Image quality of iterative reconstruction in cranial CT imaging: comparison of model-based iterative reconstruction (MBIR) and adaptive statistical iterative reconstruction (ASiR)

Insights about cervical lymph nodes: Evaluating deep learning-based reconstruction for head and neck computed tomography scan

Purpose

This study aimed to investigate differences in cervical lymph node image quality on dual-energy computed tomography (CT) scan with datasets reconstructed using filter back projection (FBP), hybrid iterative reconstruction (IR), and deep learning-based image reconstruction (DLIR) in patients with head and neck cancer.

Method

Seventy patients with head and neck cancer underwent follow-up contrast-enhanced dual-energy CT examinations. All datasets were reconstructed using FBP, hybrid IR with 30 % adaptive statistical IR (ASiR-V), and DLIR with three selectable levels (low, medium, and high) at 2.5- and 0.625-mm slice thicknesses. Herein, signal, image noise, signal-to-noise ratio, and contrast-to-noise ratio of lymph nodes and overall image quality, artifact, and noise of selected regions of interest were evaluated by two radiologists. Next, cervical lymph node sharpness was evaluated using full width at half maximum.

Results

DLIR exhibited significantly reduced noise, ranging from 3.8 % to 35.9 % with improved signal-to-noise ratio (11.5-105.6 %) and contrast-to-noise ratio (10.5-107.5 %) compared with FBP and ASiR-V, for cervical lymph nodes (p < 0.001). Further, 0.625-mm-thick images reconstructed using DLIR-medium and DLIR-high had a lower noise than 2.5-mm-thick images reconstructed using FBP and ASiR-V. The lymph node margins and vessels on DLIR-medium and DLIR-high were sharper than those on FBP and ASiR-V (p < 0.05). Both readers agreed that DLIR had a better image quality than the conventional reconstruction algorithms.

Conclusion

DLIR-medium and -high provided superior cervical lymph node image quality in head and neck CT. Improved image quality affords thin-slice DLIR images for dose-reduction protocols in the future.

Utility of follow-up ultra-high-resolution CT angiography with model-based iterative reconstruction after flow diverter treatment for cerebral aneurysms

PURPOSE

Follow-up examinations after flow diverter (FD) treatment for cerebral aneurysms typically involve magnetic resonance imaging (MRI) or digital subtraction angiography (DSA). However, MRI is prone to vascular defects due to metal artifacts from FD, and DSA carries a risk of ischemic complications. In the context of computed tomography angiography (CTA), this study compares the efficacy of ultra-high-resolution CT (UHRCT) and novel reconstruction techniques, such as model-based iterative reconstruction (MBIR), against conventional methods such as filtered back projection (FBP) and hybrid iterative reconstruction (IR), to determine if they are a viable alternative to DSA in clinical settings.

MATERIALS AND METHODS

A phantom study was conducted with the full-width half-maximum considered as the FD thickness. This study compared three reconstruction methods: MBIR, FBP, and hybrid IR. A clinical study was also conducted with 21 patients who underwent follow-up CTA after FD treatment. The FD's visibility was assessed using a 4-point scale in FBP, hybrid IR, and MBIR compared to cone-beam CT (CBCT) with angiographic systems.

RESULTS

In the phantom study, FBP, hybrid IR, and MBIR visualized thinner FD thicknesses and improved detail rendering in that order. MBIR proved to be significantly superior in both the phantom and clinical study.

CONCLUSION

UHRCT with MBIR is highly effective for follow-up evaluations after FD treatment and may become the first-choice modality in the future.

Pediatric low-dose head CT: Image quality improvement using iterative model reconstruction

PURPOSE

To evaluate the differences in pediatric non-contrast low-dose head computed tomography (CT) between filtered-back projection and iterative model reconstruction using objective and subjective image quality evaluation.

METHODS

A retrospective study evaluated children undergoing low-dose non-contrast head CT. All CT scans were reconstructed using both filtered-back projection and iterative model reconstruction. Objective image quality analysis was performed using contrast and signal-to-noise ratios for the supra- and infratentorial brain regions of identical regions of interest on the two reconstruction methods. Two experienced pediatric neuroradiologists evaluated subjective image quality, visibility of structures, and artifacts.

