Ultra-low Dose CT Research Articles

Ultra-low-dose CT detects synovitis in patients with suspected rheumatoid arthritis

PurposeTo prove the feasibility and measure the diagnostic accuracy of contrast-enhanced ultra-low-dose CT (ULD-CT) for the depiction of inflammatory soft-tissue changes (synovitis, tenosynovitis and peritendonitis) in patients with arthritis of...

Ultra-low radiation dose CT angiography of the lower extremity using the iterative model reconstruction (IMR) algorithm

To investigate the image quality of lower-extremity computed tomography (CT) angiography (CTA) with ultra-low radiation dose using the iterative model reconstruction (IMR) algorithm. Lower-extremity CTA was acquired using a 256-multidetector CT system from 90 patients assigned into three groups: (1) the routine dose (RD) group: 120 kVp, automatic tube current modulation (ACTM) with an image quality index of 12, and filtered back projection (FBP); (2) the low-dose (LD) group: 80 kVp, ACTM with an image quality index of 1, and IMR; and (3) the ultra-low dose (ULD) group: 80 kVp, 20 mAs, and IMR. CT attenuation, image noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) of the lower-extremity arteries were calculated. Subjective image quality of lower-extremity segments was assessed. Effective radiation dose was recorded. The radiation dose was reduced by 91.4% and 67.3% in the ULD group (0.15±0.02 mSv) compared to the RD group (1.86±0.51 mSv) and the LD group (0.49±0.08 mSv; both p<0.05). Higher CT attenuation, SNR, CNR, and lower image noise were obtained in the ULD group and the LD group compared to the RD group (all p<0.05). Better subjective image quality in lower leg segments was obtained in the ULD group and the LD group compared to the RD group (all p<0.05). No difference was found between the ULD and LD groups in both objective and subjective image quality (all p>0.05). By using IMR during lower-extremity CTA, the radiation dose is reduced by up to 91.4% without compromising image quality.

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

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

Ultralow dose CT for follow-up of solid pulmonary nodules

Solid pulmonary nodules are a common finding requiring serial computed tomography (CT) imaging. We sought to explore the detection and measurement accuracy of an ultralow-dose CT (ULDCT) protocol compared with our standard low-dose CT (LDCT) nodule follow-up protocol.In this pragmatic single-center pilot prospective cohort study, patients scheduled for clinically indicated CT surveillance of 1 or more known solid pulmonary nodules >2 mm underwent ULDCT immediately after routine LDCT. The Bland-Altman 95% limits of agreement for diameter and volumetry were calculated.In all, 57 patients underwent 60 imaging episodes, with 170 evaluable nodules. ULDCT detected all known solid pulmonary nodules >2 mm. Bland-Altman analyses demonstrated clinically agreement for both nodule diameter and volume, both of which fell within prespecified limits.This single-center pilot study suggests that ULDCT may be of use in surveillance of known solid pulmonary nodules >2 mm.

