Sinogram-affirmed Iterative Reconstruction Research Articles

Low Tube Voltage Intermediate Tube Current Liver MDCT: Sinogram-Affirmed Iterative Reconstruction Algorithm for Detection of Hypervascular Hepatocellular Carcinoma

The purpose of this study was to compare image quality and lesion detectability in the evaluation of hypervascular hepatocellular carcinoma (HCC) on low-tube-voltage half-dose liver CT scans subjected to sinogram-affirmed iterative reconstruction (SAFIRE) with the quality and detectability on full-dose scans reconstructed with filtered back projection (FBP). A total of 126 patients with suspected HCC who underwent liver CT including arterial phase scanning at 80 kVp in the dual-source mode (300 mAs for each tube) were included in the study. The half-dose arterial scans were reconstructed with FBP, iterative reconstruction in image space (IRIS), and five SAFIRE strengths (S1-S5) and were compared with full-dose virtual scans (600 mA) reconstructed with FBP. We assessed image noise, contrast-to-noise ratio (CNR) of the liver and blood vessels, and lesionto-liver CNR. Two radiologists evaluated image quality and lesion detectability attained with the different imaging sets. Image noise on SAFIRE images was significantly lower than that on the other images, and the CNRs on SAFIRE images were higher than those on half-dose FBP images (p < 0.001). In addition, lesion-to-liver CNR on the half-dose S5 SAFIRE images was higher than on IRIS and full-dose FBP images (p < 0.05). Among the half-dose scans, SAFIRE images had significantly better image quality than FBP images (p < 0.05). Regarding lesion detection, half-dose SAFIRE images were better than half-dose FBP images and were comparable with full-dose FBP images (observer 1, 91.8% vs 96%; observer 2, 98% vs 98%; p > 0.05). Performing half-dose 80-kVp liver CT with SAFIRE technique may increase image quality and afford comparable lesion detectability of hypervascular HCC at a reduced radiation dose compared with full-dose CT with FBP.

Coronary artery stent imaging with CT using an integrated electronics detector and iterative reconstructions: First in vitro experience

BackgroundDespite continuous improvements in CT technology, accurate stent lumen delineation remains challenging. PurposeThe aim was to evaluate the quality of coronary stent lumen delineation with CT using a detector with integrated electronics. MethodsTwelve coronary stents placed in plastic tubes and filled with contrast agent (CT number 250 HU) were imaged with either a 128-section dual-source CT machine equipped with conventional detector or with integrated electronics. On both scanners, images were reconstructed with filtered back projection (slice thickness 0.6 mm; increment 0.4 mm) and sinogram-affirmed iterative reconstruction (slice thickness 0.6 mm; increment 0.4 mm), and with iterative reconstruction (slice thickness 0.5 mm; increment 0.3 mm) on the integrated scanner. Two blinded, independent readers assessed image quality, noise, in-stent diameter, in-stent attenuation, and image sharpness by using signal intensity profiles across stents. ResultsInterreader agreement for image quality assessment was substantial (κ = 0.798). Both readers rated best image quality in data sets from integrated detector at highest spatial resolution (86 or 72% of stents rated best quality). Image noise was significantly lower in data sets scanned with integrated detector, being lowest at 0.6 mm slice thickness (14.3 vs 21.0 HU; P < .001). Differences between measured and true in-stent diameters and differences in attenuation across stents were smallest, and average/maximum image sharpness was highest in data sets from the integrated detector using iterative reconstructions. ConclusionCT coronary stent imaging is significantly improved by using a detector with integrated electronics combined with iterative reconstructions.

Detection of coronary artery stenosis with sub-milliSievert radiation dose by prospectively ECG-triggered high-pitch spiral CT angiography and iterative reconstruction

