Estimation of the radiation exposure of a chest pain protocol with ECG-gating in dual-source computed tomography

Dedicated CCTA Followed by High-Pitch Scanning versus TRO-CT for Contrast Media and Radiation Dose Reduction: A Retrospective Study

We aimed to compare dedicated coronary computed tomography angiography (CCTA) followed by high-pitch scanning and triple-rule-out computed tomography angiography (TRO-CTA) in terms of radiation dose, contrast media (CM) use, and image quality. Patients with acute chest pain were retrospectively enrolled and assigned to group A (n = 55; scanned with dedicated CCTA followed by high-pitch scanning) or group B (n = 45; with TRO-CTA). Patient characteristics, radiation dose, CM use, and quantitative parameters (CT value, image noise, signal-to-noise ratio, contrast-to-noise ratio, and image quality score) of pulmonary arteries (PAs), thoracic aortae (TAs), and coronary arteries (CAs) were compared. The total effective dose was significantly lower in group A (6.25 ± 2.94 mSv) than B (8.93 ± 4.08 mSv; p < 0.001). CM volume was significantly lower in group A (75.7 ± 8.9 mL) than B (95.0 ± 0 mL; p < 0.001). PA and TA image quality were significantly better in group B, whereas that of CA was significantly better in group A. Qualitative image scores of PA and TA scans rated by radiologists were similar, whereas that of CA scans was significantly higher in group A than B (p < 0.001). Dedicated CCTA followed by high-pitch scanning demonstrated lower radiation doses and CM volume without debasing qualities of PA, TA, and CA scans than did TRO-CTA.

Comparison of Chest Pain Protocols for Electrocardiography-Gated Dual-Source Cardiothoracic CT in Children and Adults: The Effect of Tube Current Saturation on Radiation Dose Reduction

Objective

To compare radiation doses between conventional and chest pain protocols using dual-source retrospectively electrocardiography (ECG)-gated cardiothoracic computed tomography (CT) in children and adults and assess the effect of tube current saturation on radiation dose reduction.

Materials and Methods

This study included 104 patients (16.6 ± 7.7 years, range 5–48 years) that were divided into two groups: those with and those without tube current saturation. The estimated radiation doses of retrospectively ECG-gated spiral cardiothoracic CT were compared between conventional, uniphasic, and biphasic chest pain protocols acquired with the same imaging parameters in the same patients by using paired t tests. Dose reduction percentages, patient ages, volume CT dose index values, and tube current time products per rotation were compared between the two groups by using unpaired t tests. A p value < 0.05 was considered significant.

Results

The volume CT dose index values of the biphasic chest pain protocol (10.8 ± 3.9 mGy) were significantly lower than those of the conventional protocol (12.2 ± 4.7 mGy, p < 0.001) and those of the uniphasic chest pain protocol (12.9 ± 4.9 mGy, p < 0.001). The dose-saving effect of biphasic chest pain protocol was significantly less with a saturated tube current (4.5 ± 10.2%) than with unsaturated tube current method (14.8 ± 11.5%, p < 0.001). In 76 patients using 100 kVp, patient age showed no significant differences between the groups with and without tube current saturation in all protocols (p > 0.05); the groups with tube current saturation showed significantly higher volume CT dose index values (p < 0.01) and tube current time product per rotation (p < 0.001) than the groups without tube current saturation in all protocols.

Conclusion

The radiation dose of dual-source retrospectively ECG-gated spiral cardiothoracic CT can be reduced by approximately 15% by using the biphasic chest pain protocol instead of the conventional protocol in children and adults if radiation dose parameters are further optimized to avoid tube current saturation.

[Possibilities for exposure reduction in computed tomography examination of acute chest pain]

CLINICAL/METHODICAL ISSUE

Electrocardiogram-gated (ECG) computed tomography (CT) investigations can be accompanied by high amounts of radiation exposure. This is particularly true for the investigation of patients with unclear and acute chest pain.

STANDARD RADIOLOGICAL METHODS

The common approach in patients with acute chest pain is standard spiral CT of the chest.

