Visual impression and texture analysis of advanced modeled iterative reconstruction (ADMIRE): improved assessment of image quality in CT for better estimation of dose reduction potential.

To evaluate the image quality (IQ) of advanced modeled iterative reconstruction (ADMIRE; Siemens Healthcare, Forchheim, Germany) applying image texture and image visual impression as a supplement to physical parameters such as noise level and spatial resolution. An ACR-phantom with four modules was examined at different radiation dose levels. To characterise the image texture, two Haralick texture parameters, contrast and entropy, were assessed at different dose levels and reconstruction algorithms. The visual impression of images and the low-contrast detectability were evaluated by the structural similarity index (SSIM). The spatial resolution was determined by the modulation transfer functions and the line spread function. The Haralick texture parameters, contrast and entropy, decreased with increasing ADMIRE levels. ADMIRE III, IV and V offered a comparable contrast and entropy to those calculated by filtered back projection (FBP) with a radiation dose reduction up to 50%. SSIM (low-contrast detectability) improved with increasing ADMIRE levels. SSIM calculated by ADMIRE IV and V revealed comparable IQ to FBP with a decreased CTDIvolup to 50%. Spatial resolution was retained up to 90% dose reduction. Compared to FBP at the same dose level, the image noise decreased up to 61% with higher ADMIRE levels (σFBP= 17.3 HU andσADMIREV= 10.6 HU at 6.65 mGy). Taking texture analysis and visual perception into account, a more realistic assessment of the dose reduction potential of ADMIRE can be achieved than quality metrics based alone on physical measurements.

Arterial attenuation in individualized computed tomography pulmonary angiography injection protocol adjusted based on the patient's body mass index.

BACKGROUND: The aim of this study was to optimize computed tomography pulmonary angiography (CTPA) protocols with regard to improve vascular attenuation without increasing contrast media (CM) volumes. Therefore, we compared the standard CTPA protocol to an individualized contrast media injection protocols adjusted for the patient's body mass index (BMI). MATERIALS AND METHODS: Two groups of 295 patients with suspected pulmonary embolism (PE) have been receiving CTPA. Group 1 received a standard protocol without taking patient's BMI into account. Group 2 received a CTPA scan, where dose and flow rate of CM injections were adjusted for the patient's BMI. Images were retrospectively analyzed by drawing regions of interests in defined positions in the superior vena cava, descending aorta, the pulmonary main trunk as well as the left and right lower lobe arteries. Intravascular attenuation, contrast volumes, and flow rates were compared using unpaired t-tests. Furthermore, a qualitative image analysis was performed by two experienced readers blinded for the protocol used for image acquisition to evaluate the image quality and arterial attenuation. RESULTS: Patient's BMI was similar in both the groups (27.5 ± 1.5 kg/m2 vs. 28.4 ± 2.1 kg/m2; P = 0.67). Contrast volumes were lower (54.2 ± 4.8 ml vs. 55 ml; P < 0.05), and flow rates (4.1 ± 0.3 ml/s vs. 3.5 ml/s; P < 0.05) were significantly higher in the individualized protocol. The qualitative image analysis yielded an agreement on diagnostic interpretability in the individualized and standard group of 49% and 51% (95% Wilson confidence interval for mean), respectively. CONCLUSION: An individualized CTPA protocol based on the patient's BMI reduced the contrast media volume and led to an increased pulmonary artery enhancement improving image quality, particularly in the evaluation of the peripheral pulmonary arteries. Thus, contrast media volumes in CTPA should be adjusted for the patient's BMI.

Radiation doses from low-dose CT scans in SPECT/CT and PET/CT examinations: A survey in Germany.

AIM: Recently, dose reference levels (DRLs) have been defined in Germany for auxiliary low-dose CT scans in hybrid SPECT/CT and PET/CT examinations, based on data from 2016/17. Here, another survey from 2020 was evaluated and compared with the new DRLs as well as with similar surveys from foreign countries. METHODS: The survey, which had already been conducted in the Nordic countries, queried for various examinations including the following values: patient weight and height, volume CT dose index (CTDIvol), dose length product (DLP). For each examination, statistical parameters such as the third quartile (Q3) were determined from all submitted CTDIvol and DLP values. Additionally, for examinations comprising datasets from at least 10 systems, the third quartile (Q3-Med) of the respective median values of each system was calculated. Q3 and Q3-Med were compared with the newly published DRLs from Germany and values from similar studies from other countries. RESULTS: Data from 15 SPECT/CT and 13 PET/CT systems from 15 nuclear medicine departments were collected. For the following examinations datasets from more than 10 systems were submitted: SPECT lung VQ, SPECT bone, SPECT&PET cardiac, PET brain, PET oncology. Especially for examinations of the thorax and heart, the new DRLs are very strict compared to this study. The CTDIvol values for examinations of the head were lower in this study than the DRLs prescribe now. CONCLUSIONS: For certain examination types, there is a need for dose optimization at some clinics and devices in order to take into account the new DRLs in Germany in the future.