To evaluate the diagnostic accuracy of sub-milliSievert (mSv) coronary CT angiography (cCTA) using prospectively ECG-triggered high-pitch spiral CT acquisition combined with iterative image reconstruction. Forty consecutive patients (52.9 ± 8.7 years; 30 men) underwent dual-source cCTA using prospectively ECG-triggered high-pitch spiral acquisition. The tube current-time product was set to 50 % of standard-of-care CT examinations. Images were reconstructed with sinogram-affirmed iterative reconstruction. Image quality was scored and diagnostic performance for detection of ≥50 % stenosis was determined with catheter coronary angiography (CCA) as the reference standard. CT was successfully performed in all 40 patients. Of the 601 assessable coronary segments, 543 (90.3 %) had diagnostic image quality. Per-patient sensitivity for detection of ≥50 % stenosis was 95.7 % [95 % confidence interval (CI), 76.0-99.8 %] and specificity was 94.1 % (95 % CI, 69.2-99.7 %). Per-vessel sensitivity was 89.5 % (95 % CI, 77.8-95.6 %) with 93.2 % specificity (95 % CI, 86.0-97.0 %). The area under the receiver-operating characteristic curve on per-patient and per-vessel levels was 0.949 and 0.913. Mean effective dose was 0.58 ± 0.17 mSv. Mean size-specific dose estimate was 3.14 ± 1.15 mGy. High-pitch prospectively ECG-triggered cCTA combined with iterative image reconstruction provides high diagnostic accuracy with a radiation dose below 1 mSv for detection of coronary artery stenosis. • Cardiac CT with sub-milliSievert radiation dose is feasible in many patients • High-pitch spiral CT acquisition with iterative reconstruction detects coronary stenosis accurately. • Iterative reconstruction increases who can benefit from low-radiation cardiac CT.

SU‐E‐I‐52: Improvement in CT Contrast‐To‐Noise Ratio in Low Contrast Spherical Simulated Liver Lesions Using Iterative Reconstruction

Purpose: Contrast‐to‐Noise ratio (CNR) is one measure to assess image quality and lesion detectability for CT exams. The purpose of this study is to calculate the change in CNR between standard filtered back‐projection (FBP) and sinogram‐affirmed iterative reconstruction (SAFIRE) by using an anthropomorphic phantom with spherical simulated liver lesions. Methods: An anthropomorphic phantom with embedded spherical liver lesions was custom‐designed to assess low contrast lesion detection at different CT doses and reconstruction techniques. This phantom consists of 36 spherical lesions with 3 different sizes (5mm, 10mm, and 15mm). Each size has three different contrast levels. All spherical lesions were embedded non‐uniformly to minimize the memory bias for a concurrent human observer study. Phantom was scanned with a MDCT (Siemens Definition Flash) at 4 dose levels and images were reconstructed with both FBP and SAFIRE using strength setting 3. CNR was computed as the ratio of the difference of the mean CT number at the center of the lesion and the liver background to the standard deviation of the CT numbers from the liver background. CNR was evaluated for the each lesion size at the center slice that intersected the middle of the lesion to minimize the error from the partial volume effect. Results: Averaged across all lesion sizes and the contrast levels (vs. the liver background), the CNR improvement from FBP to SAFIRE (strength 3) was 34% ±10% (mean ± standard deviation) at 50mAs,(p&lt;0.0001), 33%±11% at 100mAs (p&lt;0.0002), 36% ± 9% at 150mAs (p&lt;0.0001) and 36% ± 7% at 200mAs (p&lt;0.0003). Noise reduction from SAFIRE contributed almost entirely to the CNR improvement. Conclusion: Iterative reconstruction (SAFIRE) improved CNR of spherical low‐contrast liver lesions, but almost entirely due to noise reduction, with little improvement in lesion contrast. The overall CNR improvement was uniform for each dose level tested. Dr. Herts and Dr. Baker are funded by Siemens Healthcare for research in the field of abdominal CT imaging.

Sinogram affirmed iterative reconstruction in head CT: Improvement of objective and subjective image quality with concomitant radiation dose reduction