RESULTS

We evaluated 233 low-dose brain CT scans of 148 pediatric patients. There was a ∼2-fold improvement in the contrast-to-noise ratio between gray and white matter in the infra- and supratentorial regions (p < 0.001) using iterative model reconstruction compared to filtered-back projection. The white and gray matter signal-to-noise ratio improved more than 2-fold using iterative model reconstruction (p < 0.001). Furthermore, radiologists graded anatomical details, gray-white matter differentiation, beam hardening artifacts, and image quality using iterative model reconstructions as superior to filtered-back projection reconstructions.

CONCLUSION

Iterative model reconstructions had better contrast-to-noise and signal-to-noise ratios with fewer artifacts in pediatric CT brain scans using low-dose radiation protocols. This image quality improvement was demonstrated in the supra- and infratentorial regions. This method thus comprises an important tool for reducing children's exposure while maintaining diagnostic capability.

A novel protocol for abdominal low-dose CT scans adapted with a model-based iterative reconstruction method

PURPOSE

This study aims to introduce a novel low-dose abdominal computed tomography (CT) protocol adapted with model-based iterative reconstruction (MBIR), To validate the adaptability of this protocol, objective image quality and subjective clinical scores of low-dose MBIR images are compared with the normal-dose images.

METHODS

Normal-dose abdominal CT images of 58 patients and low-dose abdominal CT images of 52 patients are reconstructed using both conventional filtered back projection (FBP) and MBIR methods with and without smooth applying. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) are used to compare image quality between the normal-dose and low-dose CT scans. CT dose indices (CTDI) of normal-dose and low-dose abdominal CT images on post-contrast venous phase are also compared.

RESULTS

The SNR, CNR and clinical score of low-dose MBIR images all show significant higher values (Bonferroni p < 0.05) than those of normal-dose images with conventional FBP method. A total of around 40% radiation dose reduction (CTDI: 5.3 vs 8.7 mGy) could be achieved via our novel abdominal CT protocol.

CONCLUSIONS

With the higher SNR/CNR and clinical scores, the low-dose CT abdominal imaging protocol with MBIR could effectively reduce the radiation for patients and provide equal or even higher image quality and also its adaptability in clinical abdominal CT image diagnosis.

Model-based reconstruction algorithm in the detection of acute trauma-related lesions in brain CT examinations

BACKGROUND AND PURPOSE

To evaluate the added value of a model-based reconstruction algorithm in the assessment of acute traumatic brain lesions in emergency non-enhanced computed tomography, in comparison with a standard hybrid iterative reconstruction approach.

MATERIALS AND METHODS

We retrospectively evaluated a total of 350 patients who underwent a 256-row non-enhanced computed tomography scan at the emergency department for brain trauma. Images were reconstructed both with hybrid and model-based iterative algorithm. Two radiologists, blinded to clinical data, recorded the presence, nature, number, and location of acute findings. Subjective image quality was performed using a 4-point scale. Objective image quality was determined by computing the signal-to-noise ratio and contrast-to-noise ratio. The agreement between the two readers was evaluated using k-statistics.

RESULTS

A subjective image quality analysis using model-based iterative reconstruction gave a higher detection rate of acute trauma-related lesions in comparison to hybrid iterative reconstruction (extradural haematomas 116 vs. 68, subdural haemorrhages 162 vs. 98, subarachnoid haemorrhages 118 vs. 78, parenchymal haemorrhages 94 vs. 64, contusive lesions 36 vs. 28, diffuse axonal injuries 75 vs. 31; all P<0.001). Inter-observer agreement was moderate to excellent in evaluating all injuries (extradural haematomas k=0.79, subdural haemorrhages k=0.82, subarachnoid haemorrhages k=0.91, parenchymal haemorrhages k=0.98, contusive lesions k=0.88, diffuse axonal injuries k=0.70). Quantitatively, the mean standard deviation of the thalamus on model-based iterative reconstruction images was lower in comparison to hybrid iterative one (2.12 ± 0.92 vsa 3.52 ± 1.10; P=0.030) while the contrast-to-noise ratio and signal-to-noise ratio were significantly higher (contrast-to-noise ratio 3.06 ± 0.55 vs. 1.55 ± 0.68, signal-to-noise ratio 14.51 ± 1.78 vs. 8.62 ± 1.88; P<0.0001). Median subjective image quality values for model-based iterative reconstruction were significantly higher (P=0.003).

CONCLUSION

Model-based iterative reconstruction, offering a higher image quality at a thinner slice, allowed the identification of a higher number of acute traumatic lesions than hybrid iterative reconstruction, with a significant reduction of noise.

