Adaptive statistical iterative reconstruction reduces patient radiation dose in neuroradiology CT studies

Introduction

Adaptive statistical iterative reconstruction (ASIR) can decrease image noise, thereby generating CT images of comparable diagnostic quality with less radiation. The purpose of this study is to quantify the effect of systematic use of ASIR versus filtered back projection (FBP) for neuroradiology CT protocols on patients’ radiation dose and image quality.

Methods

We evaluated the effect of ASIR on six types of neuroradiologic CT studies: adult and pediatric unenhanced head CT, adult cervical spine CT, adult cervical and intracranial CT angiography, adult soft tissue neck CT with contrast, and adult lumbar spine CT. For each type of CT study, two groups of 100 consecutive studies were retrospectively reviewed: 100 studies performed with FBP and 100 studies performed with ASIR/FBP blending factor of 40 %/60 % with appropriate noise indices. The weighted volume CT dose index (CTDI_vol), dose–length product (DLP) and noise were recorded. Each study was also reviewed for image quality by two reviewers. Continuous and categorical variables were compared by t test and free permutation test, respectively.

Results

For adult unenhanced brain CT, CT cervical myelography, cervical and intracranial CT angiography and lumbar spine CT both CTDI_vol and DLP were lowered by up to 10.9 % (p?<?0.001), 17.9 % (p?=?0.005), 20.9 % (p?<?0.001), and 21.7 % (p?=?0.001), respectively, by using ASIR compared with FBP alone. Image quality and noise were similar for both FBP and ASIR.

Conclusion

We recommend routine use of iterative reconstruction for neuroradiology CT examinations because this approach affords a significant dose reduction while preserving image quality.     

Low-dose CT of the lung: potential value of iterative reconstructions

Objectives

To prospectively assess the impact of sinogram-affirmed iterative reconstruction (SAFIRE) on image quality of nonenhanced low-dose lung CT as compared to filtered back projection (FBP).

Methods

Nonenhanced low-dose chest CT (tube current-time product: 30?mAs) was performed on 30 patients at 100?kVp and on 30 patients at 80?kVp. Images were reconstructed with FBP and SAFIRE. Two blinded, independent readers measured image noise; two readers assessed image quality of normal anatomic lung structures on a five-point scale. Radiation dose parameters were recorded.

Results

Image noise in datasets reconstructed with FBP (57.4?±?15.9) was significantly higher than with SAFIRE (31.7?±?9.8, P?<?0.001). Image quality was significantly superior with SAFIRE than with FBP (P?<?0.01), without significant difference between FBP at 100?kVp and SAFIRE at 80?kVp (P?=?0.68). Diagnostic image quality was present with FBP in 96% of images at 100?kVp and 88% at 80?kVp, and with SAFIRE in 100% at 100?kVp and 98% at 80?kVp. There were significantly more datasets with diagnostic image quality with SAFIRE than with FBP (P?<?0.01). Mean CTDI_vol and effective doses were 1.5?±?0.7?mGy·cm and 0.7?±?0.2?mSv at 100?kVp, and 1.4?±?2.8?mGy·cm and 0.5?±?0.2?mSv at 80?kVp (P?<?0.001, both).

Conclusions

Use of SAFIRE in low-dose lung CT reduces noise, improves image quality, and renders more studies diagnostic as compared to FBP.

Key Points

? Low-dose computed tomography is an important thoracic investigation tool. ? Radiation dose can be less than 1?mSv with iterative reconstructions. ? Iterative reconstructions render more low-dose lung CTs diagnostic compared to conventional reconstructions.     

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.     

Computed tomography of the chest with model-based iterative reconstruction using a radiation exposure similar to chest X-ray examination: preliminary observations

Objectives

The purpose of this study was to assess the diagnostic image quality of ultra-low-dose chest computed tomography (ULD-CT) obtained with a radiation dose comparable to chest radiography and reconstructed with filtered back projection (FBP), adaptive statistical iterative reconstruction (ASIR) and model-based iterative reconstruction (MBIR) in comparison with standard dose diagnostic CT (SDD-CT) or low-dose diagnostic CT (LDD-CT) reconstructed with FBP alone.

Methods

Unenhanced chest CT images of 42 patients acquired with ULD-CT were compared with images obtained with SDD-CT or LDD-CT in the same examination. Noise measurements and image quality, based on conspicuity of chest lesions on all CT data sets were assessed on a five-point scale.

