Prediction of aortic enhancement on coronary CTA images using a test bolus of diluted contrast material

Double low-dose computed tomography (CT) angiography of craniocervical arteries using a test bolus of diluted contrast medium and a personalized contrast protocol

AIM

To prospectively assess the value of a test bolus of diluted contrast medium (CM) combined with a personalized contrast protocol in craniocervical computed tomography angiography (cc-CTA) with low radiation and CM doses.

MATERIALS AND METHODS

Eighty-six consecutive subjects were divided into two groups at random (43 in each one): group A: 100/Sn140 kVp, filtered back-projection reconstruction, iopromide (370 mgI/ml) 50 ml; group B: 80/Sn140 kVp, iterative reconstruction, iodixanol (270 mgI/ml). In group B, the test bolus contained 27 ml of diluted CM, a personalized protocol with low-concentration CM was used for angiography, and the test bolus injection duration in angiography remained the same. Artery values over 200 Hounsfield units were considered significant.

RESULTS

Image quality for all cases was found to be diagnostic. No significant differences were found in the arterial densities of the ascending aorta or basilar artery between the groups. The values of the common carotid artery, internal carotid artery, and middle cerebral artery in group B were significantly lower. The effective dose and average iodine uptake were significantly lower in group B.

CONCLUSION

With double-low-dose cc-CTA, test bolus scanning based on diluted CM combined with a personalized contrast protocol can yield diagnostic-quality images and significantly reduce the radiation and CM doses.

[Comparison of Contrast Enhancement between Bolus-tracking and Test-bolus Methods on Coronary CT Angiography]

PURPOSE

To compare the contrast enhancement between bolus-tracking (BT) and test-bolus (TB) methods in coronary computed tomography angiography (CCTA).

METHOD

We enrolled 300 patients who underwent CCTA by BT (245 mg I/kg main bolus) or TB (77.4 mg I/kg test bolus with 245 mg I/kg main bolus) methods. In group BT (n=150), scanning was started automatically 5-second after contrast enhancement exceeded a predefined threshold of 150 Hounsfield units (HU). In group TB (n=150), TB peak attenuation plus 2-second was used as a delay. We recorded the CT number in the ascending aorta and determined whether the CT number was equivalent in two groups. For the equivalence test, we adopted 70 HU as the equivalence margin. The standard deviation (SD) in the CT number and the rate of patients with an acceptable CT number were compared. We also compared total iodine dose and total dose length product (DLP).

RESULT

The CT number of the ascending aorta was 437.6±68.9 HU in group BT and 438.9±69.7 HU in group TB; the 95% confidence interval for the difference between the groups was from -11.6 to 20.2 HU and within the range of the equivalence margins. The SD of the CT number and the rate of patients with acceptable CT number did not differ significantly between the two groups (p=0.857 and p=0.614, respectively). Total iodine dose in group TB was significantly higher than in group BT (p<0.001), and total DLP was not statistically significant (p=0.197).

CONCLUSION

The contrast enhancement between BT and TB methods in CCTA was equivalent, and the distribution was not significantly different between the two groups.

An Optimized Test Bolus Contrast Injection Protocol for Consistent Coronary Artery Luminal Enhancement for Coronary CT Angiography

OBJECTIVES

Consistent levels of coronary artery enhancement are essential for quantitative analysis of coronary artery plaque. We studied three contrast injection protocols for coronary CT angiography (CCTA) and compared mean attenuation level and consistency of vascular contrast enhancement. We hypothesized that test bolus adjusted protocols will have a superior consistency of coronary attenuation compared to a weight-based protocol.

MATERIALS AND METHODS

We prospectively evaluated a standard test bolus injection protocol (protocol 1, 32 subjects) and an optimized test bolus injection protocol (protocol 2, 59 subjects) in comparison to a body weight-based injection protocol (60 subjects). The test bolus was diluted contrast (20%-30% iopamidol 370 mixed with normal saline); peak aortic attenuation was measured and used to calculate a specific water/contrast mixture for the CCTA. The mean attenuation of the coronary lumen was measured on CCTA. Metrics of optimum arterial enhancement included the percentage of patients within a predetermined range for coronary attenuation (325-500 HU) and optimal timing with maximal ascending aortic attenuation. In addition, interpatient variation in coronary enhancement was quantified as percentage standard deviation of the attenuation.

