Evaluation of an adaptive detector collimation for prospectively ECG-triggered coronary CT angiography with third-generation dual-source CT

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.

Can the Coronary Artery Calcium Score Scan Reduce the Radiation Dose in Coronary Computed Tomography Angiography?

RATIONALE AND OBJECTIVES

Radiation exposure from coronary computed tomography angiography (CCTA) remains a cause for concern. The objective of this study was to investigate whether using the coronary artery calcium score scan (CACS) would reduce the radiation dose for CCTA scanning and the overall radiation exposure (ORE).

MATERIALS AND METHODS

In total, 256 patients were examined with a third-generation dual-source CT (n = 200) or 256-row CT (n = 56), among whom 105 (Group A) and 28 patients (Group B), respectively, underwent CCTA with CACS for field of view planning. The remaining patients, with the scout view for field of view planning, constituted Group A1 and B1. The scanning parameter settings were standardized between groups.

RESULTS

Shorter scan lengths were observed in Group A (9.98 ± 0.79 cm) compared to Group A1 (13.64 ± 1.79 cm; p < 0.001), which also resulted in a lower dose-length product (DLP) in Group A (115.04 ± 64.13) relative to Group A1 (138.67 ± 68.87; p < 0.05). Similarly, shorter scan lengths were found in Group B (14.92 ± 1.17 cm) compared to Group B1 (15.79 ± 0.63 cm; p = 0.001); this resulted in a lower DLP (322.07 ± 45.39) compared to Group B1 (354.34 ± 65.27; p = 0.036). The CACS resulted in an increase in ORE in both groups.

CONCLUSION

CACS may have a critical role in the reduction of radiation dose in CCTA scanning, but the potential effectiveness of CACS in reducing ORE is weak.

Evaluation of Organ Dose and Image Quality Metrics of Pediatric CT Chest-Abdomen-Pelvis (CAP) Examination: An Anthropomorphic Phantom Study

The aim of this study is to investigate the impact of CT acquisition parameter setting on organ dose and its influence on image quality metrics in pediatric phantom during CT examination. The study was performed on 64-slice multidetector CT scanner (MDCT) Siemens Definition AS (Siemens Sector Healthcare, Forchheim, Germany) using various CT CAP protocols (P1–P9). Tube potential for P1, P2, and P3 protocols were fixed at 100 kVp while P4, P5, and P6 were fixed at 80 kVp with used of various reference noise values. P7, P8, and P9 were the modification of P1 with changes on slice collimation, pitch factor, and tube current modulation (TCM), respectively. TLD-100 chips were inserted into the phantom slab number 7, 9, 10, 12, 13, and 14 to represent thyroid, lung, liver, stomach, gonads, and skin, respectively. The image quality metrics, signal to noise ratio (SNR) and contrast to noise ratio (CNR) values were obtained from the CT console. As a result, this study indicates a potential reduction in the absorbed dose up to 20% to 50% along with reducing tube voltage, tube current, and increasing the slice collimation. There is no significant difference (p > 0.05) observed between the protocols and image metrics.

Diagnostic accuracy of ultra-low-dose CT for torsion measurement of the lower limb

Objectives

The study aimed to investigate the diagnostic performance of simulated ultra-low-dose CT (ULD-CT) for torsion measurement of the lower limb.

Methods

Thirty retrospectively identified patients were included (32.3 ± 14.2 years; 14 women, 16 men). ULD-CT simulations were generated at dose levels of 100%, 10%, 5%, and 1% using two reconstruction methods: standard filtered back projection (FBP) and iterative reconstruction (ADMIRE). Two readers measured the lower limb torsion in all data sets. The readers also captured image noise in standardized anatomical landmarks. All data sets were evaluated regarding subjective diagnostic confidence (DC; 5-point Likert scale). Effective radiation dose of the original data sets and the simulated ULD-CT was compared.

Results

There was no significant difference of measured lower limb torsion in any simulated dose level compared to the original data sets in both readers. Dose length product (DLP) of the original examinations was 402.1 ± 4.3 mGy cm, which resulted in an effective radiation dose of 4.00 ± 2.12 mSv. Calculated effective radiation dose in ULD-CT at 1% of the original dose was 0.04 mSv. Image noise increased significantly with dose reduction (p < 0.0001) and was dependent on the reconstructional method (p < 0.0001) with less noise using ADMIRE compared to FBP. Both readers rated DC at doses 100%, 10%, and 5% with 5.0/5: there were no ratings worse than 3/5 at 1% dose level.

Conclusions

The results suggest that radiation dose reduction down to 1% of original CT dose levels may be achieved in CT torsion measurements of the lower limb without compromising diagnostic accuracy.

Key Points

• Modern CT delivers exceptional high image quality in musculoskeletal imaging, especially for evaluation of osseous structures.

• Usually, this high image quality is accompanied by significant radiation exposure to the patient and may not always be required for the intended purpose, e.g., pure delineation of cortical bone of the lower limb.

• This study shows the tremendous prospects of radiation dose reduction without compromising diagnostic confidence in CT torsion measurement of the lower limb.

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.

Qualitative and quantitative image analysis of 16 cm wide-coverage computed tomography compared to new-generation dual-source CT

BACKGROUND

Diagnostic quality of computed tomography (CT) images depends on numerous factors. Recently, two different modalities were introduced for coronary CT angiography (CCTA).

OBJECTIVE

This study aims to compare the performance of 16 cm wide-coverage detector CT (WDCT) using the snapshot freeze technique with a new-generation dual-source CT (DSCT) with 66 ms temporal resolution for CCTA.

METHODS

Total 101 patients with suspected coronary heart disease were enrolled. Of these, 50 and 51 patients were examined on WDCT and DSCT, respectively. CT values, image noise, signal-to-noise ratio, and contrast-to-noise ratio were measured. The image processing efficiency was recorded, followed by statistical comparison of diagnostic accuracy and radiation dose.

RESULTS

Ninety-nine patients (98.02%) had satisfactory diagnostic image quality. DSCT was significantly better than WDCT in terms of quantitative image quality, image processing efficiency, and qualitative analysis (P < 0.05). However, radiation dose was significantly lower on WDCT (P < 0.05) as compared to DSCT.

CONCLUSIONS

Image processing efficiency and image quality of CCTA was higher on DSCT compared to WDCT due to the limitation of maximal tube current of WDCT.

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.