Knowledge-based Iterative Model Reconstruction Research Articles

Dose Optimization Using a Deep Learning Tool in Various CT Protocols for Urolithiasis: A Physical Human Phantom Study.

Background and Objectives: We attempted to determine the optimal radiation dose to maintain image quality using a deep learning application in a physical human phantom. Materials and Methods: Three 5 × 5 × 5 mm3 uric acid stones were placed in a physical human phantom in various locations. Three tube voltages (120, 100, and 80 kV) and four current-time products (100, 70, 30, and 15 mAs) were implemented in 12 scans. Each scan was reconstructed with filtered back projection (FBP), statistical iterative reconstruction (IR, iDose), and knowledge-based iterative model reconstruction (IMR). By applying deep learning to each image, we took 12 more scans. Objective image assessments were calculated using the standard deviation of the Hounsfield unit (HU). Subjective image assessments were performed by one radiologist and one urologist. Two radiologists assessed the subjective assessment and found the stone under the absence of information. We used this data to calculate the diagnostic accuracy. Results: Objective image noise was decreased after applying a deep learning tool in all images of FBP, iDose, and IMR. There was no statistical difference between iDose and deep learning-applied FBP images (10.1 ± 11.9, 9.5 ± 18.5 HU, p = 0.583, respectively). At a 100 kV-30 mAs setting, deep learning-applied FBP obtained a similar objective noise in approximately one third of the radiation doses compared to FBP. In radiation doses with settings lower than 100 kV-30 mAs, the subject image assessment (image quality, confidence level, and noise) showed deteriorated scores. Diagnostic accuracy was increased when the deep learning setting was lower than 100 kV-30 mAs, except for at 80 kV-15 mAs. Conclusions: At the setting of 100 kV-30 mAs or higher, deep learning-applied FBP did not differ in image quality compared to IR. At the setting of 100 kV-30 mAs, the radiation dose can decrease by about one third while maintaining objective noise.

Letter to the Editor Regarding “Ossification of the Ligamentum Flavum at the Thoracic and Lumbar Region in an Achondroplastic Patient”

To evaluate the image quality and diagnostic confidence of reduced-dose computed tomography (CT) of the lumbar spine (L-spine) reconstructed with knowledge-based iterative model reconstruction (IMR).Prospectively, group A consisted of 55 patients imaged with standard acquisition reconstructed with filtered back-projection. Group B consisted of 58 patients imaged with half tube current, reconstructed with hybrid iterative reconstruction (iDose4) in Group B1 and knowledge-based IMR in Group B2. Signal-to-noise ratio (SNR) of different regions, the contrast-to-noise ratio between the intervetebral disc (IVD) and dural sac (D-D CNR), and subjective image quality of different regions were compared. Higher strength IMR was also compared in spinal stenosis cases.The SNR of the psoas muscle and D-D CNR were significantly higher in the IMR group. Except for the facet joint, subjective image quality of other regions including IVD, intervertebral foramen (IVF), dural sac, peridural fat, ligmentum flavum, and overall diagnostic acceptability were best for the IMR group. Diagnostic confidence of narrowing IVF and IVD was good (kappa = 0.58–0.85). Higher strength IMR delineated IVD better in spinal stenosis cases.Lower dose CT of L-spine reconstructed with IMR demonstrates better tissue differentiation than iDose4 and standard dose CT with FBP.

Comparison of Knowledge-based Iterative Model Reconstruction (IMR) with Hybrid Iterative Reconstruction (iDose4) Techniques for Evaluation of Hepatocellular Carcinomas Using Computed Tomography

