Dual-energy CT angiography of abdomen with routine concentration contrast agent in comparison with conventional single-energy CT with high concentration contrast agent

The role of dual-energy computed tomography (DECT) in emergency radiology: a visual guide to advanced diagnostics

Dual-energy computed tomography (DECT) has become an essential tool in emergency radiology, significantly enhancing diagnostic capabilities for a variety of acute conditions. By utilising two distinct X-ray energy spectra, DECT differentiates materials based on their attenuation properties, providing detailed insights into tissue composition and pathology. In emergency settings, DECT is used in thoracic imaging for the detection of pulmonary embolism, in abdominal imaging to enhance the diagnosis and characterisation of conditions such as pancreatitis, appendicitis, gastrointestinal bleeding, and bowel ischaemia and in the genitourinary system for identifying kidney stones, pyelonephritis, and urinary bleeding. In neuroimaging, DECT enables image optimisation through virtual monochromatic images and the reduction of metal artifacts. It helps in the differential diagnosis of haemorrhage versus tumour-related haemorrhage, haemorrhage versus contrast extravasation, and in the dating of vertebral collapse. DECT offers several advantages, including enhanced visualisation, the potential to reduce radiation exposure and contrast medium, and improved diagnostic accuracy across a wide range of conditions. However, its routine clinical adoption is still evolving due to challenges such as limited availability, cost, and the need for specialised training. This pictorial essay aims to encourage the broader integration of DECT into emergency imaging protocols by showcasing its clinical applications and benefits.

Photon-counting versus energy-integrating CT of abdomen-pelvis: a phantom study on the potential for reducing iodine contrast media

BACKGROUND

To assess the potential of virtual monoenergetic images (VMIs) on a photon-counting computed tomography (PCCT) for reducing the amount of injected iodine contrast media compared to an energy-integrating CT (EICT).

METHODS

A multienergy phantom was scanned with a PCCT and EICT at 11 mGy with abdomen-pelvis examination parameters. VMIs were generated at 40 keV, 50 keV, 60 keV, and 70 keV. For all VMIs, the contrast-to-noise ratio (CNR) of iodine inserts with concentrations of 1 mg/mL, 2 mg/mL, 5 mg/mL, 10 mg/mL, and 15 mg/mL was calculated by dividing the signal difference between HU in iodine inserts versus solid water by the noise value assessed on solid water. The potential reduction in iodine media was calculated by the rate of reduction in iodine concentration with PCCT while maintaining the same CNR obtained with EICT for the reference concentration.

RESULTS

Significantly higher CNR values were found with PCCT at all VMI energy levels for iodine concentrations above 1 mg/mL. The highest reduction was observed at 40 keV, with a value of 48.9 ± 1.6% (mean ± standard deviation). It decreased as the energy level increased, by 38.5 ± 0.5%, and 30.8 ± 0.8% for 50 and 60 keV, respectively. For 70 keV, the potential reduction of 24.4 ± 1.1% was found for iodine concentrations above 1 mg/mL. This reduction reached 57 ± 2.3% at 40 keV with PCCT compared to 60 keV with EICT.

CONCLUSION

For abdomen-pelvis protocols, the use of VMIs with PCCT significantly improved the CNR of iodine, offering the potential to reduce the required contrast medium.

RELEVANCE STATEMENT

The use of VMIs with PCCT may reduce the quantity of iodine contrast medium to be injected compared with EICT, limiting costs, the risk of adverse effects, and the amount of contrast agent released into the wastewater.

KEY POINTS

PCCT improves the image quality of VMIs. PCCT offers the potential for reducing the amount of injected contrast medium. PCCT potential for reducing the injected contrast medium depends on energy level.

