Unbiased zero-count correction method in low-dose high-resolution photon counting detector CT

OBJECTIVE

To address the zero-count problem in low-dose, high-spatial-resolution photon counting detector CT (PCD-CT) without introducing statistical biases and without degrading spatial resolution.

Approach: The classical approach to generate the sinogram projection data for estimating the line integrals of the linear attenuation coefficients of the image object is to take a log transform of detector counts, which requires zero counts to be replaced by positive numbers. Both the log transform and the zero-count replacement introduce biases. After analyzing the statistical properties of the zero-count replaced pre-log and post-log data, a formula for the statistical sinogram bias was derived, based on which a new sinogram estimator was empirically constructed to cancel the statistical biases. Dose- and object-independent free parameters in the proposed estimator were learned from simulated data, and then the estimator was applied to experimental low-dose PCD-CT data of physical phantoms for validation and generalizability testing. Both bias and noise performances of the proposed method were evaluated and compared with those of previous zero-count correction methods, including zero-weighting, zero-replacement, and adaptive filtration-based methods. The impact of these correction methods on spatial resolution was also quantified using line-pair patterns. 

Main Results: For all objects and reduced-dose levels, the proposed method reduces the statistical CT number biases to be within $\pm10$ HU, which is significantly lower than the biases given by the classical zero-count correction methods. The Bland-Altman analysis demonstrated that the proposed led to negligible sinogram biases at all attenuation levels, whereas the other correction methods did not. Additionally, the proposed method was found to have no discernible impact on image noise and spatial resolution.

Significance: The proposed zero-count correction scheme allows the CT numbers of low-dose, high-spatial-resolution PCD-CT images to match those of standard-dose and standard-resolution PCD-CT images.&#xD.

Hounsfield Units measured in low dose CT reliably assess vertebral trabecular bone density changes over two years in axial spondyloarthritis

OBJECTIVES

To describe low dose Computed Tomography (ldCT) Hounsfield Units (HU) two-year change-from-baseline values (expressing trabecular bone density changes) and analyse their inter-reader reliability per vertebra in radiographic axial spondyloarthritis (r-axSpA).

METHODS

We used 49 patients with r-axSpA from the multicentre two-year Sensitive Imaging in Ankylosing Spondylitis (SIAS) study. LdCT HU were independently measured by two trained readers at baseline and two years. Mean (standard deviation, SD) for the change-from-baseline HU values were provided per vertebra by reader. Intraclass correlation coefficients (ICC; absolute agreement, two-way random effect), Bland-Altman plots and smallest detectable change (SDC) were obtained. Percentages of vertebrae in which readers agreed on the direction of change and on change >|SDC| were computed.

RESULTS

Overall, 1,053 (98% of all possible) vertebrae were assessed by each reader both at baseline and two years. Over two years, HU mean change values varied from -23 to 28 and 29 for reader 1 and 2, respectively. Inter-reader reliability of the two-year change-from-baseline values per vertebra was excellent: ICC:0.91-0.99; SDC:6-10; Bland-Altman plots were homoscedastic, with negligible systematic error between readers. Readers agreed on the direction of change in 88-96% and on change >|SDC| in 58-94% of vertebrae, per vertebral level, from C3 to L5. Overall, similar results were obtained across all vertebrae.

CONCLUSION

LdCT measurement of HU is a reliable method to assess two-year changes in trabecular bone density at each vertebra from C3-L5. Being reliable across all vertebrae, this methodology can aid the study of trabecular bone density changes over time in r-axSpA, a disease affecting the whole spine.

CT imaging of esophageal foreign bodies in children: a pictorial essay

Foreign body (FB) ingestion is common in children, particularly from 6 months to 3 years of age. As young children may be unable to provide a clinical history and the ingestion is often unwitnessed, imaging plays an important role in diagnosis, predicting outcomes and detecting complications that require surgical intervention. Since 2015, our institution's diagnostic algorithm for suspected airway foreign bodies has included a noncontrast airway FB CT (FB-CT) with the z-axis coverage spanning from the larynx to the proximal segmental bronchi of the lower lung zones. The effective dose of radiation from this FB-CT airway protocol is typically less than 1 mSv, compared to an effective dose of just under 1 mSv to up to 3 mSv for a fluoroscopic esophagram in children under 10 years of age and 1-3 mSv for a routine pediatric CT chest. In using the FB-CT airway protocol at our institution, we observed that esophageal rather than airway FBs were sometimes encountered on these exams. However, the confidence among radiologists for definitively diagnosing an esophageal foreign body on noncontrast CT was variable. Consequently, we created a teaching module of positive cases for our group of 21 pediatric body radiologists to increase their diagnostic confidence. This pictorial essay illustrates our institutional experience and can help others to confidently diagnose esophageal foreign bodies using a dedicated CT foreign body imaging protocol. At a similar radiation dose to a fluoroscopic esophagram, CT provides the additional advantage of an expedited diagnosis without the need for a radiologist on site.

