Myocardial extracellular volume quantification by cardiac CT in pulmonary hypertension: Comparison with cardiac MRI.

PURPOSE: Myocardial extracellular volume (ECV) measured by cardiac magnetic resonance imaging (MRI) has been suggested as a marker of disease severity in pulmonary hypertension (PH). However, consistency between ECVs quantified by computed tomography (CT) and MRI has not been sufficiently investigated in (PH). We investigated the utility of CT-ECV in PH, using MRI-ECV as a reference standard. METHOD: We evaluated 20 patients with known or suspected PH who underwent dual-energy CT, cardiac MRI, and right heart catheterization. We used Pearson correlation analysis to investigate correlations between CT-ECV and MRI-ECV. We also assessed correlations between ECV and mean pulmonary artery pressure (mPAP). RESULTS: CT-ECV showed a very strong correlation with MRI-ECV at the anterior (r = 0.83) and posterior right ventricular insertion points (RVIPs) (r = 0.84). CT-ECV and MRI-ECV were strongly correlated in the septum and left ventricular free wall (r = 0.79-0.73) but weakly correlated in the right ventricular free wall (r = 0.26). CT-ECV showed a strong correlation with mPAP in the anterior RVIP (r = 0.64) and a moderate correlation in the posterior RVIP and septum (r = 0.50-0.42). Compared with CT-ECV, MRI-ECV had a higher correlation with mPAP; however, the difference was not significant (anterior RVIP, r = 0.72 [MRI-ECV] vs. 0.64 [CT-ECV], p = 0.663; posterior RVIP, r = 0.67 vs. 0.50, p = 0.446). CONCLUSION: Dual-energy CT can quantify myocardial ECV and yield results comparable to those obtained using cardiac MRI. CT-ECV in the anterior RVIP could be a noninvasive surrogate marker of disease severity in PH.

Comparison between multi-shot gradient echo EPI and balanced SSFP in unenhanced 3T MRA of thoracic aorta in healthy volunteers.

PURPOSE: The purpose of this study was to compare scan time and image quality between magnetic resonance angiography (MRA) of the thoracic aorta using a multi-shot gradient echo planar imaging (MSG-EPI) and MRA using balanced steady-state free precession (b-SSFP). MATERIALS AND METHODS: Healthy volunteers (n=17) underwent unenhanced thoracic aorta MRA using balanced steady-state free precession (b-SSFP) and MSG-EPI sequences on a 3T MRI. The acquisition time, total scan time, signal-to-noise ratio (SNR) of the thoracic aorta, and the coefficient of variation (CV) of thoracic aorta were compared with paired t-tests. Two radiologists independently recorded the images' contrast, noise, sharpness, artifacts, and overall quality on a 4-point scale. RESULTS: The acquisition time was 36.2% shorter for MSG-EPI than b-SSFP (115.5±14.4 vs 181.0±14.9s, p<0.01). The total scan time was 40.4% shorter for MSG-EPI than b-SSFP (272±78 vs 456±144s, p<0.01). There was no significant difference in mean SNR between MSG-EPI and b-SSFP scans (17.3±3.6 vs 15.2±4.3, p=0.08). The CV was significantly lower for MSG-EPI than b-SSFP (0.2±0.1 vs. 0.5±0.2, p<0.01). All qualitative scores except for image noise were significantly higher in MSG-EPI than b-SSFP scans (p<0.05). CONCLUSION: The MSG-EPI sequence is a promising technique for shortening scan time and yielding more homogenous image quality in MRA of thoracic aorta on 3T scanners compared with the b-SSFP.

Impact of knowledge-based iterative model reconstruction on myocardial late iodine enhancement in computed tomography and comparison with cardiac magnetic resonance.

