Emphysema quantification on low-dose CT using percentage of low-attenuation volume and size distribution of low-attenuation lung regions: Effects of adaptive iterative dose reduction using 3D processing

PurposeTo evaluate the effects of adaptive iterative dose reduction using 3D processing (AIDR 3D) for quantification of two measures of emphysema: percentage of low-attenuation volume (LAV%) and size distribution of low-attenuation lung regions.Method and materials: Fifty-two patients who underwent standard-dose (SDCT) and low-dose CT (LDCT) were included. SDCT without AIDR 3D, LDCT without AIDR 3D, and LDCT with AIDR 3D were used for emphysema quantification. First, LAV% was computed at 10 thresholds from −990 to −900 HU. Next, at the same thresholds, linear regression on a log–log plot was used to compute the power law exponent (D) for the cumulative frequency-size distribution of low-attenuation lung regions. Bland–Altman analysis was used to assess whether AIDR 3D improved agreement between LDCT and SDCT for emphysema quantification of LAV% and D.ResultsThe mean relative differences in LAV% between LDCT without AIDR 3D and SDCT were 3.73%–88.18% and between LDCT with AIDR 3D and SDCT were −6.61% to 0.406%. The mean relative differences in D between LDCT without AIDR 3D and SDCT were 8.22%–19.11% and between LDCT with AIDR 3D and SDCT were 1.82%–4.79%. AIDR 3D improved agreement between LDCT and SDCT at thresholds from −930 to −990 HU for LAV% and at all thresholds for D.ConclusionAIDR 3D improved the consistency between LDCT and SDCT for emphysema quantification of LAV% and D.     

Radiation dose reduction in soft tissue neck CT using adaptive statistical iterative reconstruction (ASIR)

Purpose

To compare objective and subjective image quality in neck CT images acquired at different tube current–time products (275 mA s and 340 mA s) and reconstructed with filtered-back-projection (FBP) and adaptive statistical iterative reconstruction (ASIR).

Materials and methods

HIPAA-compliant study with IRB approval and waiver of informed consent. 66 consecutive patients were randomly assigned to undergo contrast-enhanced neck CT at a standard tube-current–time-product (340 mA s; n = 33) or reduced tube-current–time-product (275 mA s, n = 33). Data sets were reconstructed with FBP and 2 levels (30%, 40%) of ASIR-FBP blending at 340 mA s and 275 mA s. Two neuroradiologists assessed subjective image quality in a blinded and randomized manner. Volume CT dose index (CTDIvol), dose-length-product (DLP), effective dose, and objective image noise were recorded. Signal-to-noise ratio (SNR) was computed as mean attenuation in a region of interest in the sternocleidomastoid muscle divided by image noise.

Results

Compared with FBP, ASIR resulted in a reduction of image noise at both 340 mA s and 275 mA s. Reduction of tube current from 340 mA s to 275 mA s resulted in an increase in mean objective image noise (p = 0.02) and a decrease in SNR (p = 0.03) when images were reconstructed with FBP. However, when the 275 mA s images were reconstructed using ASIR, the mean objective image noise and SNR were similar to those of the standard 340 mA s CT images reconstructed with FBP (p > 0.05). Subjective image noise was ranked by both raters as either average or less-than-average irrespective of the tube current and iterative reconstruction technique.

Conclusion

Adapting ASIR into neck CT protocols reduced effective dose by 17% without compromising image quality.     

The effect of adaptive iterative dose reduction on image quality in 320-detector row CT coronary angiography

Objective

To evaluate the effect of adaptive iterative dose reduction (AIDR) on image noise and image quality as compared with standard filtered back projection (FBP) in 320-detector row CT coronary angiography (CTCA).

Methods

50 patients (14 females, mean age 68±9 years) who underwent CTCA (100 kV or 120 kV, 400–580 mA) within a single heartbeat were enrolled. Studies were reconstructed with FBP and subsequently AIDR. Image noise, vessel contrast and contrast-to-noise ratio (CNR) in the coronary arteries were evaluated. Overall image quality for coronary arteries was assessed using a five-point scale (1, non-diagnostic; 5, excellent).

Results

All the examinations were performed in a single heartbeat. Image noise in the aorta was significantly lower in data sets reconstructed with AIDR than in those reconstructed with FBP (21.4±3.1 HU vs 36.9±4.5 HU; p<0.001). No significant differences were observed between FBP and AIDR for the mean vessel contrast (HU) in the proximal coronary arteries. Consequently, CNRs in the proximal coronary arteries were higher in the AIDR group than in the FBP group (p<0.001). The mean image quality score was improved by AIDR (3.75±0.38 vs 4.24±0.38; p<0.001).