RESULTS

The mean attenuation of the coronary arteries was similar in all protocols (362, 364, and 375 HU for the weight-based, test bolus 1 and 2 protocols, respectively). The percentage standard deviations of the weight-based, test bolus 1 and 2 protocols for coronary attenuation were 25.3%, 27.1%, and 10.5%, respectively (p < 0.0001). Test optimized bolus protocol 2 yielded the highest percentage of scans within the preferred coronary attenuation range (88%, p = 0.002). In test bolus protocol 2, the contrast timing was optimal in 73% of cases compared to only 22% of cases in the body mass guided injection protocol (protocol 1, p < 0.0001).

CONCLUSION

An optimized test bolus guided injection protocol resulted in a marked reduction in variation in coronary enhancement for CCTA compared to a body weight-based injection protocol.

[Utility of the Contrast Injection Technique Using the Diluted Test Injection Method and the Test Bolus Tracking Method in the Coronary CT Angiography]

Although the test bolus tracking method is available as a predicting method of scan timing in the coronary computed tomography (CT) angiography, it is known that there is a problem of scan timing due to the use of a part of test bolus method. The diluted test bolus method was adopted for test bolus, and as a result of using in combination with the test bolus tracking method, it showed a higher contrast enhancement compared with the test bolus tracking method; a stable contrast enhancement with less variation in CT number was obtained. The CT number at the peak in the test scan and the CT number of the main scan showed a high correlation. The contrast injection technique using the diluted test bolus method and the test bolus tracking method is a useful method in the coronary CT angiography. We named this contrast injection technique diluted test bolus tracking method.

Contrast-to-Noise Ratio Optimization in Coronary Computed Tomography Angiography: Validation in a Swine Model

RATIONALE AND OBJECTIVES

The accuracy of coronary computed tomography (CT) angiography depends upon the degree of coronary enhancement as compared to the background noise. Unfortunately, coronary contrast-to-noise ratio (CNR) optimization is difficult on a patient-specific basis. Hence, the objective of this study was to validate a new combined diluted test bolus and CT angiography protocol for improved coronary enhancement and CNR.

MATERIALS AND METHODS

The combined diluted test bolus and CT angiography protocol was validated in six swine (28.9 ± 2.7 kg). Specifically, the aortic and coronary enhancement and CNR of a standard CT angiography protocol, and a new combined diluted test bolus and CT angiography protocol were compared to a reference retrospective CT angiography protocol. Comparisons for all data were made using box plots, t tests, regression, Bland-Altman, root-mean-square error and deviation, as well as Lin's concordance correlation.

RESULTS

The combined diluted test bolus and CT angiography protocol was found to improve aortic and coronary enhancement by 26% and 13%, respectively, as compared to the standard CT angiography protocol. More importantly, the combined protocol was found to improve aortic and coronary CNR by 29% and 20%, respectively, as compared to the standard protocol.

CONCLUSION

A new combined diluted test bolus and CT angiography protocol was shown to improve coronary enhancement and CNR as compared to an existing standard CT angiography protocol.

Timing optimization of low-dose first-pass analysis dynamic CT myocardial perfusion measurement: validation in a swine model

Background

Myocardial perfusion measurement with a low-dose first-pass analysis (FPA) dynamic computed tomography (CT) perfusion technique depends upon acquisition of two whole-heart volume scans at the base and peak of the aortic enhancement. Hence, the objective of this study was to validate an optimal timing protocol for volume scan acquisition at the base and peak of the aortic enhancement.

Methods

Contrast-enhanced CT of 28 Yorkshire swine (weight, 55 ± 24 kg, mean ± standard deviation) was performed under rest and stress conditions over 20–30 s to capture the aortic enhancement curves. From these curves, an optimal timing protocol was simulated, where one volume scan was acquired at the base of the aortic enhancement while a second volume scan was acquired at the peak of the aortic enhancement. Low-dose FPA perfusion measurements (P_FPA) were then derived and quantitatively compared to the previously validated retrospective FPA perfusion measurements as a reference standard (P_REF). The 32-cm diameter volume CT dose index, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\mathrm{CTDI}}_{\mathrm{vol}}^{32} $$\end{document}CTDIvol32 and size-specific dose estimate (SSDE) of the low-dose FPA perfusion protocol were also determined.

