5.8±3.3 P=0.01). There was no difference between need for permanent pacemaker (PPM) implantation (11% vs 9.6%, p=0.4), major complications (16% vs 15%, p=0.9), stroke (0.8% vs 1.6%, p=0.7), 30-day (3.7% vs 4%, p=0.9), and 1-year mortality (14% vs 12%, p=0.6) between males and females, respectively. Female patients required smaller bio-prosthetic valves compared with males (26±3.2 vs 30±3, p<0.001). Cox regression analysis for female patients showed BMI, hemoglobin level, and AVA independently predicted 1-year mortality, while there was no impact of severe AVC score (>1200 AU) on 1-year mortality in females. Similarly, Cox regression analysis for male patients showed there was no impact of severe AVC score (>2000 AU) on 1-year mortality in males. When males in the severe AVC group were compared with female patients in the severe AVC group, there was no difference in 30 day (4.3% vs 3.3%, p=0.82) and 1-year mortality (14.2% vs 13.3%, p=0.77). Similarly, in the severe AVC group there was no difference between need for PPM implantation (12.8% vs 12.1%, p=0.9), major complications (19.7% vs 15.8%, p=0.4), and stroke (2.2% vs 1%, p=0.6) between males and females, respectively. Conclusion There were no sex differences in the impact of AVC score on mortality and post-procedural outcomes after TAVR. Funding Acknowledgement Type of funding sources: None.

Predictive Role of Aortic Valve Calcium score on post-procedural outcomes and mortality after Transcatheter aortic valve replacement

Abstract Introduction Extent of aortic valve (AV) calcium increases as degenerative aortic valve stenosis progresses. Initial studies postulated AV calcium (AVC) score to be a predictor of complications such as need for pacemaker implantation, paravalvular regurgitation and mortality after Trans-catheter Aortic valve Replacement (TAVR). However, evidence regarding the impact of AVC score as a predictor of post-procedural complications and mortality has been conflicting. Objective This study aimed to determine the prognostic impact of AVC as predictor of post-procedural outcomes and mortality in patients with severe aortic stenosis (AS) who underwent TAVR. Methods We retrospectively abstracted the records of 497 patients with severe AS who underwent TAVR between January 2016 and July 2019 at our institution. All patients underwent a non-contrast cardiac CT scan on a Siemens Somatom Definition Flash 128 slice scanner. AVC score using the Agatston method was obtained retrospectively. Patients were divided into two groups: 1) Non-severe AVC score group [women <1200 Agatston unit (AU) and men <2000 AU]; 2) Severe AV Calcium Score group [women >1200 AU and men >2000 AU]. Primary outcome was 1-year mortality. Results Among 466 patients included in the analysis, 352 patients were included severe AVC group while 114 patients were in the non-severe AVC group. Patients in the severe AVC group were older (81±8 vs 79±8 years), were predominantly males (79% vs 71%), and had less diabetes mellitus (31% vs 42%, p=0.02). Post-TAVR AV dimensionless index (0.58±0.13 vs 0.58±0.12, p=0.8) and AV mean gradient (9.5±4.9 vs 9.2±5.4 mmHg) were not statistically different between both groups. There was no statistical difference in the need for PPM (12% vs 7%, p=0.16), post-TAVR stroke (1.5% vs 0%), post-TAVR major complications (17.4% vs 10%, p=0.07), 30 day (3.7% vs 4.4%), and 1-year mortality (13.6 vs 11.4, p=0.6) between both groups. Conclusion Our study report that the severity of AVC score does not have a prognostic impact on major post-procedural outcomes and mortality after TAVR. Funding Acknowledgement Type of funding sources: None.

Scanner-specific validation of a CT simulator using a COPD-emulated anthropomorphic phantom.

