Correction to: Pilot study of the multicentre DISCHARGE trial: image quality and protocol adherence results of computed tomography and invasive coronary angiography.

The original version of this article, published on 16 December 2019, unfortunately contained two mistakes.

Pilot study of the multicentre DISCHARGE Trial: image quality and protocol adherence results of computed tomography and invasive coronary angiography.

OBJECTIVE: To implement detailed EU cardiac computed tomography angiography (CCTA) quality criteria in the multicentre DISCHARGE trial (FP72007-2013, EC-GA 603266), we reviewed image quality and adherence to CCTA protocol and to the recommendations of invasive coronary angiography (ICA) in a pilot study. MATERIALS AND METHODS: From every clinical centre, imaging datasets of three patients per arm were assessed for adherence to the inclusion/exclusion criteria of the pilot study, predefined standards for the CCTA protocol and ICA recommendations, image quality and non-diagnostic (NDX) rate. These parameters were compared via multinomial regression and ANOVA. If a site did not reach the minimum quality level, additional datasets had to be sent before entering into the final accepted database (FADB). RESULTS: We analysed 226 cases (150 CCTA/76 ICA). The inclusion/exclusion criteria were not met by 6 of the 226 (2.7%) datasets. The predefined standard was not met by 13 of 76 ICA datasets (17.1%). This percentage decreased between the initial CCTA database and the FADB (multinomial regression, 53 of 70 vs 17 of 75 [76%] vs [23%]). The signal-to-noise ratio and contrast-to-noise ratio of the FADB did not improve significantly (ANOVA, p = 0.20; p = 0.09). The CTA NDX rate was reduced, but not significantly (initial CCTA database 15 of 70 [21.4%]) and FADB 9 of 75 [12%]; p = 0.13). CONCLUSION: We were able to increase conformity to the inclusion/exclusion criteria and CCTA protocol, improve image quality and decrease the CCTA NDX rate by implementing EU CCTA quality criteria and ICA recommendations. KEY POINTS: • Failure to meet protocol adherence in cardiac CTA was high in the pilot study (77.6%). • Image quality varies between sites and can be improved by feedback given by the core lab. • Conformance with new EU cardiac CT quality criteria might render cardiac CTA findings more consistent and comparable.

Patient Preferences for Coronary CT Angiography with Stress Perfusion, SPECT, or Invasive Coronary Angiography.

Background Patient preference is pivotal for widespread adoption of tests in clinical practice. Patient preferences for invasive versus other noninvasive tests for coronary artery disease are not known. Purpose To compare patient acceptance and preferences for noninvasive and invasive cardiac imaging in North and South America, Asia, and Europe. Materials and Methods This was a prospective 16-center trial in 381 study participants undergoing coronary CT angiography with stress perfusion, SPECT, and invasive coronary angiography (ICA). Patient preferences were collected by using a previously validated questionnaire translated into eight languages. Responses were converted to ordinal scales and were modeled with generalized linear mixed models. Results In patients in whom at least one test was associated with pain, CT and SPECT showed reduced median pain levels, reported on 0-100 visual analog scales, from 20 for ICA (interquartile range [IQR], 4-50) to 6 for CT (IQR, 0-27.5) and 5 for SPECT (IQR, 0-25) (P < .001). Patients from Asia reported significantly more pain than patients from other continents for ICA (median, 25; IQR, 10-50; P = .01), CT (median, 10; IQR, 0-30; P = .02), and SPECT (median, 7; IQR, 0-28; P = .03). Satisfaction with preparation differed by continent and test (P = .01), with patients from Asia reporting generally lower ratings. Patients from North America had greater percentages of "very high" or "high" satisfaction than patients from other continents for ICA (96% vs 82%, respectively; P < .001) and SPECT (95% vs 79%, respectively; P = .04) but not for CT (89% vs 86%, respectively; P = .70). Among all patients, CT was preferred by 54% of patients, compared with 18% for SPECT and 28% for ICA (P < .001). Conclusion For cardiac imaging, patients generally favored CT angiography with stress perfusion, while study participants from Asia generally reported lowest satisfaction. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Woodard and Nguyen in this issue.