PurposeIterative reconstruction has recently been revisited as a promising concept for substantial CT dose reduction. The purpose of this study was to assess the potential benefit of sinogram affirmed iterative reconstruction (SAFIRE) in head CT by comparing objective and subjective image quality at reduced tube current with standard dose filtered back projection (FBP). Materials and methodsNon-contrast reduced dose head CT (255mAs, CTDIvol 47.8mGy) was performed in thirty consecutive patients and reconstructed with SAFIRE and FBP. Images were assessed in terms of quantitative and qualitative image quality and compared with FBP of standard dose acquisitions (320mAs, CTDIvol 59.7mGy). ResultsIn reduced dose CT examinations, use of SAFIRE versus FBP resulted in 47% increase in contrast-to-noise ratio (CNR) (2.49 vs. 1.69; p<0.0001). While reduction of tube current was associated with 13% decrease in CNR, quantitative degradation of image quality at lower dose was more than compensated through SAFIRE (2.49 vs. 1.96; p=0.0004). Objective measurements of image sharpness were comparable between FBP and SAFIRE reconstructions (575.9±74.1 vs. 583.4±74.7 change in HU/Pixel; p=0.28). Compared to standard dose FBP, subjective grading of noise as well as overall image quality scores were significantly improved when SAFIRE was used in reduced dose exams (1.3 vs. 1.6, p=0.006; 1.3 vs. 1.7, p=0.026). ConclusionAt 20% dose reduction, reconstruction of head CT by SAFIRE provides above standard objective and subjective image quality, suggesting potential for more vigorous dose savings in neuroradiology CT applications.

Influence of Sinogram Affirmed Iterative Reconstruction of CT Data on Image Noise Characteristics and Low-Contrast Detectability: An Objective Approach

ObjectivesTo utilize a novel objective approach combining a software phantom and an image quality metric to systematically evaluate the influence of sinogram affirmed iterative reconstruction (SAFIRE) of multidetector computed tomography (MDCT) data on image noise characteristics and low-contrast detectability (LCD).Materials and MethodsA low-contrast and a high-contrast phantom were examined on a 128-slice scanner at different dose levels. The datasets were reconstructed using filtered back projection (FBP) and SAFIRE and virtual low-contrast lesions (-20HU) were inserted. LCD was evaluated using the multiscale structural similarity index (MS-SIM*). Image noise texture and spatial resolution were objectively evaluated.ResultsThe use of SAFIRE led to an improvement of LCD for all dose levels and lesions sizes. The relative improvement of LCD was inversely related to the dose level, declining from 208%(±37%), 259%(±30%) and 309%(±35%) at 25mAs to 106%(±6%), 119%(±9%) and 123%(±8%) at 200mAs for SAFIRE filter strengths of 1, 3 and 5 (p<0.05). SAFIRE reached at least the LCD of FBP at a relative dose of 50%. There was no statistically significant difference in spatial resolution. The use of SAFIRE led to coarser image noise granularity.ConclusionA novel objective approach combining a software phantom and the MS-SSIM* image quality metric was used to analyze the detectability of virtual low-contrast lesions against the background of image noise as created using SAFIRE in comparison to filtered back-projection. We found, that image noise characteristics using SAFIRE at 50% dose were comparable to the use of FBP at 100% dose with respect to lesion detectability. The unfamiliar imaging appearance of iteratively reconstructed datasets may in part be explained by a different, coarser noise characteristic as demonstrated by a granulometric analysis.

Computed tomography of the cervical spine: comparison of image quality between a standard-dose and a low-dose protocol using filtered back-projection and iterative reconstruction

To compare image quality of a standard-dose (SD) and a low-dose (LD) cervical spine CT protocol using filtered back-projection (FBP) and iterative reconstruction (IR). Forty patients investigated by cervical spine CT were prospectively randomised into two groups: SD (120 kVp, 275 mAs) and LD (120 kVp, 150 mAs), both applying automatic tube current modulation. Data were reconstructed using both FBP and sinogram-affirmed IR. Image noise, signal-to-noise (SNR) and contrast-to-noise (CNR) ratios were measured. Two radiologists independently and blindly assessed the following anatomical structures at C3-C4 and C6-C7 levels, using a four-point scale: intervertebral disc, content of neural foramina and dural sac, ligaments, soft tissues and vertebrae. They subsequently rated overall image quality using a ten-point scale. For both protocols and at each disc level, IR significantly decreased image noise and increased SNR and CNR, compared with FBP. SNR and CNR were statistically equivalent in LD-IR and SD-FBP protocols. Regardless of the dose and disc level, the qualitative scores with IR compared with FBP, and with LD-IR compared with SD-FBP, were significantly higher or not statistically different for intervertebral discs, neural foramina and ligaments, while significantly lower or not statistically different for soft tissues and vertebrae. The overall image quality scores were significantly higher with IR compared with FBP, and with LD-IR compared with SD-FBP. LD-IR cervical spine CT provides better image quality for intervertebral discs, neural foramina and ligaments, and worse image quality for soft tissues and vertebrae, compared with SD-FBP, while reducing radiation dose by approximately 40 %.

