Objective
To report our clinical experience with a 256-slice multidetector computed tomography (MDCT) with a 270-ms gantry rotation system in performing CT coronary angiograms (CTCA) using both prospectively gated step and shoot (PGSS) and retrospectively gated helical (RGH) techniques.
Materials and Methods
We studied 252 patients who received CTCA; 126 patients having mean heart rate (HR) of 72.1 were imaged with RGH CTCA and 126 patients having mean HR of 58.7 were imaged with PGSS CTCA. For patients with a prescan HR ≤70 beats/min, a PGSS acquisitions trigger was used, whereas patients whose prescan HR was >70 beats/min were imaged using an RGH acquisition. The blood vessel accessibility of both PGSS and RGH techniques was evaluated by grading the image quality score from 1 (no motion artifacts) to 4 (severe motion artifacts preventing diagnosis) for each coronary artery segment. Radiation doses of the techniques were also compared.
Results
In both groups, more than 50% of segments received the best imaging score. The overall image quality scores for RGH and PGSS groups were 1.522 ± 0.317 and 1.500 ± 0.374, respectively. There was no significant difference in right coronary artery, left anterior descending artery, and left circumflex artery image quality between the two groups. Only 0.1% of segments were nonevaluative with the PGSS technique and all segments were evaluative with RGH. PGSS was associated with a 62% reduction in effective radiation dose as compared to RGH (PGSS, 5.1 mSv; RGH, 13.2 mSv).
Conclusions
There is no significant difference in image quality between PGSS and RGH in this study. Although providing similar image quality as RGH, PGSS was associated with a 62% reduction in effective radiation dose. Further study to confirm the diagnostic accuracy as compared to coronary artery angiography is warranted.
Computed tomography coronary angiography (CTCA) using 64-slice multidetector computed tomography (MDCT) and dual-source CT (DSCT) is highly accurate for the detection of coronary artery disease (CAD). Although the noninvasive nature of CT is attractive, the radiation dose of CTCA compared to catheterization remains a significant hurdle because doses for conventional coronary angiography range from 5 to 12 mSv , whereas those of retrospectively gated helical (RGH) CTCA range from 12 to 28 mSv .
With RGH, image data are acquired continuously throughout the cardiac cycle and the reconstruction phase with the least amount of motion artifact is retrospectively chosen, usually during ventricular diastole . On the other hand, prospectively gated step and shoot (PGSS) is a CT acquisition technique in which x-rays are turned on only during the cardiac phase of interest. Being prospective in nature, PGSS requires precise synchronization of the x-ray with the cardiac cycle, and its successful implementation also depends on the matching between the selected phase of the cardiac cycle and the phase with least motion. The continuous application of radiation throughout the cardiac cycle with RGH results in a higher radiation dose as compared to PGSS .
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Materials and methods
Study Population
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The 256-slice MDCT Protocol
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Table 1
Patient Demographic and RGH and PGSS Technical Data
RGH ( n = 126) PGSS ( n = 126)P Value Age (y) 56.5 ± 9.8 58.0 ± 8.0 .190 Male gender 77 (61.1) 69 (78.4) .007 ∗ Body mass index (kg/m 2 ) 25.6 ± 4.0 25.5 ± 3.3 .930 MHR (beats/min) 72.1 ± 6.9 58.7 ± 7.3 <.001 ∗ HRV (beats/min) 1.3 ± 0.7 1.0 ± 0.8 <.001 ∗ Received beta-blockers 35 (27.8) 5 (5.7) <.001 ∗ Tube voltage (kV) 120 120 N/A Tube current (mA) 565.7 ± 91.7 780.3 ± 97.8 <.001 ∗ Scan time (seconds) 4.9 ± 0.3 3.9 ± 1.4 <.001 ∗ Number of shots Continuous exposure 2–3 N/A CTDI vol (mGy) 60.0 ± 10.5 22.9 ± 3.1 <.001 ∗ Scan length (mm) 129.7 ± 13.8 131.7 ± 15.6 .300 Effective dose (mSv) 13.2 ± 2.7 5.1 ± 0.9 <.001 ∗
CTDI vol , volume computed tomography dose index; HRV, heart rate variability; MHR, mean heart rate; PGSS, prospectively gated step and shoot; RGH, retrospectively gated helical.
Data are presented as mean ± standard deviation for continuous variables and number (percentage) for categorical variables.