We evaluated the image quality and diagnostic performance of late iodine enhancement computed tomography (LIE-CT) with knowledge-based iterative model reconstruction (IMR) for the detection of myocardial infarction (MI) in comparison with late gadolinium enhancement magnetic resonance imaging (LGE-MRI). The study investigated 35 patients who underwent a comprehensive cardiac CT protocol and LGE-MRI for the assessment of coronary artery disease. The CT protocol consisted of stress dynamic myocardial CT perfusion, coronary CT angiography (CTA) and LIE-CT using 256-slice CT. LIE-CT scans were acquired 5 min after CTA without additional contrast medium and reconstructed with filtered back projection (FBP), a hybrid iterative reconstruction (HIR), and IMR. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were assessed. Sensitivity and specificity of LIE-CT for detecting MI were assessed according to the 16-segment model. Image quality scores, and diagnostic performance were compared among LIE-CT with FBP, HIR and IMR. Among the 35 patients, 139 of 560 segments showed MI in LGE-MRI. On LIE-CT with FBP, HIR, and IMR, the median SNRs were 2.1, 2.9, and 6.1; and the median CNRs were 1.7, 2.2, and 4.7, respectively. Sensitivity and specificity were 56 and 93% for FBP, 62 and 91% for HIR, and 80 and 91% for IMR. LIE-CT with IMR showed the highest image quality and sensitivity (p < 0.05). The use of IMR enables significant improvement of image quality and diagnostic performance of LIE-CT for detecting MI in comparison with FBP and HIR.

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

OBJECTIVES: 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). METHODS: 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. RESULTS: 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. CONCLUSIONS: At clinically acceptable reconstruction times, 80-kVp CTV using the IMR technique yielded better qualitative and quantitative image quality than HIR and FBP.

The Influence of Iterative Reconstruction on Coronary Artery Calcium Scoring-Phantom and Clinical Studies.

RATIONALE AND OBJECTIVES: We compared the effect of iterative model reconstruction (IMR), filtered back projection (FBP), and hybrid iterative reconstruction (HIR) on coronary artery calcium (CAC) scoring. MATERIALS AND METHODS: CAC scans of 30 consecutive patients (18 men and 12 women, age 70.1 ± 12.2 years) were reconstructed with FBP, HIR, and IMR, and the image noise was measured on all images. Two radiologists independently measured the CAC scores using semiautomated software, and interobserver agreement was evaluated. Statistical analysis included the Spearman correlation coefficient and Bland-Altman analysis. RESULTS: The mean image noise on FBP, HIR, and IMR images was 48.0 ± 7.9, 29.6 ± 4.8, and 9.3 ± 1.3 Hounsfield units, respectively. The difference among all reconstruction combinations was significant (P < .01). The CAC score on HIR and IMR scans was 4.2% and 8.9% lower, respectively, than the CAC score on FBP images. There was no significant difference in the mean CAC score among the three reconstructions. The interobserver correlation was excellent for all three reconstructions (r2 = 0.96 FBP, 0.99 HIR, 0.99 IMR); the best Bland-Altman measure of agreement was with IMR, followed by HIR and FBP. CONCLUSION: For CAC scoring, IMR can reduce the image noise and blooming artifacts, and consequently lowers the measured CAC score. IMR can lessen measurement variability and yield stable, reproducible measurements.

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

RATIONALE AND OBJECTIVES: 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). MATERIALS AND METHODS: 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. RESULTS: 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). CONCLUSION: 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.

CT Angiography in Patients with Peripheral Arterial Disease: Effect of Small Focal Spot Imaging and Iterative Model Reconstruction on the Image Quality.

