Dose Reduction of Dynamic Computed Tomography Myocardial Perfusion Imaging by Tube Voltage Change: Investigation in a Swine Model

Abstract

Background: It is unclear whether tube voltage influences the measurement of perfusion parameters. The present study sought to evaluate the influence of tube voltage change on myocardial blood flow (MBF) measurements in dynamic computed tomography myocardial perfusion imaging (CTP).

Methods and results: Seven swine [mean weight 55.8 kg ± 1.6 (standard deviation)] underwent rest and stress dynamic CTP with tube voltages of 100 and 70 kV. The image noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), radiation dose and MBF value were compared. The 70 kV images had higher CT attenuation and higher image noise (27.9 ± 2.4 vs. 21.5 ± 1.9, P < 0.001) than the 100 kV images, resulting in a higher SNR (20.5 ± 1.6 vs. 15.6 ± 1.8, P < 0.001) and CNR (17.6 ± 1.5 vs. 12.4 ± 1.7, P < 0.001). Compared to the use of conventional 100 kV, 70 kV yielded an approximately 64.6% radiation dose reduction while generating comparable MBF values, both at rest (88.3 ± 14.9 ml/100 g/min vs. 85.6 ± 17.4 ml/100 g/min, P = 0.21) and stress (101.4 ± 21.5 ml/100 g/min vs. 99.6 ± 21.4 ml/100 g/min, P = 0.58) states.

Conclusion: Dynamic CTP using 70 kV instead of 100 kV does not substantially influence the MBF value but significantly reduces the radiation dose. Additional research is required to investigate the clinical significance of this change.

Keywords: cardiac imaging techniques; computed tomography; image quality enhancement; myocardial perfusion; radiation dosage.

FIGURE 1

Dynamic perfusion acquisition at 70 kV. Fused MBF map and CT images, divided according to AHA segments (A,B). The graph view displays the AIF (displayed in blue), TAC of the myocardium (displayed in yellow), and reconvolution curve (displayed in pink). A smooth fitting curve (pink line) was obtained through the TAC of each segmental myocardium (yellow line) (C). Bull’s-eye map with quantitative MBF values, based on 70 kV of stress state (D). AHA, American Heart Association; AIF, artery input function; TAC, time attenuation curve.

FIGURE 2

Comparison of image quality between protocols. Compared to 100 kV, 70 kV image noise increased along with SNR and CNR. SNR, signal-to-noise ratio; CNR, contrast-to-noise ratio; *P < 0.001.

FIGURE 3

CT images of the identical swine at different tube voltages. CT images on the aortic peak enhancement of the dynamic series (window width = 1200, window level = 240). The CT image at 100 kV. The image noise, SNR and CNR were 20.8, 16.2, and 12.9, respectively (A). The CT image at 70 kV. The image noise, SNR and CNR were 27.7, 20.6, and 17.9, respectively (B). SNR, signal-to-noise ratio; CNR, contrast-to-noise ratio.

FIGURE 4

The AIF of the ascending aorta and TACs of the myocardium between 100 and 70 kV in an identical swine of stress state. The CT attenuation was higher at 70 kV, causing a large slope of the AIF. Therefore, the AIF of 70 kV has a sharp peak compared to 100 kV. However, both AIF and TAC showed similar trends between 70 and 100 kV. AIF, arterial input functions; TACs, time attenuation curves.

FIGURE 5

Comparison of MBF values at segment levels of 100 and 70 kV. The entire range of measured MBF values increased after stress. The MBF values were comparable between 100 and 70 kV in both rest and stress states. MBF, myocardial blood flow.