METHODICAL INNOVATIONS

The chest pain or triple-rule-out CT protocol is a relatively new ECG-gated protocol of the entire chest. This article reviews and discusses different techniques for the CT investigation of patients with acute chest pain.

PERFORMANCE

By applying the appropriate scan technique, the radiation exposure for an ECG-gated protocol must not necessarily be higher than a standard chest CT scan

ACHIEVEMENTS

Aortic pathologies are far better depicted by ECG-gated scan protocols and depending on the heart rate coronary artery disease can also be detected at the same time.

PRACTICAL RECOMMENDATIONS

The use of ECG-triggered scans will not support the diagnostics of the pulmonary arteries. However, in unspecific chest pain an ECG-triggered scan protocol can provide information on the differential diagnosis.

Incremental diagnostic and prognostic value of contemporary stress echocardiography in a chest pain unit: mortality and morbidity outcomes from a real-world setting

BACKGROUND

Clinical assessment often cannot reliably or rapidly risk stratify patients hospitalized with suspected acute coronary syndrome. The real-world clinical value of stress echocardiography (SE) in these patients is unknown. Thus, we undertook this study to assess the feasibility, safety, ability for early triaging, and prediction of hard events of SE incorporated into a chest pain unit for patients admitted with acute chest pain, nondiagnostic ECG, and negative 12-hour troponin.

METHODS AND RESULTS

Accordingly, 839 consecutive patients who underwent clinical, ECG, and SE assessments within 24 hours of admission were assessed for feasibility, safety, impact on triaging and discharge, and 30-day readmission rate and were followed up for hard events (all-cause mortality and acute myocardial infarction). Of the 839 patients, 811 (96.7%) had diagnostic SE results. Median time to SE and median length of stay for normal SE patients (77%) were both 1 day. The 30-day readmission rate was 0.5%. During long-term follow-up of 27±11 months, 39 hard events (30 deaths and 9 acute myocardial infarctions) occurred. Kaplan-Meier estimates of hard events were 0.5% versus 6.6% in the normal versus abnormal SE groups, respectively, in the first year of follow-up (15 events in the first year). Among all prognostic variables, only abnormal SE (hazard ratio, 4.08; 95% confidence interval, 2.15-7.72; P<0.001) and advancing age (hazard ratio, 1.78; 95% confidence interval, 1.39-2.37; P<0.001) predicted hard events in multivariable regression analysis.

CONCLUSIONS

SE incorporated into a chest pain unit has excellent feasibility and provides rapid assessment and discharge with accurate risk stratification of patients with suspected acute coronary syndrome but nondiagnostic ECG and negative 12-hour troponin.

High-pitch computed tomography coronary angiography-a new dose-saving algorithm: estimation of radiation exposure

Purpose. To estimate effective dose and organ equivalent doses of prospective ECG-triggered high-pitch CTCA. Materials and Methods. For dose measurements, an Alderson-Rando phantom equipped with thermoluminescent dosimeters was used. The effective dose was calculated according to ICRP 103. Exposure was performed on a second-generation dual-source scanner (SOMATOM Definition Flash, Siemens Medical Solutions, Germany). The following scan parameters were used: 320 mAs per rotation, 100 and 120 kV, pitch 3.4 for prospectively ECG-triggered high-pitch CTCA, scan range of 13.5 cm, collimation 64 × 2 × 0.6 mm with z-flying focal spot, gantry rotation time 280 ms, and simulated heart rate of 60 beats per minute. Results. Depending on the applied tube potential, the effective whole-body dose of the cardiac scan ranged from 1.1 mSv to 1.6 mSv and from 1.2 to 1.8 mSv for males and females, respectively. The radiosensitive breast tissue in the range of the primary beam caused an increased female-specific effective dose of 8.6%±0.3% compared to males. Decreasing the tube potential, a significant reduction of the effective dose of 35.8% and 36.0% can be achieved for males and females, respectively (P < 0.001). Conclusion. The radiologist and the CT technician should be aware of this new dose-saving strategy to keep the radiation exposure as low as reasonablly achievable.