RATIONALE AND OBJECTIVES: We investigated the effects of small focal spot (SFS) imaging and iterative model reconstruction (IMR) on the image quality of computed tomography angiographs (CTA) in patients with peripheral arterial disease. MATERIALS AND METHODS: We divided 60 consecutive patients with suspected or confirmed peripheral artery disease into two equal groups. One group underwent large focal spot scanning under our standard CTA protocol with hybrid iterative reconstruction (iDose(4)) (protocol 1), and the other underwent scanning with the SFS protocol and IMR (protocol 2). Quantitative image quality parameters, ie, arterial computed tomography attenuation, image noise, and the contrast-to-noise ratio, were compared and the visual image quality (depiction of each vessel) was scored on a 5-point scale. RESULTS: There was no significant difference in the arterial attenuation among all evaluated slice levels. The mean image noise was significantly lower under protocol 2 and the contrast-to-noise ratio was significantly higher at all slice levels. The visual scores assigned to the two protocols for the depiction of large vessels, such as the abdominal aorta and iliac artery, were comparable. However, the mean visual scores for small vessels in the lower extremities were significantly higher under protocol 2. CONCLUSION: CTA with SFS and IMR yielded significantly better qualitative and quantitative image quality especially for small vessels.

Low-Contrast and Low-Radiation Dose Protocol in Cardiac Computed Tomography: Usefulness of Low Tube Voltage and Knowledge-Based Iterative Model Reconstruction Algorithm.

OBJECTIVE: This study aimed to evaluate the feasibility of a low contrast, low-radiation dose protocol of 80-peak kilovoltage (kVp) with prospective electrocardiography-gated cardiac computed tomography (CT) using knowledge-based iterative model reconstruction (IMR). METHODS: Thirty patients underwent an 80-kVp prospective electrocardiography-gated cardiac CT with low-contrast agent (222-mg iodine per kilogram of body weight) dose. We also enrolled 30 consecutive patients who were scanned with a 120-kVp cardiac CT with filtered back projection using the standard contrast agent dose (370-mg iodine per kilogram of body weight) as a historical control group. We evaluated the radiation dose for the 2 groups. The 80-kVp images were reconstructed with filtered back projection (protocol A), hybrid iterative reconstruction (HIR, protocol B), and IMR (protocol C). We compared CT numbers, image noise, and contrast-to-noise ratio among 120-kVp protocol, protocol A, protocol B, and protocol C. In addition, we compared the noise reduction rate between HIR and IMR. Two independent readers compared image contrast, image noise, image sharpness, unfamiliar image texture, and overall image quality among the 4 protocols. RESULTS: The estimated effective dose (ED) of the 80-kVp protocol was 74% lower than that of the 120-kVp protocol (1.4 vs 5.4 mSv). The contrast-to-noise ratio of protocol C was significantly higher than that of protocol A. The noise reduction rate of IMR was significantly higher than that of HIR (P < 0.01). There was no significant difference in almost all qualitative image quality between 120-kVp protocol and protocol C except for image contrast. CONCLUSIONS: A 80-kVp protocol with IMR yields higher image quality with 74% decreased radiation dose and 40% decreased contrast agent dose as compared with a 120-kVp protocol, while decreasing more image noise compared with the 80-kVp protocol with HIR.

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

OBJECTIVE: 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. SUBJECTS AND METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Clinical impact of model-based type iterative reconstruction with fast reconstruction time on image quality of low-dose screening chest CT.

BACKGROUND: Model-based type iterative reconstruction algorithms with fast reconstruction times are now available. The clinical feasibility of their reconstruction has not been evaluated adequately. PURPOSE: To investigate the effects of model-based type iterative reconstruction, i.e. iterative model reconstruction (IMR), with fast reconstruction time on the qualitative and quantitative image quality at low-dose chest computed tomography (CT). MATERIAL AND METHODS: Thirty-one patients undergoing low-dose screening chest CT were enrolled. Images were reconstructed using filtered back projection (FBP), hybrid iterative reconstruction (HIR), and IMR algorithms. The CT attenuation and image noise for all reconstructions were calculated at the lung apex, middle, and base. Using a 4-point scale, two reviewers visually evaluated the image quality with respect to vessel sharpness, streak artifact, the mediastinum, and the overall image quality of each reconstruction method. RESULTS: The mean estimated effective dose was 1.0 ± 0.3 mSv. There was no significant difference in the CT attenuation among the three reconstructions. The mean image noise of FBP, HIR, and IMR images was 124.3 ± 57.3, 34.8 ± 10.2, and 22.9 ± 5.8 HU, respectively. There were significant differences for all comparison combinations among the three methods (P < 0.01). The best subjective overall image quality for the lung and mediastinum was obtained with IMR (P < 0.01). The reconstruction time for IMR was within 3 min in all cases. CONCLUSION: At low-dose chest CT, IMR can improve the qualitative and quantitative visualization of both lung and mediastinal structures especially in the lung apex at a clinically acceptable reconstruction time. Its application may improve diagnostic performance.