Strategies to Optimize Nephrolithiasis Emergency Care (STONE): Prospective Evaluation of an Emergency Department Clinical Pathway

OBJECTIVE

To convene a multi-disciplinary panel to develop a pathway for Emergency Department (ED) patients with suspected nephrolithiasis and then prospectively evaluate its effect on patient care.

MATERIALS AND METHODS

The STONE Pathway was developed and linked to order sets within our Electronic Health Record in April 2019. Records were prospectively reviewed for ED patients who underwent ultrasound or Computerized Tomography (CT) to evaluate suspected nephrolithiasis between January 2019 and August 2019 within our institution. The primary outcome measure was the proportion of patients whose ED CT was low dose (<4 mSv). Secondary outcome measures included receipt of pathway-concordant pain medications and urine strainers. Order set utilization was evaluated as a process measure. Balance measures assessed included repeat ED visits, imaging, hospitalizations, and a urologic clinic visit or surgery within 30 days of discharge.

RESULTS

441 patients underwent ED imaging, of whom 261 (59%) were evaluated for suspected nephrolithiasis. The STONE Pathway was used in 50 (30%) eligible patients. Patients treated with the Pathway were more likely to undergo low-dose CTs (49% vs. 23%, p<0.001), and receive guideline-concordant pain medications such as NSAIDs (90% vs. 62%, p<0.001), and were less likely to return to the ED within 30 days (13% vs. 2%, p=0.01). These measures demonstrated special cause variation following Pathway release.

CONCLUSIONS

Clinical pathways increase compliance with evidence-based practices for pain control and imaging in nephrolithiasis emergency care and may improve the delivery of value-based care.

Results of Second Round Lung Cancer Screening by Low-Dose CT scan - French Cohort Study (DEP-KP80)

INTRODUCTION

Over the last few years, lung cancer screening by low-dose CT scan has demonstrated a decrease in lung cancer mortality. While this method has been in use since 2013 in the United States of America, no European country has yet implemented a systematic screening program. We hereby report the results from the second round of screening from a French cohort study.

PATIENTS AND METHODS

DEP KP80 is a prospective study evaluating lung cancer screening by means of three low-dose computer tomography (CT) scans at 1-year intervals in 1,307 participants, aged 55 to 74 years old, all smokers or former smokers, having quit within the last 15 years, with over 30 pack years. The results of the first round demonstrated it was possible to conduct effective screening in real-life situations.

RESULTS

Participation was lower in this second round than in the first (35.3% vs. 73.1%, P < .001). The rate of negative results was significantly higher and that of undetermined results lower than those produced in the first round. Overall, 75% of cancers revealed were Stage 1 and 87.5% benefitted from surgical treatment. The incidence of cancer in the second round was 2.43%.

CONCLUSION

As with the first round, the results of this second round confirm the feasibility and efficacy of lung cancer screening. The lower participation rate for this second round is proof of the need to improve awareness among participants and healthcare professionals of the relevance of committing to an annual screening program.

Association between facet joint ankylosis and functional impairment in patients with radiographic axial spondyloarthritis

OBJECTIVES

To investigate the occurrence of facet joint ankylosis in the spine of patients with radiographic axial spondyloarthritis (r-axSpA) using low dose computed tomography (ldCT), and to examine the association between facet joint ankylosis and functional impairment.

METHODS

A group of 126 patients with r-axSpA was selected from Incheon Saint Mary's axSpA observational cohort and whole spine ldCT data were examined. Facet joint (right and left, C2-S1) ankylosis was scored from 0-46 (total). The presence of facet joint ankylosis was assessed by two readers, each blinded to the patient data. The inter-reader reliability of facet joint ankylosis scoring was assessed using intraclass correlation coefficients (ICCs). The CT Syndesmophyte Score (CTSS) was assessed. Lumbar spinal mobility was evaluated using the modified Schober test. Functional impairment was measured using the Bath AS functional index (BASFI).

RESULTS

The ICCs of ankylosed facet joint scores at the cervical, thoracic, lumbar and whole spine were 0.84, 0.88, 0.92 and 0.90, respectively. Facet joint ankylosis was most common in the thoracic spine. Scores for the whole spine correlated positively with the ASDAS, mSASSS and the syndesmophyte score. Multivariate analysis revealed that facet joint ankylosis was significantly associated with decreased lumbar motion. For both readers, the scores for the whole spine were independently associated with BASFI after adjusting for syndesmophyte score and disease activity.