Results

The radiation dose of ULD-CT was 0.16?±?0.006 mSv compared with 11.2?±?2.7 mSv for SDD-CT (P?<?0.0001) and 2.7?±?0.9 mSv for LDD-CT. Image quality of ULD-CT increased significantly when using MBIR compared with FBP or ASIR (P?<?0.001). ULD-CT reconstructed with MBIR enabled to detect as many non-calcified pulmonary nodules as seen on SDD-CT or LDD-CT. However, image quality of ULD-CT was clearly inferior for characterisation of ground glass opacities or emphysema.

Conclusion

Model-based iterative reconstruction allows detection of pulmonary nodules with ULD-CT with radiation exposure in the range of a posterior to anterior (PA) and lateral chest X-ray.

Key Points

? Radiation dose is a key concern with the increased use of thoracic CT ? Ultra-low-dose chest CT approximates the radiation dose of conventional chest radiography ? Ultra-low-dose chest CT can be of diagnostic quality ? Solid pulmonary nodules are clearly depicted on ultra-low-dose chest CT

     

A prospective feasibility study of sub-millisievert abdominopelvic CT using iterative reconstruction in Crohn’s disease

Objective

Iterative reconstruction (IR) allows diagnostic CT imaging with less radiation exposure than filtered back projection (FBP). We studied an IR low-dose CT abdomen/pelvis (LDCTAP) protocol, designed to image at an effective dose (ED) approximating 1 mSv in patients with Crohn’s disease (CD).

Methods

Forty patients, mean age 37?±?13.4 years (range 17–69), with CD underwent two synchronous CT protocols (conventional-dose (CDCTAP) and LDCTAP). CDCTAP and LDCTAP images were compared for diagnostic acceptability, yield, image quality and ED (in millisieverts). The optimal level of IR for LDCTAP was also studied.

Results

LDCTAP yielded a mean ED of 1.3?±?0.8 mSv compared with 4.7?±?2.9 mSv for CDCTAP, reducing ED by 73.7?±?3.3 % (mean dose reduction, 3.5?±?2.1 mSv; P?<?0.001) and dose length product by 73.6?±?2.6 % (P?<?0.001). Sub-millisievert (0.84 mSv) imaging was performed for patients with a body mass index (BMI) less than 25 (i.e. 63 % of our cohort). LDCTAP resulted in increased image noise and reduced diagnostic acceptability compared with CDCTAP despite use of IR, but detection of extra-luminal complications was comparable.

Conclusion

Patients with suspected active CD can be adequately imaged using LDCTAP, yielding comparable information regarding extent, activity and complications of CD compared with CDCTAP, but with 74 % less dose. LDCTAP at doses equivalent to that of two abdominal radiographs represents a feasible alternative to CDCTAP.

Key points

? Radiation dose is a concern when imaging patients with Crohn’s disease. ? New techniques allow low-dose abdominopelvic CT with acceptable image quality. ? Using hybrid iterative reconstruction, its diagnostic yield compares well with that of conventional CT. ? Sub-millisievert CT of patients with Crohn’s disease appears technically and clinically feasible.     

Model-based iterative reconstruction technique for radiation dose reduction in chest CT: comparison with the adaptive statistical iterative reconstruction technique

Objectives

To prospectively evaluate dose reduction and image quality characteristics of chest CT reconstructed with model-based iterative reconstruction (MBIR) compared with adaptive statistical iterative reconstruction (ASIR).

Methods

One hundred patients underwent reference-dose and low-dose unenhanced chest CT with 64-row multidetector CT. Images were reconstructed with 50?% ASIR-filtered back projection blending (ASIR50) for reference-dose CT, and with ASIR50 and MBIR for low-dose CT. Two radiologists assessed the images in a blinded manner for subjective image noise, artefacts and diagnostic acceptability. Objective image noise was measured in the lung parenchyma. Data were analysed using the sign test and pair-wise Student’s t-test.

Results

Compared with reference-dose CT, there was a 79.0?% decrease in dose–length product with low-dose CT. Low-dose MBIR images had significantly lower objective image noise (16.93?±?3.00) than low-dose ASIR (49.24?±?9.11, P?P?Conclusion Diagnostically acceptable chest CT images acquired with nearly 80?% less radiation can be obtained using MBIR. MBIR shows greater potential than ASIR for providing diagnostically acceptable low-dose CT images without severely compromising image quality.

