Low tube voltage prospectively ECG-triggered coronary CT angiography: a systematic review of image quality and radiation dose

Cardiovascular computed tomography in cardiovascular disease: An overview of its applications from diagnosis to prediction

Cardiovascular computed tomography angiography (CTA) is a widely used imaging modality in the diagnosis of cardiovascular disease. Advancements in CT imaging technology have further advanced its applications from high diagnostic value to minimising radiation exposure to patients. In addition to the standard application of assessing vascular lumen changes, CTA-derived applications including 3D printed personalised models, 3D visualisations such as virtual endoscopy, virtual reality, augmented reality and mixed reality, as well as CT-derived hemodynamic flow analysis and fractional flow reserve (FFRCT) greatly enhance the diagnostic performance of CTA in cardiovascular disease. The widespread application of artificial intelligence in medicine also significantly contributes to the clinical value of CTA in cardiovascular disease. Clinical value of CTA has extended from the initial diagnosis to identification of vulnerable lesions, and prediction of disease extent, hence improving patient care and management. In this review article, as an active researcher in cardiovascular imaging for more than 20 years, I will provide an overview of cardiovascular CTA in cardiovascular disease. It is expected that this review will provide readers with an update of CTA applications, from the initial lumen assessment to recent developments utilising latest novel imaging and visualisation technologies. It will serve as a useful resource for researchers and clinicians to judiciously use the cardiovascular CT in clinical practice.

Thin slice photon-counting CT coronary angiography compared to conventional CT: Objective image quality and clinical radiation dose assessment

BACKGROUND

Photon-counting CT (PCCT) is the next-generation CT scanner that enables improved spatial resolution and spectral imaging. For full spectral processing, higher tube voltages compared to conventional CT are necessary to achieve the required spectral separation. This generated interest in the potential influence of thin slice high tube voltage PCCT on overall image quality and consequently on radiation dose.

PURPOSE

This study first evaluated tube voltages and radiation doses applied in patients who underwent coronary CT angiography with PCCT and energy-integrating detector CT (EID-CT). Next, image quality of PCCT and EID-CT was objectively evaluated in a phantom study simulating different patient sizes at these tube voltages and radiation doses.

METHODS

We conducted a retrospective analysis of clinical doses of patients scanned on a conventional and PCCT system. Average patient water equivalent diameters for different tube voltages were extracted from the dose reports for both EID-CT and PCCT. A conical phantom made of polyethylene with multiple diameters (26/31/36 cm) representing different patient sizes and containing an iodine insert was scanned with a EID-CT scanner using tube voltages and phantom diameters that match the patient scans and characteristics. Next, phantom scans were made with PCCT at a fixed tube voltage of 120 kV and with CTDIVOL values and phantom diameters identical to the EID-CT scans. Clinical image reconstructions at 0.6 mm slice thickness for conventional CT were compared to PCCT images with 0.4 mm slice thickness. Image quality was quantified using the detectability index (d'), which estimated the visibility of a 3 mm diameter contrast-enhanced coronary artery by considering noise, contrast, resolution, and human visual perception. Alongside d', noise, contrast and resolution were also individually assessed. In addition, the influence of various kernels (Bv40/Bv44/Bv48/Bv56), quantum iterative reconstruction strengths (QIR, 3/4) and monoenergetic levels (40/45/50/55 keV) for PCCT on d' was investigated.

RESULTS

In this study, 143 patients were included: 47 were scanned on PCCT (120 kV) and the remaining on EID-CT (74 small-sized at 70 kV, 18 medium-sized at 80 kV and four large-sized at 90 kV). EID-CT showed 7%-17% higher d' than PCCT with Bv40 kernel and strength four for small/medium patients. Lower monoenergetic images (40 keV) helped mitigate the difference to 1%-6%. For large patients, PCCT's detectability was up to 31% higher than EID-CT. PCCT has thinner slices but similar noise levels for similar reconstruction parameters. The noise increased with lower keV levels in PCCT (≈30% increase), but higher QIR strengths reduced noise. PCCT's iodine contrast was stable across patient sizes, while EID-CT had 33% less contrast in large patients than in small-sized patients.