CONCLUSIONS

Facet joint ankylosis in patients with r-axSpA was associated with functional impairment and spinal mobility. Facet joints should be incorporated into a structural damage assessment method.

Prediction of Coronary Calcification and Stenosis: Role of Radiomics From Low-Dose CT

RATIONALE AND OBJECTIVES

We aimed to assess relationship between single-click, whole heart radiomics from low-dose computed tomography (LDCT) for lung cancer screening with coronary artery calcification and stenosis.

MATERIALS AND METHODS

The institutional review board-approved, retrospective study included all 106 patients (68 men, 38 women, mean age 64 ± 7 years) who underwent both LDCT for lung cancer screening and had calcium scoring and coronary computed tomography angiography in our institution. We recorded the clinical variables including patients' demographics, smoking history, family history, and lipid profiles. Coronary calcium scores and grading of coronary stenosis were recorded from the radiology information system. We calculated the multiethnic scores for atherosclerosis risk scores to obtain 10-year coronary heart disease (MESA 10-Y CHD) risk of cardiovascular disease for all patients. Deidentified LDCT exams were exported to a Radiomics prototype for automatic heart segmentation, and derivation of radiomics. Data were analyzed using multiple logistic regression and kernel Fisher discriminant analyses.

RESULTS

Whole heart radiomics were better than the clinical variables for differentiating subjects with different Agatston scores (≤400 and >400) (area under the curve [AUC] 0.92 vs 0.69). Prediction of coronary stenosis and MESA 10-Y CHD risk was better on whole heart radiomics (AUC:0.86-0.87) than with clinical variables (AUC:0.69-0.79). Addition of clinical variables or visual assessment of coronary calcification from LDCT to whole heart radiomics resulted in a modest change in the AUC.

CONCLUSION

Single-click, whole heart radiomics obtained from LDCT for lung cancer screening can differentiate patients with different Agatston and MESA risk scores for cardiovascular diseases.

Feasibility study of ultra-low-dose dedicated maxillofacial computed tomography using filter-based spectral shaping in patients with craniofacial trauma: assessment of image quality and radiation dose

Background

In the setting of multiple trauma, radiation exposure is considered a relevant issue because patients may require repeated imaging to evaluate injuries in different body parts. Recently, spectral shaping of the X-ray beam has been shown to be beneficial in reducing radiation exposure. We investigated the clinical feasibility of a tin-filtered 100 kV protocol for the diagnostic use, compared to routine dedicated maxillofacial CT at 120 kVp in patients with craniofacial trauma; we assessed the image quality, radiation dose, and interobserver agreement.

Methods

We retrospectively evaluated 100 consecutive patients who underwent dedicated maxillofacial CT for craniofacial trauma. Fifty patients were examined with a tin-filtered 100 kV protocol performed using a third-generation dual source CT. The other 50 patients were examined with a standard protocol on a different scanner. Two readers independently evaluated image quality subjectively and objectively, and the interobserver agreement was also assessed. CT dose index volume (CTDI_vol) and dose-length product (DLP) were recorded to compare radiation exposure. A quality-control phantom was also scanned to prospectively assess the impact of tin filtration.

Results

All CT scans showed diagnostic image quality for evaluating craniofacial fractures. The tin-filtered 100 kV protocol showed sufficient-to-good image quality for diagnostic use; however, overall image quality and anatomic delineation from the tin-filtered 100 kV protocol were significantly lower than from the standard protocol. Interobserver agreement was moderate to almost perfect (k=0.56-0.85). Image noises in the air, eye globe, and retrobulbar fat were comparable between the two protocols (P>0.05), whereas both signal-to-noise ratio and contrast-to-noise ratio in the eye globe and retrobulbar fat showed a significant difference (P<0.05). The tin-filtered 100 kV protocol showed a significant reduction in radiation dose compared to the standard protocol: CTDI_vol, 3.33 vs. 30.5 mGy (P<0.001); and DLP, 70.70 vs. 669.43 mGy*cm (P<0.001). The phantom study also demonstrated a lower radiation dose for the tin-filter 100 kV protocol compared to the standard protocol.

Conclusions

Dedicated maxillofacial CT using spectral shaping with tin filtration can allow a significant reduction in radiation dose while maintaining sufficient diagnostic image quality, when compared to the standard protocol.

