Submillisievert median radiation dose for coronary angiography with a second-generation 320-detector row CT scanner in 107 consecutive patients

Abstract

Purpose: To (a) use a new second-generation wide-volume 320-detector row computed tomographic (CT) scanner to explore optimization of radiation exposure in coronary CT angiography in an unselected and consecutive cohort of patients referred for clinical purposes and (b) compare estimated radiation exposure and image quality with that from a cohort of similar patients who underwent imaging with a previous first-generation CT system.

Materials and methods: The study was approved by the institutional review board, and all subjects provided written consent. Coronary CT angiography was performed in 107 consecutive patients with a new second-generation 320-detector row unit. Estimated radiation exposure and image quality were compared with those from 100 consecutive patients who underwent imaging with a previous first-generation scanner. Effective radiation dose was estimated by multiplying the dose-length product by an effective dose conversion factor of 0.014 mSv/mGy ⋅ cm and reported with size-specific dose estimates (SSDEs). Image quality was evaluated by two independent readers.

Results: The mean age of the 107 patients was 55.4 years ± 12.0 (standard deviation); 57 patients (53.3%) were men. The median body mass index was 27.3 kg/m(2) (range, 18.1-47.2 kg/m(2)); however, 71 patients (66.4%) were overweight, obese, or morbidly obese. A tube potential of 100 kV was used in 97 patients (90.6%), single-volume acquisition was used in 104 (97.2%), and prospective electrocardiographic gating was used in 106 (99.1%). The mean heart rate was 57.1 beats per minute ± 11.2 (range, 34-96 beats per minute), which enabled single-heartbeat scans in 100 patients (93.4%). The median radiation dose was 0.93 mSv (interquartile range [IQR], 0.58-1.74 mSv) with the second-generation unit and 2.67 mSv (IQR, 1.68-4.00 mSv) with the first-generation unit (P < .0001). The median SSDE was 6.0 mGy (IQR, 4.1-10.0 mGy) with the second-generation unit and 13.2 mGy (IQR, 10.2-18.6 mGy) with the first-generation unit (P < .0001). Overall, the radiation dose was less than 0.5 mSv for 23 of the 107 CT angiography examinations (21.5%), less than 1 mSv for 58 (54.2%), and less than 4 mSv for 103 (96.3%). All studies were of diagnostic quality, with most having excellent image quality. Three of four image quality indexes were significantly better with the second-generation unit compared with the first-generation unit.

Conclusion: The combination of a gantry rotation time of 275 msec, wide volume coverage, iterative reconstruction, automated exposure control, and larger x-ray power generator of the second-generation CT scanner provides excellent image quality over a wide range of body sizes and heart rates at low radiation doses.

Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.13122621/-/DC1.

Figure 1a:

Obstructive noncalcified stenosis (arrow) of proximal left anterior descending artery in 42-year-old overweight man with atypical chest pain and a heart rate of 70 beats per minute (height, 175 cm; weight,100 kg; body mass index, 32.7 kg/m²; effective diameter, 35.4 cm). Two-heartbeat acquisition was selected because this case was early in our experience with prototype scanner. (a, b) Quality of image reconstructed from data obtained with only one heartbeat (a) is nearly indistinguishable from that of image reconstructed with data segmented between two heartbeats (b). (c) Three-dimensional surface rendering of heart and coronary arteries. Estimated effective radiation dose for two-heartbeat scan was 4.0 mSv (dose-length product, 284.5 mGy ⋅ cm; CTDI_vol, 28.4 mGy; SSDE, 28.4 mGy). However, radiation dose could have been halved if only a single-heartbeat acquisition was selected. On the basis of similar initial experience, a prospectively acquired single-heartbeat scan can be obtained for heart rates slower than approximately 75 beats per minute.

Figure 1b:

Obstructive noncalcified stenosis (arrow) of proximal left anterior descending artery in 42-year-old overweight man with atypical chest pain and a heart rate of 70 beats per minute (height, 175 cm; weight,100 kg; body mass index, 32.7 kg/m²; effective diameter, 35.4 cm). Two-heartbeat acquisition was selected because this case was early in our experience with prototype scanner. (a, b) Quality of image reconstructed from data obtained with only one heartbeat (a) is nearly indistinguishable from that of image reconstructed with data segmented between two heartbeats (b). (c) Three-dimensional surface rendering of heart and coronary arteries. Estimated effective radiation dose for two-heartbeat scan was 4.0 mSv (dose-length product, 284.5 mGy ⋅ cm; CTDI_vol, 28.4 mGy; SSDE, 28.4 mGy). However, radiation dose could have been halved if only a single-heartbeat acquisition was selected. On the basis of similar initial experience, a prospectively acquired single-heartbeat scan can be obtained for heart rates slower than approximately 75 beats per minute.