Conclusion

The use of AIDR reduces image noise and improves image quality in 320-detector row CTCA.CT coronary angiography (CTCA) is a robust non-invasive imaging modality with high spatial and temporal resolution that enables accurate diagnosis or exclusion of coronary artery disease [1-4]. However, CTCA usually exposes the patient to a substantial amount of radiation (9.4–21.4 mSv) [5-7]. Therefore, several scanning techniques, such as ECG-based tube current modulation, prospective ECG triggering and reduced tube voltage scanning, have been developed to reduce the patient''s radiation exposure [6-8]. Reductions of the tube current also lead to lower radiation exposure, as the tube current correlates to dose in a linear fashion. However, lower radiation leads to an increase in CT image noise because the current reconstruction method, filtered back projection (FBP), is unable to consistently generate diagnostic-quality images with reduced tube currents [9].Recently, the adaptive iterative dose reduction technique has been developed as a new reconstruction algorithm to improve image noise [10-12], and has already been shown to reduce the radiation dose in clinical practice [13-16]. Adaptive iterative dose reduction (AIDR) developed for CT by Toshiba Medical Systems Corporation is a modified iterative reconstruction technique in which the original high-noise image undergoes a number of reconstructions that reduce image noise until the resultant image displays the desired noise level. This technique is expected to reduce the radiation dose for a similar noise level to FBP.To our knowledge, no study has evaluated the quality of CT images using AIDR. The purpose of this study was to evaluate the effect of AIDR regarding image noise and image quality in comparison with FBP, using the same raw data set for both FBP and AIDR, in 320-detector row CTCA.     

Radiation Dose Reduction of Chest CT with Iterative Reconstruction in Image Space - Part II: Assessment of Radiologists' Preferences Using Dual Source CT

Objective

To evaluate the impact of radiation dose and reconstruction algorithms on radiologists'' preferences, and whether an iterative reconstruction in image space (IRIS) can be used for dose reduction in chest CT.

Materials and Methods

Standard dose chest CT (SDCT) in 50 patients and low dose chest CT (LDCT) in another 50 patients were performed, using a dual-source CT, with 120 kVp and same reference mAs (50 mAs for SDCT and 25 mAs for LDCT) employed to both tubes by modifying the dual-energy scan mode. Full-dose data were obtained by combining the data from both tubes and half-dose data were separated from one tube. These were reconstructed by using a filtered back projection (FBP) and IRIS: full-dose FBP (F-FBP); full-dose IRIS (F-IRIS); half-dose FBP (H-FBP) and half-dose IRIS (H-IRIS). Ten H-IRIS/F-IRIS, 10 H-FBP/H-IRIS, 40 F-FBP/F-IRIS and 40 F-FBP/H-IRIS pairs of each SDCT and LDCT were randomized. The preference for clinical usage was determined by two radiologists with a 5-point-scale system for the followings: noise, contrast, and sharpness of mediastinum and lung.

Results

Radiologists preferred IRIS over FBP images in the same radiation dose for the evaluation of the lungs in both SDCT (p = 0.035) and LDCT (p < 0.001). When comparing between H-IRIS and F-IRIS, decreased radiation resulted in decreased preference. Observers preferred H-IRIS over F-FBP for the lungs in both SDCT and LDCT, even with reduced radiation dose by half in IRIS image (p < 0.05).

Conclusion

Radiologists'' preference may be influenced by both radiation dose and reconstruction algorithm. According to our preliminary results, dose reduction at 50% with IRIS may be feasible for lung parenchymal evaluation.     

Adaptive Iterative Dose Reduction Algorithm in CT: Effect on Image Quality Compared with Filtered Back Projection in Body Phantoms of Different Sizes

Objective

To evaluate the impact of the adaptive iterative dose reduction (AIDR) three-dimensional (3D) algorithm in CT on noise reduction and the image quality compared to the filtered back projection (FBP) algorithm and to compare the effectiveness of AIDR 3D on noise reduction according to the body habitus using phantoms with different sizes.

Materials and Methods

Three different-sized phantoms with diameters of 24 cm, 30 cm, and 40 cm were built up using the American College of Radiology CT accreditation phantom and layers of pork belly fat. Each phantom was scanned eight times using different mAs. Images were reconstructed using the FBP and three different strengths of the AIDR 3D. The image noise, the contrast-to-noise ratio (CNR) and the signal-to-noise ratio (SNR) of the phantom were assessed. Two radiologists assessed the image quality of the 4 image sets in consensus. The effectiveness of AIDR 3D on noise reduction compared with FBP were also compared according to the phantom sizes.

