Reduced iodinated contrast volume and radiation dose in the new protocol for CT coronary angiography using dual-source imaging with low tube voltage compared with the conventional protocol

Tóm tắt

Background

This study's objective was to assess the effectiveness and utility of a low-contrast-volume, coronary computed tomography angiography (CCTA) protocol that leverages a lower tube peak voltage (80 kVp) compared to the conventionally employed 120 kVp in patients referred for diagnostic CCTA.

Methods

120 patients (60M, 60F, ages between 23 to 86 years were randomly assigned to two groups of n=60 who were scanned with either  the 80 kVp (“Group A”) or the 120 kVp (“Group B”)protocols using retrospective ECG gating. All patients had body mass index (BMI) under 25 kg/m2 and heart rates under 120 beats per minute. On a patient-by-patient and segment-by-segment basis, the signal-to-noise (S/N) and contrast-to-noise (C/N) ratios, effective radiation dose given in mSv, and diagnostic confidence (DC) were assessed for both groups by two independent readers with 8 and 7 years experience in CCTA.

Results

Patients in group A received a significantly reduced radiation dose of 2.57 mSv compared with 7.07 mSv in group B(p<0.001). The total administered amount of Iodine per scan was also significantly lower in Group A (17.5g) than in Group B (24.5g).

A significant reduction in image noise with higher S/N and C/N ratios in coronary vessels was seen in group B (p<0.001). S/N ratios in group A were 18.7, 18.6, 18.7 and 18.6 for left main, proximal left anterior descending, proximal left circumflex arteries, proximal right coronary, respectively, and 16.7, 17.4 and 18.3 for distal left anterior descending, distal left circumflex, distal right coronary arteries, respectively, in group A. Conversely, in group B the S/R values were 22.5, 22.0, 22.0, 21.4,19.0, 18.8 and 21.7 in group B patients. C/N ratios were 22.2, 22.1, 21.9, 22.1, 20.5, 21.0 and 21.9 in group A compared with group B patients, who had ratios of 26.6, 26.1, 25.9, 25.5, 23.2, 23.0 and 25.6 (in a vessel-by-vessel assessment, each vessel in group B had P < 0.001). Importantly, no significant difference in DC per patient was seen between the groups (ICC 1.0 for Group A and 0.9 for Group B).

Conclusion

The retrospective ECG-gated low-kVp low-volume contrast CCTA protocol used in this study provides angiograms without penalty in diagnostic confidence in patients with BMI up to 25 kg/m2 and heart rates of less than 120 beats/min.  The protocol also provided  an average 2.75 times reduction in radiation dose and required an average 1.5 times less contrast volume. The reduced volume of contrast can be used to reduce the cost of contrast agent as well as the chance of contrast-induced nephropathy. With the ability to use a lower Iodine dilution ratio in the low kVp protocol, it is also possible to safely rescan patients who require a rescan right away due to poor image quality caused by, e.g.,  inadequate holding breath, arrythmia, or thoracic outlet syndrome. It is also good for patients who have to scan many parts of the body at the same time. It is obviously beneficial for patients whose kidney functions are not good and for those who increased risk for extravasations. Further, extravasation occurring with dynamic bolus CT may involve large volumes of contrast media.