Expanding Role of Dual-Energy CT for Genitourinary Tract Assessment in the Emergency Department, From the AJR Special Series on Emergency Radiology

Among explored applications of dual-energy CT (DECT) in the abdomen and pelvis, the genitourinary (GU) tract represents an area where accumulated evidence has established the role of DECT to provide useful information that may change management. This review discusses established applications of DECT for GU tract assessment in the emergency department (ED) setting, including characterization of renal stones, evaluation of traumatic injuries and hemorrhage, and characterization of incidental renal and adrenal findings. Use of DECT for such applications can reduce the need for additional multiphase CT or MRI examinations and reduce follow-up imaging recommendations. Emerging applications are also highlighted, including use of low-energy virtual monoenergetic images (VMIs) to improve image quality and potentially reduce contrast media doses and use of high-energy VMIs to mitigate renal mass pseudoenhancement. Finally, implementation of DECT into busy ED radiology practices is presented, weighing the trade-off of additional image acquisition, processing time, and interpretation time against potential additional useful clinical information. Automatic generation of DECT-derived images with direct PACS transfer can facilitate radiologists' adoption of DECT in busy ED environments and minimize impact on interpretation times. Using the described approaches, radiologists can apply DECT technology to improve the quality and efficiency of care in the ED.

Initial Investigation of Clinical Value of Noise-Optimized Virtual Monoenergetic Images Derived From Dual-Energy Computed Tomography Angiography in Preoperative Perforator Planning of Anterolateral Thigh Flap Transplantation

OBJECTIVE

To objectively and subjectively assess the image characteristics of noise-optimized virtual monoenergetic images [MEI (+)] and polyenergetic images (PEIs) from dual-energy computed tomography angiography and then to explore the clinical value of the optimal MEI (+) in preoperative perforator planning of anterolateral thigh (ALT) flap transplantation.

METHODS

Sixteen patients (32 thighs) who underwent lower extremity run-off dual-energy computed tomography angiography for planning ALT flap transplantation were enrolled. One standard PEI and 5 MEI (+) in 10-keV intervals (range, 40-80 keV) were reconstructed. First, we compared the image quality subjectively (branch order, image quality, and vascular network continuity) and objectively (vascular attenuation, image noise, signal-to-noise ratio, and the contrast-to-noise ratio). Then, we compared the clinical value (number, type, source artery, pedicle length, caliber, and location of all sizable perforators) between the optimal MEI (+) and PEI groups.

RESULTS

The 40-keV MEI (+) was rated superior subjective and objective image quality metrics to PEI (all P < 0.001). Compared with PEI, 40 keV MEI (+) increased the number of visible perforators, the percentage of perforators with identifiable types, and the measurable length of perforator pedicle (all P < 0.001).

CONCLUSIONS

We recommend 40 keV MEI (+) for the visualization of perforators and their contribution to the selection and location of suitable perforators in preoperative planning for ALT flaps.

Optimized Bolus Threshold for Dual-Energy CT Angiography with Monoenergetic Images: A Randomized Clinical Trial

Background The bolus-tracking technique from single-energy CT has been applied to dual-energy CT (DECT) without optimization or validation. Further optimization is imperative because of a paucity of literature and differences in the attenuation profile of virtual monoenergetic images (VMIs). Purpose To determine the optimal trigger threshold with bolus-tracking technique for DECT angiography (DECTA) in a phantom study and assess the feasibility of an optimized threshold for bolus-tracking technique in DECTA at 40 keV with a 50% reduced iodine dose in human participants. Materials and Methods A phantom study with rapid kilovoltage-switching DECT was performed to determine the optimal threshold for each kiloelectron-volt VMI. In a prospective study, consecutive participants who underwent whole-body CT angiography (CTA) from August 2018 to July 2019 were randomized into three groups: single-energy CTA (SECTA) with standard iodine dose (600 mg of iodine per kilogram), DECTA with 50% reduced iodine dose (300 mg of iodine per kilogram) by using a conventional threshold, and DECTA with 300 mg of iodine per kilogram by using an optimized threshold. A trigger threshold of 100 HU at 120 kVp was used as a reference for comparison. Injected iodine doses and aortic CT numbers were compared among the three groups using Kruskal-Wallis test. Results Ninety-six participants (mean age ± standard deviation, 72 years ± 9; 80 men) were evaluated (32 participants in each group). The optimized threshold for VMIs at 40 keV was 30 HU. The median iodine dose was lower in the optimized DECTA group (13 g) compared with conventional DECTA (19 g) and SECTA (26 g) groups (P < .017 for each comparison). The median aortic CT numbers were higher in the order corresponding to conventional DECTA (655-769 HU), optimized DECTA (543-610 HU), and SECTA (343-359 HU) groups (P < .001). Conclusion The optimized trigger threshold of 30 HU for bolus-tracking technique during dual-energy CT angiography at 40 keV achieved lower iodine load while maintaining aortic enhancement. ©RSNA, 2021 Online supplemental material is available for this article. See also the editorial by Malayeri in this issue.