Improving Utilization of Lung Cancer Screening Through Incorporating a Video-Based Educational Tool Into Smoking Cessation Counseling

BACKGROUND

Lung cancer screening (LCS) with low-dose computed tomography (LDCT) reduces lung cancer mortality in high-risk patients, but most of those eligible are not referred for screening, and most eligible smokers are not aware of LCS. Smoking cessation counseling may be an opportune time to educate smokers about LCS. Here we investigate the effect of LCS educational information on LDCT utilization and smoking cessation in LCS-eligible patients receiving smoking cessation counseling.

PATIENTS AND METHODS

We randomized 1281 smokers aged 55-80 who underwent smoking cessation services to view a web-based educational video about LCS (n = 1026) or to receive usual care (n = 255). Outcomes included the utilization of chest computed tomographic (CT) scan during 6 months of follow-up, responses to survey questions, and patient-reported abstinence from smoking at 6 months.

RESULTS

One hundred forty-six participants (14%) watched the video. Overall, 87 participants (8.5%) in the intervention group underwent any chest CT and 37 (3.6%) underwent LDCT compared to 22 (8.6%) and 11 (4.3%) in the control group during the 6-month follow-up period (P = .94 and .59, respectively). Among participants who completed watching the video, 27 (18.5%) underwent any chest CT and 13 (8.9%) underwent LDCT, compared to 22 (8.6%) and 11 (4.3%) in controls during follow-up (P = .0037 and .062, respectively). There was no difference in abstinence from smoking between groups.

CONCLUSION

An LCS educational intervention may be effective in improving utilization of LDCT in eligible individuals who currently smoke at the time of smoking cessation counseling. Further research on the effect of LCS education in the context of smoking cessation counseling is needed.

X-ray induced acoustic computed tomography

X-ray imaging has proved invaluable in medical diagnoses and non-destructive testing (NDT) in the past century. However, there remain two major limitations: radiation harm and inaccessibility to the sample. A recent imaging modality, X-ray induced acoustic computed tomography (XACT), allows a novel solution. In XACT, x-ray induced excitation causes localized heating (<mK) and thermoelastic expansion. This induces a detectable ultrasonic emission, thereby enabling imaging. XACT has the potential to enable low-dose, fast, 3D imaging requiring only single side access. We discuss the fundamentals of XACT and summarize milestones in its evolution over the past several years since its first demonstration using a Medical Linear Accelerator. We highlight XACT's potential applications in biomedical imaging and NDT, and discuss the latest advanced concepts and future directions.

Baseline Results of the West London lung cancer screening pilot study - Impact of mobile scanners and dual risk model utilisation

OBJECTIVES

The West London lung screening pilot aimed to identify early-stage lung cancer by targeting low-dose CT (LDCT) to high risk participants. Successful implementation of screening requires maximising participant uptake and identifying those at highest risk. As well as reporting pre-specified baseline screening metrics, additional objectives were to 1) compare participant uptake between a mobile and hospital-based CT scanner and 2) evaluate the impact on cancer detection using two lung cancer risk models.

METHODS

From primary care records, ever-smokers aged 60-75 were invited to a lung health check at a hospital or mobile site. Participants with PLCO_M2012 6-yr risk ≥1.51 % and/or LLP_v2 5-yr risk ≥2.0 % were offered a LDCT. Lung cancer detection rate, stage, and recall rates are reported. Participant uptake was compared at both sites (chi-squared test). LDCT eligibility and cancer detection rate were compared between those recruited under each risk model.

RESULTS

Of 8366 potential participants invited, 1047/5135 (20.4 %) invitees responded to an invitation to the hospital site, and 702/3231 (21.7 %) to the mobile site (p = 0.14). The median distance travelled to the hospital site was less than to the mobile site (3.3 km vs 6.4 km, p < 0.01). Of 1159 participants eligible for a scan, 451/1159 (38.9 %) had a LLP_v2 ≥2.0 % only, 71/1159 (6.1 %) had a PLCO_M2012 ≥1.5 % only; 637/1159 (55.0 %) met both risk thresholds. Recall rate was 15.9 %. Lung cancer was detected in 29/1145 (2.5 %) participants scanned (stage 1, 58.6 %); 5/29 participants with lung cancer did not meet a PLCO_M2012 threshold of ≥1.51 %; all had a LLP_v2 ≥2.0 %.

CONCLUSION

Targeted screening is effective in detecting early-stage lung cancer. Similar levels of participant uptake at a mobile and fixed site scanner were demonstrated, indicating that uptake was driven by factors in addition to scanner location. The LLP_v2 model was more permissive; recruitment with PLCO_M2012 alone would have missed several cancers.