Effect of iterative reconstruction on variability and reproducibility of epicardial fat volume quantification by cardiac CT.

BACKGROUND: The epicardial fat volume (EFV) measured by cardiac CT has emerged as an important parameter for understanding the pathophysiology of coronary atherosclerosis. OBJECTIVE: We investigated the variability and reproducibility of EFV measurements and evaluated the effect of model-based type iterative reconstruction (M-IR) on measurement results. METHODS: Non-contrast cardiac CT data (tube voltage 120-kVp, tube current time product 32 mAs) of 30 consecutive patients were reconstructed with filtered back projection (FBP), hybrid type iterative reconstruction (H-IR), and M-IR using a slice thickness of 3.0 mm. CT attenuation and image noise was measured for all reconstructions. Two observers independently quantified EFV using semi-automated software and interobserver agreement was evaluated. RESULTS: There was no significant difference in the CT attenuation of the ascending aorta among the three reconstructions. The mean image noise on FBP-, H-IR-, and M-IR images was 48.0 ± 7.9 HU, 29.6 ± 4.8 HU, and 9.3 ± 1.3 HU, respectively; there was a significant difference among all comparison combinations for the three reconstructions (p < 0.01). FBP yielded the highest EFV among the three reconstructions (171.0 ± 54.9 cm(3) [FBP], 153.8 ± 53.1 cm(3) [H-IR], and 134.0 ± 46.4 cm(3) [M-IR]). For all three reconstructions, interobserver correlations were excellent (r = 0.91 [FBP], 0.93 [H-IR], and 0.96 [M-IR]). Interobserver comparisons showed that the lowest Bland-Altman limit of agreement was with M-IR (mean difference 2.0 ± 4.9%, 95% limit of agreement, -24.0 to 28.0%) followed by H-IR (-2.6 ± 7.1%, -39.8 to 34.6%) and FBP (-0.2 ± 8.6%, -45.3- to 45.0%). CONCLUSION: For the quantification of epicardial fat by cardiac CT, model-based iterative reconstruction can improve the image quality and lessen measurement variability.

Comparison of iterative model, hybrid iterative, and filtered back projection reconstruction techniques in low-dose brain CT: impact of thin-slice imaging.

INTRODUCTION: The purpose of this study was to evaluate the utility of iterative model reconstruction (IMR) in brain CT especially with thin-slice images. METHODS: This prospective study received institutional review board approval, and prior informed consent to participate was obtained from all patients. We enrolled 34 patients who underwent brain CT and reconstructed axial images with filtered back projection (FBP), hybrid iterative reconstruction (HIR) and IMR with 1 and 5 mm slice thicknesses. The CT number, image noise, contrast, and contrast noise ratio (CNR) between the thalamus and internal capsule, and the rate of increase of image noise in 1 and 5 mm thickness images between the reconstruction methods, were assessed. Two independent radiologists assessed image contrast, image noise, image sharpness, and overall image quality on a 4-point scale. RESULTS: The CNRs in 1 and 5 mm slice thickness were significantly higher with IMR (1.2 ± 0.6 and 2.2 ± 0.8, respectively) than with FBP (0.4 ± 0.3 and 1.0 ± 0.4, respectively) and HIR (0.5 ± 0.3 and 1.2 ± 0.4, respectively) (p < 0.01). The mean rate of increasing noise from 5 to 1 mm thickness images was significantly lower with IMR (1.7 ± 0.3) than with FBP (2.3 ± 0.3) and HIR (2.3 ± 0.4) (p < 0.01). There were no significant differences in qualitative analysis of unfamiliar image texture between the reconstruction techniques. CONCLUSION: IMR offers significant noise reduction and higher contrast and CNR in brain CT, especially for thin-slice images, when compared to FBP and HIR.

