Ultra-low Dose CT Research Articles

Dose-reduced CT with model-based iterative reconstruction in evaluations of hepatic steatosis: How low can we go?

PurposeTo determine whether dose-reduced CT with model-based iterative image reconstruction (MBIR) is a useful tool with which to diagnose hepatic steatosis. Materials and methodsThis prospective clinical study approved by our Institutional Review Board included 103 (67 men and 36 women; mean age, 64.3 years) patients who provided written informed consent to undergo unenhanced CT. Images of reference-dose CT (RDCT) with filtered back projection (R-FBP) and low- and ultralow-dose CT (dose-length product; 24 and 9% of that of RDCT) with MBIR (L-MBIR and UL-MBIR) were reconstructed. Mean CT numbers of liver (CT[L]) and spleen (CT[S]), and quotient (CT[L/S]) of CT[L] and CT[S] were calculated from selected regions of interest. Bias and limits of agreement (LOA) of CT[L] and CT[L/S] in L-MBIR and UL-MBIR (vs. R-FBP) were assessed using Bland–Altman analyses. Diagnostic methods for hepatic steatosis of CT[L]<48 Hounsfield units (HU) and CT[L/S]<1.1 were applied to L-MBIR and UL-MBIR using R-FBP as the reference standard. ResultsBias was larger for CT[L] in UL-MBIR than in L-MBIR (−3.18HU vs. −1.73HU). The LOA of CT[L/S] was larger for UL-MBIR than for L-MBIR (±0.425 vs. ±0.245) and outliers were identified in CT[L/S] of UL-MBIR. Accuracy (0.92–0.95) and the area under the receiver operating characteristics curve (0.976–0.992) were high for each method, but some were slightly lower in UL-MBIR than L-MBIR. ConclusionDose-reduced CT reconstructed with MBIR is applicable to diagnose hepatic steatosis, however, a low dose of radiation might be preferable.

Influence of radiation dose and iterative reconstruction algorithms for measurement accuracy and reproducibility of pulmonary nodule volumetry: A phantom study

PurposeTo evaluate the influence of radiation dose settings and reconstruction algorithms on the measurement accuracy and reproducibility of semi-automated pulmonary nodule volumetry. Materials and methodsCT scans were performed on a chest phantom containing various nodules (10 and 12mm; +100, −630 and −800HU) at 120kVp with tube current–time settings of 10, 20, 50, and 100mAs. Each CT was reconstructed using filtered back projection (FBP), iDose4 and iterative model reconstruction (IMR). Semi-automated volumetry was performed by two radiologists using commercial volumetry software for nodules at each CT dataset. Noise, contrast-to-noise ratio and signal-to-noise ratio of CT images were also obtained. The absolute percentage measurement errors and differences were then calculated for volume and mass. The influence of radiation dose and reconstruction algorithm on measurement accuracy, reproducibility and objective image quality metrics was analyzed using generalized estimating equations. ResultsMeasurement accuracy and reproducibility of nodule volume and mass were not significantly associated with CT radiation dose settings or reconstruction algorithms (p>0.05). Objective image quality metrics of CT images were superior in IMR than in FBP or iDose4 at all radiation dose settings (p<0.05). ConclusionSemi-automated nodule volumetry can be applied to low- or ultralow-dose chest CT with usage of a novel iterative reconstruction algorithm without losing measurement accuracy and reproducibility.

Image quality assessment of ultra low-dose chest CT using sinogram-affirmed iterative reconstruction

To assess the image quality of ultra-low-dose computed tomography (ULDCT) using sinogram-affirmed iterative reconstruction (SAFIRE) compared to reduced dose CT (RDCT). Eighty-one consecutive patients underwent non-enhanced ULDCT using 80 kVp and 30 mAs and contrast-enhanced RDCT using automated tube potential selection and tube current modulation. CT images were reconstructed with SAFIRE. Image noise and subjective image quality of normal structures and various pulmonary lesions were assessed. The mean effective doses were 0.29 ± 0.03 and 2.88 ± 1.11mSv for ULDCT and RDCT, respectively. ULDCT had significantly higher noise (p < 0.001). Image quality of five normal structures was diagnostic in 91.1% of ULDCT and 100% of RDCT. With ULDCT, the frequencies of non-diagnostic image quality were 2.0 (1/50), 4.6 (13/280), 25.5 (14/55), and 40.0 (8/20)% for BMIs of < 20, 20-25, 25-30, and >30. In the assessment of pulmonary lesions, non-diagnostic image quality was observed for 11.2% of all lesions, 60.9% of decreased attenuation (significantly more frequent for upper lung lesions), and 23.5% of ground-glass nodules. ULDCT generates diagnostic images in patients with a BMI ≤25, but is of limited use for lesions with decreased attenuation, ground-glass nodules, or those located in the upper lobe. • Iterative reconstruction enables ultra-low-dose CT (ULDCT) with very low radiation doses. • Image quality of ULDCT depends on the patient body mass index (BMI). • Selection of kVp and mAs depends on both BMI and lesion type. • Diagnosis of pulmonary emphysema or ground-glass nodules requires higher radiation doses.