Investigation of Low-Dose CT Image Denoising Using Unpaired Deep Learning Methods

Low-dose computed tomography (LDCT) is desired due to prevalence and ionizing radiation of CT, but suffers elevated noise. To improve LDCT image quality, an image-domain denoising method based on cycle-consistent generative adversarial network ("CycleGAN") is developed and compared with two other variants, IdentityGAN and GAN-CIRCLE. Different from supervised deep learning methods, these unpaired methods can effectively learn image translation from the low-dose domain to the full-dose (FD) domain without the need of aligning FDCT and LDCT images. The results on real and synthetic patient CT data show that these methods can achieve peak signal-to-noise ratio (PSNR) and structural similarity index (SSIM) comparable to, if not better than, the other state-of-the-art denoising methods. Among CycleGAN, IdentityGAN, and GAN-CIRCLE, the later achieves the best denoising performance with the shortest computation time. Subsequently, GAN-CIRCLE is used to demonstrate that the increasing number of training patches and of training patients can improve denoising performance. Finally, two non-overlapping experiments, i.e. no counterparts of FDCT and LDCT images in the training data, further demonstrate the effectiveness of unpaired learning methods. This work paves the way for applying unpaired deep learning methods to enhance LDCT images without requiring aligned full-dose and low-dose images from the same patient.

Two stage residual CNN for texture denoising and structure enhancement on low dose CT image

BACKGROUND AND OBJECTIVE

X-ray computed tomography (CT) plays an important role in modern medical science. Human health problems caused by CT radiation have attracted the attention of the academic community widely. Reducing radiation dose results in a deterioration in image quality and further affects doctor's diagnosis. Therefore, this paper introduces a new denoise method for low dose CT (LDCT) images, called two stage residual convolutional neural network (TS-RCNN).

METHODS

There are two important parts with respect to our network. 1) The first stage RCNN is proposed for texture denoising via the stationary wavelet transform (SWT) and the perceptual loss. Specifically, SWT is performed on each normal dose CT (NDCT) image and generated four wavelet images are considered as the labels. 2) The second stage RCNN is established for structure enhancement via the average NDCT model on the basis of the first network's result. Finally, the denoised CT image is obtained via inverse SWT.

RESULTS

Our proposed TS-RCNN is trained on three groups of simulated LDCT images in 1123 images per group and evaluated on 129 simulated LDCT images for each group. Besides, to demonstrate the clinical application of TS-RCNN, we also test our method on the 2016 Low Dose CT Grand Challenge dataset. Quantitative results show that TS-RCNN almost achieves the best results in terms of MSE, SSIM and PSNR compared to other methods.

CONCLUSIONS

The experimental results and comparisons demonstrate that TS-RCNN not only preserves more texture information, but also enhances structural information on LDCT images.

Computerized identification of the vasculature surrounding a pulmonary nodule

OBJECTIVES

The idea of inferring the prognosis of lung tumor via its surrounding vasculature is novel, but not supported by available technology. In this study, we described and validated a computerized method to identify the vasculature surrounding a pulmonary nodule depicted on low-dose computed tomography (LDCT).

MATERIALS AND METHODS

The proposed computerized scheme identified the vessels surrounding a lung nodule by using novel computational geometric solutions and quantified them by decomposing the vessels into independent vessel branches. We validated this scheme by testing it on a dataset consisting of 100 chest CT examinations, with 50-paired benign and malignant nodules. Two experienced pulmonologists were asked to measure the vessel branches associated with a nodule under the aid of a visualization tool. We used the Bland-Altman plots and the concordance correlation coefficient (CCC) to assess the agreement between the results of the computer algorithm and two experienced pulmonologists.

RESULTS

Bland-Altman different analysis demonstrated a mean bias of 0.61 ± 4.17 in terms of vessel branches between the computer results and the human experts, while the inter-rater mean bias was -0.61 ± 1.60. The CCC-based agreements between the computer and the two raters were 0.90 / 0.86, 0.79 / 0.83 for benign and malignant nodules, respectively.

CONCLUSION

The small width of the limits of agreement between the computer algorithm and the human experts suggests that the results from the computer and the pulmonologist experts were relatively consistent, namely the computerized scheme is capable of reliably identifying the vasculature surrounding a nodule.

Noise insertion in CT for cocaine body packing: where is the limit of extensive dose reduction?

Background

To evaluate the detection rate and image quality in CT-body-packer-screening at different radiation-dose levels and to determine a dose threshold that enables a reliable detection of incorporated body packs and incidental findings with a maximum of dose saving.