Perfusion CT of the Brain and Liver and of Lung Tumors: Use of Monte Carlo Simulation for Patient Dose Estimation for Examinations With a Cone-Beam 320-MDCT Scanner.

OBJECTIVE: The purpose of this study was to estimate the patient dose from perfusion CT examinations of the brain, lung tumors, and the liver on a cone-beam 320-MDCT scanner using a Monte Carlo simulation and the recommendations of the International Commission on Radiological Protection (ICRP). MATERIALS AND METHODS: A Monte Carlo simulation based on the Electron Gamma Shower Version 4 package code was used to calculate organ doses and the effective dose in the reference computational phantoms for an adult man and adult woman as published by the ICRP. Three perfusion CT acquisition protocols--brain, lung tumor, and liver perfusion--were evaluated. Additionally, dose assessments were performed for the skin and for the eye lens. Conversion factors were obtained to estimate effective doses and organ doses from the volume CT dose index and dose-length product. RESULTS: The sex-averaged effective doses were approximately 4 mSv for perfusion CT of the brain and were between 23 and 26 mSv for the perfusion CT body protocols. The eye lens dose from the brain perfusion CT examination was approximately 153 mGy. The sex-averaged peak entrance skin dose (ESD) was 255 mGy for the brain perfusion CT studies, 157 mGy for the lung tumor perfusion CT studies, and 172 mGy for the liver perfusion CT studies. CONCLUSION: The perfusion CT protocols for imaging the brain, lung tumors, and the liver performed on a 320-MDCT scanner yielded patient doses that are safely below the threshold doses for deterministic effects. The eye lens dose, peak ESD, and effective doses can be estimated for other clinical perfusion CT examinations from the conversion factors that were derived in this study.

A Survey of Radiation Doses in CT Urography Before and After Implementation of Iterative Reconstruction.

OBJECTIVE: The purpose of this study was to survey the radiation dose used in CT urography (CTU) in routine clinical practice, both before and after implementation of a scanning protocol that uses iterative reconstruction (Adaptive Iterative Dose Reduction 3D [AIDR 3D]). MATERIALS AND METHODS: We retrospectively surveyed dose reports from consecutive CTU examinations performed in 2011 with the use of 64- and 320-MDCT scanners that were reconstructed with filtered back projection (FBP) and from CTU examinations performed from May 2012 through November 2013 that were reconstructed with the use of AIDR 3D. Findings from these dose reports were then correlated with such patient characteristics as weight and body mass index (BMI; weight in kilograms divided by the square of height in meters). Only dose reports from single-bolus three-phase CTU examinations were included in the study. The volume CT dose index, dose-length product (DLP), and effective dose were surveyed both per examination and per phase by use of published effective dose DLP conversion factors. Image quality was evaluated subjectively for a subset of patients. RESULTS: The two study cohorts included 82 patients (median patient weight, 75.0 kg; median BMI, 25.3) who underwent CTU with FBP and 85 patients (median patient weight, 78.0 kg; median BMI, 24.5) who underwent CTU with AIDR 3D. The median total DLP and median effective dose were 924 mGy · cm and 13.0 mSv, respectively, in the CTU with the FBP cohort and 433 mGy · cm and 6.1 mSv, respectively, in the CTU with the AIDR 3D cohort. The median DLP in the unenhanced, nephrogenic, and excretory phases was 218, 300, and 441 mGy · cm, respectively, in patients undergoing CTU with FBP and 114, 121, and 190 mGy · cm, respectively, in patients undergoing CTU with AIDR 3D. Image quality was diagnostic in both groups, with relatively fewer artifacts noted on scans obtained using CTU with AIDR 3D. CONCLUSION: Our study presents detailed dose data from three-phase CTU examinations performed both before and after implementation of iterative reconstruction. Implementation of a CTU protocol using iterative reconstruction resulted in a mean effective dose of 6.1 mSv with preservation of clinical diagnostic image quality.

Comprehensive assessment of radiation dose estimates for the CORE320 study.