Reduced-Dose Low-Voltage Chest CT Angiography with Sinogram-affirmed Iterative Reconstruction versus Standard-Dose Filtered Back Projection

To evaluate image quality of low-voltage chest computed tomographic (CT) angiography with raw data-based iterative reconstruction (sonogram-affirmed iterative reconstruction) in comparison with image quality of standard-dose standard-voltage filtered back projection (FBP) CT. This prospective study was approved by the institutional review board, and the informed consent requirement was waived. Eighty consecutive patients who were referred for follow-up chest CT angiography underwent reduced-dose CT (hereafter, T2 examination) under technical conditions similar to those of the initial examination (hereafter, T1 examination), except the voltage selection was reduced by 20 kV with adaptation of the tube current to ensure a 50% reduction in CT dose index, and regular FBP was replaced by iterative reconstruction with sonogram-affirmed iterative reconstruction. The two techniques were compared by using paired tests (Student t test, Wilcoxon test, or McNemar test, according to the nature of variables). When compared with standard-dose T1 studies, reduced-dose T2 images showed: (a) significantly less objective noise at the level of the trachea on mediastinal and lung parenchymal images (P < .001) and no significant difference in objective noise at the level of the aorta on mediastinal images (P = .507); (b) significantly higher signal-to-noise and contrast-to-noise (P < .001) ratios; (c) similar visual perception of noise on mediastinal (P = .132) and lung (P = .366) images, mainly rated as moderate; and (d) similar overall subjective image quality (P = .405). Raw data-based iterative reconstruction yielded equivalent subjective and improved objective image quality of low-voltage half-dose CT angiograms compared with standard-dose FBP CT images for an average dose-length product of less than 80 mGy · cm in this population. http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12120414/-/DC1.

Sinogram-Affirmed Iterative Reconstruction of Low-Dose Chest CT: Effect on Image Quality and Radiation Dose

OBJECTIVE. The purpose of this study is to compare sinogram-affirmed iterative reconstruction (SAFIRE) and filtered back projection (FBP) reconstruction of chest CT acquired with 65% radiation dose reduction. MATERIALS AND METHODS. In this prospective study involving 24 patients (11 women and 13 men; mean [± SD] age, 66 ± 10 years), two scan series were acquired using 100 and 40 Quality Reference mAs over a 10-cm scan length in the chest with a 128-MDCT scanner. The 40 Quality Reference mAs CT projection data were reconstructed with FBP and four settings of SAFIRE (S1, S2, S3, and S4). Six image datasets (FBP with 100 and 40 Quality Reference mAs, and S1, S2, S3, S4 with 40 Quality Reference mAs) were displayed on a DICOM-compliant 55-inch 2-megapixel monitor for blinded evaluation by two thoracic radiologists for number and location of lesions, lesion size, lesion margins, visibility of small structures and fissures, and diagnostic confidence. Objective noise and CT values were measured in thoracic aorta for each image series, and the noise power spectrum was assessed. Data were analyzed with analysis of variance and Wilcoxon signed rank tests. RESULTS. All 186 lesions were seen on 40 Quality Reference mAs SAFIRE images. Diagnostic confidence on SAFIRE images was higher than that for FBP images. Except for the minor blotchy appearance on SAFIRE settings S3 and S4, no significant artifacts were noted. Objective noise with 40 Quality Reference mAs S1 images (21.1 ± 6.1 SD of HU) was significantly lower than that for 40 Quality Reference mAs FBP images (28.5 ± 8.1 SD of HU) (p < 0.001). Noise power spectra were identical for SAFIRE and FBP with progressive noise reduction with higher iteration SAFIRE settings. CONCLUSION. Iterative reconstruction (SAFIRE) allows reducing the radiation exposure by approximately 65% without losing diagnostic information in chest CT.

