Comparison of image quality and radiation dose between split-filter dual-energy images and single-energy images in single-source abdominal CT.

OBJECTIVES: To compare image quality and radiation dose of abdominal split-filter dual-energy CT (SF-DECT) combined with monoenergetic imaging to single-energy CT (SECT) with automatic tube voltage selection (ATVS). METHODS: Two-hundred single-source abdominal CT scans were performed as SECT with ATVS (n = 100) and SF-DECT (n = 100). SF-DECT scans were reconstructed and subdivided into composed images (SF-CI) and monoenergetic images at 55 keV (SF-MI). Objective and subjective image quality were compared among single-energy images (SEI), SF-CI and SF-MI. CNR and FOM were separately calculated for the liver (e.g. CNRliv) and the portal vein (CNRpv). Radiation dose was compared using size-specific dose estimate (SSDE). Results of the three groups were compared using non-parametric tests. RESULTS: Image noise of SF-CI was 18% lower compared to SEI and 48% lower compared to SF-MI (p < 0.001). Composed images yielded higher CNRliv over single-energy images (23.4 vs. 20.9; p < 0.001), whereas CNRpv was significantly lower (3.5 vs. 5.2; p < 0.001). Monoenergetic images overcame this inferiority in CNRpv and achieved similar results compared to single-energy images (5.1 vs. 5.2; p > 0.628). Subjective sharpness was equal between single-energy and monoenergetic images and diagnostic confidence was equal between single-energy and composed images. FOMliv was highest for SF-CI. FOMpv was equal for SEI and SF-MI (p = 0.78). SSDE was significant lower for SF-DECT compared to SECT (p < 0.022). CONCLUSIONS: The combined use of split-filter dual-energy CT images provides comparable objective and subjective image quality at lower radiation dose compared to single-energy CT with ATVS. KEY POINTS: • Split-filter dual-energy results in 18% lower noise compared to single-energy with ATVS. • Split-filter dual-energy results in 11% lower SSDE compared to single-energy with ATVS. • Spectral shaping of split-filter dual-energy leads to an increased dose-efficiency.

Impact of model-based iterative reconstruction on low-contrast lesion detection and image quality in abdominal CT: a 12-reader-based comparative phantom study with filtered back projection at different tube voltages.

OBJECTIVES: To evaluate the impact of model-based iterative reconstruction (MBIR) on image quality and low-contrast lesion detection compared with filtered back projection (FBP) in abdominal computed tomography (CT) of simulated medium and large patients at different tube voltages. METHODS: A phantom with 45 hypoattenuating lesions was placed in two water containers and scanned at 70, 80, 100, and 120 kVp. The 120-kVp protocol served as reference, and the volume CT dose index (CTDIvol) was kept constant for all protocols. The datasets were reconstructed with MBIR and FBP. Image noise and contrast-to-noise-ratio (CNR) were assessed. Low-contrast lesion detectability was evaluated by 12 radiologists. RESULTS: MBIR decreased the image noise by 24% and 27%, and increased the CNR by 30% and 29% for the medium and large phantoms, respectively. Lower tube voltages increased the CNR by 58%, 46%, and 16% at 70, 80, and 100 kVp, respectively, compared with 120 kVp in the medium phantom and by 9%, 18% and 12% in the large phantom. No significant difference in lesion detection rate was observed (medium: 79-82%; large: 57-65%; P > 0.37). CONCLUSIONS: Although MBIR improved quantitative image quality compared with FBP, it did not result in increased low-contrast lesion detection in abdominal CT at different tube voltages in simulated medium and large patients. KEY POINTS: • MBIR improved quantitative image quality but not lesion detection compared with FBP. • Increased CNR by low tube voltages did not improve lesion detection. • Changes in image noise and CNR do not directly influence diagnostic accuracy.

"Green Fingerprint" Project: Evaluation of the Power Consumption of Reporting Stations in a Radiology Department.

RATIONALE AND OBJECTIVES: To quantify the power or energy consumption of reporting stations in a radiology department and to consider a hypothetical scenario to reduce energy waste. METHODS: We measured the energy consumption of 36 radiology reporting stations over a mean time frame of about 194 days and then extrapolated results to 1 year. Reporting stations were configured (by default) to enter a stand-by mode after 4 hours of inactivity. A hypothetical scenario was calculated in which stand-by was skipped and the reporting stations were shut down after 1 hour of inactivity. RESULTS: Data from four stations was corrupted. The overall power consumption of the 32 remaining reporting stations was 53,170 kWh/a, equivalent to 12 family households (4500 kWh/a per household in Switzerland in 2014) or 97.2 barrels of oil. We identified three main power consumption patterns of the reporting stations: mainly off, mainly on, and always off. The on-mode consumption per year was 40,763 kWh/a, the stand-by consumption was 10,010 kWh/a, and the off-mode consumption was 2397 kWh/a. The reporting stations spent half of their on-mode time awaiting the initiation of stand-by, resulting in a wait-time consumption of 18,243 kWh/a. With the hypothetical scenario, we achieved an energy consumption saving of 23,692 kWh/a, a reduction of about 45% of the initial energy consumption, equivalent to 5 households or 40.8 barrels of oil consumed. CONCLUSION: The power consumption of the reporting stations is not negligible. Reducing energy waste in the radiology department can be established through simple changes in device configuration which will simultaneously promote energywise habits. ADVANCES IN KNOWLEDGE: Minor changes to the settings of the reporting stations in a radiology department can result in significant long-term energy savings and promote energy-wise habits.

Systematic radiation dose optimization of abdominal dual-energy CT on a second-generation dual-source CT scanner: assessment of the accuracy of iodine uptake measurement and image quality in an in vitro and in vivo investigations.

PURPOSE: To assess the accuracy of iodine quantification in a phantom study at different radiation dose levels with dual-energy dual-source CT and to evaluate image quality and radiation doses in patients undergoing a single-energy and two dual-energy abdominal CT protocols. METHODS: In a phantom study, the accuracy of iodine quantification (4.5-23.5 mgI/mL) was evaluated using the manufacturer-recommended and three dose-optimized dual-energy protocols. In a patient study, 75 abdomino-pelvic CT examinations were acquired as follows: 25 CT scans with the manufacturer-recommended dual-energy protocol (protocol A); 25 CT scans with a dose-optimized dual-energy protocol (protocol B); and 25 CT scans with a single-energy CT protocol (protocol C). CTDIvol and objective noise were measured. Five readers scored each scan according to six subjective image quality parameters (noise, contrast, artifacts, visibility of small structures, sharpness, overall diagnostic confidence). RESULTS: In the phantom study, differences between the real and measured iodine concentrations ranged from -8.8% to 17.0% for the manufacturer-recommended protocol and from -1.6% to 20.5% for three dose-optimized protocols. In the patient study, the CTDIvol of protocol A, B, and C were 12.5 ± 1.9, 7.5 ± 1.2, and 6.5 ± 1.7 mGycm, respectively (p < 0.001), and the average image noise values were 6.6 ± 1.2, 7.8 ± 1.4, and 9.6 ± 2.2 HU, respectively (p < 0.001). No significant differences in the six subjective image quality parameters were observed between the dose-optimized dual-energy and the single-energy protocol. CONCLUSION: A dose reduction of 41% is feasible for the manufacturer-recommended, abdominal dual-energy CT protocol, as it maintained the accuracy of iodine measurements and subjective image quality compared to a single-energy protocol.