PD37-11 EFFECTIVE ULTRA LOW DOSE CT PROTOCOL WITH LOWER RADIATION DOSE THAN ABDOMINAL X-RAY

You have accessJournal of UrologyImaging/Radiology: Uroradiology III1 Apr 2018PD37-11 EFFECTIVE ULTRA LOW DOSE CT PROTOCOL WITH LOWER RADIATION DOSE THAN ABDOMINAL X-RAY Kymora Scotland, Jean Buckley, James Nugent, Savvas Nicolaou, Charles Zwirewich, Patrick McLaughlin, and Ben Chew Kymora ScotlandKymora Scotland More articles by this author , Jean BuckleyJean Buckley More articles by this author , James NugentJames Nugent More articles by this author , Savvas NicolaouSavvas Nicolaou More articles by this author , Charles ZwirewichCharles Zwirewich More articles by this author , Patrick McLaughlinPatrick McLaughlin More articles by this author , and Ben ChewBen Chew More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2018.02.1746AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Standard computed tomography of the kidneys, ureters and bladder (CT-KUB) is the most definitive modality used to identify renal calculi. However its use is concerning for radiation exposure particularly in recurrent stone formers. At this institution, KUB radiographs are routinely performed immediately prior to shockwave lithotripsy (SWL). Conventional low dose CT-KUBs (2.2-3.0 mSv) are only performed if stones are not visible on KUB (10-15% of cases). One disadvantage of routinely using low dose CT instead of KUB in this setting is the radiation exposure. Recent advances in integrated circuit CT detector design and image reconstruction algorithms have made sub-milliSievert ultra-low dose CT (ULDCT) acquisition feasible, but the diagnostic performance of these ULDCTs in comparison with KUB has not yet been reported. In this prospective study we compare the radiation dose and diagnostic performance of ULDCT to KUB in patients prior to SWL. We hypothesized that ULDCT will detect more symptomatic calculi than KUB at less radiation exposure prior to SWL. METHODS Patients were enrolled prospectively to receive a KUB and an ULDCT prior to SWL. If no stones were identified, they received a standard low dose abdominal CT. Radiation exposure parameters were recorded and both examinations were read in random order by 2 blinded radiologists to determine image quality and diagnostic accuracy. RESULTS 102 patients with a mean age of 55.7 ± 13.8y were enrolled. ULDCT detected stones with 95% sensitivity and 98% specificity with effective radiation dose 48% lower (0.28 ±0.08 mSv) compared to KUB (0.54 ±0.11 mSv, p<0.001). Negative and positive predictive values were 95% and 98% for ULDCT (83%, 92% for KUB).The number of stones seen on both modalities was similar: KUB was 1.59 ±1.27 vs 1.92±01.51 for ULDCT (p=0.35). However in 12 cases (12%), the ULDCT localized ureteral stones that were not detected on KUB. Measurement of stone size was equivalent using ULDCT (6.47 ±3.34mm) compared to KUB (6.98 ±3.41mm, p=0.455). ULDCT reduced the requirement for repeat conventional dose CTKUB. CONCLUSIONS ULDCT delivers 48% less radiation than a KUB radiograph and is superior at detecting the number and size of stones. In 12% of cases, ULDCT identified and localized ureteric stones prior to SWL that were not seen on KUB.ULDCT can be safely and effectively used in recurrent stone formers with smaller radiation dose than low dose CT. © 2018FiguresReferencesRelatedDetails Volume 199Issue 4SApril 2018Page: e735 Advertisement Copyright & Permissions© 2018MetricsAuthor Information Kymora Scotland More articles by this author Jean Buckley More articles by this author James Nugent More articles by this author Savvas Nicolaou More articles by this author Charles Zwirewich More articles by this author Patrick McLaughlin More articles by this author Ben Chew More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

1056 - Assessing the diagnostic accuracy of low and ultra-low radiation dose CT of the urinary tract for the investigation of urolithiasis

1056 - Assessing the diagnostic accuracy of low and ultra-low radiation dose CT of the urinary tract for the investigation of urolithiasis

Ultralow Dose MSCT Imaging in Dental Implantology.

Introduction:The Council Directive 2013/59 Euratom has a clear commitment for keeping medical radiation exposure as low as reasonably achievable and demands a regular review and use of diagnostic reference levels.Methods:In dental implantology, the range of effective doses for cone beam computed tomography (CBCT) shows a broad overlap with multislice computed tomography (MSCT). More recently, ultralow dose imaging with new generations of MSCT scanners may impart radiation doses equal to or lower than CBCT. Dose reductions in MSCT have been further facilitated by the introduction of iterative image reconstruction technology (IRT), which provides substantial noise reduction over the current standard of filtered backward projection (FBP).Aim:The aim of this article is to review the available literature on ultralow dose CT imaging and IRTs in dental implantology imaging and to summarize their influence on spatial and contrast resolution, image noise, tissue density measurements, and validity of linear measurements of the jaws.Conclusion:Application of ultralow dose MSCT with IRT technology in dental implantology offers the potential for very large dose reductions compared with standard dose imaging. Yet, evaluation of various diagnostic tasks related to dental implantology is still needed to confirm the results obtained with various IRTs and ultra-low doses so far.

