Optimizing Contrast Media Injection Protocols in Computed Tomography Angiography at Different Tube Voltages: Evaluation in a Circulation Phantom

Evaluation of a Tube Voltage-Based Contrast Media Adaptation in Coronary Computed Tomography Angiography Using Personalized Triphasic Injection Protocols: A Matched Case-Control Study

RATIONALE AND OBJECTIVES

Coronary CT angiography (CCTA) has recently been established as a first-line test in patients with suspected coronary artery disease (CAD). Due to the increased use of CCTA, strategies to reduce radiation and contrast medium (CM) exposure are of high importance. The aim of this study was to evaluate the performance of automated tube voltage selection (ATVS)-adapted CM injection protocol for CCTA compared to a clinically established triphasic injection protocol in terms of image quality, radiation exposure, and CM administration MATERIAL AND METHODS: Patients undergoing clinically indicated CCTA were prospectively enrolled from July 2021 to July 2023. Patients underwent CCTA using a modified triphasic CM injection protocol tailored to the tube voltage by the ATVS algorithm, in a range of 70 to 130 kV with a 10 kV interval. The injection protocol consisted of two phases of mixed CM and saline boluses with different proportions to assure a voltage-specific iodine delivery rate, followed by a third phase of saline flush. This cohort was compared to a control group identified retrospectively and scanned on the same CT system but with a standard triphasic CM protocol. Radiation and contrast dose, subjective and objective image quality (contrast-to-noise-ratio [CNR] and signal-to-noise-ratio [SNR]) were compared between the two groups.

RESULTS

The final population consisted of 120 prospective patients matched with 120 retrospective controls, with 20 patients in each kV group. The 120 kV group was excluded from the statistical analysis due to insufficient sample size. A significant CM reduction was achieved in the prospective group overall (46.0 [IQR 37.0-52.0] vs. 51.3 [IQR 40.1-73.0] mL, p < 0.001) and at all kV levels too (all pairwise p < 0.001). There were no significant differences in radiation dose (6.13 ± 4.88 vs. 5.97 ± 5.51 mSv, p = 0.81), subjective image quality (median score of 4 [3-5] vs. 4 [3-5], p = 0.40), CNR, and SNR in the aorta and the left anterior descending coronary artery (all p > 0.05).

CONCLUSION

ATVS-adapted CM injection protocol allows for diagnostic quality CCTA with reduced CM volume while maintaining similar radiation exposure, subjective and objective image quality.

Impact of iodinated contrast media concentration on image quality for dual-energy CT and single-energy CT with low tube voltage settings

BACKGROUND

Contrast-induced nephropathy (CIN) is an adverse reaction associated with the use of intravenous contrast media (CM).

PURPOSE

To investigate the impact of low tube voltage settings on single-energy computed tomography (SECT) and rapid kV switching dual-energy CT (DECT) with reduced concentrations of iodinated CM.

MATERIAL AND METHODS

A phantom containing four different concentrations of CM (original concentration CM, 20%, 40%, and 60% reductions) was scanned using SECT mode with varying tube voltages (70, 80, 100, and 120 kVp) and DECT mode through reconstructing monoenergetic energy (50 keV and 70 keV) images. ATCM system with different noise index (NI) settings were set, and the images were reconstructed using ASiR-V. Image quality were measured for individual phantom sizes and protocols and compared to a reference protocol for SECT of 120 kVp, NI = 18, threshold contrast enhancement ≥280 HU, and CNR ≥17.

RESULTS

Tube voltage settings of 70 kVp together with 40% reduction in the iodinated CM is suitable for small phantom size, those of 80 kVp and 20% reduction is suitable for the medium and large sizes. This allows radiation doses to be reduced by 12%-30%. Values of CNR and contrast for DECT are better than those for SECT with the same NI setting.

CONCLUSION

Diagnostic reference of image quality can be maintained by using SECT with lower tube voltage and DECT with reductions of iodinated CM concentration and radiation dose. Therefore, the NI setting can be increased when DECT is used to achieve a similar image quality.

Reduced Iodinated Contrast Media Administration in Coronary CT Angiography on a Clinical Photon-Counting Detector CT System: A Phantom Study Using a Dynamic Circulation Model

PURPOSE

The aim of this study was to evaluate strategies to reduce contrast media volumes for coronary computed tomography (CT) angiography on a clinical first-generation dual-source photon-counting detector (PCD)-CT system using a dynamic circulation phantom.