Pilot Study of Detection, Radiologist Confidence and Image Quality With Sinogram-Affirmed Iterative Reconstruction at Half–Routine Dose Level

The objective of this study was to determine the effect of Sinogram-Affirmed Iterative Reconstruction (SAFIRE) on radiological detection, diagnostic confidence, and image quality at half-dose, contrast-enhanced abdominopelvic computed tomography. Forty dual-source examinations were reconstructed using routine-dose with filtered back projection, half-dose filtered back projection, and half-dose SAFIRE. Three radiologists detected lesions in abdominopelvic organs, reporting findings of potential medical significance, diagnostic confidence, and image quality. There was greater than 78% concordance between full- and half-dose images ± SAFIRE, and no difference in the detection of lesions within organs between half-dose images ± SAFIRE (P = 0.22 - 1.0). Detection of potentially important findings varied by reader, but not between dose/reconstruction methods. Diagnostic confidence varied widely (P < 0.001 to P > 0.91). Sinogram-Affirmed Iterative Reconstruction significantly improved image quality in the pelvis (P ≤ 0.04). Half-dose images ± SAFIRE had organ-specific detections similar to routine-dose images. Sinogram-Affirmed Iterative Reconstruction improved image quality in the pelvis, but diagnostic confidence and image quality scores in the abdomen depended on the reader.

Radiation Dose Reduction via Sinogram Affirmed Iterative Reconstruction and Automatic Tube Voltage Modulation (CARE kV) in Abdominal CT

ObjectiveTo evaluate the feasibility of sinogram-affirmed iterative reconstruction (SAFIRE) and automated kV modulation (CARE kV) in reducing radiation dose without increasing image noise for abdominal CT examination.Materials and MethodsThis retrospective study included 77 patients who received CT imaging with an application of CARE kV with or without SAFIRE and who had comparable previous CT images obtained without CARE kV or SAFIRE, using the standard dose (i.e., reference mAs of 240) on an identical CT scanner and reconstructed with filtered back projection (FBP) within 1 year. Patients were divided into two groups: group A (33 patients, CT scanned with CARE kV); and group B (44 patients, scanned after reducing the reference mAs from 240 to 170 and applying both CARE kV and SAFIRE). CT number, image noise for four organs and radiation dose were compared among the two groups.ResultsImage noise increased after CARE kV application (p < 0.001) and significantly decreased as SAFIRE strength increased (p < 0.001). Image noise with reduced-mAs scan (170 mAs) in group B became similar to that of standard-dose FBP images after applying CARE kV and SAFIRE strengths of 3 or 4 when measured in the aorta, liver or muscle (p ≥ 0.108). Effective doses decreased by 19.4% and 41.3% for groups A and B, respectively (all, p < 0.001) after application of CARE kV with or without SAFIRE.ConclusionCombining CARE kV, reduction of mAs from 240 to 170 mAs and noise reduction by applying SAFIRE strength 3 or 4 reduced the radiation dose by 41.3% without increasing image noise compared with the standard-dose FBP images.

Physician Preference Between Low-Dose Computed Tomography With a Sinogram-Affirmed Iterative Reconstruction Algorithm and Routine-Dose Computed Tomography With Filtered Back Projection in Abdominopelvic Imaging

The aim of this study was to directly compare the preference between low-dose sinogram-affirmed iterative reconstruction (SAFIRE) and routine filtered back projection (FBP) abdominopelvic computed tomography (CT). A retrospective review identified 41 subjects who had undergone 2 different CT examinations at different times (a CT with reduced radiation dose SAFIRE and also a CT with routine-dose FBP). Radiation dose, patient size, and image noise were recorded. Two independent readers assessed the paired CT studies for preference in image quality in regard to 3 clinically relevant diagnostic endpoints (bowel pathology, biliary pathology, and general purpose). Radiation dose was significantly lower for SAFIRE (mean, 7.6 mGy; range, 4.1-15.4 mGy) than FBP (12.9 mGy; 6.7-31.6 mGy) (P < 0.001). Sinogram-affirmed iterative reconstruction was preferred for the general purpose and bowel evaluations, particularly when the level of radiation dose reduction was less than 33%. The preference for interpretation of the biliary system was equivocal, especially when the level of radiation reduction was increased greater than 33%. Filtered back projection was preferred when SAFIRE had a radiation reduction from FBP of greater than 50%. For abdominopelvic CT, low-dose CT with SAFIRE may produce preferred image quality over FBP up to levels of 50% dose reduction.