Estimation of radiation exposure of retrospective gated and prospective triggered 128-slice triple-rule-out CT angiography

BACKGROUND

CT has become an important role in the differential diagnosis of acute chest pain to exclude an aortic dissection, pulmonary embolism and acute coronary artery syndrome. However, the additional radiation exposure is a cause of concern and dose saving strategies should be applied, if possible.

PURPOSE

To estimate effective dose of retrospective gated and prospective ECG-triggered triple-rule-out computed tomography angiography (TRO-CTA).

MATERIAL AND METHODS

An Alderson-Rando-phantom equipped with thermoluminescent dosimeters was used for dose measurements. Exposure was performed on a 128-slice single source scanner. The following scan parameters were used (retrospective ECG-gated): 120 kV, 190 mAs/rot., collimation 128x0.6 mm, rotation time 0.3 s. Protocols with a simulated heart rate (HR) of 60 and 100 bpm were performed using the standard ECG-pulsing as well as MinDose. Additionally, a prospective triggered TRO-CTA was acquired (HR 60 bpm).

RESULTS

The estimated effective dose of retrospective ECG-gated TRO-CTA ranged from 7.4-13.4 mSv and from 10.1-17.5 mSv for men and women, respectively. Due to radiosensitive breast tissue, women received a significant increased effective dose of up to 64.7% ± 0.03% (p = 0.028) compared to men. MinDose reduces radiation exposure of up to 33.0% ± 6.5% in comparison to standard ECG-pulsing (p < 0.001). The effective dose increased significantly with lower heart rates (p < 0.001). Prospective ECG-triggered TRO-CTA showed an effective dose of 5.9 mSv and 8.2 mSv for men and women, respectively. Compared to retrospective ECG-gated TRO-CTA a significant dose reduction was observed (p < 0.001).

CONCLUSION

Due to the significant different dose exposure, scan protocols should be specifically adapted in a patient- and problem-oriented manner.

Diagnostic performance of 320-slice multidetector computed tomography coronary angiography in patients after coronary artery bypass grafting

Objectives

To evaluate the diagnostic performance of 320-slice computed tomography coronary angiography (CTA) in the evaluation of patients with prior coronary artery bypass grafting (CABG). Invasive coronary angiography (ICA) served as the standard of reference, using a quantitative approach.

Methods

CTA studies were performed using CT equipment with 320 detector-rows, each 0.5 mm wide, and a gantry rotation time of 0.35 s. All grafts, recipient and nongrafted vessels were deemed interpretable or uninterpretable. The presence of significant (≥50%) stenosis and occlusion were determined on vessel and patient basis. Results were compared to ICA using quantitative coronary angiography.

Results

A total of 40 patients (28 men, 76 ± 15 years), with 89 grafts, were included in the study. On a graft analysis, the sensitivity, specificity, positive and negative predictive values in the evaluation of significant stenosis were 96%, 92%, 83% and 98% respectively. The diagnostic accuracy for the assessment of recipient and nongrafted vessels was 89% and 80%, respectively. The diagnostic accuracy for the assessment of graft, recipient and nongrafted vessel occlusion was 96%, 92% and 100%, respectively.

Conclusions

320-slice CTA allows accurate non-invasive assessment of significant graft, recipient vessel and nongrafted vessel stenosis in patients with prior CABG.

The effect of heart rhythm on patient radiation dose with dual-source cardiac computed tomography

BACKGROUND

To lower the radiation exposure associated with cardiac CT, it is essential to identify all factors that influence radiation dose.

OBJECTIVES

We explored the effect of heart rhythm during scan acquisition on radiation dose with a 64-slice dual-source cardiac CT.

METHODS

Patient and scan data were collected prospectively in 302 consecutive patients referred for a clinical dual-source cardiac CT. Electrocardiograms recorded during acquisition were interpreted by a cardiologist and categorized as (1) normal sinus rhythm (NSR), (2) premature atrial contraction (PAC) or premature ventricular contraction (PVC), or (3) atrial fibrillation or flutter.

