Optical tracking of contrast medium bolus to optimize bolus shape and timing in dynamic computed tomography

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.

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.

Revival of monophasic contrast injection protocols: superiority of a monophasic injection protocol compared to a biphasic injection protocol in high-pitch CT angiography

BACKGROUND

Biphasic injection protocols are frequently used because they yield homogenous contrast enhancement. We hypothesize that with faster scanners and shorter scan times, biphasic injection protocols are no longer necessary.

PURPOSE

To evaluate whether a monophasic injection protocol is equivalent to a biphasic protocol in terms of contrast enhancement and homogeneity.

MATERIAL AND METHODS

Repeated high-pitch CTA (pitch 3) and conventional standard-pitch computed tomography angiography (CTA) (pitch 1.2) from the cervical region to the symphysis was performed in seven beagles (11.2 ± 2.5 kg) in a cross-over study design. Arterial contrast enhancement was measured along the z-axis in the ascending, descending, and abdominal aorta and the iliac arteries. The z-axis is the longitudinal axis of the human body and at the same time the direction in which the CT table is moving. The data were analyzed using repeated measures ANOVA with a post-hoc t-test and visual assessment of the scans.

RESULTS

In high-pitch CTA, monophasic injection protocols were superior to biphasic injection protocols in enhancement levels (P < 0.05) and enhancement homogeneity along the z-axis (P < 0.05). In conventional CTA, enhancement levels did not differ. Contrast homogeneity was better for biphasic protocols.

CONCLUSION

High-pitch CTA monophasic injection protocols are superior to biphasic injection protocols, due to a higher and more homogeneous contrast enhancement with the same amount of contrast medium used.

Automatic scan triggering software "confused": Computed tomography angiography in foot arteriovenous malformation!

Multidetector computed tomography angiography (MDCTA) has become a well-established modality for limb angiography for a variety of indications. The technique of MDCTA depends on the scanner features including the number of detector rows, rotation speeds and single or dual source energy. Integral to a diagnostic quality CTA is the acquisition timing. Various techniques are available for determining the appropriate timing of scan acquisition which includes fixed delay, test bolus and the bolus tracking technique. The transit times of contrast from the aorta to the peripheral arteries shows a wide variability and is dependent upon the inter individual hemodynamic states. The bolus tracking technique is the most preferred one which allows reliable scan timing with acceptable contrast volume and radiation dose. Pitfalls with all these techniques are well described and we report one such technical pitfall in a case of left foot arteriovenous malformation (AVM) where the bolus tracking technique employed for scan triggering failed to initiate acquisition.