To compare tumor conspicuity of small hepatocellular carcinomas (HCCs) and image quality on knowledge-based iterative model reconstruction low-dose computed tomography (IMR-LDCT) with hybrid iterative reconstruction standard-dose CT (iDose4-SDCT). Thirty-two patients (mean age 61.9 ± 9.7 years; male:female 27:5; mean body mass index 25.6 ± 3.8 kg/m2) with cirrhosis and 40 HCCs in IMR-LDCT group and 33 patients (mean age 60.1 ± 7.4 years; male:female 28:5; body mass index 26.7 ± 3.2 kg/m2) with cirrhosis and 40 HCCs in iDose4-SDCT group were included in this retrospective study. Objective analysis of reconstructed iDose4 and IMR images was done for contrast-to-noise ratio of HCCs (CNRHCC), image noise, signal-to-noise ratio of portal vein (SNRPV), and inferior vena cava (SNRIVC). Subjective analysis of tumor conspicuity and image quality was done by two independent reviewers in a blinded manner. Mean volume CT dose index, dose length product, and effective dose for both groups were compared. The CNRHCC was significantly higher in IMR-LDCT compared to iDose4-SDCT in both arterial phase (AP), p < 0.0001, and delayed phase (DP), p < 0.0001. Image noise was significantly lower in IMR-LDCT compared to iDose4-SDCT in AP, portal venous phase, and DP with p < 0.0001. IMR-LDCT showed significantly higher SNRPV (p < 0.0001) and SNRIVC (p < 0.0001) compared to iDose4-SDCT. On subjective analysis, IMR-LDCT images showed better image quality in AP, portal venous phase, and DP and better tumor conspicuity in AP and DP. IMR-LDCT (21.4 ± 4.6 mSv) achieved 36.9% reduction in the effective dose compared to iDose4-SDCT (33.9 ± 6.2 mSv). IMR algorithm provides better image quality and tumor conspicuity with considerable decrease in image noise compared to iDose4 reconstruction technique even on LDCT.

Improved visualization of a fine intrahepatic biliary duct on drip infusion cholangiography-computed tomography: Impact of knowledge-based iterative model reconstruction.

The purpose of this study was to investigate the visualization of fine biliary ducts with knowledge-based iterative model reconstruction (IMR) in low-dose drip infusion computed tomography (CT) cholangiography (DIC-CT) as compared with filtered back projection (FBP) and hybrid iterative reconstruction (iDose4 ). A total of 38 patients underwent DIC-CT for living donor liver transplantation. CT was performed approximately 20min after the end of the infusion of meglumine iotroxate (100mL). Images were reconstructed using FBP, iDose4 , and IMR, and 1-mm slice images at fixed window level and width were prepared for assessment. Two reviewers independently evaluated the quality of visualization of the fine biliary ducts of the caudate lobe (B1) using a 5-point scale. The visualization scores of three reconstructed images were compared using the Kruskal-Wallis test and Mann-Whitney U-test. For reviewer1, the visualization score of IMR was significantly higher than that of FBP (P = 0.012), and tended to be higher than that of iDose4 (P = 0.078). For reviewer2, the visualization score of IMR was significantly higher than those of both FBP and iDose4 (P < 0.01). IMR showed better visualization of B1 on DIC-CT than FBP or iDose4 . DIC-CT reconstructed with IMR may be useful to the anatomical grasp of biliary tracts in cases of hepatectomy.

Impact of Knowledge-Based Iterative Model Reconstruction on Image Quality and Hemodynamic Parameters in Dynamic Myocardial Computed Tomography Perfusion Using Low-Tube-Voltage Scan: A Feasibility Study.

Knowledge-based iterative model reconstruction (IMR) yields diagnostically acceptable image quality in low-dose static computed tomography (CT). We aimed to evaluate the feasibility of IMR in dynamic myocardial computed tomography perfusion (CTP). We enrolled 24 patients who underwent stress dynamic CTP using a 256-slice CT. Images were reconstructed using filtered back projection (FBP), hybrid IR, and IMR. Image quality and hemodynamic parameters were compared among three algorithms. Qualitative image quality and contrast-to-noise ratio were significantly higher by IMR than by FBP or hybrid IR (visual score: 4.1 vs. 3.0 and 3.5; contrast-to-noise ratio: 12.4 vs. 6.6 and 8.4; P < 0.05). No significant difference was observed among algorithms in CTP-derived myocardial blood flow (1.68 vs. 1.73 and 1.70 mL/g/min). The use of knowledge-based iterative model reconstruction improves image quality without altering hemodynamic parameters in low-dose dynamic CTP, compared with FBP or hybrid IR.

Coronary CT Angiography with Knowledge-Based Iterative Model Reconstruction for Assessing Coronary Arteries and Non-Calcified Predominant Plaques.