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CT Data Analysis
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Radiation Dose
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Statistical Analysis
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Results
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Table 2
RGH and PGSS Image Quality Scores for All Segments
RGH PGSS Segment ∗ Score 1 (%) Score 2 (%) Score 3 (%) Score 4 (%) Score 1 (%) Score 2 (%) Score 3 (%) Score 4 (%) 1 57.1 (72/126) 42.1 (53/126) 0.8 (1/126) 0.0 (0/126) 58.4 (73/125) 39.2 (49/125) 2.4 (3/125) 0.0 (0/125) 2 21.4 (27/126) 59.5 (75/126) 19.0 (24/126) 0.0 (0/126) 26.4 (33/125) 54.4 (68/125) 18.4 (23/125) 0.8 (1/125) 3 56.3 (67/119) 42.9 (51/119) 0.8 (1/119) 0.0 (0/119) 53.8 (64/119) 45.4 (54/119) 0.8 (1/119) 0.0 (0/119) 4 42.7 (50/117) 54.7 (64/117) 2.6 (3/117) 0.0 (0/117) 52.9 (63/119) 46.2 (55/119) 0.8 (1/119) 0.0 (0/119) 5 87.2 (109/125) 12.8 (16/125) 0.0 (0/125) 0.0 (0/125) 80.0 (100/125) 19.2 (24/125) 0.8 (1/125) 0.0 (0/125) 6 78.6 (99/126) 21.4 (27/126) 0.0 (0/126) 0.0 (0/126) 75.2 (94/125) 22.4 (28/125) 2.4 (3/125) 0.0 (0/125) 7 53.6 (67/125) 46.4 (58/125) 0.0 (0/125) 0.0 (0/125) 54.4 (68/125) 44.8 (56/125) 0.8 (1/125) 0.0 (0/125) 8 32.8 (41/125) 64.0 (80/125) 3.2 (4/125) 0.0 (0/125) 31.2 (39/125) 64.0 (80/125) 4.8 (6/125) 0.0 (0/125) 9 48.4 (60/124) 50.0 (62/124) 1.6 (2/124) 0.0 (0/124) 62.4 (78/125) 36.8 (46/125) 0.8 (1/125) 0.0 (0/125) 10 41.5 (27/65) 55.4 (36/65) 3.1 (2/65) 0.0 (0/65) 58.1 (54/93) 39.8 (37/93) 2.2 (2/93) 0.0 (0/93) 11 64.0 (80/125) 36.0 (45/125) 0.0 (0/125) 0.0 (0/125) 67.7 (84/124) 29.8 (37/124) 2.4 (3/124) 0.0 (0/124) 12 33.6 (39/116) 64.7 (75/116) 1.7 (2/116) 0.0 (0/116) 41.4 (48/116) 55.2 (64/116) 3.4 (4/116) 0.0 (0/116) 13 40.2 (45/112) 58.0 (65/112) 1.8 (2/112) 0.0 (0/112) 43.1 (47/109) 53.2 (58/109) 3.7 (4/109) 0.0 (0/109) 14 39.7 (27/68) 57.4 (39/68) 2.9 (2/68) 0.0 (0/68) 32.9 (23/70) 61.4 (43/70) 5.7 (4/70) 0.0 (0/70) 15 62.5 (5/8) 37.5 (3/8) 0.0 (0/8) 0.0 (0/8) 60.0 (3/5) 40.0 (2/5) 0.0 (0/5) 0.0 (0/5) 16 47.6 (20/42) 52.4 (22/42) 0.0 (0/42) 0.0 (0/42) 75.0 (42/56) 23.2 (13/56) 1.8 (1/56) 0.0 (0/56) All segments 50.6 (835/1649) 46.8 (771/1649) 2.6 (43/1649) 0.0 (0/1649) 54.2 (913/1686) 42.3 (714/1686) 3.4 (58/1686) 0.1 (1/1686)
PGSS, prospectively gated step and shoot; RGH, retrospectively gated helical.
Data in parentheses are raw data used to calculate the percentage. Image quality score obtained at best R-R interval: score 1, no motion artifacts; score 2, mild motion artifacts; score 3, moderate motion artifacts; score 4, severe motion artifacts.
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Table 3
Comparison of Image Quality for RGH and PGSS Techniques
RGH PGSS Difference Between Techniques ∗ Coronary Vessel Group A1
(All HRs, n = 126) Group A2
(HR ≤75, n = 84) Group B
(HR ≤75, n = 126) Group A1 vs. B Group A2 vs. B Overall image quality 1.522 ± 0.317 1.472 ± 0.313 1.500 ± 0.374 0.023 (0.23) -0.028 (0.96) RCA 1.623 ± 0.442 1.571 ± 0.431 1.580 ± 0.465 0.043 (0.39) -0.009 (0.95) LAD 1.429 ± 0.331 1.388 ± 0.328 1.424 ± 0.377 0.005 (0.45) -0.036 (0.86) LCX 1.556 ± 0.430 1.467 ± 0.446 1.547 ± 0.469 0.009 (0.68) -0.080 (0.26)
HR, heart rate; LAD, left anterior descending coronary artery; LCX, left circumflex coronary artery; PGSS, prospectively gated step and shoot; RCA, right coronary artery; RGH, retrospectively gated helical.
Group A1 includes all patients scanned by RGH; group A2 are patients with HR <75 beats/min, scanned by RGH; group B includes patients with HR <75 beats/min, scanned by PGSS. Group data are presented as mean ± standard deviation.
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Discussion
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