Value of using adaptive statistical iterative reconstruction-V (ASIR-V) technology in pediatric head CT dose reduction

Background

With widespread use of pediatric head CT, it is critically important to protect patients from radiation hazards, using reduced dose CT techniques. In this regard, adaptive statistical iterative reconstruction-V (ASIR-V) algorithm can decrease image noise, generating CT images of reasonable diagnostic quality with less radiation. The objective of this study was radiation dose assessment, quantitative and qualitative evaluation of reduced dose pediatric head CT using ASIR-V 60% and 80% reconstruction.

Results

Retrospective analysis was performed on two groups of pediatric head CT examinations, a reduced dose CT examination group with ASIR-V reconstruction (ASIR group) (n = 27) and a standard dose CT examination group without ASIR reconstruction (non-ASIR group) (n = 14). The average effective dose (ED) of ASIR group was significantly lower than that of the non-ASIR group (1.04 ± 0.1 mS vs 3.48 ± 0.45 mS; p = 0.001). Quantitative analysis revealed comparable results of signal to noise ratio (SNR) and contrast to noise ratio (CNR) of ASIR and non-ASIR groups (p > 0.05). Qualitative evaluation of resulting images by two readers revealed comparable results of both ASIR and non-ASIR groups (p > 0.05) with excellent inter-reader agreement (κ = 0.97). Both quantitative and qualitative assessment demonstrated better ASIR-V 80% than ASIR-V 60% reconstructed images.

Conclusion

ASIR-V algorithm is a promising technology for effective dose reduction of pediatric head CT with preservation of diagnostic image quality.

Combination of Deep Learning-Based Denoising and Iterative Reconstruction for Ultra-Low-Dose CT of the Chest: Image Quality and Lung-RADS Evaluation

OBJECTIVE. The objective of our study was to assess the effect of the combination of deep learning-based denoising (DLD) and iterative reconstruction (IR) on image quality and Lung Imaging Reporting and Data System (Lung-RADS) evaluation on chest ultra-low-dose CT (ULDCT). MATERIALS AND METHODS. Forty-one patients with 252 nodules were evaluated retrospectively. All patients underwent ULDCT (mean ± SD, 0.19 ± 0.01 mSv) and standard-dose CT (SDCT) (6.46 ± 2.28 mSv). ULDCT images were reconstructed using hybrid iterative reconstruction (HIR) and model-based iterative reconstruction (MBIR), and they were postprocessed using DLD (i.e., HIR-DLD and MBIR-DLD). SDCT images were reconstructed using filtered back projection. Three independent radiologists subjectively evaluated HIR, HIR-DLD, MBIR, and MBIR-DLD images on a 5-point scale in terms of noise, streak artifact, nodule edge, clarity of small vessels, homogeneity of the normal lung parenchyma, and overall image quality. Two radiologists independently evaluated the nodules according to Lung-RADS using HIR, MBIR, HIR-DLD, and MBIR-DLD ULDCT images and SDCT images. The median scores for subjective analysis were analyzed using Wilcoxon signed rank test with Bonferroni correction. Intraobserver agreement for Lung-RADS category between ULDCT and SDCT was evaluated using the weighted kappa coefficient. RESULTS. In the subjective analysis, ULDCT with DLD showed significantly better scores than did ULDCT without DLD (p < 0.001), and MBIR-DLD showed the best scores among the ULDCT images (p < 0.001) for all items. In the Lung-RADS evaluation, HIR showed fair or moderate agreement (reader 1 and reader 2: κw = 0.46 and 0.32, respectively); MBIR, moderate or good agreement (κw = 0.68 and 0.57); HIR-DLD, moderate agreement (κw = 0.53 and 0.48); and MBIR-DLD, good agreement (κw = 0.70 and 0.72). CONCLUSION. DLD improved the image quality of both HIR and MBIR on ULDCT. MBIR-DLD was superior to HIR_DLD for image quality and for Lung-RADS evaluation.

Comparison of Iterative Model Reconstruction versus Filtered Back-Projection in Pediatric Emergency Head CT: Dose, Image Quality, and Image-Reconstruction Times

BACKGROUND AND PURPOSE

Noncontrast CT of the head is the initial imaging test for traumatic brain injury, stroke, or suspected nonaccidental trauma. Low-dose head CT protocols using filtered back-projection are susceptible to increased noise and decreased image quality. Iterative reconstruction noise suppression allows the use of lower-dose techniques with maintained image quality. We review our experience with children undergoing emergency head CT examinations reconstructed using knowledge-based iterative model reconstruction versus standard filtered back-projection, comparing reconstruction times, radiation dose, and objective and subjective image quality.

