Author: mh/ktg

Coronary CTA Contrast Protocol gets Personalised

Adapting coronary CT angiography to the patient’s blood volume results in diagnostic image quality.

Session Topic: Cardiac CT: contrast agent and radiation dose
Session Date: Thursday, March 2nd 2017
Presentation Code: B-0143
Presentation Title: Individualisation of injection protocols to the individual patient’s blood volume and automated tube voltage selection in coronary CTA
Name of Speaker: Nienke Eijsvoogel, Maastricht University Medical Center, The Netherlands
Congress: ECR 2017, Vienna

Background

Coronary CT angiography (CCTA) is especially useful in patients with low and intermediate risk for coronary artery disease (CAD). “As patients with CAD frequently have multiple risks for the development of contrast-induced nephropathy, individualised contrast protocols gain more attraction,” said Nienke Eijsvoogel, Maastricht University Medical Center, The Netherlands. This can be achieved by either personalising the kV-settings chosen by the scanner, or by personalizing the contrast dose according to the patient’s body weight.
“The drawback of the body weight approach is that patients may have high body weight due to high muscle tissue or high fatty tissue,” explained Eijsvoogel: The more muscle tissue, the higher the blood volume. Therefore, these patients need more contrast volume, she said.

The purpose of this study was to assess the performance of individualised contrast media protocols based on the patient’s blood volume and automated tube voltage selection in CCTA.

CCTA Scan Protocol

138 patients referred for CCTA were included in the study. For CCTA at a 3rd-generation Dual-Source scanner, one of three standard protocols was used: either a prospectively or a retrospectively helical ECG-triggered sequence or a FLASH protocol.

Calculating the Contrast Dose

This is how Eijsvoogel and her colleagues calculated the contrast medium dosage: first, they used the Nadler formula – based on the patient’s sex, weight and height – to estimate the patient’s blood volume. Based on blood volume and the kV-setting chosen by the scanner, they calculated the individual flow rate. With the known scan time and three imaging protocols, they calculated the individual contrast volume to achieve a diagnostic attenuation of approximately 340 Hounsfield Units (HU).

Assessing Image Quality

Overall and segmental image quality was assessed by the achieved attenuation (HU), contrast-to-noise ratio (CNR), signal-to-noise ration (SNR), and subjectively by using a Likert scale.

Results

The mean age of the 138 patients was 58 years, their mean blood volume was 5.4 L for male and 4.1 L for female patients.

The overall attenuation was diagnostic in most cases. “We had some difficulties in the higher kVp settings,” said Eijsvoogel. “But this affected only nine patients and subjective image quality was rated diagnostic in all cases.”

Image quality was good or excellent even in the distal coronary artery segments.

The overall mean attenuation was higher than 325 HU in 93.6% of the patients. Overall CNR was higher than 10 and subjective image quality was between sufficient and excellent in all scans.

Segmental image quality: A total of 93.2% of all segments were assessable. A mean attenuation of at least 300 HU was achieved in 88.7% of all segments. Most cases in which the attenuation fell below 300 HU were in the distal segments. Only 0.2% proximal segments were not diagnostic due to motion artifacts. The mean CNR was higher than 10. An image quality between excellent and sufficient was achieved in 94.7% of all segments.

Conclusion

“We achieved diagnostic attenuation in 93.6% of all scans,” concluded Eijsvoogel. “Therefore, we think it is feasible to adapt coronary CT angiography to the patient’s blood volume and automated tube voltage selection.