MATERIALS AND METHODS

Coronary CT angiograph is an established method for the assessment of coronary artery disease that relies on the administration of iodinated contrast media. Reduction of contrast media volumes while maintaining diagnostic image quality is desirable. In this study, a dynamic phantom containing a 3-dimensional-printed model of the thoracic aorta and coronary arteries was evaluated using a clinical contrast injection protocol with stepwise reduced contrast agent concentrations (100%, 75%, 50%, 40%, 30%, and 20% contrast media content of the same 50 mL bolus, resulting in iodine delivery rates of 1.5, 1.1, 0.7, 0.6, 0.4 and 0.3 gl/s) on a first-generation, dual-source PCD-CT. Polychromatic images (T3D) and virtual monoenergetic images were reconstructed in the range of 40 to 70 keV in 5-keV steps. Attenuation and noise were measured in the coronary arteries and background material and the contrast-to-noise ratio (CNR) were calculated. Attenuation of 350 HU and a CNR of the reference protocol at 70 keV were regarded as sufficient for simulation of diagnostic purposes. Vessel sharpness and noise power spectra were analyzed for the aforementioned reconstructions.

RESULTS

The standard clinical contrast protocol (bolus with 100% contrast) yielded diagnostic coronary artery attenuation for all tested reconstructions (>398 HU). A 50% reduction in contrast media concentration demonstrated sufficient attenuation of the coronary arteries at 40 to 55 keV (>366 HU). Virtual monoenergetic image reconstructions of 40 to 45 and 40 keV allowed satisfactory attenuation of the coronary arteries for contrast concentrations of 40% and 30% of the original protocol. A reduction of contrast agent concentration to 20% of the initial concentration provided insufficient attenuation in the target vessels for all reconstructions. The highest CNR was found for virtual monoenergetic reconstructions at 40 keV for all contrast media injection protocols, yielding a sufficient CNR at a 50% reduction of contrast agent concentration.

CONCLUSIONS

Using virtual monoenergetic image reconstructions at 40 keV on a dual-source PCD-CT system, contrast media concentration could be reduced by 50% to obtain diagnostic attenuation and objective image quality for coronary CT angiography in a dynamic vessel phantom. These initial feasibility study results have to be validated in clinical studies.

Optimization of contrast medium volume for abdominal CT in oncologic patients: prospective comparison between fixed and lean body weight-adapted dosing protocols

Background

Patient body size represents the main determinant of parenchymal enhancement and by adjusting the contrast media (CM) dose to patient weight may be a more appropriate approach to avoid a patient over dosage of CM. To compare the performance of fixed-dose and lean body weight (LBW)-adapted contrast media dosing protocols, in terms of image quality and parenchymal enhancement.

Results

One-hundred cancer patients undergoing multiphasic abdominal CT were prospectively enrolled in this multicentric study and randomly divided in two groups: patients in fixed-dose group (n = 50) received 120 mL of CM while in LBW group (n = 50) the amount of CM was computed according to the patient’s LBW. LBW protocol group received a significantly lower amount of CM (103.47 ± 17.65 mL vs. 120.00 ± 0.00 mL, p < 0.001). Arterial kidney signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) and pancreatic CNR were significantly higher in LBW group (all p ≤ 0.004). LBW group provided significantly higher arterial liver, kidney, and pancreatic contrast enhancement index (CEI) and portal venous phase kidney CEI (all p ≤ 0.002). Significantly lower portal vein SNR and CNR were observed in LBW-Group (all p ≤ 0.020).

Conclusions

LBW-adapted CM administration for abdominal CT reduces the volume of injected CM and improves both image quality and parenchymal enhancement.

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.

Impact of iodine concentration and scan parameters on image quality, contrast enhancement and radiation dose in thoracic CT

Background

We investigated the impact of varying contrast medium (CM) densities and x-ray tube potentials on contrast enhancement (CE), image quality and radiation dose in thoracic computed tomography (CT) using two different scanning techniques.

Methods

Seven plastic tubes containing seven different CM densities ranging from of 0 to 600 HU were positioned inside a commercial chest phantom with padding, representing three different patient sizes. Helical scans of the phantom in single-source mode were obtained with varying tube potentials from 70 to 140 kVp. A constant volume CT dose index (CTDIvol) depending on phantom size and automatic dose modulation was tested. CE (HU) and image quality (contrast-to-noise ratio, CNR) were measured for all combinations of CM density and tube potential. A reference threshold of CE and kVp was defined as ≥ 200 HU and 120 kVp.