ObjectiveTo assess the effects of iterative model reconstruction (IMR) on image quality for demonstrating non-calcific high-risk plaque characteristics of coronary arteries.Materials and MethodsThis study included 66 patients (53 men and 13 women; aged 39–76 years; mean age, 55 ± 13 years) having single-vessel disease with predominantly non-calcified plaques evaluated using prospective electrocardiogram-gated 256-slice CT angiography. Paired image sets were created using two types of reconstruction: hybrid iterative reconstruction (HIR) and IMR. Plaque characteristics were compared using the two algorithms. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the images and the CNR between the plaque and adjacent adipose tissue were also compared between the two reformatted methods.ResultsSeventy-seven predominantly non-calcified plaques were detected. Forty plaques showed napkin-ring sign with the IMR reformatted method, while nineteen plaques demonstrated napkin-ring sign with HIR. There was no statistically significant difference in the presentation of positive remodeling, low attenuation plaque, and spotty calcification between the HIR and IMR reconstructed methods (all p > 0.5); however, there was a statistically significant difference in the ability to discern the napkin-ring sign between the two algorithms (χ2 = 12.12, p < 0.001). The image noise of IMR was lower than that of HIR (10 ± 2 HU versus 12 ± 2 HU; p < 0.01), and the SNR and CNR of the images and the CNR between plaques and surrounding adipose tissues on IMR were better than those on HIR (p < 0.01).ConclusionIMR can significantly improve image quality compared with HIR for the demonstration of coronary artery and atherosclerotic plaques using a 256-slice CT.

Non-inferior low-dose coronary computed tomography angiography image quality with knowledge-based iterative model reconstruction for overweight patients.

We investigated the feasibility of low-dose coronary computed tomography angiography (CCTA), using a prospective electrocardiogram (ECG)-triggered axial scan protocol, knowledge-based iterative model reconstruction (IMR), and fixed tube current, in overweight subjects. Forty non-overweight (group A; body-mass index [BMI] < 25 kg/m2) and 40 overweight individuals (group B; BMI = 25–30 kg/m2), who underwent CCTA for coronary artery disease screening, were retrospectively and consecutively enrolled. A 64-slice CT scanner was used at 100-kVp tube voltage and 150-mA tube current, and images were reconstructed using IMR techniques. Image noise, attenuation at the aorta, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) at the proximal right and left main coronary arteries (pRCA and LMCA) were calculated. CCTA images were qualitatively evaluated using a four-point scale (1, poor; 4, excellent) and analyzed using a non-inferiority test with a pre-defined non-inferiority margin of -0.2. The mean CCTA radiation dose (Group A: 1.33 ± 0.02 mSv; Group B: 1.35 ± 0.10 mSv; p = 0.151) and mean aortic root CT attenuation values (Group A: 447.9 ± 81.6 HU; Group B: 439.5 ± 63.6 HU; p = 0.571) did not differ significantly between the two groups. The mean noise in groups A and B was 26.0 ± 4.8 HU and 29.2 ± 4.4 HU, respectively (p = 0.005). The noise reduction ratio in the groups, compared to filtered back projection, was 65.0% and 68.1%, respectively. The mean grade of image quality did not differ significantly (3.75 ± 0.04 vs. 3.71 ± 0.04, p = 0.478). Group B CCTA image quality was non-inferior (mean difference = -0.043, 95% CI = -0.162–0.077) to that of Group A. We concluded that low-dose CCTA with prospective ECG-triggering and IMR might be applied to overweight subjects, as well as to normal-weight subjects, by using a fixed tube current without an increase in tube current based on the patient’s body size.

Value of CT Angiography Using Low Tube Voltage and Low Contrast Combined with Iterative Model Reconstruction in Patients with Coronary Artery Bypass Grafts

Objective To assess the value of CT angiography using low-voltage and low-concentration contrast media (CM) combined with knowledge-based iterative model reconstruction (IMR) in patients with coronary artery bypass grafts (CABG).Methods Totally 71 patients after CABG undergoing CT angiography in our center from June to November 2016 were prospectively enrolled and randomly assigned into groups A and B. The scan protocol for group A was 80 kVp with 300 mgI/ml contrast at an injection rate of 4 ml/s;images were reconstructed by IMR algorithm. The scan protocol for group B was 100 kVp with 370 mgI/ml contrast at an injection rate of 5 ml/s;images were reconstructed by hybrid iterative reconstruction technique. Aorta,left ventricular,and grafts were chosen as regions of interest. The image quality,radiation dose,and contrast load were compared between two groups.Results The signal to noise ratio (SNR) and contrast to noise ratio (CNR) of the ascending aorta,descending aorta,left ventricular,and venous bridge in group A [SNR:19±5,20±5.7,19.1±4.9,and 37±34;CNR:17±4.7,18±5,16±5.4,and 34±32] were significantly higher than those in group B [SNR:16±6 (P=0.012),15.6±5.5 (P=0.002),15±6 (P=0.002),24±8.3 (P=0.035);CNR:14±5.5 (P=0.010),13.8±5(P=0.002),13±5.7 (P=0.014),21±7.8 (P=0.031)],except for left internal mammary artery graft (LIMA),which was not inferior to that in group B. An effective radiation dose reduction of 49% was achieved in group A [(2.3±0.4) mSv,compared with group B (4.5±0.5) mSv (P=0.000)]. The iodine load of group A was (20±1.4) g compared with (29±1.6) g in group B,resulting in a reduction of 31% (P=0.000).Conclusions The low tube voltage (80 kVp) and low contrast protocol combined with IMR in patients with CABG can reduce radiation dose and improve image quality of aorta,left ventricular and venous graft. The image quality of LIMA graft in low dose group is not inferior to that in regular dose group.