Value of knowledge-based iterative model reconstruction in low-kV 256-slice coronary CT angiography.

BACKGROUND: Most current iterative reconstruction algorithms for CT imaging are a mixture of iterative reconstruction and filtered back projection. The value of "fully" iterative reconstruction in coronary CT angiography remains poorly understood. OBJECTIVE: We aimed to assess the value of the knowledge-based iterative model reconstruction (IMR) algorithm on the qualitative and quantitative image quality at 256-slice cardiac CT. METHODS: We enrolled 21 patients (mean age: 69 ± 11 years) who underwent retrospectively ECG gated coronary CT anhgiography at 100 kVp tube voltage. Images were reconstructed with the filtered back projection (FBP), hybrid iterative reconstruction (IR), and IMR algorithms. CT attenuation and the contrast-to-noise ratio (CNR) of the coronary arteries were calculated. With the use of a 4-point scale, 2 reviewers visually evaluated the coronary arteries and cardiac structures. RESULTS: The mean CT attenuation of the proximal coronary arteries was 369.3 ± 73.6 HU, 363.9 ± 75.3 HU, and 363.3 ± 74.5 HU, respectively, for FBP, hybrid IR, and IMR and was not significantly different. The image noise of the proximal coronary arteries was significantly lower with IMR (11.3 ± 2.8 HU) than FBP (51.9 ± 12.9 HU) and hybrid IR (23.2 ± 5.2 HU). The mean CNR of the proximal coronary arteries was 9.4 ± 2.4, 20.2 ± 4.7, and 41.8 ± 9.5 with FBP, hybrid IR and IMR, respectively; it was significantly higher with IMR. The best subjective image quality for coronary vessels was obtained with IMR (proximal vessels: FBP, 2.6 ± 0.5; hybrid IR, 3.4 ± 0.5; IMR, 3.8 ± 0.4; distal vessels: FBP, 2.3 ± 0.5; hybrid IR. 3.1 ± 0.5; IMR, 3.7 ± 0.5). IMR also yielded the best visualization for cardiac systems, that is myocardium and heart valves. CONCLUSION: The novel knowledge-based IMR algorithm yields significantly improved CNR and better subjective image quality of coronary vessels and cardiac systems with reliable CT number measurements for cardiac CT imaging.

Image quality assessment of an iterative reconstruction algorithm applied to abdominal CT imaging.

PURPOSE: To compare the noise and accuracy on images of the whole porcine liver acquired with iterative reconstruction (IMR, Philips Healthcare, Cleveland, OH, USA) and filtered back projection (FBP) methods. MATERIALS AND METHODS: We used non-enhanced porcine liver to simulate the human liver and acquired it 100 times to obtain the average FBP value as the ground-truth. The mean and the standard deviation ("inter-scan SD") of the pixel values on the 100 image acquisitions were calculated for FBP and for three levels of IMR (L1, L2, and L3). We also calculated the noise power spectrum (NPS) and the normalized NPS for the 100 image acquisitions. RESULTS: The spatial SD for the porcine liver parenchyma on these slices was 9.92, 4.37, 3.63, and 2.30 Hounsfield units with FBP, IMR-L1, IMR-L2, and IMR-L3, respectively. The detectability of small faint features was better on single IMR than single FBP images. The inter-scan SD value for IMR-L3 images was 53% larger at the liver edges than at the liver parenchyma; it was only 10% larger on FBP images. Assessment of the normalized NPS showed that the noise on IMR images was comprised primarily of low-frequency components. CONCLUSION: IMR images yield the same structure informations as FBP images and image accuracy is maintained. On level 3 IMR images the image noise is more strongly suppressed than on IMR images of the other levels and on FBP images.

A knowledge-based iterative model reconstruction algorithm: can super-low-dose cardiac CT be applicable in clinical settings?