RESULTS

Of the 302 patients, 227 (75.2%) were in NSR and had no ectopy, 55 (18.2%) had PAC/PVC, and 20 (6.6%) had atrial fibrillation or flutter during the scan. Patients with irregular rhythm (PAC/PVC and atrial fibrillation or flutter) were older than patients with regular rhythm (61.0 vs 54.8 years; P = 0.006). Patients with NSR had the lowest estimated radiation dose, followed by PAC/PVC and atrial fibrillation/flutter (9.4, 14.5, 20.9 mSv; P < 0.001). The difference remained significant after adjustments for differences in examination type, tube current and voltage, scan length, pitch, and use of tube current modulation (9.8, 14.1, 17.9 mSv; P < 0.001). No significant association was observed between heart rhythm and subjective image quality although scans with regular rhythm and no ectopy had higher signal-to-noise and contrast-to-noise ratios (P < 0.01).

CONCLUSION

Compared to patients with NSR, patients with atrial fibrillation/flutter had the highest radiation exposure, followed by those with PAC/PVC. Even after adjustment for factors associated with radiation exposure, a significant difference in radiation dose persisted. These findings can be used to identify patients who are more likely to receive higher radiation dose when undergoing cardiac CT and to develop future more-efficient scanner algorithms for use in patients with arrhythmias.

Correlation of radiation dose and heart rate in dual-source computed tomography coronary angiography

BACKGROUND

Computed tomography coronary angiography (CTCA) has been widely used since the introduction of 64-slice scanners and dual-source CT technology, but the relatively high radiation dose remains a major concern.

PURPOSE

To evaluate the relationship between radiation exposure and heart rate (HR), in dual-source CTCA.

MATERIAL AND METHODS

Data from 218 CTCA examinations, performed with a dual-source 64-slices scanner, were statistically evaluated. Effective radiation dose, expressed in mSv, was calculated as the product of the dose-length product (DLP) times a conversion coefficient for the chest (mSv = DLPx0.017). Heart rate range and mean heart rate, expressed in beats per minute (bpm) of each individual during CTCA, were also provided by the system. Statistical analysis of effective dose and heart rate data was performed by using Pearson correlation coefficient and two-sample t-test.

RESULTS

Mean HR and effective dose were found to have a borderline positive relationship. Individuals with a mean HR >65 bpm observed to receive a statistically significant higher effective dose as compared to those with a mean HR ≤65 bpm. Moreover, a strong correlation between effective dose and variability of HR of more than 20 bpm was observed.

CONCLUSION

Dual-source CT scanners are considered to have the capability to provide diagnostic examinations even with high HR and arrhythmias. However, it is desirable to keep the mean heart rate below 65 bpm and heart rate fluctuation less than 20 bpm in order to reduce the radiation exposure.

Comparison of radiation dose and image quality of triple-rule-out computed tomography angiography between conventional helical scanning and a strategy incorporating sequential scanning

Triple-rule-out computed tomographic angiography (TRO CTA), performed to evaluate the coronary arteries, pulmonary arteries, and thoracic aorta, has been associated with high radiation exposure. The use of sequential scanning for coronary computed tomographic angiography reduces the radiation dose. The application of sequential scanning to TRO CTA is much less well defined. We analyzed the radiation dose and image quality from TRO CTA performed at a single outpatient center, comparing the scans from a period during which helical scanning with electrocardiographically controlled tube current modulation was used for all patients (n = 35) and after adoption of a strategy incorporating sequential scanning whenever appropriate (n = 35). Sequential scanning was able to be used for 86% of the cases. The sequential-if-appropriate strategy, compared to the helical-only strategy, was associated with a 61.6% dose decrease (mean dose-length product of 439 mGy × cm vs 1,144 mGy × cm and mean effective dose of 7.5 mSv vs 19.4 mSv, respectively, p <0.0001). Similarly, a 71.5% dose reduction occurred among the 30 patients scanned with the sequential protocol compared to the 40 patients scanned with the helical protocol using either strategy (326 mGy × cm vs 1,141 mGy × cm and 5.5 mSv vs 19.4 mSv, respectively, p <0.0001). Although the image quality did not differ between the strategies, a nonstatistically significant trend was seen toward better quality in the sequential protocol than in the helical protocol. In conclusion, approaching TRO CTA with a diagnostic strategy of sequential scanning, as appropriate, can offer a marked reduction in the radiation dose while maintaining the image quality.