CONCLUSION

At 120 kV, thin slice PCCT enables CCTA in phantom scans representing large patients without raising radiation dose or affecting vessel detectability. However, higher doses are needed for small and medium-sized patients to obtain a similar image quality as in EID-CT. The alternative of using lower mono-energetic levels requires further evaluation in clinical practice.

Recommendations for reducing exposure to medical X-ray irradiation (Review)

With the increasing frequency of X-ray examinations in clinical medicine, public concern regarding the harm caused by exposure to X-ray radiation is also increasing. However, some physicians are not completely aware of the dangers of exposure to X-ray irradiation. Individuals specialized in this field, including physicians, have a better understanding of these dangers, which limits the use of X-rays in medicine. The present study aimed to address strategies for reducing the harm caused by exposure to medical X-rays and increase public awareness regarding X-ray radiation. Through a literature search and review, combined with the current status of clinical X-ray examination and the authors' professional experience, the present study highlights the importance of reducing X-ray exposure, and proposes several specific recommendations and measures for reducing the frequency or dose of X-ray irradiation. On the whole, the finding discussed in the present review suggest the minimal use of medical X-ray examinations and that alternative tests should be selected whenever possible. When medical X-ray screening and treatments are necessary, the risk-benefit ratio should be assessed, possibly aiming to achieve avoidable exposure. Further attention should be paid to protect sensitive glands and reduce the risks in children.

Influence of Contrast Agent Injection Scheme Customized by Dual-Source CT Based on Automatic Tube Voltage Technology on Image Quality and Radiation Dose of Coronary Artery Imaging

Objective

To explore the influence of a contrast agent injection scheme customized by dual-source CT based on automatic tube voltage technology on coronary imaging image quality and radiation dose.

Methods

A total of 205 patients who underwent coronary CT angiography (CCTA) in our hospital from June 2021 to September 2021 were selected. 105 patients in the control group who underwent routine scanning according to body mass (BMI) and 100 patients in the observation group who set tube voltage and contrast agent dosage according to automatic tube voltage selection technology. CT values of the aortic root (AO); left anterior descending (LAD) branch; proximal, middle, and distal segments of the right coronary artery (RCA); and proximal and distal segments of left circumflex (LCX) branch were measured. We calculated the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the image. Image quality scoring and effective dose (ED) calculation were carried out.

Results

There was no significant difference in the CT value, SNR value, and CNR value of each part of the artery between the two groups (P > 0.05). Image quality scores of the control group and the observation group were 1.28 ± 0.25 and 1.25 ± 0.23, respectively, and there was no significant difference in scores (P > 0.05). In the control group, the dosage of comparator was 43.81 ± 6.74 ml, and the ED was 4.92 ± 1.26 mSv. The dosage of contrast agent in the observation group was 34.23 ± 6.39 ml, and ED was 3.05 ± 0.94 mSv. The dosage of contrast agent and ED in the observation group were lower than those in the control group (P < 0.05).

Conclusion

The contrast agent injection scheme customized by dual-source CT based on automatic tube voltage technology can meet the clinical requirements of coronary image quality, reduce the radiation dose and contrast agent consumption, and help doctors choose a more accurate and reasonable examination scheme, which has certain clinical application value.

Comparing feasibility of different tube voltages and different concentrations of contrast medium in coronary CT angiography of overweight patients

OBJECTIVES

To compare image quality, radiation dose, and iodine intake of coronary computed tomography angiography (CCTA) acquired by wide-detector using different tube voltages and different concentrations of contrast medium (CM) for overweight patients.

MATERIALS AND METHODS

A total of 150 overweight patients (body mass index≥25 kg/m2) who underwent CCTA are enrolled and divided into three groups according to scan protocols namely, group A (120 kVp, 370 mgI/ml CM); group B (100 kVp, 350 mgI/ml CM); and group C (80 kVp, 320 mgI/ml CM). The CT values, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and figure-of-merit (FOM) of all images are calculated. Images are subjectively assessed using a 5-point scale. In addition, the CT dose index volume (CTDIvol) and dose length product (DLP) of each patient are recorded. The effective radiation dose (ED) is also calculated. Above data are then statistically analyzed.

