Spiral Scanning Mode Research Articles

Effect of spiral scan distance on the nanosecond-pulsed-laser lap joint of Al/Cu

The T2 Cu with a thickness of 0.2 mm and 6063 Al alloy with a thickness of 0.4 mm were joined via nanosecond pulsed laser welding in an inner spiral scanning mode. The lap configuration was Cu (upper)/Al (under). The influence of spiral scan distance (spiral distance for short) on the weld formation, microstructure and mechanical property was investigated. The results showed that circular holes and arc-shaped cracks formed on the weld surface at the spiral distance of 0.02 mm, and these defects disappeared at higher spiral distances. The tendency of porosity increased initially and decreased afterwards as the spiral distance increased. The interfacial morphology exhibited a wave-shaped structure at the spiral distance of 0.02 mm, and a continuous lump θ-CuAl2 phase was produced at the interface. When the spiral distance was larger than 0.02 mm, the wave-shaped structure disappeared and V-shaped areas were generated due to the invasion of Al element into Cu base metal. α-Al and θ-CuAl2 phases were possibly produced in these areas. The Cu-rich areas generated on the sidewall of the weld could cause the formation of θ-CuAl2. According to the tensile-shear load results, the maximum shear force reached 107.7 N at the spiral distance of 0.04 mm. The satisfactory weld formation and larger effective bounding area contributed to the superior bonding strength. Three fracture modes (button pulling out failure, weld shear failure and interface failure) were observed in this study.

Study on laser drilling induced defects of CFRP plates with different scanning modes based on multi-pass strategy

There are two kinds of scanning modes based on multi-pass strategy, including concentric scanning mode (CSM) and spiral scanning mode (SSM), which can realize 3D hole drilling of CFRP plates by a nanosecond UV laser. The mechanism of the CFRP laser drilling and defects formation under these two different scanning modes has been described. Several experiments are conducted to explore and compare the drilling defects including heat-affected zone (HAZ), dimension error, and machined surface micro-defects under these two different scanning modes. The results show that SSM can significantly reduce the width of HAZ compared with CSM. Under the most obvious reduction of parameters, the use of SSM (84.76 μm) is 33.42% less than the HAZ of CSM (127.3 μm). For MR, it is reduced by 24.83% (45.75–34.39 μm). Due to the special spiral trajectory of SSM, the dimension errors are increased when using SSM, including the taper error (maximum 26.11%) and slight circularity error. The micro-defects of laser processed surfaces with CSM are more serious than those with SSM, especially the obvious delamination, cracks, matrix loss, and fibre tip expansion formed fibre fusion caused by the significant thermal effect at a high laser repetition rate. This is consistent with the influence on HAZ at the hole edge.

Thoracic CTA in infants and young children: Image quality of dual-source CT (DSCT) with high-pitch spiral scan mode (turbo flash spiral mode) with or without general anesthesia with free-breathing technique.

To determine whether diagnostic quality thoracic computed tomography angiography (CTA) studies can be obtained without general anesthesia (GA) in infants and young children using dual-source computed tomography (DSCT) with turbo flash spiral mode (TFSM) and free-breathing technique. All consecutive infants and young children (≤ 6 years old) who underwent thoracic CTA studies from January 2018 to October 2020 for suspected congenital thoracic disorders were categorized into two groups: with GA (Group 1) and without GA (Group 2). All thoracic CTA studies were performed on a DSCT scanner using TFSM and free-breathing technique. Two pediatric thoracic radiologists independently evaluated motion artifact in three lung zones (upper, mid, and lower). Degree of motion artifact was graded 0-3 (0, none; 1, mild; 2, moderate; and 3, severe). Logistic models adjusted for age and gender were used to compare the degree of motion artifact between lung zones. Interobserver agreement between reviewers was evaluated with kappa statistics. There were a total of 73 pediatric patients (43 males (59%) and 30 females (41%); mean age, 1.4 years; range, 0-5.9 years). Among these 73 patients, 42 patients (58%) underwent thoracic CTA studies with GA (Group 1) and the remaining 31 patients (42%) underwent thoracic CTA studies without GA (Group 2). Overall, the degree of motion artifact was higher for Group 2 (without GA). However, only a very small minority (1/31, 3%) of Group 2 (without GA) thoracic CTA studies had severe motion artifact. There was no significant difference between the two groups with respect to the presence of severe motion artifact (odds ratio [OR] = 6, p = .222). When two groups were compared with respect to the presence of motion artifact for individual lung zones, motion artifact was significantly higher in the upper lung zone for Group 2 (without GA) (OR = 20, p = .043). Interobserver agreement for motion artifact was high, the average Kappa being 0.81 for Group 1 and 0.95 for Group 2. Although the degree of motion artifact was higher in the group without GA, only a small minority (3%) of thoracic CTA studies performed without GA had severe motion artifact, rendering the study nondiagnostic. Therefore, the results of this study support the use of thoracic CTA without GA using DSCT with TFSM and free-breathing in infants and young children. In addition, given that motion artifact was significantly higher in the upper lung zone without GA, increased stabilization in the upper chest and extremities should be considered.