Noise reduction approach in pediatric abdominal CT combining deep learning and dual-energy technique

OBJECTIVES

To evaluate the image quality of low iodine concentration, dual-energy CT (DECT) combined with a deep learning-based noise reduction technique for pediatric abdominal CT, compared with standard iodine concentration single-energy polychromatic CT (SECT).

METHODS

From December 2016 to May 2017, DECT with 300 mg•I/mL contrast medium was performed in 29 pediatric patients (17 boys, 12 girls; age, 2-19 years). The DECT images were reconstructed using a noise-optimized virtual monoenergetic reconstruction image (VMI) with and without a deep learning method. SECT images with 350 mg•I/mL contrast medium, performed within the last 3 months before the DECT, served as reference images. The quantitative and qualitative parameters were compared using paired t tests and Wilcoxon signed-rank tests, and the differences in radiation dose and total iodine administration were assessed.

RESULTS

The linearly blended DECT showed lower attenuation and higher noise than SECT. The 60-keV VMI showed an increase in attenuation and higher noise than SECT. The combined 60-keV VMI plus deep learning images showed low noise, no difference in contrast-to-noise ratios, and overall image quality or diagnostic image quality, but showed a higher signal-to-noise ratio in the liver and lower enhancement of lesions than SECT. The overall image and diagnostic quality of lesions were maintained on the combined noise reduction approach. The CT dose index volume and total iodine administration in DECT were respectively 19.6% and 14.3% lower than those in SECT.

CONCLUSION

Low iodine concentration DECT, combined with deep learning in pediatric abdominal CT, can maintain image quality while reducing the radiation dose and iodine load, compared with standard SECT.

KEY POINTS

• An image noise reduction approach combining deep learning and noise-optimized virtual monoenergetic image reconstruction can maintain image quality while reducing radiation dose and iodine load. • The 60-keV virtual monoenergetic image reconstruction plus deep learning images showed low noise, no difference in contrast-to-noise ratio, and overall image quality, but showed a higher signal-to-noise ratio in the liver and a lower enhancement of lesion than single-energy polychromatic CT. • This combination could offer a 19.6% reduction in radiation dose and a 14.3% reduction in iodine load, in comparison with a control group that underwent single-energy polychromatic CT with the standard protocol.

Evaluating the Image Quality of Monoenergetic Images From Dual-Energy Computed Tomography With Low-Concentration and Low-Flow-Rate Contrast Media for the Arterials Supply to the Nipple-Areola Complex in Breast Cancer Compared With Conventional Computed Tomography Angiography

Objective

The objective of this study was to evaluate the image quality of monoenergetic images (MEIs (+)) acquired from dual-energy computed tomography with low-concentration and low-flow-rate contrast media for the arterial supply to the nipple-areola complex (NAC) in breast cancer compared with conventional computed tomography angiography (CTA).

Methods

We enrolled 25 patients (MEI (+)₃₀₀ group, 300 mg/mL and 2.5 mL/s of contrast media) and 23 patients (CTA₃₇₀ group, 370 mg/mL and 3.5 mL/s of contrast media) for assessing NAC blood supply angiography. The image quality of the 2 groups was evaluated objectively and subjectively.