Estimation of radiation exposure of different dose saving techniques in 128-slice computed tomography coronary angiography

PURPOSE

To estimate the effective dose of cardiac CT with different dose saving strategies dependent on varying heart rates.

MATERIALS AND METHODS

For dose measurements, an Alderson-Rando-phantom equipped with thermoluminescent dosimeters was used. The effective dose was calculated according to ICRP 103. Exposure was performed on a 128-slice single source scanner providing a rotation time of 0.30s and standard protocols with 120 kV and 160 mAs/rot. Protocols were evaluated without ECG-pulsing, with two different ECG-pulsing techniques, and automated exposure control with a simulated heart rate of 60 and 100 beats per minute.

RESULTS

Depending on different dose saving techniques and heart rate, the effective whole-body dose of a cardiac scan ranged from 2.8 to 9.5 mSv and from 4.3 to 16.0 mSv for males and females, respectively. The radiation-sensitive breast tissue in the primary scan range results in an increased female dose of 66.7 ± 6.0%. Prospective triggering has the greatest potential to reduce the effective dose to 27.8%, compared to a comparable scan protocol with retrospective ECG-triggering with no ECG-pulsing. Furthermore, the heart rate influences the radiation exposure by increasing significantly at lower heart rates.

CONCLUSION

Due to this broad variability in radiation exposure of a cardiac CT, the radiologist and the CT technician should be aware of the different dose reduction strategies.

Current Concepts in Cardiac CT Angiography for Patients With Acute Chest Pain

This article presents specific examples of delayed diagnosis of acute coronary syndrome, acute aortic dissection, and pulmonary embolism resulting from evaluating patients with nonspecific acute chest pain who did not undergo immediate dedicated coronary CT angiography (CTA) or triple rule-out protocol (TRO). These concrete examples of delayed diagnosis may advance the concept of using cardiac CTA (i.e., dedicated coronary CTA versus TRO) to triage patients with nonspecific acute chest pain. This article also provides an overall understanding of how to choose the most appropriate examination based on the specific clinical situation in the emergency department (i.e., dedicated coronary CTA versus TRO versus dedicated pulmonary or aortic CTA), how to interpret the CTA results, and the pros and cons of biphasic versus triphasic administration of intravenous contrast material during TRO examination. A precise understanding of various cardiac CTA protocols will improve the diagnostic performance of radiologists while minimizing hazards related to radiation exposure and contrast use.

Estimation of radiation exposure of 128-slice 4D-perfusion CT for the assessment of tumor vascularity

Objective

We aimed to estimate the effective dose of 4D-Perfusion-CT protocols of the lung, liver, and pelvis for the assessment of tumor vascularity.

Materials and Methods

An Alderson-Rando phantom equipped with thermoluminescent dosimeters was used to determine the effective dose values of 4D-Perfusion-CT. Phantom measurements were performed on a 128-slice single-source scanner in adaptive 4D-spiral-mode with bidirectional table movement and a total scan range of 69 mm over a time period of nearly 120 seconds (26 scans). Perfusion measurements were simulated for the lung, liver, and pelvis under the following conditions: lung (80 kV, 60 mAs), liver (80 kV/80 mAs and 80 kV/120 mAs), pelvis (100 kV/80 mAs and 100 kV/120 mAs).

Results

Depending on gender, the evaluated body region and scan protocol, an effective whole-body dose between 2.9-12.2 mSv, was determined. The radiation exposure administered to gender-specific organs like the female breast tissue (lung perfusion) or to the ovaries (pelvic perfusion) led to an increase in the female specific dose by 86% and 100% in perfusion scans of the lung and the pelvis, respectively.

Conclusion

Due to a significant radiation dose of 4D-perfusion-CT protocols, the responsible use of this new promising technique is mandatory. Gender- and organ-specific differences should be considered for indication and planning of tumor perfusion scans.