OBJECTIVE. The purpose of this study was to comprehensively study estimated radiation doses for subjects included in the main analysis of the Combined Non-invasive Coronary Angiography and Myocardial Perfusion Imaging Using 320 Detector Computed Tomography (CORE320) study ( ClinicalTrials.gov identifier NCT00934037), a clinical trial comparing combined CT angiography (CTA) and perfusion CT with the reference standard catheter angiography plus myocardial perfusion SPECT. SUBJECTS AND METHODS. Prospectively acquired data on 381 CORE320 subjects were analyzed in four groups of testing related to radiation exposure. Radiation dose estimates were compared between modalities for combined CTA and perfusion CT with respect to covariates known to influence radiation exposure and for the main clinical outcomes defined by the trial. The final analysis assessed variations in radiation dose with respect to several factors inherent to the trial. RESULTS. The mean radiation dose estimate for the combined CTA and perfusion CT protocol (8.63 mSv) was significantly (p < 0.0001 for both) less than the average dose delivered from SPECT (10.48 mSv) and the average dose from diagnostic catheter angiography (11.63 mSv). There was no significant difference in estimated CTA-perfusion CT radiation dose for subjects who had false-positive or false-negative results in the CORE320 main analyses in a comparison with subjects for whom the CTA-perfusion CT findings were in accordance with the reference standard SPECT plus catheter angiographic findings. CONCLUSION. Radiation dose estimates from CORE320 support clinical implementation of a combined CT protocol for assessing coronary anatomy and myocardial perfusion.

Adaptive iterative dose reduction 3D versus filtered back projection in CT: evaluation of image quality.

OBJECTIVE: The purpose of this study was to evaluate image quality with filtered back projection (FBP) and adaptive iterative dose reduction 3D (AIDR 3D). MATERIALS AND METHODS: Phantom acquisitions were performed at six dose levels to assess spatial resolution, noise, and low-contrast detectability (LCD). Spatial resolution was assessed with the modulation transfer function at high and low contrast levels. Noise power spectrum and SD of attenuation were assessed. LCD was calculated with a mathematic model observer applied to phantom CT images. The subjective image quality of clinical CT scans was assessed by five radiologists. RESULTS: Compared with FBP, AIDR 3D resulted in substantial noise reduction at all frequencies with a similar shape of the noise power spectrum. Spatial resolution was similar for AIDR 3D and FBP. LCD improved with AIDR 3D, which was associated with a potential average dose reduction of 36% (range, 9-86%). The observer study showed that overall image quality improved and artifacts decreased with AIDR 3D. CONCLUSION: AIDR 3D performs better than FBP with regard to noise and LCD, resulting in better image quality, and performs similarly with respect to spatial resolution. The evaluation of image quality of clinical CT scans was consistent with the objective assessment of image quality with a phantom. The amount of dose reduction should be investigated for each clinical indication in studies with larger numbers of patients.

Metal artifact reduction for CT: development, implementation, and clinical comparison of a generic and a scanner-specific technique.

PURPOSE: To develop, implement, and compare two metal artifact reduction methods for CT. METHODS: Two methods for metal artifact reduction were developed. The first is based on applying corrections in a Radon transformation of the CT images. The second method is based on a forward projection of the CT images and applying corrections in the scanner's original raw data. The first method is generic since it does not depend on the scanner specifications. For the second method, detailed information on the design of the CT scanner and the raw data of the study is required. Clinical implementation and evaluation were performed using pre- and post-operative CT scans of four patients with shoulder prosthesis. For comparison of these methods, the authors developed a quantitative technique that compares improvement in image quality for the two metal artifact reduction techniques with the image quality of the uncorrected images. RESULTS: Metal artifact reduction using either of the two methods yields a decrease of noise and artifacts in CT scans of patients with shoulder prostheses. Artifacts that appeared as bright and dark streaks were reduced or eliminated and as a result image quality improved. Quantitative assessment of clinical images showed improved image quality for both techniques of metal artifact reduction, but the method based on correction in original raw data performed better in all comparisons. CONCLUSION: Both methods are effective for metal artifact reduction, but better performance was observed for the method that is based on correcting the original raw data. The used evaluation technique provides an objective way of evaluating the metal artifacts in clinical CT images.

Radiation exposure to patients in a multicenter coronary angiography trial (CORE 64).