Traditional methods of quantitative analysis of CT images typically involve working with patient data, which is often expensive and limited in terms of ground truth. To counter these restrictions, quantitative assessments can instead be made through Virtual Imaging Trials (VITs) which simulate the CT imaging process. This study sought to validate DukeSim (a scanner-specific CT simulator) utilizing clinically relevant biomarkers for a customized anthropomorphic chest phantom. The physical phantom was imaged utilizing two commercial CT scanners (Siemens Somatom Force and Definition Flash) with varying imaging parameters. A computational version of the phantom was simulated utilizing DukeSim for each corresponding real acquisition. Biomarkers were computed and compared between the real and virtually acquired CT images to assess the validity of DukeSim. The simulated images closely matched the real images both qualitatively and quantitatively, with the average biomarker percent difference of 3.84% (range 0.19% to 18.27%). Results showed that DukeSim is reasonably well validated across various patient imaging conditions and scanners, which indicates the utility of DukeSim for further VIT studies where real patient data may not be feasible.

CT Perfusion in Evaluation of Cervical Lymph Node Metastasis in Head and Neck Malignancies: A Cross-sectional Study

Introduction: Though, many cross-sectional modalities are available for evaluation of cervical lymph node metastasis but their results are highly variable. There is paucity of the literature in India, regarding lymph nodal assessment using Computed Tomography (CT) perfusion in head and neck malignancies even though, there is high incidence of oral cancer in India. Aim: To assess the role of Computed Tomography Perfusion (CTP) in evaluation of cervical lymph nodes in head and neck malignancies, by using CT perfusion parameters as compared to histopathology. Materials and Methods: This cross-sectional study was conducted in the Department of Radiodiagnosis in collaboration with the Department of Surgery and Pathology at Vardhman Mahavir Medical College and Safdarjung Hospital, Delhi, India, from October 2017 to April 2019. The study included 30 newly diagnosed head and neck cancer patients, with 46 nodes planned for surgical neck dissection. Computed tomography scan of neck was acquired using Siemens Somatom Definition Flash 256CT scanner. Reconstruction and post processing was performed on workstation and perfusion parameters were obtained to generate the CT perfusion maps. Differentiation between benign and malignant lymph nodes was done, on the basis of CT perfusion parameters such as Blood Flow (BF), Blood Volume (BV), Mean Transit Time (MTT) and Permeability Surface (PS), which were compared with histopathological findings of resected lymph nodes. McNemar’s test was applied for comparison and statistical analysis. Receiver Operating Characteristic (ROC) curve of quantitative parameters were obtained, for the detection of sensitivity, specificity, Positive Predictive Value (PPV), Negative Predictive Value (NPP) and diagnostic accuracy. Results: Out of 46 nodes, 23 were metastatic and 23 were non metastatic. The average value of BF in metastatic nodes was 174.61±71.76 mL/100g/min, BV was 16.32±11.9 mL/100g, MTT was 4.83±2.54 seconds and PS was 49.3±28.59 mL/100g/min. The average values for non metastatic nodes were: BF 88.06±34.4 mL/100g/min, BV: 9.89±7.63 mL/100g, MTT: 13.11±18.58 seconds and PS: 37.07±29.26 mL/100g/ min. The differences between the parameters like blood flow (p-value <0.0001), blood volume (p-value=0.005) and MTT (p-value=0.002) in malignant and benign nodes were significant. In case of blood flow, sensitivity was 82.61% and diagnostic accuracy was 84.78%. In case of blood volume, sensitivity was 91.30% and diagnostic accuracy was 73.91%. In case of mean transit time, sensitivity was 56.52% and diagnostic accuracy was 73.91%. In case of permeability surface, sensitivity was 91.30% and diagnostic accuracy was 67.39%. Conclusion: Blood flow and blood volume values were significantly increased in metastatic cervical lymph nodes as compared to non metastatic nodes, whereas MTT was significantly low. Permeability surface showed equivocal results.