Intraindividual variation of dose parameters in oncologic CT imaging.

The objective of this study is to identify essential aspects influencing radiation dose in computed tomography [CT] of the chest, abdomen and pelvis by intraindividual comparison of imaging parameters and patient related factors. All patients receiving at least two consecutive CT examinations for tumor staging or follow-up within a period of 22 months were included in this retrospective study. Different CT dose estimates (computed tomography dose index [CTDIvol], dose length product [DLP], size-specific dose estimate [SSDE]) were correlated with patient's body mass index [BMI], scan length and technical parameters (tube current, tube voltage, pitch, noise level, level of iterative reconstruction). Repeated-measures-analysis was initiated with focus on response variables (CTDIvol, DLP, SSDE) and possible factors (age, BMI, noise, scan length, peak kilovoltage [kVp], tube current, pitch, adaptive statistical iterative reconstruction [ASIR]). A univariate-linear-mixed-model with repeated-measures-analysis followed by Bonferroni adjustments was used to find associations between CT imaging parameters, BMI and dose estimates followed by a subsequent multivariate-mixed-model with repeated-measures-analysis with Bonferroni adjustments for significant parameters. A p-value <0.05 was considered statistically significant. We found all dose estimates in all imaging regions were substantially affected by tube current. The iterative reconstruction significantly influenced all dose estimates in the thoracoabdominopelvic scans as well as DLP and SSDE in chest-CT. Pitch factor affected all dose parameters in the thoracoabdominopelvic CT group. These results provide further evidence that tube current has a pivotal role and potential in radiation dose management. The use of iterative reconstruction algorithms can substantially decrease radiation dose especially in thoracoabdominopelvic and chest-CT-scans. Pitch factor should be kept at a level of ≥1.0 in order to reduce radiation dose.

Impact of Patient Alignment on Image Quality in C-Arm Computed Tomography - Evaluation Using an ACR Phantom.

PURPOSE: To evaluate the influence of patient alignment and thereby heel effect on the image quality (IQ) of C-arm flat-panel detector computed tomography (CACT). MATERIALS AND METHODS: An ACR phantom placed in opposite directions along the z-axis (setup A and B) on the patient support was imaged using CACT. Image acquisition was performed with three different image acquisition protocols. The images were reconstructed with four convolution kernels. IQ was assessed in terms of high contrast using the modulation transfer function (MTF) and low contrast by assessing the image noise, signal-to-noise ratio (SNR) and contrast-to-noise ratios (CNR) as well as the reliability of density measurements. Furthermore, the dose intensity profiles were measured free-in-air. RESULTS: The MTF in setup B is higher than the MTF measured in setup A (p < 0.01). The image noises measured in setup A for the air and bone inserts were higher compared to those measured in setup B (p > 0.05). Opposite behavior has been observed for the polyethylene, water-equivalent and acrylic inserts. The SNR for all inserts is inversely related to the image noise. A systematically increasing or decreasing trend of CNR could not be observed (p > 0.05). The intensity profile measured by the detector system free-in-air showed that the anode heel effect is perpendicular to the z-axis. CONCLUSION: The patient alignment has a minor influence on the IQ of CACT. This effect is not based on the X-ray anode heel effect but is caused mainly by the non-symmetrical rotation of CACT. KEY POINTS: · The impact of patient alignment and thereby the heel effect on the image quality of CACT was analyzed.. · The patient alignment has a minor influence on the physical parameters related to image quality, such as noise, SNR, and MTF.. · This effect is based mainly on the non-symmetrical rotation of CACT.. CITATION FORMAT: · Alikhani B, Renne J, Maschke S et al. Impact of Patient Alignment on Image Quality in C-Arm Computed Tomography - Evaluation Using an ACR Phantom. Fortschr Röntgenstr 2021; 193: 417 - 426.