MATERIALS AND METHODS

This was a retrospective study comparing 173 children scanned using standard age-based noncontrast head CT protocols reconstructed with filtered back-projection with 190 children scanned using low-dose protocols reconstructed with iterative model reconstruction. ROIs placed on the frontal white matter and thalamus yielded signal-to-noise and contrast-to-noise ratios. Volume CT dose index and study reconstruction times were recorded. Random subgroups of patients were selected for subjective image-quality review.

RESULTS

The volume CT dose index was significantly reduced in studies reconstructed with iterative model reconstruction compared with filtered back-projection, (mean, 24.4 ± 3.1 mGy versus 31.1 ± 6.0 mGy, P < .001), while the SNR and contrast-to-noise ratios improved 2-fold (P < .001). Radiologists graded iterative model reconstruction images as superior to filtered back-projection images for gray-white matter differentiation and anatomic detail (P < .001). The average reconstruction time of the filtered back-projection studies was 101 seconds, and with iterative model reconstruction, it was 147 seconds (P < .001), without a practical effect on work flow.

CONCLUSIONS

In children referred for emergency noncontrast head CT, optimized low-dose protocols with iterative model reconstruction allowed us to significantly reduce the relative dose, on average, 22% compared with filtered back-projection, with significantly improved objective and subjective image quality.

A "one-stop-shop" 4D CTA protocol using 320-row CT for advanced imaging in acute ischemic stroke: a technical note

This technical note describes a novel CT scan protocol that includes a non-enhanced CT, dynamic CTA, and perfusion of the whole brain and CTA of the carotid arteries using a 320-row area detector CT scanner, with a unique contrast injection and acceptable radiation exposure dose in patients presenting with acute ischemic stroke. The acquisition parameters and reconstruction parameters will be discussed including the use of model-based iterative reconstruction (MBIR), time summing (tMIP), and subtraction techniques to optimize the results of this protocol.Key Points• Scanning on a 320-row area detector CT can achieve both brain perfusion with dynamic angiography and reconstructed arterial and venous CTA, and supra aortic trunk angiography, in a single acquisition. • It provides, in a single exam, a full diagnostic workup, i.e., all the acquisitions that are needed to make a quick decision, with reasonable exposure to ionizing radiation and reduced amount of medium contrast, in case of acute ischemic stroke presentation.

Comparison of image noise and image quality between full-dose abdominal computed tomography scans reconstructed with weighted filtered back projection and half-dose scans reconstructed with improved sinogram-affirmed iterative reconstruction (SAFIRE*)

PURPOSE

To retrospectively compare the image noise, signal-to-noise ratio (SNR), and subjective image quality between CT images acquired with a dual-source, split-dose imaging protocol reconstructed at full and half doses with weighted filtered back projection (wFBP) and an improved sinogram-affirmed iterative reconstruction algorithm (SAFIRE*).

METHODS

Fifty-three consecutive patients underwent contrast-enhanced CT of the abdomen using a standardized dual-source, single energy CT protocol. Half-dose images were retrospectively generated using data from one detector only. Full-dose datasets were reconstructed with wFBP, while half-dose datasets were reconstructed with wFBP and SAFIRE* strengths 1-5. Region of interest analysis was performed to assess SNR and noise. Diagnostic acceptability, subjective noise, and spatial resolution were graded on a 10-point scale by two readers. Statistical analysis was carried out with repeated measures analysis of variance, Wilcoxon signed rank test, and Cohen's κ test.

RESULTS

With the increasing strengths of SAFIRE*, a progressive reduction in noise and increase in SNR (p < 0.01) was observed. There was a statistically significant decrease in objective noise and increase in SNR in half-dose SAFIRE* strength 4 and 5 reconstructions compared to full-dose reconstructions using wFBP (p < 0.01). Qualitative analysis revealed a progressive increase in diagnostic acceptability, decrease in subjective noise and increase in spatial resolution for half-dose images reconstructed with the increasing strengths of SAFIRE* (p < 0.01).

CONCLUSIONS

Half-dose CT images reconstructed with SAFIRE* at strength 4 and 5 have superior image quality compared to full-dose images reconstructed with wFBP. SAFIRE* potentially allows dose reductions in the order of 50% over wFBP.

