Step and shoot coronary CT angiography using 256-slice CT: effect of heart rate and heart rate variability on image quality

A Novel Reconstruction Technique to Reduce Stair-Step Artifacts in Sequential Mode Coronary CT Angiography

PURPOSE

Prospective electrocardiography-triggering is one of the most commonly used cardiac computed tomography (CT) scan modes but can be susceptible to stair-step artifacts in the transition areas of an acquisition over multiple cardiac cycles. We evaluated a novel reconstruction algorithm to reduce the occurrence and severity of such artifacts in sequential coronary CT angiography.

MATERIALS AND METHODS

In this institutional review board-approved, retrospective study, 50 consecutive patients (16 females; mean age, 58.9 ± 15.2) were included who underwent coronary CT angiography on a dual-source photon-counting detector CT in the sequential ultra-high-resolution mode with a detector collimation of 120 × 0.2 mm. Each scan was reconstructed without (hereafter called standard reconstruction) and with the novel ZeeFree reconstruction algorithm, which aims to minimize stair-step artifacts. The presence and extent of stair-step artifacts were rated by 2 independent, blinded readers on a 4-point discrete visual scale. The relationship between the occurrences of artifacts was correlated with the average and variability of heart rate and with patient characteristics.

RESULTS

A total of 504 coronary segments were included into the analyses. In standard reconstructions, reader 1 reported stair-step artifacts in 40/504 (7.9%) segments, from which 12/504 led to nondiagnostic image quality (2.4% of all segments). Reader 2 reported 56/504 (11.1%) stair-step artifacts, from which 11/504 lead to nondiagnostic image quality (2.2% of all segments). With the ZeeFree algorithm, 9/12 (75%) and 8/11 (73%) of the nondiagnostic segments improved to a diagnostic quality for readers 1 and 2, respectively. The ZeeFree reconstruction algorithm significantly reduced the frequency and extent of stair-step artifacts compared with standard reconstructions for both readers ( P < 0.001, each). Heart rate variability and body mass index were significantly related to the occurrence of stair-step artifacts ( P < 0.05).

CONCLUSIONS

Our study demonstrates the feasibility and effectiveness of a novel reconstruction algorithm leading to a significant reduction of stair-step artifacts and, hence, a reduction of coronary segments with a nondiagnostic image quality in sequential ultra-high-resolution coronary photon-counting detector CT angiography.

Heart Rate-Dependent Degree of Motion Artifacts in Coronary CT Angiography Acquired by a Novel Purpose-Built Cardiac CT Scanner

Although reaching target heart rate (HR) before coronary CT angiography (CCTA) is still of importance, adequate HR control remains a challenge for many patients. Purpose-built cardiac scanners may provide optimal image quality at higher HRs by further improving temporal resolution. We aimed to compare the amount of motion artifacts on CCTA acquired using a dedicated cardiac CT (DCCT) compared to a conventional multidetector CT (MDCT) scanner. We compared 80 DCCT images to 80 MDCT scans matched by sex, age, HR, and coronary dominance. Image quality was graded on a per-patient, per-vessel and per-segment basis. Motion artifacts were assessed using Likert scores (1: non-diagnostic, 2: severe artifacts, 3: mild artifacts, 4: no artifacts). Patients were stratified into four groups according to HR (<60/min, 60−65/min, 66−70/min and >70/min). Overall, 2328 coronary segments were evaluated. DCCT demonstrated superior overall image quality compared to MDCT (3.7 ± 0.4 vs. 3.3 ± 0.7, p < 0.001). DCCT images yielded higher Likert scores in all HR ranges, which was statistically significant in the 60−65/min, 66−70/min and >70/min ranges (3.9 ± 0.2 vs. 3.7 ± 0.2, p = 0.008; 3.5 ± 0.5 vs. 3.1 ± 0.6, p = 0.048 and 3.5 ± 0.4 vs. 2.7 ± 0.7, p < 0.001, respectively). Using a dedicated cardiac scanner results in fewer motion artifacts, which may allow optimal image quality even in cases of high HRs.