Figure 1c:

Obstructive noncalcified stenosis (arrow) of proximal left anterior descending artery in 42-year-old overweight man with atypical chest pain and a heart rate of 70 beats per minute (height, 175 cm; weight,100 kg; body mass index, 32.7 kg/m²; effective diameter, 35.4 cm). Two-heartbeat acquisition was selected because this case was early in our experience with prototype scanner. (a, b) Quality of image reconstructed from data obtained with only one heartbeat (a) is nearly indistinguishable from that of image reconstructed with data segmented between two heartbeats (b). (c) Three-dimensional surface rendering of heart and coronary arteries. Estimated effective radiation dose for two-heartbeat scan was 4.0 mSv (dose-length product, 284.5 mGy ⋅ cm; CTDI_vol, 28.4 mGy; SSDE, 28.4 mGy). However, radiation dose could have been halved if only a single-heartbeat acquisition was selected. On the basis of similar initial experience, a prospectively acquired single-heartbeat scan can be obtained for heart rates slower than approximately 75 beats per minute.

Figure 2a:

(a) Obstructive coronary CT angiogram of proximal portion of obtuse marginal (OM, arrows) and (b) corresponding invasive angiogram in 67-year-old man (height, 67.7 cm; weight, 176 kg; body mass index, 29.5 kg/m²; effective diameter, 31.3 cm; heart rate, 44 beats per minute). Nonobstructive mixed calcified and noncalcified coronary artery disease (*) of proximal left anterior descending coronary artery (LAD) is present on both (c) coronary CT angiogram and (b) invasive angiogram. Estimated effective radiation dose was 0.90 mSv (dose-length product, 64.1 mGy ⋅ cm; CTDI_vol, 5.3 mGy; SSDE, 6.16 mGy).

Figure 2b:

(a) Obstructive coronary CT angiogram of proximal portion of obtuse marginal (OM, arrows) and (b) corresponding invasive angiogram in 67-year-old man (height, 67.7 cm; weight, 176 kg; body mass index, 29.5 kg/m²; effective diameter, 31.3 cm; heart rate, 44 beats per minute). Nonobstructive mixed calcified and noncalcified coronary artery disease (*) of proximal left anterior descending coronary artery (LAD) is present on both (c) coronary CT angiogram and (b) invasive angiogram. Estimated effective radiation dose was 0.90 mSv (dose-length product, 64.1 mGy ⋅ cm; CTDI_vol, 5.3 mGy; SSDE, 6.16 mGy).

Figure 2c:

(a) Obstructive coronary CT angiogram of proximal portion of obtuse marginal (OM, arrows) and (b) corresponding invasive angiogram in 67-year-old man (height, 67.7 cm; weight, 176 kg; body mass index, 29.5 kg/m²; effective diameter, 31.3 cm; heart rate, 44 beats per minute). Nonobstructive mixed calcified and noncalcified coronary artery disease (*) of proximal left anterior descending coronary artery (LAD) is present on both (c) coronary CT angiogram and (b) invasive angiogram. Estimated effective radiation dose was 0.90 mSv (dose-length product, 64.1 mGy ⋅ cm; CTDI_vol, 5.3 mGy; SSDE, 6.16 mGy).

Figure 3a:

(a) Three-dimensional surface rendering and (b) normal coronary CT angiogram in obese woman (height, 162.6 cm; weight, 94.8 kg; body mass index, 35.9 kg/m²; effective patient diameter, 34.1 cm) imaged at 100-kV tube potential. The more powerful x-ray generator with automated exposure control combined to select a tube potential of 100 kV despite guidelines suggesting 120-kV imaging for patients with a body mass index greater than 30 kg/m². A tube potential of 100 kV is theoretically better suited for attenuation characteristics of iodinated contrast media and lowers radiation dose compared with 120-kV settings. Estimated effective radiation dose was 0.7 mSv (dose-length product, 48.9 mGy ⋅ cm; CTDI_vol, 4.1 mGy; SSDE, 4.3 mGy).

Figure 3b:

(a) Three-dimensional surface rendering and (b) normal coronary CT angiogram in obese woman (height, 162.6 cm; weight, 94.8 kg; body mass index, 35.9 kg/m²; effective patient diameter, 34.1 cm) imaged at 100-kV tube potential. The more powerful x-ray generator with automated exposure control combined to select a tube potential of 100 kV despite guidelines suggesting 120-kV imaging for patients with a body mass index greater than 30 kg/m². A tube potential of 100 kV is theoretically better suited for attenuation characteristics of iodinated contrast media and lowers radiation dose compared with 120-kV settings. Estimated effective radiation dose was 0.7 mSv (dose-length product, 48.9 mGy ⋅ cm; CTDI_vol, 4.1 mGy; SSDE, 4.3 mGy).