The accuracy of helium ion CT based particle therapy range prediction: an experimental study comparing different particle and x-ray CT modalities

This work provides a quantitative assessment of helium ion CT (HeCT) for particle therapy treatment planning. For the first time, HeCT based range prediction accuracy in a heterogeneous tissue phantom is presented and compared to single-energy x-ray CT (SECT), dual-energy x-ray CT (DECT) and proton CT (pCT). HeCT and pCT scans were acquired using the US pCT collaboration prototype particle CT scanner at the Heidelberg Ion-Beam Therapy Center. SECT and DECT scans were done with a Siemens Somatom Definition Flash and converted to RSP. A Catphan CTP404 module was used to study the RSP accuracy of HeCT. A custom phantom of 20 cm diameter containing several tissue equivalent plastic cubes was used to assess the spatial resolution of HeCT and compare it to DECT. A clinically realistic heterogeneous tissue phantom was constructed using cranial slices from a pig head placed inside a cylindrical phantom (ø150 mm). A proton beam (84.67 mm range) depth-dose measurement was acquired using a stack of GafchromicTM EBT-XD films in a central dosimetry insert in the phantom. CT scans of the phantom were acquired with each modality, and proton depth-dose estimates were simulated based on the reconstructions. The RSP accuracy of HeCT for the plastic phantom was found to be 0.3 ± 0.1%. The spatial resolution for HeCT of the cube phantom was 5.9 ± 0.4 lp cm−1 for central, and 7.6 ± 0.8 lp cm−1 for peripheral cubes, comparable to DECT spatial resolution (7.7 ± 0.3 lp cm−1 and 7.4 ± 0.2 lp cm−1, respectively). For the pig head, HeCT, SECT, DECT and pCT predicted range accuracy was 0.25%, −1.40%, −0.45% and 0.39%, respectively. In this study, HeCT acquired with a prototype system showed potential for particle therapy treatment planning, offering RSP accuracy, spatial resolution, and range prediction accuracy comparable to that achieved with a commercial DECT scanner. Still, technical improvements of HeCT are needed to enable clinical implementation.

Automatic segmentation of the pharyngeal airway space with convolutional neural network

ObjectivesThis study proposed and investigated the performance of a deep learning based three-dimensional (3D) convolutional neural network (CNN) model for automatic segmentation of the pharyngeal airway space (PAS). MethodsA dataset of 103 computed tomography (CT) and cone-beam CT (CBCT) scans was acquired from an orthognathic surgery patients database. The acquisition devices consisted of 1 CT (128-slice multi-slice spiral CT, Siemens Somatom Definition Flash, Siemens AG, Erlangen, Germany) and 2 CBCT devices (Promax 3D Max, Planmeca, Helsinki, Finland and Newtom VGi evo, Cefla, Imola, Italy) with different scanning parameters. A 3D CNN-based model (3D U-Net) was built for automatic segmentation of the PAS. The complete CT/CBCT dataset was split into three sets, training set (n = 48) for training the model based on the ground-truth observer-based manual segmentation, test set (n = 25) for getting the final performance of the model and validation set (n = 30) for evaluating the model's performance versus observer-based segmentation. ResultsThe CNN model was able to identify the segmented region with optimal precision (0.97±0.01) and recall (0.96±0.03). The maximal difference between the automatic segmentation and ground truth based on 95% hausdorff distance score was 0.98±0.74mm. The dice score of 0.97±0.02 confirmed the high similarity of the segmented region to the ground truth. The Intersection over union (IoU) metric was also found to be high (0.93±0.03). Based on the acquisition devices, Newtom VGi evo CBCT showed improved performance compared to the Promax 3D Max and CT device. ConclusionThe proposed 3D U-Net model offered an accurate and time-efficient method for the segmentation of PAS from CT/CBCT images. Clinical significanceThe proposed method can allow clinicians to accurately and efficiently diagnose, plan treatment and follow-up patients with dento-skeletal deformities and obstructive sleep apnea which might influence the upper airway space, thereby further improving patient care.

PATIENT-SPECIFIC DOSE ESTIMATES IN DYNAMIC COMPUTED TOMOGRAPHY MYOCARDIAL PERFUSION EXAMINATION.