Comparison of axial scanning mode and traditional spiral scanning mode of 16 cm wide-detector CT in wrist, elbow, knee and ankle examination.

article: Comparison of axial scanning mode and traditional spiral scanning mode of 16 cm wide-detector CT in wrist, elbow, knee and ankle examination - Minerva Medica 2022 June;113(3):588-9 - Minerva Medica - Journals

Analysis and comparison of laser cutting performance of solar float glass with different scanning modes

Cutting quality and efficiency have always been important indicators of glass laser cutting. Laser scanning modes have two kinds, namely, the spiral and concentric circle scanning modes. These modes can achieve high-performance hole cutting of thick solar float glass using a 532-nm nanosecond laser. The mechanism of the glass laser cutting under these two different scanning modes has been described. Several experiments are conducted to explore the effect of machining parameters on cutting efficiency and quality under these two scanning modes. Results indicate that compared with the spiral scanning mode, the minimum area of edge chipping (218340 µm2) and the minimum Ra (3.01 µm) in the concentric circle scanning mode are reduced by 9.4% and 16.4% respectively. Moreover, the best cutting efficiency scanning mode is 14.2% faster than that in the spiral scanning mode. The best parameter combination for the concentric circle scanning mode is as follows: Scanning speed: 2200 mm/s, number of inner circles: 6, and circle spacing: 0.05 mm. This parameter combination reduces the chipping area and sidewall surface roughness by 8.8% and 9.6% respectively at the same cutting efficiency compared with the best spiral processing parameters. The range of glass processing that can be achieved in the concentric circle scanning mode is wider than that in the spiral counterpart. The analyses of surface topography, white spots, microstructures, and sidewall surface element composition are also performed. The study concluded that the concentric circle scanning mode shows evident advantages in the performance of solar float glass hole cutting.

CT-perfusion in assessment of the malignant gliomas hemodynamics

Aim. To study the role of CT perfusion in the differential diagnosis of histological subtypes of supratentorial malignant gliomas and to determine the degree of their malignancy. Materials and methods. The study included 34 patients (20 men and 14 women, with an average age of 52 years) with newly detected supratenorial glial tumors, who subsequently underwent neurosurgical treatment in the NMIC of neurosurgery with histological verification of the diagnosis. Depending on the histological diagnosis, three groups of patients were identified: 1) anaplastic astrocytomas, 2) glioblastomas, 3) anaplastic oligodendrogliomas. The CT-perfusion protocol was performed on a 64-slice Optima 660 (GE) scanner and consisted of three separate parts: a low-dose axial CT of the brain with a slice thickness of 5 mm (90 kV), a perfusion protocol performed according to a prolonged scheme, with two consecutive continuous series of scans, and a post-contrast series of CT images in a spiral scanning mode. In addition, all patients underwent an MRI examination (using a Signa Hdxt 3.0 T (GE) MR scanner, in T2, T2-FLAIR, SWAN, DWI, and T1 modes before and after contrast enhancement).Results. The study demonstrated that anaplastic astrocytomas are characterized by significantly low absolute and normalized hemodynamics parameters (BF, BV, PS) when compared with glioblastomas, and significantly low absolute maximum values of blood flow (BF) and blood volume (BV) when compared with the group of anaplastic oligodendrogliomas. CT perfusion using the normalized permeability index (PS) can reliably differentiate glioblastomas and anaplastic oligodendrogliomas. Perfusion parameters, both absolute and normalized, did not show statistically significant differences in the differential diagnosis of various molecular and genetic subtypes of anaplastic astrocytomas.Conclusion. CT perfusion using all hemodynamic parameters demonstrated high reliability and efficacy in distinguishing between glioblastomas and anaplastic astrocytomas. Further research is required to evaluate the effectiveness of the method in distinguishing glioblastomas from anaplastic oligodendrogliomas.