Results

Adaptive iterative dose reduction 3D significantly reduced the image noise compared with FBP and enhanced the SNR and CNR (p < 0.05) with improved image quality (p < 0.05). When a stronger reconstruction algorithm was used, greater increase of SNR and CNR as well as noise reduction was achieved (p < 0.05). The noise reduction effect of AIDR 3D was significantly greater in the 40-cm phantom than in the 24-cm or 30-cm phantoms (p < 0.05).

Conclusion

The AIDR 3D algorithm is effective to reduce the image noise as well as to improve the image-quality parameters compared by FBP algorithm, and its effectiveness may increase as the phantom size increases.     

全模型迭代重建联合靶重建对甲状腺低剂量CT影像质量的影响

目的 探讨全模型迭代重建（IMR）联合靶重建对甲状腺低剂量CT影像质量的影响,以期在降低辐射剂量的同时满足甲状腺疾病诊断要求。方法 前瞻性分析拟行CT平扫及增强检查的临床可疑甲状腺病变病人100例,男46例,女54例,平均年龄（56.89±12.67）岁。采用随机数表法将病人分为2组,即80 kV低剂量扫描（LDCT组,50例）和120 kV标准剂量扫描（SDCT组,50例）。LDCT组的影像分别选取不同的迭代重建算法和靶重建参数进行处理,获得3组影像,即LDCT1组[混合迭代重建iDose4+显示野（DFOV）300×300]、LDCT2组（iDose4+DFOV 150×150）、LDCT3组（IMR+DFOV 150×150）;SDCT组采用常规方法进行重建（iDose4+DFOV 300×300）。采用Friedman M检验比较LDCT的3组影像信噪比（SNR）、对比噪声比（CNR）及影像质量评分。选出LDCT影像质量最优组与SDCT组进一步比较,采用Wilcoxon秩和检验比较这2组间的客观影像质量和主观影像质量评分。结果 LDCT 3组间CNR、SNR间差异均有统计学意义...     

Image quality and radiation dose of low dose coronary CT angiography in obese patients: Sinogram affirmed iterative reconstruction versus filtered back projection

Purpose

To investigate the image quality and radiation dose of low radiation dose CT coronary angiography (CTCA) using sinogram affirmed iterative reconstruction (SAFIRE) compared with standard dose CTCA using filtered back-projection (FBP) in obese patients.

Materials and methods

Seventy-eight consecutive obese patients were randomized into two groups and scanned using a prospectively ECG-triggered step-and-shot (SAS) CTCA protocol on a dual-source CT scanner. Thirty-nine patients (protocol A) were examined using a routine radiation dose protocol at 120 kV and images were reconstructed with FBP (protocol A). Thirty-nine patients (protocol B) were examined using a low dose protocol at 100 kV and images were reconstructed with SAFIRE. Two blinded observers independently assessed the image quality of each coronary segment using a 4-point scale (1 = non-diagnostic, 4 = excellent) and measured the objective parameters image noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Radiation dose was calculated.

Results

The coronary artery image quality scores, image noise, SNR and CNR were not significantly different between protocols A and B (all p > 0.05), with image quality scores of 3.51 ± 0.70 versus 3.55 ± 0.47, respectively. The effective radiation dose was significantly lower in protocol B (4.41 ± 0.83 mSv) than that in protocol A (8.83 ± 1.74 mSv, p < 0.01).

Conclusion

Compared with standard dose CTCA using FBP, low dose CTCA using SAFIRE can maintain diagnostic image quality with 50% reduction of radiation dose.     

The adaptive statistical iterative reconstruction-V technique for radiation dose reduction in abdominal CT: comparison with the adaptive statistical iterative reconstruction technique

Objective:

To investigate whether reduced radiation dose abdominal CT images reconstructed with adaptive statistical iterative reconstruction V (ASIR-V) compromise the depiction of clinically competent features when compared with the currently used routine radiation dose CT images reconstructed with ASIR.

Methods:

27 consecutive patients (mean body mass index: 23.55 kg m⁻² underwent CT of the abdomen at two time points. At the first time point, abdominal CT was scanned at 21.45 noise index levels of automatic current modulation at 120 kV. Images were reconstructed with 40% ASIR, the routine protocol of Dong-A University Hospital. At the second time point, follow-up scans were performed at 30 noise index levels. Images were reconstructed with filtered back projection (FBP), 40% ASIR, 30% ASIR-V, 50% ASIR-V and 70% ASIR-V for the reduced radiation dose. Both quantitative and qualitative analyses of image quality were conducted. The CT dose index was also recorded.