RESULTS

The mean CT values, SNR, CNR, and subjective image quality of group A are significantly lower than those of groups B and C (P < 0.001), but there is no significant difference between groups B and C (P > 0.05). FOMs show a significantly increase trend from group A to C (P < 0.001). The ED values and total iodine intake in groups B and C are 30.34% and 68.53% and 10.22% and 16.85% lower than those in group A, respectively (P < 0.001).

CONCLUSION

The lower tube voltage and lower concentration of CM based on wide-detector allows for significant reduction in iodine load and radiation dose in CCTA for overweight patients comparing to routine scan protocols. It also enhances signal intensity of CCTA and maintains image quality.

Patient-tailored Contrast Delivery Protocols for Computed Tomography Coronary Angiography: Lower Contrast Dose and Better Image Quality

PURPOSE

The first objective of this study was to evaluate the efficacy of a patient-tailored contrast delivery protocol for coronary computed tomography angiography (CTCA), in terms of diagnostic coronary attenuation and total iodine load (TIL), by adjusting the iodine delivery rate (IDR) via dilution for body weight and tube voltage (kV), as compared with a protocol with a fixed bolus of contrast in a clinical setting. The secondary objective was to assess the association between the test-bolus data and luminal attenuation in CTCA.

MATERIALS AND METHODS

Patients who underwent CTCA with fixed IDR contrast delivery (cohort 1) or with IDR adjusted for body weight and kV settings (70 to 120 kV) (cohort 2) were included, and compared for intravascular luminal attenuation and TIL. The association between intravascular luminal attenuation and test-bolus scan data was investigated with linear regression.

RESULTS

In cohort 1 (176 patients), the mean luminal attenuation differed markedly between kV categories, whereas in cohort 2 (154 patients), there were no marked differences. The mean TIL reduced significantly (20.1±1.2 g in cohort 1, 17.7±3.0 g in cohort 2, P<0.001). The peak height of the test-bolus scan was independently associated with luminal attenuation in the ascending aorta, with a 0.58 HU increase per HU peak-height increase (SE=0.18, P<0.001).

CONCLUSION

Clinical implementation of a patient-tailored contrast delivery protocol for CTCA, adjusted for body weight and kV, improves luminal attenuation and significantly reduces the TIL. The peak height of the test-bolus scan is associated with luminal attenuation in the ascending aorta in the CTCA scan.

Coronary CT Angiography in Patients With Non-ST-Segment Elevation Acute Coronary Syndrome

BACKGROUND

In patients with non-ST-segment elevation acute coronary syndrome (NSTEACS), coronary pathology may range from structurally normal vessels to severe coronary artery disease.

OBJECTIVES

The purpose of this study was to test if coronary computed tomography angiography (CTA) may be used to exclude coronary artery stenosis ≥50% in patients with NSTEACS.

METHODS

The VERDICT (Very Early Versus Deferred Invasive Evaluation Using Computerized Tomography in Patients With Acute Coronary Syndromes) trial (NCT02061891) evaluated the outcome of patients with confirmed NSTEACS randomized 1:1 to very early (within 12 h) or standard (48 to 72 h) invasive coronary angiography (ICA). As an observational component of the trial, a clinically blinded coronary CTA was conducted prior to ICA in both groups. The primary endpoint was the ability of coronary CTA to rule out coronary artery stenosis (≥50% stenosis) in the entire population, expressed as the negative predictive value (NPV), using ICA as the reference standard.

RESULTS

Coronary CTA was conducted in 1,023 patients-very early, 2.5 h (interquartile range [IQR]: 1.8 to 4.2 h), n = 583; and standard, 59.9 h (IQR: 38.9 to 86.7 h); n = 440 after the diagnosis of NSTEACS was made. A coronary stenosis ≥50% was found by coronary CTA in 68.9% and by ICA in 67.4% of the patients. Per-patient NPV of coronary CTA was 90.9% (95% confidence interval [CI]: 86.8% to 94.1%) and the positive predictive value, sensitivity, and specificity were 87.9% (95% CI: 85.3% to 90.1%), 96.5% (95% CI: 94.9% to 97.8%) and 72.4% (95% CI: 67.2% to 77.1%), respectively. NPV was not influenced by patient characteristics or clinical risk profile and was similar in the very early and the standard strategy group.

CONCLUSIONS

Coronary CTA has a high diagnostic accuracy to rule out clinically significant coronary artery disease in patients with NSTEACS.