Results

For the medium-sized phantom, with a specific CE of 100–600 HU, the diagnostic CE (200 HU) at 70 kVp was ~ 90% higher than at 120 kVp, for both scan techniques (p < 0.001). Changes in CM density/specific HU together with lower kVp resulted in significantly higher CE and CNR (p < 0.001). When changing only the kVp, no statistically significant differences were observed in CE or CNR (p ≥ 0.094), using both dose modulation and constant CTDIvol.

Conclusions

For thoracic CT, diagnostic CE (≥ 200 HU) and maintained CNR were achieved by using lower CM density in combination with lower tube potential (< 120 kVp), independently of phantom size.

Design, Implementation, and Validation of a Pulsatile Heart Phantom Pump

The developments in Computed Tomography (CT) and Magnetic Resonance allow visualization of blood flow in vivo using these techniques. However, validation tests are needed to determine a gold standard. For the validation tests, controllable systems that can generate pulsatile flow are needed. In this study, we aimed to develop an affordable pulsatile pump and an artificial circulatory system to simulate the blood flow for validation purposes. Initially, the prerequisites for the phantom were pulsating flow output equal to that of the human cardiac pulse pattern; the flow pattern of the mimicked cardiac output should be equal to that of a human, a variable stroke volume (40-120 ml/beat), and a variable heart rate (60-170 bpm). The developed phantom setup was tested with CT scanner. A washout profile was created based on the image intensity of the selected slice. The test was successful for a heart rate of 70 bpm and a stroke volume of 68 ml, but the system failed to work at various heartbeats and stroke volumes. This was due to the problems with software of the microcontroller. As conclusion in this study, we present a proof of concept for a pulsatile heart phantom pump that can be used in validation tests.

Proactive Air Management in CT Power Injections: A Comprehensive Approach to Reducing Air Embolization

OBJECTIVE

Venous air embolism as a complication of contrast media administration from power injection systems in CT is found to occur in 7%-55% of patients, impacting patient safety, diagnostic image quality, workflow efficiency, and patient and radiographer satisfaction. This study reviews the challenges associated with reactive air management approaches employed on contemporary systems, proposes a novel air management approach using proactive methods, and compares the impact of reactive and proactive approaches on injected air volumes under simulated clinical use.

METHODS

Injected air volumes from three power injection systems were measured under simulated clinical use via custom air trap fixture. Two of the systems employed reactive air management approaches, while a new system implemented the proposed proactive air management approach.

RESULTS

The proactive system injected significantly less air (average of 0.005 mL ± 0.006 mL with a maximum of 0.017 mL) when compared to two systems with reactive approaches (averages of 0.130 mL ± 0.082 mL and 0.106 mL ± 0.094 mL with maximums of 0.259 mL and 0.311 mL, respectively) (p < 0.05). CT images were taken of static and dynamic 0.1 mL air bubbles inside of a vascular phantom, both of which were clearly visible. Additionally, the dynamic bubble was shown to introduce image artifacts similar to those observed clinically.

CONCLUSION

Comparison of the injected air volumes show that a system with a proactive air management approach injected significantly less air compared to tested systems employing reactive approaches.

SIGNIFICANCE

The results indicate that the use of a proactive approach could significantly reduce the prevalence of observable, and potentially artifact-inducing, venous air embolism in contrast-enhanced CT procedures.

Impact of CT Injector Technology and Contrast Media Viscosity on Vascular Enhancement: Evaluation in a Circulation Phantom

Objective:

To assess the impact of piston-based vs peristaltic injection system technology and contrast media viscosity on achievable iodine delivery rates (IDRs) and vascular enhancement in a pre-clinical study.

Methods:

Four injectors were tested: MEDRAD^® Centargo, MEDRAD^® Stellant, CT Exprès^®, and CT motion^™ using five contrast media [iopromide (300 and 370 mgI ml⁻¹), iodixanol 320 mgI ml⁻¹, iohexol 350 mgI ml⁻¹, iomeprol 400 mgI ml⁻¹]. Three experiments were performed evaluating achievable IDR and corresponding enhancement in a circulation phantom.

Results:

Experiment I: Centargo provided the highest achievable IDRs with all tested contrast media (p < 0.05). Iopromide 370 yielded the highest IDR with an 18G catheter (3.15 gI/s); iopromide 300 yielded the highest IDR with 20G (2.70 gI/s) and 22G (1.65 gI/s) catheters (p < 0.05).