Reduction of cardiac motion artifact in step-and-shoot coronary CT angiography with third-generation as compared with second-generation dual-source CT scanners

PURPOSE

We aimed to compare the effects of misregistration (stair-step artifact) occurrence during coronary computed tomography angiography (CCTA) using third- and second-generation dual-source computed tomography (DSCT) scanners. METHODSÇ: CCTA was performed in consecutive patients with suspected coronary heart disease. Patients were randomly assigned to two groups and imaged using a third-generation (n=68; group A) or second-generation (n=63; group B) DSCT scanner. Heart rate (HR), heart rate variability (HRV), the number of acquisition steps required, and the anatomical cardiac length of each patient were recorded and compared between the two groups. Qualitative interpretation and analyses were scored with respect to subjective image quality and misregistration (stair-step artifact) by two interpreters. Cohen's kappa was used to evaluate the consistency between the observers.

RESULTS

All CCTA images (100%) on both DSCT scanners yielded satisfactory image quality, with a subjective image quality score of 4.21±0.17. The consistency between the two observers with respect to misregistration and subjective scores were good (κ= 0.91 and 0.92, respectively). Both the number of acquisition steps required and the scan length of each patient in group A differed significantly (p < 0.001) from those in group B; there were significantly fewer artifacts in group A than in group B (p < 0.001). Misregistration artifacts did not correlate with the HRs or HRVs between two required acquisition steps (p > 0.20).

CONCLUSION

As compared with second-generation DSCT, the reduced number of acquisition steps required and the shorter scan length in third-generation DSCT reduced the occurrence of misregistration artifacts in CCTA images.

Contrast medium administration with a body surface area protocol in step-and-shoot coronary computed tomography angiography with dual-source scanners

We evaluated the feasibility and image quality of prospective electrocardiography (ECG)-triggered coronary computed tomography angiography (CCTA) using a body surface area (BSA) protocol for contrast-medium (CM) administration on both second- and third-generation scanners (Flash and Force CT), without using heart rate control. One-hundred-and-eighty patients with suspected coronary heart disease undergoing CCTA were divided into groups A (BSA protocol for CM on Flash CT), B (body mass index (BMI)-matched patients; BMI protocol for CM on Flash CT), and C (BMI-matched patients; BSA protocol for CM on Force CT). Patient characteristics, quantitative and qualitative measures, and radiation dose were compared between groups A and B, and A and C. Of the 180 patients, 99 were male (median age, 62 years). Average BSA in groups A, B, and C was 1.80 ± 0.17 m², 1.74 ± 0.16 m², and 1.64 ± 0.17 m², respectively, with groups A and C differing significantly (P < 0.001). Contrast volume (50.50 ± 8.57 mL vs. 45.00 ± 6.18 mL) and injection rate (3.90 ± 0.44 mL/s vs. 3.63 ± 0.22 mL/s) differed significantly between groups A and C (P < 0.001). Groups A and C (both: all CT values > 250 HU, average scores > 4) achieved slightly lower diagnostic image quality than group B. The BSA protocol for CM administration was feasible in both Flash and Force CT, and therefore may be valuable in clinical practice.

Second-generation motion correction algorithm improves diagnostic accuracy of single-beat coronary CT angiography in patients with increased heart rate

OBJECTIVE

To assess the effect of a second-generation motion correction algorithm on the diagnostic accuracy of coronary computed tomography angiography (CCTA) using a 256-detector row CT in patients with increased heart rates.

METHODS

Eighty-one consecutive symptomatic cardiac patients with increased heart rates (≥ 75 beats per min) were enrolled. All patients underwent CCTA and invasive coronary angiography (ICA). CCTA was performed with a 256-detector row CT using prospectively ECG-triggered single-beat protocol. Images were reconstructed using standard (STD) algorithm, first-generation intra-cycle motion correction (MC1) algorithm, and second-generation intra-cycle motion correction (MC2) algorithm. The image quality of coronary artery segments was assessed by two experienced radiologists using a 4-point scale (1: non-diagnostic and 4: excellent), according to the 18-segment model. Diagnostic performance for segments with significant lumen stenosis (≥ 50%) was compared between STD, MC1, and MC2 by using ICA as the reference standard.

RESULTS

The mean effective dose of CCTA was 1.0 mSv. On per-segment level, the overall image quality score and interpretability were improved to 3.56 ± 0.63 and 99.2% due to the use of MC2, as compared to 2.81 ± 0.85 and 92.5% with STD and 3.21 ± 0.79 and 97.2% with MC1. On per-segment level, compared to STD and MC1, MC2 improved the sensitivity (92.2% vs. 79.2%, 80.7%), specificity (97.8% vs. 82.1%, 90.8%), positive predictive value (89.9% vs. 48.4%, 65.1%), negative predictive value (98.3% vs. 94.9%, 95.7%), and diagnostic accuracy (96.8% vs. 81.5%, 89.0%).