Knowledge-based iterative model reconstruction: Comparative image quality with low tube voltage cerebral CT angiography.

The aim of this study was to compare image quality of low tube voltage cerebral computed tomography angiography (CTA) reconstructed with knowledge-based iterative model reconstruction (IMR), filtered back projection (FBP), and hybrid iterative reconstruction (HIR).A total of 101 patients with suspected cerebrovascular diseases were enrolled and randomized into 2 groups, 100 kVp tube voltage (n = 53) and reduced tube voltage (80 kVp) (n = 48). Computed tomography data were reconstructed with IMR, FBP, and HIR algorithms. The image noise, vascular attenuation, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were measured and calculated. Two blinded radiologists independently evaluated image quality based on diagnostic confidence on a 3-point scale. Quantitative and qualitative assessments were compared between different groups and reconstruction subgroups.Vascular attenuation was higher in the reduced tube voltage group than in 100-kVp tube voltage group, but showed no significant difference within each group. In both groups, the image noise, vascular SNR, and CNR were significantly improved by IMR as compared with FBP and HIR. Inter-group comparison indicated that IMR with reduced tube voltage showed better image quality with lower image noise and higher vascular SNR and CNR than FBP and HIR at 100 kVp, but slightly inferior to IMR at 100 kVp. IMR also yields the best qualitative image quality, and improves the diagnostic confidence of atherosclerosis and aneurysm. Compared with the standard 120-kVp protocol (1.86mSv), the radiation doses of 100 kVp (1.13mSv) and 80 kVp (0.56mSv) were 39% and 70% less, respectively.The quantitative and qualitative image quality obtained by IMR was superior to that obtained by FBP and HIR for low tube voltage cerebral CTA.

Feasibility of a low-dose orbital CT protocol with a knowledge-based iterative model reconstruction algorithm for evaluating Graves' orbitopathy

PurposeTo evaluate the clinical feasibility of low-dose orbital CT with a knowledge-based iterative model reconstruction (IMR) algorithm for evaluating Graves' orbitopathy. MethodsLow-dose orbital CT was performed with a CTDIvol of 4.4 mGy. In 12 patients for whom prior or subsequent non-low-dose orbital CT data obtained within 12 months were available, background noise, SNR, and CNR were compared for images generated using filtered back projection (FBP), hybrid iterative reconstruction (iDose4), and IMR and non-low-dose CT images. Comparison of clinically relevant measurements for Graves' orbitopathy, such as rectus muscle thickness and retrobulbar fat area, was performed in a subset of 6 patients who underwent CT for causes other than Graves' orbitopathy, by using the Wilcoxon signed-rank test. ResultsThe lens dose estimated from skin dosimetry on a phantom was 4.13 mGy, which was on average 59.34% lower than that of the non-low-dose protocols. Image quality in terms of background noise, SNR, and CNR was the best for IMR, followed by non-low-dose CT, iDose4, and FBP, in descending order. A comparison of clinically relevant measurements revealed no significant difference in the retrobulbar fat area and the inferior and medial rectus muscle thicknesses between the low-dose and non-low-dose CT images. ConclusionsLow-dose CT with IMR may be performed without significantly affecting the measurement of prognostic parameters for Graves' orbitopathy while lowering the lens dose and image noise.