Results:

At the follow-up study, the mean dose reduction relative to the currently used common radiation dose was 35.37% (range: 19–49%). The overall subjective image quality and diagnostic acceptability of the 50% ASIR-V scores at the reduced radiation dose were nearly identical to those recorded when using the initial routine-dose CT with 40% ASIR. Subjective ratings of the qualitative analysis revealed that of all reduced radiation dose CT series reconstructed, 30% ASIR-V and 50% ASIR-V were associated with higher image quality with lower noise and artefacts as well as good sharpness when compared with 40% ASIR and FBP. However, the sharpness score at 70% ASIR-V was considered to be worse than that at 40% ASIR. Objective image noise for 50% ASIR-V was 34.24% and 46.34% which was lower than 40% ASIR and FBP.

Conclusion:

Abdominal CT images reconstructed with ASIR-V facilitate radiation dose reductions of to 35% when compared with the ASIR.

Advances in knowledge:

This study represents the first clinical research experiment to use ASIR-V, the newest version of iterative reconstruction. Use of the ASIR-V algorithm decreased image noise and increased image quality when compared with the ASIR and FBP methods. These results suggest that high-quality low-dose CT may represent a new clinical option.     

Assessment of dose exposure and image quality in coronary angiography performed by 640-slice CT: a comparison between adaptive iterative and filtered back-projection algorithm by propensity analysis

Purpose

This study was performed to confirm, by propensity score matching, whether the use of adaptive–iterative dose reduction (AIDR 3D) with a built-in automatic exposure control system provides clinical and dosimetric advantages with respect to the traditional filtered back-projection (FBP) algorithm without automatic exposure modulation.

Materials and methods

A total of 200 consecutive patients undergoing coronary computed tomography (CT) angiography on a 640-slice CT scanner were studied. A protocol with exposure parameters based on patient body mass index (BMI) and with images reconstructed using FBP (group A) was compared with a protocol with images acquired using tube current decided by an automatic exposure control system and reconstructed using AIDR (group B). Mean effective dose and image quality with both objective and subjective measurements were assessed.

Results

Mean effective dose was 23.6 % lower in group B than in group A (2.56 versus 3.34 mSv; p < 0.0001). Noise was significantly lower in group B with consequent higher signal-to-noise (SNR) and contrast-to-noise (CNR) (p < 0.0001) compared with group A. Subjective quality parameters were also significantly higher in group B.

Conclusions

Comparative analysis by propensity score matching confirms that AIDR 3D with automatic exposure control is able to reduce significantly the mean radiation dose and improve the image quality compared with traditional FBP without exposure modulation.     

Hepatic CT perfusion measurements: A feasibility study for radiation dose reduction using new image reconstruction method

Objectives

To assess the effects of image reconstruction method on hepatic CT perfusion (CTP) values using two CT protocols with different radiation doses.

Materials and methods

Sixty patients underwent hepatic CTP and were randomly divided into two groups. Tube currents of 210 or 250 mA were used for the standard dose group and 120 or 140 mA for the low dose group. The higher currents were selected for large patients. Demographic features of the groups were compared. CT images were reconstructed by using filtered back projection (FBP), image filter (quantum de-noising, QDS), and adaptive iterative dose reduction (AIDR). Hepatic arterial and portal perfusion (HAP and HPP, ml/min/100 ml) and arterial perfusion fraction (APF, %) were calculated using the dual-input maximum slope method. ROIs were placed on each hepatic segment. Perfusion and Hounsfield unit (HU) values, and image noises (standard deviations of HU value, SD) were measured and compared between the groups and among the methods.

Results

There were no significant differences in the demographic features of the groups, nor were there any significant differences in mean perfusion and HU values for either the groups or the image reconstruction methods. Mean SDs of each of the image reconstruction methods were significantly lower (p < 0.0001) for the standard dose group than the low dose group, while mean SDs for AIDR were significantly lower than those for FBP for both groups (p = 0.0006 and 0.013). Radiation dose reductions were approximately 45%.

Conclusions

Image reconstruction method did not affect hepatic perfusion values calculated by dual-input maximum slope method with or without radiation dose reductions. AIDR significantly reduced images noises.     