Whole-body ultra-low dose CT using spectral shaping for detection of osteolytic lesion in multiple myeloma.

The aim of this study was to investigate the radiation dose and image quality of a whole-body low-dose CT (WBLDCT) using spectral shaping at 100 kV (Sn 100 kV) for the assessment of osteolytic lesions in patients with multiple myeloma. Thirty consecutive patients were retrospectively selected, who underwent a WBLDCT on a third-generation dual-source CT (DSCT) (Sn 100 kV, ref. mAs: 130). They were matched with patients, who were examined on a second-generation DSCT with a standard low-dose protocol (100 kV, ref. mAs: 111). Objective and subjective image quality, radiation exposure as well as the frequency of osteolytic lesions were evaluated. All scans were of diagnostic image quality. Subjective overall image quality was significantly higher in the study group (p = 0.0003). Objective image analysis revealed that signal intensities, signal-to-noise ratio and contrast-to-noise ratio of the bony structures were equal or significantly higher in the control group. There was no significant difference in the frequency of osteolytic lesions (p = 0.259). The median effective dose of the study protocol was significantly lower (1.45 mSv vs. 5.65 mSv; p < 0.0001). WBLDCT with Sn 100 kV can obtain sufficient image quality for the depiction of osteolytic lesions while reducing the radiation dose by approximately 74%. • Spectral shaping using tin filtration is beneficial for whole-body low-dose CT • Sn 100 kV yields sufficient image quality for depiction of osteolytic lesions • Whole-body low-dose CT can be performed with a median dose of 1.5 mSv.

Detection of artificial pulmonary lung nodules in ultralow-dose CT using an ex vivo lung phantom.

ObjectivesTo assess the image quality of 3 different ultralow-dose CT protocols on pulmonary nodule depiction in a ventilated ex vivo-system.Materials and methodsFour porcine lungs were inflated inside a dedicated chest phantom and prepared with n = 195 artificial nodules (0.5–1 mL). The artificial chest wall was filled with water to simulate the absorption of a human chest. Images were acquired with a 2x192-row detector CT using low-dose (reference protocol with a tube voltage of 120 kV) and 3 different ULD protocols (respective effective doses: 1mSv and 0.1mSv). A different tube voltage was used for each ULD protocol: 70kV, 100kV with tin filter (100kV_Sn) and 150kV with tin filter (150kV_Sn). Nodule delineation was assessed by two observers (scores 1–5, 1 = unsure, 5 = high confidence).ResultsThe diameter of the 195 detected artificial nodules ranged from 0.9–21.5 mm (mean 7.84 mm ± 5.31). The best ULD scores were achieved using 100kV_Sn and 70 kV ULD protocols (4.14 and 4.06 respectively). Both protocols were not significantly different (p = 0.244).The mean score of 3.78 in ULD 150kV_Sn was significantly lower compared to the 100kV_Sn ULD protocol (p = 0.008).ConclusionThe results of this experiment, conducted in a realistic setting show the feasibility of ultralow-dose CT for the detection of pulmonary nodules.

Ultra-low dose quantitative CT myocardial perfusion imaging with sparse-view dynamic acquisition and image reconstruction: A feasibility study

PurposeWe implemented and validated a compressed sensing (CS) based algorithm for reconstructing dynamic contrast-enhanced (DCE) CT images of the heart from sparsely sampled X-ray projections. MethodsDCE CT imaging of the heart was performed on five normal and ischemic pigs after contrast injection. DCE images were reconstructed with filtered backprojection (FBP) and CS from all projections (984-view) and 1/3 of all projections (328-view), and with CS from 1/4 of all projections (246-view). Myocardial perfusion (MP) measurements with each protocol were compared to those with the reference 984-view FBP protocol. ResultsBoth the 984-view CS and 328-view CS protocols were in good agreements with the reference protocol. The Pearson correlation coefficients of 984-view CS and 328-view CS determined from linear regression analyses were 0.98 and 0.99 respectively. The corresponding mean biases of MP measurement determined from Bland-Altman analyses were 2.7 and 1.2ml/min/100g. When only 328 projections were used for image reconstruction, CS was more accurate than FBP for MP measurement with respect to 984-view FBP. However, CS failed to generate MP maps comparable to those with 984-view FBP when only 246 projections were used for image reconstruction. ConclusionDCE heart images reconstructed from one-third of a full projection set with CS were minimally affected by aliasing artifacts, leading to accurate MP measurements with the effective dose reduced to just 33% of conventional full-view FBP method. The proposed CS sparse-view image reconstruction method could facilitate the implementation of sparse-view dynamic acquisition for ultra-low dose CT MP imaging.

