Mathematical analysis of arterial enhancement and optimization of bolus geometry for CT angiography using the discrete fourier transform

Contrast media timing optimization for coronary CT angiography: a retrospective validation study in swine

OBJECTIVES

The objective was to retrospectively develop a protocol in swine for optimal contrast media timing in coronary CT angiography (CCTA).

METHODS

Several dynamic acquisitions were performed in 28 swine (55 ± 24 kg) with cardiac outputs between 1.5 and 5.5 L/min, for 80 total acquisitions. The contrast was injected (1mL/kg, 5mL/s, Isovue 370), followed by dynamic scanning of the entire aortic enhancement curve, from which the true peak time and aortic and coronary enhancements were recorded as the reference standard. Each dataset was then used to simulate two different CCTA protocols-a new optimal protocol and a standard clinical protocol. For the optimal protocol, the CCTA was acquired after bolus tracking-based trigging using a variable time delay of one-half the contrast injection time interval plus 1.5 s. For the standard protocol, the CCTA was acquired after bolus tracking-based triggering using a fixed time delay of 5 s. For both protocols, the CCTA time, aortic enhancement, coronary enhancement, and coronary contrast-to-noise ratio (CNR) were quantitatively compared to the reference standard measurements.

RESULTS

For the optimal protocol, the angiogram was acquired within -0.15 ± 0.75 s of the true peak time, for a mean coronary CNR within 7% of the peak coronary CNR. Conversely, for the standard CCTA protocol, the angiogram was acquired within -1.82 ± 1.71 s of the true peak time, for a mean coronary CNR that was 23% lower than the peak coronary CNR.

CONCLUSIONS

The optimal CCTA protocol improves contrast media timing and coronary CNR by acquiring the angiogram at the true aortic root peak time.

KEY POINTS

• This study in swine retrospectively developed the mathematical basis of an improved approach for optimal contrast media timing in CCTA. • By combining dynamic bolus tracking with a simple contrast injection timing relation, CCTA can be acquired at the peak of the aortic root enhancement. • CCTA acquisition at the peak of the aortic root enhancement should maximize the coronary enhancement and CNR, potentially improving the accuracy of CT-based assessment of coronary artery disease.

CT Angiography of Venoarterial Extracorporeal Membrane Oxygenation

Imaging plays a central role in the workup of thromboembolic events and bleeding complications in patients treated with venoarterial extracorporeal membrane oxygenation (ECMO) (VA-ECMO), and radiologists should be familiar with the expected hemodynamic changes and flow-related artifacts associated with the VA-ECMO system. VA-ECMO is a form of temporary mechanical circulatory support for critically ill patients with acute, refractory cardiac or cardiopulmonary failure. As the use of VA-ECMO continues to increase, it is important to be aware of associated hemodynamic changes and challenges at imaging. Patients treated with VA-ECMO are at high risk for thromboembolic events and bleeding complications and, thus, often require evaluation with CT angiography (CTA). VA-ECMO can be implemented by using central or peripheral cannulation. The peripheral femorofemoral VA-ECMO circuit in particular alters the sequence and direction of contrast medium enhancement substantially, resulting in flow-related artifacts that can mimic or obscure disease at CTA. Nonopacification can be mistaken for spurious thrombus or simulate complete vascular occlusion, while mixing artifacts can mimic dissections. Misinterpretation of flow-related CTA artifacts can lead to inappropriate surgical or medical intervention. A methodical and multiphasic approach should be taken to CTA imaging strategies and interpretation for patients treated with VA-ECMO. There is no universal CTA protocol for patients on VA-ECMO. Each protocol must be designed for the study indication, with consideration of the configuration of the ECMO cannulas, contrast material injection site, region of interest, native cardiac output, and ECMO flow rate. The authors provide examples of common and unusual VA-ECMO-related artifacts, with a focus on strategies for optimizing CTA image acquisition. Online supplemental material is available for this article. ^©RSNA, 2021.

Optimization of computed tomography contrast studies with a new, simple dosing regimen incorporating body size: examination of contrast effects in the thoracoabdominal aorta

The dosage of contrast agents for computed tomography contrast studies is calculated based on the parameter of actual body weight (ABW) to ensure reproducibility. The use of lean body weight (LBW) and adjustment for physique (lean or obese) improves accuracy. However, this method is complex, because LBW is not a general body parameter and requires a special device to measure. To solve this problem, contrast body weight (CBW), has been proposed as a new and simple parameter that considers physique. CBW is calculated by determining the blood volume ratio based on body height, ABW, and sex and can potentially correct for body size. It can be calculated by entering a formula in a Microsoft Excel sheet. Since CBW can be easily obtained using this general tool, we decided to compare the two body parameters of ABW and CBW. We compared ABW and CBW and demonstrated a higher correlation between CBW-based dosing and the amount of iodine used per body weight than with ABW-based dosing. CBW-based dosing allows correction for body size. This indicates that contrast enhancement over a spectrum of lean or obese examinees can be linearly evaluated. To date, this method has shown good results.