Noise-based tube current reduction method with iterative reconstruction for reduction of radiation exposure in coronary CT angiography

Purpose

To investigate the potential of noise-based tube current reduction method with iterative reconstruction to reduce radiation exposure while achieving consistent image quality in coronary CT angiography (CCTA).

Materials and methods

294 patients underwent CCTA on a 64-detector row CT equipped with iterative reconstruction. 102 patients with fixed tube current were assigned to Group 1, which was used to establish noise-based tube current modulation formulas, where tube current was modulated by the noise of test bolus image. 192 patients with noise-based tube current were randomly assigned to Group 2 and Group 3. Filtered back projection was applied for Group 2 and iterative reconstruction for Group 3. Qualitative image quality was assessed with a 5 point score. Image noise, signal intensity, volume CT dose index, and dose-length product were measured.

Results

The noise-based tube current modulation formulas were established through regression analysis using image noise measurements in Group 1. Image noise was precisely maintained at the target value of 35.00 HU with small interquartile ranges for Group 2 (34.17–35.08 HU) and Group 3 (34.34–35.03 HU), while it was from 28.41 to 36.49 HU for Group 1. All images in the three groups were acceptable for diagnosis. A relative 14% and 41% reduction in effective dose for Group 2 and Group 3 were observed compared with Group 1.

Conclusion

Adequate image quality could be maintained at a desired and consistent noise level with overall 14% dose reduction using noise-based tube current reduction method. The use of iterative reconstruction further achieved approximately 40% reduction in effective dose.     

The optimal dose reduction level using iterative reconstruction with prospective ECG-triggered coronary CTA using 256-slice MDCT

Aim

To assess the image quality (IQ) of an iterative reconstruction (IR) technique (iDose⁴) from prospective electrocardiography (ECG)-triggered coronary computed tomography angiography (coronary CTA) on a 256-slice multi-detector CT (MDCT) scanner and determine the optimal dose reduction using IR that can provide IQ comparable to filtered back projection (FBP).

Method and materials

110 consecutive patients (69 men, 41 women; age: 54 ± 10 years) underwent coronary CTA on a 256-slice MDCT (Brilliance iCT, Philips Healthcare). The control group (Group A, n = 21) were scanned using the conventional tube output (120 kVp, 210 mAs) and reconstructed using FBP. The other 4 groups were scanned with the same kVp but successively reduced tube output as follows: B[n = 15]: 125 mAs; C[n = 22]: 105 mAs; D[n = 36]: 84 mAs: E[n = 16]: 65 mAs) and reconstructed using IR levels of L3 (Group B), L4 (Group C) and L5 (Groups D and E), to compensate for the noise increase. All images were reconstructed using the same kernel (XCB). Two radiologists graded IQ in a blinded fashion on a 4-point scale (4 – excellent, 3 – good, 2 – fair and 1 – poor). Quantitative measurements of CT values, image noise and contrast-to-noise (CNR) were measured in each group. A receiver-operating characteristic (ROC) analysis was performed to determine a radiation reduction threshold up to which excellent IQ was maintained.

Results

There were no significant differences in objective noise, SNR and CNR values among Groups A, B, C, D, and E (P = 0.14, 0.09, 0.17, respectively). There were no significant differences in the scores of the subjective IQ between Group A, and Groups B, C, D, E (P = 0.23–0.97). Significant differences in image sharpness and study acceptability were observed between groups A and E (P < 0.05). Using the criterion of excellent IQ (score 4), the ROC curve of dose levels and IQ acceptability established a reduction of 60% of tube output (Group D) as optimum cutoff point (AUC: 0.72, 95% CI: 0.59–0.86). Group D (84 mAs with L5) provided equivalent subjective image ranking (with lumen sharpness taken into account) and objective IQ measurements (noise: 36.5 ± 10.7; SNR: 13.6 ± 4.9; CNR: 16.28 ± 5.4) compared with FBP images in Group A (noise: 35.5 ± 9.4; SNR: 12.4 ± 2.5; CNR: 15.4 ± 3.2) (P = 0.14, 0.09, 0.17, respectively). The effective dose (ED) of Group D was 63% lower than that of Group A (1.2 ± 0.1 mSv versus 3.2 ± 0.6 mSv).

Conclusion

Iterative reconstruction techniques can provide 63% ED reduction in prospectively-triggered coronary CTA using 256-slice MDCT while maintaining excellent image quality.     

Radiation dose reduction with the adaptive statistical iterative reconstruction (ASIR) technique for chest CT in children: An intra-individual comparison

Objective

To retrospectively compare radiation dose and image quality of pediatric chest CT using a routine dose protocol reconstructed with filtered back projection (FBP) (the Routine study) and a low-dose protocol with 50% adaptive statistical iterative reconstruction (ASIR) (the ASIR study).