Results

P_FPA were related to the reference standard by P_FPA = 0.95 · P_REF + 0.07 (r = 0.94, root-mean-square error = 0.27 mL/min/g, root-mean-square deviation = 0.04 mL/min/g). The \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\mathrm{CTDI}}_{\mathrm{vol}}^{32} $$\end{document}CTDIvol32 and SSDE of the low-dose FPA perfusion protocol were 9.2 mGy and 14.6 mGy, respectively.

Conclusions

An optimal timing protocol for volume scan acquisition at the base and peak of the aortic enhancement was retrospectively validated and has the potential to be used to implement an accurate, low-dose, FPA perfusion technique.

Usefulness of diluted contrast medium for test-scanning of infants scheduled for contrast-enhanced cardiovascular computed tomography angiography

OBJECTIVE:

To compare the ability of test scans with undiluted and diluted contrast medium (CM) to predict contrast enhancement (CE) on cardiovascular CT angiography (CCTA) images of infants.

METHODS:

We divided 120 consecutive infants who had undergone CCTA on a 64-MDCT scanner into two equal groups. In one group, the test bolus consisted of undiluted CM [protocol 1 (P1): injection volume = total  body weight × 1.2  ml, injection time 5  s], in the other (P2) it was total  body weight × 4.0  ml (CM 15%, saline 85%, injection time 16  s). CE on the test scans was recorded on a 3-point visual scale. We investigated the relation for CE in the pulmonary artery and ascending aorta between the P1 or P2 test scans and CCTA images.

RESULTS:

While peak CE was observed on all test scans performed with P2, in approximately 10 % of test scans obtained under P1, peak CE was not visualized. There was a strong positive linear correlation for CE of the pulmonary artery and ascending aorta on P2 images (r = 0.61  and r = 0.63, p < 0.01); under P1 the correlation was weak (r = 0.26  and r = 0.33, p < 0.01).

CONCLUSION:

Test-scanning with diluted CM revealed the optimal CE peak time and was useful for predicting CE on CCTA scans of the pulmonary artery and ascending aorta in infants with congenital heart disease.

ADVANCES IN KNOWLEDGE:

Diluted test scans help to select the optimal scan parameters for the CCTA study of infants by using contrast-to-noise-based scanning.

Effect of Patient Characteristics on Vessel Enhancement in Pediatric Chest Computed Tomography Angiography

INTRODUCTION

To evaluate the effect of sex, age, height, cardiac output (CO), total body weight (TBW), body surface area (BSA), and lean body weight (LBW) on vessel enhancement of the ascending aorta in pediatric chest computed tomography angiography (c-CTA).

MATERIALS AND METHODS

This retrospective study received institutional review board approval; parental prior informed consent for inclusion was obtained for all patients. All 50 patients were examined using our routine protocol; iodine (600 mg/kg) was the contrast medium (CM). Unenhanced and contrast-enhanced scans were obtained. We calculated the CM volume per vessel enhancement and performed univariate and multivariate linear regression analysis of the relationship between CM volume per vessel enhancement and each of the body parameters.

RESULTS

All patient characteristics were significantly related to CM volume per vessel enhancement (P < .05). Multivariate linear regression analysis revealed a significant correlation between CM volume per vessel enhancement and TBW, BSA, and LBW, but not the patient sex, age, CO, and height. The LBW model for CM volume per vessel enhancement yielded the highest determination coefficient (R² = .913) and the lowest Akaike Information Criterion (400.324).

CONCLUSIONS

Our findings support the delivery of an iodine dose adjusted to the LBW at c-CTA.

Development and Validation of Generalized Linear Regression Models to Predict Vessel Enhancement on Coronary CT Angiography

Objective

We evaluated the effect of various patient characteristics and time-density curve (TDC)-factors on the test bolus-affected vessel enhancement on coronary computed tomography angiography (CCTA). We also assessed the value of generalized linear regression models (GLMs) for predicting enhancement on CCTA.

Materials and Methods

We performed univariate and multivariate regression analysis to evaluate the effect of patient characteristics and to compare contrast enhancement per gram of iodine on test bolus (ΔHUTEST) and CCTA (ΔHUCCTA). We developed GLMs to predict ΔHUCCTA. GLMs including independent variables were validated with 6-fold cross-validation using the correlation coefficient and Bland–Altman analysis.