IMPACT OF KNOWLEDGE-BASED ITERATIVE MODEL RECONSTRUCTION ON THE FEASIBILITY OF CORONARY COMPUTED TOMOGRAPHY ANGIOGRAPHY IN OBESE PATIENTS

Background: Obesity is a common clinical problem that can complicate investigation of coronary artery disease (CAD). Knowledge-based iterative model reconstruction (IMR) represents a novel reconstruction technique in coronary computed tomography angiography (CCTA) with reduced radiation and improved image quality. The purpose of this study is to assess the feasibility of IMR-CCTA in patients with a Body Mass Index (BMI) ≥ 30 kg/m2. Methods: We evaluated 407 symptomatic patients between January 2015 and March 2017 undergoing CCTA on a Philips iCT 256 slice scanner with an IMR algorithm. An experienced interpreter evaluated for non-diagnostic segments, severity (>50% stenosis) and plaque morphology in a standard 16-segment model. Diagnostic scans were determined by need for additional functional or anatomical assessment due to non-definite segment severity. Logistic regression was used for data analysis. Results: Diagnostic scans were comparable between both BMI groups (89%/88%). Subgroup analysis (BMI≥30) revealed improved diagnostic ability with lower age 40) but with increased radiation dose. Conclusion: CCTA represents an excellent modality to investigate CAD, and a knowledge-based IMR algorithm demonstrates high diagnostic ability in patients with increased BMI (≥ 30). Feasibility of diagnostic scans is also high in morbidly obese patients (BMI>40) but with increased radiation dose.

Contrast-Enhanced CT with Knowledge-Based Iterative Model Reconstruction for the Evaluation of Parotid Gland Tumors: A Feasibility Study.

ObjectiveThe purpose of this study was to determine the diagnostic utility of low-dose CT with knowledge-based iterative model reconstruction (IMR) for the evaluation of parotid gland tumors.Materials and MethodsThis prospective study included 42 consecutive patients who had undergone low-dose contrast-enhanced CT for the evaluation of suspected parotid gland tumors. Prior or subsequent non-low-dose CT scans within 12 months were available in 10 of the participants. Background noise (BN), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were compared between non-low-dose CT images and images generated using filtered back projection (FBP), hybrid iterative reconstruction (iDose4; Philips Healthcare), and knowledge-based IMR. Subjective image quality was rated by two radiologists using five-point grading scales to assess the overall image quality, delineation of lesion contour, image sharpness, and noise.ResultsWith the IMR algorithm, background noise (IMR, 4.24 ± 3.77; iDose4, 8.77 ± 3.85; FBP, 11.73 ± 4.06; p = 0.037 [IMR vs. iDose4] and p < 0.001 [IMR vs. FBP]) was significantly lower and SNR (IMR, 23.93 ± 7.49; iDose4, 10.20 ± 3.29; FBP, 7.33 ± 2.03; p = 0.011 [IMR vs. iDose4] and p < 0.001 [IMR vs. FBP]) was significantly higher compared with the other two algorithms. The CNR was also significantly higher with the IMR compared with the FBP (25.76 ± 11.88 vs. 9.02 ± 3.18, p < 0.001). There was no significant difference in BN, SNR, and CNR between low-dose CT with the IMR algorithm and non-low-dose CT. Subjective image analysis revealed that IMR-generated low-dose CT images showed significantly better overall image quality and delineation of lesion contour with lesser noise, compared with those generated using FBP by both reviewers 1 and 2 (4 vs. 3; 4 vs. 3; and 3–4 vs. 2; p < 0.05 for all pairs), although there was no significant difference in subjective image quality scores between IMR-generated low-dose CT and non-low-dose CT images.ConclusionIterative model reconstruction-generated low-dose CT is an alternative to standard non-low-dose CT without significantly affecting image quality for the evaluation of parotid gland tumors.

Low Tube Voltage and Iterative Model Reconstruction in Follow-up CT Angiography After Thoracic Endovascular Aortic Repair: Ultra-low Radiation Exposure and Contrast Medium Dose