Key Points

? Model-based iterative reconstruction (MBIR) creates high-quality low-dose CT images. ? MBIR significantly improves image noise and artefacts over adaptive statistical iterative techniques. ? MBIR shows greater potential than ASIR for diagnostically acceptable low-dose CT. ? The prolonged processing time of MBIR may currently limit its routine use in clinical practice.     

Chest computed tomography using iterative reconstruction vs filtered back projection (Part 2): image quality of low-dose CT examinations in 80 patients

Purpose

To evaluate the image quality of an iterative reconstruction algorithm (IRIS) in low-dose chest CT in comparison with standard-dose filtered back projection (FBP) CT.

Materials and methods

Eighty consecutive patients referred for a follow-up chest CT examination of the chest, underwent a low-dose CT examination (Group 2) in similar technical conditions to those of the initial examination, (Group 1) except for the milliamperage selection and the replacement of regular FBP reconstruction by iterative reconstructions using three (Group 2a) and five iterations (Group 2b).

Results

Despite a mean decrease of 35.5% in the dose-length-product, there was no statistically significant difference between Group 2a and Group 1 in the objective noise, signal-to-noise (SNR) and contrast-to-noise (CNR) ratios and distribution of the overall image quality scores. Compared to Group 1, objective image noise in Group 2b was significantly reduced with increased SNR and CNR and a trend towards improved image quality.

Conclusion

Iterative reconstructions using three iterations provide similar image quality compared with the conventionally used FBP reconstruction at 35% less dose, thus enabling dose reduction without loss of diagnostic information. According to our preliminary results, even higher dose reductions than 35% may be feasible by using more than three iterations.     

Image quality of ultra-low radiation exposure coronary CT angiography with an effective dose <0.1 mSv using high-pitch spiral acquisition and raw data-based iterative reconstruction

Objectives

We evaluated the potential of prospectively ECG-triggered high-pitch spiral acquisition with low tube voltage and current in combination with iterative reconstruction to achieve coronary CT angiography with sufficient image quality at an effective dose below 0.1 mSv.

Methods

Contrast-enhanced coronary dual source CT angiography (2?×?128?×?0.6 mm, 80 kV, 50 mAs) in prospectively ECG-triggered high-pitch spiral acquisition mode was performed in 21 consecutive individuals (body weight <100 kg, heart rate ≤60/min). Images were reconstructed with raw data-based filtered back projection (FBP) and iterative reconstruction (IR). Image quality was assessed on a 4-point scale (1 = no artefacts, 4 = unevaluable).

Results

Mean effective dose was 0.06?±?0.01 mSv. Image noise was significantly reduced in IR (128.9?±?46.6 vs. 158.2?±?44.7 HU). The mean image quality score was lower for IR (1.9?±?1.1 vs. 2.2?±?1.0, P?<?0.0001). Of 292 coronary segments, 55 in FBP and 40 in IR (P?=?0.12) were graded “unevaluable”. In patients with a body weight ≤75 kg, both in FBP and in IR, the rates of fully evaluable segments were significantly higher in comparison to patients >75 kg.

Conclusions

Coronary CT angiography with an estimated effective dose <0.1 mSv may provide sufficient image quality in selected patients through the combination of high-pitch spiral acquisition and raw data-based iterative reconstruction.

Key Points

? Coronary CT angiography with an estimated effective dose <0.1 mSv is possible. ? Combination of high-pitch spiral acquisition with iterative reconstruction achieves sufficient image quality. ? Diagnostic accuracy remains to be assessed in future trials.     

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.     

Cardiovascular CT angiography in neonates and children: Image quality and potential for radiation dose reduction with iterative image reconstruction techniques

Objectives

To evaluate image quality (IQ) of low-radiation-dose paediatric cardiovascular CT angiography (CTA), comparing iterative reconstruction in image space (IRIS) and sinogram-affirmed iterative reconstruction (SAFIRE) with filtered back-projection (FBP) and estimate the potential for further dose reductions.

Methods

Forty neonates and children underwent low radiation CTA with or without ECG synchronisation. Data were reconstructed with FBP, IRIS and SAFIRE. For ECG-synchronised studies, half-dose image acquisitions were simulated. Signal noise was measured and IQ graded. Effective dose (ED) was estimated.

Results

Mean absolute and relative image noise with IRIS and full-dose SAFIRE was lower than with FBP (P?<?0.001), while SNR and CNR were higher (P?<?0.001). Image noise was also lower and SNR and CNR higher in half-dose SAFIRE studies compared with full-and half-dose FBP studies (P?<?0.001). IQ scores were higher for IRIS, full-dose SAFIRE and half-dose SAFIRE than for full-dose FBP and higher for half-dose SAFIRE than for half-dose FBP (P?<?0.05). Median weight-specific ED was 0.3 mSv without and 1.36 mSv with ECG synchronisation. The estimated ED of half-dose SAFIRE studies was 0.68 mSv.