Experiment II: with higher achievable IDRs, piston-based injectors provided significantly higher peak vascular enhancement (up to 48% increase) than the peristaltic injectors with programmed IDRs from 1.8 to 2.4 gI/s (p < 0.05).

Experiment III: with programmed IDRs (e.g. 1.5 gI/s) achievable by all injection systems, Centargo, with sharper measured bolus shape, provided significant increases in enhancement of 34–73 HU in the pulmonary artery with iopromide 370 (p < 0.05).

Conclusion:

The tested piston-based injection systems combined with low viscosity contrast media provide higher achievable IDRs and higher peak vascular enhancement than the tested peristaltic-based injectors. With equivalent IDRs, Centargo provides higher peak vascular enhancement due to improved bolus shape.

Advances in knowledge:

This paper introduces a new parameter to compare expected performance among contrast media: the concentration/viscosity ratio. Additionally, it demonstrates previously unexplored impacts of bolus shape on vascular enhancement.

Regadenoson dynamic computed tomography myocardial perfusion using low-dose protocol for evaluation of the ischemic burden. ULYSSES study

BACKGROUND

The purpose of this study was to assess the feasibility of low-dose dynamic regadenoson computed tomography perfusion (CTP) protocol, and to determine which parameters provide the best diagnostic yield for the presence and burden of ischemia in reference to the magnetic resonance myocardial perfusion imaging (MR MPI).

METHODS

Fifty six patients with ≥1 intermediate (50-90%) coronary artery stenosis on CTA underwent dynamic stress CTP and MR MPI. The distribution of contrast agent in CTP was represented for each myocardial segment as either absolute or indexed: myocardial blood flow (MBF), myocardial blood volume (MBV), perfused capillary blood volume (PCBV), peak value (PV), time to peak (TTP), respectively.

RESULTS

Of 56 patients (25 females, 63.5 ± 8.5y), 15 (27%) were diagnosed with reversible ischemia and 3 (5%) with fixed ischemia on the MR MPI. The median radiation dose for dynamic CTP scan was 352.00 [276.4-496.6] mGy*cm. The optimal cut-off point for the prediction of reversible ischemia on MR MPI for the absolute parameters were: MBF ≤156.49 (AUC=0.899), MBV ≤15.06 (AUC=0.901), PCBV ≤7.90 (AUC=0.880), PV ≤ 88.30 (AUC=0.766), TTP ≥22.58 (AUC=0.595); and for the indexed: indexed MBF ≤0.78 (AUC=0.926), indexed MBV ≤0.81 (AUC=0.924), indexed PCBV ≤0.70 (AUC=0.894); indexed PV ≤ 0.79 (AUC=0.869), indexed TTP ≤0.87 (AUC=0.685). The best parameters for ischemia detection were indexed MBF and indexed MBV, with sensitivities 91% and 89%, specificities 97% and 96%, NPV 99% and 99%, PPV 76% and 69%, and accuracies 96% and 95%, respectively. In per patient analysis, indexed MBF correlated significantly better with the ischemia burden than any of the absolute parameters (p < 0.01 for all comparisons).

CONCLUSIONS

Regadenoson dynamic CTP using low-dose protocol is feasible while maintaining high diagnostic accuracy. The best diagnostic value may be provided by indexed parameters, of which indexed MBF and indexed MBV may provide best incremental value in identification of the presence and burden of ischemia.

Advanced Virtual Monoenergetic Imaging: Improvement of Visualization and Differentiation of Intramuscular Lesions in Portal-Venous-phase Contrast-enhanced Dual-energy CT

PURPOSE

To evaluate the effect of advanced monoenergetic imaging (MEI+) postprocessing algorithm on the visualization of various intramuscular lesions on portal-venous-phase contrast-enhanced dual-energy computed tomography (DECT).

MATERIAL AND METHODS

Thirty-nine patients (64.3 ± 11.1 years; 26 males) with various intramuscular lesions ranging from malignancy, bleeding, inflammation, edematous changes, and benign neoplasms were included and underwent DECT (100/Sn150kV). Postprocessing with MEI+ technique was used to reconstruct images at four different keV levels (40, 60, 80, 100) and compared to the standard portal-venous-phase CT (CT_pv) images. Image quality was assessed qualitatively (conspicuity, delineation, sharpness, noise, and confidence) by two independent readers using 5-point Likert scales, 5 = excellent; as well as quantitatively by calculating signal-to-noise ratios (SNR), contrast-to-noise ratios (CNR), and area under the receiver operating characteristic (ROC) curve (AUC) for lesion characterization.