Results

The 40 keV MEI (+)₃₀₀ demonstrated higher attenuation and contrast-to-noise ratio than CTA₃₇₀ group (P < 0.001). The subjective image quality and visualization of the arteries were comparable between 2 groups.

Conclusions

The 40 keV MEI (+)₃₀₀ acquired from dual-energy computed tomography can achieve comparable image quality of arterial supply to NAC with low-concentration and low-flow-rate contrast media in breast cancer compared with CTA₃₇₀.

Dual-Energy CT: A Paradigm Shift in Acute Traumatic Abdomen

Abdominal trauma, one of the leading causes of death under the age of 45, can be broadly classified into blunt and penetrating trauma, based on the mechanism of injury. Blunt abdominal trauma usually results from motor vehicle collisions, fall from heights, assaults, and sports and is more common than penetrating abdominal trauma, which is usually seen in firearm injuries and stab wounds. In both blunt and penetrating abdominal trauma, an optimized imaging approach is mandatory to exclude life-threatening injuries. Easy availability of the portable ultrasound in the emergency department and trauma bay makes it one of the most commonly used screening imaging modalities in the abdominal trauma, especially to exclude hemoperitoneum. Evaluation of the visceral and vascular injuries in a hemodynamically stable patient, however, warrants intravenous contrast-enhanced multidetector computed tomography scan. Dual-energy computed tomography with its postprocessing applications such as iodine selective imaging and virtual monoenergetic imaging can reliably depict the conspicuity of traumatic solid and hollow visceral and vascular injuries.

Improved coronary artery contrast enhancement using noise-optimised virtual monoenergetic imaging from dual-source dual-energy computed tomography

PURPOSE

To define optimal kiloelectron volt (keV) settings for virtual monoenergetic imaging (VMI) reconstruction at dual-energy coronary computed tomography angiography (DE-CCTA).

METHOD

Fifty-one DE-CCTA data sets (33 men; mean age, 63.9 ± 13.2 years) were reconstructed as standard linearly-blended images (F_0.6; 60% of 90 kVp, 40% of 150 kVpSn), and with traditional (VMI) and noise-optimised (VMI+) algorithms from 40 to 100 keV in 10-keV intervals. Objective image quality was assessed with signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) measurements. Three observers subjectively evaluated vascular contrast, image sharpness, noise and delineation of coronary plaques.

RESULTS

Median values for objective image analysis were highest in VMI + series at 40 keV (SNR, 44.5; CNR: 33.5), significantly superior (allp < 0.001) to the best VMI series at 70 keV (SNR, 28.1; CNR, 18.4) and standard F_0.6 images (SNR, 23.2; CNR, 15.6). Overall subjective metrics achieved higher scores at 40-keV VMI+ series in comparison to 70-keV VMI series and F_0.6 images (all p < 0.001), with optimal vascular contrast (5; ICC, 0.90), good image sharpness (4; 0.88), low noise (4; 0.82), and optimal plaque delineation (5; 0.89).

CONCLUSIONS

DE-CCTA image reconstruction with 40-keV VMI + allows for significant improvement of both objective and subjective image quality.

Dual-Energy CT Urography With 50% Reduced Iodine Dose Versus Single-Energy CT Urography With Standard Iodine Dose

OBJECTIVE

The purpose of this study was to compare dual-energy CT (DECT) urography with a 50% reduced iodine dose to single-energy CT (SECT) urography with a standard iodine dose with respect to attenuation of renal vascular and urinary tract structures and with respect to image quality.

SUBJECTS AND METHODS

The study included 62 patients undergoing evaluation of urinary tract lithiasis, tumor, or hematuria. Thirty-one patients underwent DECT urography with a 50% reduced iodine dose and reconstruction at 50 and 77 keV. These subjects were sex, age, and size matched to a group of 31 patients who underwent 120-kVp SECT urography with a standard iodine dose. The mean iodine dose was 22 g for DECT and 44 g for SECT. Attenuation was measured at seven locations in the renal arteries, renal veins, and urinary tract. Two reviewers subjectively scored the image quality parameters image noise, sharpness of urinary tract contours, enhancement of urinary structures, and streak artifacts.