Conclusions

IR improves image noise, SNR, CNR and subjective IQ compared with FBP in low-radiation-dose paediatric CTA and allows further dose reductions without compromising diagnostic IQ.

Key Points

? Iterative reconstruction techniques significantly improve non-invasive cardiovascular CT in children. ? Using half traditional radiation dose image quality is higher with iterative reconstruction. ? Iterative reconstruction techniques may allow further radiation reductions in paediatric cardiovascular CT.     

Application of a full model-based iterative reconstruction (MBIR) in 80 kVp ultra-low-dose paranasal sinus CT imaging of pediatric patients

Objective

To evaluate the clinical application of a full model-based iterative reconstruction (MBIR) algorithm in the ultra-low-dose paranasal sinus CT imaging of children.

Materials and methods

In the first phase, 16 low-dose CT dacryocystography (DCG) (80 kV/64 mAs) scans were reconstructed with MBIR and filtered back-projection (FBP) to demonstrate noise reduction capability of MBIR. MBIR images were also compared with the images of 21 standard-dose paranasal sinus patients reconstructed with adaptive statistical iterative reconstruction (ASIR) algorithm. In the second phase, 14 pediatric tumors patients (images with ASIR in the initial scan) who came for follow-up paranasal sinus CT scan were prospectively enrolled with reduced radiation and MBIR algorithm. In both study phases, image noise and the contrast noise ratio (CNR) of sphenoid was measured; and subjective image quality was evaluated. CTDIvol and DLP were recorded, and effective dose calculated.

Results

The CTDIvol value for the DCG group was 63.9% lower than the standard-dose sinus group (1.09 ± 0.01 mGy vs. 3.02 ± 0.35 mGy). Compared with the ASIR reconstruction in the standard-dose sinus patient group, images with MBIR in the ultra-low-dose DCG group had 39.9% lower noise (9.5 ± 0.8HU vs. 15.8 ± 3.3HU) and 63.6% higher CNR (14.4 ± 4.7 vs. 8.8 ± 2.2), with similar subjective image quality score. For the tumor patients, 65.5% dose reduction was achieved. Subjective quality scores were similar between the initial and follow-up scans. Objective noise was significantly lower for the follow-up group.

Conclusion

MBIR provided equal or better image quality with significantly reduced radiation dose in paranasal sinus CT imaging of pediatric patients compared with standard-dose CT with ASIR algorithm.

     

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.     

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.     

Quantitative analysis of emphysema and airway measurements according to iterative reconstruction algorithms: comparison of filtered back projection,adaptive statistical iterative reconstruction and model-based iterative reconstruction

Objectives

To evaluate filtered back projection (FBP) and two iterative reconstruction (IR) algorithms and their effects on the quantitative analysis of lung parenchyma and airway measurements on computed tomography (CT) images.

Methods

Low-dose chest CT obtained in 281 adult patients were reconstructed using three algorithms: FBP, adaptive statistical IR (ASIR) and model-based IR (MBIR). Measurements of each dataset were compared: total lung volume, emphysema index (EI), airway measurements of the lumen and wall area as well as average wall thickness. Accuracy of airway measurements of each algorithm was also evaluated using an airway phantom.

Results

EI using a threshold of ?950 HU was significantly different among the three algorithms in decreasing order of FBP (2.30 %), ASIR (1.49 %) and MBIR (1.20 %) (P?<?0.01). Wall thickness was also significantly different among the three algorithms with FBP (2.09 mm) demonstrating thicker walls than ASIR (2.00 mm) and MBIR (1.88 mm) (P?<?0.01). Airway phantom analysis revealed that MBIR showed the most accurate value for airway measurements.

Conclusion

The three algorithms presented different EIs and wall thicknesses, decreasing in the order of FBP, ASIR and MBIR. Thus, care should be taken in selecting the appropriate IR algorithm on quantitative analysis of the lung.

Key Points

? Computed tomography is increasingly used to provide objective measurements of intra-thoracic structures. ? Iterative reconstruction algorithms can affect quantitative measurements of lung and airways. ? Care should be taken in selecting reconstruction algorithms in longitudinal analysis. ? Model-based iterative reconstruction seems to provide the most accurate airway measurements.     

