Results
Ultra-low dose CTA and ICA were successfully performed in 36 patients (6 women, 30 men; mean age 61.9 ± 8.4 years; age range 44 to 76 years), of whom 30 patients underwent ICA the same day as CTA and 6 patients underwent ICA within a mean of 32.7 ± 12.8 days. No patients were excluded because of poor CTA image quality. One patient had known CAD, and no patients had a history of coronary revascularization.
The study population included a large range of body weight (62 to 144 kg, IQR: 75 to 88 kg) and BMI (16.8 to 39.5 kg/m, IQR: 25 to 30 kg/m). Prior to CTA, intravenous metoprolol for heart rate control was administered in 33 patients (mean 12.7 ± 8.2 mg, range 2 to 25 mg), after which the mean heart rate was 57.6 ± 6.2 beats/min (range 42 to 73 beats/min) during CTA.
The mean DLP from CTA was 20.4 ± 8.9 mGy·cm (range 11.2 to 37.8 mGy·cm), corresponding to a mean radiation dose of 0.29 ± 0.12 mSv (range 0.16 to 0.53 mSv). The mean DLP from tracker scan was 1.31 ± 1.16 mGy·cm (range 0.85 to 2.32 mGy·cm), accounting for additional 0.018 ± 0.006 mSv (range 0.012 to 0.032 mSv). The mean dose-area product from ICA, which was purely diagnostic (n = 20), was 62.2 ± 43.9 Gy·cm (range 6.4 to 141.0 Gy·cm), resulting in an estimated mean radiation dose of 13.7 ± 9.7 mSv (range 1.4 to 31.0 mSv) (p < 0.0001 vs. CTA).
The mean contrast media bolus was 73.3 ± 13.8 ml (range 55.0 to 105.0 ml) for CTA and 116.8 ± 57.3 ml (range 40.0 to 242.0 ml) for purely diagnostic ICA (p < 0.0001) (Table 3).
Of the possible 576 segments in 36 patients with 16 coronary segments, both readers evaluated a total of 144 vessels and 450 coronary artery segments, whereas 126 segments were missing because of anatomical variants (n = 75) or had a diameter <1.5 mm (n = 51) at their origin. The 75 segments were missing for reasons not associated with the methodology, as these segments simply did not exist. The remaining 51 segments were categorized as <1.5 mm in diameter and thus were not evaluable by the gold standard of ICA with QCA. Thus, the missing data do not seem to introduce a selection bias into the final analysis yielding 96.9% (436 of 450) interpretable segments.
In 17 (47%) patients and 26 coronary arteries, ICA with QCA documented 33 stenoses. Single-vessel disease was present in 7 patients, 2-vessel disease in 2 patients, and 3-vessel disease in 2 patients. Ultra-low-dose CTA correctly detected CAD in all 17 patients and in 22 of 26 vessels. The latter had no impact on the per-patient–based accuracy, as all 4 false negative per-vessel findings resulted from underestimation of intermediate lesions in 4 different patients with extensive CAD, and significant lesions in other portions of the coronary tree were correctly depicted by CTA. Figures Figure 1 and Figure 2 demonstrate an example of CAD detection by CTA and ICA, whereas Figure 3 illustrates an example of a false negative finding by CTA. CAD was correctly ruled out by CTA in 14 of 19 patients and in 101 of 118 vessels. An example of normal coronary arteries is given in Figure 4.
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Figure 1.
Left Anterior Descending Stenosis
Proximal left anterior descending stenosis in a 72-year-old patient, diagnosed by invasive coronary angiography (ICA) (A), is correctly depicted by computed tomography angiography (CTA) with volume-rendered (B) and curved multiplanar reconstruction with (C) and without (D) model-based iterative reconstruction (MBIR). Body mass index was 34 kg/m, and the radiation dose from CTA was 0.37 mSv.
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Figure 2.
Right Coronary Stenosis
Proximal right coronary stenosis in a 74-year-old patient, diagnosed by ICA (A), is correctly depicted by CTA with volume-rendered (B) and curved multiplanar reconstruction with (C) and without (D) MBIR reconstruction. Body mass index was 27 kg/m, and radiation dose from CTA was 0.23 mSv. Abbreviations as in Figure 1.
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Figure 3.
False Negative Findings
Illustration of a coronary stenosis detected by ICA (A, white arrow) that was underestimated (false negative) by CTA (B, white arrow). In the same vessel, both techniques concordantly detected a stenosis in the more proximal segments of the coronary artery (white arrowheads). Abbreviations as in Figure 1.
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Figure 4.
Normal Coronary Arteries
Illustration of normal coronary arteries in a 53-year-old patient (body mass index 17 kg/m) by CTA with 0.19 mSv. Images without MBIR: (A) left anterior descending, (B) left circumflex, and (C) right coronary artery. Images with MBIR: (D) left anterior descending, (E) left circumflex, and (F) right coronary artery. (G) Three-dimensional volume-rendered computed tomography image. (H and I) ICA confirming normal left and right coronary vessels. Abbreviations as in Figure 1.
The findings resulted in a sensitivity, specificity, and accuracy of 100% (95% CI: 77% to 100%), 74% (95% CI: 49% to 91%), and 86% per patient and 85% (95% CI: 65% to 96%), 86% (95% CI: 78% to 91%), and 85% per vessel, respectively (Table 4).