This study aimed to investigate the feasibility of reducing radiation exposure and contrast medium (CM) dose in follow-up computed tomography angiography (CTA) after thoracic endovascular aortic repair (TEVAR) using low tube voltage and knowledge-based iterative model reconstruction (IMR). Thirty-six patients that required follow-up CTA after TEVAR were included in this intra-individual study. The conventional protocol with standard tube voltage of 120 kVp and CM volume of 70 mL was applied in the first follow-up CTA of all the patients (control group A). The ultra-low CM dose protocol with low tube voltage of 80 kVp and weight-adapted CM volume of 0.4 mL/kg was utilized in the second follow-up CTA (study group B). Set A.FBP (group A filtered back-projection) contained images for group A that were reconstructed through FBP method. Three sets (B.FBP, B.HIR, and B.IMR) for group B were reconstructed using three methods, FBP, hybrid iterative reconstruction (HIR), and IMR, respectively. Objective measurements including aortic attenuations, image noise, contrast-to-noise ratios (CNRs), and figure of merit of CNR (FOMCNR), and subjective rating scores of the four image sets were compared. Compared to the images in set A.FBP, the images in set B.IMR had better quality in terms of equivalent attenuation values, equivalent subjective scores, lower noise, higher or equivalent CNRs, and higher FOMCNR. The quality of images in sets B.FBP and B.HIR was unacceptable. The radiation exposure and CM dose in group B were 1.94 mGy and 28 ± 5 mL, respectively, representing reductions of 77.6% (P < .001) and 60% (P < .001) as compared to those in group A. In follow-up examinations after TEVAR, CTA with ultra-low radiation exposure and CM dose is feasible using low tube voltage and IMR for nonobese patients.

Usefulness of a Low Tube Voltage: Knowledge-Based Iterative Model Reconstruction Algorithm for Computed Tomography Venography.

The objective of this study was to evaluate the use of 80-kVp scans with knowledge-based iterative model reconstruction (IMR) for computed tomography venography (CTV). This prospective study received institutional review board approval; a previous informed consent was obtained from all participants. We enrolled 30 patients with suspected deep venous thrombosis or pulmonary embolism who were to undergo 80-kVp CTV studies. The images were reconstructed with filtered back projection (FBP), hybrid iterative reconstruction (HIR), and IMR. The venous attenuation, image noise, and contrast-to-noise ratio at the iliac, femoral, and popliteal veins were compared on FBP, HIR, and IMR images. We performed qualitative image analysis (image noise, image contrast, image sharpness, streak artifacts, and overall image quality) of the 3 reconstruction methods and measured their reconstruction times. There was no significant difference in venous attenuation among the 3 reconstruction methods (P > 0.05). On IMR images, the image noise was lowest at all 3 venous locations, and the contrast-to-noise ratio was highest. Qualitative evaluation scores were also highest for IMR images. The reconstruction time for FBP, HIR, and IMR imaging was 25.4 ± 1.9 seconds, 43.3 ± 3.3 seconds, and 78.7 ± 6.0 seconds, respectively. At clinically acceptable reconstruction times, 80-kVp CTV using the IMR technique yielded better qualitative and quantitative image quality than HIR and FBP.

Delayed contrast-enhanced computed tomography in patients with known or suspected cardiac sarcoidosis: A feasibility study.

To evaluate the diagnostic value of delayed contrast-enhanced computed tomography (DE-CT) for cardiac sarcoidosis (CS) in patients with or without implantable devices, including a quantitative comparison with late gadolinium enhancement cardiac magnetic resonance (LGE-CMR). Twenty-four patients (mean age, 64 ± 9years; 17 women) with known or suspected CS underwent retrospective electrocardiogram-gated DE-CT at 80kV with knowledge-based iterative model reconstruction. Fourteen patients without implantable devices also underwent LGE-CMR, while ten with pacemakers or implantable cardioverter-defibrillators did not. The presence of hyperenhanced myocardium was assessed visually and quantitatively using a 5-standard deviation threshold above the mean of remote myocardium. Inter-observer agreement for visual detection of hyperenhanced segments on DE-CT was excellent in patients with implantable devices and in those without (κ = 0.91 and κ = 0.94, respectively). Comparisons of the percent area of hyperenhanced myocardium between DE-CT and LGE-CMR on both per-patient and per-segment analyses showed good correlations (r = 0.96 and r = 0.83, respectively; p < 0.001). The sensitivity and specificity of DE-CT for the diagnosis of CS were 94% and 33%. The extent of hyperenhanced lesion with DE-CT showed good agreement with LGE-CMR results. DE-CT showed high sensitivity for detecting CS and may be useful particularly in patients with contraindications to CMR. • Delayed contrast-enhanced CT (DE-CT) can be applied to patients with implantable devices. • DE-CT can detect cardiac sarcoidosis (CS) lesions similarly to cardiac MRI. • DE-CT shows high sensitivity for detecting CS. • DE-CT may be useful particularly in patients with contraindications to cardiac MRI.