CONCLUSION

A second-generation intra-cycle motion correction algorithm for single-beat CCTA significantly improves image quality and diagnostic accuracy in patients with increased heart rate.

KEY POINTS

• A second-generation motion correction (MC2) algorithm can further improve the image quality of all coronary arteries than a first-generation motion correction (MC1). • MC2 algorithm can significantly reduce the number of false positive segments compared to standard and MC1 algorithm.

Image Quality and Dose Reduction by Dual Source Computed Tomography Coronary Angiography: Protocol Comparison

Purpose:

To compare image quality and radiation dose among different protocols in patients who underwent a 128-slice dual source computed tomography coronary angiography (DSCT-CTCA).

Methods:

Ninety patients were retrospectively grouped according to heart rate (HR): 26 patients (group A) with stable HR ≤60 bpm were acquired using high pitch spiral mode (FLASH); 48 patients (group B) with irregular HR ≤60 bpm or stable HR between 60 and 70 bpm using step and shoot mode; and 16 patients (group C) with irregular HR >60 bpm or stable HR ≥70 bpm by retrospective electrocardiogram pulsing acquisition. Signal to noise ratio (SNR) and contrast to noise ratio (CNR) were measured for the main vascular structures. Moreover, the dose-length product and the effective dose were assessed.

Results:

Both SNR and CNR were higher in group A compared to group C (18.27 ± 0.32 vs 11.22 ± 0.50 and 16.75 ± 0.32 vs 10.17 ± 0.50; P = .001). The effective dose was lower in groups A and B (2.09 ± 1.27 mSv and 4.60 ± 2.78 mSv, respectively) compared to group C (9.61 ± 5.95 mSv) P < .0001.

Conclusion:

The correct selection of a low-dose, HR-matched CTCA scan protocol with a DSCT scanner provides substantial reduction of radiation exposure and better SNR and CNR.

Reduction of Coronary Motion Artifacts in Prospectively Electrocardiography-Gated Coronary Computed Tomography Angiography Using Monochromatic Imaging at Various Energy Levels in Combination With a Motion Correction Algorithm on Single-Source Fast Tube Voltage Switching Dual-Energy Computed Tomography: A Phantom Experiment

OBJECTIVES

The aim of this study was to assess the effect of monochromatic imaging at various energy levels in combination with a motion correction algorithm (MCA) in single-source dual-energy coronary computed tomography angiography (CCTA) with fast switching of tube voltage on the reduction of coronary motion artifacts (CMA) in a phantom setting.

MATERIALS AND METHODS

Using this dual-energy computed tomography technique with a phantom comprising models of coronary vessels filled with contrast medium and pulsating at constant heart rates of 60 to 100 beats per minute, we reconstructed monochromatic images of CCTA obtained at 50 to 90 keV with and without use of MCA. Cardiac motion was modeled by simulating the in vivo time-volume curve of the left ventricle. Two independent readers graded CMA in 9 coronary segments using a 5-point scale (1, poor; 3 to 5, interpretable; 5, excellent). At each heart rate, we compared the average score of CMA between images obtained at 50 to 90 keV with and without use of MCA using Wilcoxon signed rank test, and we compared the score among images obtained at 50 to 90 keV with use of MCA using Kruskal-Wallis and post hoc tests. We also compared the percentages of image interpretability and improvement in image interpretability among images obtained at 50 to 90 keV with use of MCA.

RESULTS

With the use of MCA, the average score of CMA was significantly higher for images obtained at each energy level from 50 to 70 keV (P < 0.05) and was comparable at 80 and 90 keV, and it was comparable among those obtained at 50 to 70 keV. With its use, the percentages of image interpretability were similarly high at 50 to 70 keV at 60 to 80 beats per minute (78%-100%), and they were higher at 50 to 60 keV (72%-83%) than at 70 keV at 90 to 100 beats per minute (50%-56%). The percentages of improved image interpretability with MCA were similarly high at 50 to 70 keV at 60 to 80 beats per minute (56%-100%), and they were higher at 50 to 60 keV (62%-77%) than at 70 keV at 90 to 100 beats per minute (36%-43%). The percentages of image interpretability and improved image interpretability with MCA were insufficient at 80 and 90 keV.