Results

In multivariate analysis, only total body weight (TBW) and ΔHUTEST maintained their independent predictive value (p < 0.001). In validation analysis, the highest correlation coefficient between ΔHUCCTA and the prediction values was seen in the GLM (r = 0.75), followed by TDC (r = 0.69) and TBW (r = 0.62). The lowest Bland–Altman limit of agreement was observed with GLM-3 (mean difference, −0.0 ± 5.1 Hounsfield units/grams of iodine [HU/gI]; 95% confidence interval [CI], −10.1, 10.1), followed by ΔHUCCTA (−0.0 ± 5.9 HU/gI; 95% CI, −11.9, 11.9) and TBW (1.1 ± 6.2 HU/gI; 95% CI, −11.2, 13.4).

Conclusion

We demonstrated that the patient's TBW and ΔHUTEST significantly affected contrast enhancement on CCTA images and that the combined use of clinical information and test bolus results is useful for predicting aortic enhancement.

Improved Calcium Scoring at Dual-Energy Computed Tomography Angiography Using a High-Z Contrast Element and Novel Material Separation Technique

OBJECTIVES

The aim of this study was to compare the accuracy of existing dual-energy computed tomography (CT) angiography coronary artery calcium scoring methods to those obtained using an experimental tungsten-based contrast material and a recently described contrast material extraction process (CMEP).

METHODS

Phantom coronary arteries of varied diameters, with different densities and arcs of simulated calcified plaque, were sequentially filled with water, iodine, and tungsten contrast materials and scanned within a thorax phantom at rapid-kVp-switching dual-energy CT. Calcium and contrast density images were obtained by material decomposition (MD) and CMEP. Relative calcium scoring errors among the 4 reconstructed datasets were compared with a ground truth, 120-kVp dataset.

RESULTS

Compared with the 120-kVp dataset, tungsten CMEP showed a significantly lower mean absolute error in calcium score (6.2%, P < 0.001) than iodine CMEP, tungsten MD, and iodine MD (9.9%, 15.7%, and 40.8%, respectively).

CONCLUSIONS

Novel contrast elements and material separation techniques offer improved coronary artery calcium scoring accuracy and show potential to improve the use of dual-energy CT angiography in a clinical setting.

Radiation dose reduction based on CNR index with low-tube voltage scan for pediatric CT scan: experimental study using anthropomorphic phantoms

Background

To figure out the relationship between image noise and contrast noise ratio (CNR) at different tube voltages, using anthropomorphic new-born and 1-year-old phantoms, and to discuss the feasibility of radiation dose reduction, based on the obtained CNR index from image noise. We performed helical scans of the anthropomorphic new-born and 1-year-old phantoms. The CT numbers of the simulated aorta and image noise of the simulated mediastinum were measured; then CNR was calculated on 80, 100, and 120-kVp images reconstructed with filtered back projection (FBP) and iterative reconstruction (IR). We also measured the center and surface dose in the case of CNR of 14 using radio-photoluminescence glass dosimeters.

Results

The CT number of the simulated aorta was increased with decreasing tube voltage from 120 to 80 kVp (362.5–535.1 HU for the new-born, 358.9–532.6 HU for the 1-year-old). At CNR of 14, the center dose was 0.4, 0.6 and 0.9 mGy at FBP and 0.5, 0.6 and 0.9 mGy at IR and with the new-born phantom acquired at 80, 100 and 120 kVp, respectively. The center dose for FBP image was reduced by 56% at 80 kVp, 34% at 100 kVp for the new-born and 36% at 80 kVp, 22% at 100 kVp for the 1-year-old compared with that at 120 kVp. We obtained a relationship between image noise and CNR at different tube voltages using the anthropomorphic new-born and 1-year-old phantoms.

Conclusion

The use of index of CNR with low-tube voltage may achieve further radiation dose reduction in pediatric CT examination.

Feasibility of a low concentration test bolus in CT angiography

AIM

To investigate the feasibility of using a low-concentration test bolus in abdominal aorta computed tomography (CT) angiography (CTA).

MATERIALS AND METHODS

In 10 patients referred for CTA of the abdominal aorta with a body mass index (BMI) ≤28 kg/m², a standard test bolus of 10 ml contrast medium (CM; 350 mg iodine/ml) was compared with a low-concentration test bolus (5 ml CM; 350 mg iodine/ml; 1:1 diluted with saline) in terms of time to peak enhancement (tPE) and peak enhancement (PE).

RESULTS

No significant differences were found between the standard and low-concentration test bolus in terms of tPE and PE.

CONCLUSIONS

A low-concentration test bolus (5 ml, 1:1 diluted with saline) is feasible in patients with a BMI ≤28 kg/m².