"Hyperdense artery sign" in early ischemic stroke: diagnostic value of model-based reconstruction approach in comparison with standard hybrid iterative reconstruction algorithm

PURPOSE

Hyperdense artery sign is the earliest sign of ischemic stroke on non-enhanced computed tomography and it can be visible long before parenchymal changes. The aim of our study was to compare diagnostic value of model-based iterative reconstruction algorithm (IMR) with that of iterative reconstruction algorithm (iDose4) in identifying hyperdense artery sign.

METHODS

We selected 56 consecutive patients suspected for ischemic stroke, who underwent a NCCT and that demonstrated a vessel occlusion at angio-CT or developed ischemic lesion at follow-up CT. Two readers randomly analyzed images of NCCT reconstructed both with iDose4 (4 mm) and IMR (2 mm), reporting presence of hyperdense artery sign (0: no; 1: yes; 2: not sure). They rated image quality on a 4-point scale (1: unacceptable; 4: more than average) and recorded HU values of clot and of normal vessel and measured noise index, CNR and SNR.

RESULTS

Mean values of CTDI, DLP, and ED were respectively of 43 mGy, 819.7 mGy cm, and 1.72 mSv. By analyzing the IMR reconstruction, both readers were able to recognize hyperdense vessel sign in 55/56 patients, while only in 12/56 patients were identified with iDose. IMR obtained better rating of image quality (mean score for IMR 3.32 vs 2.53 for iDose), higher clot density (57.2 vs 46.7 HU), lower noise index (5 vs 2), higher CNR and SNR (respectively 4.2 vs 2 and 16.8 vs 8.5).

CONCLUSIONS

Model-based approach significantly increases sensitivity in detecting hyperdense artery sign, offering higher SNR and CNR in brain CT images in comparison with standard hybrid reconstruction algorithm.

Low-dose CT imaging of the acute abdomen using model-based iterative reconstruction: a prospective study

OBJECTIVES

Performance of a modified abdominopelvic CT protocol reconstructed using full iterative reconstruction (IR) was assessed for imaging patients presenting with acute abdominal symptoms.

MATERIALS AND METHODS

Fifty-seven patients (17 male, 40 female; mean age of 56.5 ± 8 years) were prospectively studied. Low-dose (LD) and conventional-dose (CD) CTs were contemporaneously acquired between November 2015 and March 2016. The LD and CD protocols imparted radiation exposures approximating 10-20% and 80-90% those of routine abdominopelvic CT, respectively. The LD images were reconstructed with model-based iterative reconstruction (MBIR), and CD images with hybrid IR (40% adaptive statistical iterative reconstruction (ASIR)). Image quality was assessed quantitatively and qualitatively. Independent clinical interpretations were performed with a 6-week delay between reviews.

RESULTS

A 74.7% mean radiation dose reduction was achieved: LD effective dose (ED) 2.38 ± 1.78 mSv (size-specific dose estimate (SSDE) 3.77 ± 1.97 mGy); CD ED 7.04 ± 4.89 mSv (SSDE 10.74 ± 5.5 mGy). LD-MBIR images had significantly lower objective and subjective image noise compared with CD-ASIR (p < 0.0001). Noise reduction for LD-MBIR studies was greater for patients with BMI < 25 kg/m² than those with BMI ≥ 25 kg/m² (5.36 ± 3.2 Hounsfield units (HU) vs. 4.05 ± 3.1 HU, p < 0.0001). CD-ASIR studies had significantly better contrast resolution, and diagnostic acceptability (p < 0.0001 for all). LD-MBIR studies had significantly lower streak artifact (p < 0.0001). There was no difference in sensitivity for primary findings between the low-dose and conventional protocols with the exception of one case of enteritis.

CONCLUSIONS

Low-dose abdominopelvic CT performed with MBIR is a feasible radiation dose reduction strategy for imaging patients presenting with acute abdominal pain.

Pulmonary Emphysema Quantification on Ultra-Low-Dose Computed Tomography Using Model-Based Iterative Reconstruction With or Without Lung Setting

OBJECTIVES

To evaluate the influence of model-based iterative reconstruction (MBIR) with lung setting and conventional setting on pulmonary emphysema quantification by ultra-low-dose computed tomography (ULDCT) compared with standard-dose CT (SDCT).