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.

Evaluation of four injection profiles for uniform contrast-enhanced signal intensity profiles in MR angiography

BACKGROUND

Gadolinium concentration variation during acquisition of contrast-enhanced MR angiography (CE-MRA) may lead to artifacts.

PURPOSE

To compare signal intensity (SI) profiles of four different contrast agent injection strategies during CE-MRA with the goal of minimizing SI variation during acquisition.

STUDY TYPE

Prospective.

SUBJECTS

Forty subjects randomized to receive one of four injection profiles of gadobenate dimeglumine (0.1 mmol/kg), either undiluted (0.5 M) or diluted to 40 ml total volume. Tested profiles: 1) nondiluted single-phase ("standard" NS; 1.6 ml/s), 2) diluted single-phase (DS; 1.6 ml/s), 3) diluted biphasic (DB; 9 ml @ 3.3 ml/s, 29 ml @ 1.4 ml/s), 4) patient-tailored protocol using linear prediction (DT).

FIELD STRENGTH/SEQUENCE

Time-resolved SI measured at 3T with spoiled gradient echo sequences having analogous parameters to those of CE-MRA.

ASSESSMENT

Plateau arrival time, rise time, duration, peak and tail SI, plateau quality (sum of squared residuals; SSR), average SI for each injection type derived were used.

STATISTICAL TEST

Two-tailed t-test.

RESULTS

Peak SI, arrival, and rise times were not significantly different between groups, excepting peak SI DB slightly > DS (P = 0.042). Duration of NS vs. the diluted groups was significantly shorter (all P < 0.0001), and DS duration was significantly shorter than that of DT and DB (NS 11.4 ± 3.5 vs. DS 22.9 ± 4.3, DB 25.4 ± 2.3, DT 28.3 ± 4.1 sec). Quality (SSR) of the 20-second plateau was significantly better for DS, DB, DT as compared with NS (all P < 0.001).

DATA CONCLUSION

Three different strategies to power-inject diluted gadobenate dimeglumine targeting a 20-second plateau produced SI profiles with longer duration, more consistent plateau, and no significant loss in peak SI. Such injection profiles may provide more uniform SI during CE-MRA, potentially reducing blurring artifacts.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:1808-1816.

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.

[Effects of Mathematical Analysis of Test Injection on the CT Value Estimation of the Aorta]

The circulation time and the mechanical acceleration time (MA time) of an automatic injector were simulated using pharmacokinetic analysis. The addition method and transfer-function method, which are mathematical techniques used for analyzing the test bolus method in multi-detector computed tomography, were used to verify the accuracy of estimation of the time-enhancement curve (TEC) of the main bolus. The TEC estimated using the addition method, and the TEC of the main bolus matched completely only if the MA time of the automatic injector was set to 0 seconds. Moreover, the estimation accuracy of the TEC deteriorated when the MA time was set according to the TEC estimated by the addition method. In contrast, the TEC estimated using the transfer-function method, except when the MA time of the automatic injector was 0 seconds, had higher accuracy than the TEC estimated using the addition method. In this study, the addition method, a number of additions of TEC, and MA time of the automatic injector were found to have a negative effect on the estimation accuracy of the main bolus. The use of the transfer-function method for determining the TEC and the MA time has a positive effect on the estimation accuracy of the main bolus.

Improved image-quality consistency in coronary CT angiography using a test-bolus-based individually tailored contrast medium injection protocol

AIM

To develop and validate a test bolus (TB)-based quantitative model to create an individualised contrast medium injection protocol for use at coronary computed tomography angiography (CCTA) to improve patient-to-patient uniformity of intracoronary attenuation.

MATERIALS AND METHODS

In the model-building phase, 175 patients who underwent CCTA using a traditional contrast medium injection protocol were recruited. A personalised injection equation was proposed according to the relationship between aortic enhancement and the haemodynamic parameters obtained from the TB. In the model-validation phase, a target aortic enhancement of 350 HU was set. Two hundred and fifteen additional CCTA examinations were performed using the proposed personalised injection model. Comparisons of inter-individual variability between the traditional and the proposed personalised injection protocol were performed.

RESULTS

In the model-building phase, a high positive correlation between aortic enhancement and the haemodynamic parameters obtained from the TB was found. As a result, a personalised injection equation was determined using linear regression. In the model-validation phase, the average aortic enhancement was 350.5 HU, without significant differences from the preset level. Using the TB-based personalised injection protocol, inter-individual variability of aortic enhancement was significantly reduced (71.8 versus 38.9 HU, p<0.001) and patients who were scanned at 100 kVp had a reduction in the average contrast medium flow rate from 4.1 to 3.2 ml/s (p<0.001).

CONCLUSIONS

The proposed TB-based injection protocol can achieve a desired preset and stable aortic enhancement.

