Effect of automated tube voltage selection, integrated circuit detector and advanced iterative reconstruction on radiation dose and image quality of 3rd generation dual-source aortic CT angiography: An intra-individual comparison

Deep learning reconstruction algorithm and high-concentration contrast medium: feasibility of a double-low protocol in coronary computed tomography angiography

OBJECTIVE

To evaluate radiation dose and image quality of a double-low CCTA protocol reconstructed utilizing high-strength deep learning image reconstructions (DLIR-H) compared to standard adaptive statistical iterative reconstruction (ASiR-V) protocol in non-obese patients.

MATERIALS AND METHODS

From June to October 2022, consecutive patients, undergoing clinically indicated CCTA, with BMI < 30 kg/m2 were prospectively included and randomly assigned into three groups: group A (100 kVp, ASiR-V 50%, iodine delivery rate [IDR] = 1.8 g/s), group B (80 kVp, DLIR-H, IDR = 1.4 g/s), and group C (80 kVp, DLIR-H, IDR = 1.2 g/s). High-concentration contrast medium was administered. Image quality analysis was evaluated by two radiologists. Radiation and contrast dose, and objective and subjective image quality were compared across the three groups.

RESULTS

The final population consisted of 255 patients (64 ± 10 years, 161 men), 85 per group. Group B yielded 42% radiation dose reduction (2.36 ± 0.9 mSv) compared to group A (4.07 ± 1.2 mSv; p < 0.001) and achieved a higher signal-to-noise ratio (30.5 ± 11.5), contrast-to-noise-ratio (27.8 ± 11), and subjective image quality (Likert scale score: 4, interquartile range: 3-4) compared to group A and group C (all p ≤ 0.001). Contrast medium dose in group C (44.8 ± 4.4 mL) was lower than group A (57.7 ± 6.2 mL) and B (50.4 ± 4.3 mL), all the comparisons were statistically different (all p < 0.001).

CONCLUSION

DLIR-H combined with 80-kVp CCTA with an IDR 1.4 significantly reduces radiation and contrast medium exposure while improving image quality compared to conventional 100-kVp with 1.8 IDR protocol in non-obese patients.

CLINICAL RELEVANCE STATEMENT

Low radiation and low contrast medium dose coronary CT angiography protocol is feasible with high-strength deep learning reconstruction and high-concentration contrast medium without compromising image quality.

KEY POINTS

Minimizing the radiation and contrast medium dose while maintaining CT image quality is highly desirable. High-strength deep learning iterative reconstruction protocol yielded 42% radiation dose reduction compared to conventional protocol. "Double-low" coronary CTA is feasible with high-strength deep learning reconstruction without compromising image quality in non-obese patients.

Effect of X-ray tube on image quality and pancreatic ductal adenocarcinoma conspicuity in pancreatic protocol dual-energy CT

AIM

To compare the radiation dose, image quality, and conspicuity of pancreatic ductal adenocarcinoma (PDAC) in pancreatic protocol dual-energy computed tomography (CT) between two X-ray tubes mounted in the same CT machine.

MATERIAL AND METHODS

This retrospective study comprised 80 patients (median age, 73 years; 45 men) who underwent pancreatic protocol dual-energy CT from January 2019 to March 2022 using either old (Group A, n=41) or new (Group B, n=39) X-ray tubes mounted in the same CT machine. The imaging parameters were completely matched between the two groups, and CT data were reconstructed at 70 and 40 keV. The CT dose-index volume (CTDIvol); CT attenuation of the abdominal aorta, pancreas, and PDAC; background noise; and qualitative scores for the image noise, overall image quality, and PDAC conspicuity were compared between the two groups.

RESULTS

The CTDIvol was lower in Group B than Group A (7.9 versus 9.2 mGy; p<0.001). The CT attenuation of all anatomical structures at 70 and 40 keV was comparable between the two groups (p=0.06-0.78). The background noise was lower in Group B than Group A (12 versus 14 HU at 70 keV, p=0.046; and 26 versus 30 HU at 40 keV, p<0.001). Qualitative scores for image noise and overall image quality at 70 and 40 keV and PDAC conspicuity at 40 keV were higher in Group B than Group A (p<0.001-0.045).