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

Extremely low-dose CT acquisitions for the purpose of PET attenuation correction will have a high level of noise and biasing artifacts due to factors such as photon starvation. This work explores a priori knowledge appropriate for CT iterative image reconstruction for PET attenuation correction. We investigate the maximum a posteriori (MAP) framework with cluster-based, multinomial priors for the direct reconstruction of the PET attenuation map. The objective function for direct iterative attenuation map reconstruction was modeled as a Poisson log-likelihood with prior terms consisting of quadratic (Q) and mixture (M) distributions. The attenuation map is assumed to have values in 4 clusters: air+background, lung, soft tissue, and bone. Under this assumption, the MP was a mixture probability density function consisting of one exponential and three Gaussian distributions. The relative proportion of each cluster was jointly estimated during each voxel update of direct iterative coordinate decent (dICD) method. Noise-free data were generated from NCAT phantom and Poisson noise was added. Reconstruction with FBP (ramp filter) was performed on the noise-free (ground truth) and noisy data. For the noisy data, dICD reconstruction was performed with the combination of different prior strength parameters (β and γ) of Q- and M-penalties. The combined quadratic and mixture penalties reduces the RMSE by 18.7% compared to post-smoothed iterative reconstruction and only 0.7% compared to quadratic alone. For direct PET attenuation map reconstruction from ultra-low dose CT acquisitions, the combination of quadratic and mixture priors offers regularization of both variance and bias and is a potential method to derive attenuation maps with negligible patient dose. However, the small improvement in quantitative accuracy relative to the substantial increase in algorithm complexity does not currently justify the use of mixture-based PET attenuation priors for reconstruction of CT images for PET attenuation correction.

Ultra low dose CT for left atrium and pulmonary veins imaging using VEO (model-based iterative reconstruction)

Ultra low dose CT for left atrium and pulmonary veins imaging using VEO (model-based iterative reconstruction)

Model-based iterative reconstruction for reduction of radiation dose in abdominopelvic CT: comparison to adaptive statistical iterative reconstruction

PurposeTo evaluate dose reduction and image quality of abdominopelvic computed tomography (CT) reconstructed with model-based iterative reconstruction (MBIR) compared to adaptive statistical iterative reconstruction (ASIR).Materials and methodsIn this prospective study, 85 patients underwent referential-, low-, and ultralow-dose unenhanced abdominopelvic CT. Images were reconstructed with ASIR for low-dose (L-ASIR) and ultralow-dose CT (UL-ASIR), and with MBIR for ultralow-dose CT (UL-MBIR). Image noise was measured in the abdominal aorta and iliopsoas muscle. Subjective image analyses and a lesion detection study (adrenal nodules) were conducted by two blinded radiologists. A reference standard was established by a consensus panel of two different radiologists using referential-dose CT reconstructed with filtered back projection.ResultsCompared to low-dose CT, there was a 63% decrease in dose-length product with ultralow-dose CT. UL-MBIR had significantly lower image noise than L-ASIR and UL-ASIR (all p<0.01). UL-MBIR was significantly better for subjective image noise and streak artifacts than L-ASIR and UL-ASIR (all p<0.01). There were no significant differences between UL-MBIR and L-ASIR in diagnostic acceptability (p>0.65), or diagnostic performance for adrenal nodules (p>0.87).ConclusionMBIR significantly improves image noise and streak artifacts compared to ASIR, and can achieve radiation dose reduction without severely compromising image quality.