METHODS

Forty-five patients who underwent ULDCT (0.18 ± 0.02 mSv) and SDCT (6.66 ± 2.69 mSv) were analyzed in this retrospective study. Images were reconstructed using filtered back projection (FBP) with smooth and sharp kernels and MBIR with conventional and lung settings. Extent of emphysema was evaluated using fully automated software. Correlation between ULDCT and SDCT was assessed by interclass correlation coefficiency (ICC) and Bland-Altman analysis.

RESULTS

Excellent correlation was seen between MBIR with conventional setting on ULDCT and FBP with smooth kernel on SDCT (ICC, 0.97; bias, -0.31%) and between MBIR with lung setting on ULDCT and FBP with sharp kernel on SDCT (ICC, 0.82; bias, -2.10%).

CONCLUSION

Model-based iterative reconstruction improved the agreement between ULDCT and SDCT on emphysema quantification.

Impact of model-based iterative reconstruction (MBIR) on image quality in cerebral CT angiography before and after intracranial aneurysm treatment

PURPOSE

To subjectively and objectively assess the impact of model-based iterative reconstruction(MBIR) on image quality in cerebral computed tomography angiography compared to adaptive statistical iterative reconstruction (ASIR).

METHODS

107 patients (mean age: 58 ± 14 years) were included prior to (n = 38) and after (n = 69) intracranial aneurysm treatment. Images were acquired using a routine protocol and reconstructed with MBIR and ASIR. Image noise, signal-to-noise (SNR) and contrast-to-noise (CNR) ratios in the internal carotid and middle cerebral arteries were compared between MBIR and ASIR using the Wilcoxon signed-rank test. Additionally, two neuroradiologists subjectively assessed noise, artefacts, vessel sharpness and overall quality using a semi-quantitative assessment scale.

RESULTS

Objective assessment revealed that MBIR reduced noise (p < 0.0001) and additionally improved SNR (p < 0.0001) and CNR (p < 0.0001) compared to ASIR in untreated and treated patients. Subjective assessment revealed that in untreated patients, MBIR improved noise reduction, artefacts, vessel sharpness and overall quality relative to ASIR (p < 0.0001). In the treated groups, noise and vessel sharpness were improved (p < 0.0001) with no change in artefacts on images reconstructed with MBIR compared to ASIR.

CONCLUSION

MBIR significantly improves noise, SNR, CNR and vessel sharpness in untreated and treated patients with intracranial aneurysms. MBIR does not reduce artefacts generated by metallic devices following intracranial aneurysm treatment.

Could new reconstruction CT techniques challenge MRI for the detection of brain metastases in the context of initial lung cancer staging?

OBJECTIVES

To evaluate the diagnostic performance of brain CT images reconstructed with a model-based iterative algorithm performed at usual and reduced dose.

METHODS

115 patients with histologically proven lung cancer were prospectively included over 15 months. Patients underwent two CT acquisitions at the initial staging, performed on a 256-slice MDCT, at standard (CTDIvol: 41.4 mGy) and half dose (CTDIvol: 20.7 mGy). Both image datasets were reconstructed with filtered back projection (FBP) and iterative model-based reconstruction (IMR) algorithms. Brain MRI was considered as the reference. Two blinded independent readers analysed the images.

RESULTS

Ninety-three patients underwent all examinations. At the standard dose, eight patients presented 17 and 15 lesions on IMR and FBP CT images, respectively. At half-dose, seven patients presented 15 and 13 lesions on IMR and FBP CT images, respectively. The test could not highlight any significant difference between the standard dose IMR and the half-dose FBP techniques (p-value = 0.12). MRI showed 46 metastases on 11 patients. Specificity, negative and positive predictive values were calculated (98.9-100 %, 93.6-94.6 %, 75-100 %, respectively, for all CT techniques).

CONCLUSION

No significant difference could be demonstrated between the two CT reconstruction techniques.

KEY POINTS

• No significant difference between IMR100 and FBP50 was shown. • Compared to FBP, IMR increased the image quality without diagnostic impairment. • A 50 % dose reduction combined with IMR reconstructions could be achieved. • Brain MRI remains the best tool in lung cancer staging.

The Acceptability of Iterative Reconstruction Algorithms in Head CT: An Assessment of Sinogram Affirmed Iterative Reconstruction (SAFIRE) vs. Filtered Back Projection (FBP) Using Phantoms

BACKGROUND

Computed tomography (CT) is the primary imaging investigation for many neurologic conditions with a proportion of patients incurring cumulative doses. Iterative reconstruction (IR) allows dose optimization, but head CT presents unique image quality complexities and may lead to strong reader preferences.