CONCLUSION

The latest X-ray tube could reduce the radiation dose and improve image quality in pancreatic protocol dual-energy CT.

Quantifying image quality in chest computed tomography angiography: Evaluation of different contrast-to-noise ratio measurement methods

BACKGROUND

Contrast-to-noise ratio is used to objectively evaluate image quality in chest computed tomography angiography (CTA). Different authors define and measure contrast-to-noise ratio using different methods.

PURPOSE

To summarize and evaluate the different contrast-to-noise ratio calculation formulas in the current literature.

MATERIAL AND METHODS

A systematic review of the recent literature for studies using contrast-to-noise ratio was performed. Contrast-to-noise ratio measurement methods reported by the different authors were recorded and reproduced in three patients who underwent chest CTA in our department for exploring variations among the different measurement methods.

RESULTS

The search resulted in 109 articles, of which 26 were included. The studies involved 69 different measurements and overall, three different formula patterns. In all three, aorta and pulmonary arteries comprised the objects of interest in the numerator. In the denominator, standard deviation of the attenuation of the object of interest itself or of another background were used to reflect image noise. Some authors averaged the ratio values at different levels to obtain global ratio values. Using the object of interest itself for image noise calculation in the denominator compared to the usage of another background caused the most prominent variances of contrast-to-noise ratio between the two different protocols used for the reproduction of the measurements.

CONCLUSION

We recommend using the standard deviation of the attenuation of a background indicator as image noise rather than the object of interest itself for more reliable and comparative values. Global contrast-to-noise ratios based on averaging the values of different measurement levels should be avoided.

Synthetic Extracellular Volume Fraction Derived Using Virtual Unenhanced Attenuation of Blood on Dual-Energy Contrast-Enhanced Cardiac CT in Nonischemic Cardiomyopathy

Background: Current methods for calculating myocardial extracellular volume fraction (ECV) require blood sampling to obtain serum hematocrit. Synthetic hematocrit and thus synthetic ECV may be derived using unenhanced attenuation of blood. By use of virtual unenhanced (VUE) attenuation of blood, contrast-enhanced dual-energy CT (DECT) may allow synthetic ECV calculations without unenhanced acquisition. Objective: To compare synthetic ECV using synthetic hematocrit derived from VUE images versus conventional ECV using serum hematocrit, both obtained by contrast-enhanced DECT, using MRI-derived ECV as reference. Methods: This retrospective study included 51 patients (26 men, 25 women; mean age 59.9 ± 15.6 years) with nonischemic cardiomyopathy who, as part of an earlier prospective investigation, underwent equilibrium-phase contrast-enhanced cardiac DECT and cardiac MRI, with serum hematocrit measured within 6 hours of both tests. A separate retrospective sample of 198 patients who underwent same-day contrast-enhanced thoracic DECT for suspected pulmonary embolism and serum hematocrit measurement was identified to derive a synthetic hematocrit formula using VUE attenuation of blood by linear regression analysis. In the primary sample, two radiologists independently used DECT iodine maps to obtain conventional ECV using serum hematocrit and synthetic ECV using synthetic hematocrit based on the independently derived formula. Concordance correlation coefficient (CCC) was computed between conventional ECV and synthetic ECV from DECT. Conventional ECV and synthetic ECV from DECT were compared with MRI-derived ECV in Bland-Altman analyses. Results: The linear regression formula for synthetic hematocrit in the independent sample was: synthetic hematocrit = 0.85 x (VUE attenuation of blood) - 5.40. In the primary sample, conventional ECV and synthetic ECV from DECT showed excellent agreement (CCC = 0.95). Bland-Altman analysis showed small bias of -0.44% with 95% limits of agreement from -5.10% to 4.22% between MRI-derived ECV and conventional ECV from DECT, and small bias of -0.78% with 95% limits of agreement from -5.25% to 3.69% between MRI-derived ECV and synthetic ECV from DECT. Conclusion: Synthetic ECV and conventional ECV from DECT show excellent agreement and comparable association with ECV from cardiac MRI. Clinical Impact: Synthetic hematocrit from VUE attenuation of blood may allow myocardial tissue characterization on DECT without inconvenience of blood sampling.