Contrast Gradient-Based Blood Velocimetry With Computed Tomography: Theory, Simulations, and Proof of Principle in a Dynamic Flow Phantom

OBJECTIVES

The aim of this study was to introduce a new theoretical framework describing the relationship between the blood velocity, computed tomography (CT) acquisition velocity, and iodine contrast enhancement in CT images, and give a proof of principle of contrast gradient-based blood velocimetry with CT.

MATERIALS AND METHODS

The time-averaged blood velocity (v(blood)) inside an artery along the axis of rotation (z axis) is described as the mathematical division of a temporal (Hounsfield unit/second) and spatial (Hounsfield unit/centimeter) iodine contrast gradient. From this new theoretical framework, multiple strategies for calculating the time-averaged blood velocity from existing clinical CT scan protocols are derived, and contrast gradient-based blood velocimetry was introduced as a new method that can calculate v(blood) directly from contrast agent gradients and the changes therein. Exemplarily, the behavior of this new method was simulated for image acquisition with an adaptive 4-dimensional spiral mode consisting of repeated spiral acquisitions with alternating scan direction. In a dynamic flow phantom with flow velocities between 5.1 and 21.2 cm/s, the same acquisition mode was used to validate the simulations and give a proof of principle of contrast gradient-based blood velocimetry in a straight cylinder of 2.5 cm diameter, representing the aorta.

RESULTS

In general, scanning with the direction of blood flow results in decreased and scanning against the flow in increased temporal contrast agent gradients. Velocity quantification becomes better for low blood and high acquisition speeds because the deviation of the measured contrast agent gradient from the temporal gradient will increase. In the dynamic flow phantom, a modulation of the enhancement curve, and thus alternation of the contrast agent gradients, can be observed for the adaptive 4-dimensional spiral mode and is in agreement with the simulations. The measured flow velocities in the downslopes of the enhancement curves were in good agreement with the expected values, although the accuracy and precision worsened with increasing flow velocities.

CONCLUSIONS

The new theoretical framework increases the understanding of the relationship between the blood velocity, CT acquisition velocity, and iodine contrast enhancement in CT images, and it interconnects existing blood velocimetry methods with research on transluminary attenuation gradients. With these new insights, novel strategies for CT blood velocimetry, such as the contrast gradient-based method presented in this article, may be developed.

Individually adapted tube current selection and contrast medium injection protocol of coronary CT angiography based on test bolus parameters: a feasibility study

BACKGROUND

Test bolus is mostly used to determine the starting point of a full cardiac scanning with respect to injection of a larger bolus of contrast material. So far there are limited data demonstrating the feasibility of using information obtained from a test bolus to adjust contrast delivery protocols and tube current individually during coronary computed tomography angiography (CCTA).

PURPOSE

To evaluate the feasibility of individually adapted tube current selection and contrast injection protocols of CCTA based on test bolus parameters.

MATERIAL AND METHODS

Test bolus followed by CCTA was performed in 93 patients at 100 kV and in 81 patients at 120 kV, respectively. Simulated attenuation of the descending aorta (SimDA) of CCTA was calculated at a fixed contrast injection rate of 4 mL/s. Univariate and multivariate comparisons were performed to identify associations of SimDA and image noise of CCTA (NoiseCCTA) with test bolus information and patient-related factors including body weight (BW), body mass index (BMI), and body surface area (BSA).

RESULTS

Compared with BW, BMI, and BSA, SimDA was more closely related to the peak time of left ventricle and peak enhancement of right ventricle obtained from test bolus (r = 0.495 and r = 0.642 for 100 and 120 kV protocol, respectively). Similarly, NoiseTB was much more closely related to NoiseCCTA (r = 0.740 and r = 0.630 for 100 and 120 kV protocol, respectively) when compared with BW, BMI, and BSA.

CONCLUSION

It is feasible to individually adapt tube current and contrast injection protocol of CCTA based on the information of test bolus.

A new method with variable injection parameters in contrast-enhanced CT: a phantom study for evaluating an aortic peak enhancement

Contrast-enhanced CT employs a standard uniphasic single-injection method (SIM), wherein administration is based on two parameters: the iodine administration rate (mgI/s) and the injection duration (s). However, as the SIM uses a fixed iodine administration rate, only a uniform contrast enhancement can be achieved with this method. The iodine administration rate can be increased only by increasing the iodine dose or shortening the injection duration, and no arbitrary adjustments can be made to the peak enhancement characteristics of the time-enhancement curves (TECs) at the fixed injection parameters used in the SIM. To address this problem, we developed a variable injection method (VIM) with a new parameter, the variation factor (VF), to adjust the TECs. A phantom study with the VIM indicated that arbitrary adjustments to the iodine administration rate could be made without changing the injection duration or increasing the iodine load. In our study, VFs of 0.3 and 0.5, which showed earlier achievement of peak enhancements, showed better temporal separation between arterial vasculature and parenchyma or the venous vasculature than that obtained with the SIM. The higher peak enhancement provided by the VF of 0.3 was also considered to improve the contrast in qualitative diagnostic examinations. A VF of 0.5 increased the duration of the enhancement and was considered to produce stable enhancement of contrast in vascular investigations. The VF is now an essential parameter, and the VIM is useful as a reasonable contrast method that may contribute to both improved visualization and improvement in the accuracy of morphologic diagnosis.