OBJECTIVES

This study evaluates the relationships between image quality metrics, image texture, and applied radiation dose within the context of IR head CT protocol optimization in the simulated patient setting. A secondary objective was to determine the influence of optimized protocols on diagnostic confidence using a custom phantom.

METHODS AND SETTING

A three-phase phantom study was performed to characterize reconstruction methods at the local reference standard and a range of exposures. CT numbers and pixel noise were quantified supplemented by noise uniformity, noise power spectrum, contrast-to-noise ratio (CNR), high- and low-contrast resolution. Reviewers scored optimized protocol images based on established reporting criteria.

RESULTS

Increasing strengths of IR resulted in lower pixel noise, lower noise variance, and increased CNR. At the reference standard, the image noise was reduced by 1.5 standard deviation and CNR increased by 2.0. Image quality was maintained at ≤24% relative dose reduction. With the exception of image sharpness, there were no significant differences between grading for IR and filtered back projection reconstructions.

CONCLUSIONS

IR has the potential to influence pixel noise, CNR, and noise variance (image texture); however, systematically optimized IR protocols can maintain the image quality of filtered back projection. This work has guided local application and acceptance of lower dose head CT protocols.

Diagnostic accuracy of contemporary multidetector computed tomography (MDCT) for the detection of lumbar disc herniation

OBJECTIVES

To evaluate the diagnostic accuracy of multidetector CT (MDCT) for detection of lumbar disc herniation with MRI as standard of reference.

METHODS

Patients with low back pain underwent indicated MDCT (128-row MDCT, helical pitch), 60 patients with iterative reconstruction (IR) and 67 patients with filtered back projection (FBP). Lumbar spine MRI (1.5 T) was performed within 1 month. Signal-to-noise ratios (SNR) of cerebrospinal fluid (CSF), annulus fibrosus (AF) and the spinal cord (SC) were determined for all modalities. Two readers independently rated image quality (IQ), diagnostic confidence and accuracy in the diagnosis of lumbar disc herniation using MRI as standard of reference. Inter-reader correlation was assessed with weighted κ.

RESULTS

Sensitivity, specificity, precision and accuracy of MDCT for disc protrusion were 98.8%, 96.5%, 97.1%, 97.8% (disc level), 97.7%, 92.9%, 98.6%, 96.9% (patient level). SNR of IR was significantly higher than FBP. IQ was significantly better in IR owing to visually reduced noise and improved delineation of the discs. κ (>0.90) was excellent for both algorithms.

CONCLUSION

MDCT of the lumbar spine yields high diagnostic accuracy for detection of lumbar disc herniation. IR improves image quality so that the provided diagnostic accuracy is principally equivalent to MRI.

KEY POINTS

• MDCT is an accurate alternative to MRI in disc herniation diagnosis. • By IR enhanced image quality improves MDCT diagnostic confidence similar to MRI. • Advances in CT technology contribute to improved diagnostic performance in lumbar spine imaging.

Image Quality Required for the Diagnosis of Skull Fractures Using Head CT: A Comparison of Conventional and Improved Reconstruction Kernels

BACKGROUND AND PURPOSE

Although skull fractures are generally assessed on bone images obtained by using head CT, the combined multikernel technique that enables evaluation of both brain and bone through a change in the window settings of an image set has been reported. The purpose of this retrospective study was to determine the image quality required for the accurate assessment of skull fractures by using head CT.

MATERIALS AND METHODS

A random sample of 50 patients (25 nonfracture and 25 simple nondisplaced skull fractures) was selected, and sets of conventional brain and bone images and improved combined multikernel images were reconstructed (4614 images). Three radiologists indicated their confidence levels regarding the presence of skull fractures by marking on a continuous scale for each image set. The mean area under the receiver operating characteristic curve was calculated for each kernel, and the statistical significance of differences was tested by using the Dorfman-Berbaum-Metz method.

RESULTS

Although a difference in the diagnostic performance of the 3 radiologists was suggested, the mean area under the curve value showed no significant differences among the 3 reconstruction kernels (P = .95 [bone versus combined]), P = .91 [bone versus brain]), and P = .88 [brain versus combined]). However, the quality of brain images was distinctly poorer than the quality of the other 2 images.

CONCLUSIONS

There was no significant difference in the diagnostic performance of brain, bone, and combined multikernel images for skull fractures. Skull fracture diagnosis is made possible by brain image assessments. Combined multikernel images offer the advantage of high-quality brain and bone images.