RESULTS

Highest lesion enhancement and diagnostic confidence were observed in MEI+ 40 keV, with significant differences to CT_pv (p < 0.001), as well as for malignant lesions (highest conspicuity, noise, and sharpness in MEI+ 40 keV; p < 0.001). CNR calculations revealed highest values for MEI+ 40 keV followed by 60 keV with significant differences to CT_pv, and increasing energy levels. ROC analysis showed highest diagnostic accuracy for 40-keV MEI+ datasets regarding the detection of malignant/benign lesions with AUC values of 98.9% (95%-confidence interval: 96.5, 100) and a standard error of 1.2, further AUC values decreased to 83.6% for MEI+100.

CONCLUSION

MEI+ at low keV levels can significantly improve lesion detection of benign versus malignant intramuscular entities in patients undergoing portal-venous-phase DECT scans due to increased CNR.

Computed tomography pulmonary angiography and venography with a low dose of contrast medium

The authors developed a method to ensure sufficient opacification of pulmonary vasculature for separate depiction of arteries and veins in three-dimensional form with a small dose of contrast medium utilizing a test injection to determine optimal timing of computed tomography (CT) scanning. The dose was determined by a simulation based on a pharmacokinetic model. The contrast medium was administered at a rate of 5.0 mL/s for 3 s, followed by helical scanning at the timing determined by a dynamic CT scanning following the test injection. Images of 20 consecutive patients acquired with a 64-row CT scanner were evaluated. Quality of vessel depiction was assessed on the basis of the following: HU values at the main pulmonary artery (MPA) and left atrium (LA), distance between the pleural surface and the distal end of the pulmonary vessels on three-dimensional CT pulmonary arteriography and venography (3D-CTPAV), and subjective visual assessment of quality of the 3D-CTPAV images. Time to generate the 3D-CTPAV images was recorded. The mean ± standard deviation (SD) of the HU values at MPA/LA and the distances to the pleural surface for pulmonary arteries/veins were 448.0 ± 123.1/277.3 ± 60.85 HU and 9.21 ± 3.60/10.7 ± 5.45 mm, respectively. The image quality was visually rated as excellent for all of the patients. The mean time ± SD to generate 3D-CTPAV images was 13.6 ± 6.7 min. In conclusion, three-dimensional images of the pulmonary vasculature can be created using 21 mL (including 6 mL for the test injection) of contrast medium.

Contrast media injection protocol optimization for dual-energy coronary CT angiography: results from a circulation phantom

OBJECTIVES

To investigate the minimum iodine delivery rate (IDR) required to achieve diagnostic coronary attenuation (300 HU) with dual-energy coronary CTA.

METHODS

Acquisitions were performed on a circulation phantom with a third- generation dual-source CT scanner. Contrast media was injected for a fixed time whilst IDRs varied from 1.0 to 0.3 gI/s in 0.1-gI/s intervals. Noise-optimized virtual monoenergetic imaging (VMI+) reconstructions from 40 to 90 keV in 5 keV increments were generated. Contrast-to-noise ratio (CNR) and coronary HU were measured for each injection.

RESULTS

VMI+ from 40-70 keV reached diagnostic attenuation with at least one IDR. The minimum IDR achieving a diagnostic attenuation ranged from 0.4 gI/s at 40 keV (312.8 HU) to 1.0 gI/s at 70 keV (334.1 HU). Attenuation values reached with IDR of 1.0 gI/s were significantly higher at each keV level (p<0.001). CNR showed a near perfect correlation with the IDR (ρ≥0.962; p<0.001), the IDR of 1.0 gI/s provided the highest CNR at each keV level, achieving the highest overall value at 40 keV (54.0±3.1).

CONCLUSIONS

IDRs from 0.4-1.0 gI/s associated with VMI+ from 40-70 keV provide diagnostic coronary attenuation with dual-energy coronary CTA.

KEY POINTS

• Iodine delivery rate (IDR) is a major determinant of contrast enhancement. • Low-keV noise-optimized monoenergetic images (VMI+) maximize iodine attenuation. • Low-keV VMI+ allows for lower IDRs while maintaining adequate coronary attenuation. • Lowest IDR to reach 300 HU was 0.4 gI/s, 40 keV VMI+.