Materials and methods

We retrospectively included 27 individuals who underwent an abdominal CT with automated exposure control due to suspected body packing. CT images were reconstructed at different radiation-dose levels of 50%, 10, 5% and 1% using iterative reconstructions. All 135 CT reconstructions were evaluated by three independent readers. Reviewers determined the presence of foreign bodies and evaluated the image quality using a 5-point ranking scale. In addition, visualization of incidental findings was assessed.

Results

A threshold of 5% (effective dose 0.11 ± 0.07 mSv) was necessary to correctly identify all 27 patients with suspected body packing. Extensive noise insertion to a dose level of 1% (0.02 ± 0.01 mSV) led to false-positive solid cocaine findings in three patients. Image quality was comparable between 100 and 50%. The threshold for correct identification of incidental findings was 10% of the initial dose (effective dose 0.21 ± 0.13 mSv).

Conclusions

Our results indicate that dose of abdominal CT for the detection of intracorporeal cocaine body packets can be markedly reduced to up to 5% of the initial dose while still providing sufficient image quality to detect ingested body packets. However, a minimum effective dose of 0.21 mSv (10% of initial dose) seems to be required to properly identify incidental findings.

Sociocultural Barriers to Lung Cancer Screening Among Korean Immigrant Men

Lung cancer is a commonly occurring cancer among Korean American men. Korean Americans have lower rates of cancer screening participation than other Asian American sub-groups. However, little is known about factors that influence the cancer screening behavior of Korean immigrants. The purpose of this study was to explore facilitators of and barriers to lung cancer screening (i.e., low dose CT of the chest) among Korean immigrant men, using qualitative individual interviews and focus groups. A convenience sample of 24 Korean men who were immigrants, Washington State residents, able to speak Korean, aged 55-79, and eligible for lung cancer screening (based on current guidelines) were recruited from Korean churches and senior centers. Five focus groups (that included between two and five men) and nine individual interviews were conducted. Content analysis was used to analyze the qualitative data. Facilitators of lung cancer screening included perceptions about positive aspects of the health care system in South Korea, recommendations from others (physicians, family members, and community organizations), existing health problems and respiratory symptoms, interest in health, and the health consequences of aging. Barriers included costs of health care in the US, lack of time, lack of knowledge (about lung cancer and screening), attitudes about prevention, and lack of physician recommendation. This study adds new knowledge to a field where little information is available. It also lays the groundwork for developing culturally relevant lung cancer screening interventions for Korean Americans and the health care providers who serve them.

Structurally-sensitive Multi-scale Deep Neural Network for Low-Dose CT Denoising

Computed tomography (CT) is a popular medical imaging modality and enjoys wide clinical applications. At the same time, the x-ray radiation dose associated with CT scannings raises a public concern due to its potential risks to the patients. Over the past years, major efforts have been dedicated to the development of Low-Dose CT (LDCT) methods. However, the radiation dose reduction compromises the signal-to-noise ratio (SNR), leading to strong noise and artifacts that downgrade CT image quality. In this paper, we propose a novel 3D noise reduction method, called Structurally-sensitive Multi-scale Generative Adversarial Net (SMGAN), to improve the LDCT image quality. Specifically, we incorporate three-dimensional (3D) volumetric information to improve the image quality. Also, different loss functions for training denoising models are investigated. Experiments show that the proposed method can effectively preserve structural and textural information in reference to normal-dose CT (NDCT) images, and significantly suppress noise and artifacts. Qualitative visual assessments by three experienced radiologists demonstrate that the proposed method retrieves more information, and outperforms competing methods.

Vasculature surrounding a nodule: A novel lung cancer biomarker

PURPOSE

To investigate whether the vessels surrounding a nodule depicted on non-contrast, low-dose computed tomography (LDCT) can discriminate benign and malignant screen detected nodules.

MATERIALS AND METHODS

We collected a dataset consisting of LDCT scans acquired on 100 subjects from the Pittsburgh Lung Screening study (PLuSS). Fifty subjects were diagnosed with lung cancer and 50 subjects had suspicious nodules later proven benign. For the lung cancer cases, the location of the malignant nodule in the LDCT scans was known; while for the benign cases, the largest nodule in the LDCT scan was used in the analysis. A computer algorithm was developed to identify surrounding vessels and quantify the number and volume of vessels that were connected or near the nodule. A nonparametric receiver operating characteristic (ROC) analysis was performed based on a single nodule per subject to assess the discriminability of the surrounding vessels to provide a lung cancer diagnosis. Odds ratio (OR) were computed to determine the probability of a nodule being lung cancer based on the vessel features.