Improved image quality with simultaneously reduced radiation exposure: Knowledge-based iterative model reconstruction algorithms for coronary CT angiography in a clinical setting

BackgroundThe aim of this study was to assess the potential for radiation dose reduction using knowledge-based iterative model reconstruction (K-IMR) algorithms in combination with ultra-low dose body mass index (BMI)-adapted protocols in coronary CT angiography (coronary CTA). MethodsForty patients undergoing clinically indicated coronary CTA were randomly assigned to two groups with BMI-adapted (I: <25.0 kg/m2, II: <28.0 kg/m2, III: <30.0 kg/m2, IV: ≥30.0 kg/m2) low dose (LD, I: 100kVp/75 mAs, II: 100kVp/100 mAs, III: 100kVp/150 mAs, IV: 120kVp/150 mAs, n = 20) or ultra-low dose (ULD, I: 100kVp/50 mAs, II: 100kVp/75 mAs, III: 100kVp/100 mAs, IV: 120kVp/100 mAs, n = 20) protocols. Prospectively-triggered coronary CTA was performed using a 256-MDCT with the lowest reasonable scan length. Images were generated with filtered back projection (FBP), a noise-reducing hybrid iterative algorithm (iD, levels 2/5) and K-IMR using cardiac routine (CR) and cardiac sharp settings, levels 1–3. ResultsGroups were comparable regarding anthropometric parameters, heart rate, and scan length. The use of ULD protocols resulted in a significant reduction of radiation exposure (0.7 (0.6–0.9) mSv vs. 1.1 (0.9–1.7) mSv; p < 0.02). Image quality was significantly better in the ULD group using K-IMR CR 1 compared to FBP, iD 2 and iD 5 in the LD group, resulting in fewer non-diagnostic coronary segments (2.4% vs. 11.6%, 9.2% and 6.1%; p < 0.05). ConclusionsThe combination of K-IMR with BMI-adapted ULD protocols results in significant radiation dose savings while simultaneously improving image quality compared to LD protocols with FBP or hybrid iterative algorithms. Therefore, K-IMR allows for coronary CTA examinations with high diagnostic value and very low radiation exposure in clinical routine.

Coronary Computed Tomographic Angiography at 80 kVp and Knowledge-Based Iterative Model Reconstruction Is Non-Inferior to that at 100 kVp with Iterative Reconstruction.

The aims of this study were to compare the image noise and quality of coronary computed tomographic angiography (CCTA) at 80 kVp with knowledge-based iterative model reconstruction (IMR) to those of CCTA at 100 kVp with hybrid iterative reconstruction (IR), and to evaluate the feasibility of a low-dose radiation protocol with IMR. Thirty subjects who underwent prospective electrocardiogram-gating CCTA at 80 kVp, 150 mAs, and IMR (Group A), and 30 subjects with 100 kVp, 150 mAs, and hybrid IR (Group B) were retrospectively enrolled after sample-size calculation. A BMI of less than 25 kg/m2 was required for inclusion. The attenuation value and image noise of CCTA were measured and the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated at the proximal right coronary artery and left main coronary artery. The image noise was analyzed using a non-inferiority test. The CCTA images were qualitatively evaluated using a four-point scale. The radiation dose was significantly lower in Group A than Group B (0.69 ± 0.08 mSv vs. 1.39 ± 0.15 mSv, p < 0.001). The attenuation values were higher in Group A than Group B (p < 0.001). The SNR and CNR in Group A were higher than those of Group B. The image noise of Group A was non-inferior to that of Group B. Qualitative image quality of Group A was better than that of Group B (3.6 vs. 3.4, p = 0.017). CCTA at 80 kVp with IMR could reduce the radiation dose by about 50%, with non-inferior image noise and image quality than those of CCTA at 100 kVp with hybrid IR.