The study aimed to implement realistic source models of a computed tomography (CT) scanner and Monte Carlo simulations to actual patient data and to calculate patient-specific organ and effective dose estimates for patients undergoing dynamic CT myocardial perfusion examinations. Source models including bowtie filter, tube output and x-ray spectra were determined for a dual-source Siemens Somatom Definition Flash scanner. Twenty CT angiography patient datasets were merged with a scaled International Commission on Radiological Protection (ICRP) 110 voxel phantom. Dose simulations were conducted with ImpactMC software. Effective dose estimates varied from 5.0 to 14.6 mSv for the 80 kV spectrum and from 8.9 to 24.7 mSv for the 100 kV spectrum. Significant differences in organ doses and effective doses between patients emphasise the need to use actual patient data merged with matched anthropomorphic anatomy in the dose simulations to achieve a reasonable level of accuracy in the dose estimation procedure.

Quantitative imaging performance of MARS spectral photon-counting CT for radiotherapy.

To evaluate the quantitative imaging performance of a spectral photon-counting computed tomography (SPCCT) scanner for radiotherapy applications. An experimental comparison of the quantitative performance of a Siemens dual-energy CT (DECT) and a MARS SPCCT scanner is performed to estimate physical properties relevant to radiotherapy of human substitute materials and contrast agent solutions. In human substitute materials, the accuracy of quantities relevant to photon therapy, proton therapy, and Monte-Carlo simulations, such as the electron density, proton stopping power, and elemental composition is evaluated. For contrast agent solutions, the accuracy of the contrast agent concentrations and the virtual non-contrast (VNC) electron density is evaluated. Human tissue substitute phantoms (Gammex 467 and 472) as well as diluted solutions of contrast agents (iodine and gadolinium based) are scanned with two commercial systems: a Siemens dual-source CT (SOMATOM Definition Flash, Siemens Healthineers, Forchheim, Germany) and a MARS spectral photon-counting micro-CT (MARS V5.2, MARS Bioimaging Ltd., Christchurch, New Zealand). Material decomposition is performed in a maximum a posteriori framework with an optimized material basis tailored to characterize either human substitute materials or contrast agents in the context of experimental multi-energy CT data. The root-mean-square error (RMSE) of the electron density calculated over all Gammex inserts is reduced from 1.09 to 0.89% when going from DECT to SPCCT. For the proton stopping power, the RMSE is reduced from 1.92 to 0.89%. Elemental mass fractions of hydrogen, carbon, nitrogen, oxygen, and calcium are more accurately estimated with the MARS scanner. The RMSE on the iodine-based contrast agents concentration is reduced from 0.27 to 0.12mg/mL with SPCCT, and the VNC electron density from 0.40 to 0.22%. In the present phantom study, a MARS photon-counting scanner provides superior accuracy compared to a Siemens SOMATOM Definition Flash DECT scanner to quantify physical parameters relevant to radiotherapy. This work experimentally demonstrates the benefits of using more energies to characterize human tissue equivalent materials. This highlights the potential of SPCCT for particle therapy, where more accurate tissue characterization is needed, as well as for Monte-Carlo based planning, which requires accurate elemental mass fractions.

Assessment of imaging protocol and patient radiation exposure in pediatric computed tomography angiography

Computed tomography angiography (CTA), a noninvasive imaging procedure, is frequently used for the diagnosis of blood vessel diseases. Pediatric patients are more sensitive to radiation than adults due to their rapidly dividing cells and long life expectancy. Thus, evaluation of pediatric exposure is crucial to ensure that the procedure is justified and the practice is optimized. The objectives of this study were to evaluate pediatric patients' exposure and imaging protocols for different CTA procedures and to estimate the cancer risk incidence. A total of 147 pediatric CTA procedures were performed at King Fahad Medical City using three CT machines (Philips Brilliance CT- 64-slice scanner, Siemens Somatom Definition Flash dual source 128 CT slice scanner and GE 750 HD DISCOVERY dual energy 64 CT slice scanner). The image protocol and patient safety measures were evaluated according to American College of Radiology (ACR) criteria. The Ethics and Research Committee approved the study and informed consent was obtained from children's parents. The mean, standard deviation (sd) and range of patients weight (kg) was 8.1 ± 13.2 (3.5–58.7). The mean, sd, median and range of patient dose (mGy.cm) for circle of willis, carotid arteries, thoracic and abdominal aorta, heart and vessels, renal artery, pulmonary artery, abdominal aorta, thoracic aorta, upper lim and lower limb were 992 ± 798, 759.0 (204–2829), 285 ± 157, 660.0 (56.7–652), 500 ± 457, 210.1 (112–1387), 472 ± 317, 411.4, (175–3909) and 350 ± 346, 589.7 (284–1431), respectively. Pediatric average radiation cancer risk incidence was 36 × 10−4. Patients' doses showed wide variation among the three CT machines and even for the same machine and the same clinical investigation. The dose per procedure is higher compared to previous studies, suggesting that the dose is not yet optimized. Protection of radiosensitive organs is highly recommended for pediatric patients.