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

RATIONALE AND OBJECTIVES

The purpose of our study was to compare test bolus techniques using undiluted or diluted contrast material for their ability to predict aortic enhancement on coronary computed tomographic angiography (c-CTA) images.

MATERIALS AND METHODS

We divided 200 consecutive patients who underwent c-CTA on a 64-MDCT scanner into two groups. In group A (n = 100), we used a test bolus of undiluted contrast material and in group B (n = 100), the contrast material was diluted. The injection volume was body weight × 0.2 (contrast material 100%) in group A and body weight × 0.7 (contrast material 30%, saline 70%) in group B. We then compared the CT number in the ascending aorta on c-CTA images obtained with undiluted and diluted contrast media to the CT number on c-CTA images.

RESULTS

The mean CT number in the ascending aorta was significantly higher in group B than group A (217.1 vs. 157.4 HU, P < .001). There was a significant difference in the correlation between the CT number of the ascending aorta on c-CTA images and on images acquired with the test bolus using undiluted or diluted test bolus (P < .001). In group B, the correlation had a strong positive linear relationship (r = 0.72, P < .001), whereas in group A the positive linear relationship was weak (r = 0.36).

CONCLUSIONS

The test bolus with diluted contrast material was useful for predicting aortic enhancement before c-CTA scanning.

Use of high-concentration contrast media in multiple-detector-row CT: principles and rationale

Contrast-medium-enhanced multiple-detector-row CT (MDCT) is a powerful technique for vascular and hepatic imaging. With increasingly faster acquisition speeds, which have become possible with latest 8- and 16-channel scanner systems, contrast medium delivery is becoming increasingly difficult. This article reviews the pharmacokinetic and physiologic principles of vascular and hepatic enhancement following the intravenous injection of iodinated contrast medium. The effects of user-selectable injection parameters, such as the injection rate, the injection duration, and the contrast medium concentration on arterial and parenchymal enhancement are elucidated. Equipped with this knowledge, rational injection strategies for CT angiographic protocols for scanners with different acquisition speeds are derived. Furthermore, injection and timing protocols, optimized for hepatic MDCT during the early arterial, late arterial, and parenchymal phases, are developed.

Novel contrast-injection protocol for coronary computed tomographic angiography: contrast-injection protocol customized according to the patient's time-attenuation response

We developed a new individually customized contrast-injection protocol for coronary computed tomography (CT) angiography based on the time-attenuation response in a test bolus, and investigated its clinical applicability. We scanned 60 patients with suspected coronary diseases using a 64-detector CT scanner, who were randomly assigned to one of two protocols. In protocol 1 (P1), we estimated the contrast dose to yield a peak aortic attenuation of 400 HU based on the time-attenuation response to a small test-bolus injection (0.3 ml/kg body weight) delivered over 9 s. Then we administered a customized contrast dose over 9 s. In protocol 2 (P2), the dose was tailored to the patient's body weight; this group received 0.7 ml/kg body weight with an injection duration of 9 s. We compared the two protocols for dose of contrast medium, peak attenuation, variations in attenuation values of the ascending aorta, and the success rate of adequate attenuation (250-350 HU) of the coronary arteries. The contrast dose was significantly smaller in P1 than in P2 (36.9 ± 9.2 vs 43.1 ± 7.0 ml, P < 0.01). Peak aortic attenuation was significantly less under P1 than under P2 (384.1 ± 25.0 vs 413.5 ± 45.7, P < 0.01). The mean variation (standard deviation) of the attenuation values was smaller in P1 than in P2 (25.0 vs 45.7, P < 0.01). The success rate of adequate attenuation of the coronary arteries was significantly higher with P1 than with P2 (85.0 vs 65.8 %, P < 0.01). P1 facilitated a reduction in the contrast dose, reduced the individual variations in peak aortic attenuation, and achieved optimal coronary CT attenuation (250-350 HU) more frequently than P2.

Multi-detector CT angiographic imaging in the follow-up of patients after endovascular abdominal aortic aneurysm repair (EVAR)

BACKGROUND

Multidetector computed tomography (MDCT) angiography represents the standard of reference in the follow-up of patients after endovascular abdominal aortic aneurysm repair (EVAR), being effective in the detection of the full spectrum of possible complications on both axial and 3D images.

METHODS

The purpose of this article is to review the normal CT angiography findings of the different types of stent-grafts and to describe the radiological findings of early and late complications after EVAR on axial and reconstructed images. A selection of cases of post-EVAR MDCT angiography is presented to learn the techniques most commonly used for endovascular treatment, the correct CT scanning technique to acquire the data, the full gamut of possible procedure-related complications and how these complications usually appear on CT images.