Model-Based Iterative Reconstruction Technique for Ultralow-Dose Chest CT

The purpose of this study was to evaluate whether model-based iterative reconstruction (MBIR) enables dose reduction over adaptive iterative reconstruction (ASIR) while maintaining diagnostic performance. In this institutional review board-approved and Health Insurance Portability and Accountability Act-compliant study, 59 patients (mean [SD] age, 64.7 [13.4] years) gave informed consent to undergo reference-, low-, and ultralow-dose chest computed tomography (CT) with 64-row multidetector CT. The reference- and low-dose CT involved the use of automatic tube current modulation with fixed noise indices (31.5 and 70.44 at 0.625 mm, respectively) and were reconstructed with 50% ASIR-filtered back projection blending. The ultralow-dose CT was acquired with a fixed tube current-time product of 5 mA s and reconstructed with MBIR. Two radiologists evaluated 2.5- and 0.625-mm-slice-thick axial images from low-dose ASIR and ultralow-dose MBIR, recorded the pattern of each nodule candidate, and assigned each a confidence score. A reference standard was established by a consensus panel of 2 different radiologists, who identified 84 noncalcified nodules with diameters of 4 mm or greater on reference-dose ASIR (ground-glass opacity, n = 18; partly solid, n = 11; solid, n = 55). Sensitivity in nodule detection was assessed using the McNemar test. Jackknife alternative free-response receiver operating characteristic (JAFROC) analysis was applied to assess the results including confidence scores. Compared with the low-dose CT, a 78.1% decrease in dose-length product was seen with the ultralow-dose CT. No significant differences were observed between the low-dose ASIR and the ultralow-dose MBIR for overall nodule detection in sensitivity (P = 0.48-0.69) or the JAFROC analysis (P = 0.57). Likewise, no significant differences were seen for ground-glass opacity, partly solid, or solid nodule detection in sensitivity (P = 0.08-0.65) or the JAFROC analysis (P = 0.21-0.90). Model-based iterative reconstruction enables nearly an 80% reduction in radiation dose for chest CT from a low-dose level to an ultralow-dose level, without affecting nodule detectability.

Abdominal CT with model-based iterative reconstruction (MBIR): initial results of a prospective trial comparing ultralow-dose with standard-dose imaging.

The purpose of this study was to report preliminary results of an ongoing prospective trial of ultralow-dose abdominal MDCT. Imaging with standard-dose contrast-enhanced (n = 21) and unenhanced (n = 24) clinical abdominal MDCT protocols was immediately followed by ultralow-dose imaging of a matched series of 45 consecutively registered adults (mean age, 57.9 years; mean body mass index, 28.5). The ultralow-dose images were reconstructed with filtered back projection (FBP), adaptive statistical iterative reconstruction (ASIR), and model-based iterative reconstruction (MBIR). Standard-dose series were reconstructed with FBP (reference standard). Image noise was measured at multiple predefined sites. Two blinded abdominal radiologists interpreted randomly presented ultralow-dose images for multilevel subjective image quality (5-point scale) and depiction of organ-based focal lesions. Mean dose reduction relative to the standard series was 74% (median, 78%; range, 57-88%; mean effective dose, 1.90 mSv). Mean multiorgan image noise for low-dose MBIR was 14.7 ± 2.6 HU, significantly lower than standard-dose FBP (28.9 ± 9.9 HU), low-dose FBP (59.2 ± 23.3 HU), and ASIR (45.6 ± 14.1 HU) (p < 0.001). The mean subjective image quality score for low-dose MBIR (3.0 ± 0.5) was significantly higher than for low-dose FBP (1.6 ± 0.7) and ASIR (1.8 ± 0.7) (p < 0.001). Readers identified 213 focal noncalcific lesions with standard-dose FBP. Pooled lesion detection was higher for low-dose MBIR (79.3% [169/213]) compared with low-dose FBP (66.2% [141/213]) and ASIR (62.0% [132/213]) (p < 0.05). MBIR shows great potential for substantially reducing radiation doses at routine abdominal CT. Both FBP and ASIR are limited in this regard owing to reduced image quality and diagnostic capability. Further investigation is needed to determine the optimal dose level for MBIR that maintains adequate diagnostic performance. In general, objective and subjective image quality measurements do not necessarily correlate with diagnostic performance at ultralow-dose CT.

