Rationale and Objectives
Using lower tube voltage can reduce the exposure to radiation and the dose of contrast agent. However, lower tube voltage is often linked to more noise and poor image quality, which create a need for more effective technology to resolve this problem. To explore the feasibility of coronary computed tomographic angiography (CCTA) in patients with obesity at low tube voltage (100 kV) and low contrast agent concentration (270 mg/mL) using iterative reconstruction.
Materials and Methods
A total of 48 patients with body mass index greater than 30 kg/m 2 were included and randomly divided into two groups. Group A received a traditional protocol (iopromide 370 mg/mL + 120 kV); group B received a protocol with low tube voltage (100 kV), low contrast agent concentration (270 mg/mL), and iterative reconstruction. The effective dose (ED), average attenuation values, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), the figure of merit (FOM), image quality scores, and the total iodine intake were compared.
Results
No significant differences in average CT attenuations, SNR, CNR, and subjective scores were noticed between the two groups ( P > 0.05), whereas the FOM of group B was significantly higher than that of group A. Effective radiation dose, total iodine, and iodine injection rate in group B were lower than those of group A ( P < 0.01).
Conclusions
In patients with obesity, isotonic contrast agent with low iodine concentration and low-dose CCTA were feasible. Substantial reduction in radiation dose and the iodine intake could be achieved without compromising the image quality.
Introduction
Currently, coronary computed tomographic angiography (CCTA) is being widely used in clinical practice with remarkable accuracy. However, the exposure to X-ray radiation and the risk of renal impairment associated with contrast agents are the main limitations . In recent years, rational use of radiation (as lower as reasonably achievable) has been recommended , and research on reducing the radiation dose while maintaining the diagnostic performance of CT scan has become a hot topic . Using lower tube voltage is an effective way to reduce the radiation dose. At the same time, decreasing the dose of contrast agent has also drawn attention as it can reduce the risk of contrast-induced nephropathy (CIN) . On the contrary, lower tube voltage is often linked to more noise and poor image quality. Therefore, iterative reconstruction (IR) technology was developed to reduce the image noises and improve image quality, thereby showing advantages over traditional filtered back projection (FBP) technology , which lays the foundation for the application of low concentrations of contrast agents. Recently, adaptive iterative dose reduction (AIDR) IR algorithm has been used in clinical practice. It compares the imaging data to a noise model based on statistics that takes into account the electronic and photon noise. This method can greatly improve the image reconstruction speed, reduce wax-like artifacts in the reconstructed image, and improve the SNR and the CNR .
Obesity is closely associated with coronary artery disease (CAD), and it has a high degree of correlation with coronary artery calcification. In recent years, there has been a steady growth in the prevalence of obesity . On coronary artery examination in patients with obesity, increased noise and decreased image quality are often noticed due to the decreased X-ray penetration, which may even affect the diagnostic accuracy . The process of conducting a low-dose examination in patients with obesity is challenging. According to the International Steering Committee of Cardiovascular CT recommendations, while performing CCTA in patients weighing <85 kg or with a body mass index (BMI) of <30 kg/m 2 , 100 kV tube voltage is preferred . Many previous reports have demonstrated the feasibility of low concentrations of contrast agents and low tube voltage applied to CCTA in patients with BMI < 30 kg/m 2 . In a recent study, a “double low” scanning protocol (low tube voltage/low iodine dose contrast agent) and the AIDR reconstruction algorithm were used for CCTA in patients with a BMI of 26–30 kg/m 2 . The results showed that the use of 320-row CT with a “double low” scanning protocol not only provided images of diagnostic quality, but also reduced both radiation dose and the iodine intake during scanning .
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Materials and Methods
Patients
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Scanning Parameters
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Image Reconstruction and Postprocessing
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Subjective Evaluation of Image Quality
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Objective Assessment of Image Quality
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Radiation Dose and the Total Iodine Intake
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Contrast Agent-related Side Effects
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Statistics
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Results
Patient Demographics
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Table 1
Comparison of the Patient Demographics, Radiation Dose, Total Iodine, and Iodine Uptake Rate between the Two Groups
Group No. of Cases Male/Female Age (Years) Height (m) Weight (kg) BMI (kg/m 2 ) Heart Rate (beats/min) Scanning Length (cm) CTDI vol (mGy) DLP (mGy⋅cm) ED (mSv) Contrast Volume (mL) Total Iodine (g) Iodine Uptake Rate (g/s) A 24 17/7 56.5 ± 10.5 1.67 ± 0.07 93.6 ± 12.29 33.6 ± 2.81 70.5 ± 8.8 14.2 ± 1.43 18.6 ± 6.25 260.3 ± 78.09 3.64 ± 1.09 74.8 ± 9.82 27.3 ± 4.28 2.31 ± 0.30 B 24 19/5 63.0 ± 13.7 1.68 ± 0.10 96.86 ± 14.73 33.8 ± 2.92 69.6 ± 9.01 14.1 ± 1.17 8.1 ± 2.16 115.6 ± 29.62 1.61 ± 0.41 77.47 ± 11.79 20.9 ± 3.18 1.7 ± 0.26 T values 0.111 a −1.797 −0.818 −1.020 −0.383 0.362 0.00 7.647 8.373 8.373 −1.015 7.628 8.480P values >0.05 >0.05 >0.05 >0.05 >0.05 >0.05 >0.05 <0.01 <0.01 <0.01 >0.05 <0.01 <0.01
BMI, body mass index; CTDI vol , volumetric CT dose index; DLP, dose length product; ED, effective dose.