OBJECTIVE: The objective of this study was to assess the exposure of patients to radiation for the cardiac CT acquisition protocol of the multicenter Coronary Artery Evaluation Using 64-Row Multidetector Computed Tomography Angiography (CORE 64) trial. MATERIALS AND METHODS: An algorithm for patient dose assessment with Monte Carlo dosimetry was developed for the Aquilion 64-MDCT scanner. During the CORE 64 study, different acquisition protocols were used depending on patient size and sex; therefore, six patient models were constructed representing three men and three women in the categories of small, normal size, and obese. Organ dose and effective dose resulting from the cardiac CT protocol were assessed for these six patient models. RESULTS: The average effective dose for coronary CT angiography (CTA) calculated according to Report 103 of the International Commission on Radiological Protection (ICRP) is 19 mSv (range, 16-26 mSv). The average effective dose for the whole cardiac CT protocol including CT scanograms, bolus tracking, and calcium scoring is slightly higher-22 mSv (range, 18-30 mSv). An average conversion factor for the calculation of effective dose from dose-length product of 0.030 mSv/mGy · cm was derived for coronary CTA. CONCLUSION: The current methods of assessing patient dose are not well suited for cardiac CT acquisitions, and published effective dose values tend to underestimate effective dose. The effective dose of cardiac CT is approximately 25% higher when assessed according to the preferred ICRP Report 103 compared with ICRP Report 60. Underestimation of effective dose by 43% or 53% occurs in coronary CTA according to ICRP Report 103 when a conversion factor (E / DLP, where E is effective dose and DLP is dose-length product) for general chest CT of 0.017 or 0.014 mSv/mGy · cm, respectively, is used instead of 0.030 mSv/mGy · cm.

Development and validation of segmentation and interpolation techniques in sinograms for metal artifact suppression in CT.

PURPOSE: Metal prostheses cause artifacts in computed tomography (CT) images. The purpose of this work was to design an efficient and accurate metal segmentation in raw data to achieve artifact suppression and to improve CT image quality for patients with metal hip or shoulder prostheses. METHODS: The artifact suppression technique incorporates two steps: metal object segmentation in raw data and replacement of the segmented region by new values using an interpolation scheme, followed by addition of the scaled metal signal intensity. Segmentation of metal is performed directly in sinograms, making it efficient and different from current methods that perform segmentation in reconstructed images in combination with Radon transformations. Metal signal segmentation is achieved by using a Markov random field model (MRF). Three interpolation methods are applied and investigated. To provide a proof of concept, CT data of five patients with metal implants were included in the study, as well as CT data of a PMMA phantom with Teflon, PVC, and titanium inserts. Accuracy was determined quantitatively by comparing mean Hounsfield (HU) values and standard deviation (SD) as a measure of distortion in phantom images with titanium (original and suppressed) and without titanium insert. Qualitative improvement was assessed by comparing uncorrected clinical images with artifact suppressed images. RESULTS: Artifacts in CT data of a phantom and five patients were automatically suppressed. The general visibility of structures clearly improved. In phantom images, the technique showed reduced SD close to the SD for the case where titanium was not inserted, indicating improved image quality. HU values in corrected images were different from expected values for all interpolation methods. Subtle differences between interpolation methods were found. CONCLUSIONS: The new artifact suppression design is efficient, for instance, in terms of preserving spatial resolution, as it is applied directly to original raw data. It successfully reduced artifacts in CT images of five patients and in phantom images. Sophisticated interpolation methods are needed to obtain reliable HU values close to the prosthesis.

Assessment of Agatston coronary artery calcium score using contrast-enhanced CT coronary angiography.