RESULTS

Mean DECT attenuation at 50 keV was the same as or greater than SECT attenuation at each of the seven locations. Measured image noise was highest at 50-keV DECT but was the same for 77-keV DECT and 120-kVp SECT. Mean subjective scores for DECT image quality parameters were the same as or higher than those of SECT, except for streak artifact and sharpness of urinary tract contours.

CONCLUSION

DECT urography with a 50% reduced iodine dose may result in measured renal vascular and urinary tract attenuation the same as or higher than and image quality measurements and scores similar to those obtained with 120-kVp SECT urography with a standard iodine dose.

Dual-Energy Computed Tomography: Dose Reduction, Series Reduction, and Contrast Load Reduction in Dual-Energy Computed Tomography

Evolution in computed tomography technology and image reconstruction have significantly changed practice. Dual energy computed tomography is being increasingly adopted owing to benefits of material separation, quantification, and improved contrast-to-noise ratio. The radiation dose can match that from single energy computed tomography. Spectral information derived from a polychromatic x-ray beam at different energies yields in image reconstructions that reduce the number of phases in a multiphasic examination and decrease the absolute amount of contrast media. This increased analytical and image processing capability provides new avenues for addressing radiation dose and iodine exposure concerns.

Automatic spectral imaging protocol selection combined with iterative reconstruction can enhance image quality and decrease radiation and contrast dosage in abdominal CT angiography

PURPOSE

To investigate the effect of automatic spectral imaging protocol selection (ASIS) and adaptive statistical iterative reconstruction (ASIR) technology in reducing radiation and contrast dosage.

METHODS

Sixty-four patients were randomly divided into two groups for abdominal computed tomography (CT): the experiment group with ASIS plus 50% ASIR and the control with 120 kVp voltage.

RESULTS

The CT dose-index volume decreased by 23.68 and 23.57% and the dose-length product dropped by 25.59 and 18.45% in the arterial and portal venous phases, respectively, in the experiment than control group. The contrast dose was reduced by 16.86% in the experiment group. In the 55 keV + 50% ASIR group, the arterial contrast-to-noise ratio and scores were significantly (P < 0.05) higher than in the control group in the arterial phase while the portal contrast-to-noise ratio and scores were not significantly different between the two groups (P > 0.05).

CONCLUSION

The ASIS technique plus 50% ASIR can enhance image quality of the abdominal structures while decreasing the radiation and contrast dosage compared with the conventional scan mode.

Poly-energetic and virtual mono-energetic images from a novel dual-layer spectral detector CT: optimization of window settings is crucial to improve subjective image quality in abdominal CT angiographies

PURPOSE

We aimed to determine optimal window settings for poly-energetic (PolyE) and virtual mono-energetic images (MonoE) derived from abdominal angiographic studies on a novel dual-layer spectral detector CT (SDCT) system.

METHODS

From 50 patients, SDCT datasets PolyE and MonoE at 70 and 40 keV levels were reconstructed and best individual window width and level (BI-W/L) manually assessed. Through regression analysis, the so-called optimized individual (OI-W/L) values were obtained. Subjective image quality parameters and vessel diameters were measured to determine influences of different W/L settings.

RESULTS

Image noise was lower and attenuation and contrast-to-noise ratio were higher in MonoE compared to PolyE (all p ≤ 0.002). Mean BI-W/L values for PolyE, 70, and 40 keV were 637/284, 647/291, and 1568/691, respectively. Mean OI-W/L values were 631/276, 628/286, and 1516/667, respectively. Compared to standard settings, all adjusted W/L settings varied significantly and yielded higher subjective scoring. No between-group differences were found between manually adjusted and mathematically calculated W/L settings.

CONCLUSION

PolyE and MonoE from abdominal angiographic SDCT studies require appropriate W/L settings especially at low energy reconstruction levels. Individual adjustment reaches the best image quality but is time consuming. From our data, predefined W/L settings of 640/280 (PolyE/MonoE 70 keV) and 1570/690 (MonoE 40 keV) as a non-individualized starting point for abdominal angiographic studies from the novel SDCT system are suggested.