Intra-individual diagnostic image quality and organ-specific-radiation dose comparison between spiral cCT with iterative image reconstruction and z-axis automated tube current modulation and sequential cCT

•

Superiority of spiral versus sequential cCT in image quality and organ-specific-radiation dose.

•

Spiral cCT: lower organ-specific-radiation-dose in eye lense compared to tilted sequential cCT.

•

State-of-the-art IR spiral cCT techniques has significant advantages over sequential cCT techniques.

Objectives

To prospectively evaluate image quality and organ-specific-radiation dose of spiral cranial CT (cCT) combined with automated tube current modulation (ATCM) and iterative image reconstruction (IR) in comparison to sequential tilted cCT reconstructed with filtered back projection (FBP) without ATCM.

Methods

31 patients with a previous performed tilted non-contrast enhanced sequential cCT aquisition on a 4-slice CT system with only FBP reconstruction and no ATCM were prospectively enrolled in this study for a clinical indicated cCT scan. All spiral cCT examinations were performed on a 3rd generation dual-source CT system using ATCM in z-axis direction. Images were reconstructed using both, FBP and IR (level 1–5). A Monte-Carlo-simulation-based analysis was used to compare organ-specific-radiation dose. Subjective image quality for various anatomic structures was evaluated using a 4-point Likert-scale and objective image quality was evaluated by comparing signal-to-noise ratios (SNR).

Results

Spiral cCT led to a significantly lower (p < 0.05) organ-specific-radiation dose in all targets including eye lense. Subjective image quality of spiral cCT datasets with an IR reconstruction level 5 was rated significantly higher compared to the sequential cCT acquisitions (p < 0.0001). Consecutive mean SNR was significantly higher in all spiral datasets (FBP, IR 1–5) when compared to sequential cCT with a mean SNR improvement of 44.77% (p < 0.0001).

Conclusions

Spiral cCT combined with ATCM and IR allows for significant-radiation dose reduction including a reduce eye lens organ-dose when compared to a tilted sequential cCT while improving subjective and objective image quality.

Submillisievert CT using model-based iterative reconstruction with lung-specific setting: An initial phantom study

OBJECTIVE

To assess image quality of filtered back-projection (FBP) and model-based iterative reconstruction (MBIR) with a conventional setting and a new lung-specific setting on submillisievert CT.

METHODS

A lung phantom with artificial nodules was scanned with 10 mA at 120 kVp and 80 kVp (0.14 mSv and 0.05 mSv, respectively); images were reconstructed using FBP and MBIR with conventional setting (MBIR_Stnd) and lung-specific settings (MBIR_RP20/Tx and MBIR_RP20). Three observers subjectively scored overall image quality and image findings on a 5-point scale (1 = worst, 5 = best) compared with reference standard images (50 mA-FBP at 120, 100, 80 kVp). Image noise was measured objectively.

RESULTS

MBIR_RP20/Tx performed significantly better than MBIR_Stnd for overall image quality in 80-kVp images (p < 0.01), blurring of the border between lung and chest wall in 120p-kVp images (p < 0.05) and the ventral area of 80-kVp images (p < 0.001), and clarity of small vessels in the ventral area of 80-kVp images (p = 0.037). At 120 kVp, 10 mA-MBIR_RP20 and 10 mA-MBIR_RP20/Tx showed similar performance to 50 mA-FBP. MBIR_Stnd was better for noise reduction. Except for blurring in 120 kVp-MBIR_Stnd, MBIRs performed better than FBP.

CONCLUSION

Although a conventional setting was advantageous in noise reduction, a lung-specific setting can provide more appropriate image quality, even on submillisievert CT.

KEY POINTS

• Lung-specific submillisievert 10 mA-MBIR CT setting has similar performance to 50 mA-FBP • The new lung-specific settings improve vessel clarity and blurring of borders • The new settings may provide more appropriate images than conventional settings.

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.

CT radiation dose and iterative reconstruction techniques

1. CT radiation dose optimization is one of the major concerns for the scientific community. 2. CT image quality is dependent on the selected image reconstruction algorithm. 3. Iterative reconstruction algorithms have reemerged with the potential of radiation dose optimization by lowering image noise. 4. Tube current is the most common parameter used to reduce radiation dose along with iterative reconstruction. 5. Tube potential (kV) is also used for dose optimization with iterative reconstruction in CT angiography protocols and small patients.