Clinical Applications of Wide-Detector CT Scanners for Cardiothoracic Imaging: An Update

Technical developments in multidetector computed tomography (CT) have increased the number of detector rows on the z-axis, and 16-cm wide-area-coverage CT scanners have enabled volumetric scanning of the entire heart. Beyond coronary arterial imaging, such innovations offer several advantages during clinical imaging in the cardiothoracic area. The wide-detector CT scanner markedly reduces the image acquisition time to less than 1 second for coronary CT angiography, thereby decreasing the volume of contrast material and radiation dose required for the examination. It also eliminates stair-step artifacts, allowing robust improvements in myocardial function and perfusion imaging. Additionally, new imaging techniques for the cardiothoracic area, including subtraction imaging and free-breathing scans, have been developed and further improved by using the wide-detector CT scanner. This article investigates the technical developments in wide-detector CT scanners, summarizes their clinical applications in the cardiothoracic area, and provides a review of the recent literature.

Coronary CT angiography by modifying tube voltage and contrast medium concentration: Evaluation of image quality and radiation dose

BACKGROUND

Currently, there is an increasing interest in noninvasive imaging of cardiovascular system such as computed tomography coronary angiography (CCTA). The risks of radiation-induced cancer and contrast-induced nephropathy (CIN) have always been regarded as concerns which increased demand for CCTA using reduced radiation dose and iodine intake. We aimed to evaluate the image quality and radiation dose of CCTA by modifying tube voltage and concentration of contrast media.

METHODS

The present study includes 105 patients who underwent CCTA for clinical indications. Specific inclusion and exclusion criteria in terms of patient's weight, body mass index, calcium score, and stenting were used. First group of patients scanned by 120 kV and 370 mg I/mL contrast medium, compared with second and third groups for which scanning was performed using 100 kV and 370 mg I/mL and 100 kV and 300 mg I/mL, respectively. Image quality was evaluated both subjectively and objectively. The effective dose and iodine intake were also measured.

RESULTS

Using low kV protocols led to radiation dose reduction up to 38% and applying low contrast medium concentration with consequent reduced iodine intake up to 21%. Moreover, there were significant differences in image quality of new scanning protocols.

CONCLUSION

Reduction in tube voltage with lowering of contrast medium concentration can reduce radiation dose and iodine intake with acceptable image quality.

Personalized administration of contrast medium with high delivery rate in low tube voltage coronary computed tomography angiography

Background

High delivery rate is an important factor in optimizing contrast medium administration in coronary computed tomography angiography (CCTA). A personalized contrast volume calculation algorithm incorporating high iodine delivery rate (IDR) can reduce total iodine dose (TID) and produce optimal vessel contrast enhancement (VCE) in low tube voltage CCTA. In this study, we developed and validated an algorithm for calculating the volume of contrast medium delivered at a high rate for patients undergoing retrospectively ECG-gated CCTA with low tube voltage protocol.

Methods

The algorithm for an IDR of 2.22 gI·s^-1 was developed based on the relationship between VCE and contrast volume in 141 patients; test bolus parameters and characteristics in 75 patients; and, tube voltage in a phantom study. The algorithm was retrospectively tested in 45 patients who underwent retrospectively ECG-gated CCTA with a 100 kVp protocol. Image quality, TID and radiation dose exposure were compared with those produced using the 120 kVp and routine contrast protocols.

Results

Age, sex, body surface area (BSA) and peak contrast enhancement (PCE) were significant predictors for VCE (P<0.05). A strong linear correlation was observed between VCE and contrast volume (r=0.97, P<0.05). The 100-to-120 kVp contrast enhancement conversion factor (E_c) was calculated at 0.81. Optimal VCE (250 to 450 HU) and diagnostic image quality were obtained with significant reductions in TID (32.1%) and radiation dose (38.5%) when using 100 kVp and personalized contrast volume calculation algorithm compared with 120 kVp and routine contrast protocols (P<0.05).

Conclusions

The proposed algorithm could significantly reduce TID and radiation exposure while maintaining optimal VCE and image quality in CCTA with 100 kVp protocol.