Influence of Adaptive Statistical Iterative Reconstructions on CT Radiomic Features in Oncologic Patients

Iterative reconstructions (IR) might alter radiomic features extraction. We aim to evaluate the influence of Adaptive Statistical Iterative Reconstruction-V (ASIR-V) on CT radiomic features. Patients who underwent unenhanced abdominal CT (Revolution Evo, GE Healthcare, USA) were retrospectively enrolled. Raw data of filtered-back projection (FBP) were reconstructed with 10 levels of ASIR-V (10–100%). CT texture analysis (CTTA) of liver, kidney, spleen and paravertebral muscle for all datasets was performed. Six radiomic features (mean intensity, standard deviation (SD), entropy, mean of positive pixel (MPP), skewness, kurtosis) were extracted and compared between FBP and all ASIR-V levels, with and without altering the spatial scale filter (SSF). CTTA of all organs revealed significant differences between FBP and all ASIR-V reconstructions for mean intensity, SD, entropy and MPP (all p < 0.0001), while no significant differences were observed for skewness and kurtosis between FBP and all ASIR-V reconstructions (all p > 0.05). A per-filter analysis was also performed comparing FBP with all ASIR-V reconstructions for all six SSF separately (SSF0-SSF6). Results showed significant differences between FBP and all ASIR-V reconstruction levels for mean intensity, SD, and MPP (all filters p < 0.0315). Skewness and kurtosis showed no differences for all comparisons performed (all p > 0.05). The application of incremental ASIR-V levels affects CTTA across various filters. Skewness and kurtosis are not affected by IR and may be reliable quantitative parameters for radiomic analysis.

Simulated Radiation Dose Reduction in Whole-Body CT on a 3rd Generation Dual-Source Scanner: An Intraindividual Comparison

To evaluate the effect of radiation dose reduction on image quality and diagnostic confidence in contrast-enhanced whole-body computed tomography (WBCT) staging. We randomly selected March 2016 for retrospective inclusion of 18 consecutive patients (14 female, 60 ± 15 years) with clinically indicated WBCT staging on the same 3rd generation dual-source CT. Using low-dose simulations, we created data sets with 100, 80, 60, 40, and 20% of the original radiation dose. Each set was reconstructed using filtered back projection (FBP) and Advanced Modeled Iterative Reconstruction (ADMIRE^®, Siemens Healthineers, Forchheim, Germany) strength 1–5, resulting in 540 datasets total. ADMIRE 2 was the reference standard for intraindividual comparison. The effective radiation dose was calculated using commercially available software. For comparison of objective image quality, noise assessments of subcutaneous adipose tissue regions were performed automatically using the software. Three radiologists blinded to the study evaluated image quality and diagnostic confidence independently on an equidistant 5-point Likert scale (1 = poor to 5 = excellent). At 100%, the effective radiation dose in our population was 13.3 ± 9.1 mSv. At 20% radiation dose, it was possible to obtain comparably low noise levels when using ADMIRE 5 (p = 1.000, r = 0.29). We identified ADMIRE 3 at 40% radiation dose (5.3 ± 3.6 mSv) as the lowest achievable radiation dose with image quality and diagnostic confidence equal to our reference standard (p = 1.000, r > 0.4). The inter-rater agreement for this result was almost perfect (ICC ≥ 0.958, 95% CI 0.909–0.983). On a 3rd generation scanner, it is feasible to maintain good subjective image quality, diagnostic confidence, and image noise in single-energy WBCT staging at dose levels as low as 40% of the original dose (5.3 ± 3.6 mSv), when using ADMIRE 3.

Diagnostic Performance of Different Simulated Low-Dose Levels in Patients with Suspected Cervical Abscess Using a Third-Generation Dual-Source CT Scanner