Liver perfusion CT during hepatic arteriography for the hepatocellular carcinoma: Dose reduction and quantitative evaluation for normal- and ultralow-dose protocol

ObjectivesThe purpose of this study was to investigate whether substantial reduction of the computed tomography (CT) dose is possible in liver CT perfusion imaging by comparing the results of ultralow-dose CT perfusion imaging with those of conventional CT perfusion imaging the same patients and under the same conditions. Materials and methodsThe study was composed following two parts: computer simulation and patients study. In computer simulation, noise was added to the images so that the standard deviation (SD) of the CT values in the liver parenchyma became various values using ImageJ. Time density curves (TDCs) were created from the simulated data, and the influence of difference in the SDs on the shapes of the TDCs was investigated. In the patient study, CT perfusion during intra-arterial injection was performed in 30 consecutive patients undergoing transcatheter arterial chemoembolization. CT perfusion images were acquired twice, at 100mA (CTDIvol, 300mGy) for normal and at 20mA (CTDIvol, 60mGy) for the ultralow radiation doses, under the same conditions. ResultsNo change was observed in the shape of the TDCs and peak values in the analysis of simulation images. A very good correlation was observed between the normal- and ultralow-dose CT images for all analyzed values (R2=0.9885 for blood flow, 0.9269 for blood volume, and 0.8424 for mean transit time). ConclusionsOur results demonstrated that there was no significant difference in the analysis results of perfusion CT between ultralow-dose CT performed using 20% of the conventional dose and normal-dose CT perfusion.

Computed tomography of the chest with model-based iterative reconstruction using a radiation exposure similar to chest X-ray examination: preliminary observations

The purpose of this study was to assess the diagnostic image quality of ultra-low-dose chest computed tomography (ULD-CT) obtained with a radiation dose comparable to chest radiography and reconstructed with filtered back projection (FBP), adaptive statistical iterative reconstruction (ASIR) and model-based iterative reconstruction (MBIR) in comparison with standard dose diagnostic CT (SDD-CT) or low-dose diagnostic CT (LDD-CT) reconstructed with FBP alone. Unenhanced chest CT images of 42 patients acquired with ULD-CT were compared with images obtained with SDD-CT or LDD-CT in the same examination. Noise measurements and image quality, based on conspicuity of chest lesions on all CT data sets were assessed on a five-point scale. The radiation dose of ULD-CT was 0.16 ± 0.006 mSv compared with 11.2 ± 2.7 mSv for SDD-CT (P < 0.0001) and 2.7 ± 0.9 mSv for LDD-CT. Image quality of ULD-CT increased significantly when using MBIR compared with FBP or ASIR (P < 0.001). ULD-CT reconstructed with MBIR enabled to detect as many non-calcified pulmonary nodules as seen on SDD-CT or LDD-CT. However, image quality of ULD-CT was clearly inferior for characterisation of ground glass opacities or emphysema. Model-based iterative reconstruction allows detection of pulmonary nodules with ULD-CT with radiation exposure in the range of a posterior to anterior (PA) and lateral chest X-ray.

Ultra-low dose CT scanning in clinical practice ? A preliminary study in 30 patients

Tuesday 11 September Proffered papers 3: Dose managment - Presenting Author: Dr Varut Vardhanabhuti

Pädiatrische Frakturdiagnostik – Ultra-low-dose-CT mit der effektiven Dosis von Röntgenaufnahmen

Computed tomography (CT) plays an important role in trauma diagnosis in children, especially for complex fractures. The aim of this study was to examine the diagnostic value of ultra-low-dose-CT (ULD-CT) with an effective dose equal to that of radiographs in an experimental study and to compare its results with those of radiographs. Limb bones of dead young pigs served as a model for pediatric bones. A total of 51 fractured and non-fractured bones were examined with a 64 multislice-CT with a standard dose protocol as gold standard, with two ultra-low-dose-protocols, and with standard radiographs with different exposures. In spite of high background noise the examinations of ULD-CT were not adequate only in 2 of 204 cases. ULD-CT was slightly superior to radiographs in detection of fractures. ULD-CT could significantly better characterize the fractures than radiographs. The overall result of ULD-CT was significantly better than that of radiographs with standard exposure. ULD-CT with the effective dose of radiographs is successfully applicable in pediatric fracture diagnosis, and its overall result is significantly better than that of radiographs.