CONCLUSION

MDCT angiography is an effective and specific technique in both the pre- and postoperative settings of EVAR procedures. A better understanding of the procedure, the devices, the normal postoperative imaging features and the possible procedure-related complications ensures optimal planning and follow-up of patients undergoing an EVAR procedure.

Thoraco-abdominal high-pitch dual-source CT angiography: experimental evaluation of injection protocols with an anatomical human vascular phantom

OBJECTIVE

To experimentally evaluate three different contrast injection protocols at thoraco-abdominal high-pitch dual-source computed tomography angiography (CTA), with regard to level and homogeneity of vascular enhancement at different cardiac outputs.

MATERIALS AND METHODS

A uniphasic, a biphasic as well as an individually tailored contrast protocol were tested using a human vascular phantom. Each protocol was scanned at 5 different cardiac outputs (3-5L/min, steps of 0.5L/min) using an extracorporeal cardiac pump. Vascular enhancement of the thoraco-abdominal aorta was measured every 5 cm. Overall mean enhancement of each protocol and mean enhancement for each cardiac output within each protocol were calculated. Enhancement homogeneity along the z-axis was evaluated for each cardiac output and protocol.

RESULTS

Overall mean enhancement was significantly higher in the uniphasic than in the other two protocols (all p<.05), whereas the difference between the biphasic and tailored protocol was not significant (p=.76). Mean enhancement among each of the 5 cardiac outputs within each protocol was significantly different (all p<.05). Only within the tailored protocol mean enhancement differed not significantly at cardiac outputs of 3.5L/min vs. 5L/min (484 ± 25 HU vs. 476 ± 19 HU, p=.14) and 4 vs. 5L/min (443 ± 49 HU vs. 476 ± 19 HU, p=.05). Both, uniphasic and tailored protocol yielded homogenous enhancement at all cardiac outputs, whereas the biphasic protocol failed to achieve homogenous enhancement.

CONCLUSION

This phantom study suggests that diagnostic and homogenous enhancement at thoraco-abdominal high-pitch dual-source CTA is feasible with either a uniphasic or an individually tailored contrast protocol.

Indications, imaging technique, and reading of cardiac computed tomography: survey of clinical practice

OBJECTIVES

To obtain an overview of the current clinical practice of cardiac computed tomography (CT).

METHODS

A 32-item questionnaire was mailed to a total of 750 providers of cardiac CT in 57 countries.

RESULTS

A total of 169 questionnaires from 38 countries were available for analysis (23%). Most CT systems used (94%, 207/221) were of the latest generation (64-row or dual-source CT). The most common indications for cardiac CT was exclusion of coronary artery disease (97%, 164/169). Most centres used beta blockade (91%, 151/166) and sublingual nitroglycerine (80%, 134/168). A median slice thickness of 0.625 mm with a 0.5-mm increment and an 18-cm reconstruction field of view was used. Interpretation was most often done using source images in orthogonal planes (92%, 155/169). Ninety percent of sites routinely evaluate extracardiac structures on a large (70%) or cardiac field of view (20%). Radiology sites were significantly more interested in jointly performing cardiac CT together with cardiology than cardiologists. The mean examination time was 18.6 ± 8.4 min, and reading took on average 28.7 ± 17.8 min.

CONCLUSIONS

Cardiac CT has rapidly become established in clinical practice, and there is emerging consensus regarding indications, conduct of the acquisition, and reading.

The optimal contrast media policy in CT of the liver. Part I: Technical notes

Latest developments of multidetector computed tomography (MDCT), which is today considered a real volumetric technique, have revolutionized abdominal imaging. Technological improvements such as higher spatial resolution, larger volume coverage and higher temporal resolution, have reduced scan times allowing CT studies of the abdomen within a single breath-hold. Furthermore, the increased number of slices, the submillimetric collimation, and the use of multiple dynamic post-contrast phases per single examination, may all contribute to increase the radiation exposure of single patients. The aim of this review is to discuss different parameters affecting contrast media enhancement, as vascular enhancement, parenchymal enhancement and timing, in order to minimize the amount of contrast medium injected and the radiation exposure.

Cardiothoracic CT angiography: current contrast medium delivery strategies

OBJECTIVE

Over the last decade, rapid technologic evolution in CT has resulted in improved spatial and temporal resolution and acquisition speed, enabling cardiothoracic CT angiography to become a viable and effective noninvasive alternative in the diagnostic algorithm. These new technologic advances have imposed new challenges for the optimization of contrast medium delivery and image acquisition strategies.

CONCLUSION

Thorough understanding of contrast medium dynamics is essential for the design of effective acquisition and injection protocols. This article provides an overview of the fundamentals affecting contrast enhancement, emphasizing the modifications to contrast material delivery protocols required to optimize cardiothoracic CT angiography.

