Rationale and Objectives
Cardiac computed tomographic angiography algorithms emphasize radiation reduction while maintaining diagnostic image quality (IQ). The aim of this study was to evaluate IQ and interreader variability using prospective electrocardiographically triggered high-pitch spiral cardiac computed tomographic angiography (FLASH-CT) compared to retrospective electrocardiographic gating (RETRO-CT) for coronary artery disease evaluation in a patient population including overweight and obese individuals.
Materials and Methods
Seventy patients (24 women; mean age, 60 years) matched for gender, age, body mass index (27.4 ± 5.5 kg/m 2 ), and calcium score (184 ± 328) underwent cardiac computed tomographic angiography, 35 with FLASH-CT (Definition Flash) and 35 with RETRO-CT (Somatom Definition). Images were reconstructed using standard protocols and least motion phase for RETRO-CT acquisitions. Two independent, blinded readers evaluated the coronary arteries using an 18-segment model, grading IQ on a 5-point, Likert-type scale and coronary stenosis on a 5-point semiquantitative and binary scale.
Results
Effective radiation dose (1.50 vs 17.3 mSv, P < .0001) and mean heart rate (58 vs 62 beats/min, P < .05) were significantly lower for FLASH-CT compared to RETRO-CT. Seven hundred forty segments (>1.5 mm) were evaluated. There was no significant difference between FLASH-CT and RETRO-CT scans in overall per-segment IQ (3.11 ± 0.75 vs 3.10 ± 0.82, P = .94). FLASH-CT had noninferior IQ relative to RETRO-CT (95% confidence interval, −0.25 to 0.26). There was no significant difference in interreader variability in diagnosis between FLASH-CT and RETRO-CT for all coronary segments (77.5% vs 78.2%, P = .83).
Conclusions
FLASH-CT is an acceptable coronary computed tomographic angiographic method for reducing radiation dose without compromising IQ for a patient population including overweight and obese individuals.
Cardiac computed tomographic (CT) angiography (CCTA) is a reliable, noninvasive technique for evaluating coronary artery disease (CAD) . Although the noninvasive nature of CCTA is ideal, the associated radiation exposure of standard cardiac CT angiographic techniques should be minimized and continually monitored. In a recent multicenter, multivendor trial, the median effective radiation dose was 12 mSv for retrospective electrocardiographic gating techniques, with doses exceeding 30 mSv for some sites .
Novel cardiac CT angiographic algorithms focus on methods for radiation reduction while maintaining diagnostic image quality (IQ). Prospective electrocardiographically triggered axial CCTA (step-and-shoot mode) is one algorithm that reduces radiation exposure by limiting tube current to predefined time points of the cardiac cycle while keeping the table stationary at each station. This method has demonstrated high diagnostic accuracy, with mean effective radiation doses of 1.2 to 4.3 mSv, depending on the patient’s heart rate, scanner specifications, and total time of radiation exposure .
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Materials and methods
Study Population
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Image Acquisition
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Image Analysis
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Statistical Analysis
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Results
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Table 1
Patient and Coronary CTA Characteristics