Low-Dose Chest Computed Tomography With Sinogram-Affirmed Iterative Reconstruction, Iterative Reconstruction in Image Space, and Filtered Back Projection

This study aimed to determine optimal strength of sinogram-affirmed iterative reconstruction (SAFIRE) and to evaluate image quality (IQ) of low-dose chest computed tomography (LDCT) using SAFIRE compared with iterative reconstruction in image space (IRIS) and filtered back projection (FBP). Thirty patients underwent LDCT. Computed tomography (CT) was reconstructed using 5 strengths of SAFIRE (S1-S5), IRIS, and FBP. Objective noise of CT was measured. Two radiologists evaluated CT for subjective IQ, beam-hardening artifacts, and overall IQ. Measured noise was highest in FBP, followed by S1, S2, S3, IRIS, S4, and S5. S2 and S3 demonstrated significantly higher overall IQ scores than the other strengths (P < 0.05). Overall IQ and beam-hardening artifacts of S2 and S3 were significantly better than those in FBP and IRIS (P < 0.001). S2 or S3 strengths of SAFIRE can be used practically in clinical routines and may have more potential than IRIS and FBP for LDCT with improved IQ.

Performance of Iterative Reconstruction and Automated Tube Voltage Selection on the Image Quality and Radiation Dose in Abdominal CT Scans

To study the impact of sinogram-affirmed iterative reconstruction (SAFIRE) and concurrent application of automated tube voltage selection (ATVS) on image quality (IQ) and radiation dose. A phantom was scanned using various computed tomography (CT) parameters (kV, 80-120; mAs, 50-200). Abdomen contrast-enhanced CT (CECTs) in 170 adults were performed using dose-modified protocols: in 145 patients (group I), ATVS was applied (mAs, 111-649); in 25 (group II), the kV was fixed at 120 (reference mAs, 150). In 95 patients, standard-dose (SD) scan was available. Two readers evaluated the IQ of filtered back projection (FBP) and SAFIRE (levels 1, 3, and 5) images. In phantom, nonlinear drop in noise with increasing strengths of IR (levels S1-S5) was noted. The dose-modified IR scan was rated diagnostic in all 170 patients, with IQ score comparable to that of SD-FBP (P = 0.3). Lower kV (100/80) was prescribed by ATVS in 70% examinations in group I. In comparison with SD-FBP, the mean dose in CT dose index in group I (IR, 3.2 mGy; SD-FBP, 13.02 mGy; P < 0.0001) and in group II (IR, 4.8 mGy; SD-FBP, 11.8 mGy; P < 0.001) was 75.4% and 59.3% lower. Use of SAFIRE and ATVS provides diagnostic quality images at 59.3% to 75.4% reduced dose compared with SD-FBP scan.

Can Sinogram-Affirmed Iterative (SAFIRE) Reconstruction Improve Imaging Quality on Low-Dose Lung CT Screening Compared With Traditional Filtered Back Projection (FBP) Reconstruction?

To evaluate the performance of sinogram-affirmed iterative (SAFIRE) reconstruction on image quality of low-dose lung computed tomographic (CT) screening compared with filtered back projection (FBP). Three hundred four patients for annual low-dose lung CT screening were examined by a dual-source CT system at 120 kilovolt (peak) with reference tube current of 40 mA·s. Six image serials were reconstructed, including one data set of FBP and 5 data sets of SAFIRE with different reconstruction strengths from 1 to 5. Image noise was recorded; and subjective scores of image noise, images artifacts, and the overall image quality were also assessed by 2 radiologists. The mean ± SD weight for all patients was 66.3 ± 12.8 kg, and the body mass index was 23.4 ± 3.2. The mean ± SD dose-length product was 95.2 ± 30.6 mGy cm, and the mean ± SD effective dose was 1.6 ± 0.5 mSv. The observation agreements for image noise grade, artifact grade, and the overall image quality were 0.785, 0.595 and 0.512, respectively. Among the overall 6 data sets, both the measured mean objective image noise and the subjective image noise of FBP was the highest, and the image noise decreased with the increasing of SAFIRE reconstruction strength. The data sets of S3 obtained the best image quality scores. Sinogram-affirmed iterative reconstruction can significantly improve image quality of low-dose lung CT screening compared with FBP, and SAFIRE with reconstruction strength 3 was a pertinent choice for low-dose lung CT.

