Optimization of tube current in coronary multidetector computed tomography angiography: assessment of a standardized method to individualize current selection based on body habitus

Evaluation of a chest circumference-adapted protocol for low-dose 128-slice coronary CT angiography with prospective electrocardiogram triggering

Objective

To assess the effect of chest circumference-adapted scanning protocol on radiation exposure and image quality in patients undergoing prospective electrocardiogram (ECG)-triggered coronary CT angiography (CCTA).

Materials and Methods

One hundred-eighty-five consecutive patients, who had undergone prospective ECG triggering CCTA with a 128-slice CT, were included in the present study. Nipple-level chest circumference, body weight and height were measured before CT examinations. Patients were divided into four groups based on kV/ref·mAs = 100/200, 100/250, 120/200, and 120/250, when patient's chest circumference was ≤ 85.0 (n = 56), 85.0-90.0 (n = 53), 90.0-95.0 (n = 44), and > 95.0 (n = 32), respectively. Image quality per-segment was independently assessed by two experienced observers. Image noise and attenuation were also measured. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. The effective radiation dose was calculated using CT dose volume index and the dose-length product.

Results

A significant correlation was observed between patients' chest circumference and body mass index (r = 0.762, p < 0.001). Chest circumference ranged from 74 to 105 cm, and the mean effective radiation dose was 1.9-3.8 mSv. Diagnostic image quality was obtained in 98.5% (2440/2478) of all evaluated coronary segments without any significant differences among the four groups (p = 0.650). No significant difference in image noise was observed among the four groups (p = 0.439), thus supporting the validity of the chest circumference-adapted scanning protocol. However, vessel attenuation, SNR and CNR were significantly higher in the 100 kV groups than in the 120 kV groups (p < 0.05).

Conclusion

A measure of chest circumference can be used to adapt tube voltage and current for individualized radiation dose control, with resultant similar image noise and sustained diagnostic image quality.

Reduced radiation dose and improved image quality at cardiovascular CT angiography by automated attenuation-based tube voltage selection: intra-individual comparison

OBJECTIVES

To evaluate the effect of automated tube voltage selection on radiation dose and image quality at cardiovascular CT angiography (CTA).

METHODS

We retrospectively analysed paired studies in 72 patients (41 male, 60.5 ± 16.5 years), who had undergone CTA acquisitions of the heart or aorta both before and after the implementation of an automated x-ray tube voltage selection algorithm (ATVS). All other parameters were kept identical between the two acquisitions. Subjective image quality (IQ) was rated and objective IQ was measured by image noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and figure of merit (FOM). Image quality parameters and effective dose were compared between acquisitions.

RESULTS

Overall subjective image quality improved with the percentage of cases scored as adequate or higher increasing from 79 % to 92 % after implementation of ATVS (P = 0.03). SNR (14.1 ± 5.9, 15.7 ± 6.1, P = 0.009), CNR (11.6 ± 5.3, 13.2 ± 5.6, P = 0.011), and FOM (19.9 ± 23.3, 43.8 ± 51.1, P < 0.001) were significantly higher after implementation of ATVS. Mean image noise (24.1 ± 8.4 HU, 22.7 ± 7.1 HU, P = 0.048) and mean effective dose (10.6 ± 5.9 mSv, 8.8 ± 5.0 mSv, P = 0.003) were significantly lower after implementation of ATVS.

CONCLUSIONS

Automated tube voltage selection can operator-independently optimize cardiovascular CTA image acquisition parameters with improved image quality at reduced dose.

KEY POINTS

• Automatic tube voltage selection optimizes tube voltage for each individual patient. • In this population, overall radiation dose decreased while image quality improved. • This tool may become valuable for improving dose/quality ratio.

Minimizing radiation dose for coronary CT angiography

Coronary CT angiography is a rapidly growing technique that offers distinct advantages over traditional imaging techniques. However, because of rapid growth of this technique, radiation dose safety has been placed under the spotlight. There are several main determinants of total radiation dose, and these are outlined in this review. Integration of these dose-saving techniques will go a long way in maintaining diagnostic image quality and improving patient safety.

Effects of iopamidol-370 versus iodixanol-320 on coronary contrast, branch depiction, and heart rate variability in dual-source coronary MDCT angiography

OBJECTIVE

The purpose of this article is to assess whether iopamidol-370 provides superior vascular contrast of the coronaries and depiction of anatomic detail without affecting heart rate and beat-to-beat variability during coronary dual-source MDCT compared with iodixanol-320.