Current contrast media delivery strategies for cardiac and pulmonary multidetector-row computed tomography angiography

Recent advances in multidetector-row computed tomography (MDCT) have led to substantial improvements in coverage area, acquisition speed, and temporal/spatial resolution, which have strengthened the performance of thoracic and cardiac MDCT angiography but have also imposed new challenges for optimization of contrast medium enhancement and scan acquisition strategies. Understanding contrast media dynamics is fundamental for the design of scan acquisition and injection protocols. This article examines the fundamentals of the physiological and contrast delivery factors that determine the quality of contrast enhancement, emphasizing the modifications required in contrast delivery protocols for optimizing cardiothoracic MDCT angiography with modern-era MDCT scanners.

Contrast material injection protocol with the dose adjusted to the body surface area for MDCT aortography

OBJECTIVE

The objective of our study was to investigate the effect on aortic enhancement of contrast material volumes adjusted for a patient's body surface area (BSA) at CT angiography (CTA).

SUBJECTS AND METHODS

A 64-MDCT scanner was used to perform CTA of the whole aorta in 89 patients (mean age, 68.7 years) with confirmed or suspected aortoiliac disease. The patients were divided into groups: a body weight (BW) group (n = 45) and a BSA (n = 44) group. The contrast dose was 360 mg I/kg BW in the BW group and 12,753 mg I/m(2) BSA in the BSA group. Because the average BW of Japanese adults is approximately 60 kg, the contrast dose in the two protocols was identical in patients weighing 60 kg. We compared aortic enhancement achieved with the two protocols using the two-tailed Student's t test, and we used the generalized linear model to analyze the effect of patient age, sex, and BW on aortic enhancement in each protocol group.

RESULTS

The mean aortic enhancement in the BW and BSA groups was 324.2 and 311.7 HU, respectively; the difference was not significant (p = 0.26). In the BW group, BW had a statistically significant effect on aortic enhancement (p < 0.01), whereas neither patient age nor sex did (p = 0.08 and 0.07, respectively). In the BSA group, the age, sex, BW, and BW by sex had no statistically significant effect on aortic enhancement (p = 0.33, 023, 0.10, and 0.16, respectively).

CONCLUSION

Under the BSA protocol, aortic enhancement tended to be consistent and adequate regardless of patient BW.

A personalized and optimal approach for dosing contrast material at coronary computed tomography angiography

A method for constructing a personalized contrast medium protocol at contrast enhanced, Coronary CT Angiography (CCTA) is presented. A one compartment pharmacokinetic model is parameterized and identified with a minimal data set from a test-bolus injection. A direct-search optimization is performed to construct a protocol that achieves target enhancement in the cardiac structures. Clinical results demonstrating the method's ability to achieve prospectively chosen image enhancement levels while reducing contrast medium dose are presented.

Adaptive Bolus-chasing Computed Tomography Angiography in the Cases of Symmetric and Asymmetric Arterial Flows in Peripheral Arteries

Synchronization of the contrast bolus peak and CT imaging aperture is a crucial issue for computed tomography angiography (CTA). It affects the CTA image quality and the amount of contrast dose. A whole-body CTA procedure means to scan from the abdominal aorta to pedal arteries. In this context, the synchronization is much more difficult with the asymmetric arterial flow in lower extremities than in the case of symmetric arterial flow. In this paper, we propose an adaptive optimal controller to chase the contrast bolus peak while it propagates in the aorta and lower extremities with symmetric flow. In the case of asymmetric flow after the contrast bolus splitting into two lower limbs, we propose a dynamic programming approach to cover the lower limbs optimally. Simulation and experimental results show that the proposed methods outperform the current constant-speed method substantially.

Self-tracking of contrast kinetics for automatic triggering of contrast-enhanced whole-heart coronary magnetic resonance angiography

PURPOSE

To develop a method for automatically triggering centric data acquisition during contrast-enhanced whole-heart coronary magnetic resonance angiography (MRA).

MATERIALS AND METHODS

The hypothesis of this work is that the blood signal changes during contrast infusion can be estimated by obtaining a projection of the heart during inversion-recovery prepared data acquisition. A validation study was performed on seven healthy volunteers to test this hypothesis. The peak blood signal enhancement detected from the projection was then used to automatically trigger the start of central k-space data acquisition. Simulations were performed to compare the signal-to-noise ratio (SNR) of the proposed self-triggering method with the fixed delay method. Six healthy volunteers were scanned on a 3T MR system using the proposed self-triggered method to test its effectiveness on coronary artery visualization.

RESULTS

Based on the validation study, the self-triggering method provides an accurate representation of the contrast enhancement. Based on the simulations, self-triggering with centric ordering is expected to give a 27% higher SNR than linear ordering with a fixed imaging delay. Self-triggering was successfully used in all volunteers and showed excellent depiction of the major coronary arteries.

CONCLUSION

The self-triggering method can be used to automatically determine the optimal delay time for central k-space acquisition, for each individual subject, without the need of any extra setup or user interaction.