The aim of this study was to investigate the effects of dose reduction on diagnostic accuracy and image quality of cervical computed tomography (CT) in patients with suspected cervical abscess. Forty-eight patients (mean age 45.5 years) received a CT for suspected cervical abscess. Low-dose CT (LDCT) datasets with 25%, 50%, and 75% of the original dose were generated with a realistic simulation. The image data were reconstructed with filtered back projection (FBP) and with advanced modeled iterative reconstruction (ADMIRE) (strengths 3 and 5). A five-point Likert scale was used to assess subjective image quality and diagnostic confidence. The signal-to-noise ratio (SNR) of the sternocleidomastoid muscle and submandibular gland and the contrast-to-noise ratio (CNR) of the sternocleidomastoid muscle and submandibular glandular fat were calculated to assess the objective image quality. Diagnostic accuracy was calculated for LDCT using the original dose as the reference standard. The prevalence of cervical abscesses was high (72.9%) in the cohort; the mean effective dose for all 48 scans was 1.8 ± 0.8 mSv. Sternocleidomastoid and submandibular SNR and sternocleidomastoid muscle fat and submandibular gland fat CNR increased with higher doses and were significantly higher for ADMIRE compared to FBP, with the best results in ADMIRE 5 (all p < 0.001). Subjective image quality was highest for ADMIRE 5 at 75% and lowest for FBP at 25% of the original dose (p < 0.001). Diagnostic confidence was highest for ADMIRE 5 at 75% and lowest for FBP at 25% (p < 0.001). Patient-based diagnostic accuracy was high for all LDCT datasets, down to 25% for ADMIRE 3 and 5 (sensitivity: 100%; specificity: 100%) and lower for FBP at 25% dose reduction (sensitivity: 88.6-94.3%; specificity: 92.3-100%). The use of a modern dual-source CT of the third generation and iterative reconstruction allows a reduction in the radiation dose to 25% (0.5 mSv) of the original dose with the same diagnostic accuracy for the assessment of neck abscesses.

Application of full-field organ dose modulation on cervical- thoraco-abdominopelvic contrast-enhanced computed tomography

BACKGROUND AND OBJECTIVE

To study the radiation dose and image quality on the use of full-field organ dose modulation (ODM) on cervical-thoracic-abdominal-pelvic contrast-enhanced computed tomography (CT) scanning on female chemotherapy patients.

METHODS

Eighty female chemotherapy patients undergoing cervical-thoracic-abdominal-pelvic contrast-enhanced CT were prospectively enrolled and randomly divided into two groups: group A and group B, each with 40 patients. Full-field ODM technique was used on group A and regular scanning patterns were used on group B. We calculated and recorded the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), subjective scores, mean tube currents of the anterior, left, posterior, and right aspects of the thyroid, breast, and ovary layers of all the images. The CT dose index volume (CTDIvol) and dose-length product (DLP) of each patient were recorded and the effective radiation dose (ED) was calculated. The above data were statistically analyzed.

RESULTS

There were no statistically significant differences in the SNR, CNR, and image quality scores of the thyroid, breast, and ovary layers of groups A and B during the arterial and venous phases (P > 0.05). The tube current on the anterior, left, posterior, and right aspects of the thyroid, breast, and ovary layers during the arterial and venous phases (thyroid: 324.46 ± 53.2 and 327.97 ± 61.34; breast: 243.13 ± 50.04 and 248.32 ± 60.33; ovary: 332.28 ± 71.50 and 339.78 ± 76.69; respectively) of group A were (statistically) significantly lower than those of group B (thyroid: 407.60 ± 96.81 and 402.73 ± 90.15; breast: 313.00 ± 106.68 and 315.20 ± 106.73; ovary: 457.78 ± 106.56 and 459.63 ± 106.27; respectively) (P < 0.05). The respective mean CTDIvol and DLP in group A were 22% and 24% lower than those of group B. The mean EDs of the neck, chest, and abdominal-pelvic region in group A were 19.3%, 21.4%, and 26.4% lower than those of group B, respectively (P < 0.05).

CONCLUSION

The use of ODM can reduce radiation dose of female chemotherapy patients undergoing cervical-thoracic-abdominal-pelvic contrast-enhanced CT, especially radiation-sensitive organs, while maintaining overall image quality.