Optimization of window settings for standard and advanced virtual monoenergetic imaging in abdominal dual-energy CT angiography

OBJECTIVES

To determine the optimal window setting for displaying virtual monoenergetic reconstructions of third generation dual-source, dual-energy CT (DECT) angiography of the abdomen.

METHODS

Forty-five patients were evaluated with DECT angiography (90/150 kV, 180/90 ref. mAs). Three datasets were reconstructed: standard linear blending (M_0.6), 70 keV traditional virtual monoenergetic (M70), and 40 keV advanced noise-optimized virtual monoenergetic (M40+). The best window setting (width and level, W/L) was assessed by two blinded observers and was correlated with aortic attenuation to obtain the Optimized W/L setting (O-W/L). Subjective image quality was assessed, and vessel diameters were measured to determine any possible influences between different W/L settings. Repeated measures of variance were used to evaluate comparison of W/L values, image quality, and vessel sizing between M_0.6, M70, and M40+.

RESULTS

The Best W/L (B-W/L) for M70 and M40+ was 880/280 and 1410/450, respectively. Results from regression analysis inferred an O-W/L of 850/270 for M70 and 1350/430 for M40+. Significant differences for W and L were found between the Best and the Optimized W/L for M40+, and between M70 and M40+ for both the Best and Optimized W/L. No significant differences for vessel measurements were found using the O-W/L for M40+ compared to the standard M_0.6 (p ≥ 0.16), and significant differences were observed when using the B-W/L with M40+ compared to M_0.6 (p ≤ 0.04).

CONCLUSION

In order to optimize virtual monoenergetic imaging with both traditional M70 and advanced M40+, adjusting the W/L settings is necessary. Our results suggest a W/L setting of 850/270 for M70 and 1350/430 for M40+.

Prospective comparison of dual-energy CT aortography using 70% reduced iodine dose versus single-energy CT aortography using standard iodine dose in the same patient

PURPOSE

To compare dual-energy computed tomography (DECT) aortography using a 70% reduced iodine dose to single-energy CT (SECT) aortography using a standard iodine dose in the same patient.

METHODS

Twenty-one patients with a prior SECT aortography using standard iodine dose had DECT aortography using 70% reduced iodine dose. Section 120 kVp images were compared to DECT images reconstructed at both 50 and 77 keV. Reviewers measured image noise and attenuation in the aorta at eight locations from proximal to distal and subjectively scored vascular enhancement on a four-point scale. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. The volume CT dose index (CTDI_vol) for each exam was recorded.

RESULTS

Mean iodine dose was 50 g for SECT and 15 g for DECT (70% reduction). Mean aortic attenuation was similar for section 120 kVp (350 ± 67 HU) and DECT 50 keV (338 ± 57 HU, p = 0.547) but was lower at 77 keV (152 ± 23 HU). Measured image noise was greatest at 50 keV (12 ± 5 HU) and was lowest at 77 keV (7 ± 2 HU, p > 0.001). There was no difference in SNR or CNR between 120 kVp and 50 keV (p > 0.05). Mean subjective vascular enhancement scores for SECT were between good and excellent (3.33-3.69), and for DECT at 50 keV were between moderate and good (2.54-2.93, p < 0.0001). CTDI_vol was 13.6 mGy for SECT and 13.1 mGy for DECT (p = 0.637).

CONCLUSION

70% Reduced iodine DECT aortography may result in similar aortic attenuation, CNR, SNR, and lower although acceptable subjective image scores when compared to standard iodine SECT aortography in the same patient.

Prospective Comparison of Reduced-Iodine-Dose Virtual Monochromatic Imaging Dataset From Dual-Energy CT Angiography With Standard-Iodine-Dose Single-Energy CT Angiography for Abdominal Aortic Aneurysm

OBJECTIVE

The purpose of this study was to compare the image quality of reduced-iodine-dose single-source dual-energy CT angiography (CTA) with that of standard-iodine-dose single-energy CTA in examinations of patients with abdominal aortic aneurysm and to assess the effect of the concentration of iodinated contrast medium on intravascular enhancement and image quality of reduced-iodine-dose CTA.