CONCLUSIONS

Coronary motion artifacts were significantly reduced in images of monochromatic CCTA obtained at 50 to 70 keV in combination with MCA compared with those obtained without MCA, and the percentages of image interpretability and improved image interpretability with use of MCA were relatively high at 50 to 70 keV, and particularly at 50 to 60 keV, even at 90 to 100 beats per minute.

Image quality in coronary CT angiography: challenges and technical solutions

Multidetector CT angiography (CTA) has become a widely accepted examination for non-invasive evaluation of the heart and coronary arteries. Despite its ongoing success and worldwide clinical implementation, it remains an often-challenging procedure in which image quality, and hence diagnostic value, is determined by both technical and patient-related factors. Thorough knowledge of these factors is important to obtain high-quality examinations. In this review, we discuss several key elements that may adversely affect coronary CTA image quality as well as potential measures that can be taken to mitigate their impact. In addition, several recent vendor-specific advances and future directions to improve image quality are discussed.

Locating the Human Cardiac Conduction System Using a 3D Model of Its Nutritious Arteries

It is difficult for anatomists to dissect the human cardiac conduction system (CCS) on specimens as well as for cardiovascular clinicians to locate the CCS during cardiac operations. Here, we demonstrate a new method for locating the CCS using a 3D model of its nutritious arteries. First, we perfused the coronary arteries with contrast material and then acquired a set of data of thin computer tomography (CT) scans. Then, we generated a 3D model of the coronary artery and distinguished the arteries that supply the CCS. We then located the CCS on the 3D model via its nutritious arteries and dissected the CCS. Finally, the structures that were dissected were removed for histological and immunofluorescent staining. The results of histological and immunofluorescence examination proved the structure to be the CCS. Thus, we successfully located the CCS using a 3D model of its nutritious arteries. We suggest that with this new method, cardiac surgeons can locate a patient’s CCS during cardiac surgeries such as transcatheter aortic valve implantation (TAVI) or radiofrequency catheter ablation (RFCA).

Coronary Computed Tomography Angiography: Patient-related factors determining image quality using a second-generation 320-slice CT scanner

PURPOSE

To investigate the diagnostic confidence of Coronary Computed Tomography Angiography (CCTA) and the effect of patient-related factors on CCTA image quality using a second-generation 320-slice scanner.

METHODS AND RESULTS

200 consecutive patients (mean age 60±12years; 109 men) prospectively underwent CCTA. The mean body mass index (BMI) was 27.1±4.9kg/m(2); the median heart rate (HR) was 60.0 (interquartile range (IQR), 53.9-66.1) beats per minute (bpm). The median segment's diameter was 2.8 (IQR, 2.2-3.4) mm. For each coronary segment ≥1.5mm in diameter, two readers scored: diameter narrowing as < or ≥50%, overall diagnostic confidence and motion-related image quality, with interobserver agreement kappa-values of 0.89, 0.91 and 0.61 respectively. Seventy-nine of the 2505 evaluated segments (3.2%) had non-diagnostic image quality because of coronary calcifications (66/79; 83.5%), stent- (6/79; 7.5%), pacemaker- (2/79; 2.5%) or motion-related artifacts (5/79; 6.5%). The effect of patient-related factors on motion-related image quality was investigated by multinomial logistic regression in 181 patients with calcium score (IQR, 0-446.5). Increasing coronary diameter was the most improving image quality factor (odds ratio (OR), 1.8637; p<0.001), marginally followed by lower HR (OR, 0.9547; p<0.001) and calcium score (OR, 0.9997; p=0.04). Gender (p=0.70), age (p=0.24) and BMI (p=0.45) did not affect image quality.

CONCLUSION

Using a second-generation 320-slice scanner, CCTA diagnostic confidence is predominantly affected by coronary calcifications, whereas motion-related image quality is non-diagnostic only in exceptional cases and mainly influenced by the coronary diameter. For future developments, our study findings therefore suggest greater requirements concerning spatial resolution and calcium-related artifact removal than concerning temporal resolution, especially to improve diagnostic confidence in patient groups with smaller coronary diameters.