OBJECTIVE: The purpose of this article is to evaluate to what extent Agatston scores may be derived from CT coronary angiography (CTA) examinations, compared with traditional unenhanced CT calcium scores. MATERIALS AND METHODS: Fifty patients with a CT calcium score-Agatston score of zero and 50 patients with a CT calcium score-Agatston score of 1 or greater whose CT calcium scores had been calculated and who had undergone CTA using volumetric 320-MDCT were included. Agatston scores were obtained at 3.0-mm slices for CT calcium score and CTA. Method agreement, interobserver agreement, and diagnostic performance of CTA for detecting coronary calcium were evaluated. RESULTS: Of 50 patients with a positive CT calcium score-Agatston score, coronary artery calcium was detected with CTA in 43 patients by observer 1 (mean CTA score, 102 ± 202; mean CT calcium score, 254 ± 501) and in 46 patients by observer 2 (mean CTA score, 94 ± 147; mean CT calcium score, 272 ± 531). Of the 50 patients with a CT calcium score-Agatston score of zero, 49 (98%, observer 1) and 50 (100%, observer 2) had a zero score with CTA as well. An intraclass correlation of 0.78 and 0.62 was found between CT calcium score and CTA (p < 0.01), whereas higher Agatston scores were underestimated with CTA. For observer 1, the sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy for detection of coronary calcium with CTA were 86%, 98%, 98%, 88%, and 92%, respectively, and the corresponding values for observer 2 were 92%, 100%, 100%, 93%, and 96%, respectively. Interobserver agreement was 0.996 for CT calcium score and 0.93 for CTA. CONCLUSION: Coronary artery calcium can be detected on CTA images with high accuracy. The Agatston calcium score derived from CTA images shows good correlation with unenhanced CT calcium score and is highly reproducible. However, higher Agatston scores are systematically underestimated when derived from CTA images.

Scan time and patient dose for thoracic imaging in neonates and small children using axial volumetric 320-detector row CT compared to helical 64-, 32-, and 16- detector row CT acquisitions.

BACKGROUND: Recently a 320-detector-row CT (MDCT) scanner has become available that allows axial volumetric scanning of a 16-cm-long range (50 cm field of view) in a single 0.35-s rotation. For imaging neonates and small children, volume scanning is potentially of great advantage as the entire scan range can be acquired in 0.35 s, which can reduce motion artefacts and may reduce the need for sedation in clinical CT imaging. Also, because there is no over-ranging associated with axial volumetric scanning, this may reduce patient radiation dose. OBJECTIVE: To evaluate, by means of a phantom study, scan time and patient dose for thoracic imaging in neonates and small children by using axial cone-beam and helical fan-beam MDCT acquisitions. MATERIALS AND METHODS: Paediatric imaging protocols were assessed for a 320-MDCT volumetric scanner (Aquilion ONE, Toshiba, Otawara, Japan). The 320-MDCT scanner allows for cone-beam acquisitions with coverage up to 160 mm, but it also allows for helical fan-beam acquisitions in 64-, 32-, or 16-MDCT modes. The acquisition configurations that were evaluated were 320 x 0.5 mm, 240 x 0.5 mm, and 160 x 0.5 mm for axial volumetric scanning, and 64 x 0.5 mm, 32 x 0.5 mm, and 16 x 0.5 mm for helical scanning. Dose assessment was performed for clinically relevant paediatric angiographic or chest/mediastinum acquisition protocols with tube voltages of 80 or 100 kVp and tube currents between 40 and 80 mA. RESULTS: Scan time was 0.35 s for 320-MDCT acquisitions, scan times varied between 1.9 s and 8.3 s for helical acquisitions. Dose savings varying between 18% and 40% were achieved with axial volumetric scanning as compared to helical scanning (for 320- versus 64-MDCT at 160 mm and 80 kVp, and for 320- versus 16-MDCT at 80 mm and 100 kVp, respectively). Statistically significant reduction in radiation dose was found for axial 320-MDCT volumetric scanning compared to helical 64-, 32-, and 16-MDCT scanning. CONCLUSION: Axial thoracic CT of neonates and small children with volumetric 320-MDCT can be performed between 5 and 24 times faster compared to helical scanning and can save patient dose.

Assessment of patient and occupational dose in established and new applications of MDCT fluoroscopy.