Model-Based Iterative Reconstruction Technique for Ultralow-Dose Computed Tomography of the Lung

The aim of this study was to assess the effectiveness of a model-based iterative reconstruction (MBIR) in improving image quality and diagnostic performance of ultralow-dose computed tomography (ULDCT) of the lung. The institutional review board approved this study, and all patients provided written informed consent. Fifty-two patients underwent low-dose computed tomography (LDCT) (screening-dose, 50 mAs) and ULDCT (4 mAs) of the lung simultaneously. The LDCT images were reconstructed with filtered back projection (LDCT-FBP images) and ULDCT images were reconstructed with both MBIR (ULDCT-MBIR images) and FBP (ULDCT-FBP images). On all the 156 image series, objective image noise was measured in the thoracic aorta, and 2 blinded radiologists independently assessed subjective image quality. Another 2 blinded radiologists independently evaluated the ULDCT-MBIR and ULDCT-FBP images for the presence of noncalcified and calcified pulmonary nodules; LDCT-FBP images served as the reference. Paired t test, Wilcoxon signed rank sum test, and free-response receiver-operating characteristic analysis were used for statistical analysis of the data. Compared with LDCT-FBP and ULDCT-FBP, ULDCT-MBIR had significantly reduced objective noise (both P <; 0.001). Subjective noise on the ULDCT-MBIR images was comparable with that on the LDCT-FBP images but lower than that on the ULDCT-FBP images (P <; 0.001). Artifacts on ULDCT-MBIR images were more numerous than those on the LDCT-FBP images (P = 0.007) but fewer than those on the ULDCT-FBP images (P <; 0.001). Compared with the LDCT-FBP images, ULDCT-MBIR and ULDCT-FBP images showed reduced image sharpness (both P <; 0.001). All the ULDCT-MBIR images showed a blotchy pixelated appearance; however, the performance of ULDCT-MBIR was significantly superior to that of ULDCT-FBP for the detection of noncalcified pulmonary nodules (P = 0.002). The average true-positive fractions for significantly sized noncalcified nodules (≥4 mm) and small noncalcified nodules (<;4 mm) on the ULDCT-MBIR images were 0.944 and 0.884, respectively, when LDCT-FBP images were used as reference. All of the calcified nodules were detected by both the observers on both the ULDCT-MBIR and ULDCT-FBP images. As compared with FBP, MBIR enables significant reduction of the image noise and artifacts and also better detection of noncalcified pulmonary nodules on ULDCT of the lung. Compared with LDCT-FBP images, ULDCT-MBIR images showed significantly reduced objective noise and comparable subjective image noise. Almost all of the noncalcified nodules and all of the calcified nodules could be detected on the ULDCT-MBIR images, when LDCT-FBP images were used as the reference.

2183 ULTRA-LOW DOSE CT COMPARABLE TO STANDARD CT IN PATIENTS WITH SUSPECTED RENAL COLIC

You have accessJournal of UrologyImaging/Radiology: Uroradiology II1 Apr 20122183 ULTRA-LOW DOSE CT COMPARABLE TO STANDARD CT IN PATIENTS WITH SUSPECTED RENAL COLIC Jason Archambault, Carmen Hrymak, Sri Sivalingam, and Iain Kirkpatrick Jason ArchambaultJason Archambault Winnipeg, Canada More articles by this author , Carmen HrymakCarmen Hrymak Winnipeg, Canada More articles by this author , Sri SivalingamSri Sivalingam Madison WI More articles by this author , and Iain KirkpatrickIain Kirkpatrick Winnipeg, Canada More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2012.02.2357AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Non-contrast computed tomography (CT) is currently the standard radiologic investigation for patients with suspected renal colic. Concerns over the number of CT scans being performed along with the long-term effects of CT radiation exposure have led to the evaluation of low dose radiation CT scans in diagnosing renal calculi. Our objective was to compare an ultra-low dose (study) CT scan protocol to standard CT in the evaluation of patients with suspected renal colic. METHODS Fifty-six emergency room patients with suspected renal colic underwent both a standard and study CT to assess for renal colic. The study CT protocol lowered the radiation exposure approximately 95% by fixing the tube current at 20 milliampere-seconds (mAs). Both CT scans were read twice by a group of 4 blinded radiologists. The primary outcome was stone detection rate. Secondary outcomes included signs of obstruction, inter-observer agreement, and stone characteristics. Patient body mass index (BMI) and alternative diagnosis were also evaluated. Patients were excluded if they were clinically unstable, or unable to provide informed consent. Study approval was received from the institutional health research ethics board. RESULTS Fifty-six patients had data available for comparison. Thirty-three of the 36 patients with a positive standard CT were identified on the study CT. This equates to a 92% sensitivity and 100% specificity for stone detection. Study CT sensitivity increased to >97% for stones > 2mm in size. There was no statistically significant difference between the two CT scans when directly compared for stone detection (McNemar's test p=0.63, alpha < 0.05). Inter-observer agreement for stone detection was excellent between all observers (all kappa values were greater than 0.8 with a combined mean of 0.9). The only false negative (no stone detected) with no indirect signs of obstruction was a 2mm distal stone in a patient with a BMI of 48. Although the false negative rate was low, stone size appeared significant based on 95% confidence intervals between group means. A similar comparison did not show significance for BMI. CONCLUSIONS Our ultra-low dose CT protocol approaches the sensitivity and specificity of standard non-contrast CTs in patients with suspected renal colic. This data strengthens the argument for developing reduced radiation CT protocols for screening patients with suspected renal colic. © 2012 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 187Issue 4SApril 2012Page: e880 Peer Review Report Advertisement Copyright & Permissions© 2012 by American Urological Association Education and Research, Inc.MetricsAuthor Information Jason Archambault Winnipeg, Canada More articles by this author Carmen Hrymak Winnipeg, Canada More articles by this author Sri Sivalingam Madison WI More articles by this author Iain Kirkpatrick Winnipeg, Canada More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Evaluation of Ultra-Low Dose CT in the Diagnosis of Pediatric-Like Fractures Using an Experimental Animal Study