Submillisievert Radiation Dose Coronary CT Angiography: Clinical Impact of the Knowledge-Based Iterative Model Reconstruction

The purpose of this study was to evaluate the noise and image quality of images reconstructed with a knowledge-based iterative model reconstruction (knowledge-based IMR) in ultra-low dose cardiac computed tomography (CT). We performed submillisievert radiation dose coronary CT angiography on 43 patients. We also performed a phantom study to evaluate the influence of object size with the automatic exposure control phantom. We reconstructed clinical and phantom studies with filtered back projection (FBP), hybrid iterative reconstruction (hybrid IR), and knowledge-based IMR. We measured effective dose of patients and compared CT number, image noise, and contrast noise ratio in ascending aorta of each reconstruction technique. We compared the relationship between image noise and body mass index for the clinical study, and object size for phantom study. The mean effective dose was 0.98 ± 0.25 mSv. The image noise of knowledge-based IMR images was significantly lower than those of FBP and hybrid IR images (knowledge-based IMR: 19.4 ± 2.8; FBP: 126.7 ± 35.0; hybrid IR: 48.8 ± 12.8, respectively) (P < .01). The contrast noise ratio of knowledge-based IMR images was significantly higher than those of FBP and hybrid IR images (knowledge-based IMR: 29.1 ± 5.4; FBP: 4.6 ± 1.3; hybrid IR: 13.1 ± 3.5, respectively) (P < .01). There were moderate correlations between image noise and body mass index in FBP (r = 0.57, P < .01) and hybrid IR techniques (r = 0.42, P < .01); however, these correlations were weak in knowledge-based IMR (r = 0.27, P < .01). Compared to FBP and hybrid IR, the knowledge-based IMR offers significant noise reduction and improvement in image quality in submillisievert radiation dose cardiac CT.

Knowledge-based iterative model reconstruction technique in computed tomography of lumbar spine lowers radiation dose and improves tissue differentiation for patients with lower back pain

PurposeTo evaluate the image quality and diagnostic confidence of reduced-dose computed tomography (CT) of the lumbar spine (L-spine) reconstructed with knowledge-based iterative model reconstruction (IMR). Materials and methodsProspectively, group A consisted of 55 patients imaged with standard acquisition reconstructed with filtered back-projection. Group B consisted of 58 patients imaged with half tube current, reconstructed with hybrid iterative reconstruction (iDose4) in Group B1 and knowledge-based IMR in Group B2. Signal-to-noise ratio (SNR) of different regions, the contrast-to-noise ratio between the intervetebral disc (IVD) and dural sac (D-D CNR), and subjective image quality of different regions were compared. Higher strength IMR was also compared in spinal stenosis cases. ResultsThe SNR of the psoas muscle and D-D CNR were significantly higher in the IMR group. Except for the facet joint, subjective image quality of other regions including IVD, intervertebral foramen (IVF), dural sac, peridural fat, ligmentum flavum, and overall diagnostic acceptability were best for the IMR group. Diagnostic confidence of narrowing IVF and IVD was good (kappa=0.58–0.85). Higher strength IMR delineated IVD better in spinal stenosis cases. ConclusionLower dose CT of L-spine reconstructed with IMR demonstrates better tissue differentiation than iDose4 and standard dose CT with FBP.

Impact of Knowledge-Based Iterative Model Reconstruction in Abdominal Dynamic CT With Low Tube Voltage and Low Contrast Dose.

The purpose of this study was to compare iterative model reconstruction (IMR) and hybrid iterative reconstruction (HIR) of 80-kVp abdominal dynamic CT scans obtained with a low-dose contrast agent. A group of 27 consecutively registered patients underwent abdominal dynamic CT with an 80-kVp protocol and a low dose of contrast agent (300 mg I/kg). Another 27 patients who had previously undergone a 120-kVp protocol with filtered back projection (FBP) and a standard contrast dose (600 mg I/kg) acted as control subjects. Effective dose, image noise, CT number, and contrast-to-noise ratio were compared between the 120-kVp and 80-kVp images with FBP, HIR, and IMR. Image contrast, image noise, image sharpness, noise texture, and overall image quality were evaluated for the four protocols. The effective dose of the 80-kVp protocol was lower than that with the 120-kVp protocol. The 80-kVp protocol with HIR and IMR decreased image noise by 45% and 70% compared with the 80-kVp protocol with FBP. The contrast-to-noise ratio of the 80-kVp protocol with IMR was higher than that of the 120-kVp protocol. Qualitatively, the 80-kVp protocol with IMR improved image noise more than the 120-kVp protocol did, but noise texture was worse. HIR and the 120-kVp protocol yielded similar subjective image quality. Use of the 80-kVp protocol with HIR allowed an approximately 50% reduction in contrast dose and an approximately 40% reduction in radiation dose compared with use of the 120-kVp protocol while preserving image quality. IMR reduced image noise more than HIR with this protocol but worsened noise texture.