RESULTS

The areas under the ROC curves (AUCs) for vessel count and vessel volume were 0.722 (95% CI=0.616-0.811, p<0.01) and 0.676 (95% CI=0.565-0.772), respectively. The number of vessels attached to a nodule was significantly higher in the lung cancer group 9.7 (±9.6) compared to the non-lung cancer group 4.0 (±4.3) CONCLUSION: Our preliminary results showed that malignant nodules are often surrounded by more vessels compared to benign nodules, suggesting that the surrounding vessel characteristics could serve as lung cancer biomarker for indeterminate nodules detected during LDCT lung cancer screening using only the information collected during the initial visit.

Influence of dose reduction and iterative reconstruction on CT calcium scores: a multi-manufacturer dynamic phantom study

To evaluate the influence of dose reduction in combination with iterative reconstruction (IR) on coronary calcium scores (CCS) in a dynamic phantom on state-of-the-art CT systems from different manufacturers. Calcified inserts in an anthropomorphic chest phantom were translated at 20 mm/s corresponding to heart rates between 60 and 75 bpm. The inserts were scanned five times with routinely used CCS protocols at reference dose and 40 and 80% dose reduction on four high-end CT systems. Filtered back projection (FBP) and increasing levels of IR were applied. Noise levels were determined. CCS, quantified as Agatston and mass scores, were compared to physical mass and scores at FBP reference dose. For the reference dose in combination with FBP, noise level variation between CT systems was less than 18%. Decreasing dose almost always resulted in increased CCS, while at increased levels of IR, CCS decreased again. The influence of IR on CCS was smaller than the influence of dose reduction. At reference dose, physical mass was underestimated 3–30%. All CT systems showed similar CCS at 40% dose reduction in combinations with specific reconstructions. For some CT systems CCS was not affected at 80% dose reduction, in combination with IR. This multivendor study showed that radiation dose reductions of 40% did not influence CCS in a dynamic phantom using state-of-the-art CT systems in combination with specific reconstruction settings. Dose reduction resulted in increased noise and consequently increased CCS, whereas increased IR resulted in decreased CCS.

[Early recognition of lung cancer in workers occupationally exposed to asbestos]

Despite the fact that working with asbestos and placing it on the market have been banned in Germany since 1993 according to the Ordinance on Hazardous Substances, asbestos-related diseases of the lungs and pleura are still the leading cause of death in occupational diseases. The maximum industrial usage of asbestos was reached in former West Germany in the late 1970s and in former East Germany the late 1980s. Occupational diseases, mainly mesotheliomas and lung cancer emerging now are thus caused by asbestos exposure which occurred 30-40 years earlier. It is known that the combination of smoking and asbestos exposure results in a superadditive increase in the risk to develop lung cancer. No suitable screening methods for early detection of malignant mesothelioma are currently available and the therapeutic options are still very limited; however, the national lung screening trial (NLST) has shown for the first time that by employing low-dose computed tomography (LDCT) in heavy smokers, lung cancer mortality can be significantly reduced. According to current knowledge the resulting survival benefits far outweigh the potential risks involved in the diagnostic work-up of suspicious lesions. These results in association with the recommendations of international medical societies and organizations were pivotal as the German statutory accident insurance (DGUV) decided to provide LDCT as a special occupational medical examination for workers previously exposed to asbestos and with a particularly high risk for developing lung cancer.

[Diagnostic work-up of pulmonary nodules : Management of pulmonary nodules detected with low‑dose CT screening]

Pulmonary nodules are the most frequent pathological finding in low-dose computed tomography (CT) scanning for early detection of lung cancer. Early stages of lung cancer are often manifested as pulmonary nodules; however, the very commonly occurring small nodules are predominantly benign. These benign nodules are responsible for the high percentage of false positive test results in screening studies. Appropriate diagnostic algorithms are necessary to reduce false positive screening results and to improve the specificity of lung cancer screening. Such algorithms are based on some of the basic principles comprehensively described in this article. Firstly, the diameter of nodules allows a differentiation between large (>8 mm) probably malignant and small (<8 mm) probably benign nodules. Secondly, some morphological features of pulmonary nodules in CT can prove their benign nature. Thirdly, growth of small nodules is the best non-invasive predictor of malignancy and is utilized as a trigger for further diagnostic work-up. Non-invasive testing using positron emission tomography (PET) and contrast enhancement as well as invasive diagnostic tests (e.g. various procedures for cytological and histological diagnostics) are briefly described in this article. Different nodule morphology using CT (e.g. solid and semisolid nodules) is associated with different biological behavior and different algorithms for follow-up are required. Currently, no obligatory algorithm is available in German-speaking countries for the management of pulmonary nodules, which reflects the current state of knowledge. The main features of some international and American recommendations are briefly presented in this article from which conclusions for the daily clinical use are derived.