RATIONALE AND OBJECTIVES: To investigate whether "full" iterative reconstruction, a knowledge-based iterative model reconstruction (IMR), enables radiation dose reduction by 80% at cardiac computed tomography (CT). MATERIALS AND METHODS: A total of 23 patients (15 men, eight women; mean age 64.3 ± 13.4 years) who underwent retrospectively electrocardiography-gated cardiac CT with dose modulation were evaluated. We compared full-dose (FD; 730 mAs) images reconstructed with filtered back projection (FBP) technique and the low-dose (LD; 146 mAs) images reconstructed with FBP and IMR techniques. Objective and subjective image quality parameters were compared among the three different CT images. RESULTS: There was no significant difference in the CT attenuation among the three reconstructions. The mean image noise of LD-IMR (18.3 ± 10.6 Hounsfield units [HU]) was significantly lowest among the three reconstructions (41.9 ± 15.3 HU for FD-FBP and 109.9 ± 42.6 HU for LD-FBP; P < .01). The contrast-to-noise ratio of LD-IMR was better than that of FD-FBP and LD-FBP (P < .01). Visual evaluation score was also highest for LD-IMR. CONCLUSIONS: The IMR can provide improved image quality at super-low-dose cardiac CT with 20% of the standard tube current.

[Image quality assessment of Step&Shoot overlap reconstruction (SSOR) for cardiac computed tomography (CT)].

BACKGROUND: Step&Shoot cardiac computed tomography (CT) provides the benefit of significant reduction in radiation dose compared to helical cardiac CT acquisitions. We think that a difference occurs in image quality by presence of overlap reconstruction (fractionated sentence, attempted to clarify). PURPOSE: We studied the utility of Step&Shoot overlap reconstruction (SSOR). METHODS: We evaluated image quality of SSOR by comparing z-axis spatial resolution on various s in scanners that SSOR is possible and for those that are impossible. RESULTS: SSOR indicated better z-axis spatial resolution and less variation over the field of view (FOV) (in z & x-y directions) as compared with Step&Shoot without overlap reconstruction (SS). In addition, SS showed inadequate image reproducibility due to aliasing error in z-direction (lack of sampling interval). CONCLUSIONS: SSOR would contribute to improvement of the image quality of Step&Shoot cardiac CT.

Tunnel location in transparent 3-dimensional CT in anatomic double-bundle anterior cruciate ligament reconstruction with the trans-tibial tunnel technique.

It is difficult to precisely identify the locations of tunnels after double-bundle anterior cruciate ligament (ACL) reconstruction postoperatively. Using our novel transparent 3-dimensional computed tomography (T-3DCT), we evaluated intra-articular outlet locations and the angles of the anteromedial (AM) and posterolateral (PL) tunnels after anatomic double-bundle ACL reconstruction using the trans-tibial technique. A prospective study was performed with 123 consecutive patients. Tunnel outlet locations were identified on T-3DCT images showing the true lateral view of the femur and indicated by our originally defined X, Y coordinates. We also determined the angles between the tunnel axis and a joint surface line in the coronal plane, the long axis of the femur in the sagittal plane, and the posterior condyle line in the axial plane of both the femur and the tibia. The mean X, Y coordinates of the AM and PL tunnel outlets were 21, 43% and 0, 33%, respectively. In the coronal, sagittal, and axial planes, the mean AM femoral tunnel angles were 63 degrees, 48 degrees, and 55 degrees, respectively; the mean AM tibial tunnel angles in the tibia were 63 degrees, 49 degrees, and 71 degrees, respectively; the mean PL femoral tunnel angles were 38 degrees, 58 degrees, and 43 degrees, respectively; and the mean PL tibial tunnel angles were 46 degrees, 53 degrees, and 45 degrees, respectively. The AM and PL tunnel outlets and angles could be detailed precisely in three dimensions by using T-3DCT. This imaging technique may be useful to confirm surgical techniques and to improve clinical outcomes.