Reducing both radiation and contrast doses in coronary CT angiography in lean patients on a 16-cm wide-detector CT using 70 kVp and ASiR-V algorithm, in comparison with the conventional 100-kVp protocol

OBJECTIVE

To investigate the value of prospectively ECG-triggered coronary CT angiography (CCTA) for lean patients with body mass index (BMI) ≤ 23 kg/m² using 70 kVp and high-level volume-based adaptive statistical iterative reconstruction (ASiR-V) algorithm on a 16-cm wide-detector CT system for reducing both radiation and contrast doses in comparison with the conventional 100-kVp protocol.

MATERIALS AND METHODS

Thirty patients (group A) were prospectively enrolled to undergo 70-kVp CCTA on a 16-cm wide-detector CT scanner with noise index (NI) of 36 HU and at weight-dependent contrast dose rate of 16 mg I/kg/s for 9-s injection. Images were reconstructed with 80% ASiR-V. Radiation dose, contrast dose, and image quality were statistically compared with 30 patients (group B) in database with matching BMI who underwent conventional 100-kVp CCTA with NI of 25 HU, and at 25 mg I/kg/s rate for 10-s injection and reconstructed with 60% ASiR-V.

RESULTS

There was no significant difference in patient demographics between the two groups (all p > 0.05). The two groups also had similar mean CT values and contrast-noise ratio (CNR) and subjective image quality (all p > 0.05). However, group A with 70 kVp reduced the effective dose by 75.3% compared with group B (0.43 ± 0.20 mSv vs. 1.74 ± 1.01 mSv, p < 0.001), and required 42.4% less contrast dose than group B (22.46 ± 2.94 ml vs. 38.99 ± 5.10 ml, p < 0.001).

CONCLUSIONS

Prospectively ECG-triggered CCTA using 70 kVp and high-level ASiR-V on a 16-cm wide-detector CT system provides diagnostic images with substantial reduction in both radiation and contrast doses for patients with BMI ≤ 23 kg/m² compared to the conventional 100-kVp protocol.

KEY POINTS

• 70-kVp CCTA produces excellent images at sub-millisievert radiation. • 70-kVp CCTA reduces both radiation and contrast doses over conventional protocol. • Achieving low-dose CCTA with combined low kVp and high-level ASIR-V.

Computed tomography coronary angiography in patients without known coronary artery disease can demonstrate possible non-cardiovascular causes of non-acute retrosternal chest pain

OBJECTIVES

To assess the computed tomography coronary angiography (CTCA) accuracy for demonstrating possible non-cardiovascular causes of non-acute retrosternal chest pain in patients without known coronary artery disease (CAD) and to correlate CTCA results with the patient management and relief from pain.

METHODS

This prospective observational study was approved by the ethical committee. Consecutive patients suffering non-acute chest pain who underwent CTCA and with not known CAD were enrolled and classified as having coronary diseases (CD) or extracardiac diseases (ECD). Association between age, sex, body mass index (BMI), cardiovascular risk factors, and type of chest pain with CD or ECD was estimated. Correlation between BMI classes and each risk factor was also calculated.

RESULTS

A total of 106 patients (60 males; age 62 ± 14 years [mean ± standard deviation]; mean BMI 27) were enrolled. Hypertension was found in 71/106 (67%); smoking was significantly more frequent among males (p = 0.003) and hypercholesterolemia among females (p = 0.017); hypertension and hypercholesterolemia significantly correlated with age, and hypertension also with BMI. Pain was atypical in 70/106 (66%) patients. The kind of pain did not correlate with disease or gender. CTCA showed possible causes of chest pain in 69/106 (65%) patients; 32/69 (47%) having only CD, 23/69 (33%) only ECD, and 14/69 (20%) both CD and ECD. Prevalence was: hiatal hernia 35/106 (33%); significant CAD 24/106 (23%); myocardial bridging 22/106 (21%). At follow-up of 94/106 (89%) patients, 71/94 (76%) were pain-free, 14/17 (82%) significant CAD had been treated, and only one patient with non-significant CAD was treated after CTCA.

CONCLUSION

CTCA suggested possible causes of non-acute pain in 65% of patients.

MAIN MESSAGES

• CTCA can either rule in or rule out possible causes of chest pain alternative to CAD. • Clinically relevant findings were detected in 65% of patients with non-acute chest pain. • Non-cardiovascular diseases potentially explained symptoms in 35% of patients.