Coronary artery calcium scoring on different 64-detector scanners using a low-tube voltage (80 kVp)

Histogram-derived modified thresholds for coronary artery calcium scoring with lower tube voltage

We aimed to determine the proper modified thresholds for detecting and weighting CAC scores at 100 kV through histogram matching in comparison with 120 kV as a standard reference. From the training set (680 participants), modified thresholds at 100 kV were obtained through histogram matching of calcium pixels to 120 kV. From the validation set (213 participants), a standard CAC score at 120 kV, and modified CAC score at 100 kV using modified thresholds were compare through the paired t test and the Bland–Altman plot. Agreement for risk categories (no, minimal, mild, moderate, and severe) was evaluated using kappa statistics. Radiation doses were also compared. For the validation set, there was no significant difference between standard (median, 18.7; IQR, 0.0–207.0) and modified (median, 17.3; IQR, 0.0–220.9) CAC scores (P = 0.689). A small bias was achieved (0.74) with 95% limits of agreement from − 52.35 to 53.83. Agreements for risk categories were excellent (κ = 0.994). The mean dose-length-product of 100-kV scanning (30.1 ± 0.8 mGy * cm) was significantly decreased compared to 120-kV scanning (42.9 ± 0.6 mGy * cm) (P < 0.001). Histogram-derived modified thresholds at 100 kV can enable accurate CAC scoring while reducing radiation exposure.

Comparison of artery-based methods for ordinal grading of coronary artery calcium on low-dose chest computed tomography

OBJECTIVES

To identify the optimal artery-based method for ordinal grading of coronary artery calcium (CAC) on non-electrocardiogram (ECG)-gated low-dose chest computed tomography (LDCT) among three methods.

METHODS

A total of 120 asymptomatic subjects who underwent both LDCT and ECG-gated calcium scoring CT on the same day were retrospectively enrolled. Three cardiothoracic radiologists independently assessed CAC severity on LDCT (1.25-mm and 2.5-mm slice thickness) and classified it into four categories (none, mild, moderate, or severe) using three artery-based ordinal scoring methods (extent-based scoring, Weston scoring, and length-based scoring). Inter- and intra-observer CAC severity agreements of each method were assessed by Fleiss kappa statistics. Agreements between each method and ECG-gated calcium scoring CT were assessed by weighted kappa statistics.

RESULTS

The inter-observer agreement was highest with length-based method for both 1.25-mm (Fleiss kappa 0.735 for extent-based method, 0.801 for Weston score, and 0.813 for length-based method) and 2.5-mm slice thickness evaluation (Fleiss kappa 0.755 for extent-based method, 0.776 for Weston score, and 0.833 for extent-based method). Agreement across the three grading methods for the same observer was poor to moderate on 1.25-mm (Fleiss kappa 0.379-0.441) and moderate on 2.5-mm thickness evaluation (Fleiss kappa 0.427-0.461). Agreement of CAC severity between each method and ECG-gated calcium scoring CT was highest with the length-based method for all three observers on both 1.25-mm (weighted kappa 0.773-0.786) and 2.5-mm (weighted kappa 0.794-0.825) LDCT images.

CONCLUSION

Among the three artery-based ordinal grading methods, the length-based method appears to be the most reliable for evaluating CAC on non-ECG-gated LDCT.

KEY POINTS

• The length-based method showed the highest inter-observer agreement and the highest agreement with the ECG-gated calcium scoring CT, compared with the extent-based method and the Weston score.

Coronary artery calcium scoring at lower tube voltages - Dose determination and scoring mechanism

PURPOSE

Population dose has been a concern with coronary artery calcium scoring CT since it is performed in adults with borderline risk. Lower tube voltage acquisitions are appealing but there are no agreed schemes for reduced dose determination. Moreover, conventional scoring cannot be used without changing the multiple Agatston thresholds.

METHODS

By applying consistent calcium contrast-to-noise ratio to two anthropomorphic heart phantoms (medium and large) with 3-cm hydroxyapatite (HA) inserts, scanned using a dual-source CT, the relationship was derived between the volume CT dose index (CTDI_vol) at lower tube voltages and the baseline CTDI_vol at 120 kVp. The baseline CTDI_vol was obtained using the noise thresholds from the images acquired at 120 kVp. To preserve the conventional Agatston thresholds, down-scaling with the found factors was applied to images acquired at lower voltages with a dynamic heart module and 1.2-5 mm inserts (50-400 mg/cc) on the coronary tracks. Scores were evaluated on the scaled images by six readers.