A new centering method of the measuring probe for spiral scanning-based surface profile measurement systems

Spiral scanning is a high-efficiency scanning mode for surface profile measurement systems. The most important priority to realize the spiral scanning mode is to accurately align the measuring probe with the rotational centre of the spindle. This paper proposes a novel centre alignment method of the measuring probe, which is considered to be suitable for any type of spiral scanning surface measurement systems. The proposed method, which only needs a tilted flat mirror as the artefact, makes the time-consuming centre alignment process of the measuring probe become much easier and faster. The operational steps of the proposed method are presented. Experiments have also been carried out based on a self-developed optical profiler with spiral scanning operation to verity the feasibility of the proposed method. The experimental results show that the proposed method is capable of conducting a fast alignment (only takes 3 min) while maintaining a high alignment accuracy. Evaluation of the alignment accuracy shows that the centering error is less than 10 µm on the mechanical guide rail stage and about 1.7 µm on the air-bearing stage.

Computed Tomography Angiography with a 192-slice Dual-source Computed Tomography System: Improvements in Image Quality and Radiation Dose.

Purpose:This study aims to compare image quality, radiation dose, and the influence of the heart rate on image quality of high-pitch spiral coronary computed tomography angiography (CCTA) using 128-slice (second generation) dual-source CT (DSCT) and a 192-slice DSCT (third generation) scanner.Materials and Methods:Two consecutive cohorts of fifty patients underwent CCTA by high-pitch spiral scan mode using 128 or 192-slice DSCT. The 192-slice DSCT system has a more powerful roentgen tube (2 × 120 kW) that allows CCTA acquisition at lower tube voltages, wider longitudinal coverage for faster table speed (732 m/s), and the use of iterative reconstruction. Objective image quality was measured as the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). Subjective image quality was evaluated using a Likert scale.Results:While the effective dose was lower with 192-slice DSCT (1.2 ± 0.5 vs. 0.6 ± 0.3 mSv; P < 0.001), the SNR (18.9 ± 4.3 vs. 11.0 ± 2.9; P < 0.001) and CNR (23.5 ± 4.8 vs. 14.3 ± 4.1; P < 0.001) were superior to 128-slice DSCT. Although patients scanned with 192-slice DSCT had a faster heart rate (59 ± 7 vs. 56 ± 6; P = 0.045), subjective image quality was scored higher (4.2 ± 0.8 vs. 3.0 ± 0.7; P < 0.001) compared to 128-slice DSCT.Conclusions:High-pitch spiral CCTA by 192-slice DSCT provides better image quality, despite a higher average heart rate, at lower radiation doses compared to 128-slice DSCT.

The effects of joint optimization of CT scanning-modes and CT angiography starting-modes on image quality and patients' radiation dose in cervicocerebral CT angiography

Objective To study the effects of joint optimization of CT scanning-modes and CTA starting-modes on the image quality, the patients' radiation doses and contrast volumes in cervicocerebral CTA. Method According to the date of examination from December 2013 to January 2014, 188 consecutive patients were prospectively selected and underwent cervicocerebral CTA using different CT scanning-modes and CTA starting-modes. These patients wererandomly divided into 4 groups: A1 (45 cases), A2 (48 cases), B1 (45 cases) and B2 (50 cases). Group A1 were Flash mode combined with test bolus, Group A2 were Flash mode combined with bolus tracking, group B1 were the common spiral scanning mode combined with test bolus and group B2 were the common spiral scanning mode combined with bolus tracking. The objective image quality evaluation criteria included the CT value comparison at the aortic arch(Pa1), carotid artery bifurcation (Pa2), basal artery (Pa3), superior vena cava (Pv1), internal jugular (pv2), transverse sinus (Pv3) and image objective noise. The subjective image quality assessments criteria included the contrast hardening artifact and diagnose acceptability. The radiation dose and contrast volumes of every patient were recorded and analyzed. The analysis of variance, the chi-square tests and the rank sum tests (Kruskal-Wallis) were used for data statistics. Results There were significant differences on the CT value at transverse sinus among the four groups, they were (124±30), (151±34), (130±37) and (160±37) HU, and different starting-modes had impacts on venous reflux (P 0.05). The image noise had significant differences in four groups (P 0.05), however there were significant differences on contrast hardening artifacts (P< 0.05) among the four groups. With the same scanning mode, the artifacts of group A1 were more serious than A2 and B1 were more serious than B2.There were significant differences on the patients' contrast volumes in the four groups (P<0.05), they were (45±5), (49±4), (35±4) and (35±4) ml, the contrast volumes in groups A1 and B1 were more than groups A2 and B2. There were significant differences among the four groups on patients' ED (P<0.05), which were (0.79±0.07), (0.81±0.08), (1.49±0.11) and (1.51±0.12) mSv. The radiation dose in groups A1, A2 were lower than those in B1 and B2. Conclusion The joint use of Flash mode and bolus tracking technique is recommended in application of cervicocerebral CTA, for its advantages of better image quality, good diagnosis acceptability, the patient's low radiation dose and low contrast volumes. Key words: Angiography; Tomography,X-ray computed; Radiation dosage; Contrast media; Comparative study