OBJECTIVE: This study aimed to assess patient dose and occupational dose in established and new applications of MDCT fluoroscopy. MATERIALS AND METHODS: Electronic personal dosimeters were used to measure occupational dose equivalent. Effective patient dose was derived from the recorded dose-length product. Acquisition parameters that were observed during CT fluoroscopy (CTF) provided the basis for the estimation of an entrance skin dose profile. Two hundred ten CT-guided interventional procedures were included in the study. RESULTS: The median effective patient dose was 10 mSv (range, 0.1-235 mSv; 107 procedures). The median peak entrance skin dose was 0.4 Sv (0.1-2.1 Sv; 27 procedures). From 547 measurements of occupational dose equivalent, a median occupational effective dose of 3 muSv per procedure was derived for the interventional radiologists and 0.4 muSv per procedure for the assisting radiologists and radiology technologists. The estimated maximum occupational effective dose reached 0.4 mSv. CONCLUSION: The study revealed high effective patient doses, up to 235 mSv, mainly for relatively new applications such as CTF-guided radiofrequency ablations using MDCT, vertebroplasty, and percutaneous ethanol injections of tumors. Entrance doses were occasionally in the range of the warning level for deterministic skin effects but were always below the threshold for serious deterministic effects. The complexity of the procedure, expected benefits of the treatment, and general health state of the patient contribute to the justification of observed high effective patient doses.

A technique for simulating the effect of dose reduction on image quality in digital chest radiography.

PURPOSE: The purpose of this study is to provide a pragmatic tool for studying the relationship between dose and image quality in clinical chest images. To achieve this, we developed a technique for simulating the effect of dose reduction on image quality of digital chest images. MATERIALS AND METHODS: The technique was developed for a digital charge-coupled-device (CCD) chest unit with slot-scan acquisition. Raw pixel values were scaled to a lower dose level, and a random number representing noise to each specific pixel value was added. After adding noise, raw images were post processed in the standard way. Validation was performed by comparing pixel standard deviation, as a measure of noise, in simulated images with images acquired at actual lower doses. To achieve this, a uniform test object and an anthropomorphic phantom were used. Additionally, noise power spectra of simulated and actual images were compared. Also, detectability of simulated lesions was investigated using a model observer. RESULTS: The mean difference in noise values between simulated and real lower-dose phantom images was smaller than 5% for relevant clinical settings. Noise power spectra appeared to be comparable on average but simulated images showed slightly higher noise levels for higher spatial frequencies and slightly lower noise levels for lower spatial frequencies. Comparable detection performance was shown in simulated and actual images with slightly worse detectability for simulated lower dose images. CONCLUSION: We have developed and validated a method for simulating dose reduction. Our method seems an acceptable pragmatic tool for studying the relationship between dose and image quality.

Added Value of Ultra-low-dose Computed Tomography, Dose Equivalent to Chest X-Ray Radiography, for Diagnosing Chest Pathology.

PURPOSE: The purpose of this study was to assess the clinical value of ultra-low-dose computed tomography (ULDCT) compared with chest x-ray radiography (CXR) for diagnosing chest pathology. MATERIALS AND METHODS: A total of 200 patients referred for CXR by outpatient clinics or general practitioners were enrolled prospectively. They underwent CXR (posteroanterior and lateral) and ULDCT (120 kV, 3 mAs) on the same day. In-room time and effective dose were recorded for each examination. Studies were categorized whether they were diagnostic or not, relevant radiologic diagnostic findings were reported, and confidence for diagnosis was recorded by a Likert scale. Differences in diagnostic confidence and effect on management decision were compared. RESULTS: In-room time was <2 minutes for CXR and <3 minutes for ULDCT. Effective dose was 0.040 mSv for CXR and 0.071 mSv for ULDCT. CXR was considered diagnostic in 98% and ULDCT in 100%. The mean perceived confidence for diagnosis was 88±12% with CXR and 98±2% with ULDCT (P<0.0001), whereas discrepant findings between CXR and ULDCT were found in 101 of 200 patients. As compared with CXR, ULDCT had added value for management decisions in 40 of 200 patients. CONCLUSIONS: ULDCT provided added value to the radiologist by improved perceived confidence with a reduction in false-positive and false-negative CXR investigations that had management implications in 20% of patients. The effective dose of ULDCT will not be a limiting factor for introducing ULDCT of the chest on a broad scale in clinical practice.

Development of a 3D printed anthropomorphic lung phantom for image quality assessment in CT.