Age-related differences in image quality of prospectively ECG-triggered axial and helical scans for coronary CT angiography

We investigated the underlying reasons for the occurrence of misalignment artifacts in prospectively ECG-triggered axial coronary CT angiography scans. In this study we analyzed 56 consecutive patients scanned in axial mode and 66 consecutive patients scanned in helical mode. Predictors for the occurrence of misalignment artifacts were evaluated by multivariable logistic regression analysis for those patients scanned in the axial mode; advanced age was identified as the sole independent predictor (odds ratio: 1.088; 95 % CI: 1.012-1.170; p = 0.0228). In a comparison with the patients scanned in the helical mode, the image quality score for patients aged 65 years or older was significantly higher in helical mode than in axial mode (2.6 ± 0.5 and 2.4 ± 0.7, respectively; p = 0.0313). Misalignment artifacts in the image are more common in the elderly than in younger. Helical mode should be preferred in this older patient population to allow for good diagnostic image quality.

Effect of heart rate on the diagnostic accuracy of 256-slice computed tomography angiography in the detection of coronary artery stenosis: ROC curve analysis

The aim of the present study was to investigate the effect of heart rate (HR) on the diagnostic accuracy of 256-slice computed tomography angiography (CTA) in the detection of coronary artery stenosis. Coronary imaging was performed using a Philips 256-slice spiral CT, and receiver operating characteristic (ROC) curve analysis was conducted to evaluate the diagnostic value of 256-slice CTA in coronary artery stenosis. The HR of the research subjects in the study was within a certain range (39-107 bpm). One hundred patients suspected of coronary heart disease underwent 256-slice CTA examination. The cases were divided into three groups: Low HR (HR <75 bpm), moderate HR (75≤ HR <90 bpm) and high HR (HR ≥90 bpm). For the three groups, two observers independently assessed the image quality for all coronary segments on a four-point ordinal scale. An image quality of grades 1-3 was considered diagnostic, while grade 4 was non-diagnostic. A total of 97.76% of the images were diagnostic in the low-HR group, 96.86% in the moderate-HR group and 95.80% in the high-HR group. According to the ROC curve analysis, the specificity of CTA in diagnosing coronary artery stenosis was 98.40, 96.00 and 97.60% in the low-, moderate- and high-HR groups, respectively. In conclusion, 256-slice coronary CTA can be used to clearly show the main segments of the coronary artery and to effectively diagnose coronary artery stenosis. Within the range of HRs investigated, HR was found to have no significant effect on the diagnostic accuracy of 256-slice coronary CTA for coronary artery stenosis.

Improved image quality at 256-slice coronary CT angiography in patients with a high heart rate and coronary artery disease: comparison with 64-slice CT imaging

BACKGROUND

The 256-slice computed tomography (CT) scanners with wider detector coverage and faster gantry rotation speed are now available. The performance of scanners that feature a rotation speed of 270 ms at coronary CT angiography (CCTA) has not been evaluated in patients with a higher heart rate.

PURPOSE

To evaluate the image quality of 256-slice CT with faster gantry rotation speed in patients undergoing CCTA.

MATERIAL AND METHODS

We enrolled 886 patients; 357(40.3%) underwent study on a 64-slice CT at a rotation speed of 420 ms, the other 529 (59.7%) were examined using a 256-slice CT scanner at 270 ms. Two observers judged the image quality of 2658 imaged coronary arteries on a 4-point scale.

RESULTS

The mean image quality score was significantly higher for the 256 - than the 64-slice CT scans (3.94 ± 0.28 vs. 3.73 ± 0.61; P < 0.01). There was no significant difference in the image quality scores between 64 - and 256-slice scans in patients whose heart rate (HR) was <60 bpm. However, in patients whose HR exceeded 60 bpm these scores were significantly higher for 256-slice CT images (P < 0.01).

CONCLUSION

CCTA performed on the 256-slice CT scanner yielded significantly better image quality in patients with an HR exceeding 60 bpm.

Single- versus multi-phase acquisition protocol for prospective-triggered sequential dual-source CT coronary angiography: comparison of image quality and radiation dose

OBJECTIVE

To investigate image quality and radiation dose of single- versus multi-phase acquisition protocol for prospective-triggered sequential dual-source computed tomography (CT) coronary angiography.