Evaluation of a Tube Voltage-Tailored Contrast Medium Injection Protocol for Coronary CT Angiography: Results From the Prospective VOLCANIC Study

OBJECTIVE. The purpose of this study was to prospectively evaluate, using software support, the feasibility and the quantitative and qualitative image quality parameters of a tube voltage-tailored contrast medium (CM) application protocol for patient-specific injection during coronary CT angiography (CCTA). SUBJECTS AND METHODS. In the Voltage-Based Contrast Media Adaptation in Coronary Computed Tomography Angiography (VOLCANIC-CTA) study, a single-center trial, 120 patients referred for CCTA were prospectively assigned to a tube voltage-tailored CM injection protocol. Automated tube voltage levels were selected in 10-kV intervals and ranged from 70 to 130 kV, and the iodine delivery rate (IDR) was adapted to the tube voltage level using dedicated software. The administered CM volume (370 mg I/mL) ranged from 33 mL at 70 kV (IDR, 0.7 g I/s) to 65 mL at 130 kV (IDR, 1.7 g I/s). Attenuation was measured in the aorta and coronary arteries to calculate quantitative signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR), and 5-point scales were used to evaluate overall image quality. Radiation metrics were also assessed and compared among the protocols. RESULTS. The mean age of the study patients was 62.5 ± 11.9 (SD) years. Image quality was rated as diagnostic in all patients. Contrast attenuation peaked at 70 kV (p < 0.001), whereas SNR and CNR parameters showed no significant differences between tube voltage levels (p ≥ 0.085). Additionally, no significant differences in subjective image quality parameters were found among the different protocols (p ≥ 0.139). The lowest radiation dose values were observed in the group assigned to the 70-kV protocol, which had a median radiation effective dose of 2.0 mSv (p < 0.001). CONCLUSION. The proposed tube voltage-tailored injection protocol allows individualized scanning of patients undergoing CCTA and significantly reduces CM and radiation dose while maintaining a high diagnostic image quality.

Low-dose CT perfusion with combined use of CTP and CTP-derived coronary CT angiography at 70 kVp: validation with invasive fractional flow reserve

OBJECTIVES

To investigate the diagnostic performance of 70-kVp stress dynamic myocardial CT perfusion (CTP) as a low-dose, one-stop cardiac CT examination in clinical application.

MATERIALS AND METHODS

Consecutive symptomatic patients were prospectively recruited and scanned with stress dynamic myocardial CTP. The CTP phase with the best enhancement of the coronary arteries was selected and extracted as the CTP-derived single-phase coronary CT angiography (SP-CTA). The diagnostic performance of CTP and CTP+SP-CTA for functionally significant CAD was assessed. Invasive coronary angiography and fractional flow reserve were used as the reference standard for the myocardial ischemia evaluation.

RESULTS

In total, 71 patients (43 men and 28 women; 63.6 ± 8.8 years old) underwent the stress dynamic myocardial CTP; 63 vessels (36.2%) from 42 of the patients (59.2%) were identified as causing ischemia. On a per-vessel basis, the sensitivity, specificity, PPV, NPV, and diagnostic accuracy for CTP and CTP+SP-CTA were 77.8%, 93.7%, 87.5%, 88.1%, and 87.9% and 84.1%, 93.7%, 88.3%, 91.2%, and 90.2%, respectively. The area under the curve (AUC) of CTP+SP-CTA (AUC = 0.963; 95%CI, 0.938-0.989) was significantly superior to that of CTP (AUC = 0.922; 95%CI, 0.880-0.964) and that of SP-CTA (AUC = 0.833; 95%CI, 0.765-0.900) alone (all p < 0.01). The mean radiation dose of the CTP examination was 3.8 ± 1.4 mSv.

CONCLUSION

CTP-derived SP-CTA improved the diagnostic value of CTP. With a promising performance of myocardial ischemia detection and low radiation dose, the innovative low-dose, one-stop CTP examination is clinically feasible for patients who need to receive a myocardial perfusion assessment.

KEY POINTS

• Myocardial CTP performed well in the evaluation of hemodynamically significant CAD. • CTP-derived single-phase CCTA improved the diagnostic value of CTP. • The combined use of low-dose CTP and CTP-derived CCTA at 70 kVp is clinically feasible for CAD patients who need to receive a myocardial perfusion assessment.

Updates in Vascular Computed Tomography

Computed tomography angiography (CTA) has become a mainstay for the imaging of vascular diseases, because of high accuracy, availability, and rapid turnaround time. High-quality CTA images can now be routinely obtained with high isotropic spatial resolution and temporal resolution. Advances in CTA have focused on improving the image quality, increasing the acquisition speed, eliminating artifacts, and reducing the doses of radiation and iodinated contrast media. Dual-energy computed tomography provides material composition capabilities that can be used for characterizing lesions, optimizing contrast, decreasing artifact, and reducing radiation dose. Deep learning techniques can be used for classification, segmentation, quantification, and image enhancement.