SUBJECTS AND METHODS

In a prospective randomized clinical trial, 66 consecutively registered patients with abdominal aortic aneurysm who had previously undergone single-energy CTA (30-37 g I) underwent follow-up CTA at a reduced dose (21-27 g I) of iodinated contrast medium of either 270 mg I/mL (n = 33) or 320 mg I/mL (n = 33). Two readers independently evaluated virtual monochromatic imaging datasets (40-140 keV) and single-energy CTA images for image quality and noise and their preference for optimal energy virtual monochromatic imaging dataset. A value of p < 0.05 was considered statistically significant.

RESULTS

All 66 dual-energy CTA examinations were rated diagnostic with mean image quality and image noise scores of 4.8 and 4.5 for reader 1 and 3.8 and 3.4 for reader 2 compared with single-energy CTA results of 4.5 and 4.2 for reader 1 and 4.5 and 4.1 for reader 2. Low-energy virtual monochromatic images (40-60 keV) from reduced-iodine-dose (28%) dual-energy CTA had significantly higher intravascular aortic attenuation (26-185%) and contrast-to-noise ratio (CNR) (20-25%) than standard-iodine-dose single-energy CTA images (p < 0.0001). No significant difference was found between patients who received 270 and those who received 320 mg I/mL with respect to intravascular aortic attenuation (p = 0.6331) or CNR (p = 0.9775).

CONCLUSION

Low-energy virtual monochromatic imaging datasets from reduced-iodine (24 g I) single-source dual-energy CTA of the abdomen provide up to 185% higher attenuation and 25% higher CNR than standard-iodine-dose (33.3 g I) single-energy CTA while offering a wide range of energy settings irrespective of the concentration of IV contrast medium used.

Feasibility of spectral imaging with low-concentration contrast medium in abdominal CT angiography of obese patients

OBJECTIVE

To explore the application value of dual-energy spectral imaging scanning with low radiation dose and low-concentration contrast medium (270 mg I/mL) in abdominal CT angiography (CTA) of obese patients.

METHODS

A total of 127 obese patients (BMI≥25 kg/m(2) and waist circumference ≥900 mm) referred for abdominal CTA were prospectively enrolled in the study. The patients were divided into two groups; in group A (n=69), a spectral imaging scan mode and 270 mg I/mL iodine concentration contrast medium was used, and in group B (n=58), a conventional imaging scan mode using 120 kVp and 350 mg I/mL iodine concentration contrast medium was used. The image quality of the right renal artery in the two groups was evaluated by two observers using a 5-point scale, and the scores were compared using the Mann-Whitney U-test; the inter-observer agreement for the scores was analysed using the Kappa test. The CT values of the abdominal aorta, the superior mesenteric artery, the common hepatic artery and the splenic artery, and the CT value and standard deviation (SD) of the erector spinae at the level of the right renal hilum in groups A and B were measured by two observers; the inter-observer agreement of the measurement data was analysed using the inter-class correlation coefficient test. The following parameters were compared between the two groups using an independent sample t-test: the CT values of the abdominal aorta and its main branches; the image contrast-to-noise ratio (CNR) and figure of merit (FOM) of the abdominal aorta; the CT dose index (CTDIvol ); the dose length product (DLP); and the total iodine intake of the patients. P<.05 suggested a statistically significant difference.

RESULTS

The image scores of the right renal artery in groups A (4.59±0.60) and B (4.53±0.63) were the same (P=.57), with good inter-observer agreement. The CT values of the abdominal aorta, the superior mesenteric artery, the common hepatic artery and the splenic artery were >300 HU in both the groups; there was no statistically significant difference between the two groups (all P>.05), and inter-observer agreement was also good. Group A had significantly higher CNR and FOM values in the abdominal aorta than group B (all P<.001). Compared with group B, the CTDIvol and DLP values in group A were decreased by 46% and 35%, respectively. The total iodine intake for patients in group A was 27 g, 23% lower than the 35 g intake for patients in group B.