Radiation dose and diagnostic accuracy of high-pitch dual-source coronary angiography in the evaluation of coronary artery stenoses.

"Flash Spiral" imaging is a new prospective ECG-triggered spiral scan mode that uses a very high-pitch for coronary computed tomography angiography (CTA). This enables complete image acquisition within one cardiac cycle with a very low radiation exposure. The aim of this study was to investigate the diagnostic accuracy, image quality, and effective radiation dose of prospectively ECG-triggered high-pitch spiral method (Flash spiral mode) of coronary CTA using dual-source technology for the evaluation of coronary artery stenoses. The study included 186 consecutive patients (115men, 71women; mean age: 53.37years) who underwent coronary CTA. Coronary CTA was performed with a 128×2-slice dual-source CT (Somatom Definition Flash, Siemens, Germany) using a prospectively ECG-triggered high-pitch spiral mode. Patients were divided into three groups according to heart rate (≤65bpm, 66-75bpm, ≥76bpm) and body mass index (BMI) (20-24kg/m(2), 25-29kg/m(2), 30-34kg/m(2)) values. The correlation between heart rates, image quality and BMI values are investigated. A four-point scale (1=excellent, 4=poor/non-diagnostic) was used to rank the comparative image quality. Effective radiation doses were calculated. Also the correlation between radiation dose, sex and BMI values were investigated. In addition, diagnostic accuracy of CTA for detection of significant (≥50%) coronary artery stenoses was compared with invasive coronary angiography findings of 612vessel segments in 38patients. The sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy rate were calculated. A total of 2976coronary artery segments were present. Of all coronary artery segments, 2381 (80%) had an image quality score of 1, and 1.5% segments were rated as "poor/non-diagnostic". When the correlation between heart rate and image quality is investigated, there was a significant difference between ≤65bpm and ≥76bpm groups. However, there was no significant difference between ≤65bpm and 66-75bpm groups. The mean effective dose was found as 1.3mSv (min: 0.5, max: 2.4mSv). The correlation between effective radiation dose and BMI was moderate. However, the correlation between gender and radiation dose was significant. Sensitivity, specificity, negative predictive value and accuracy of coronary CTA on a per-vessel segment were 90.1%, 97.4%, 98.6%, and 96.5%, respectively. Prospectively ECG-triggered high-pitch spiral mode coronary CTA provides high image quality and diagnostic accuracy, with very low radiation dose for evaluation and exclusion of coronary artery stenoses.

CT dose reduction using prospectively triggered or fast-pitch spiral technique employed in cardiothoracic imaging (the CT dose study)

ObjectivesTo establish current radiation dose levels with contemporary scanners capable of prospectively triggered or high-pitch spiral scan modes to previous generation scanners among patients evaluated for coronary artery disease, pulmonary embolism, aortic disease, and “triple rule out” in a large population of patients at multiple centers. BackgroundPrevious small-scale studies with carefully controlled scan protocols report that CT scanners that facilitate prospectively triggered scanning and provide high-pitch spiral CT scan modes drastically lower radiation doses. However, diagnostic reference levels should be selected by medical bodies on the basis of large surveys of representative sites and reviewed at appropriate time intervals. MethodsScan data including dose and image quality parameters were collected retrospectively from 64 slice scanners (control) and prospectively after sites installed 128-slice dual-source scanners with high-pitch capability (study). Protocol selection was purposely not specified to survey “real world” results. Blinded quantitative image analysis was performed on every fifth scan. ResultsFrom April 2011 to March 2012, 2085 patients at 9 sites completed the study: 1051 coronary artery disease (509 control, 542 study), 528 pulmonary embolism (267 control, 261 study), 419 aortic disease (268 control, 151 study), and 87 triple rule out (53 control, 34 study). There was a significant reduction in median dose-length product (DLP) from 669 mGy∙cm (interquartile range [IQR]: 419–1026 mGy∙cm) in the control group to 260 mGy∙cm (IQR: 159–441 mGy∙cm) in the study group, a reduction by 61% (P < .0001) and was lower in all categories. No significant differences were noted in image quality. ConclusionUse of advanced scanners facilitating prospectively triggered or high-pitch spiral scan modes results in marked dose reduction across a variety of cardiovascular studies, with no compromise in image quality. These findings may contribute to new target dose recommendations in societal guidelines.