PURPOSE: To design a 3D printed anthropomorphic lung vessel phantom for CT image quality assessment and to evaluate the phantom image and dose characteristics. METHODS: An in-house algorithm generated a vessel tree model, based on human lungs anatomy, which was 3D printed using a multi jet modeling printer (0.25 mm ≤ vessel diameters ≤ 8.25 mm) and inserted in an elliptical holder (thorax surrogate). The phantom was scanned (Toshiba Aquilion Genesis CT) and compared in terms of attenuation (Hounsfield units, HU) and dose characteristics with studies of five patients (normal BMI) and a commercial torso phantom, performed with the same thorax protocol. The pixel value distribution in the lung area was assessed with histograms. To investigate the adjustment of tube current modulation, tube load and CTDI were compared. RESULTS: The histogram peaks for respectively vessels and surrounding tissue were at 105 HU and -985 HU (3D printed phantom), at -25 HU and -1000 HU (torso phantom) and at 25 HU and -875 HU (average patient). The contrast between vessels and surrounding was -1090 HU (3D printed), -975 HU (torso phantom), and -900 HU (average patient). The measured HU values (soft tissue and vertebra) were (32 ±â€¯15) HU and (210 ±â€¯71) HU (average patient); (4 ±â€¯4) HU, (390 ±â€¯39) HU (torso phantom) and (119 ±â€¯5) HU, (951 ±â€¯31) HU (3D printed phantom and holder). CTDIvol was (1.9 ±â€¯4.7 mGy) for patients, 1.9 mGy for the torso phantom and 2.1 mGy for the 3D printed lung phantom. CONCLUSIONS: An anthropomorphic 3D printed lung phantom was developed and its CT image and dose characteristics evaluated. The phantom has the potential to provide clinically relevant and reproducible measures of CT image quality.

Meta-analysis of 40- and 64-MDCT angiography for assessing coronary artery stenosis.

OBJECTIVE: The purpose of our study was to assess the diagnostic performance of thin-slice (< or = 0.625 mm) MDCT coronary angiography compared with invasive coronary angiography for the detection of significant (> or = 50%) stenosis. MATERIALS AND METHODS: Twenty-two articles on 40- and 64-MDCT coronary angiography were included. Sensitivity and specificity were calculated on a per-patient and per-segment basis; in addition, proximal versus distal segments were evaluated. The effect of nonevaluable patients, nonevaluable segments, and disease prevalence on diagnostic performance was assessed. RESULTS: Pooled sensitivity on a patient level was 97.7% ([95% CI] 96.2-98.7%) and specificity 91.0% (88.5-93.1%). Pooled sensitivity on a segmental level was 90.8% (89.0-92.4%) and specificity 95.7% (95.2-96.1%); for proximal segments, respectively, 94.2% (92.3-95.7%) and 94.1% (93.4-94.8%), and for distal segments 84.8% (81.1-88.0%) and 96.9% (96.4-97.4%). If nonevaluable MDCT investigations were included, the per-patient specificity was reduced from 91.0% to 89.1% (p > 0.05) when allocating excluded patients as having significant coronary artery stenosis, and the sensitivity was reduced from 97.7% to 96.2% (p > 0.05) when allocating excluded patients as not having significant stenosis. The per-patient prevalence of coronary artery stenosis had no significant influence on the sensitivity for detecting significant stenosis. CONCLUSION: Forty- and 64-MDCT provide good-to-excellent performance in detecting or ruling out significant coronary artery stenosis, with better results for proximal than for distal coronary artery segments.

Automated cardiac phase selection with 64-MDCT coronary angiography.

OBJECTIVE: The aim of this study was to assess three different phase-selection methods for obtaining optimal CT coronary artery image quality. MATERIALS AND METHODS: ECG-gated CT coronary angiography scans of 40 patients (23 men, 17 women; mean age, 56 years) were retrieved. The patient group was composed of 20 consecutive patients with heart rates < or = 65 beats per minute (bpm) and 20 consecutive patients with heart rates > 65 bpm. Three phase-selection methods were evaluated: fixed phase selection, manual phase selection, and automated phase selection. Two scoring systems were used to evaluate diagnostic quality: scoring of axial images on a 5-point scale and scoring of multiplanar reconstructions (MPRs) on a forced-choice 3-point preference scale. Differences were tested by Wilcoxon's signed rank test for the entire patient group and the two subgroups including patients with heart rates < or = 65 bpm and those with heart rates > 65 bpm. RESULTS: Axial image evaluation of the entire patient group showed statistically significant superior image quality for the manual phase-selection method compared with the predefined phase-selection method and no statistically significant differences were found for the other comparisons. Analysis at heart rates < or = 65 bpm showed no significant differences between phase-selection methods. Analysis at heart rates > 65 bpm showed the best results for the automated phase-selection method, and image quality was significantly better for the automated and manual phase-selection methods than for the predefined phase-selection method. CONCLUSION: The automated phase-selection method accurately detects the optimal diagnostic phase for CT coronary artery evaluation and has the potential to reduce operator time needed for image reconstruction.