RESULTS

The CTDI_vol at lower voltages was related to the baseline CTDI_vol following a power form of the voltage (index 1.246), regardless of the phantom size. The baseline CTDI_vol was 1.5 and 4.5 mGy, for the medium and large phantoms, respectively. Correspondingly, the reduced CTDI_vol at 100-70 kVp were 1.28-0.76 mGy, and 3.57-2.32 mGy. The downscaling factors were 0.88-0.63. The calcium scores at lower voltages were found within 12 % of the ground-truths.

CONCLUSION

A vendor-independent approach was established to obtain the reduced dose and correct coronary calcium scores at lower tube voltages.

Impact of Abdominal Aortic Calcification on Central Haemodynamics and Decline of Glomerular Filtration Rate in Patients with Chronic Kidney Disease Stages 3 and 4

BACKGROUND/AIM

Calcifications of large arteries are frequent in chronic kidney disease (CKD) and may contribute to the high cardiovascular risk in this population. The aim of this study was to examine whether abdominal aortic calcification volume (AACV) was a predictor of the rate of decline in glomerular filtration rate (GFR) in a cohort of patients with CKD stages 3 and 4.

METHODS

Eighty-four patients with CKD stages 3 and 4 were enrolled in this prospective observational study. At study entry, and annually, GFR was measured by plasma 51Cr-EDTA clearance. At baseline, haemodynamics was assessed and AACV was determined by computer tomography.

RESULTS

The mean follow-up time was 3.4 years and mean decline in GFR was -2.69 mL/min/1.73 m2 per year. At baseline, abdominal aortic calcification (AAC) was detected in 66 patients (79%). A binary logistic regression analysis revealed that age was the only statistically significant independent predictor of AAC. In patients with AAC, male gender (B = 0.413, p = 0.030), aortic diastolic blood pressure (B = -0.025, p = 0.001) and ankle-brachial index (B = -1.666, p = 0.002) were independently associated with AACV using a multiple linear regression analysis. Neither the presence nor the extent of AAC was significantly associated with the rate of change in GFR during follow-up.

CONCLUSION

In this cohort of patients with CKD stages 3 and 4, only age was an independent predictor of the presence of AAC. AACV was not associated with the rate of decline in GFR.

Coronary Artery Calcium Imaging in the ROBINSCA Trial: Rationale, Design, and Technical Background

RATIONALE AND OBJECTIVES

To describe the rationale, design, and technical background of coronary artery calcium (CAC) imaging in the large-scale population-based cardiovascular disease screening trial (Risk Or Benefit IN Screening for CArdiovascular Diseases [ROBINSCA]).

MATERIALS AND METHODS

First, literature search was performed to review the logistics, setup, and settings of previously performed CAC imaging studies, and current clinical CAC imaging protocols of participating centers in the ROBINSCA trial were evaluated. A second literature search was performed to evaluate the impact of computed tomography parameter settings on CAC score.

RESULTS

Based on literature reviews and experts opinion an imaging protocol accompanied by data management protocol was created for ROBINSCA. The imaging protocol should consist of a fixed tube voltage, individually tailored tube current setting, mid-diastolic electrocardiography-triggering, fixed field-of-view, fixed reconstruction kernel, fixed slice thickness, overlapping reconstruction and without iterative reconstruction. The analysis of scans is performed with one type and version of CAC scoring software, by two dedicated and experienced researchers. The data management protocol describes the organization of data handling between the coordinating center, participating centers, and core analysis center.

CONCLUSION

In this paper we describe the rationale and technical considerations to be taken in developing CAC imaging protocol, and we present a detailed protocol that can be implemented for CAC screening purposes.

Dose reduction techniques in coronary calcium scoring: The effect of iterative reconstruction combined with low tube voltage on calcium scores in a thoracic phantom

OBJECTIVES

To define a dose-reduced coronary calcium CT protocol that provides similar calcium score values as a conventional 120kVp protocol.

METHODS

A thorax phantom containing 100 calcifications was scanned with the reference protocol (120kVp, 90 ref mAs, FBP) and 30 dose-reduced protocols (70-110kVp, 90 ref mAs, FBP and iterative reconstruction (IR) levels 1-5) with 3rd generation dual-source CT. For protocols that yielded similar detectability and calcium scores as the reference protocol, additional scans were acquired at reduced ref mAs. Kendall's τ_b and independent-samples-median test were used to determine trends and differences in contrast/signal-to-noise ratio (CNR and SNR), dose and calcium scores.