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Subjective Evaluation of Image Quality
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Table 2
Comparison of the Image Quality Scores between the Two Groups
Group Average Score a No. of Score 5 b No. of Score 4 b No. of Score 3 b No. of Score 2 b No. of Score 1 b A 4.47 ± 0.77 169 (60.6%) 83 (29.7%) 17 (6.1%) 10 (3.6%) 0 (0%) B 4.53 ± 0.71 183 (63.5%) 84 (29.2%) 13 (4.5%) 8 (2.8%) 0 (0%)
Group A: iopromide 370 + 120 kV + FBP; group B: iodixanol 270 + 100 kV + AIDR.
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![Figure 2, (a–c) A female (body mass index [BMI] = 30.3 kg/m 2 ) from group A scanning program (Iopromide 370 + 120 kV + filtered back projection [FBP]); the coronary arteries were clearly shown with sharp edges and no motion artifacts, and subjective score for image quality is 5; (d–f) a male (BMI = 32.5 kg/m 2 ) from group B scanning program (iodixanol l270 + 100 kV + adaptive iterative dose reduction [AIDR]-3D); each main coronary artery displays sharp edges and no motion artifacts, and the subjective score for image quality is 5. Both sets of images clearly showed the coronary artery with no obvious visual difference.](https://storage.googleapis.com/dl.dentistrykey.com/clinical/CoronaryComputedTomographicAngiographyatLowConcentrationofContrastAgentandLowTubeVoltageinPatientswithObesity/1_1s20S1076633216000076.jpg)
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Objective Evaluation of Image Quality
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Table 3
Comparison of the Imaging Parameters and the Image Quality of Different Sections of the Coronary Artery (t ± s)
Group Left Main Coronary Artery Left Anterior Descending Artery Left Circumflex Artery Right Coronary Artery Attenuation (HU) CNR SNR FOM Attenuation (HU) CNR SNR FOM Attenuation (HU) CNR SNR FOM Attenuation (HU) CNR SNR FOM A 399.3 ± 41.18 12.4 ± 3.75 11.8 ± 1.48 92.8 ± 15.80 391.9 ± 43.13 12.5 ± 3.17 9.7 ± 1.15 90.0 ± 16.17 389.3 ± 38.42 11.9 ± 3.45 11.9 ± 1.23 88.5 ± 14.82 393.9 ± 52.33 12.4 ± 3.07 12.2 ± 1.94 92.0 ± 12.17 B 388.6 ± 30.94 14.6 ± 2.81 12.0 ± 1.96 158.4 ± 25.32 386.37 ± 31.23 14.4 ± 2.62 9.8 ± 1.46 153.2 ± 25.93 382.7 ± 30.28 14.2 ± 2.86 12.5 ± 2.31 153.4 ± 26.22 386.8 ± 35.25 14.22 ± 2.59 12.6 ± 2.28 168.2 ± 73.2 T values 1.473 −1.955 −0.439 −9.25 0.699 −1.941 −0.286 −8.604 0.893 −2.215 −1.222 −9.158 0.697 −1.971 −0.864 −5.341P values >0.05 >0.05 >0.05 <0.05 >0.05 >0.05 >0.05 <0.05 >0.05 >0.05 >0.05 <0.05 >0.05 >0.05 >0.05 <0.05
CNR, contrast-to-noise ratio; SNR, signal-to-noise ratio; FOM, figure of merit.
Group A: iopromide 370 + 120 kV + FBP; group B: iodixanol 270 + 100 kV + AIDR-3D.
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Radiation Dose and Iodine Intake
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Side Effects after Injection of Contrast Agent
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Table 4
Comparison of the Frequency and Degree of Injection-related Discomfort
Group A Group B_P_ values None Mild Severe None Mild Severe Hotness 3 (12.5%) 10 (41.7%) 11 (45.8) 15 (62.5%) 8 (33.3%) 1 (4.2%) <0.001 Coldness 24 (100%) 0 (0) 0 (0) 23 (95.8) 1 (4.2%) 0 (0) 0.500 Pain 17 (70.8%) 6 (25%) 1 (4.2%) 23 (95.8) 1 (4.2%) 0 (0) 0.044
Group A: iopromide 370 + 120 kV + FBP; group B: iodixanol 270 + 100 kV+ AIDR-3D. Values are presented as number of discomfort (percentage).
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Discussions
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