CONCLUSION

Compared with conventional CT, spectral CT imaging significantly reduces both radiation dose and contrast dose while maintaining image quality in abdominal CTA for patients with central obesity and high BMI.

Dual-energy CT Aortography with 50% Reduced Iodine Dose Versus Single-energy CT Aortography with Standard Iodine Dose

RATIONALE AND OBJECTIVES

Because many patients with aortic pathology also have compromised renal function, we wished to investigate dual-energy computed tomography (DECT) aortography with 50% reduced iodine dose compared to single-energy computed tomography (SECT) aortography with standard iodine dose.

MATERIALS AND METHODS

Fifty patients had DECT aortography with 50% reduced iodine dose. Thirty-four of these patients had prior SECT aortography with standard iodine dose. DECT images were reconstructed at both 50 and 77 keV and were compared to SECT 120 kVp images. Reviewers measured aortic attenuation, image noise, and scored vascular enhancement. Signal-to-noise ratios (SNR) and contrast-to-noise ratios (CNR) were calculated. Volume CT dose index was recorded.

RESULTS

Mean iodine dose was 47 g for SECT and 24 g for DECT. Aortic attenuation was highest at reduced iodine dose DECT 50 keV (570 ± 105 Hounsfield units [HU]) compared to 77 keV (239 ± 40 HU) or to standard iodine dose SECT 120 kVp (356 ± 69 HU) (P < 0.05). Image noise was greatest at 50 keV compared to 77 keV and 120 kVp (P < 0.05) but was similar between 77 keV and 120 kVp (P > 0.05). SNR and CNR were the same at 50 keV and 120 kVp (P > 0.05). Mean vascular enhancement scores were all above 3.0 (good, typical enhancement). Volume CT dose index was 11.7 mGy for DECT and 11.8 mGy for SECT (P = 0.37).

CONCLUSIONS

DECT aortography with 50% reduced iodine reconstructed at 50 keV resulted in significantly greater aortic attenuation, good subjective vascular enhancement, and comparable SNR and CNR compared to standard iodine dose SECT. DECT image noise at 77 keV was similar to SECT at 120 kVp.

Automatic spectral imaging protocol selection and iterative reconstruction in abdominal CT with reduced contrast agent dose: initial experience

OBJECTIVE

To evaluate the feasibility, image quality, and radiation dose of automatic spectral imaging protocol selection (ASIS) and adaptive statistical iterative reconstruction (ASIR) with reduced contrast agent dose in abdominal multiphase CT.

METHODS

One hundred and sixty patients were randomly divided into two scan protocols (n = 80 each; protocol A, 120 kVp/450 mgI/kg, filtered back projection algorithm (FBP); protocol B, spectral CT imaging with ASIS and 40 to 70 keV monochromatic images generated per 300 mgI/kg, ASIR algorithm. Quantitative parameters (image noise and contrast-to-noise ratios [CNRs]) and qualitative visual parameters (image noise, small structures, organ enhancement, and overall image quality) were compared.

RESULTS

Monochromatic images at 50 keV and 60 keV provided similar or lower image noise, but higher contrast and overall image quality as compared with 120-kVp images. Despite the higher image noise, 40-keV images showed similar overall image quality compared to 120-kVp images. Radiation dose did not differ between the two protocols, while contrast agent dose in protocol B was reduced by 33 %.

CONCLUSION

Application of ASIR and ASIS to monochromatic imaging from 40 to 60 keV allowed contrast agent dose reduction with adequate image quality and without increasing radiation dose compared to 120 kVp with FBP.

KEY POINTS

• Automatic spectral imaging protocol selection provides appropriate scan protocols. • Abdominal CT is feasible using spectral imaging and 300 mgI/kg contrast agent. • 50-keV monochromatic images with 50 % ASIR provide optimal image quality.