Whole-body ultra-low dose CT using spectral shaping for detection of osteolytic lesion in multiple myeloma

Objectives

The aim of this study was to investigate the radiation dose and image quality of a whole-body low-dose CT (WBLDCT) using spectral shaping at 100 kV (Sn 100 kV) for the assessment of osteolytic lesions in patients with multiple myeloma.

Methods

Thirty consecutive patients were retrospectively selected, who underwent a WBLDCT on a third-generation dual-source CT (DSCT) (Sn 100 kV, ref. mAs: 130). They were matched with patients, who were examined on a second-generation DSCT with a standard low-dose protocol (100 kV, ref. mAs: 111). Objective and subjective image quality, radiation exposure as well as the frequency of osteolytic lesions were evaluated.

Results

All scans were of diagnostic image quality. Subjective overall image quality was significantly higher in the study group (p = 0.0003). Objective image analysis revealed that signal intensities, signal-to-noise ratio and contrast-to-noise ratio of the bony structures were equal or significantly higher in the control group. There was no significant difference in the frequency of osteolytic lesions (p = 0.259). The median effective dose of the study protocol was significantly lower (1.45 mSv vs. 5.65 mSv; p < 0.0001).

Conclusion

WBLDCT with Sn 100 kV can obtain sufficient image quality for the depiction of osteolytic lesions while reducing the radiation dose by approximately 74%.

Key points

? Spectral shaping using tin filtration is beneficial for whole-body low-dose CT? Sn 100 kV yields sufficient image quality for depiction of osteolytic lesions? Whole-body low-dose CT can be performed with a median dose of 1.5 mSv

     

Comparison of the image qualities of filtered back-projection,adaptive statistical iterative reconstruction,and model-based iterative reconstruction for CT venography at 80 kVp

Purpose

To evaluate the subjective and objective qualities of computed tomography (CT) venography images at 80 kVp using model-based iterative reconstruction (MBIR) and to compare these with those of filtered back projection (FBP) and adaptive statistical iterative reconstruction (ASIR) using the same CT data sets.

Materials and methods

Forty-four patients (mean age: 56.1?±?18.1) who underwent 80 kVp CT venography (CTV) for the evaluation of deep vein thrombosis (DVT) during 4 months were enrolled in this retrospective study. The same raw data were reconstructed using FBP, ASIR, and MBIR. Objective and subjective image analysis were performed at the inferior vena cava (IVC), femoral vein, and popliteal vein.

Results

The mean CNR of MBIR was significantly greater than those of FBP and ASIR and images reconstructed using MBIR had significantly lower objective image noise (p?<?.001). Subjective image quality and confidence of detecting DVT by MBIR group were significantly greater than those of FBP and ASIR (p?<?.005), and MBIR had the lowest score for subjective image noise (p?<?.001).

Conclusion

CTV at 80 kVp with MBIR was superior to FBP and ASIR regarding subjective and objective image qualities.

Key Points

? MBIR provides superior image quality compared with FBP and ASIR ? CTV at 80kVp with MBIR improves diagnostic confidence in diagnosing DVT ? CTV at 80kVp with MBIR presents better image quality with low radiation

     

CT angiography after carotid artery stenting: assessment of the utility of adaptive statistical iterative reconstruction and model-based iterative reconstruction

Introduction

Follow-up CT angiography (CTA) is routinely performed for post-procedure management after carotid artery stenting (CAS). However, the stent lumen tends to be underestimated because of stent artifacts on CTA reconstructed with the filtered back projection (FBP) technique. We assessed the utility of new iterative reconstruction techniques, such as adaptive statistical iterative reconstruction (ASIR) and model-based iterative reconstruction (MBIR), for CTA after CAS in comparison with FBP.

Methods

In a phantom study, we evaluated the differences among the three reconstruction techniques with regard to the relationship between the stent luminal diameter and the degree of underestimation of stent luminal diameter. In a clinical study, 34 patients who underwent follow-up CTA after CAS were included. We compared the stent luminal diameters among FBP, ASIR, and MBIR, and performed visual assessment of low attenuation area (LAA) in the stent lumen using a three-point scale.

Results

In the phantom study, stent luminal diameter was increasingly underestimated as luminal diameter became smaller in all CTA images. Stent luminal diameter was larger with MBIR than with the other reconstruction techniques. Similarly, in the clinical study, stent luminal diameter was larger with MBIR than with the other reconstruction techniques. LAA detectability scores of MBIR were greater than or equal to those of FBP and ASIR in all cases.