Coronary risk assessment at X-ray dose equivalent ungated chest CT: Results of a multi-reader study

ObjectivesTo determine the value of ultra-low dose chest CT with tin filtration for ordinal coronary artery calcium (CAC) risk scoring. Methods50 patients were prospectively included and underwent clinical standard dose chest CT (1.8±0.7mSv) and ultra-low dose CT (0.13±0.01mSv). Four radiologists estimated presence and extent of CAC. ResultsWeighted kappa values for CAC were 0.76–0.97 in standard dose and 0.75–0.95 in ultra-low dose CT (p<0.001). Good to excellent agreement was observed for CAC ordinal risk assessment, with readers reporting identical risk in 81% of cases. ConclusionCAC risk can be qualitatively assessed from X-ray dose equivalent ungated chest CT.

Diagnostic accuracy of chest X-ray dose-equivalent CT for assessing calcified atherosclerotic burden of the thoracic aorta.

To determine the value of ultralow-dose chest CT for estimating the calcified atherosclerotic burden of the thoracic aorta using tin-filter CT and compare its diagnostic accuracy with chest direct radiography. A total of 106 patients from a prospective, IRB-approved single-centre study were included and underwent standard dose chest CT (1.7 ± 0.7 mSv) by clinical indication followed by ultralow-dose CT with 100 kV and spectral shaping by a tin filter (0.13 ± 0.01 mSv) to achieve chest X-ray equivalent dose in the same session. Two independent radiologists reviewed the CT images, rated image quality and estimated presence and extent of calcification of aortic valve, ascending aorta and aortic arch. Conventional radiographs were also reviewed for presence of aortic calcifications. The sensitivity of ultralow-dose CT for the detection of calcifications of the aortic valve, ascending aorta and aortic arch was 93.5, 96.2 and 96.2%, respectively, compared with standard dose CT. The sensitivity for the detection of thoracic aortic calcification was significantly lower on chest X-ray (52.3%) compared with ultralow-dose CT (p < 0.001). A reliable estimation of calcified atherosclerotic burden of the thoracic aorta can be achieved with modern tin-filter CT at dose values comparable to chest direct radiography. Advances in knowledge: Our findings suggest that ultralow-dose CT is an excellent tool for assessing the calcified atherosclerotic burden of the thoracic aorta with higher diagnostic accuracy than conventional chest radiography and importantly without the additional cost of increased radiation dose.

Comparison of low- and ultralow-dose computed tomography protocols for quantitative lung and airway assessment.