Materials and methods

We retrospectively reviewed chest CT performed in pediatric patients who underwent both the Routine study and the ASIR study on different days between January 2010 and August 2011. Volume CT dose indices (CTDIvol), dose length products (DLP), and effective doses were obtained to estimate radiation dose. The image quality was evaluated objectively as noise measured in the descending aorta and paraspinal muscle, and subjectively by three radiologists for noise, sharpness, artifacts, and diagnostic acceptability using a four-point scale. The paired Student's t-test and the Wilcoxon signed-rank test were used for statistical analysis.

Results

Twenty-six patients (M:F = 13:13, mean age 11.7) were enrolled. The ASIR studies showed 60.3%, 56.2%, and 55.2% reductions in CTDIvol (from 18.73 to 7.43 mGy, P < 0.001), DLP (from 307.42 to 134.51 mGy × cm, P < 0.001), and effective dose (from 4.12 to 1.84 mSv, P < 0.001), respectively, compared with the Routine studies. The objective noise was higher in the paraspinal muscle of the ASIR studies (20.81 vs. 16.67, P = 0.004), but was not different in the aorta (18.23 vs. 18.72, P = 0.726). The subjective image quality demonstrated no difference between the two studies.

Conclusion

A low-dose protocol with 50% ASIR allows radiation dose reduction in pediatric chest CT by more than 55% while maintaining image quality.     

Radiation Dose Reduction of Chest CT with Iterative Reconstruction in Image Space - Part I: Studies on Image Quality Using Dual Source CT

Objective

To determine whether the image quality (IQ) is improved with iterative reconstruction in image space (IRIS), and whether IRIS can be used for radiation reduction in chest CT.

Materials and Methods

Standard dose chest CT (SDCT) in 50 patients and low dose chest CT (LDCT) in another 50 patients were performed, using a dual-source CT, with 120 kVp and same reference mAs (50 mAs for SDCT and 25 mAs for LDCT) employed to both tubes by modifying a dual-energy scan mode. Full-dose data were obtained by combining the data from both tubes and half-dose data were separated from a single tube. These were reconstructed by using a filtered back projection (FBP) and IRIS: full-dose FBP (F-FBP); full-dose IRIS (F-IRIS); half-dose FBP (H-FBP) and half-dose IRIS (H-IRIS). Objective noise was measured. The subjective IQ was evaluated by radiologists for the followings: noise, contrast and sharpness of mediastinum and lung.

Results

Objective noise was significantly lower in H-IRIS than in F-FBP (p < 0.01). In both SDCT and LDCT, the IQ scores were highest in F-IRIS, followed by F-FBP, H-IRIS and H-FBP, except those for sharpness of mediastinum, which tended to be higher in FBP. When comparing CT images between the same dose and different reconstruction (F-IRIS/F-FBP and H-IRIS/H-FBP) algorithms, scores tended to be higher in IRIS than in FBP, being more distinct in half-dose images. However, despite the use of IRIS, the scores were lower in H-IRIS than in F-FBP.

Conclusion

IRIS generally helps improve the IQ, being more distinct at the reduced radiation. However, reduced radiation by half results in IQ decrease even when using IRIS in chest CT.     

Periradicular infiltration of the lumbar spine: is iterative reconstruction software necessary to establish ultra-low-dose protocols? A quantitative and qualitative approach

Purpose

Computed tomography (CT)-guided periradicular infiltration therapy has emerged as an effective treatment option for patients with low back pain. Concern about radiation exposure requires approaches allowing significant dose reduction. The purpose of this study is to evaluate the need for iterative reconstruction software in CT-guided periradicular infiltration therapy with an ultra-low-dose protocol.

Materials and methods

One hundred patients underwent CT-guided periradicular infiltration therapy of the lumbar spine using an ultra-low-dose protocol with adaptive iterative dose reduction 3D (AIDR 3D) for image reconstruction. In addition, images were reconstructed with filtered back-projection (FBP). Four experienced raters evaluated both reconstruction types for conspicuity of anatomical and instrumental features important for ensuring safe patient treatment. Image noise was measured as a quantitative marker of image quality.

Results

Interrater agreement was good for both AIDR 3D (Kendall’s W?=?0.83) and FBP (0.78) reconstructions. Readers assigned the same scores for all features and both reconstruction algorithms in 81.3% of cases. Image noise was significantly lower (average SD of 60.07 vs. 99.54, p?<?0.05) for AIDR 3D-reconstructed images.