축방향 CT 스캔과 나선형 CT 스캔에서 영·유아의 장기흡수선량 비교 평가

성인에 비해 방사선에 민감하고 검사건수가 증가하고 있는 영 유아의 CT 스캔 시의 장기흡수선량을 평가하기 위해 스캔부위를 머리부위와 가슴부위로 구분하고 64 MDCT를 이용하여 축방향 스캔과 나선형 스캔으로 비교했다. 스캔부위에 상관없이 나선형 스캔 시의 선량이 축방향 스캔 시 보다 유의하게 낮은 것으로 나타났다. 축방향 스캔과 비교해서 나선형 스캔 중 피치 1.355를 사용했을 때가 나머지 두 피치(0.525, 0.988)를 사용했을 때보다 가슴부위 스캔의 평균 장기흡수선량이 유의하게 높게(평균 -12.03%) 나왔다. 나선형 스캔 시 장기흡수선량이 축방향 스캔보다 평균 20.54% 낮게 나왔다. 결과적으로 인체모형을 통한 장기흡수선량을 평가한 본 연구는 몬테카를로 시뮬레이션 결과값을 실증하고, CT 검사를 받는 영 유아의 장기흡수선량의 보다 정확한 평가에 기여할 것이다. This study presents comparison results between axial and spiral scanning in the head and chest region with 64 MDCT to evaluate organ doses in infants and toddlers, who are more radiosensitive to radiation than adults and rise in the number of CT examinations, during CT scanning. Organ doses were significantly lower in spiral scanning than axial scanning regardless of scanned regions. The average organ dose for the chest scan using pitch of 1.355 was found to be significantly higher(average -12.03%) than for the other two pitch settings(0.525 and 0.988) in the spiral scanning mode compared with the axial one. Organ doses in the spiral scanning mode were lower by average 20.54% than the axial scanning mode. The results of the study that evaluated organ doses with an anthropomorphic phantom will help to demonstrate the result values of Monte Carlo simulations and make a contribution to more accurate evaluations of organ doses in toddlers undergoing a CT examination.

Comparison of prospective electrocardiography-gating high-pitch mode and without electrocardiography-synchronization high-pitch mode acquisition for the image quality and radiation doses of the aortic using dual-source CT

Objective To evaluate the application of prospective ECG-gating Flash spiral scan mode dual-source CT in aortography,and compare it's image quality and radiation dose with without ECG-synchronization high-pitch spiral scanning mode. Methods Fifty consecutive patients (Group A) with suspected aortic dissection or after operations for the aortic dissection were scanned with prospective ECG-gated high-pitch scan and another 50 consecutive patients (Group B) were analyzed by non-ECG-gated high-pitch scan.Image quality of the aortic was assessed by two independent readers.Image noise was measured,radiation dose estimates were calculated.The imaging quality of the aortic and the radiation dose were compared with Mann-whitney U and t test. Results The average image quality score[ (1.18±0.40) in group A and (1.23±0.31) in group B] showed no significant difference between group A and group B (U=1.20,P=0.23).The mean radiation dose of group A was lower than that of group B[ (1.49±0.38) mSv in group A,(2.79±0.54) mSv in group B,t=13.677,P<0.05]. Conclusion Prospective ECG-gated dual-source CT Flash spiral scanning with low radiation dose and good image quality in the aortic dissection with high value of clinical application. Key words: Aortography; Radiation dose; Tomography,X-ray computed; Quality control

128-slice Dual-source Computed Tomography Coronary Angiography in Patients with Atrial Fibrillation: Image Quality and Radiation Dose of Prospectively Electrocardiogram-triggered Sequential Scan Compared with Retrospectively Electrocardiogram-gated Spiral Scan