Variable FLASH–CT ( n = 35) RETRO–CT ( n = 35)P Baseline demographics Men 23 (66%) 23 (66%) 1.00 Age (y) 60.1 ± 10.4 60.8 ± 10.6 .62 Height (in) 68.1 ± 4.4 (60–77) 67.9 ± 3.8 (61–74) .88 Weight (lb) 182.4 ± 44.8 (102–265) 180.4 ± 40.1 (107–255) .88 BMI (kg/m 2 ) 27.4 ± 5.8 (19.5–48.8) 27.4 ± 5.4 (19.4–44.3) .81 Overweight patients (BMI 25–30 kg/m 2 ) 12 (34%) 13 (37%) 1.00 Obese patients (BMI >30 kg/m 2 ) 11 (31%) 10 (29%) 1.00 Hypertension 11 (31%) 13 (37%) .80 Diabetes mellitus 3 (8.6%) 2 (5.7%) 1.00 Dyslipidemia 21 (60%) 26 (74%) .31 Tobacco history 8 (23%) 10 (29%) .79 Family history of CAD 18 (51%) 17 (49%) 1.00 CTA scan parameters Pre-exam β-blocker administration 23 (66%) 5 (14%) <.00001 Contrast volume (mL) 81 ± 6 104 ± 20 <.001 Contrast flow rate (mL/s) 6.1 ± 0.4 6.1 ± 0.4 .32 Effective tube current–time product 394 ± 51 340 ± 81 <.005 CT dose index 5.4 ± 0.1 70.6 ± 1.0 <.0001 Dose-length product 105.8 ± 1.5 1208.5 ± 16.9 <.0001 Effective dose (mSv) 1.50 ± 0.5 17.3 ± 5.7 <.0001 Heart rate (beats/min) 58 ± 4 62 ± 10 .04 Signal (HU) 461 ± 139 426 ± 101 .23 Noise (HU) 27 ± 8 27 ± 10 .93 Contrast (HU) 526 ± 142 492 ± 100 .26 Signal-to-noise ratio 14.0 ± 3.9 11.6 ± 3.4 <.01 Contrast-to-noise ratio 20.4 ± 7.9 19.9 ± 8.9 .80
BMI, body mass index; CAD, coronary artery disease; CT, computed tomographic; CTA, computed tomographic angiographic; FLASH-CT, prospective electrocardiographically triggered high-pitch spiral computed tomographic acquisition; HU, Hounsfield units; RETRO-CT, standard retrospective gated low-pitch spiral computed tomographic acquisition.
Data are expressed as number (percentage) or as mean ± standard deviation (range).
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Table 2
Coronary CT Angiographic Evaluation
CT Result FLASH-CT RETRO-CT_P_ CAD status .79 No CAD 17% (6/35) 11% (4/35) .50 Nonobstructive CAD 60% (21/35) 63% (22/35) .81 Obstructive CAD 23% (8/35) 26% (9/35) .78 Calcium score 205.6 ± 372.5 161.8 ± 281.3 .56 Diagnostic image quality Per patient 89% (31/35) 80% (28/35) .48 All segments 98.93% (738/746) 96.73% (710/734) .12 Left main 100% (70/70) 98.49% (65/66) .99 Left anterior descending 99.24% (260/262) 95.11% (253/266) .03 Left circumflex 98.26% (169/172) 99.34% (151/152) .88 Right coronary artery 98.76% (239/242) 96.40% (241/250) .32 Image quality score All segments 3.11 ± 0.75 3.10 ± 0.82 .94 Left main 3.39 ± 0.69 3.44 ± 0.70 .72 Left anterior descending 3.02 ± 0.72 2.97 ± 0.83 .71 Left circumflex 3.22 ± 0.71 3.24 ± 0.71 .88 Right coronary artery 3.05 ± 0.79 3.05 ± 0.87 .96
CAD, coronary artery disease; CT, computed tomographic; FLASH-CT, prospective electrocardiographically triggered high-pitch spiral computed tomographic acquisition; RETRO-CT, standard retrospective gated low-pitch spiral computed tomographic acquisition.
Data are expressed as percentage (number) or as mean ± standard deviation.
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Table 3
Reader Concordance
Variable FLASH-CT RETRO-CT_P_ Stenosis graded 0–4 All segments 77.48% (289/373) 78.20% (287/367) .83 Left main 71.43% (25/35) 72.73% (24/33) .91 Left anterior descending 70.99% (93/131) 67.67% (90/133) .60 Left circumflex 82.56% (71/86) 88.16% (67/76) .32 Right coronary artery 82.64% (100/121) 84.80% (106/125) .72 Stenosis graded on binary -scale (significant or nonsignificant) All segments 98.37% (361/367) 97.86% (365/373) .57 Left main 100% (33/33) 100% (35/35) 1.00 Left anterior descending 96.99% (129/133) 96.95% (127/131) .98 Left circumflex 100% (76/76) 98.84% (85/86) .99 Right coronary artery 98.40% (123/125) 97.52% (118/121) .62
FLASH-CT, prospective electrocardiographically triggered high-pitch spiral computed tomographic acquisition; RETRO-CT, standard retrospective gated low-pitch spiral computed tomographic acquisition.
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Discussion
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Conclusions
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