Adaptive Bolus Chasing Computed Tomography Angiography: Control Scheme and Experimental Results

In this paper, a new adaptive bolus-chasing control scheme is proposed to synchronize the bolus peak in a patient's vascular system and the imaging aperture of a computed tomography (CT) scanner. The proposed control scheme is theoretically evaluated and experimentally tested on a modified Siemens SOMATOM Volume Zoom CT scanner. The first set of experimental results are reported on bolus-chasing CT angiography using realistic bolus dynamics, real-time CT imaging and adaptive table control with physical vasculature phantoms. The data demonstrate that the proposed control approach tracks the bolus propagation well, and clearly outperforms the constant-speed scheme that is the current clinical standard.

Optimization of cardiac MSCT contrast injection protocols: dependency of the main bolus contrast density on test bolus parameters and patients' body weight

RATIONALE AND OBJECTIVES

Our aim was to evaluate the correlation of test bolus (TB) curve parameters with main bolus (MB) contrast density for cardiac 16-slice computed tomography, and to correlate observed enhancement with patient body weight.

MATERIALS AND METHODS

Sixty patients with known or suspected coronary artery disease were included in a prospective double-blind study. Contrast material containing 300 mg iodine/mL (Iomeprol 300; Imeron 300, Bracco Imaging SpA, Milan, Italy) and 400 mg iodine/mL (Iomeprol 400; Imeron 400) was injected at a rate of 1 g of iodine/second. Contrast densities (Hounsfield units) of the MB were determined in the left cardiac system. The peak density (PD) of maximum attenuation and the area under the curve (AUC) of the TB curve were calculated for each patient. The dependency of MB contrast attenuation on these parameters and on patient body weight was evaluated.

RESULTS

Positive correlations (r = 0.52 and r = 0.56, respectively; P < .0001) were obtained between the PD and AUC of the TB curve with the mean density of the MB. Stronger correlations (r = 0.63 and r = 0.64, respectively; P < .0001) between PD and AUC of the TB curve and MB attenuation were found when patient body weight was included in the analysis.

CONCLUSIONS

Strong correlation of the PD and AUC of the TB curve with the mean density of the MB is observed when patient body weight is considered. Contrast injection protocols may be optimized, and variations of MB contrast density in the left ventricle and main coronary arteries reduced, by taking these TB parameters and the weight of the patient into account.

Optimal dose and injection duration (injection rate) of contrast material for depiction of hypervascular hepatocellular carcinomas by multidetector CT

PURPOSE

The aim of this study was to investigate the optimal dose and injection duration of contrast material (CM) for depicting hypervascular hepatocellular carcinomas (HCCs) during the hepatic arterial phase with multidetector row computed tomography (CT).

MATERIALS AND METHODS

The study population consisted of 71 patients with hypervascular HCCs. After unenhanced scans, the first (early arterial phase, or EAP), second (late arterial phase, or LAP), and third (equilibrium phase) scanning was started at 30, 43, and 180 s after injection of contrast material (CM). During a 33-s period, patients with a body weight < or =50 kg received 100 ml of non-ionic CM with an iodine concentration of 300 mg I/ml; patients whose body weight was >50 kg received 100 ml of CM with an iodine concentration of 370 mg I/ml. First, we measured enhancement in the abdominal aorta and tumor-to-liver contrast (TLC) during the EAP and LAP. Next, to investigate the relation between aortic enhancement and TLC during the LAP, two radiologists visually assessed the conspicuity of hypervascular HCCs during the LAP using a 3-point scale: grade 1, poor; grade 2, fair; grade 3, excellent. Finally, to examine the effect of the CM dose and injection duration on aortic enhancement during the EAP, we simulated aortic enhancement curves using test bolus data obtained for 10 HCC patients and the method of Fleischmann and Hittmair.

RESULTS

A relatively strong correlation was observed between aortic enhancement during the EAP and TLC during the LAP (correlation coefficient r = 0.75, P < 0.001). The 95% confidence intervals for the population mean for aortic enhancement during EAP in patients with tumor conspicuity grades of 1, 2, and 3 were 188.5, 222.4; 228.8, 259.3; and 280.2, 322.5 HU (Hounsfield Unit), respectively. Thus, we considered the lower limit of the aortic enhancement value for excellent depiction of HCCs during EAP to be 280 HU. To achieve an aortic enhancement value of >280 HU for aortic enhancement simulations during EAP, the injection duration should be <25 s for patients receiving a CM dose of 1.7 ml/kg with 300 mg I/ml iodine and <30 s for those receiving 2.0 ml/kg.

CONCLUSIONS

For excellent depiction of hypervascular HCCs during the hepatic arterial phase, the injection duration should be <25 s in patients receiving a CM dose of 1.7 ml/kg with 300 mg I/ml iodine and <30 s for patients receiving 2.0 ml/kg.