Objective To evaluate the image quality (IQ) and radiation dose of 128-slice dual-source computed tomography (DSCT) coronary angiography using prospectively electrocardiogram (ECG)-triggered sequential scan mode compared with ECG-gated spiral scan mode in a population with atrial fibrillation. Methods Thirty-two patients with suspected coronary artery disease and permanent atrial fibrillation referred for a second-generation 128-slice DSCT coronary angiography were included in the prospective study. Of them, 17 patients (sequential group) were randomly selected to use a prospectively ECG-triggered sequential scan, while the other 15 patients (spiral group) used a retrospectively ECG-gated spiral scan. The IQ was assessed by two readers independently, using a four-point grading scale from excel-lent (grade 1) to non-assessable (grade 4), based on the American Heart Association 15-segment model. IQ of each segment and effective dose of each patient were compared between the two groups. Results The mean heart rate (HR) of the sequential group was 96±27 beats per minute (bpm) with a variation range of 73±25 bpm, while the mean HR of the spiral group was 86±22 bpm with a variationrange of 65±24 bpm. Both of the mean HR (t=1.91, P=0.243) and HR variation range (t=0.950, P=0.350) had no significant difference between the two groups. In per-segment analysis, IQ of the sequential group vs. spiral group was rated as excellent (grade 1) in 190/244 (78%) vs. 177/217 (82%) by reader1 and 197/245 (80%) vs. 174/214 (81%) by reader2, as non-assessable (grade 4) in 4/244 (2%) vs. 2/217 (1%) by reader1 and 6/245 (2%) vs. 4/214 (2%) by reader2. Overall averaged IQ per-patient in the sequential and spiral group showed equally good (1.27±0.19 vs. 1.25±0.22, Z=-0.834, P=0.404). The effective radiation dose of the sequential group reduced significantly compared with the spiral group (4.88±1.77 mSv vs. 10.20±3.64 mSv; t=-5.372, P=0.000). Conclusion Compared with retrospectively ECG-gated spiral scan, prospectively ECG-triggered sequential DSCT coronary angiography provides similarly diagnostically valuable images in patients with atrial fibrillation and significantly reduces radiation dose.

Fast scanning mode and its realization in a scanning acoustic microscope

The scanning speed of the two-dimensional stage dominates the efficiency of mechanical scanning measurement systems. This paper focused on a detailed scanning time analysis of conventional raster and spiral scan modes and then proposed two fast alternative scanning modes. Performed on a self-developed scanning acoustic microscope (SAM), the measured images obtained by using the conventional scan mode and fast scan modes are compared. The total scanning time is reduced by 29% of the two proposed fast scan modes. It will offer a better solution for high speed scanning without sacrificing the system stability, and will not introduce additional difficulties to the configuration of scanning measurement systems. They can be easily applied to the mechanical scanning measuring systems with different driving actuators such as piezoelectric, linear motor, dc motor, and so on. The proposed fast raster and square spiral scan modes are realized in SAM, but not specially designed for it. Therefore, they have universal adaptability and can be applied to other scanning measurement systems with two-dimensional mechanical scanning stages, such as atomic force microscope or scanning tunneling microscope.

Optimized imaging quality and radiation dose for coronary artery angiography using 128-slice,dual-source Flash Spiral CT under the natural heart rate

Objective To compare the quality and radiation doses of coronary artery angiography under the natural heart rate condition between Flash spiral heart mode and prospective electrocardiogramtriggering sequence mode using dual-source,in order to choose personalized low doses of coronary artery scanning mode.Methods Sixty patients who underwent coronary angiography(CTA)on a 128-slice,dualsource CT scanner were divided into 2 group i.e,group A(27cases)and group B(33 cases).Flash spiral heart scan mode was employed for group A.Inclusion criteria included:heart rate 75 bpm),date acquisition was set at 30%-50%of the R-R interval. (3)At the arrhythmias,premature beat,fibrillation atrial,date acquisition was set at 20%-90%of the R-R interval.In both gronps,patients with a BMI≥25.0kg/m2 were examined with a tube voltage of 120 kV.while the other patients with a BMI<25.0 kg/m2 were examined with a tube voltage of 100 kV.The BMl was(24.6±1.0)kg/m2 in group A,while that was (24.6±0.9)kg/m2 in group B.In both groups,all images were transferred to the workstation for further processing and analysis.The imaging quality of coronary artery segments and the radiation dose were compared with t test.Results A total of 336 coronary artery segments were evaluated in group A and 412 segments were evaluated in group B.The imaging quality of coronary artery segments were scored.Excellent or good was achieved in 98.2%(330 of 336)artery segments in group A,and that was 98.1%(404 of 412)in group B.There was no statistical difference in imaging quality between the two groups(t=0.513,P=0.608).The average effective dose was(0.74±0.29)mSv in group A,whereas that was(3.67±1.37)mSv in group B.There was a significant difference between the two groups(t=-10.858,P=0.000).Conclusions The personalized low doses coronary artery scanning mode can substantially reduce radiation damage while preserving good imaging quality. Key words: Radiation doses; Tomography spiral computed; Coronary vessels; Heart rate