Quantitative computed tomography (CT) measures are increasingly being developed and used to characterize lung disease. With recent advances in CT technologies, we sought to evaluate the quantitative accuracy of lung imaging at low- and ultralow-radiation doses with the use of iterative reconstruction (IR), tube current modulation (TCM), and spectral shaping. We investigated the effect of five independent CT protocols reconstructed with IR on quantitative airway measures and global lung measures using an invivo large animal model as a human subject surrogate. A control protocol was chosen (NIH-SPIROMICS+TCM) and five independent protocols investigating TCM, low- and ultralow-radiation dose, and spectral shaping. For all scans, quantitative global parenchymal measurements (mean, median and standard deviation of the parenchymal HU, along with measures of emphysema) and global airway measurements (number of segmented airways and pi10) were generated. In addition, selected individual airway measurements (minor and major inner diameter, wall thickness, inner and outer area, inner and outer perimeter, wall area fraction, and inner equivalent circle diameter) were evaluated. Comparisons were made between control and target protocols using difference and repeatability measures. Estimated CT volume dose index (CTDIvol) across all protocols ranged from 7.32mGy to 0.32mGy. Low- and ultralow-dose protocols required more manual editing and resolved fewer airway branches; yet, comparable pi10 whole lung measures were observed across all protocols. Similar trends in acquired parenchymal and airway measurements were observed across all protocols, with increased measurement differences using the ultralow-dose protocols. However, for small airways (1.9±0.2mm) and medium airways (5.7±0.4mm), the measurement differences across all protocols were comparable to the control protocol repeatability across breath holds. Diameters, wall thickness, wall area fraction, and equivalent diameter had smaller measurement differences than area and perimeter measurements. In conclusion, the use of IR with low- and ultralow-dose CT protocols with CT volume dose indices down to 0.32mGy maintains selected quantitative parenchymal and airway measurements relevant to pulmonary disease characterization.

Implementation of ultra-low-dose lung protocols in CT-guided lung biopsies: feasibility and safety in the clinical setting.

ObjectiveTo evaluate the use of ultra-low-dose computed tomography (ULDCT) for CT-guided lung biopsy versus standard-dose CT (SDCT).MethodsCT-guided lung biopsies from 115 patients (50 ULDCT, 65 SDCT) were analyzed retrospectively. SDCT settings were 120 kVp with automatic mAs modulation. ULDCT settings were 80 kVp with fixed exposure (20 mAs). Two radiologists evaluated image quality (i.e., needle artifacts, lesion contouring, vessel recognition, visibility of interlobar fissures). Complications and histological results were also evaluated.ResultsULDCT was considered feasible for all lung interventions, showing the same diagnostic accuracy as SDCT. Its mean total radiation dose (dose–length product) was significantly reduced to 34 mGy-cm (SDCT 426 mGy-cm). Image quality and complication rates (P = 0.469) were consistent.ConclusionsULDCT for CT-guided lung biopsies appears safe and accurate, with a significantly reduced radiation dose. We therefore recommend routine clinical use of ULDCT for the benefit of patients and interventionalists.

Performance of ultra-low-dose CT for the evaluation of coronary calcification: a direct comparison with coronary calcium score

To evaluate the diagnostic performance of ultra-low-dose computed tomography (ULDCT) in comparison to standard coronary calcium score (CCS) acquisition for the evaluation of coronary artery calcification (CAC). Standard CCS acquisition and ULDCT were performed in patients referred for coronary CT angiography for the evaluation of coronary artery disease. CAC in ULDCT was graded subjectively using a four-point scale (from 0, no calcification, to 3, severe calcification) for the complete study and for each individual coronary segment. The summation of all individual coronary segment scores generated an ULDCT total CAC score. ULDCT results were compared to standard Agatston score and sensitivity and specificity of ULDCT were calculated. CCS and ULDCT were performed in 74 patients, with a mean DLP of 77.7 mGy·cm (±12.1) and 9.3 mGy·cm (±0.6), respectively (p<0.001). Coronary calcification was detected in 47 patients (63.5%) in standard CCS acquisition (median Agatston score of 41; interquartile range [IQR]:0263), in comparison to 42 patients (56.8%) in ULDCT (p<0.001). The sensitivity and specificity of the ULDCT total CAC score ≥1 was 80.9% and 85.2%, respectively, with an accuracy of 82.4%. The area under the receiver operating characteristic curve for the presence of CAC was 0.87. ULDCT shows good sensitivity, specificity, and overall accuracy for the detection of coronary calcification with a markedly lower radiation dose in comparison to CCS. ULDCT is unlikely to miss coronary calcification in individuals with at least moderate calcium load (Agatston score >100).

Pediatric chest CT at chest radiograph doses: when is the ultralow-dose chest CT clinically appropriate?