ObjectiveThe aim of this prospective study was to evaluate the performance of ultra-low dose CT for the diagnosis of pediatric-like fractures and ascertain the lowest dose level sufficient for diagnostics.Materials and MethodsFifty-one bones of young pig cadavers were artificially fractured and subsequently examined by using a 64 multi-detector CT with 36 various dose levels down to a dose comparable with that of X-rays. Two pediatric radiologists analysed the CT scans according to the presence or absence of a fracture, determination of the fracture type and the displacement as well as the diagnostic certainty. For each dose protocol, a success rate for the correct determination of the above-mentioned CT analyses was calculated. A success rate of at least 95% was considered sufficient for diagnostics.ResultsAll but the lowest dose levels were sufficient to identify the fracture. Only the two lowest dose levels were insufficient to detect the fracture type. All dose levels were adequate for the identification of the displacement. The lowest dose level sufficient for diagnostics was 120 kVp, 11 mAs, and pitch 1.5, with a CTDIvol of 10% of a standard dose and an effective dose three times as large as that of X-rays.ConclusionUltra-low dose CT provides the feasibility of a significant dose reduction, still allowing sufficient diagnostics of pediatric-like fractures.

Ultra-low dose CT attenuation correction for PET/CT

A challenge for positron emission tomography/computed tomography (PET/CT) quantitation is patient respiratory motion, which can cause an underestimation of lesion activity uptake and an overestimation of lesion volume. Several respiratory motion correction methods benefit from longer duration CT scans that are phase matched with PET scans. However, even with the currently available, lowest dose CT techniques, extended duration cine CT scans impart a substantially high radiation dose. This study evaluates methods designed to reduce CT radiation dose in PET/CT scanning. We investigated selected combinations of dose reduced acquisition and noise suppression methods that take advantage of the reduced requirement of CT for PET attenuation correction (AC). These include reducing CT tube current, optimizing CT tube voltage, adding filtration, CT sinogram smoothing and clipping. We explored the impact of these methods on PET quantitation via simulations on different digital phantoms. CT tube current can be reduced much lower for AC than that in low dose CT protocols. Spectra that are higher energy and narrower are generally more dose efficient with respect to PET image quality. Sinogram smoothing could be used to compensate for the increased noise and artifacts at radiation dose reduced CT images, which allows for a further reduction of CT dose with no penalty for PET image quantitation. When CT is not used for diagnostic and anatomical localization purposes, we showed that ultra-low dose CT for PET/CT is feasible. The significant dose reduction strategies proposed here could enable respiratory motion compensation methods that require extended duration CT scans and reduce radiation exposure in general for all PET/CT imaging.