Conclusion

Although it significantly lowers image noise, iterative reconstruction software is not mandatory to achieve adequate image quality with an ultra-low-dose CT protocol for guiding periradicular infiltration therapy of the lumbar spine.

     

Dose reduction with adaptive statistical iterative reconstruction for paediatric CT: phantom study and clinical experience on chest and abdomen CT

Objectives

To assess the benefit and limits of iterative reconstruction of paediatric chest and abdominal computed tomography (CT).

Methods

The study compared adaptive statistical iterative reconstruction (ASIR) with filtered back projection (FBP) on 64-channel MDCT. A phantom study was first performed using variable tube potential, tube current and ASIR settings. The assessed image quality indices were the signal-to-noise ratio (SNR), the noise power spectrum, low contrast detectability (LCD) and spatial resolution. A clinical retrospective study of 26 children (M:F?=?14/12, mean age: 4 years, range: 1–9 years) was secondarily performed allowing comparison of 18 chest and 14 abdominal CT pairs, one with a routine CT dose and FBP reconstruction, and the other with 30 % lower dose and 40 % ASIR reconstruction. Two radiologists independently compared the images for overall image quality, noise, sharpness and artefacts, and measured image noise.

Results

The phantom study demonstrated a significant increase in SNR without impairment of the LCD or spatial resolution, except for tube current values below 30–50 mA. On clinical images, no significant difference was observed between FBP and reduced dose ASIR images.

Conclusion

Iterative reconstruction allows at least 30 % dose reduction in paediatric chest and abdominal CT, without impairment of image quality.

Key points

? Iterative reconstruction helps lower radiation exposure levels in children undergoing CT. ? Adaptive statistical iterative reconstruction (ASIR) significantly increases SNR without impairing spatial resolution. ? For abdomen and chest CT, ASIR allows at least a 30 % dose reduction.     

Improving low-dose abdominal CT images by Weighted Intensity Averaging over Large-scale Neighborhoods

Purpose

Though highly desirable in radiologic procedures, low-dose CT (LDCT) images tend to be severely degraded by quantum noise and non-stationary artifacts. The purpose of this paper is to improve the abdominal LDCT images by the approach of Weighted Intensity Averaging over Large-scale Neighborhoods (WIA-LN).

Materials and methods

In the implementation of the proposed WIA-LN method, the processed pixel intensities are adaptively calculated as the weighted intensity averaging of the pixels with similar surrounding structures throughout a large-scale neighborhood. Both phantom and clinical abdominal CT images from a 16 detector rows Siemens CT were acquired at standard and 80% reduced tube current time products (150 mA s and 30 mA s corresponding to standard-dose and low-dose protocols, respectively). Visual comparison, statistical qualitative analysis (image quality scores and hepatic cyst diagnosis), and quantitative calculation (noise and contrast-to-noise ratio) are made.

Results

Better vision and quantitative performance are realized using the proposed WIA-LN method. Compared to original LDCT and standard-dose CT (SDCT) images, statistically significant improvement of noise/artifacts suppression, contrast preservation and hepatic cyst detection in LDCT images are achieved by using the proposed method (P < 0.05).

Conclusion

With the tube current reduced to approximate one-fifth of the standard tube current setting, clinically acceptable images can still be obtained by using the proposed method.     

Cranial CT with adaptive statistical iterative reconstruction: improved image quality with concomitant radiation dose reduction

BACKGROUND AND PURPOSE:To safeguard patient health, there is great interest in CT radiation-dose reduction. The purpose of this study was to evaluate the impact of an iterative-reconstruction algorithm, ASIR, on image-quality measures in reduced-dose head CT scans for adult patients.MATERIALS AND METHODS:Using a 64-section scanner, we analyzed 100 reduced-dose adult head CT scans at 6 predefined levels of ASIR blended with FBP reconstruction. These scans were compared with 50 CT scans previously obtained at a higher routine dose without ASIR reconstruction. SNR and CNR were computed from Hounsfield unit measurements of normal GM and WM of brain parenchyma. A blinded qualitative analysis was performed in 10 lower-dose CT datasets compared with higher-dose ones without ASIR. Phantom data analysis was also performed.RESULTS:Lower-dose scans without ASIR had significantly lower mean GM and WM SNR (P = .003) and similar GM-WM CNR values compared with higher routine-dose scans. However, at ASIR levels of 20%–40%, there was no statistically significant difference in SNR, and at ASIR levels of ≥60%, the SNR values of the reduced-dose scans were significantly higher (P < .01). CNR values were also significantly higher at ASIR levels of ≥40% (P < .01). Blinded qualitative review demonstrated significant improvements in perceived image noise, artifacts, and GM-WM differentiation at ASIR levels ≥60% (P < .01).CONCLUSIONS:These results demonstrate that the use of ASIR in adult head CT scans reduces image noise and increases low-contrast resolution, while allowing lower radiation doses without affecting spatial resolution.