276. A novel methodology for quantification of absolute overscan dose in helical multisection CT

Purpose Recent helical multisection CT provides rapid and wide-coverage scans, but delivers an extra-dose amount at the beginning and at the end of the scan (overscanning) resulting in quite significant contribution to patient exposure. This study aims to quantify the overscan dose contribution for different scan parameters through experimental measurements and simulations. Methods Overscan dose was quantified by means of a previously validated methodology [1] based on novel CT measurement setup and dosimetric formalism. Waveforms, dose-rate versus time, at center and periphery of head and body phantoms were acquired with a 128-detector-row CT-scanner (Siemens SOMATOM Definition Flash) varying protocols, pitches, rotation times and scanning lengths. In order to take into account the random start angle of CT tube, experimental waveforms were used to simulate a simultaneous acquisition at center and periphery of the phantom. The effect of scanning parameters on overscan dose was quantified calculating the DLP due to overscan ( DLP overscan ) as a weighted average of the values at center and periphery. Results The overscan length showed a positive correlation for pitch values ranging from 0.35 to 1.0 (r values, 0.98-1.00); it becomes slightly constant for pitch values higher than 1.0. The contribution of DLP overscan decreases from 36% to 4% increasing the overscan length from 2.5 to 30 cm. The dependence of absolute DLP value due to overscan from pitch was obtained for different rotation times and protocols, showing a positive correlation (r values, 0.99-1.00) in both head and body phantoms. Conclusions This method for quantifying the DLP in overscan range can be used to evaluate the clinical implication of overscanning and to optimize scanning protocols in order to reduce the impact of this extra-dose especially on critical organs.

Experimental validation of two dual-energy CT methods for proton therapy using heterogeneous tissue samples.

The purpose of this work is to evaluate the performance of dual-energy CT (DECT) for determining proton stopping power ratios (SPRs) in an experimental environment and to demonstrate its potential advantages over conventional single-energy CT (SECT) in clinical conditions. Water equivalent range (WER) measurements of 12 tissue-equivalent plastic materials and 12 fresh animal tissue samples are performed in a 195MeV broad proton beam using the dose extinction method. SECT and DECT scans of the samples are performed with a dual-source CT scanner (Siemens SOMATOM Definition Flash). The methods of Schneider etal. (1996), Bourque etal. (2014), and Lalonde etal. (2017) are used to predict proton SPR on SECT and DECT images. From predicted SPR values, the WER of the proton beam through the sample is predicted for SECT and DECT using Monte Carlo simulations and compared to the measured WER. For homogeneous tissue-equivalent plastic materials, results with DECT are consistent with experimental measurements and show a systematic reduction of SPR uncertainty compared to SECT, with root-mean-square errors of 1.59% versus 0.61% for SECT and DECT, respectively. Measurements with heterogeneous animal samples show a clear reduction of the bias on range predictions in the presence of bones, with -0.88% for SECT versus -0.58% and -0.14% for both DECT methods. An uncertainty budgetallows isolating the effect of CT number conversion to SPR and predicts improvements by DECT over SECT consistently with theoretical predictions, with 0.34% and 0.31% for soft tissues and bones in the experimental setup compared to 0.34% and 1.14% with the theoretical method. The present work uses experimental measurements in a realistic clinical environment to show potential benefits of DECT for proton therapy treatment planning. Our results show clear improvements over SECT in tissue-equivalent plastic materials and animal tissues. Further work towards using Monte Carlo simulations for treatment planning with DECT data and a more detailed investigation of the uncertainties on I-value and limitations on the Bragg additivity rule could potentially further enhance the benefits of this imaging technology for proton therapy.