Impact of active dose management on radiation exposure and image quality in computed tomography: An observational study in 1315 patients.

PURPOSE: To determine the clinical impact of CT dose management team on radiation exposure and image quality. METHODS: 2026 clinical routine CT examinations of 1315 patients were evaluated retrospectively. A CT dose management team was established as an integral part of the radiological department. It identified 5 CT protocols (A-E), where national reference values were exceeded the most. Those reference values included specifically the mean volumetric CT dose index (CTDIvol) and the mean dose-length product (DLP). Baseline data (period 1) and follow up data (period 2) were obtained after reduction of tube voltage and increase of pitch or noise index. Signal-to-noise ratios (SNR) and contrast-to-noise ratios (CNR) were calculated to compare image quality. Two-sided t-tests were performed. RESULTS: Mean CTDIvol and mean DLP of the chest protocol (A) decreased after reduction of tube voltage (P < 0.01). In the chest/abdomen/pelvis protocol (B), the increase of noise index resulted in a significant mean CTDIvol decrease (P < 0.02) without statistical significance of mean DLP (P < 0.12). In the abdomen/pelvis protocol (C), mean CTDIvol (P = 0.01) and mean DLP (P < 0.01) were significantly lower after noise index increase. In the staging of hepatocellular carcinoma (D), mean CTDIvol and mean DLP were significantly lower after increase of pitch and noise index (P < 0.01). The lung protocol (E) yielded no significant changes after modulation (P > 0.05). SNR (protocol A) was significantly higher in period 2 (P < 0.04). Protocol D showed significantly lower selected SNR and CNR (P < 0.02). CONCLUSIONS: Establishing an operating dose management team as a standard for good clinical practice helps to considerably reduce CT radiation dose while preserving image quality.

Image Quality Performance of Virtual Single-Source CT Using Dual-Source Computed Tomography.

RATIONALE AND OBJECTIVES: The aim of this study is to analyze the image quality provided by a dual-source (DS) data set and a single-source (SS) data set at the same radiation exposure, in order to evaluate a dose splitting method for dual-source scanning protocols. MATERIALS AND METHODS: A 192-slice dual-source third generation CT (Somatom Force; Siemens Healthcare, Forchheim, Germany) was used to image a Catphan phantom (Catphan503; The Phantom Laboratory, Salem, New York) utilizing different X-ray tube voltages from 70 to 120 kVp with an organ-based tube-current modulation technique (X-CARE; Siemens Healthcare, Forchheim, Germany). In order to keep the radiation dose (given by volume computed tomography dose index) in a clinically relevant range, different X-ray tube time-current products ranging from 80 to 300 mAs were selected. The data sets by each X-ray tube voltage were collected using a single-source as well as a dual-source mode. The measurements in the dual-source mode were performed with five different tube currents of the X-ray tube A and B. Thereby, the tube current ratios were 50%|50% (DS 0.5), 60%|40% (DS 0.6), 70%|30% (DS 0.7), 80%|20% (DS 0.8), and 90%|10% (DS 0.9). The images were reconstructed by the use of a filter-back projection (Br40) and an advanced mode led iterative reconstruction algorithms (advanced modeled iterative reconstruction algorithms [ADMIRE]; Siemens Healthcare, Forchheim, Germany) with a strength range of 1-5. The image quality was evaluated in terms of noise, contrast-to-noise ratio (CNR), low-contrast detectability expressed as the structural similarity index (SSIM) and spatial resolution quantified by the full width at half maximum of the line-spread function. RESULTS: Image noise decreased by the use of the dual-source mode, which led to improvement of their CNR compared to the single-source mode. SSIM showed an almost constant behavior by both modes. The spatial resolution indicated a lower trend by the dual-source mode in comparison to the single-source mode. However, the loss of the spatial resolution performance was lower than 5% for the dual-source modes. CONCLUSION: The presented phantom study demonstrated that SSIM and spatial resolution performance obtained by dual-source CT protocols showed a negligible variation to those by the single-source CT. However, the noise and CNR displayed an improvement for the dual-source CT. Therefore, the use of the dual-source CT enables to split the radiation dose between X-ray tubes and to compare the data sets with different radiation dose levels without loss in the image quality.