MATERIALS AND METHODS

A total of 140 patients were randomly assigned to single- or multi-phase group. Image quality and radiation dose were compared.

RESULTS

No significant difference was found in image quality between the two groups. Effective dose of single-phase group was 21.6% lower than that of multi-phase group (P<.001).

CONCLUSIONS

Prospective-triggered sequential dual-source CT coronary angiography using single-phase protocol can reduce radiation dose without sacrifice of image quality in diastole compared with multi-phase protocol.

A comparison of bolus injection of landiolol versus oral administration of propranolol before cardiac computed tomography

Heart rate (HR) reduction is essential to achieve good image quality for cardiac computed tomography (CCT). We evaluated the efficacy of a bolus injection of landiolol, an ultra-short acting β-blocker, without the administration of oral β-blocker to reduce HR prior to CCT. We enrolled 678 consecutive patients who underwent CCT from December 2011 to March 2012 and divided them into three groups, which were a propranolol group (n = 277), a low-dose landiolol group (n = 188), and a high-dose landiolol group (n = 213). Patients in the propranolol group received oral propranolol (10–20 mg) prior to CCT. Patients in the low-dose and high-dose landiolol groups were administered a bolus injection of landiolol (0.125 mg/kg), while the high-dose group received an additional 3.75 mg of landiolol if the baseline HR was ≥75/min. Although the average HR was significantly lower in the propranolol group (61.6 ± 8.0/min) than in the low-dose landiolol group (64.1 ± 7.4/min, P < 0.001), there was no significant difference in the image quality (P = 0.91). Among patients with baseline HR ≥75/min, the average HR tended to be lower in the high-dose landiolol group (67.2 ± 6.9/min) compared with the low-dose landiolol group (69.0 ± 6.9/min, P = 0.10), and there was a corresponding difference in image quality between these two groups (P = 0.02). In conclusion, Although the decrease of HR was significantly larger in the propranolol group than in the landiolol groups, the image quality was similar. Among the patients who received landiolol, a higher dose was associated with a lower HR and better image quality. Further investigation to assess higher-dose bolus injection of landiolol or bolus injection following oral administration of a β-blocker would be needed.

Correlation between low tube voltage in dual source CT coronary artery imaging with image quality and radiation dose

The influence of low tube voltage in dual source CT (DSCT) coronary artery imaging on image quality and radiation dose and its application value in clinical practice were investigated. Totally, 300 cases of chest pain with low body mass index (BMI <18.5 kg/m(2)) subjected to DSCT coronary artery imaging were prospectively enrolled. The heart rate in all patients were greater than 65/min. The retrospective ECG gated scanning mode and simple random sampling method were used to assign the patients into groups A, B and C (n=100 each). The patients in groups A, B and C experienced 120-, 100-, and 80-kV tube voltage imaging respectively, and the image quality was evaluated. The CT volume dose index (CTDIvol) and dose length product (DLP) were recorded, and the effective dose (ED) was calculated in each group. The image quality scores and radiation doses in groups were compared, and the influence of tube voltage on image quality and radiation dose was analyzed. The results showed that the excellent rate of image quality in groups A, B and C was 95.69%, 94.72% and 96.33% respectively with the difference being not statistically significant among the three groups (P>0.05). The CTDIvol values in groups A, B and C were 51.35±12.21, 21.28±7.13 and 6.34±3.34 mGy, respectively, with the difference being statistically significant (P<0.05). The ED values in groups A, B and C were 9.27±1.63, 4.56±2.29 and 2.29±1.69 mSv, respectively, with the difference being statistically significant (P<0.05). It was suggested that for the patients with low BMI, the application of DSCT coronary artery imaging with low tube voltage can obtain satisfactory image quality, and simultaneously, significantly reduce the radiation dose.

256-slice CT angiographic evaluation of coronary artery bypass grafts: effect of heart rate, heart rate variability and Z-axis location on image quality

Purpose

The objective of this study is to assess the effect of heart rate, heart rate variability and z-axis location on coronary artery bypass graft (CABG) image quality using a 256-slice computed tomography (CT) scanner.

Methods

A total of 78 patients with 254 CABG (762 graft segments) were recruited to undergo CABG assessment with 256-slice CT and prospective ECG-gating. Two observers rated graft segments for image quality on a 5-point scale. Quantitative measurements were also made. Logistic and cumulative link mixed models were used to assess the predictors of graft image quality.