Evaluation of Intracranial Vascular Status in Patients with Acute Ischemic Stroke by Time Maximum Intensity Projection CT Angiography: A Preliminary Study

RATIONALE AND OBJECTIVES

To describe the application of time maximum intensity projection CTA (t-MIP CTA) in acute ischemic stroke and compare t-MIP CTA and single-phase CTA (sCTA) in assessing collateral circulation and predicting prognosis.

MATERIALS AND METHODS

Twenty-nine acute ischemic stroke patients who underwent one-stop CT angiography (CTA)-CT perfusion scan were reviewed retrospectively. sCTA and t-MIP CTA were developed by CT perfusion scanning data. Image quality and collateral circulation were compared between the sCTA and t-MIP CTA groups. CT attenuation values, image noise, signal to noise , contrast to noise, and subjective image quality were obtained and compared between these two groups. The correlations of clinical prognosis and infarct volume with collateral status on t-MIP CTA and sCTA were analyzed, separately. Receiver operating characteristic curve was used to reveal the sensitivity and specificity of t-MIP CTA and sCTA in predicting outcome.

RESULTS

All images exhibited good quality for diagnosis. In objective evaluation, the noise level of t-MIP CTA was significantly lower than that of sCTA (p < 0.001). Vascular attenuation (signal to noise and contrast to noise) of t-MIP were higher than those of sCTA (all, p < 0.001). The collateral status on t-MIP CTA and sCTA were both negatively correlated with modified Rankin Scale scores (t-MIP CTA, r = -0.709, p < 0.001; sCTA, r = -0.551, p = 0.024) and the final infarction volume (t-MIP CTA, r = -0.716, p = 0.001; sCTA, r = -0.629, p = 0.003). t-MIP CTA was better for predicting prognosis (AUC, 0.956; sensitivity, 0.917; specificity, 0.941; p < 0.001) than sCTA (AUC, 0.824; sensitivity, 0.500; specificity, 0.941; p = 0.003).

CONCLUSION

In comparison with sCTA, t-MIP images showed higher image quality of intracranial vascularity and MIP could reveal vascular occlusion and evaluate collateral circulation more accurately. It was speculated that t-MIP could predict the prognosis more precisely.

Acquisition time, radiation dose, subjective and objective image quality of dual-source CT scanners in acute pulmonary embolism: a comparative study

OBJECTIVES

To compare the scan acquisition time, radiation dose, subjective and objective image quality of two dual-source CT scanners (DSCT) for detection of acute pulmonary embolism.

METHODS

Two hundred twenty-one scans performed on the 2nd-generation DSCT and 354 scans on the 3rd-generation DSCT were included in this large retrospective study. In a randomized blinded design, two radiologists independently reviewed the scans using a 5-point Likert scale. Radiation dose and objective image quality parameters were calculated.

RESULTS

Mean acquisition time was significantly lower in the 3rd-generation DSCT (2.81 s ± 0.1 in comparison with 9.7 s ± 0.15 [mean ± SD] respectively; p < 0.0001) with the 3rd generation 3.4 times faster. The mean subjective image quality score was 4.33/5 and 4/5 for the 3rd- and 2nd-generation DSCT respectively (p < 0.0001) with strong interobserver reliability agreement. DLP, CTDI_vol, and ED were significantly lower in the 3rd than the 2nd generation (175.6 ± 63.7 mGy cm; 5.3 ± 1.9 mGy and 2.8 ± 1.2 mSv in comparison with 266 ± 255 mGy.cm; 7.8 ± 2.2 mGy and 3.8 ± 4.3 mSv). Noise was significantly lower in the 3rd generation (p < 0.01). Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and figure of merit (FOM), a dose-insensitive index for CNR, were significantly higher in the 3rd-generation DSCT (33.5 ± 23.4; 29.0 ± 21.3 and 543.7 ± 1037 in comparison with 23.4 ± 17.7; 19.4 ± 16.0 and 170.5 ± 284.3).