Assessment of structural similarity in CT using filtered backprojection and iterative reconstruction: a phantom study with 3D printed lung vessels.

OBJECTIVE: To compare the performance of three generations of CT reconstruction techniques using structural similarity (SSIM) as a measure of image quality for CT scans of a chest phantom with 3D printed lung vessels. METHODS: CT images of the chest phantom were acquired at seven dose levels by changing the tube current while other acquisition parameters were kept constant. Three CT reconstruction techniques were applied on each acquisition. The first technique was filtered backprojection (FBP), the second technique was FBP with iterative filtering (adaptive iteration dose reduction in 3 dimensions (AIDR 3D)) and the third technique was model-based iterative reconstruction (Forward projected model-based Iterative Reconstruction SoluTion (FIRST)). Image quality of the CT data was quantified in terms of SSIM. The SSIM index was used for image quality comparison between the dose levels and different reconstruction techniques. The SSIM index gives a value between 0 and 1, with 0 as the lowest image quality and 1 as an excellent image quality. RESULTS: The lowest SSIM index was observed for FBP at all dose levels. The reconstruction technique with the highest SSIM depends on the dose level. For tube currents higher than 80 mA, AIDR 3D showed the highest SSIM index, and for tube currents lower or equal to 80 mA FIRST showed the highest SSIM index. CONCLUSION: SSIM index is a robust quantity and is correlated to the image quality as perceived by the humans. Advanced CT reconstruction techniques provide better image quality in all conditions compared to FBP. Advances in knowledge: SSIM is a robust measure to compare CT image quality for advanced reconstruction techniques relative to a reference. The 3D print technology is an useful method for the development of dedicated phantoms for CT image quality evaluation.

SimDoseCT: dose reporting software based on Monte Carlo simulation for a 320 detector-row cone-beam CT scanner and ICRP computational adult phantoms.

This study aims to develop and test software for assessing and reporting doses for standard patients undergoing computed tomography (CT) examinations in a 320 detector-row cone-beam scanner. The software, called SimDoseCT, is based on the Monte Carlo (MC) simulation code, which was developed to calculate organ doses and effective doses in ICRP anthropomorphic adult reference computational phantoms for acquisitions with the Aquilion ONE CT scanner (Toshiba). MC simulation was validated by comparing CTDI measurements within standard CT dose phantoms with results from simulation under the same conditions. SimDoseCT consists of a graphical user interface connected to a MySQL database, which contains the look-up-tables that were generated with MC simulations for volumetric acquisitions at different scan positions along the phantom using any tube voltage, bow tie filter, focal spot and nine different beam widths. Two different methods were developed to estimate organ doses and effective doses from acquisitions using other available beam widths in the scanner. A correction factor was used to estimate doses in helical acquisitions. Hence, the user can select any available protocol in the Aquilion ONE scanner for a standard adult male or female and obtain the dose results through the software interface. Agreement within 9% between CTDI measurements and simulations allowed the validation of the MC program. Additionally, the algorithm for dose reporting in SimDoseCT was validated by comparing dose results from this tool with those obtained from MC simulations for three volumetric acquisitions (head, thorax and abdomen). The comparison was repeated using eight different collimations and also for another collimation in a helical abdomen examination. The results showed differences of 0.1 mSv or less for absolute dose in most organs and also in the effective dose calculation. The software provides a suitable tool for dose assessment in standard adult patients undergoing CT examinations in a 320 detector-row cone-beam scanner.