RESULTS

The detectability and calcium scores decreased at increasing IR levels (τb<-0.825, p<0.001) and increasing tube voltage (τ_b<-0.679, p<0.001). For 90kVp-IR3 and 100kVp-IR1, similar detectability and calcium score was found compared to the reference protocol (p>0.206). For these protocols, lower tube currents did not affect the detectability and Agatston score (p>0.206), while CNR and SNR were similar/higher compared to the reference protocol (0.008<p<0.206). Dose reduction was 60.6% (90kVp-IR3) and 43.6% (100kVp-IR1).

CONCLUSIONS

The protocol of 90kVp-IR3 and 100kVp-IR1 yielded similar calcium detectability, Agatston score and image quality as the reference protocol, with dose reduction up to 60.6%.

Feasibility of spectral shaping for detection and quantification of coronary calcifications in ultra-low dose CT

Objectives

To evaluate detectability and quantification of coronary calcifications for CT with a tin filter for spectral shaping.

Methods

Phantom inserts with 100 small and 9 large calcifications, and a moving artificial artery with 3 calcifications (speed 0–30 mm/s) were placed in a thorax phantom simulating different patient sizes. The phantom was scanned in high-pitch spiral mode at 100 kVp with tin filter (Sn100 kVp), and at a reference of 120 kVp, with electrocardiographic (ECG) gating. Detectability and quantification of calcifications were analyzed for standard (130 HU) and adapted thresholds.

Results

Sn100 kVp yielded lower detectability of calcifications (9 % versus 12 %, p = 0.027) and lower Agatston scores (p < 0.008), irrespective of calcification, patient size and speed. Volume scores of the moving calcifications for Sn100 kVp at speed 10–30 mm/s were lower (p < 0.001), while mass scores were similar (p = 0.131). For Sn100 kVp with adapted threshold of 117 HU, detectability (p = 1.000) and Agatston score (p > 0.206) were similar to 120 kVp. Spectral shaping resulted in median dose reduction of 62.3 % (range 59.0–73.4 %).

Conclusions

Coronary calcium scanning with spectral shaping yields lower detectability of calcifications and lower Agatston scores compared to 120 kVp scanning, for which a HU threshold correction should be developed.

Key points

• Sn100kVp yields lower detectability and lower Agatston scores compared to 120kVp

• Adapted HU threshold for Sn100kVp provides Agatston scores comparable to 120kVp

• Sn100 kVp considerably reduces dose in calcium scoring versus 120 kVp

The feasibility of low-dose CT protocols for coronary artery calcium scoring and PET attenuation correction in cardiac PET/CT

INTRODUCTION

The purpose of this study was to investigate the feasibility of using low-dose computed tomography (CT) in coronary artery calcium scoring and PET attenuation correction for patients in different weight categories undergoing cardiac PET/CT examinations.

MATERIALS AND METHODS

Calcium scoring computed tomography (CSCT) scans and PET scans of anthropomorphic cardiac phantoms simulating normal-weight, mildly obese, and severely obese patients were acquired with a hybrid PET/CT scanner. CSCT images were acquired at 120 kVp, with tube current ranging from 10 to 550 mA. PET scans were performed in three-dimensional mode, with acquisition time of 3 min/bed position. The image quality of cardiac PET/CT was evaluated by assessing the signal-to-noise ratio. CT-based coronary artery calcium quantification was performed using the Agatston scoring system.

RESULTS

On the basis of our results, the CSCT protocols using tube currents of 50 and 150 mA should be able to achieve the lowest possible radiation dose while maintaining the desired image quality for normal-weight and mildly obese patients undergoing cardiac PET/CT examinations, respectively. When the proposed low-dose CSCT protocols were performed, radiation dose could be reduced by 83.34 and 50% compared with those from CSCT scans acquired with standard tube current settings for normal-weight and mildly obese patients, respectively. In the scanning of severely obese patients, an increase in tube voltage or current would help improve the reliability of image information provided by cardiac PET/CT.

CONCLUSION

Our study demonstrated the feasibility of low-dose CT protocols for coronary artery calcium scoring and PET attenuation correction in cardiac PET/CT to examine patients in different weight categories. The calculations performed in this work should be able to provide practical information to achieve necessary diagnostic information while keeping radiation dose as low as reasonably achievable.