Evaluation of the patient with acute chest pain

The past decade has brought rapid advances in CT technology, which allows increasingly precise application to the study of coronary arteries and acute chest pain. The literature has expanded to lend quantifiable justification to the intuitive appeal of a rapid, reproducible, 3D study of the heart and vasculature. More complete analysis of efficacy and costs on broader populations will further refine our understanding of how best to implement what may become the new gold standard. Meanwhile, evolving technology promises to further challenge radiologists and clinicians to optimize approach and diagnosis to acute chest pain.

High-pitch electrocardiogram-triggered computed tomography of the chest: initial results

OBJECTIVES

Chest pain is one of the most frequent symptoms in the emergency department. A variety of different diseases, some of them acutely life threatening, can be the underlying cause. Electrocardiogram (ECG)-gated computed tomography angiography of the thorax has been proposed as a cost and time effective imaging technique for these patients. We describe a new high-pitch scan mode, which has been developed specifically for low-dose ECG-triggered computed tomography angiography using dual source computed tomography (CT).

MATERIAL AND METHODS

Twenty-four patients were examined with this technique on a second generation dual source CT system. The scan mode uses a pitch of 3.2 to acquire a spiral CT data set of the complete thorax in less than 1 second with a temporal resolution of 75 ms (scan parameters: 128 x 0.6 mm collimation, 0.28 seconds gantry rotation time, 370 mAs at 100 kV [15 patients] and 320 mAs at 120 kV [9 patients], reconstructed slice thickness 0.6 mm, increment 0.4 mm). Data acquisition was prospectively triggered at 50% to 60% of the RR interval to cover the range over the heart in diastole. A triple phase contrast injection protocol (total volume: 80 mL) was used to optimize enhancement of the pulmonary and systemic arterial vessels. Image quality was evaluated using a 4-point scale (1 = absence of motion artifacts; 2 = slight motion artifacts, fully evaluable; 3 = motion artifacts, but evaluable; 4 = unevaluable) on a per-segment basis.

RESULTS

The patients had an average heart rate of 68 +/- 15 bpm (range: 43-111 bpm) during data acquisition. Motion artifact free visualization of the aorta and pulmonary vessels was possible in each case, of 344 coronary artery segments, 242 (70%) had an image quality score of 1, 60 segments (17%) a score of 2, 28 segments (8%) a score of 3, and 14 segments (4%) were rated as "unevaluable." In 17 patients (10 patients with a heart rate < or =60 bpm) all segments were evaluable. The average dose length product was 113 +/- 11 mGy x cm per scan (mean effective dose 1.6 +/- 0.2 mSv) at 100 kV and 229 +/- 31 mGy x cm per scan (mean effective dose 3.2 +/- 0.4 mSv) at 120 kV.

CONCLUSION

Our initial results indicate that this high-pitch scan mode allows motion artifact free and accurate visualization of the thoracic vessels, and diagnostic image quality of the coronary arteries in patients with low and stable heart rates at a very low radiation exposure.

[Dual-source computed tomography in inpatients with atypical chest pain]

OBJECTIVE

To evaluate the potential usefulness of dual-source CT (DSCT) in the diagnostic work-up of inpatients with atypical chest pain of unknown etiology.

MATERIAL AND METHODS

Forty-one consecutive inpatients (25 male, 16 female; mean age 55.6+/-17.39 years) with atypical chest pain underwent DSCT to determine the cause of pain. Images were acquired with retrospective ECG gating after the administration of 120ml of iodinated contrast medium at 4ml/s using the bolus tracking technique. Two readers analyzed the images in consensus.

RESULTS

DSCT was diagnostic in all patients. We detected pulmonary embolisms in five patients and aortic disease in two (one aortic ulcer and one sacular aneurysm). Anomalies of the coronary arteries were depicted in 15 patients, two of whom presented luminal stenosis >50%. Extracardiovascular findings at DSCT included pneumonia in eleven patients, sarcoidosis in one, and non-small cell lung carcinoma in one. Pleural effusion was detected in four patients and pericardial effusion in another four. No pathological findings were observed in 22% of subjects. Evolution was favorable in all patients. No patients were readmitted for persistent pain or new onset of acute chest pain during the follow-up period.

CONCLUSION

DSCT can rule out most life-threatening clinical conditions that cause chest pain and is useful in determining the cause of chest pain in inpatients.