The use of CT is increasing rapidly at a rate of approximately 10% per year, and >68 million CT studies were performed in the United States during 2008.^1–3 The foremost concern with the increasing use of CT technology is the associated dose of ionizing radiation and the potential risk of cancer development later in life.¹ The situation is even more worrisome in the pediatric population, which is at greater risk than adults from a given dose of radiation.¹ However, dose reduction in CT is hindered by the increased image noise in lower radiation-dose protocols by using the current FBP reconstructions.CT imaging demands the development of more efficient reconstruction techniques to diminish radiation dose. Iterative reconstruction techniques promise to drastically reduce image noise and artifacts, thereby allowing significant dose reduction. Most of these techniques are computationally intensive and require long reconstruction times. The most comprehensive iterative-reconstruction algorithm models the system optics by taking into account the finite size of the pixel and the focal spot as well as the shape and size of the detector-cell spacing. In addition, it also models the photon statistics in x-ray attenuation. ASIR (GE Healthcare, Chalfont St. Giles, UK) is a modified iterative-reconstruction technique that is time-efficient and already clinically available. It models the photon statistics in x-ray attenuation but does not model the system optics. Thus, it is more computationally complex than FBP but considerably less computationally complex than more comprehensive iterative-reconstruction methods.³ This technique produces significant noise reduction that potentially improves image quality and allows reduction in radiation dose. High levels of ASIR processing create image texture (smooth appearance) and noise characteristics unfamiliar to radiologists.^3,4 In clinical practice, one can use variably blended images created with FBP and ASIR techniques to produce different levels of ASIR.The purpose of this study was to evaluate the impact of ASIR on both qualitative and quantitative measures of image quality in reduced-dose head CT scans for adult patients. Our hypothesis was that the use of ASIR decreases CT image noise resulting in increased SNR and CNR ratios as well as improved qualitative scores of contrast resolution without compromising spatial resolution. We evaluated its effect on quantitative and qualitative measures of brain image quality in adult reduced-dose head CT scans at multiple ASIR levels in comparison with regular-dose CT studies.     

The feasibility of Forward-projected model-based Iterative Reconstruction SoluTion (FIRST) for coronary 320-row computed tomography angiography: A pilot study

Background

We aimed to assess and compare the influence of Forward projected model-based Iterative Reconstruction SoluTion (FIRST), a recently introduced full iterative reconstruction method, on radiation doses and image quality with that of Adaptive Iterative Dose Reduction (AIDR) 3D for 320-row cardiac computed tomography (CT).

Split-bolus CT-urography using dual-energy CT: Feasibility, image quality and dose reduction

Purpose

To prospectively evaluate the feasibility of dual-energy (DE) split-bolus CT-urography (CTU) and the quality of virtual non-enhanced images (VNEI) and DE combined nephrographic-excretory phase images (CNEPI), and to estimate radiation dose reduction if true non-enhanced images (TNEI) could be omitted.

Patients and methods

Between August and September 2011, 30 consecutive patients with confirmed or suspected urothelial cancer or with hematuria underwent DE CT. Single-energy TNEI and DE CNEPI were obtained. VNEI was reconstructed from CNEPI. Image quality of CNEPI and VNEI was evaluated using a 5-point scale. The attenuation of urine in the bladder on TNEI and VNEI was measured. The CT dose index volume (CTDI (vol)) of the two scans was recorded.

Results

The mean image quality score of CNEPI and VNEI was 4.7 and 3.3, respectively. The mean differences in urine attenuation between VNEI and TNEI were 14 ± 15 [SD] and −16 ± 29 in the anterior and posterior parts of the bladder, respectively. The mean CTDI (vol) for TNEI and CNEPI was 11.8 and 10.9 mGy, respectively. Omission of TNEI could reduce the total radiation dose by 52%.

Conclusion

DE split-bolus CTU is technically feasible and can reduce radiation exposure; however, an additional TNEI scan is necessary when the VNEI quality is poor or quantitative evaluation of urine attenuation is required.