Stenosis Quantification in Coronary CT Angiography

The objective of this study was to assess the value of an integrated circuit (IC) detector, potentially improving spatial resolution by means of reduced cross talk between detector channels, in coronary computed tomographic (CT) angiography regarding image quality and stenosis quantification compared with conventional detector technology. In the ex vivo part of the study, a coronary phantom including 63 defined stenoses and 7 plaque densities (degree of stenosis, 10%-90%; plaque densities, -100 to 1000 Hounsfield unit [HU]) was loaded with contrast agent diluted to 300 HU and placed in an anthropomorphic chest phantom. The phantom was scanned in 0-, 45-, and 90-degree orientations to the z-axis of the CT scanner table. Images were acquired using 128-section dual-source CT equipped with IC and with conventional detector technology. Data were reconstructed with filtered back projection (FBP) and with sinogram-affirmed iterative reconstruction (IR) at a slice thickness of 0.6 mm (increment, 0.4 mm). Data acquired with the IC detector were additionally reconstructed with a slice thickness of 0.5 mm (increment, 0.3 mm) combined with IR. Two readers rated image quality; image noise and degree of stenosis were assessed. In the in vivo part of the study, phantom observations were validated in 30 consecutive patients (11 women; mean [SD] age, 62 [13] years; mean [SD] heart rate, 81 [17] beats per minute) undergoing coronary CT angiography with IC for clinical indications. Images of the patients were reconstructed with FBP (slice thickness, 0.6 mm) and with IR (slice thickness, 0.5 mm) and were assessed for image quality and degree of stenosis. Interreader agreement for image quality was evaluated using intraclass correlation coefficients. The image quality was compared with the Wilcoxon signed rank test. The image noise and the degree of stenosis were compared with the Student t test for paired samples. The interreader agreement for the assessment of image quality was substantial (intraclass correlation coefficients, 0.79). The image quality was significantly (P < 0.001) higher for the images acquired with the IC detector as compared with the conventional detector. The image noise with IR was significantly (P = 0.020) reduced for the IC detector as compared with the conventional detector. The IC detector yielded significantly more accurate results regarding stenosis grading when compared with the images acquired with the conventional detector regarding both FBP (mean [SD] error FBP, 12.1% [7.6%] vs 13.7% [7.6%]; P = 0.043) and IR (mean [SD] error IR, 10.5% [6.6%] vs 13.0% [6.9%]; P < 0.001). The images with a slice thickness of 0.5 mm reconstructed with IR (mean [SD] error, 8.8% [5.9%]) obtained by the IC detector significantly (P < 0.001) improved measurement accuracy in the phantom as compared with FBP with a slice thickness of 0.6 mm (mean [SD] error, 12.1% [7.6%]). In the patients, we found a significantly (P < 0.001) higher image quality, and stenoses were quantified significantly (P = 0.009) smaller with FBP as compared with IR (mean stenosis, 47.6% vs 42.1%; mean difference, 5.5%). Our ex vivo and patient study indicates significantly reduced image noise and more accurate stenosis quantification in coronary CT angiography when acquiring data using an IC detector and combining IR with high-resolution images as compared with conventional detector technology and FBP reconstructions.

Performance of Iterative Image Reconstruction in CT of the Paranasal Sinuses: A Phantom Study