Quantitative imaging of peripheral trabecular bone microarchitecture using MDCT.

Osteoporosis associated with reduced bone mineral density (BMD) and microarchitectural changes puts patients at an elevated risk of fracture. Modern multidetector row CT (MDCT) technology, producing high spatial resolution at increasingly lower dose radiation, is emerging as a viable modality for trabecular bone (Tb) imaging. Wide variation in CT scanners raises concerns of data uniformity in multisite and longitudinal studies. A comprehensive cadaveric study was performed to evaluate MDCT-derived Tb microarchitectural measures. A human pilot study was performed comparing continuity of Tb measures estimated from two MDCT scanners with significantly different image resolution features. Micro-CT imaging of cadaveric ankle specimens (n=25) was used to examine the validity of MDCT-derived Tb microarchitectural measures. Repeat scan reproducibility of MDCT-based Tb measures and their ability to predict mechanical properties were examined. To assess multiscanner data continuity of Tb measures, the distal tibias of 20 volunteers (age:26.2±4.5Y,10F) were scanned using the Siemens SOMATOM Definition Flash and the higher resolution Siemens SOMATOM Force scanners with an average 45-day time gap between scans. The correlation of Tb measures derived from the two scanners over 30% and 60% peel regions at the 4% to 8% of distal tibia was analyzed. MDCT-based Tb measures characterizing bone network area density, plate-rod microarchitecture, and transverse trabeculae showed good correlations (r∈0.85,0.92) with the gold standard micro-CT-derived values of matching Tb measures. However, other MDCT-derived Tb measures characterizing trabecular thickness and separation, erosion index, and structure model index produced weak correlation (r<0.8) with their micro-CT-derived values. Most MDCT Tb measures were found repeatable (ICC∈0.94,0.98). The Tb plate-width measure showed a strong correlation (r = 0.89) with experimental yield stress, while the transverse trabecular measure produced the highest correlation (r = 0.81) with Young's modulus. The data continuity experiment showed that, despite significant differences in image resolution between two scanners (10% MTF along xy-plane and z-direction - Flash: 16.2 and 17.9 lp/cm; Force: 24.8 and 21.0 lp/cm), most Tb measures had high Pearson correlations (r > 0.95) between values estimated from the two scanners. Relatively lower correlation coefficients were observed for the bone network area density (r = 0.91) and Tb separation (r = 0.93) measures. Most MDCT-derived Tb microarchitectural measures are reproducible and their values derived from two scanners strongly correlate with each other as well as with bone strength. This study has highlighted those MDCT-derived measures which show the greatest promise for characterization of bone network area density, plate-rod and transverse trabecular distributions with a good correlation (r ≥ 0.85) compared with their micro-CT-derived values. At the same time, other measures representing trabecular thickness and separation, erosion index, and structure model index produced weak correlations (r < 0.8) with their micro-CT-derived values, failing to accurately portray the projected trabecular microarchitectural features. Strong correlations of Tb measures estimated from two scanners suggest that image data from different scanners can be used successfully in multisite and longitudinal studies with linear calibration required for some measures. In summary, modern MDCT scanners are suitable for effective quantitative imaging of peripheral Tb microarchitecture if care is taken to focus on appropriate quantitative metrics.

Image noise and dose performance across a clinical population: Patient size adaptation as a metric of CT performance.