Coronary CT Angiography

Owing to ongoing technical refinements and intense scientific and clinical evaluations, computed tomography (CT) of the heart has left the research realm and matured into a clinical application that is about to fulfill its promise to replace invasive cardiac catheterization in selected patient populations. CT coronary angiography is technically more challenging than other CT applications owing to the nature of its target, the continuously moving heart. Rapid technical developments in this field require constant adaptation of acquisition protocols. These challenges, however, are in no way insurmountable for users with knowledge of the general CT technique. The intent of this communication is to provide those interested in and involved with coronary CT angiography with a step-by-step "manual" describing the authors' approach to performing coronary CT angiography. Included are considerations regarding appropriate patient selection, patient medication, radiation protection, contrast enhancement, acquisition and reconstruction parameters, image display and analysis techniques, and the radiology report. The recommendations are based on the authors' experience, which spans the evolution of multi-detector row CT for cardiac applications, from its beginning to the advent of the most current generations of 64-section and dual-source CT technologies, which they believe herald the entrance of this examination into routine clinical practice.

Coronary Angiography by 64-Detector Row Computed Tomography Using Low Dose of Contrast Material with Saline Chaser

OBJECTIVE

To assess the influence of total injection volume on thoracic great vessels and coronary arteries enhancement in 64-detector row computed tomography (CT) coronary angiography using low dose of contrast material.

METHODS

Sixty patients underwent cardiac CT (64 x 0.5 mm, 0.4 rot/s) using 40 mL of contrast material (350 mg of Iodine per milliliter) in 30 patients and 50 mL in 30 patients. Computed tomography densities (Hounsfield units) in ascending aorta, descending aorta, and main pulmonary artery were measured at every second with the time of CT data acquisition recorded in each reconstructed image. Computed tomography densities of proximal and distal coronary arteries were also measured. Differences in CT densities between 40 and 50 mL contrast material were assessed with the Student t test. In addition, the relation between the injection volume (mL) of contrast material per kilogram body weight and contrast enhancement in coronary arteries was studied.

RESULTS

The average attenuations in the ascending and descending aorta and coronary arteries were significantly lower in 40-mL group than in 50-mL group (<0.05). In addition, the average attenuations in the pulmonary artery were significantly lower in 40-mL group than 50-mL group (<0.01). Every patient with the total injection volume of more than 0.9 mL/kg body weight showed a contrast enhancement more than 250 Hounsfield units.

CONCLUSIONS

The reduction of total injection volume lowered the enhancement of thoracic great vessels and coronary arteries in 64-detector row cardiac CT. The injection volume of at least 0.9 mL/kg body weight was necessary for a steady contrast enhancement in coronary arteries.

Patient-specific Contrast Injection Protocols for Cardiovascular Multidetector Row Computed Tomography

OBJECTIVE

To develop patient-specific contrast injections for uniform enhancement of cardiovascular multidetector row computed tomography (MDCT) images.

METHODS

Sixty-two patients were imaged using electrocardiogram (ECG)-gated spiral MDCT. Thirty patients (group 1) received a uniphasic injection; the remaining 32 patients (group 2) received patient-specific multiphasic injections. For group 2 patients, the vasculature between injection and imaging sites was considered a "gray box" whose transfer function was determined from a test bolus injection and the resulting enhancement in the left side of the heart. This transfer function was used to determine the injection necessary to achieve 250 Hounsfield units in the left side of the heart. Intraindividual and interindividual variation of enhancement were determined for both groups. Superior vena cava (SVC) artifacts were graded on a 4-point scale.

RESULTS

The measured indices of intraindividual variation were significantly smaller in group 2 than in group 1 (P < 0.05), indicating improved uniformity with patient-specific injections. The interindividual variation of mean enhancement in group 2 was smaller than in group 1, but the difference was not significant. The severity of SVC artifacts was significantly reduced (P < 0.05) for thinner patients (<83 kg) in group 2 compared with similar patients in group 1.

CONCLUSIONS

Patient-specific multiphasic contrast injections yielded more uniform enhancement in the left side of the heart on MDCT images with reduced intraindividual variation of enhancement compared with standard uniphasic injections. Patient-specific injections also reduced SVC artifacts in patients <83 kg.

Coronary CTA

Computed tomography (CT) of the heart, because of ongoing technical refinement and intense scientific and clinical evaluation, has left the research realm and has matured into a clinical application that is about to fulfill its promise to replace invasive cardiac catheterization in some patient populations. By nature of its target, the continuously moving heart, CT coronary angiography is technically more challenging than other CT applications. Also, rapid technical development requires constant adaptation of acquisition protocols. Those challenges, however, are in no way insurmountable for users with knowledge of general CT technique. The intent of this communication is to provide for those interested in and involved with coronary CT angiography a step-by-step manual, introducing our approach to performing coronary CT angiography. Included are considerations regarding appropriate patient selection, patient medication, radiation protection, contrast enhancement, acquisition and reconstruction parameters, image display and analysis techniques and also the radiology report. Our recommendations are based on our experience which spans the evolution of multidetector-row CT for cardiac applications from its beginnings to the most current iterations of advanced acquisition modalities, which we believe herald the entrance of this test into routine clinical practice.