Ultra low-dose CT feasibility with statistical iterative reconstruction for anatomical localization in PET-CT imaging

Ultra low-dose CT feasibility with statistical iterative reconstruction for anatomical localization in PET-CT imaging

Ultra–low-dose Protocol for CT-guided Lung Biopsies

Purpose Computed tomography (CT) scans are a significant source of radiation to patients. It was hypothesized that technical success and complication rates would not be significantly changed by radically lowering the CT dose during lung biopsies with an ultra–low-dose (ULD) protocol. Materials and Methods A total of 100 consecutive patients aged 11–89 years who underwent biopsies of lung lesions were evaluated. Technical parameters were altered halfway through the study from the standard dose (140 kV localizing/100 kV subsequent guiding scans with auto-mA) to a ULD protocol (100 kV, 7.5 mAs) as part of a quality initiative. ULD studies were evaluated subjectively for image quality on a five-point scale. Patients' body mass indexes, total estimated radiation doses (dose–length product), technical success rates, and complications were compared between the standard-dose and the ULD groups. Results Average radiation dose was reduced from 677.5 mGy·cm for the standard-dose group to 18.3 mGy·cm for the ULD group ( P < .0001). In the ULD group, image quality was rated as adequate or better in 96% of cases. Pneumothoraces necessitating chest tube placements occurred in 10% and 6% of cases in the ULD and standard dose groups, respectively ( P = .715). Technical success rates of 92% and 98% were obtained in the ULD and standard dose groups, respectively ( P = .362). Conclusions Radiation dose to the chest during CT-guided percutaneous lung biopsies is reduced greater than 95% versus a standard protocol through the use of a ULD CT protocol without decreasing technical success or patient safety.

Strategies to reduce radiation dose in cardiac PET/CT

Abstract Background Our aim was to investigate CT dose reduction strategies on a hybrid PET/CT scanner for cardiac applications. Materials Image quality and dose estimation of different CT scanning protocols for CT coronary angiography (CTCA), and CT-based attenuation correction for PET imaging were investigated. Fifteen patients underwent CTCA, perfusion PET imaging at rest and under stress, and FDG PET for myocardial viability. These patients were divided into three groups based on the CTCA technique performed: retrospectively gated helical (RGH), ECG tube current modulation (ETCM), and prospective gated axial (PGA) acquisitions. All emission images were corrected for photon attenuation using CT images obtained by default setting and an ultra-low dose CT (ULDCT) scan. Results Radiation dose in RGH technique was 22.2±4.0 mSv. It was reduced to 10.95±0.82 and 4.13±0.31 mSv using ETCM and PGA techniques, respectively. Radiation dose in CT transmission scan was reduced by 96.5% (from 4.53±0.5 to 0.16±0.01 mSv) when applying ULDCT as compared to the default CT. No significant difference in terms of image quality was found among various protocols. Conclusion The proposed CT scanning strategies, i.e. ETCM or PGA for CTCA and ULDCT for PET attenuation correction, could reduce radiation dose up to 47% without degrading imaging quality in an integrated cardiac PET/CT coronary artery examination.

The reduction of image noise and streak artifact in the thoracic inlet during low dose and ultra-low dose thoracic CT

Increased pixel noise and streak artifact reduce CT image quality and limit the potential for radiation dose reduction during CT of the thoracic inlet. We propose to quantify the pixel noise of mediastinal structures in the thoracic inlet, during low-dose (LDCT) and ultralow-dose (uLDCT) thoracic CT, and assess the utility of new software (quantum denoising system and BOOST3D) in addressing these limitations. Twelve patients had LDCT (120 kV, 25 mAs) and uLDCT (120 kV, 10 mAs) images reconstructed initially using standard mediastinal and lung filters followed by the quantum denoising system (QDS) to reduce pixel noise and BOOST3D (B3D) software to correct photon starvation noise as follows: group 1 no QDS, no B3D; group 2 B3D alone; group 3 QDS alone and group 4 both QDS and B3D. Nine regions of interest (ROIs) were replicated on mediastinal anatomy in the thoracic inlet, for each patient resulting in 3456 data points to calculate pixel noise and attenuation. QDS reduced pixel noise by 18.4% (lung images) and 15.8% (mediastinal images) at 25 mAs. B3D reduced pixel noise by ∼8% in the posterior thorax and in combination there was a 35.5% reduction in effective radiation dose (E) for LDCT (1.63–1.05 mSv) in lung images and 32.2% (1.55–1.05 mSv) in mediastinal images. The same combination produced 20.7% reduction (0.53–0.42 mSv) in E for uLDCT, for lung images and 17.3% (0.51–0.42) for mediastinal images. This quantitative analysis of image quality confirms the utility of dedicated processing software in targeting image noise and streak artifact in thoracic LDCT and uLDCT images taken in the thoracic inlet. This processing software potentiates substantial reductions in radiation dose during thoracic LDCT and uLDCT.