Computed tomography (CT) use in emergency departments represents a significant contribution to pediatric patients' exposure to ionizing radiation. Here, we evaluate whether ultralow-dose chest CT can be diagnostically adequate for other diagnoses and whether model-based iterative reconstruction (MBIR) can improve diagnostic adequacy compared to adaptive statistical iterative reconstruction (ASIR) at ultralow doses. Twenty children underwent chest CTs: 10 standard-dose reconstructed with ASIR and 10 ultralow-dose reconstructed with ASIR and MBIR. Four radiologists assessed images for their adequacy to exclude five hypothetical diagnoses: foreign body, fracture, lung metastasis, pulmonary infection, and interstitial lung disease. Additionally, pairwise comparison for subjective image quality was used to compare ultralow-dose chest CT with ASIR and MBIR. Radiation dose and objective image noise measures were obtained. For exclusion of an airway foreign body, the adequacy of ultralow-dose CT was comparable to standard-dose (p=0.6). For the remaining diagnoses, ultralow-dose CT was inferior to standard-dose (p=0.03-<0.001). MBIR partially recovered the adequacy of ultralow-dose CT to exclude pulmonary infection (p=0.017), but was suboptimal for the other diagnoses. Image noise was significantly lower with MBIR compared to ASIR in ultralow-dose CT (p<0.001), although subjective preference showed only a slight advantage of MBIR (58 versus 42%). Ultralow-dose chest CT may be adequate for airway assessment, but suboptimal for the evaluation parenchymal lung disease. Although MBIR improves objective and subjective image quality, it does not completely restore the diagnostic adequacy of ultralow-dose CT when compared to standard-dose CT.

Emphysema quantification and lung volumetry in chest X-ray equivalent ultralow dose CT – Intra-individual comparison with standard dose CT

ObjectivesTo determine whether ultralow dose chest CT with tin filtration can be used for emphysema quantification and lung volumetry and to assess differences in emphysema measurements and lung volume between standard dose and ultralow dose CT scans using advanced modeled iterative reconstruction (ADMIRE). Methods84 consecutive patients from a prospective, IRB-approved single-center study were included and underwent clinically indicated standard dose chest CT (1.7±0.6mSv) and additional single-energy ultralow dose CT (0.14±0.01mSv) at 100kV and fixed tube current at 70mAs with tin filtration in the same session. Forty of the 84 patients (48%) had no emphysema, 44 (52%) had emphysema. One radiologist performed fully automated software-based pulmonary emphysema quantification and lung volumetry of standard and ultralow dose CT with different levels of ADMIRE. Friedman test and Wilcoxon rank sum test were used for multiple comparison of emphysema and lung volume. Lung volumes were compared using the concordance correlation coefficient. ResultsThe median low-attenuation areas (LAA) using filtered back projection (FBP) in standard dose was 4.4% and decreased to 2.6%, 2.1% and 1.8% using ADMIRE 3, 4, and 5, respectively. The median values of LAA in ultralow dose CT were 5.7%, 4.1% and 2.4% for ADMIRE 3, 4, and 5, respectively. There was no statistically significant difference between LAA in standard dose CT using FBP and ultralow dose using ADMIRE 4 (p=0.358) as well as in standard dose CT using ADMIRE 3 and ultralow dose using ADMIRE 5 (p=0.966). In comparison with standard dose FBP the concordance correlation coefficients of lung volumetry were 1.000, 0.999, and 0.999 for ADMIRE 3, 4, and 5 in standard dose, and 0.972 for ADMIRE 3, 4 and 5 in ultralow dose CT. ConclusionsUltralow dose CT at chest X-ray equivalent dose levels allows for lung volumetry as well as detection and quantification of emphysema. However, longitudinal emphysema analyses should be performed with the same scan protocol and reconstruction algorithms for reproducibility.

Spatial and contrast resolution of ultralow dose dentomaxillofacial CT imaging using iterative reconstruction technology.