One-mSv CT colonography: Effect of different iterative reconstruction algorithms on radiologists' performance

PURPOSE

To analyze the effect of different reconstruction algorithms on image noise and radiologists' performance at ultra-low dose CT colonography (CTC) in human subjects.

MATERIALS AND METHODS

This retrospective study had institutional review board approval, with waiver of the need to obtain informed consent. CTC and subsequent colonoscopy were performed at the same day in 28 patients. CTC was scanned at the supine/prone positions using 120/100kVp and fixed 10mAs, and reconstructed using filtered back projection (FBP), adaptive statistical iterative reconstruction (ASIR), and model-based IR (Veo) algorithms. Size-specific dose estimates (SSDE) and effective radiation doses were recorded. Image noise was compared among the three datasets using repeated measures analysis of variance (ANOVA). Per-polyp sensitivity and figure-of-merits were compared among the datasets using the McNemar test and jackknife alternative free-response receiver operating characteristic (JAFROC) analysis, respectively, by one novice and one expert reviewer in CTC.

RESULTS

Mean SSDE and effective radiation dose of CTC were 1.732mGy and 1.002mSv, respectively. Mean image noise at supine/prone position datasets was significantly lowest with Veo (17.2/13.3), followed by ASIR (52.4/38.9) and FBP (69.9/50.8) (P<0.0001). Forty-two polyps in 25 patients were reference polyps. For both readers, per-polyp sensitivity of all 42 polyps was highest with Veo reconstruction (81.0%, 64.3%), followed by ASIR (73.8%, 54.8%) and FBP (57.1%, 50.0%) with statistical significance between Veo and FBP for reader 1 (P=0.002). JAFROC analysis revealed that the figure-of-merit for the detection of polyps was highest with Veo (0.917, 0.786), followed by ASIR (0.881, 0.750) and FBP (0.750, 0.746) with statistical significances between Veo or ASIR and FBP for reader 1 (P<0.05).

CONCLUSION

One-mSv CTC was not feasible using the standard FBP algorithm. However, diagnostic performance expressed as per-polyp sensitivity and figures-of-merit can be improved with the application of IR algorithms, particularly Veo.

Initial LDCT appearance of incident lung cancers in the ITALUNG trial

OBJECTIVES

To characterize early features of lung cancers detected with low-dose computed tomography (LDCT) screening.

MATERIALS AND METHODS

Two radiologists reviewed prior LDCTs in 20 incident cancers diagnosed at annual repeat screening rounds and 83 benign nodules observed in the ITALUNG trial.

RESULTS

No abnormality was observed in 3 cancers. Focal abnormalities in prior LDCT were identified in 17(85%) cancers (14 adenocarcinomas; 14 stage I). Initial abnormalities were intra-pulmonary in 10, subpleural in 4 and perifissural in 3. Average mean diameter was 9mm (range 4.5-18mm). Nine exhibited solid, 4 part-solid and 4 non-solid density. The margins were smooth and regular in 5 cases, lobulated in 6, irregular with spiculations in 3 and blurred in 3. Ten (59%) initial focal abnormalities had a round or oval nodular shape, but 7(41%) had a non-nodular complex (n=5) or "stripe-like" (n=2) shape. Bronchus sign was observed in 3 cases and association with cystic airspace in 2 cases. Non-solid density, complex or "stripe-like" shape, bronchus sign and association with cystic airspace had a specificity higher than 90%, but positive predictive value of every feature of incident lung cancers was low (range 10.4-50%).

CONCLUSIONS

The vast majority of cancers diagnosed at annual repeat show corresponding focal lung abnormalities in prior LDCTs. Perifissural location and non-nodular shape do not exclude the possibility of early lung cancer. Since specificity of the early features of incident lung cancer is incomplete and their positive predictive value is low, all focal pulmonary abnormalities detected in screened subjects should be re-evaluated in subsequent LDCTs.

CT radiation dose optimization and estimation: an update for radiologists

In keeping with the increasing utilization of CT examinations, the greater concern about radiation hazards from examinations has been addressed. In this regard, CT radiation dose optimization has been given a great deal of attention by radiologists, referring physicians, technologists, and physicists. Dose-saving strategies are continuously evolving in terms of imaging techniques as well as dose management. Consequently, regular updates of this issue are necessary especially for radiologists who play a pivotal role in this activity. This review article will provide an update on how we can optimize CT dose in order to maximize the benefit-to-risk ratio of this clinically useful diagnostic imaging method.