SUBJECTS AND METHODS

In this prospective trial, coronary CT angiography was performed on 60 adult patients using either iopamidol-370 or iodixanol-320. Cohorts were matched by age, habitus, sex, and baseline heart rate, with cohort sizes determined by power analysis. All studies were performed on a dual-source MDCT scanner with retrospective ECG-gating utilizing automatic pitch adjustment. Data assessment focused on heart rate variability during contrast administration statistically evaluated as Student t test comparisons within and between cohorts, coronary contrast-to-noise ratio analysis of the main coronary arteries utilizing Student t test comparisons between cohorts, and coronary branch depiction and distribution analysis in dual-reader consensus decisions between cohorts.

RESULTS

Thirty patients matched for age, habitus, sex, and heart rate were evaluated in each cohort. ECG analyses found a statistically significant (p = 0.013) decrease in heart rate during administration of iodixanol-320. Beat-to-beat variations, expressed as coefficient of variation, within and among cohorts were low (coefficient of variation, < 0.05). Contrast-to-noise ratio was significantly increased for iopamidol-370 versus iodixanol-320 (aortic root, p = 0.021; left main, p = 0.032; left anterior descending, p = 0.033; left circumflex, p = 0.039; and right, p = 0.009). Analysis of coronary branch visualization revealed improved depiction for iopamidol-370 compared with iodixanol-320.

CONCLUSION

Iopamidol-370, with its higher iodine concentration, provided greater vascular contrast of the arterial coronary tree and improved depiction of anatomic detail without significantly impacting cardiac heart rate during coronary MDCT imaging, as compared with iodixanol-320.

Low-dose unenhanced CT for IV contrast bolus timing: is it reliable to assess hepatic steatosis?

RATIONALE AND OBJECTIVES

To determine whether an unenhanced low-dose image acquired during automated contrast bolus timing can be used to assess hepatic steatosis.

MATERIALS AND METHODS

Fifty subjects (29 male, 21 female; 26-92 years; mean body mass index (BMI; 26.9) with abdominal multiphasic computed tomography were included. Abdominal diameters and circumferences were derived from anteroposterior and lateral scout radiographs. Hepatic attenuation (HA) was measured on unenhanced low-dose images (120 kV; 40 mA; 0.5 seconds' rotation time) and corresponding unenhanced standard-dose images (120 kV, z-axis automatic tube current modulation, noise index 11.5). Noise estimates were measured in surrounding air. Pearson correlation was calculated between abdominal circumference and BMI. Mean HA assessed on low-dose images and standard-dose images was compared using a paired Student's t-test and Bland Altman plots.

RESULTS

Abdominal circumference (mean, 142.8cm) correlated well with BMI (r = 0.83). No significant difference was found for HA on low-dose images (mean +57.7 HU) compared to HA on standard-dose images (+56.0 HU) (P = .077). Image noise (+11.5 HU) was significantly higher on low-dose images compared to image noise (+8.1 HU) on standard-dose images (P < .05). For HA mean difference comparing low- and standard-dose images was -1.7 HU (limits of agreement: -14.6, 11.2).

CONCLUSION

In all subjects, hepatic attenuation can be correctly assessed on unenhanced low-dose images.

Coronary CT angiography with low radiation dose

With the introduction of 64-slice CT and dual-source CT technology, coronary CT angiography(CCTA) has emerged as a useful diagnostic imaging modality for the noninvasive assessment of coronary heart disease. Recently, the risks associated with ionizing radiation on CT have raised serious concerns.The main concern of exposure to ionizing radiation is the potential risk of cancer. CCTA involves much higher radiation dose with the advances in the spatial and temporal resolution of cardiac CT. Currently,various dose-saving algorithms, such as ECG (electrocardiography)-based dose modulation, reduced tube voltage, and prospective ECG gating, high-pitch helical scanning are available to lower radiation exposure during cardiac CT. Therefore, careful selection of CT scanning protocols is needed to keep the radiation exposure 'as low as reasonably achievable (ALARA)'. In this review we will discuss the radiation dose safety issues, the measurement of radiation dose and current use of dose-saving techniques in CCTA.