CONCLUSION

Objective and subjective image quality are significantly higher on the 3rd-generation DSCT with significantly lower mean acquisition time and radiation dose.

KEY POINTS

• The 3rd-generation DSCT scanner provides an improved image quality, less perceived artifacts, and lower radiation dose in comparison with the 2nd-generation DSCT, when operating in dual-energy (DE) mode. • The 3.4-times-faster 3rd-generation DSCT scanner can be of particular value in patients with chronic lung diseases or breathing difficulties that prevent adequate breathhold.

Single- and dual-energy CT pulmonary angiography using second- and third-generation dual-source CT systems: comparison of radiation dose and image quality

OBJECTIVES

To evaluate radiation exposure and image quality in matched patient cohorts for CT pulmonary angiography (CTPA) acquired in single- and dual-energy mode using second- and third-generation dual-source CT (DSCT) systems.

METHODS

We retrospectively included 200 patients (mean age, 65.5 years ± 15.7 years) with suspected pulmonary embolism-equally divided into four study groups (n = 50) and matched by gender and body mass index. CTPA was performed with vendor-predefined second-generation (group A, 100-kV single-energy computed tomography (SECT); group B, 80/Sn140-kV dual-energy computed tomography (DECT)) or third-generation DSCT (group C, 100-kV SECT; group D, 90/Sn150-kV DECT) devices. Radiation metrics were assessed using a normalized scan range of 27.5 cm. For objective image quality evaluation, dose-independent figure-of-merit (FOM) contrast-to-noise ratios (CNRs) were calculated. Subjective image analysis included ratings for overall image quality, reader confidence, and image artifacts using five-point Likert scales.

RESULTS

Calculations of the effective dose (ED) of radiation for a normalized scan range of 27.5 cm showed nonsignificant differences between SECT and DECT acquisitions for each scanner generation (p ≥ 0.253). The mean effective radiation dose was lower for third-generation groups C (1.5 mSv ± 0.8 mSv) and D (1.4 mSv ± 0.7 mSv) compared to second-generation groups A (2.5 mSv ± 0.9 mSv) and B (2.3 mSv ± 0.6 mSv) (both p ≤ 0.013). FOM-CNR measurements were highest for group D. Qualitative image parameters of overall image quality, reader confidence, and image artifacts showed nonsignificant differences among the four groups (p ≥ 0.162).

CONCLUSIONS

Third-generation DSCT systems show lower radiation dose parameters for CTPA compared to second-generation DSCT. DECT can be performed with both scanner generations without radiation dose penalty or detrimental effects on image quality compared to SECT.

KEY POINTS

• Radiation exposure showed nonsignificant differences between SECT and DECT for both DSCT scanner devices. • Dual-energy CTPA provides equivalent image quality compared to standard image acquisition. • Subjective image quality assessment was similar among the four study groups.

Radiation dose reduction using two orthogonal topograms associated with automatic tube voltage selection for lung CT scanning as compared with a single anteroposterior topogram

OBJECTIVE

To evaluate the effectiveness of two orthogonal topograms on radiation dose and image quality (IQ) associated with topogram-based automatic tube voltage selection (ATVS) for lung CT scanning.

METHODS

Thirty-seven patients were enrolled in this study. At baseline, only an anteroposterior topogram was obtained and at follow-up, both anteroposterior and lateral topograms were performed. ATVS was turned on during all scans. Objective and subjective IQ evaluations were performed and compared; tube voltage and radiation dose of each scan were noted and analyzed.

RESULTS

A significant difference was observed regarding the objective parameters between baseline and follow-up only in image noise and signal-noise ratio (SNR) in the upper one-third of the image (image noise: 7.49 ± 1.08 vs. 9.10 ± 1.13, p < 0.001; SNR: 4.08 ± 0.87 vs. 3.37 ± 0.63, p < 0.001). No differences were found between baseline and follow-up in the subjective assessment of IQ. The radiation dose was significantly lower at follow-up than that at baseline (2.73 ± 0.83 mSv vs. 3.55 ± 1.24 mSv, respectively; p < 0.001).

CONCLUSIONS

Using two orthogonal topograms associated with ATVS could significantly reduce the total radiation dose for lung CT scanning, while subjective IQ was maintained.