Korean J Radiol.  2020 Jan;21(1):58-67. 10.3348/kjr.2019.0323.

Myocardial Coverage and Radiation Dose in Dynamic Myocardial Perfusion Imaging Using Third-Generation Dual-Source CT

Affiliations
  • 1Department of Radiology, Mie University Hospital, Mie, Japan. kakuya@clin.medic.mie-u.ac.jp

Abstract


OBJECTIVE
Third-generation dual-source computed tomography (3rd-DSCT) allows dynamic myocardial CT perfusion imaging (dynamic CTP) with a 10.5-cm z-axis coverage. Although the increased radiation exposure associated with the 50% wider scan range compared to second-generation DSCT (2nd-DSCT) may be suppressed by using a tube voltage of 70 kV, it remains unclear whether image quality and the ability to quantify myocardial blood flow (MBF) can be maintained under these conditions. This study aimed to compare the image quality, estimated MBF, and radiation dose of dynamic CTP between 2nd-DSCT and 3rd-DSCT and to evaluate whether a 10.5-cm coverage is suitable for dynamic CTP.
MATERIALS AND METHODS
We retrospectively analyzed 107 patients who underwent dynamic CTP using 2nd-DSCT at 80 kV (n = 54) or 3rd-DSCT at 70 kV (n = 53). Image quality, estimated MBF, radiation dose, and coverage of left ventricular (LV) myocardium were compared.
RESULTS
No significant differences were observed between 3rd-DSCT and 2nd-DSCT in contrast-to-noise ratio (37.4 ± 11.4 vs. 35.5 ± 11.2, p = 0.396). Effective radiation dose was lower with 3rd-DSCT (3.97 ± 0.92 mSv with a conversion factor of 0.017 mSv/mGy·cm) compared to 2nd-DSCT (5.49 ± 1.36 mSv, p < 0.001). Incomplete coverage was more frequent with 2nd-DSCT than with 3rd-DSCT (1.9% [1/53] vs. 56% [30/54], p < 0.001). In propensity score-matched cohorts, MBF was comparable between 3rd-DSCT and 2nd-DSCT in non-ischemic (146.2 ± 26.5 vs. 157.5 ± 34.9 mL/min/100 g, p = 0.137) as well as ischemic myocardium (92.7 ± 21.1 vs. 90.9 ± 29.7 mL/min/100 g, p = 0.876).
CONCLUSION
The radiation increase inherent to the widened z-axis coverage in 3rd-DSCT can be balanced by using a tube voltage of 70 kV without compromising image quality or MBF quantification. In dynamic CTP, a z-axis coverage of 10.5 cm is sufficient to achieve complete coverage of the LV myocardium in most patients.

Keyword

Multidetector computed tomography; Cardiac imaging techniques; Myocardial perfusion imaging; Image enhancement; Radiation dosage

MeSH Terms

Cardiac Imaging Techniques
Cohort Studies
Cytidine Triphosphate
Humans
Image Enhancement
Multidetector Computed Tomography
Myocardial Perfusion Imaging*
Myocardium
Perfusion Imaging
Radiation Dosage
Radiation Exposure
Retrospective Studies
Cytidine Triphosphate

Figure

  • Fig. 1 Flowchart shows patient selection protocol used to enroll patients in study.AF = atrial fibrillation, CABG = coronary artery bypass graft, CTP = computed tomography perfusion imaging, 2nd-DSCT = second-generation dual-source computed tomography, 3rd-DSCT = third-generation dual-source computed tomography

  • Fig. 2 Example of calculation for determining percentage z-axis coverage of LV myocardium on stress CTP.Z-axis coverage obtained by systolic stress CTP is 61 mm with 2nd-DSCT in this example, while 65 mm is required to cover entire LV myocardium according to systolic CCTA. Z-axis coverage in this case is therefore 94% (61 mm/65 mm). CCTA = coronary computed tomography angiography, LV = left ventricular, tMIP = time maximum intensity projection

  • Fig. 3 Box plots of CNR (A) and effective dose (B) of 2nd-DSCT at 80 kV and 3rd-DSCT at 70 kV.Center lines show medians, box limits indicate 25th and 75th percentiles, and whiskers extend 1.5-times interquartile range from 25th to 75th percentiles. CNR = contrast-to-noise ratio

  • Fig. 4 tMIP of stress dynamic CTP with 2nd-DSCT at 80 kV and 3rd-DSCT at 70 kV in 8 consecutive patients, respectively.Z-axis coverage of 2nd-DSCT is incomplete in all of presented cases. On the other hand, entire LV myocardium is covered in all cases with 3rd-DSCT.

  • Fig. 5 Dynamic CTP using 2nd-DSCT in 71-year-old man.Short-axis MBF maps (A) show mildly reduced perfusion in anteroseptal wall (arrows). Coronary angiography demonstrated moderate stenosis in left anterior descending artery (arrow) (B), while no stenosis was found in right coronary artery (C). Although z-axis scan length of 7.3 cm resulted in incomplete (96%) myocardial coverage with partial missing of basal anterior wall in this patient, all myocardial segments were still assessable. MBF = myocardial blood flow

  • Fig. 6 Dynamic CTP using 3rd-DSCT in 55-year-old man.Short-axis MBF maps (A) show severely reduced perfusion in anteroseptal wall (arrows). Coronary angiography demonstrated total occlusion in proximal left anterior descending artery (arrow) (B) with collateral vessel from right coronary artery (C). Dynamic CTP with z-axis scan length of 10.5 cm provided complete coverage of LV myocardium.


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