Results

Graft image quality was judged as diagnostic (scores 5 (excellent), 4 (good) and 3 (moderate)) in 96.6% of the 762 segments. Interobserver agreement was excellent (kappa ≥0.90). Graft image quality was not affected by heart rate level. However, high heart rate variability was associated with an important and significant image quality deterioration (odds ratio 4.31; p  =  0.036). Distal graft segments had significantly lower image quality scores than proximal segments (p ≤ 0.02). Significantly higher noise was noted at the origin of the mammary grafts (p  =  0.001), owing to streak artifacts from the shoulders.

Conclusion

CABG imaging with 270-msec rotation 256-slice CT and prospective ECG-gating showed an adequate image quality in 96.6% of graft segments, and an excellent interobserver agreement. Graft image quality was not influenced by heart rate level. Image quality scores were however significantly decreased in patients with high heart rate variability, as well as in distal graft segments, which are closer to the heart.

Dynamic CT perfusion imaging of the myocardium: a technical note on improvement of image quality

Objective

To improve image and diagnostic quality in dynamic CT myocardial perfusion imaging (MPI) by using motion compensation and a spatio-temporal filter.

Methods

Dynamic CT MPI was performed using a 256-slice multidetector computed tomography scanner (MDCT). Data from two different patients–with and without myocardial perfusion defects–were evaluated to illustrate potential improvements for MPI (institutional review board approved). Three datasets for each patient were generated: (i) original data (ii) motion compensated data and (iii) motion compensated data with spatio-temporal filtering performed. In addition to the visual assessment of the tomographic slices, noise and contrast-to-noise-ratio (CNR) were measured for all data. Perfusion analysis was performed using time-density curves with regions-of-interest (ROI) placed in normal and hypoperfused myocardium. Precision in definition of normal and hypoperfused areas was determined in corresponding coloured perfusion maps.

Results

The use of motion compensation followed by spatio-temporal filtering resulted in better alignment of the cardiac volumes over time leading to a more consistent perfusion quantification and improved detection of the extend of perfusion defects. Additionally image noise was reduced by 78.5%, with CNR improvements by a factor of 4.7. The average effective radiation dose estimate was 7.1±1.1 mSv.

Conclusion

The use of motion compensation and spatio-temporal smoothing will result in improved quantification of dynamic CT MPI using a latest generation CT scanner.

Radiation dose considerations by intra-individual Monte Carlo simulations in dual source spiral coronary computed tomography angiography with electrocardiogram-triggered tube current modulation and adaptive pitch

OBJECTIVES

To evaluate radiation dose levels in patients undergoing spiral coronary computed tomography angiography (CTA) on a dual-source system in clinical routine.

METHODS

Coronary CTA was performed for 56 patients with electrocardiogram-triggered tube current modulation (TCM) and heart-rate (HR) dependent pitch adaptation. Individual Monte Carlo (MC) simulations were performed for dose assessment. Retrospective simulations with constant tube current (CTC) served as reference. Lung tissue was segmented and used for organ and effective dose (ED) calculation.

RESULTS

Estimates for mean relative ED was 7.1 ± 2.1 mSv/100 mAs for TCM and 12.5 ± 5.3 mSv/100 mAs for CTC (P < 0.001). Relative dose reduction at low HR (≤60 bpm) was highest (49 ± 5%) compared to intermediate (60-70 bpm, 33 ± 12%) and high HR (>70 bpm, 29 ± 12%). However lowest ED is achieved at high HR (5.2 ± 1.5 mSv/100 mAs), compared with intermediate (6.7 ± 1.6 mSv/100 mAs) and low (8.3 ± 2.1 mSv/100 mAs) HR when automated pitch adaptation is applied.

CONCLUSIONS

Radiation dose savings up to 52% are achievable by TCM at low and regular HR. However lowest ED is attained at high HR by pitch adaptation despite inferior radiation dose reduction by TCM.

KEY POINTS

• Monte Carlo simulations allow for individual radiation dose calculations. • ECG-triggered tube current modulation (TCM) can effectively reduce radiation dose. • Slow and regular heart rates allow for highest dose reductions by TCM. • Adaptive pitch accounts for lowest radiation dose at high heart rates. • Women receive higher effective dose than men undergoing spiral coronary CT-angiography.