Performance Assessment of Dynamic Spiral Scan Modes With Variable Pitch for Quantitative Perfusion Computed Tomography

Perfusion computed tomography is increasingly being used in diagnostic radiology. Axial coverage of the traditional approach is limited to the width of the detector. Using continuous periodic table movement coverage can be increased beyond this limit. In this study, we compared tissue flow values determined from scans with a periodic spiral implementation with variable pitch with ones determined from standard dynamic scan modes. A flow phantom (preserved porcine kidney) was scanned with 2 settings of a periodic spiral (Adaptive 4D Spiral) with a range of 100 and 148 mm and a temporal sampling of 1.5 seconds. Additionally, the whole phantom was scanned with the standard dynamic mode (detector width 38.4 mm, temporal sampling 1.0 seconds) at various overlapping positions as a reference. Scan parameters (80 kV, 140 mAs, 40s scan time) were selected similar to a typical brain perfusion study. All scans were repeated 5 times. Tissue flow was calculated with a dedicated deconvolution algorithm. In a center slice and 3 additional slices at various off center positions flow values were recorded in a total of 126 regions of interest (ROI). Reproducibility was determined from the variation of the repeat scans. Agreement between periodic spirals and standard mode was determined by Bland Altman plots and correlation analysis. The reproducibility of the tissue flow determination ranged from 2.7 to 4.4 mL/100 mL/min and was similar for all scan modes. The coefficient of variation ranged from 3.9% to 6.1%. Mean tissue flow in the 126 ROIs ranged from 35 to 121 mL/100 mL/min. There was excellent correlation between both periodic spiral ranges and the standard dynamic mode with a Pearson correlation coefficient of r = 0.97. The regression slope (intercept 0) for the 100 mm range was 1.01, for the 148 mm range it was 0.97. The absolute differences per ROI varied between 1.5 and 4.1 mL/100 mL/min, the relative differences between 1.9% and 6.5%. Differences did not depend on the slice location. Periodic spiral scan modes with variable pitch and a sampling rate of 1.5 seconds can be used for the quantitative determination of tissue flow. Their performance is equivalent to equidistant sampling with standard dynamic scan modes. The ranges of 100 and 148 mm investigated allow coverage of the whole brain or an entire organ for perfusion imaging.

Dual‐source spiral CT with pitch up to 3.2 and 75 ms temporal resolution: Image reconstruction and assessment of image quality