Modern CT systems adjust X-ray flux accommodating for patient size to achieve certain image noise values. The effectiveness of this adaptation is an important aspect of CT performance and should ideally be characterized in the context of real patient cases. The objective of this study was to characterize CT performance with a new metric that includes image noise and radiation dose across a clinical patient population. The study included 1526 examinations performed by three CT scanners (one GE Healthcare Discovery CT750HD, one GE Healthcare Lightspeed VCT, and one Siemens SOMATOM definition Flash) used for two routine clinical protocols (abdominopelvic with contrast and chest without contrast). An institutional monitoring system recorded all the data involved in the study. The dose-patient size and noise-patient size dependencies were linearized by considering a first-order approximation of analytical models that describe the relationship between ionization dose and patient size, as well as image noise and patient size. A 3D-fit was performed for each protocol and each scanner with a planar function, and the root mean square error (RMSE) values were estimated as a metric of CT adaptability across the patient population. The data show different scanner dependencies in terms of adaptability: the RMSE values for the three scanners are between 0.0385 HU1/2 and 0.0215 HU1/2 . A theoretical relationship between image noise, CTDIvol , and patient size was determined based on real patient data. This relationship may be interpreted as a new metric related to the scanners' adaptability concerning image quality and radiation dose across a patient population. This method could be implemented to investigate the adaptability related to other image quality indexes and radiation dose in a clinical population.

Size-specific optimization of CT protocols based on minimum detectability.

To develop a comprehensive model of task-based performance of CT across a broad library of CT protocols, so that radiation dose and image quality can be optimized within a large multivendor clinical facility. Eighty adult CT protocols from the Duke University Medical Center were grouped into 23 protocol groups with similar acquisition characteristics. A size-based image quality phantom (Duke Mercury Phantom 2.0) was imaged using these protocol groups for a range of clinically relevant dose levels on two CT manufacturer platforms (Siemens SOMATOM Definition Flash and GE CT750 HD). For each protocol group, phantom size, and dose level, the images were analyzed to extract task-based image quality metrics, the task transfer function (TTF), and the noise power spectrum (NPS). The TTF and NPS were further combined with generalized models of lesion task functions to predict the detectability of the lesions in terms of areas under the receiver operating characteristic curve (Az ). A graphical user interface (GUI) was developed to present Az as a function of lesion size and contrast, dose, patient size, and protocol, as well as to derive the necessary dose to achieve a detection threshold for a targeted lesion. The GUI provided the prediction of Az values modeling detection confidence for a targeted lesion, patient size, and dose. As an example, an abdomen pelvis exam for one scanner, with a reference task size/contrast of 5-mm/50-HU, and an Az of 0.9 indicated a dose requirement of 4.0, 8.9, and 16.9mGy for patient diameters of 25, 30, and 35 cm, respectively. For a constant patient diameter of 30cm and 50-HU lesion contrast, the minimum detected lesion size at those dose levels were predicted to be 8.4, 5.0, and 3.9mm, respectively. A CT protocol optimization platform was developed by combining task-based detectability calculations with a GUI that demonstrates the tradeoff between dose and image quality. The platform can be used to improve individual protocol dose efficiency, as well as to improve protocol consistency across various patient sizes and CT scanners.

Comparison between acoustic radiation force impulse quantification data and perfusion-CT parameters in hepatocellular carcinoma

ObjectiveTo find out, if ultrasound elastography of hepatocellular carcinoma (HCC) can predict patterns of tumor perfusion in volume perfusion computed tomography (VPCT). Material and methods25 consecutive patients (mean age, 68.9; range, 51–85 years) with liver cirrhosis suspected of HCC underwent VPCT and acoustic radiation force impulse (ARFI) elastography the same day. Quantitative elasticity values were registered, while blood flow (BF), blood volume (BV) and hepatic perfusion index (HPI) of the HCC lesions were calculated. Additionally, we identified histologic WHO grading, lesion size and localization. The Siemens Acuson S 3000 HELX-System with Virtual Touch™-Software and Siemens Somatom Definition Flash with Syngo® software were used. ResultsA total of 43 HCC lesions were assessed. Mean shear wave velocity was 2.6m/s (range, 1.1–4.3m/s). There was no significant linear correlation between the elasticity values and BF (p=0.751), BV (p=0.426) and HPI (p=0.437). However, elasticity values were higher, the larger the tumor was (p=0.008). Shear wave velocity declined with increasing distance of the HCC to the skin surface (p=0.028) and depending on liver segment. In addition, elasticity values were higher in less differentiated HCCs. This trend was not statistically significant (p=0.842). ConclusionTissue elasticity in HCC does not correlate with the degree of tumor vascularization, but calculated values are influenced both by the tumor size and localization inside the liver.