The objective of this study was to determine how iterative reconstruction technology (IRT) influences contrast and spatial resolution in ultralow-dose dentomaxillofacial CT imaging. A polymethyl methacrylate phantom with various inserts was scanned using a reference protocol (RP) at CT dose index volume 36.56 mGy, a sinus protocol at 18.28 mGy and ultralow-dose protocols (LD) at 4.17 mGy, 2.36 mGy, 0.99 mGy and 0.53 mGy. All data sets were reconstructed using filtered back projection (FBP) and the following IRTs: adaptive statistical iterative reconstructions (ASIRs) (ASIR-50, ASIR-100) and model-based iterative reconstruction (MBIR). Inserts containing line-pair patterns and contrast detail patterns for three different materials were scored by three observers. Observer agreement was analyzed using Cohen's kappa and difference in performance between the protocols and reconstruction was analyzed with Dunn's test at α = 0.05. Interobserver agreement was acceptable with a mean kappa value of 0.59. Compared with the RP using FBP, similar scores were achieved at 2.36 mGy using MBIR. MIBR reconstructions showed the highest noise suppression as well as good contrast even at the lowest doses. Overall, ASIR reconstructions did not outperform FBP. LD and MBIR at a dose reduction of >90% may show no significant differences in spatial and contrast resolution compared with an RP and FBP. Ultralow-dose CT and IRT should be further explored in clinical studies.

Lung cancer screening with ultra-low dose CT using full iterative reconstruction.

To investigate the diagnostic capability of ultra-low-dose CT (ULDCT) with full iterative reconstruction (f-IR) for lung cancer screening. All underwent ULDCT and/or low-dose CT (LD-CT) on a 320-detector scanner. ULDCT images were reconstructed with f-IR. We qualitatively and quantitatively studied 95 nodules in 69 subjects. Two radiologists classified the nodules on ULDCT images as solid-, part-solid-, and pure ground-glass (PGG) and recorded their mean size. Their findings were compared with the reference standard. The observer performance study included 7 other radiologists and 35 subjects with- and 15 without nodules. The results were analyzed by AFROC analysis. In the qualitative study, the kappa values between observers 1 and 2, respectively, and the reference standard were 0.70 and 0.83; the intra-class correlation coefficients for the nodule diameter between the reference standard and their measurements were 0.84 and 0.90. The 95% confidence interval (CI) for the area under the curve (AUC) difference for nodule detection on LDCT and ULDCT was -0.03 to 0.07. The 95% CI crossed the 0 difference in the AUC but not the pre-defined non-inferiority margin of -0.08. The diagnostic ability of ULDCT using f-IR is comparable to LDCT.

Direct Reconstruction of CT-based Attenuation Correction Images for PET with Cluster-Based Penalties.

Extremely low-dose CT acquisitions used for PET attenuation correction have high levels of noise and potential bias artifacts due to photon starvation. This work explores the use of a priori knowledge for iterative image reconstruction of the CT-based attenuation map. We investigate a maximum a posteriori framework with cluster-based multinomial penalty for direct iterative coordinate decent (dICD) reconstruction of the PET attenuation map. The objective function for direct iterative attenuation map reconstruction used a Poisson log-likelihood data fit term and evaluated two image penalty terms of spatial and mixture distributions. The spatial regularization is based on a quadratic penalty. For the mixture penalty, we assumed that the attenuation map may consist of four material clusters: air+background, lung, soft tissue, and bone. Using simulated noisy sinogram data, dICD reconstruction was performed with different strengths of the spatial and mixture penalties. The combined spatial and mixture penalties reduced the RMSE by roughly 2 times compared to a weighted least square and filtered backprojection reconstruction of CT images. The combined spatial and mixture penalties resulted in only slightly lower RMSE compared to a spatial quadratic penalty alone. For direct PET attenuation map reconstruction from ultra-low dose CT acquisitions, the combination of spatial and mixture penalties offers regularization of both variance and bias and is a potential method to reconstruct attenuation maps with negligible patient dose. The presented results, using a best-case histogram suggest that the mixture penalty does not offer a substantive benefit over conventional quadratic regularization and diminishes enthusiasm for exploring future application of the mixture penalty.