To present the theory for image reconstruction of a high-pitch, high-temporal-resolution spiral scan mode for dual-source CT (DSCT) and evaluate its image quality and dose. With the use of two x-ray sources and two data acquisition systems, spiral CT exams having a nominal temporal resolution per image of up to one-quarter of the gantry rotation time can be acquired using pitch values up to 3.2. The scan field of view (SFOV) for this mode, however, is limited to the SFOV of the second detector as a maximum, depending on the pitch. Spatial and low contrast resolution, image uniformity and noise, CT number accuracy and linearity, and radiation dose were assessed using the ACR CT accreditation phantom, a 30 cm diameter cylindrical water phantom or a 32 cm diameter cylindrical PMMA CTDI phantom. Slice sensitivity profiles (SSPs) were measured for different nominal slice thicknesses, and an anthropomorphic phantom was used to assess image artifacts. Results were compared between single-source scans at pitch = 1.0 and dual-source scans at pitch = 3.2. In addition, image quality and temporal resolution of an ECG-triggered version of the DSCT high-pitch spiral scan mode were evaluated with a moving coronary artery phantom, and radiation dose was assessed in comparison with other existing cardiac scan techniques. No significant differences in quantitative measures of image quality were found between single-source scans at pitch = 1.0 and dual-source scans at pitch = 3.2 for spatial and low contrast resolution, CT number accuracy and linearity, SSPs, image uniformity, and noise. The pitch value (1.6 pitch 3.2) had only a minor impact on radiation dose and image noise when the effective tube current time product (mA s/pitch) was kept constant. However, while not severe, artifacts were found to be more prevalent for the dual-source pitch = 3.2 scan mode when structures varied markedly along the z axis, particularly for head scans. Images of the moving coronary artery phantom acquired with the ECG-triggered high-pitch scan mode were visually free from motion artifacts at heart rates of 60 and 70 bpm. However, image quality started to deteriorate for higher heart rates. At equivalent image quality, the ECG-triggered high-pitch scan mode demonstrated lower radiation dose than other cardiac scan techniques on the same DSCT equipment (25% and 60% dose reduction compared to ECG-triggered sequential step-and-shoot and ECG-gated spiral with x-ray pulsing). A high-pitch (up to pitch = 3.2), high-temporal-resolution (up to 75 ms) dual-source CT scan mode produced equivalent image quality relative to single-source scans using a more typical pitch value (pitch = 1.0). The resultant reduction in the overall acquisition time may offer clinical advantage for cardiovascular, trauma, and pediatric CT applications. In addition, ECG-triggered high-pitch scanning may be useful as an alternative to ECG-triggered sequential scanning for patients with low to moderate heart rates up to 70 bpm, with the potential to scan the heart within one heart beat at reduced radiation dose.

Coronary calcium mass scores measured by identical 64-slice MDCT scanners are comparable: a cardiac phantom study

To assess whether absolute mass scores are comparable or differ between identical 64-slice MDCT scanners of the same manufacturer and to compare absolute mass scores to the physical mass and between scan modes using a calcified phantom. A non-moving anthropomorphic phantom with nine calcifications of three sizes and three densities was scanned 30 times on three 64-slice MDCT scanners of manufacturer A and on three 64-slice MDCT scanners of manufacturer B in both sequential and spiral scan mode. The mean mass scores and mass score variabilities of seven calcifications were determined for all scanners; two non-detectable calcifications were omitted. It was analyzed whether identical scanners yielded similar or significantly different mass scores. Furthermore mass scores were compared to the physical mass and mass scores were compared between scan modes. The mass score calibration factor was determined for all scanners. Mass scores obtained on identical scanners were similar for almost all calcifications. Overall, mass score differences between the scanners were small ranging from 1.5 to 3.4% for the total mass scores, and most differences between scanners were observed for high density calcifications. Mass scores were significantly different from the physical mass for almost all calcifications and all scanners. In sequential mode the total physical mass (167.8 mg) was significantly overestimated (+2.3%) for 4 out of 6 scanners. In spiral mode a significant overestimation (+2.5%) was found for system B and a significant underestimation (−1.8%) for two scanners of system A. Mass scores were dependent on the scan mode, for manufacturer A scores were higher in sequential mode and for manufacturer B in spiral mode. For system A using spiral scan mode no differences were found between identical scanners, whereas a few differences were found using sequential mode. For system B the scan mode did not affect the number of different mass scores between identical scanners. Mass scores obtained in the same scan mode are comparable between identical 64-slice CT scanners and identical 64-slice CT scanners on different sites can be used in follow-up studies. Furthermore, for all systems significant differences were found between mass scores and the physical calcium mass; however, the differences were relatively small and consistent.

High-pitch spiral acquisition: A new scan mode for coronary CT angiography

Coronary CT angiography allows high-quality imaging of the coronary arteries when state-of-the-art CT systems are used. However, radiation exposure has been a concern. We describe a new scan mode that uses a very high-pitch spiral acquisition, "Flash Spiral," which has been developed specifically for low-dose imaging with dual-source CT. The scan mode uses a pitch of 3.2 to acquire a spiral CT data set, while covering the entire volume of the heart in one cardiac cycle. Data acquisition is prospectively triggered by the electrocardiogram and starts in late systole to be completed within one cardiac cycle. Images are reconstructed with a temporal resolution that corresponds to one-quarter of the gantry rotation time. Throughout the data set, subsequent images are reconstructed at later time instants in the cardiac cycle. In a patient with a heart rate of 49 beats/min, the Flash Spiral scan mode was used with a first-generation dual-source CT system and allowed artifact-free visualization of the coronary arteries with a radiation exposure of 1.7 mSv for a 12-cm scan range at 120 kVp tube voltage.