Conclusion

MBIR improved the accuracy of assessment of stent luminal diameter and LAA detectability in the stent lumen when compared with FBP and ASIR. We conclude that MBIR is a useful reconstruction technique for CTA after CAS.     

Dose levels at coronary CT angiography��a comparison of Dual Energy-, Dual Source- and 16-slice CT

Purpose

To compare the dose estimates and image quality of Dual Energy CT (DECT), Dual Source CT (DSCT) and 16-slice CT for coronary CT angiography (cCTA).

Methods

Sixty-eight patients were examined with 16 - slice MDCT (group 1), 68 patients with DSCT (group 2) and 68 patients using DSCT in dual energy mode (DECT group 3). CT dose index volume, dose length product, effective dose, signal-to-noise, and contrast-to-noise ratio were compared. Subjective image quality was rated by two observers, blinded to technique.

Results

The mean estimated radiation dose of all patients investigated on a 16 - slice MDCT was 12?±?3.59?mSv, for DSCT in single energy 9.8?±?4.77?mSv and for DECT 4.54?±?1.87?mSv. Dose for CTA was significantly lower in group 3 compared to group 1 and 2. The image noise was significantly lower in Group 2 in comparison to group 1 and group 3. There was no significant difference in diagnostic image quality comparing DECT and DSCT.

Conclusion

cCTA shows better dose levels at both DECT and DSCT compared to 16-slice CT. Further, DECT delivers significantly less dose than regular DSCT or single source single energy cCTA while maintaining diagnostic image quality.     

CTA-enhanced perfusion CT: an original method to perform ultra-low-dose CTA-enhanced perfusion CT

Introduction

Utilizing CT angiography enhances image quality in PCT, thereby permitting acquisition at ultra-low dose.

Methods

Dynamic CT acquisitions were obtained at 80 kVp with decreasing tube current–time product [milliamperes × seconds (mAs)] in patients suspected of ischemic stroke, with concurrent CTA of the cervical and intracranial arteries. By utilizing fast Fourier transformation, high spatial frequencies of CTA were combined with low spatial frequencies of PCT to create a virtual PCT dataset. The real and virtual PCT datasets with decreasing mAs were compared by assessing contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR), and noise and PCT values and by visual inspection of PCT parametric maps.

Results

Virtual PCT attained CNR and SNR three- to sevenfold superior to real PCT and noise reduction by a factor of 4–6 (p?Conclusion Our new method of creating virtual PCT by combining ultra-low-dose PCT with CTA information yields diagnostic perfusion parametric maps from PCT acquired at 20 or 10 mAs with 80 % ASIR. Effective dose is approximately 0.20 mSv, equivalent to two chest radiographs.     

Effective dose to patient measurements in flat-detector and multislice computed tomography: a comparison of applications in neuroradiology

Purpose

Flat-detector CT (FD-CT) is used for a variety of applications. Additionally, 3D rotational angiography (3D DSA) is used to supplement digital subtraction angiography (DSA) studies. The aim was to measure and compare the dose of (1) standard DSA and 3D DSA and (2) analogous FD-CT and multislice CT (MSCT) protocols.

Methods

Using an anthropomorphic phantom, the effective dose to patients (according to ICRP 103) was measured on an MSCT and a flat-detector angiographic system using standard protocols as recommended by the manufacturer.

Results

(1) Evaluation of DSA and 3D DSA angiography protocols: ap.-lat. Standard/low-dose series 1/0.8 mSv, enlarged oblique projection 0.3 mSv, 3D DSA 0.9 mSv (limited coverage length 0.3 mSv). (2) Comparison of FD-CT and MSCT: brain parenchyma imaging 2.9 /1.4 mSv, perfusion imaging 2.3/4.2 mSv, temporal bone 0.2 /0.2 mSv, angiography 2.9/3.3 mSv, limited to the head using collimation 0.5/0.5 mSv.

Conclusion

The effective dose for an FD-CT application depends on the application used. Using collimation for FD-CT applications, the dose may be reduced considerably. Due to the low dose of 3D DSA, we recommend using this technique to reduce the number of DSA series needed to identify working projections.

Key Points

? Effective dose of FD-CT in comparison to MSCT is in comparable range. ? Collimation decreases the dose of FD-CT effectively. ? Effective dose of 3-D angiography is identical to 2-D DSA. ? Different FD-CT programs have different dose.