The impact of x-ray tube stabilization on localized radiation dose in axial CT scans: initial results in CTDI phantoms

Rise, fall, and stabilization of the x-ray tube output occur immediately before and after data acquisition on some computed tomography (CT) scanners and are believed to contribute additional dose to anatomy facing the x-ray tube when it powers on or off. In this study, we characterized the dose penalty caused by additional radiation exposure during the rise, stabilization, and/or fall time (referred to as overscanning). A 32 cm CT dose-index (CTDI) phantom was scanned on three CT scanners: GE Healthcare LightSpeed VCT, GE Healthcare Discovery CT750 HD, and Siemens Somatom Definition Flash. Radiation exposure was detected for various x-ray tube start acquisition angles using a 10 cm pencil ionization chamber placed in the peripheral chamber hole at the phantom’s 12 o’clock position. Scan rotation time, ionization chamber location, phantom diameter, and phantom centering were varied to quantify their effects on the dose penalty caused by overscanning. For 1 s single, axial rotations, CTDI at the 12 o’clock chamber position (CTDI100, 12:00) was 6.1%, 4.0%, and 4.4% higher when the start angle of the x-ray tube was aligned at the top of the gantry (12 o’clock) versus when the start angle was aligned at 9 o’clock for the Siemens Flash, GE CT750 HD, and GE VCT scanner, respectively. For the scanners’ fastest rotation times (0.285 s for the Siemens and 0.4 s for both GE scanners), the dose penalties increased to 22.3%, 10.7%, and 10.5%, respectively, suggesting a trade-off between rotation speed and the dose penalty from overscanning. In general, overscanning was shown to have a greater radiation dose impact for larger diameter phantoms, shorter rotation times, and to peripheral phantom locations. Future research is necessary to determine an appropriate method for incorporating the localized dose penalty from overscanning into standard dose metrics, as well as to assess the impact on organ dose.

TU-FG-BRB-02: The Impact of Using Dual-Energy CT for Determining Proton Stopping Powers: Comparison Between Theory and Experiments

Purpose: To evaluate the clinical performance of dual-energy CT (DECT) in determining proton stopping power ratios (SPR) and demonstrate advantages over conventional single-energy CT (SECT). Methods: SECT and DECT scans of tissue-equivalent plastics as well as animal meat samples are performed with a Siemens SOMATOM Definition Flash. The methods of Schneider et al. (1996) and Bourque et al. (2014) are used to determine proton SPR on SECT and DECT images, respectively. Waterequivalent path length (WEPL) measurements of plastics and tissue samples are performed with a 195 MeV proton beam. WEPL values are determined experimentally using the depth-dose shift and dose extinction methods. Results: Comparison between CT-based and experimental WEPL is performed for 12 tissue-equivalent plastic as well as 6 meat boxes containing animal liver, kidney, heart, stomach, muscle and bones. For plastic materials, results show a systematic improvement in determining SPR with DECT, with a mean absolute error of 0.4% compared to 1.7% for SECT. For the meat samples, preliminary results show the ability for DECT to determine WEPL with a mean absolute value of 1.1% over all meat boxes. Conclusion: This work demonstrates the potential in using DECT for determining proton SPR with plastic materials in a clinical context. Further work is required to show the benefits of DECT for tissue samples. While experimental uncertainties could be a limiting factor to show the benefits of DECT over SECT for the meat samples, further work is required to adapt the DECT formalism in the context of clinical use, where noise and artifacts play an important role.