CT in low dose technique is the criterion standard imaging modality for evaluation of the paranasal sinus. Our aim was to evaluate the dose-reduction potential of a recently available sinogram-affirmed iterative reconstruction technique, regarding noise, image quality, and time duration when evaluating this region. CT was performed on a phantom head at different tube voltages (120 kV, 100 kV) and currents (100 mAs, 50 mAs, 25 mAs). Each protocol was reconstructed (in soft tissue and bony kernel) by using standard filtered back-projection and 5 different SAFIRE strengths, and image noise was evaluated. Subjective image quality was evaluated on noise-aligned image triplets acquired at tube currents of 100% (FBP), 50% (SAFIRE), and 25% (SAFIRE) by using a 5-point scale (1 = worst, 5 = best). The time duration for image reconstruction was noted for calculations with FBP and SAFIRE. SAFIRE reduced image noise by 15%-85%, depending on the iterative strength, rendering kernel, and dose parameters. Noise reduction was stronger at a bone kernel algorithm both in 1- and 3-mm images (P < .05). Subjective quality evaluation of the noise-adapted images showed preference for those acquired at 100% tube current with FBP (4.7-5.0) versus 50% dose with SAFIRE (3.4-4.4) versus 25% dose with SAFIRE (2.0-3.1). The time duration for FBP image sets was 2.9-6.6 images per second versus SAFIRE with 0.9-1.6 images per second. For CT of the paranasal sinus, SAFIRE algorithms are suitable for image-noise reduction. Because image quality decreases with dosage, careful choice of the appropriate iterative method is necessary to achieve an optimal balance between image noise and quality.

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

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. 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. 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. 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. • 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.

Clinical Evaluation and Potential Radiation Dose Reduction of the Novel Sinogram-affirmed Iterative Reconstruction Technique (SAFIRE) in Abdominal Computed Tomography Angiography

Computed tomographic angiography is the standard in routine follow-up after endovascular aneurysm repair, causing radiation exposure; thus, dose-saving strategies should be applied. The aim of this study was to evaluate the novel sinogram-affirmed iterative reconstruction (SAFIRE) algorithm in terms of clinical usability and potential reduction of radiation exposure. Forty-six patients underwent computed tomographic angiographic follow-up after endovascular aneurysm repair. Data were acquired using a dual-source computed tomographic scanner running both x-ray tubes at the same voltage (120 kV). Raw data were reconstructed using projections of both tubes with filtered back projection (FBP) and of only one tube with FBP and SAFIRE, corresponding to synthetic acquisition with half the radiation dose of the clinical routine radiation dose. Image sets were objectively compared regarding signal-to-noise ratio and edge sharpness. Two radiologists independently assessed a set of subjective criteria, including diagnostic usability, depiction of contrasted vessels, and image noise. Half-dose (HD) SAFIRE images showed significantly higher signal-to-noise ratios compared to full-dose FBP images (P < .001), while having equal edge sharpness (P = .56). Most of the subjectively assessed parameters, such as diagnostic usability and depiction of contrasted vessels, were rated similar for HD SAFIRE and full-dose FBP images. Full-dose FBP images depicted fine anatomic structures more clearly (P < .05), while HD SAFIRE data sets showed less noise (P < .01). HD FBP images performed worse on all criteria (P < .001). Interrater agreement was good (κ = 0.74-0.80). Using the SAFIRE algorithm, the radiation dose of high-contrast abdominal computed tomographic angiography is reducible from routine clinical levels by up to 50% while maintaining good image quality and diagnostic accuracy.

CT coronary angiography: Image quality with sinogram-affirmed iterative reconstruction compared with filtered back-projection

To investigate image quality and potential for radiation dose reduction using sinogram-affirmed iterative reconstruction (SAFIRE) at computed tomography (CT) coronary angiography (CTCA) compared with filtered back-projection (FBP) reconstruction. A water phantom and 49 consecutive patients were scanned using a retrospectively electrocardiography (ECG)-gated CTCA protocol on a dual-source CT system. Image reconstructions were performed with both conventional FBP and SAFIRE. The SAFIRE series were reconstructed image data from only one tube, simulating a 50% radiation dose reduction. Two blinded observers independently assessed the image quality of each coronary segment using a four-point scale and measured image noise (the standard deviation of Hounsfield values, SD), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Radiation dose estimates were calculated. In the water phantom, image noise decreased at the same ratio as the tube current increased for both reconstruction algorithms. Despite an estimated radiation dose reduction from 7.9 ± 2.8 to 4 ± 1.4 mSv, there was no significant difference in the SD and SNR within the aortic root and left ventricular chamber between the two reconstruction methods. There was also no significant difference in the image quality between the FBP and SAFIRE series. Compared with traditional FBP, there is potential for substantial radiation dose reduction at CTCA with use of SAFIRE, while maintaining similar diagnostic image quality.