Initial Experience with Digital Patient Briefing in Computed Tomography. / Erste Erfahrungen mit einer mobilen digitalen Patientenaufklärung in der Computertomografie.

PURPOSE: To assess digital patient briefing as an alternative to conventional paper documentation. MATERIALS AND METHODS: 502 patients with a planned computed tomography (CT) examination were selected for digital patient briefing using the E-ConsentPro software from Thieme Compliance on an iPad by Apple (Cupertino, California, USA). For the analysis, three age groups were formed. The time required for the patient briefing, the number of open questions as well as the time needed for discussion with physicians were determined. Student's t-test was performed to assess statistical significance. RESULTS: There was no significant difference between patient age and briefing time which was about 20 minutes on average. The number of open or unclear questions increased with patient age. While patients younger than 30 years of age had about 2 open questions, patients over 30 and 60 years had about 4 and 5 questions, respectively. The total time needed for discussion with physicians was less than 2 minutes on average. A significant difference in the time required for discussion with physicians could not be observed between the individual age groups. CONCLUSION: Tablet-based digital briefing allows the storage of patient documents with reasonable time and effort. Furthermore, it minimizes the risk of data loss. KEY POINTS: · Tablet-based digital patient briefing in computed tomography can be performed with reasonable time and effort.. · The time required for tablet-based patient briefing is independent of patient age.. · The cost-benefit analysis presents a significant improvement in digital patient briefing compared to the paper-based process.. CITATION FORMAT: · Alikhani B, Hensen B, Grosser A et al. Initial Experience with Digital Patient Briefing in Computed Tomography. Fortschr Röntgenstr 2019; 191: 540 - 546.

Correlation of size-dependent conversion factor and body-mass-index using size-specific dose estimates formalism in CT examinations.

PURPOSE: The aim of this investigation is to establish the relationship between the size-dependent conversion factor (fsize) and the body-mass-index (BMI) and to test whether BMI can be substituted for the conventionally used patients' anterior-posterior (AP) and lateral (LAT) dimensions for calculation of fsize. By calculating fsize on the basis of BMI instead of the AP and LAT measurements, size-specific dose estimates (SSDE) could be determined prior to image acquisition. METHODS: Our institute utilizes a dose monitoring software to record radiation exposure during CT examinations. The datasets gathered during each examination contain information regarding the scan protocol, the volumetric computed tomography dose index (CTDIvol), SSDE and BMI. fsize is traditionally calculated through measurement of AP and LAT dimensions. In this work, the dose monitoring system calculates AP and LAT diameters at the middle of scout views. For purpose of this investigation, we used data from 13544 patients who underwent CT examinations of the torso, head or knee (both) to compare fsize as calculated from the AP and LAT dimensions to fsize calculated as a function of BMI. RESULTS: In the examinations of the torso, we observed an exponentially decreasing correlation between fsize and BMI. In the examinations of the head and knee (both), fsize reflected an almost independent behavior to BMI. CONCLUSION: This study demonstrates that it is possible to estimate fsize by using the patients' BMI for the torso as well as the head and knee CT, thereby enabling calculation of the probable SSDE prior to image acquisition on the basis of the presumed CTDIvol provided by the scanner. By providing information on the expected patient dose prior to image acquisition, this method is advantageous over the traditional calculation of fsize via the AP and LAT dimensions.

Non-invasive experimental determination of a CT source model.

Non-invasive methods to determine equivalent X-ray source models of a CT scanner are presented. A high-precision technique called TRIC ("Time Resolved Integrated Charge") was developed and used to characterize the bow tie filters (BT) of the CT scanner installed at Physikalisch-Technische Bundesanstalt (PTB). Aluminum (Al) and polymethyl methacrylate (PMMA) equivalent thicknesses of the BT filters at all tube high voltages were evaluated, assuming that those consist of only one material. Thereby two different dose probes were used, a solid state detector and an ionization chamber, the former characterized by a significant and the latter by an almost negligible energy dependence of the air kerma response. A method was developed to correct for the energy dependence of the solid state dose probe. Next, a two-component material was assumed and equivalent BT filters were evaluated. The latter method was also applied using the known real BT filter materials and compared with the shape of the real BT filters. Finally, the results obtained by the TRIC method were compared with those obtained by using the so-called COBRA method ("Characterization Of Bow tie Relative Attenuation"), the latter being more suitable for measurements in a clinical environment.